MARCO TEÓRICO

This thesis focuses on the ecology, distribution and relative roles of factors and processes that can influence the structure of epiphytic lichen communities in mountain beech Nothofagus solandri var. cliffortioides forests of New Zealand.

Lichens are an integral part of the epiphytic community and clearly are an important ecological component of the overall biodiversity of beech forest ecosystems. Overall, the results from this study indicate the structure of the lichen community on a mountain beech tree is a complex arrangement of species. Epiphytes are not contiguous across the trunk and the community is mostly a mosaic of patches. The lichen community structure (diversity, richness and abundance) are more similar within trees than among trees of the same age. Most differences occur across the different aged stands.

Factors that are most influential in determining abundance patterns vary with epiphyte groups though clear differences occur with age stand, where cyanolichens, squamulose lichens, and bryophytes abundance significantly increased with age stand while crustose lichen abundance decreases suggesting that these groups have more limited distribution patterns and require different habitat conditions provided by specific tree ages. Fruticose lichens showed consistent patterns across stand ages that are more widely distributed throughout. For most epiphytes distribution patterns across trunk aspects and vertical regions on the trunk, vary with age stand. This demonstrates the high variability of epiphyte distribution and complexity of characterizing the structure of the lichen community.

Distribution patterns of lichen abundance are greatest in 140year olds trees and lichen richness is highest in youngest aged stands and on branches. This indicates habitat conditions are equally, if not more important, than the area available for the epiphytic lichen communities structure in Craigieburn.

Evaluation of environmental variables showed humidity, light transmittance and bark

canopy density (average 13% canopy openness) and cool temperatures (average 5.3°C) did not. Microhabitats associated with high lichen richness have smooth acidic bark (pH 3.62), high humidity (average 87%), and higher transmitted radiation (average 19.42%), whereas lichen abundance increases with low bark acidity (4.27 pH), humidity (65%) and low radiation (average 17.33%). More variable microclimatic conditions within trees have more lichen species which emphasizes lichens are well adapted to respond to their immediate surroundings. These findings emphasize the importance of the immediate microclimate and bark morphology on lichen richness and abundance patterns.

Structurally, vertical position on the trunk was the most influential factor for determining species composition. However, not all epiphyte groups showed abundance patterns that clearly increased or decreased up the trunk, instead many groups show a patchy distribution on the tree. This suggests that species have affinities for a particular habitat which is located at various positions of the tree. Epiphyte group abundance patterns showed that crustose lichens were related to some environmental variables (light transmittance and tree height) and cyanolichen abundance was related to many environmental variables (light transmittance, tree height, tree diameter, bark pH and bark condition). This shows that these species require specialized habitats that can be determined at broader stand level scales. Foliose, green algae lichens and bryophytes were significantly associated with environmental variables within trees (bark pH and bark condition). This suggests that species are associated with distinct habitats within trees.

The investigation of entire 140year-old trees revealed clear differences in community structure between branches and trunks. Bryophytes, sooty molds, cyanolichens and squamulous lichens were more abundant on trunks with intermediate to rough bark whereas the abundance of fruticose and usnic acid-lichens was highest on branches and smooth bark. Crustose species abundance was highest in upper trunk regions and branches. Lichen richness and abundance was highest in the middle vertical regions (8-12m) of the tree and greater on secondary branches and twigs. All green algal lichen species, especially species with usnic acid significantly increase up the trunk whereas cyanolichen abundance decreases. This pattern demonstrates photobiont versatility of lichens within trees and suggests adaptation to environmental conditions.

Removal experiments using Menegazzia pertransita and Pseudocyphellaria colensoi showed that these epiphytes respond to disturbance and successfully re-established themselves after

disturbance within the same tree age and aspect. This suggests that these species are not limited by dispersal at this scale. Species responses to disturbance demonstrates that they could have

affinities for particular niches associated with these areas of 140year-old trees (southern aspect, with bark that has some cracks and ridges, bark that is less acidic, and conditions with lower light levels and increased humidity). Removal experiments could not identify one process that was more important, instead it suggests that multiple processes such as dispersal abilities, expansion in terms of high growth rates, overgrowth, species interactions including facilitation and

competition are all important mechanisms in structuring the lichen community on 140year-old trees.

Biomass of the cyanolichens P. colensoi and P. faveolata significantly increased with stand age (0.43-5.9 kgha-1). Transplants methods that used an attached mesh were successful with few thalli lost. Annual growth for P. colensoi and P. faveolata is 8%-13%. Transplants showed no growth differences across various aged stands or between vertical positions for all but 140 year- old trees, with growth significantly higher in areas where species are naturally found. In areas of higher annual growth where these species are naturally found suggests habitat and environmental conditions are more suitable in these areas of 140year-old trees. Therefore these species can survive and grow in the broad range of conditions. Manipulation experiments suggest

Pseudocyphellaria species was growing slowly because of combined dispersal limitations and

habitat requirements. Propagules may be able to disperse into different trunk positions or age stands, (with a source nearby), yet unable to establish themselves until conditions are suitable for growth of cyanobacteria. Conditions suitable for P. colensoi and P. faveolata are bark with cracks and ridges that is less acidic in combination with high humidity and low light transmittance. The results from this study indicate that mountain beech trees in Craigieburn exhibit a diverse, structurally complex assemblage of lichens where numerous factors and processes are involved in shaping the community structure. Change is constant and understanding species current

distribution patterns can assist in answering questions about ecological shifts in our changing world. This study presents very valuable baseline resources for future work on determining the full impact of lichen biodiversity on New Zealand beech forests. Lichen assemblages can provide information from a small to large scale; as distribution patterns can be linked across continents to provide a global picture of environmental change. However more research is required to make better decisions about management and restoration of these forest communities. This is especially true as these forest ecosystems are threatened with increasing risks from climate change, loss of habitat due modified landscapes and threats from exotic invasive species.