Balancing management and preservation of mediterranean scattered oak woodlands (Dehesas) in human-dominated landscapes

Texto completo

(1)UNIVERSIDAD POLITÉCNICA DE MADRID ESCUELA TÉCNICA SUPERIOR DE INGENIEROS DE MONTES. BALANCING MANAGEMENT AND PRESERVATION OF MEDITERRANEAN SCATTERED OAK WOODLANDS (DEHESAS) IN HUMAN-DOMINATED LANDSCAPES. TESIS DOCTORAL. AIDA LÓPEZ SÁNCHEZ Ingeniera de Montes. 2015.

(2)

(3) INVESTIGACIÓN FORESTAL AVANZADA ESCUELA TÉCNICA SUPERIOR DE INGENIEROS DE MONTES. BALANCING MANAGEMENT AND PRESERVATION OF MEDITERRANEAN SCATTERED OAK WOODLANDS (DEHESAS) IN HUMAN-DOMINATED LANDSCAPES. AIDA LÓPEZ SÁNCHEZ Ingeniera de Montes. DIRECTORES:. SONIA ROIG GÓMEZ. RODOLFO DIRZO MINJAREZ. Doctora Ingeniera de Montes. Doctor en Ecología. 2015.

(4)

(5) Tribunal nombrado por el Sr. Rector Magnífico de la Universidad Politécnica de Madrid, el día de de 2015. Presidente:. _. Vocal:. _. Vocal:. _. Vocal:. _. Secretario:. _. Suplente:. _. Suplente:. _. Realizado el acto de defensa y lectura de la Tesis el día 2015 en Madrid en la E.T.S.I. Montes.. de. Calificación. EL PRESIDENTE. _. LOS VOCALES. EL SECRETARIO. de.

(6)

(7) MENCIÓN DE DOCTORADO INTERNACIONAL INTERNATIONAL DOCTORATE MENTION. Esta Tesis ha sido informada positivamente para su defensa en exposición pública por los siguientes investigadores:. This Ph.D. Thesis has been positively evaluated for its public defense by the following external reviewers:. Prof. Dr. Lynn Huntsinger Department Environmental Science, Policy, and Management University of California, Berkeley (EEUU). Dr. Laura Breitsameter Johann Heinrich von Thünen Institut Institut für Ländliche Räume (GERMANY).

(8)

(9) A mis padres y hermana..

(10)

(11) AGRADECIMIENTOS “El agradecimiento es el impulso hacia la eternidad”/ “The gratitude is the impulse to the eternity” Hace bastante tiempo decidí añadir la frase anterior a mi firma de mis emails junto con mi información personal. Y no puedo empezar este documento sin antes agradecer a la multitud de personas que he ido conociendo en el transcurso del desarrollo de esta tesis y que han contribuido en lo profesional y/o personal. Seguramente me dejaré muchos nombres que me encantaría dejar escritos, pero que por motivos de espacio me es imposible mencionaros a todos. No obstante, aunque no aparezcan todos los nombres, cada uno de vosotros sabéis que estáis ahí y os agradezco enormemente vuestro apoyo. En primer lugar un agradecimiento muy especial a mis directores. A Sonia Roig Gómez por comenzar con ilusión a dirigir esta tesis. Aún están en mi mente aquellas primeras tutorías donde todavía no sabía ni por dónde empezar y ahora no me puedo creer que ya estemos en este punto. Agradezco enormemente todo lo que has ido dándome durante estos años doctorales, todos los consejos, las sugerencias, los comentarios, las correcciones, y el apoyo en todas mis iniciativas y congresos. A Rodolfo Dirzo Minjarez, en primer lugar por todo el esfuerzo que junto a su equipo emplearon para acogerme en la universidad de Stanford en un tiempo contra reloj (especialmente a Pam). Estoy muy agradecida a todos tus comentarios, correcciones y sugerencias que me has ido dando en los artículos como por supuesto en la tesis. A Alfonso San Miguel Ayanz por su gran apoyo y tutorización a lo largo de todos estos años que ya nos conocemos. Agradezco enormemente tu generosidad por ofrecerme la posibilidad de una codirección internacional la cual ya ha dado muchos frutos. Siempre has aportado el comentario adecuado para cada cuestión planteada. Muchas gracias por tus correcciones y sugerencias, y por un trato excepcional que hacen que el trabajo sea mucho más gratificante. Quiero agradecer también a mis compañeros de despacho que han seguido la evolución de mi tesis doctoral guiándome en diversos aspectos y que me han empujado siempre hacia delante en este mundo doctoral. A Mariana - quien estuvo orientándome en mis primero pasos -, a Ramón - quien ha sido una gran referencia para mí y ha seguido muy de cerca toda mi tesis -, a Ruth - quien hemos compartido tardes muy agradables con nuestras búsquedas en R, a Jesús - quien siempre me hacía mirar con ojo crítico lo que iba haciendo, y a Marta – quien ha marcado la diferencia de que el final de mi tesis sea tan gratificante). Quiero agradecer también muy especialmente a Baldomero Benito y José Cebolla que siempre han tenido una sonrisa para ayudarme en lo que necesitase pero concretamente en las dudas del reconocimiento de plantas herbáceas. Quiero agradecer a muchos profesores de la escuela que saben que han estado ahí siguiéndome y apoyándome, al personal de limpieza, a mis compañeros de las unidades de anatomía, patología, edafología, estadística, dasometría, zoología, química, botánica, etc., donde hemos compartido comidas, quedadas de investigación o congresos, deporte, y con quienes he compartido.

(12) muchas inquietudes científicas. Quiero agradecer a mi grupo de investigación ECOGESFOR por todo los buenos momentos que hemos compartido donde la ciencia y la gastronomía estaban muy presentes. Especialmente a Sergio González y Aitor Gastón por su ayuda en diversas dudas que me han ido surgiendo con los programas informáticos Arcgis y R, respectivamente. Quiero agradecer también al Dehesón del Encinar y muy especialmente a Celia López-Carrasco por facilitarme el acceso a la finca y a la disponibilidad de datos. También quería agradecer a los propietarios de las otras fincas de estudio por permitirnos realizar los trabajos de campo en las mismas. A mis colaboradores de cada una de mis estancias internacionales y sus equipos de investigación. Agradezco enormemente el apoyo mostrado, su cariño y ganas por compartir y establecer lazos y estudios comunes. Thanks to Lynn Huntsinger and lab (James Bartolome, Michele Hammond, Erica Spotswood, Gareth S. Fisher, Felix Ratcliff, Sheri Spiegal, Maggi Kelly). Thanks to Rodolfo Dirzo and lab, and all people that help me to get ranch permissions and do fieldwork (Rodolfo Dirzo, John Schroeder, Mar Sobral, Stuart Koretz, Bill Gomez, Ian Pearse, Walt Koenig, Joan Dudney, Alan Eugene Launer, Ince Voegeli, Kyra Engelberg, Christina Yen Feng, Nathaniel Foote, Ron, Vanessa). Thanks to Johannes Isselstein and lab (Anja, Monika, Bettina, Laura, Thorsten, Mohamend, Barbara). Thanks very especially to Anja Schmitz and her family for all their effort to make possible our study offering me a wonderful accommodation. Gracias a todas las personas que conocí en congresos (como María Rosa Canals – por darme muy buenos consejos) y cursos de formación durante esta etapa de tesis doctoral. Quiero agradecer también a todos los administrativos que haciendo su trabajo facilitaron la labor de todo el papeleo necesario para la tesis doctoral, especialmente a Silvia, Carolina y Carmen por toda la gestión de mi beca FPU. A mis amigos por su constante apoyo personal. A los de montes, a los de Villanueva, a los de la montaña, a los de la diócesis, a los de los coros y grupos musicales, a los lejanos en la distancia (thanks to all my international friends, especially those that have taught and help me in many regards), y a los experimentados que con su sabiduría inundan mi día a día. Especialmente quería agradecer a dos grandes amigas que han estado ahí, Charo y Ana, quienes nunca dejaron de alentarme y cuidarme. Y finalmente gracias aquellas personas que se han incorporado recientemente en mi vida y han alegrado y hecho más llevadero este último tramo de tesis. A mi familia, quien reservo este final con especial cariño. Ellos han sido un gran pilar durante toda mi vida. A mis padres y hermana María quienes nunca dudaron de mis decisiones y juntaron toda la energía necesaria para impulsarme siempre en mis proyectos y sueños. No hay folios que puedan recoger todas las palabras de gratitud que tengo hacia ellos. Hoy puedo escribir estas letras gracias a su infinita entrega por darme una gran educación. Además, agradezco especialmente su esfuerzo físico en campo quien sin su ayuda la investigación en las dehesas no se hubiese llevado a cabo con la situación actual económica existente. Muchas gracias, no hay sueños cumplidos sin un soporte de amor detrás. Y finalmente gracias al amor que todo lo inunda en mi vida..

(13) INDEX ABSTRACT. xvii. RESUMEN. xix. PREFACE. xxi. 1. INTRODUCTION. 1. 1.1. Mediterranean scattered oak woodlands in human-dominated landscapes. 3. 1.2. Biodiversity and ecosystem services of Mediterranean scattered oak woodlands 4 1.3. Effects of scattered trees and livestock grazing on herbaceous communities 5 1.4. A major threat of Mediterranean scattered oak woodlands perpetuation. 8. 1.5. Dehesas. 10. 1.6. Justification. 13. 2. OBJECTIVES. 17. 3. MATERIAL AND METHODS. 21. 3.1. Mediterranean scattered oak woodlands: Study areas. 23. 3.1.1. Study area Spanish dehesas land. 23. 3.1.2. Study area Spanish dehesas ranches. 24. 3.1.3. Study area Dehesón del Encinar. 25. 3.1.4. Study area other Mediterranean scattered oak woodlands ranches. 28. 3.2. Variables analyzed and general methodologies. 30. 3.2.1. Characterization of herbaceous layer in dehesas. 30. 3.2.2. Diversity indices. 31. 3.3. Statistical analysis and software. 32. 3.3.1. LM, GLM, GLMM, ZIGLMM and MLGLMM. 33. 3.3.2. Box-Cox transformations. 34. 3.3.3. Model selection procedure. 35. 3.3.4. Canonical Correspondence Analysis. 35. 4. EVOLUTION OF LIVESTOCK GRAZING AND TREE DENSITY IN MEDITERRANEAN DEHESAS OVER THE LAST 60 YEARS. 37. 4.1. Introduction. 39.

(14) 4.2. Material and methods. 41. 4.2.1. Study area. 41. 4.2.2. Sample design and data collection. 41. 4.2.3. Variables analyzed and statistical analysis. 43. 4.3. Results. 45. 4.3.1. Dehesa land evolution. 45. 4.3.2. Livestock stocking rates evolution. 46. 4.3.3. Tree density and tree cover evolution. 47. 4.4. Discussion. 50. 5. THE EFFECT OF TREE COVER ON THE BIOMASS AND DIVERSITY OF THE HERBACEOUS LAYER IN A MEDITERRANEAN DEHESA. 53. 5.1. Introduction. 55. 5.2. Materials and methods. 56. 5.2.1. Study area. 56. 5.2.2. Sample design and data collection. 56. 5.2.3. Variables analyzed and statistical analysis. 57. 5.3. Results. 58. 5.3.1. Herbaceous biomass beneath and outside the canopy. 58. 5.3.2. The effect of trees on the relationship between herbaceous biomass and diversity 59 5.3.3. Effects of trees and small changes in topography on herbaceous diversity. 65. 5.4. Discussion. 66. 6.. THE. IMPORTANT. ROLE. OF. SCATTERED. TREES. ON. THE. HERBACEOUS DIVERSITY OF A GRAZED MEDITERRANEAN DEHESA 71 6.1. Introduction. 73. 6.2. Materials and methods. 73. 6.2.1. Study area. 73. 6.2.2. Sample design and data collection. 73. 6.2.3. Variables analyzed and statistical analysis. 74. 6.3. Results. 75. 6.3.1. Effect of wooded plots and type of grazing on herbaceous diversity. 75. 6.3.2. Floristic composition in wooded versus open grasslands plots and by grazing regime. 77.

(15) 80. 6.4. Discussion. 7. THE ROLE OF SCATTERED TREES AND LIVESTOCK GRAZING AS KEYSTONES. FOR. EFFICIENT. USE. AND. CONSERVATION. OF. MEDITERRANEAN DEHESAS. 85. 7.1. Introduction. 87. 7.2. Methods. 87. 7.2.1. Study area. 87. 7.2.2. Sample design and data collection. 88. 7.2.3. Variables analyzed and statistical analysis. 89. 7.3. Results. 90. 7.3.1. Effect of microsites created by trees, type of grazing and water availability on herbaceous biomass. 90. 7.3.2. Effect of microsites created by trees, type of grazing and water availability on herbaceous diversity. 93. 7.3.3. Herbaceous biomass and diversity relationship. 95. 7.3.4. Floristic composition in microsites created by trees, by grazing effect and by water availability of the year. 96. 7.4. Discussion. 97. 7.4.1. Effects of grazing management on the herbaceous layer. 98. 7.4.2. Effects of microsites created by trees on the herbaceous layer. 99. 7.4.3. Herbaceous biomass and diversity relationship under influence of trees and grazing management. 100. 7.4.4. Implications for conservation management of grasslands with scattered trees 101 8. EFFECTS OF LIVESTOCK MANAGEMENT ON OAK REGENERATION IN MEDITERRANEAN DEHESAS. 103. 8.1. Introduction. 105. 8.2. Material and methods. 107. 8.2.1. Study area. 107. 8.2.2. Study sites. 107. 8.2.3. Sample design and data collection. 108. 8.2.4. Variables analyzed and statistical analysis. 109.

(16) 8.3. Results. 110. 8.3.1. Density of young oak plants depending on rangeland management and microsite 110 8.3.2. Probability of herbivory occurrence and intensity depending on rangeland management and microsite. 113. 8.3.3. Probability and intensity of herbivory depending on plant type. 115. 8.3.4. Height of young oak plants depending on rangeland management, microsite and herbivory. 115. 8.3.5. Diameter of young oak plants depending on rangeland management, microsite and herbivory. 116. 8.3.6. Height:diameter ratio of oak young plants depending on rangeland management, microsite and herbivory. 117. 8.3.7. Damage on shoot apex depending on rangeland management and microsite 118 8.3.8. Crown height:diameter ratio of bushes depending on rangeland management, microsite and herbivory. 118. 8.4. Discussion. 119. 8.4.1. Density of oak young plants. 119. 8.4.2. Probability and intensity of herbivory. 121. 8.4.3. Management effects on holm oak recruitment morphology. 121. 8.4.4. Microsite effects on holm oak recruitment morphology. 123. 8.4.5. Implications for management conservation of oak regeneration. 123. 9. EFFECTS OF CATTLE MANAGEMENT ON OAK REGENERATION IN NORTHERN CALIFORNIAN MEDITERRANEA OAK WOOLDANDS. 127. 9.1. Introduction. 129. 9.2 Materials and Methods. 130. 9.2.1. Study area. 130. 9.2.2. Sample design and data collection. 130. 9.2.3. Variables analyzed and statistical analysis. 131. 9.3. Results. 132. 9.3.1. Density of oak plants depending on the presence of cattle. 132. 9.3.2. Probability and intensity of herbivory depending on the presence of cattle. 133. 9.3.3. Diameter of oak plants depending on the presence of cattle. 135. 9.4. Discussion. 135.

(17) 10. SYNTHETIC DISCUSSION. 141. 10.1. Implications for management and conservation. 152. 11. GENERAL CONCLUSIONS. 157. 12. REFERENCES. 163. 13. ANEXES. 189.

(18)

(19) ABSTRACT Mediterranean scattered oak woodlands have great ecological and socio-economic importance, supporting high environmental and amenity values, and relatively rich biological diversity while producing important ecosystem services. They have been witnesses of different and fast changes developed in the last century. Most of the research developed in this dissertation has conducted within dehesas. This thesis provides: i) the global change evidence of the tree layer and grazing management experienced in the land-use range of a Mediterranean scattered oak woodland (dehesa) over the last 60 years; ii) the important role of scattered trees and adequate management grazing in the improvement of grassland yield, quality and diversity - which it is important, in turn, for the system profitability - under different climate scenarios and site quality; and iii) the lack of oak regeneration evidence under some given representative management regimes and how is the growth development of these plants to assure the viability and persistence of Mediterranean scattered oak woodlands. Tree layer experienced a significant reduction in dehesas during 1950-1980 period where the highest human impacts took place. Sheep herd decreased drastically during the 1970s and, in contrast, cattle have been increasing gradually since then. On the other hand, same livestock grazing management (especially cattle) during long time (minimum 30 years) within Mediterranean scattered oak woodlands reduced strongly the density of young oak plants and showed high probability of herbivory occurrence and intensity. Young plant growth pattern was greatly modified by livestock. Cattle grazing generated stunted plants and sheep grazing generated slender plants favoring the height growth. Microsites created by large trees modified the herbaceous yield according the water availability of the year and generated high plant diversity within herbaceous communities. Especially, ecotone microsite supported high values of herbaceous diversity. The presence of livestock species increased the herbaceous yield and maintained a more diverse community under continuous grazing at both moderate and high intensities; especially cattle. Thus, around the influence of scattered trees there is a high amount of different interactions among livestock, trees and grasslands maintaining and enhancing the quality of whole dehesa system. The results of this thesis highlight how important is balancing management and preservation of Mediterranean scattered oak woodlands to obtain the optimum ecosystem services while the system conservation is assured for a long-term. It is crucial to design management plans with conservation goals that include appropriate silvopastoral practices in Mediterranean scattered oak woodlands..

(20)

(21) RESUMEN Los sistemas agroforestales mediterráneos tienen una gran importancia ecológica y socioeconómica, y mantienen altos valores medioambientales y de diversidad biológica a la vez que producen importantes servicios ecosistémicos. Estos sistemas han sido testigos de diversos cambios rápidos y drásticos en su gestión y aprovechamiento durante el último siglo. La mayor parte de la investigación desarrollada en esta tesis doctoral ha sido llevada a cabo en las dehesas españolas. Esta tesis nos muestra: i) la evidencia de la existencia de un cambio global del estrato arbóreo y del manejo del pastoreo en el todo el área de distribución de la dehesa durante los últimos 60 años; ii) la importancia del papel que juega el arbolado disperso y el adecuado manejo del ganado en la mejora de la producción, calidad y diversidad de las comunidades herbáceas, que a su vez, un pasto herbáceo bien desarrollado es importante para la rentabilidad del sistema, evaluando estos efectos bajo distintos escenarios de clima y calidad de estación; y iii) la evidencia de la falta de regeneración en sistemas agroforestales mediterráneos bajo distintos tipos de manejo del pastoreo, y además se evalúa el crecimiento y desarrollo de las pocas plántulas existentes que serán las que aseguren la viabilidad y persistencia y de estos sistemas. El arbolado disperso de estos sistemas ha experimentado una reducción importante en su densidad arbórea y fracción de cabida cubierta durante el periodo entre 1950-1980 donde tuvieron lugar importantes transformaciones en la actividad agropecuaria. La cabaña ganadera de ovino disminuyó drásticamente en los años 70 en comparación a la de bovino que desde entonces ha aumentado progresivamente hasta la actualidad. Por otro lado, el mismo tipo de manejo del ganado doméstico (especialmente bovino) durante bastante tiempo (mínimo 30 años) provocó una reducción significativa de la densidad de las plántulas. Además la probabilidad de ocurrencia y la intensidad de daños por herbivoría fue mayor bajo pastoreo bovino (con daños más intensos y consistentes) que bajo pastoreo ovino o sin pastoreo doméstico (presencia de ciervos). También el patrón de crecimiento de las plantas jóvenes estuvo afectado por el tipo de manejo, generando plántulas achaparradas en el caso del bovino y plántulas esbeltas favoreciendo el crecimiento en altura en el caso del ovino. La presencia de un arbolado disperso generó una mayor diversidad y variación en la producción de las comunidades herbáceas según las condiciones de disponibilidad de agua. Especialmente, el ecotono como microhábitat sostuvo altos valores de diversidad herbácea. La presencia del ganado bajo pastoreo continuo de intensidad moderada a alta, especialmente el bovino, incrementó los rendimientos de producción y diversidad del estrato herbáceo. Los resultados de esta tesis nos muestran la importancia que tiene la existencia de un equilibrio entre la producción y la conservación de los sistemas agroforestales mediterráneos para obtener una producción sostenible de servicios ecosistémicos mientras se asegura la perpetuación del sistema a largo plazo. Es crucial diseñar planes de gestión incorporando objetivos de conservación que integren técnicas silvopastorales apropiadas para poder aplicar en los sistemas agroforestales mediterráneos..

(22)

(23) PREFACE. La presente tesis doctoral ha sido realizada gracias a una beca-contrato de Formación de Profesorado Universitario (FPU) del Ministerio de Educación, Cultura y Deporte [Orden EDU/3083/2009, de 6 de noviembre, por la que se convocan ayudas para becas y contratos de Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación, en el marco del Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica 2008-2011]. El aporte internacional de esta tesis doctoral ha podido llevarse a cabo gracias a las dos ayudas para estancias breves en el extranjero a personal investigador en formación del Programa de Formación de Profesorado Universitario. Y también, gracias a la ayuda para el fomento de la formación y la internacionalización de doctorandos del Consejo Social de la Universidad Politécnica de Madrid [XII convocatoria de ayudas del consejo social para el curso 2013-2014]. La asistencia a congresos y la realización del trabajo de campo han podido llevarse a cabo gracias al apoyo económico del proyecto Proyecto: “DEhesas y TALLares de Encina en la España mediterránea: propuestas de gestión para la sostenibilidad de dos sistemas forestales paradigmáticos” (De.Tall.E); proyecto de investigación financiado por el Plan Nacional I+D+I en el subprograma de Recursos y Tecnologías Agrarias en coordinación con las comunidades autónomas [RTA200900110]..

(24)

(25)

(26)

(27) 1. INTRODUCTION 1.1. Mediterranean scattered oak woodlands in human-dominated landscapes Within human-dominated landscapes, many different traditional and recently modified ecosystems throughout the world include remnant scattered trees in pasture lands holding livestock grazing (Guevara et al. 2005; Manning et al. 2006; Gibbons et al. 2008). They are the result of a slow long-term history of manipulations by humans, representing landscapes that have been sustained by cultural systems over thousands of years (Manning et al. 2006; Underwood et al. 2009), and now they have been forced a drastic shift over the last century. A scattered formation may exist naturally, but more often low tree density occurs as legacies of past forests or woodlands that have been cleared or thinned, where trees are maintained incidentally or deliberately as part of agroforestry systems (Pulido 1999; Manning et al. 2006; Moreno and Pulido 2009). Livestock fields cover the largest geographic extent compared to any other form of land use (Asner et al. 2004) and notably modify biodiversity and vegetation structure (Derner et al. 2009). Many of these scattered trees in pasture lands systems hold livestock which is the most important direct product of these systems. Livestock grazing is a fundamental tool for enhancing grassland quality which becomes, in turn, an essential component for livestock husbandry (Rolo et al. 2015). In particular, Mediterranean ecosystems are hotspots of biodiversity (Myers et al. 2000) in which the pasture lands with scattered (predominantly oak) trees within human-dominated landscapes highlight. Mediterranean environments present features that make them attractive both for its ecology as its human history and cultural aspects, and are especially sensitive to any climate change because it represents a transition zone between arid and humid regions of the world (Scarascia-Mugnozza et al. 2000). Such environments are found in parts of California, Chile, South Africa and Australia, and Mediterranean Basin. Mediterranean environment represents an enormous challenge to scientific and land managers because of its size, physical complexity, geological and anthropological history (Blondel and Aroson 1995). Mediterranean scattered oak woodlands (variously named as oak pastures, oak savanna woodlands, dehesas, montados) are characterized by scattered oak layer within a complex mosaic of rolling pastures, cropland and scrubland, where, frequently, livestock are extensively raised (Rolo et al. 2015). These systems have great ecological and socio-economic importance in Mediterranean regions around the world, supporting both rangeland agroforestry 3.

(28) systems and rural populations (Standiford et al. 2003; Allen-Diaz et al. 2007; Marañón et al. 2009; Bugalho et al. 2011).. 1.2. Biodiversity and ecosystem services of Mediterranean scattered oak woodlands A major feature of Earth is the existence of life, and the most extraordinary feature of life is its diversity (Cardinale et al. 2012). Biodiversity increases the stability of ecosystem functions through time. For example, the total resource capture and biomass production are generally more stable in more diverse communities (Cottingham et al. 2001; Campbell et al. 2011). Furthermore, the ecosystems produce services that benefit humanity (MA 2005). These benefits are differentiated in four service groups: provisioning services (e.g. food, water), regulating services (e.g. floods, land degradation, desiccation, pests and diseases); supporting services (e.g. nutrient cycling, soil creation) and cultural services (e.g. aesthetic pleasure, recreation, cultural and spiritual sustenance). Human activities have caused large-scale transformations to ecosystems, with important impacts on biodiversity and ecosystems services (MA 2005). As a response of that, many conservation strategies have been founded in the implementation of a “preservation approach”, based on the premise that biodiversity values can be maintained in protected areas with strict regulation of anthropogenic impact (Margules et al. 2000; Bruner 2001). However, high biodiversity is often concentrated in complex human-dominated systems (Bouma et al. 1998; Henle et al. 2008) such as croplands, grazed rangelands, or managed forests, which are able to provide rich biodiversity and vital ecosystem services (MA 2005). Conservation strategies, therefore, should reconcile the maintenance of biodiversity and ecosystem services values with socio-economic development in such systems adjusting to global change (Cardador et al. 2015). Within human-dominated landscapes, Mediterranean scattered oak woodlands have high environmental and amenity values, and support relatively rich biological diversity while producing important ecosystem services (Myers et al. 2000; Eichhorn et al. 2006; Jose 2009). Traditionally, these systems provide a large variety of ecosystems goods besides wood, including firewood, charcoal, food for humans and animals, gums, resins, dyes, pharmaceuticals, cork, and aromatic plants, hunting; but also several non-tangible benefits to society such as watershed protection, microclimate amelioration, carbon sequestration, soil stabilization and protection, land for grazing and human recreation, 4.

(29) open-space of recreational and aesthetic value and historical meaningful landscapes (Pavlick et al. 1991; Greenwood et al. 1993; Campos-Palacín et al. 2007; Palahí et al. 2009). However, it is difficult to give monetary values to these services and they provide no revenues to their private or communal owners, and hence it results in lower interest to maintain silvicultural treatments can maintain adequately the stands (Scarascia-Mugnozza et al. 2000). On the other hand, biodiversity loss impacts on the functioning of ecosystems reducing the ability of ecological communities to capture biologically essential resources, producing biomass, decomposing and recycling biologically essential nutrients (Cardinale et al. 2012). Land cover change has been the most important direct driver of global terrestrial biodiversity loss in the last 60 years, and is projected to have an increasing impact in most ecosystems (MA 2005), among which Mediterranean scattered oak woodlands stand out. Alteration and fragmentation of large habitats involve processes of native vegetation removal, change in plant of animal habitats, endangering biodiversity. Mediterranean scattered oak woodlands have been originated due to anthropogenic activities, and hence their structure and dynamics depend strongly on human activity. These systems have shown to be resilient to progressive historical landscape transformation; but at certain point, will they be unable to respond these fast disturbances in future? How long will they be able to restore by themselves? Therefore, to avoid exceeding the threshold of natural restoration and to buffer biodiversity loss adequate agroforestry techniques in such systems are necessary (Noble and Dirzo 1997).. 1.3. Effects of scattered trees and livestock grazing on herbaceous communities One of the keys to preserve Mediterranean scattered oak woodlands is to maintain an adequate balance among the interactions of their main components (livestock-treesgrasslands). These interactions are not straightforward because they depend on a variety of external factors (e.g. water availability, grazing stocking rates, forest fires) (Scholes and Archer 1997; Gea-Izquierdo et al. 2009). In Mediterranean areas, they are even more complex due to the high seasonality in natural resources availability (great intraand inter- annual rainfall fluctuations that modify these interactions), and low organic matter content in soil (Callaway and Walker 1997; Scholes and Archer 1997; Sternberg et al. 2000; Gea-Izquierdo et al. 2010). The extensive livestock rearing is one of the major basis and objectives of these systems, and hence maintaining high levels of yield 5.

(30) and diversity of the natural herbaceous communities is necessary to obtain high-quality livestock products (Olea and San Miguel 2006; Rolo et al. 2015). Scattered trees are well-valued elements due to the disproportionally wide range of important ecological functions and ecosystem services they provide relative to the small area they occupy (Manning et al. 2006). In the last few decades, researchers have examined how remnant trees in anthropic landscapes modify the understory environment creating microsites characterized by low intensity and filtered solar radiation, and less extreme thermic and hydric variations (Jackson et al. 1990; Marañón and Bartolome 1994; Power et al. 2003). Trees improve soil structure (Scholes and Archer 1997; Joffre et al. 1999); increase the amount of nutrients, organic matter content in soil and water reservoir close to their root systems (Scholes and Archer 1997; Gallardo 2003; Cubera and Moreno 2007; Rolo et al. 2012, 2015); and hence, change species composition, structure, spatial distribution, nutrient content, biomass and plant diversity of herb layer (González-Bernáldez et al. 1969; Saenz and Sawyer 1986; Bartolome and McClaran 1992; Pineda and Montalvo 1995; Ludwig et al. 2004; Rolo et al. 2015). These effects created by trees are more remarkable when trees are mature generating higher differences in herbaceous communities (e.g. yield, species diversity) located beneath their large crowns compared to those located under immature trees (Scholes and Archer 1997; Treydte et al. 2009; Spanos et al. 2010). Trees increase also carbon sequestration (Roig et al. 2010; Bugalho et al. 2011; Simón et al. 2013); add aesthetic qualities to the landscape, increasing potential for tourism and recreation (Schnabel and Ferreira 2004) and have connectivity landscape functions (Manning et al. 2006). Previous research has shown that the herbaceous biomass is lower beneath the tree canopy influence (there is a slower herbaceous growth) relative to outside canopy influence during the early spring season in California rangelands for years with little or no water stress (500-600 mm) (Marañón and Bartolome 1994). Other studies, however, have shown higher herbaceous biomass under canopies (Holland 1980; Callaway et al. 1991) or not significant differences between both microsites (Jackson et al. 1990). In dry years, when annual rainfall is low or infrequent (<450 mm), herbaceous biomass may be higher beneath than outside the canopy influence (McClaran and Bartolome 1989; Callaway 1995). In Mediterranean Basin oak woodlands with enough annual rainfall (>500 mm), the herbaceous biomass under canopy is higher compared to open grasslands but there are less differences between both microsites with dry conditions 6.

(31) (<450 mm) (Moreno 2008; Gea-Izquierdo et al. 2009). Therefore, there are no clear trends of herbaceous biomass yield in Mediterranean scattered oak woodlands. Nevertheless, at landscape level, total herbaceous yield may increase from the open grasslands (or with isolated trees) to scattered oak woodlands, but decrease as tree density increase in close woodlands (Scholes and Archer 1997). Grassland yield is not the only critical aspect to maintain a rational livestock management. Grassland quality is even more important since, in terms of nutritional value, is a major determinant of animal production efficiency (Van Soest 1985). The herb layer with high legume abundance has a higher protein and mineral content, and thus increases the pasture quality within the system (Olea and San Miguel 2006). The existence of plant diversity in grasslands avoids the dominance of certain type of species that decrease the grassland quality as, for example, grasses do (López-Carrasco et al. 2015). Also, high plant diversity raises the whole system resilience to climate and anthropogenic disruption (López-Sánchez et al. 2014a). Some studies have been focused on the relationship between diversity and biomass of the herbaceous layer (McNaughton 1968; Vázquez-de-Aldana et al. 2008). McNaughton (1968) found a negative correlation between herbaceous species richness and biomass in open grasslands. However, the way in which yield and species composition interact, and how they respond to the presence of scattered trees is still poorly understood (Ludwig et al. 2001). In the last few decades, some studies have shown that herbaceous diversity indices are lower beneath than outside the canopy influence (Marañón and Bartolome 1994; Fernández-Moya et al. 2011), although these results can change with the annual rainfall (Callaway 1995). Within the canopy area of influence, studies have revealed that distance from the trunk changes the species composition (Marañón and Bartolome 1993; Fernández-Moya et al. 2011), leading to higher alpha diversity at the edge of the crown or ecotone compared to beneath the crown itself (Marañón 1986; López-Sánchez et al. 2013). At landscape level, all these changes produced by trees increase biodiversity levels in Mediterranean environments (Marañón 1986). Trees also attract animals by providing forage (grass and browse) and shade, affording protection from full sunlight (Joffre et al. 1988, 1999; Belsky 1994) or nesting sites for multiple species (Tews et al. 2004). Large herbivores sheltering below the tree canopies compact and fertilize soil and deposit seeds through their dung (Díez et al. 1992; Peco et al. 2006); alter community nutrient pools (Binkley et al. 2003; Piñeiro et al. 2009); and, overall, change the species composition, biomass and structure of plant 7.

(32) communities (Putman et al. 1991; Frank et al. 2002). Their effect can be more decisive than the direct tree effect (Gea-Izquierdo et al. 2010). The presence of livestock grazing and scattered trees provides different characteristic herbaceous species that are better adapted or pre-adapted to them. In the Mediterranean Region, many plant species have evolved life history traits adapted to grazing, including high re-sprouting capability of woody species or summer dormancy of mainly annual herb species (Naveh and Carmel 2004; Agra and Ne’eman 2011) and tree canopy influence (Marañón and Bartolome 1993). Several studies have pointed out some species as characteristic of grazed vs. ungrazed zones and beneath vs. beyond the canopy influence in Californian rangelands (e.g. Callaway et al. 1991; Parker and Muller 1982) or in Mediterranean Basin oak woodlands (e.g. Bugalho et al. 2011; Stenberg et al. 2000).. 1.4. A major threat of Mediterranean scattered oak woodlands perpetuation Currently, the Mediterranean regions show clear signs of millennia of human habitation and use (>100,000 years; di Castri 1981). Their biodiversity is estimated to experience the greatest proportional change by 2100 owing to their sensitivity to land use and climate change (Sala et al. 2000). Their woodlands have undergone an important anthropogenic impact through their history (Naveh and Lieberman 1993); and especially climate disruption, socio-economic shifts and variety of land conversion and land-use changes since the 1950s (Blondel and Aronson 1995, 1999; Underwood et al. 2009), ranging from low-intensity farmland to extensive irrigation-based agriculture (Hobbs 1998); from oak woodlands to grasslands or croplands (Scarascia-Mugnozza et al. 2000); and population density and growth of urban areas (Rouget et al. 2003; Schwartz et al. 2006). Such changes have been developed with little or no explicitly planned conservation objectives (Roche et al. 2012), which have placed these systems under threat (Marañón et al. 2009; Underwood et al. 2009). For example, the complex and multifunctional agro-silvopastoral land-use systems have become simplified and intensified forms of livestock husbandry and agriculture (Naveh 1982; Hill et al. 2008). This intensification of land use within Mediterranean scattered oak woodlands has brought increased soil erosion and reduced forage production (Greenwood et al. 1993; Trimble and Mendel 1995; Blondel 2006). In contrast, there was also land abandonment which promoted the rapid development of shrublands which has often involved negative impacts on fire regimes (especially frequent in Mediterranean areas), losses of 8.

(33) biodiversity associated with traditional uses, losses of grassland quality in which most of the system biodiversity is located, and degradation of cultural ecosystem services (MacDonald et al. 2000). Both over- and underuse can modify ecosystem structure and functions, as Mediterranean scattered oak woodlands are tightly coupled in humandominated landscapes (De Aranzabal et al. 2008; Röder et al. 2008). One major consequence of anthropogenic impact within these systems is the apparent lack of oak recruitment occurring in the drier areas of oak ranges (Bolsinger 1988; Brown and Davis 1991; Standiford et al. 1997). Oak recruitment is necessary for population regeneration (Gibbons et al. 2008) and its absence can lead to long-term declines in natural oak populations (Brown and Davis 1991; Standiford et al. 1997; Sork et al. 2002) contributing to the desertification process; and therefore can be a long recognized threat for the persistence of many scattered oak woodlands worldwide [(e.g. Californian oak rangelands, Mediterranean basin silvopastoral oak woodlands, Spanish dehesas) Manning et al. 2006; Gibbons et al. 2008; Fischer et al. 2009]. Mediterranean scattered oak woodlands support low numbers of young oaks compared to adults, suggesting that populations are not demographically balanced (Callaway and Davis 1998). The causes of poor oak regeneration remain still unclear. Previous research have most often cited different factors as limiting oak recruitment which include: female flowers and leaf herbivory, acorn diseases, acorn predation (Swiecki et al. 1998; Díaz et al. 2004), herbivory of established young plants by wild (mainly deer) and domestic (mainly cattle) animals (Griffin 1971; Standiford et al. 1997; Dufour-Dror 2007), insect herbivory (McCreary and Tecklin 1994; Pulido and Díaz 2005), competition for water between oak seedlings and non-native annual grasses (Welker et al. 1991; Hamilton et al. 1999), soil compaction by cattle (Bolsinger 1988; Greenwood et al. 1993), lack of fire and low rainfall in some years (McClaran 1986; Tyler et al. 2002), shade resulting from dense canopy cover (Muick 1991). Furthermore, the arrival and spread of sudden oak death disease syndrome (SODS; caused by a complex disease related to the Phytophtora cinnamomi pathogen), in recent years has already led to significant oak mortality in several Mediterranean scattered oak woodlands, such as in Californian rangelands (Zavaleta et al. 2007) or Spanish dehesas (Brasier 1992; Sánchez et al. 2002). Consequently, SODS prompt a high lack of oak regeneration. However, unsuitable rangeland management practices exerted in these systems over the last century have been implicated as primary factors preventing natural oak recruitment (Dahlegren et al. 1997; Pulido et al. 2001; Plieninger et al. 2003, 2011; 9.

(34) Tyler et al. 2006). In particular, the increment of livestock stocking rates has been often related to recruitment failure (Pulido et al. 2001; Hostert et al. 2003; Plieninger et al. 2003; Cierjacks et al. 2004). Some studies in Mediterranean scattered oak woodlands worldwide (e.g. Californian rangelands or Mediterranean Basin oak woodlands) have shown important reductions in the density of saplings in cattle-grazed areas compared to areas without cattle for more than two decades (McClaran and Bartolome 1989; DufourDror 2007; López-Sánchez et al. 2014b). Additionally, the size of young plants (seedlings and saplings) was lower in cattle-grazed areas compared to those without cattle (Garbarino and Bergmeier 2014; López-Sánchez et al. 2014b). The result of a high permanent herbivory exerted by cattle is the existence of small oaks, repeatedly browsed, which finally grow out of the cow reach and form coppice-like trees with multiple stems that may eventually merge to single-stemmed tall trees with expansive, mushroom-shaped or spherical crowns (Garbarino and Bergmeier 2014). The stressing effect of herbivory could produce instability in the performance and development of plants during their growth (Møller and Shykoff 1999). In most cases of Mediterranean scattered oak woodlands there is a permanent stressing effect of herbivory that severely limits the growth of the few existent young plants, which hardly will achieve the adult stage. Herbivores generally reduce biomass and vegetation cover of the layers that are within their grazing height and destroy parts of the plants by pulling and trampling (Milchunas and Lauenroth 1993). However, livestock species have also been described as ecosystem engineers acting as important bottom-up and top-down forces to structure ecological communities (Waller and Alverson 1997; Derner et al. 2009). Low levels of herbivory generally make possible woody growth and reproduction whereas the opposite conditions (high levels) preclude plant development (Díaz et al. 2004). This circumstance may allow not only a considerable young plant density but also sustained high quality of grasslands compared to livestock absence.. 1.5. Dehesas The main research conducted in this dissertation has been developed with typical Mediterranean scattered oak woodlands, the well-studied Iberian dehesas (e.g. Larson 2000). Dehesas define much of south-western Spain landscapes (about 3.5 Mha, MAPA 2008). They have been historically shaped by humans through modification of existing evergreen oak-dominated forests (Stevenson and Harrison 1992; Joffre et al. 1999; 10.

(35) Moreno and Pulido 2009). López Sáez et al. (2007) have shown that the beginning of the dehesa landscape creation could have started approximately over four millennia before Christ. They are internationally recognized for their ecological, socioeconomic and cultural importance and support a relatively high rich biological diversity compared to those original Mediterranean woodlands which they come from (Plieninger and Wilbrand 2001; Díaz and Pulido 2009; Moreno and Pulido 2009). Hence, dehesas are considered a habitat of European Community interest: 6310 by the Directive 43/92/EEC (European Commission 1992). They are also among the best preserved, low-intensity farming systems in Europe representing an archetypal example of High Nature Value Farmland (HNVF; Hoogeveen et al. 2004); because their use as grazing lands enhances herbaceous diversity levels while producing additional important natural resources and ecosystem services (Plieninger and Wilbrand 2001; Díaz et al. 2003; Díaz and Pulido 2009). Therefore, the government is required to take adequate conservation measures to maintain, restore and ensure the future of the protected habitats and species for which the site has been designated to a favorable conservation status, in this case the dehesas. Damaging activities that could significantly disturb the protected species or habitat types must be avoided (Art. 6 Directive 43/92/EEC). The dehesa structure consists of three main elements: trees, grasslands and livestock (San Miguel 1994). The tree layer mostly is represented by holm oak (Quercus ilex ssp ballota L.) and/or cork oak (Quercus suber L.), with oak (Quercus faginea Lam.) in humid zones. Holm oak dehesas have been used for the studies developed in this dissertation. The herbaceous communities coexist according to the management and microsite climate- and topo-edaphic characteristics. They are essential for extensive livestock rearing which is the main objective of the dehesas just as of other Mediterranean scattered oak woodlands (Olea and San Miguel 2006). Plant diversity indices are high compared to other types of patches around dehesas within human-dominated landscape structure (Pineda et al. 1981; Montalvo 1992). These raised diversity levels depend mainly on climate conditions of the year, slope dynamics, characteristics and distribution of the scattered trees (González Bernáldez et al. 1969), and livestock management (Carmona et al. 2013b). Mediterranean climate impose two periods of limited natural resources for breeding livestock, summer drought and winter dormant period. As a result of this, herbaceous communities are usually annual species grasslands. Perennials play a fundamental role in valley bottoms and in dense swards created and maintained by intense and continuous grazing, known as “majadales” (San 11.

(36) Miguel 1994). The management of natural pastures is aimed at increasing their quality which means higher proportion of legumes, and hence higher protein and mineral content (Olea and San Miguel 2006). Within dehesas, livestock has an important role contributing in seed dispersal, controlling shrub encroachment, and accelerating nutrient cycle (San Miguel 1994, 2001). Livestock is represented mostly by cattle, sheep and swine. Some dehesas have other target livestock animals but less common such as goat or horse, and rarely donkey. I focused on cattle and sheep for the studies developed in this dissertation. In Spain, different breeds of cattle (e.g. “avileña-negra ibérica, morucha, retinta, lidia, blanca cacereña) and of sheep (e.g. “merina, Ille de France, Fleischscahff”) are used in dehesas (Olea and San Miguel 2006). Dehesas are linked to high-value native breeds increasing the diversity of dehesas. Native cattle breeds of dehesa system are “retinta” and “avileña-negra ibérica” and the most emblematic sheep native breed is “merina”, which has been high valued over centuries due to their exceptional yarn, great robustness, and well adapted to the territory (San Miguel 1994; Gaspar et al. 2008). Dehesas need urgently conservation management plans that may apply adequate agroforestry management techniques taking to account the knowledge generated about their conservation. The traditional use has originated this system, but it has to be maintained with new approaches adapted to global change that preserve and improve the biodiversity levels and ecosystems services, and guarantee their sustainability for long-term. The existent legislative actions are not clear enough, and even sometimes are opposing initiatives. In the recent years, the sustainability of dehesas has come into question with the trend towards more intensive and simplified management (Papanastasis 2004). But, both uses, intensification as abandonment degrade dehesas, and consequently become extinct. Dehesas are not self-sustaining systems and are tightly linked to characteristics of Mediterranean climate. They are located mainly in relatively poor soils; hence the presence of scattered trees performs a critical function as a retardant of soil erosion and desertification which are considered primary environmental concerns in the Mediterranean basin (Thornes 2000). Since soils are quite poor, the profitability of grazing plus rotational cultivation in these systems is higher than intensive cultivation alone (Plieninger et al. 2004). In addition, dehesas are located in an area which is highly sensitive to climate change (IPCC 2014) and their role as a carbon sink becomes more relevant. Especially the uppermost soil layer store roughly 50% of the soil organic carbon and it is the most sensitive layer, since it is 12.

(37) highly exposed to natural or human-induced disturbances such as livestock management or tillage (Simón et al. 2013). But cessation of livestock rearing may also involve loss of biodiversity and devastating wildfires (Papanastasis 2009). Therefore, the role of scattered trees and livestock grazing are keystones for efficient use and conservation of Mediterranean dehesas just as other Mediterranean scattered oak woodlands. An effective improved-management and restoration strategy for such emblematic systems must take into account the inherent spatially and temporally complex tree-understory plant community relationships (Fenández-Rebollo and Tejeiro 1999; Roche et al. 2012) and the consequences of anthropogenic activities (mainly livestock husbandry) developed within these systems. Consequently, it is really important to know better how the system works to avoid some of the problems caused when inappropriate or inadequate technologies are applied (Pineda and Montalvo 1995).. 1.6. Justification Research conducted on Mediterranean scattered oak woodlands has been summarized through the different sections within this general introduction. The dehesa system has been used to develop the different studies included in this dissertation as a good example of Mediterranean scattered oak woodland. Even though previous research in dehesas has been undertaken, there are still large gaps of knowledge in our understanding of Mediterranean scattered oak woodlands functioning and particularly in relationships among their components. How do tree presence and livestock grazing modify herbaceous layer both separately and as a whole? How climate variations affect these relationships and those characterized by summer drought conditions? It is especially important to understand herbaceous biomass and diversity responses to dry conditions (Lavorel 1999) due to the way that the typically unpredictable annual weather regimes dramatically affect the flora. And, which herbaceous species are the most adapted to these disturbances? Addressing these questions is needed to understand the role of trees and grazing management in the overall herbaceous yield (use) and diversity (conservation) of these systems under variable climate conditions. In particular, it is necessary to deepen more in the effects of the scattered trees (e.g. size of trees, microsites created by trees, site quality of the trees) combining with proper livestock management (e.g. animal species or management intensity) on herbaceous. 13.

(38) communities, since high quality and yield of herbaceous layer is essential for the system profitability. And profitability is essential for guaranteeing the system preservation. In addition, as we know, anthropogenic impact has been accelerated during the last century, hence the studies included in this dissertation are contextualized within the changing dehesa framework experienced in the last 60 years. It is necessary to evaluate the general evolution trend of these two major elements (trees and livestock management) that modified greatly herbaceous communities within dehesas. The balance of whole system is maintained while all components are sustainable managed. Furthermore, oak regeneration is scarce or absent in many cases as section 1.4 of dissertation has shown. Then, is oak regeneration possible in Mediterranean scattered oak woodlands holding livestock grazing? Especially, it is necessary to deepen more in the young plant density distribution, the damage of herbivore in different types of young plants and the protection effects of different microsites as a possible refuge against the strong herbivory. And, are trees simple survivors with no promising future generation within this global change framework? Do trees have a certain type of growth under these management conditions? Addressing these questions is important to understand how different management approaches conducted within these systems during long time (more than 30 years) have affected oak regeneration in order to establish best possible practices that can maximize the conservation and regeneration of Mediterranean scattered oak woodlands. Knowing more about systems will be fundamental to defend and give arguments for dehesas preservation through financial support (e.g. European Common Agricultural Policy subsidies). Therefore this dissertation aims to bring together the effect of trees and grazing management over herbaceous communities, especially in yield and diversity, and on their mutual relationship (yield-diversity). Knowing what management improves these relationships would lead us to higher levels of efficiency in the use and conservation of the whole system. This dissertation analyzes, as well, one of the major threats over oak regeneration which is linked with anthropogenic activities (mainly livestock rearing). Hence it is essential to find solutions for the sustainability and perpetuation of tree layer within these systems by means of the advanced knowledge about the effects of herbivores. Through the ages, people of the Mediterranean region have tried, not always successfully, to find a balance between exploitation and conservation of natural resources (Scarascia-Mugnozza et al. 2000). Hence, we should focus and concentrate efforts looking for synergies between management and conservation with the aim of 14.

(39) finding a balance between them, and thus of assuring their persistence in a global change framework. The dehesa management could be a good reference for other Mediterranean scattered oak woodlands and, going further, for any world-wide scattered tree woodlands supporting anthropogenic activities (mainly livestock husbandry) in rough sites.. 15.

(40)

(41)

(42)

(43) 2. OBJECTIVES The main purpose of this dissertation is to progress in definition of sustainable strategies of the Mediterranean scattered oak woodlands (dehesas). I will focus on the important role of scattered trees, the high yield-diversity of grasslands and extensivelymanaged livestock as keystones for balance of the whole system management and preservation. This general aim materializes in the following specific objectives per chapters: (i) To know the current general situation of dehesa systems and their evolution over the last 60 years in which major land use changes have taken place. The dehesa landscape development at large geographic scale, focusing on changes of tree layer density and livestock stocking rates will be analyzed (Chapter 4). (ii) To analyze and study the functioning of dehesa system looking into relationships among livestock-trees-grasslands including factors as the effect of the presence of scattered trees at the system on herbaceous yield and diversity (and their relationship) and same (Chapter 5) or different grazing management (Chapter 7). These effects may subject to the water availability of the system come from annual rainfall (Chapter 5 and 7) and site quality (Chapter 5). The study will focus on herbaceous diversity provided by zones with trees in comparison to those without trees in different grazing management regimes (Chapter 6) including the species characteristics related to trees and grazing management zones (Chapters 6 and 7). (iii) To analyze the oak regeneration condition under three representative management schemes conducted in the last decades within Mediterranean scattered oak woodlands (dehesas). The current density of young plants (and type of recruitment), the microsite location of the oak recruitment, the probability of herbivory occurrence and intensity over young plants, and the morphology condition of young plants will be studied (Chapter 8). Furthermore, oak regeneration condition will be also evaluated in other similar Mediterranean scattered oak woodland to dehesas (Chapter 9)..

(44) Chapter 5: Effect of tree cover on herbaceous layer (biomass – diversity). Differences in site quality and annual rainfall effect.. Chapter 7: Effect of tree cover and livestock grazing on herbaceous layer (biomass – diversity). Differences in annual rainfall.. Chapter 6 and 7: Species characteristics related to trees and grazing management zones.. Chapter 6: Effect of tree presence vs. absence on diversity of herbaceous layer.. Figure 2.1 Illustration of the objectives followed in this dissertation.. Chapter 8 and 9: Oak regeneration in Mediterranean scattered oak woodlands.. Chapter 4: Evolution of tree density, and cattle and sheep stocking rates..

(45)

(46)

(47) 3. MATERIAL AND METHODS 3.1. Mediterranean scattered oak woodlands: Study areas 3.1.1. Study area Spanish dehesas land The study described in chapter 4 was developed within the geographic distribution of Spanish dehesas in western and southwestern Spain. We used sample plots from the SISPARES monitoring framework (Elena-Rosselló et al. 2005 www.sispares.com; Fig. 3.1). The whole study covered an area of ca 200,000 km2. The dehesas climate is Mediterranean with high climatic variations as a rule. Dehesas have great differences between maximum and minimum temperature throughout the year and in the most continental regions. There is marked summer drought from June to September which predetermines the vegetation development and management. The common termotypes are Mesomediterranean and Supramediterranean (Rivas Martínez 1987). There are high intra-annual rainfall fluctuations, concentrating most of the rainfall during autumn and spring season. The mean values for annual rainfall range from 500 to 600 mm, although there are also a high inter-annual rainfall fluctuations with some extreme dry years and other very humid years, thus providing ombrotypes from dry to humid (Rivas Martínez 1987). Dehesas are over Paleozoic materials influenced by Cenozoic fold from Alpina Orogenia or over Cenozoic Basin with Paleozoic eroded materials (Meléndez 2004; Vera 2004). The soils have usually low fertility with scarce essential nutrients, acidic, with low organic matter content and bad physic conditions. There is also high topo-edaphic variability, and soils can be poorly developed, such as leptosols and regosols or other more developed such as cambisols and luvisols, which have accumulation soil horizons (Gómez Gutiérrez 1992; Brady and Weil 2002).. 23.

(48) Figure 3.1 Location of the selected sample landscape plots (black points) of ‘SISPARES’ Network distributed in provinces (grey color) of west and southwest of Spain.. 3.1.2. Study area Spanish dehesas ranches. The study described in chapter 8 was conducted across three oak dehesa ranches (715, 600 and 680 ha) in Toledo province, Central Spain (39-40oN, 5oW; 300-400 m a.s.l.; Fig. 3.2). The whole study covered an area of ca 108 km2, with homogeneous characteristics (largely flat and open). The climate is Mediterranean oceanic pluvioseasonal (Rivas-Martínez and Rivas-Saenz 2013) with dry, hot summers in which temperatures can reach 40ºC and with winters in which temperature can reach -9.6ºC in the coldest month. The 30-year average annual rainfall of the study area is 572 mm (Meterological station 3427C “Oropesa – Dehesón del Encinar”), concentrated in winter months, although inter-annual variation is considerable. The soils are sandy (>80% of sand), acidic (pH 5.5), and the topsoil has a low organic matter content (1% organic matter w/w). The tree canopy consists of open holm oak (Quercus ilex L. ssp. ballota (Desf.) Samp.) with some scattered cork oaks (Quercus suber L.). Shrub cover is low and is mostly dominated by xerophytic and evergreen species (Cistus ladanifer L., Lavandula stoechas Lam., Cistus salvifolius L, Halimium ocymoides (Lam.) Willk., Genista hirsuta Vahl and Rosmarinus officinalis L.). The herbaceous layer consists mainly of sub24.

(49) nitrophilous Mediterranean annual communities (Thero-Brometalia, Rivas-Martínez et al. 2001), therophytic oligotrophic communities (Tuberarietalia guttatae, Rivas-Martínez et al. 2001) and also some therophytic oligotrophic communities on sandy soils (Malcolmietalia, Rivas-Martínez et al. 2001).. Figure 3.2 Location of the sampling ranches of holm oak populations in northeast Toledo province, Central Spain. The management condition of the study sites is indicated: CW, cattle and wildlife; SW, sheep and wildlife; WO, wildlife only.. 3.1.3. Study area Dehesón del Encinar The studies described in chapters 5, 6 and 7 were developed in a typical dehesa (715 ha) in Toledo province, in Central Spain (39o59/N, 5o8/W; 350 m a.s.l.; Fig. 3.3). The climate is Mediterranean pluvioseasonal oceanic (Rivas-Martínez and Rivas-Saenz 2013), with a mean (20 years) annual rainfall of 607 mm (September-Augus period) and a mean annual temperature of 15.1ºC (López-Carrasco and Roig 2009). During the study period (2008-2013) the annual (September-August period) rainfall ranged from 274 to 25.

(50) 878 mm and spring (March-May) rainfall ranged from 82 to 318 mm as recorded by the on-ranch Meteorological station 3427C “Oropesa – Dehesón del Encinar” (Fig. 3.4). In 2008, 2009 and 2012, the annual rainfall was 10%, 39% and 55% lower than the 20-year mean and in 2010, 2011 and 2013 it was 45%, 5% and 33% higher (López-Carrasco and Roig 2009). The mean temperature for this period (2008-2013) was 15.0ºC, as recorded by the on-farm meteorological station. The soils are sandy (>80% of sand), acidic (pH 5.5), and the topsoil had a low organic matter content (1% organic matter w/w). The trees are scattered holm oak (Quercus ilex ssp ballota (Desf.) Samp.) with some scattered cork oaks (Quercus suber L.). There are some large areas without tree canopy cover due to past management. The understory mainly comprises sub-nitrophilous and nitrophilous Mediterranean annual communities (Thero-Brometalia and Sisymbretalia officinalis Rivas-Martínez et al. 2001) representing a 20% cover at each of the ranch grasslands. Therophytic oligotrophic communities (Tuberarietalia guttatae, RivasMartínez et al. 2001) are also frequent with a 25% cover of the ranch grasslands, as well as therophytic oligotrophic communities on sandy soils (Malcolmietalia, Rivas-Martínez et al. 2001) with only 5% of grassland cover. Grasslands dominated by dwarf perennial grasses and herb species promoted by intense and continuous livestock grazing (Poetea bulbosae, Rivas-Martínez et al. 2001), code 6220* by the Directive 43/92/EEC (European Commission 1992), are common with 15% cover. The farm has been grazed by livestock for over thirty years as well as by wildlife (especially red deer -Cervus elaphus L.-) at low stocking rates (less than 0.05 individual ha-1, equivalent to 0.007 cow ha-1). The cattle breed is “Avileña negra ibérica”, grazed with a stocking rate of 0.33 cow ha-1 (López-Carrasco et al. 2011). The sheep breed is “Talaverana”, grazed with a stocking rate of 1 sheep ha-1 (equivalent to 0.15 cow ha-1; 55% lower stocking rate than cattle grazing). Both are well adapted to local grasslands (López-Carrasco et al. 2011).. 26.

(51) Figure 3.3 Location of the sampling plots of chapters 5, 6 and 7 within study area “Deheson del Encinar” in northeast Toledo province, Central Spain.. Figure 3.4 Data rainfall for the study period (2008-2013) in chapters 5, 6 and 7. The annual rainfall ranges between September (i year) and August (i+1 year). The spring rainfall ranges between March and May. Horizontal line is the 20-year mean according to López-Carrasco and Roig 2009.. 27.

(52) 3.1.4. Study area other Mediterranean scattered oak woodlands ranches The study was conducted across eight ranches located in Northern California (Fig. 3.5). The whole study area covered 10,000 km2. In all ranches, predominant vertebrate herbivores (mainly black-tailed deer (Odocoileus hemionus Rafinesque)) were present. Livestock has been maintained for at least some period in all selected ranches. Four of them have had cattle for more than 100 years; three of them currently support cattle year round, and one supports cattle from November to May. The rest have not supported cattle in the last 40 years (Table 3.1). The study area has a Mediterranean climate typical of California's coastal area, with dry, hot summers in which temperatures can reach 37.7°C. However, summer temperatures are usually tempered by coastal advection fogs providing significant moisture to plant communities. The 30-year average annual rainfall of the study area is 625.3 mm, concentrated in winter months, though inter-annual variation is considerable. Soils at the study sites are of metamorphic and sedimentary origins, maintaining complex substrate distributions that support a mosaic of plant community types, but open grasslands and oak woodlands of varying canopy coverage dominate the area’s landscapes. Given the latitudinal position of the study area, aspect also affects the microclimatic conditions and therefore vegetation structure and composition. Within each ranch, we selected sites defined as open oak woodland dominated by cost live oak (Quercus agrifolia Née). Study sites ranged in size from 160 to 243 ha (Table 3.1). Sites with homogeneous characteristics (largely flat and open) were selected for study.. 28.

(53) Figure 3.5 Location of the sampling ranches of coast live oak populations in Northern California, USA. JRBP, Jasper Ridge Biological Preserve; EP, Edgewood Preserve; AP, Enid Pearson-Arrastradero Preserve; HNHR, Hastings Natural History Reservation; ORR, Oak Ridge Ranch; TD, The Dish at Stanford University; BP, Briones Regional Park; WCRP, Wildcat Canyon Regional Park. The management condition of the study sites is indicated in parenthesis: CW, cattle and wildlife; WO, wildlife only. Table 3.1 Location and main features of the ranches where coast live oak populations were sampled.. Ranch JPBR EP AP HNHR ORR TD BRP WCRP. County San Mateo San Mateo Santa Clara Monterey Monterey Santa Clara Contra Costa Contra Costa. Latitude (N) 37º24’ 37º28’ 37º22’ 37º23’ 37º23’ 37º23’ 37º56’ 37º56’. Longitude (W) 122º13’ 122º17’ 122º11’ 122º33’ 122º33’ 122º10’ 122º08’ 122º17’. Study area (ha) 175 188 237 243 160 228 201 189. Livestock No (40) No (46) No (43) No (76) Yes Yes Yes Yes. Values in parentheses indicate the number of years livestock have been absent, where applicable. JRBP, Jasper Ridge Biological Preserve; EP, Edgewood Preserve; AP, Enid Pearson-Arrastradero Preserve; HNHR, Hastings Natural History Reservation; ORR, Oak Ridge Ranch; TD, The Dish at Stanford University; BP, Briones Regional Park; WCRP, Wildcat Canyon Regional Park.. 29.

(54) 3.2. Variables analyzed and general methodologies 3.2.1. Characterization of herbaceous layer in dehesas We used subplots 50 x 50 cm as sampling points to measure all pasture variables. The total aboveground biomass (hereafter biomass) was measured mowing (using grass shears) at ground level at the end of the growing season (late May or early June, coinciding with the usual peak of the grassland yield according to Pérez-Corona 1992). The mown material from each subplot was taken immediately to the laboratory and then dried at 60-80ºC until constant dry weight. We then obtained the total dry matter (DM) and functional groups (grasses, legumes and forbs) DM (kg ha-1) for each subplot. In each subplot, we also determined floristic composition by species (or morphospecies where species-level sorting was not possible) and calculated some diversity indices (Fig. 3.6). To quantify the species abundance index of the herbaceous layer in each subplot, categories according to Braun-Blanquet (1979) were used. The categories represented the cover percent of each species inside each subplot (+ for sporadic presence, 1 for plants with <10% cover, 2 for plants with 10-25% cover, 3 for plants with 25-50% cover, 4 for plants with 50-75% cover and 5 for plants with >75% cover).. Figure 3.6 Floristic composition determinations by species or morphospecies within the subplots 50 x 50 cm.. 30.

(55) 3.2.2. Diversity indices Ecologists have long distinguished between different components of species diversity. Traditionally, three are recognized, alpha or local diversity ( ), beta diversity or differentiation ( ) and gamma or regional diversity ( ) (Koleff et al., 2003). We have measured the herbaceous diversity through alpha and beta indices. Alpha diversity measures the local diversity level within a determinate community. Species Richness index (Whittaker et al. 2001), Shannon-Wiener diversity index (Shannon and Weaver 1969) and Shannon-Wiener diversity equitability index (Begon et al. 1996) have been used in this dissertation. Species Richness index (S) S is the total number of species recorded within the considerate community. Shannon-Wiener index (H) S. H =−. S: Species richness. Pi: abundance proportion of the i-species for the total sample.. Pi ln Pi i =1. Shannon-Wiener equitability index (J) This index varies from 0 to 1, whose values close to 1 means more diverse. S. J =. H = H max. −. Pi ln Pi i =1. ln S. S: Species richness. Pi: abundance proportion of the i-species for the total sample.. Beta diversity, the spatial turnover or change in the identities of species, measures differences in species composition either between two or more local communities or between local and regional communities (Koleff et al., 2003). It is not only important to have high local diversity within the community considered, but also to have high species exchange between different communities because it gives higher system resilience. Koleff et al., (2003) showed a list of 24 different beta indices where Whittaker’s index (1960) is the most used in the review of 60 papers. Whittaker’s index (1960) has been used in this doctorate dissertation to analyze herbaceous beta diversity.. 31.

(56) Original formulation:. βw =. S. α. −1. S: the total number of species recorded for both communities. α: average number of species found within the communities.. The original equation has also been re-expressed in terms of the pairwise matching/mismatching components used in similarity/dissimilarity coefficients, and usually denoted as a, b and c (e.g. Krebs 1999). Whittaker’s index varies from 0 to 1. If two communities are completely different the value for Whittaker’s index will be 1. Formulation through components: βw =. a+b+c −1 (2 a + b + c ) / 2. a: the total number of species shared by the two communities. b: the total number of species present only on the community 1. c: the total number of species present only on the community 2.. 3.3. Statistical analysis and software The geographical information was transferred into geographic information system using ArcCatalog and ArcMap packages of ArcGis Desktop 10. Data collection of the different studies (chapters 4 to 9) done in this dissertation were processed and analyzed using R (R Development Core Team 2010, http://www.R-project.org). Some extra modules were used (Table 3.2). Table 3.2 R version and extra models used per chapters.. Chapter 4. R version 3.1.1. 5. 2.10.1. 6 and 7. 3.0.2. 8. 3.1.1. 9. 2.13.2. Extra modules 'car' (Fox and Weisberg 2011), 'lme4' (Bates et al. 2013), 'MuMIn' (Barton 2013) and 'nnet' (Venables and Ripley 2002). 'car' (Fox and Weisberg, 2011), 'lmtest' (Zeileis and Hothorn, 2002), 'MuMIn' (Barton, 2011) and 'vegan' (Oksanen et al., 2011). 'car' (Fox and Weisberg 2011), 'lme4' (Bates et al. 2013), 'MuMIn' (Barton 2013) and 'vegan' (Oksanen et al. 2013) 'car' (Fox and Weisberg 2011), 'glmmADMB' (Fournier et al. 2012), 'lme4' (Bates et al. 2012), 'MuMIn' (Barton 2011) and 'nnet' (Venables and Ripley 2002). 'car' (Fox and Weisberg 2011), 'lme4' (Bates et al. 2012) and 'nnet' (Venables and Ripley 2002).. 32.