La teoría práctica y la normatividad del derecho

Interhemispheric climatic linkages across the Americas

A major result of the Collaborative Research Network has been the consolidation and expansion of tree-ring collections across the traditional research regions of North and South America, the focusing on key areas and the start of many developments in new regions of Canada, Mexico, Peru, Bolivia, Chile and Argentina (Fig. 1). Along the western coasts of North and South America, there is a gradual environmental gradient from the dry-warm subtropics to the wet-cold high latitudes. Tree-ring records from subtropical regions, such as the southwestern US and Central Chile, are remarkably sensitive to precipitation variations (Cook et al 2004; Boninsegna 1988, LeQuesne et al, 2005). In the transitional zones to higher latitudes, tree-ring responses to climate are largely determined by site conditions. Depending on elevation, aspect, slope, and soil characteristics, tree growth can be influenced by temperature, precipitation or more commonly by a combination of both. At the extreme wet and cold environments in high- latitude upper treelines, temperature is the major limiting factor controlling tree growth (Wiles et al. 1996, 1998; Luckman et al. 1998; Villalba et al. 1997, 2003; Aravena et al. 2002; Lara et al. 2005). These changes in tree response with latitude are instrumental in setting the strategies for selecting tree-ring records sensitive to temperature and precipitation variations along the western Americas. Temperature reconstructions based on upper elevation chronologies from coastal sites around the Gulf of Alaska and northern Patagonia were selected as proxy records of temperature for North and South America, respectively. Tree-ring records from mesic to dry environments in the southern-central USA, the Bolivian Altiplano and central Chile were used for the inter-

hemispheric comparison of precipitation-sensitive records across the American Cordilleras (Fig. 1). The results of these interhemispheric comparisons are synthesized in a paper entitled “Dendroclimatology from regional to continental scales: understanding local processes to reconstruct large-scale climatic variations across the Western Americas” (Villalba et al, submitted) and will be published in the book reporting the major findings of the 2004 Tucson conference on “Tree Rings and Climate: Sharpening the Focus”. Additional information on this topic is provided in the Synthesis section of Section 3.2 of the Overview in this report.

Figure 1. Distribution of tree-ring chronologies across the Western American Cordilleras.

Rainfall-controlled tree growth in high elevation subtropical treelines

It is generally assumed that tree growth in the upper limit of a forest is mainly controlled by summer temperature. This general statement is mostly based on studies from extra-tropical mountains and has been rarely evaluated in subtropical latitudes frequently characterized by drier climates. In the subtropical mountains from Northwestern Argentina (c. 23° S), annual precipitation decreases with elevation from more than 1500 mm at 1200-1500 m, to less than 200 mm above 4000 m. In consequence, tree-growth at high elevations in the region may be seriously limited by water supply. In order to assess the influence of precipitation on tree growth, we evaluated the relationships between climatic variations and radial growth in four species growing at different altitudinal zones: Juglans australis from the montane cloud forest at 1800 m; Alnus acuminata from the montane savanna-like woodland at 2700 m; Prosopis ferox from the subalpine dryland at 3500 m; and Polylepis tarapacana from the high-elevation alpine dryland at 4750 m. Dendrochronological techniques were used to relate variations in annual ring width with instrumental climatic records. In spite of the remarkable differences in elevation and environmental conditions among the sampling sites, correlation functions with climate indicated that the radial growth of the four species is largely controlled by precipitation. In most cases, increased precipitation during the previous and current growing seasons favors tree growth, while temperatures are negatively correlated with radial growth, likely due to the negative effect

limited by summer temperatures should be carefully evaluated in low-latitude environments and does not apply to subtropical areas with severe water deficits or strong moisture seasonalities.

Dynamics of Prosopis flexuosa woodlands in the Monte formation

The Monte is an extensive area of semi-arid forest and scrublands between 26 and 36˚S in Arg

orthern, woodla

ccurs between years, the

orest management of the Monte desert, Argentina is supported by the Argentinean Agency entina. The Prosopis flexuosa (mesquite) woodlands of this region show a southward decrease in structural complexity, growth rate, and biomass, suggesting a large-scale climatic control on these forests. However, at local scale, the structure of Monte woodlands reflects the heavy logging in the early 20th century, the subsequent transformation to pastoral use, and differential recovery capacity. In the southern Monte, the dynamics are controlled by fires, which have increased in frequency during recent decades, possibly related to climatic changes.

The potential sustainable use of these woodlands varies latitudinally. Only the n

nds have the potential for lumber production. In contrast, the short, multi-stem and low productivity trees in the southern areas can only sustain a combination of local firewood production and activities such as extensive grazing by livestock. Our studies of biomass production by these forests (Villagra et al 2005) indicate that the present, uniform regulations for harvesting wood in these areas must be changed to acknowledge these differences in order to optimize wood production in, and conservation of, these woodlands.

Although synchronization of fruiting in Prosopis trees o

reproductive output is extremely variable from year to year and individual trees may produce no fruit in some years. The last reproductive period (2003-2004) with the highest fruit production also had the lowest annual rainfall of the last 10 years in the central Monte. There were no important rainfall events between late March 2003 and mid January 2004. This lack of rains during the main bloom of mesquite seems to be important to the reproductive success of this species. If the dry periods during flowering increase fruit production, the future increase in rainfall suggested by computer models for this region would decrease the probability of Prosopis fruit production and thereby reduce recruitment of this species in the Monte desert.

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for Science and Technology Development and CONICET. Ecological variables in the Monte desert from Salta (26°C) to south of Mendoza (36° S) have been measured in several plots. We combined historical, dendrochronological, tree demographic and satellite data to evaluate the relative contribution of the factors controlling the dynamics of Prosopis woodlands in the arid lands of Argentina. Traditionally, Prosopis woodlands were selected by humans for settlement. Most of the present urban and crop lands in this region are located on areas originally covered by Prosopis due to the easier access to water and the microclimatic conditions generated by woodlands. The urbanization and irrigation processes lead to the reduction of Prosopis woodlands, and to the increase of the demand of forest products from the remaining woodlands. Presently more than 20% of the original area of Prosopis woodlands in the Monte has been replaced by agriculture.

Radial growth of Prosopis caldenia (Cladén) in the semiarid Argentinan Pampas

This project is partially supported by IAI, the Argentinean Council for Research (CONI

oclimatological

ee-ring chronologies from Prosopis caldenia are the first from this species

ambial growth and tree-ring chronologies in Tierra del Fuego

New sampling was carried out in Tierra del Fuego during March 2004 and 2005 resulting CET) and the Universidad de San Luis, Argentina. It is part of Ing. Stella Bogino’s masters degree at Universidad de Cordoba, under the supervision of R. Villalba.

The mean radial growth rate, the biological rotation age and the dendr

potential of caldén (Prosopis caldenia Burkart) were determined using a combination of dendrochronological methods in four stands located in San Luis province (33°S, 65°W). For the common interval 1937-2000 (64 years) among sites, the mean accumulated radial growth varies between 172 to 243 cm, whereas the mean annual radial growth ranges from 2,69 to 3,97 mm.year-1. Depending on sites, the biological rotation age ranges between 66 and 100 years. The mean tree diameters at the time of the biological rotation ages range from 49.68-53.97 cm. in the four stands. A conspicuous common signal in tree growth was observed among individuals growing at the same stand, suggesting that tree growth from different trees responds similarly to the environmental factors influencing growth. However, the relationships between climate and tree growth are complex. Depending on the site selected linear multivariate or non-linear) relationships were observed between climate and tree growth. The radial growth of caldén can be expressed as multivariate relationships using the temperature departures at the beginning and end of the growing season (October and March at one site) or the temperature departures during the growing season (from October to April in other locations), and the annual precipitation (both sites) as predictors of tree growth. These climatic variables explain more than 40% of the total variance in caldén tree growth during the interval 1937-1989. At the El Liebral stand, the radial growth of caldén is largely linked to annual precipitation during relatively dry periods. During years with abundant precipitation (> 0.75 SD above the regional mean), temperatures during the growing season control tree growth. Tree growth increases with temperature, but during very warm summers (temperatures >1.5 SD from the regional mean), higher temperatures reduce soil moisture and radial growth. This conditional relationship between the climatic variables and tree growth (summer temperature is a limiting factor when annual precipitation is larger than 0.75 SD) accounts for 30% of the interannual variation in radial growth of caldén at El Liebral stand (r= 0.45; p< 0.01).

These four tr

Prosopis caldenia and the most easterly chronologies in Argentina. Despite the complexity in the caldén growth response to climate, these chronologies provide a unique opportunity to investigate past precipitation variations in the largest grain-and-meat producing area of South America.

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in the development of new tree ring chronologies of Nothofagus pumilio from the SE sector of the Island. The fine scale monitoring of Nothofagus pumilio growth dynamics continued during this period, completing a five-year monitoring project. This phenological and cambial monitoring network constitutes the longest detailed growth record obtained from any forest in Argentina and yielded a set of more than 3,000 wood samples that document cambial growth in this species. A publication using these data is currently in preparation. This study includes a new collaborative venture with personnel from the Laboratorio de Propagación y Producción Vegetal

(LPPV), Area de Biología Terrestre del CADIC (Austral Center of Scientific Research) at Ushuaia led by Dr Guillermo Pastur. The participants in this field and laboratory activity were: Guillermo Pastur (CADIC), Guillermina Massaccesi (IANIGLA/CADIC), Vanessa Lencinas (CADIC), Fidel Roig (IANIGLA), Victor Moyano (IANIGLA), Susana Monge (IANIGLA). The project Impact of climatic changes on water resources across the Argentinean Andes is

ght ice covered areas have been selected to reco

In southern Patagonia, three areas were intensively sampled: Adela Range (Piedras Blanca

supported by the Argentinean Agency for the Promotion of Science (PI; Ricardo Villalba) and closely related to the proposed initiative entitled “Documenting, understanding and projecting changes in the hydrological cycle in the American Cordillera”, under consideration for support by IAI (CRNII-047). One component of this project is the investigation of glacier fluctuations and their relationship to changes in temperature and precipitation. Despite the great potential for glaciological studies, remarkably little is known about glaciers in southern South America and particularly on their fluctuations during the past 1000 years, for which the available glacial evidence is usually better preserved. The available evidence from the Argentinean side of the Patagonian Andes indicates a number of glacier advances between the 16th and late-19th centuries (globally identified as Little Ice Age, LIA, Grove 1988), but the number and magnitude of glacial events differ from site to site. In agreement with glaciers from many other mountain areas of the world, the 20th century was characterized by generalized glacier front recession in the Patagonian Andes, only interrupted by a few minor glacial readvances. The extremely low number of glaciers studied and the poor accuracy of most of the dated glacial events indicate that the existing glacial chronologies should remain provisional until more detailed studies at suitable glaciers are developed in the region. Furthermore, since most of these glaciological studies were largely focused on a few large calving glaciers, the glacier history and detailed glacier/climate relationships in the region are not well established yet.

To overcome the limitations discussed above, ei

nstruct past ice front positions and monitor the present dynamics of the glaciers in the Patagonian Andes. Four glaciated areas were selected in the northern Patagonian Andes (39° - 43°S): Lanín, Tronador, Esperanza and Torrecillas. In the south Patagonian region, the areas selected for study are located between the 47° and 50°S, and from north to south are San Lorenzo, Narváez, Cordón Adela and Fitz Roy. During the austral summer of 2004 we conducted extensive sampling in northern and southern Patagonia. In the Mount Tronador area, evidence from a recent tree-ring based temperature reconstruction indicates that cold conditions prevailed between ca. 1600 and 1680, which coincides with the dendrogeomorphic dating of the outermost LIA moraine associated to the Little Ice Age (LIA) at the Frías Glacier. Crossdating established that several in situ stumps, apparently killed by an ice-dammed lake at Ventisquero Negro Glacier, died ca. 1848, providing a precise date for the formation of the outermost LIA moraine. This date coincides with a marked cold interval between 1820 and 1870 inferred from tree-ring records. Historical photographs document generalized ice front recession during the 20th century although tree-rings and instrumental climate records indicate two marked cold intervals during the early 1940s and 1970s that coincide with minor glacier readvances in the area.

s and Torre glaciers), Vespigiani Range (Huemul and two adjacent glaciers) and Lago Argentino sector centered on the Seco Glacier. Studies at Piedras Blancas and Torre glaciers show that the outermost LIA moraines were formed during the early to mid 1600s, similar to the moraines at Frias glacier . Two other large moraines at these glaciers were probably formed

during severe cold intervals in 1780-1825 and 1845-1860 indicated in dendroclimatic temperature reconstructions. Dendrogeomorphological surveys in 2005 revealed similar moraine patterns in other glaciers now under study, suggesting that they may share a common regional climatic signal. Extensive collections included living and sub-fossil samples from Nothofagus pumilio. Exploration at the Seco Glacier was conducted in collaboration with Dr. Brian Luckman, Department of Geography, UWO, Canada.

Fine-scale observations of the growth dynamics of Nothofagus pumilio

At Cerro Krund (southern Tierra del Fuego, Argentina), a network of permanent plots were es

xtension of modern tree-ring chronologies using subfossil wood in Tierra del Fuego

In Tierra del Fuego subfossil wood material is being obtained from peats and from river

fluence of climate variations on Nothofagus forest dynamics in southern Patagonia

Nothofagus pumilio tree-ring variations and stand dynamics along an altitudinal gradient in El C

along this altitudinal gradient (Figure 2).

tablished in the summer of 2000 along an altitudinal profile of Nothofagus pumilio forests between the valley bottom and timberline. Observations from these plots indicate that at any given altitudinal plot, the initial surge of earlywood production occurs after the first-formed leaves are fully expanded; later, the cambium becomes most active and finally ceases by producing latewood cells toward the late summer phenophases. The influence of altitude is seen in both in the delay of the onset of the initial growth stages (up to two weeks between the lowest and highest plots) but also in the shortening of the vegetative growth period. At lower elevations the cambium remains active for 3-4 months, compared with only 2-3 months at the tree-line. Rapid changes in temperature values seem to act as the environmental catalyst that force changes in the phenological phases of the leaf and morphological changes in the wood throughout the ring. Figure 2 shows the synchrony between a sustained increase of maximum air temperatures above a 10°C threshold and the beginning of the growth phases. Toward the end of austral summer, trees slowly end their growth cycle as maximum temperatures fall below this threshold. These links suggest that the timing of the ring formation is restricted to periods where mean maximum temperatures exceed the threshold of 10°C, time periods that would vary from year to year. The results of these fine-scale monitoring programs provide information that provides insight into the interpretation of growth-climate models.

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beds. Radiocarbon ages indicate an interesting distribution of dead logs through time. Crossdating of material radiocarbon dated to between 500 AD and 4,000 BC can be used to build long tree-ring records incrementally (most Nothofagus trees only live for a few centuries). Samples obtained during 2004 have allowed the recovery of tree-ring data that span most of the last millennium. This project is supported by CONICET and partially by CRN03, under the direction of Fidel Roig.

In

haltén, Santa Cruz, Argentina were investigated in relation to climate variations during the 20th century. Sampling plots were located at the forest-steppe border (800 m), in the mesic, well-developed forest (1010 m) and in the krummholz at the transition to alpine vegetation (1130 m). Dendrochronological analysis shows contrasting growth patterns of Nothofagus pumilio

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 No. of trees 2 4 6 No. of trees 5 10 15 20 Tree-ring index 0.4 0.7 1.0 1.3 Temperature departures (°C) -1 0 1 0.4 0.7 1.0 1.3 0.4 0.7 1.0 1.3 -1 0 1 -1 0 1 Tree establishm ent above treeline

Tree m ortality at lower treeline r = 0.56, p < 0.01

r = -0.31, p < 0.05

Figure 2. Relationships at El Chaltén between tree-growth of Nothofagus pumilio at different elevations, regional temperature variations, establishment of new individuals at upper tree-line and mortality at the forest-steppe ecotone. The temperature records are annual means from Rio Gallegos, Punta Arenas and Ushuaia expressed as departures from the interval 1960-1990. Major changes in age structure and dynamic processes are associated with a noticeable increase in temperature after 1976.

Tree ring width at the upper tree-line shows a remarkable positive trend during the 20th century. This positive trend is strongly correlated (r = 0.56, n = 70, p < 0.01) with the increase in

ean annual temperature expressed as departures from the means of Rio Gallegos, Punta Arenas and Us

y cold

ochronological dating of new

During the meeting of IAI PIs in Mendoza in January 2003 discussions between Holm to the evelopment of this collaborative project. The forest cover at one of the CRN01 study sites in the

ntario,

dendrochronological work in the Yucatan; to determine tree ages and fire events in the shifting m

huaia meteorological stations. The growth of trees located at middle elevation shows a slightly negative trend during the last 100 years. The radial growth at this level is related to temperature between 1930 to ca.1976, but temperatures and ringwidths show opposite trends thereafter. In contrast to upper-elevation trees, the growth of trees at the lower treeline shows a strong negative trend since the beginning of the 20th _{century. Temperature variations since 1930} are negatively correlated (r = -0.31, n = 70, p < 0.05) with tree growth at lower elevations.

The increase of temperature during the 20th century has favored tree growth at upper tree-