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A foundational concept in ecology is the positive relationship between habitat heterogeneity and species diversity. Epiphytes demonstrate microhabitat specialization to particular areas within a tree; thus, epiphyte communities are potentially influenced by the structural heterogeneity of host trees. We evaluated the relationship between structural features of Acer macrophyllum and epiphyte distributions and abundance in a temperate rainforest in Washington, USA. Epiphytes and structural features of three Acer macrophyllum trees were systematically surveyed using the point-intercept method from the base to the crown and on three branches for each tree. Rarefied species richness increased with structural richness. Species richness along the trunk differed significantly among types of structural features (i.e., broken branches, burls, holes, rivets, branches, and trunks); broken branches had the highest species richness and branches had the lowest, followed by trunks. Rarefied species richness increased with height and peaked at 12 m, but the relationship between structural diversity and height was not significant. The species that occurred on branches were different to those that occurred on trunks, and species composition varied significantly among trunk features. The high structural diversity in northern temperate rainforest trees influenced the fine-scale distribution of nonvascular epiphytes and may explain their coexistence in tree crowns. [ABSTRACT FROM AUTHOR]

Questions: Large trees provide structural heterogeneity that may influence the distribution and diversity of epiphytes, yet this has not been fully examined in northern temperate rainforest trees. How does epiphyte diversity, percent cover and composition vary among trunk and branch zones within northern temperate rainforest trees? Are there steep gradients in environmental conditions or resources within northern temperate rainforest trees? To what degree do species show specialization to particular zones within northern temperate rainforest trees? Location: Temperate rainforest on the Olympic Peninsula in Washington State, USA. Methods: We recorded epiphyte richness, percent cover, and composition in 78 plots from six tree zones (three trunk zones and three branch zones) in six large bigleaf maple (Acer macrophyllum) trees. At each survey point, we measured temperature, relative humidity, canopy cover, moss depth, height in tree, and branch diameter to examine the degree of habitat specialization along measured environmental and resource gradients and the importance of structural heterogeneity for epiphyte species diversity in entire trees. Results: Rarefied epiphyte richness was 25% higher on the trunk than in the branches, and there was little overlap in species composition between trunk and branch zones. Species composition changed with height as well as decreasing canopy cover along the trunk. Within the branches, epiphyte composition was related to branch diameter and moss depth; while the inner and mid‐branch zone communities were similar, the outer branch community differed. Microclimate variables did not vary significantly among tree zones and were not related to epiphyte distributions. Conclusions: The structural heterogeneity of large A. macrophyllum trees created gradients in canopy cover and substrate characteristics that enabled up to 13 different epiphyte species to coexist. Thus, these trees are critical structures for the maintenance of forest diversity. [ABSTRACT FROM AUTHOR]

Land-use change can have profound effects on forest communities, compromising seedling recruitment and growth, and long-term persistence of forests on the landscape. Continued forest conversion to agriculture causes forest fragmentation which decreases forest size, increases edge effects and forest isolation, all of which negatively impact forest health. These fragmentation effects are magnified by human use of forests, which can compromise the continued persistence of species in these forests and the ability of the forests to support the communities that depend on them. We examined the extent and influence of human disturbance (e.g. weedy taxa, native and exotic tree plantations, clearings, buildings) on the ecological status of sacred church forests in the northern highlands of South Gondar, Ethiopia and hypothesized that disturbance would have a negative effect. We found that disturbance was high across all forests (56%) and was negatively associated with tree species richness, density, and biomass and seedling richness and density. Contrary to expectation, we found that forests < 15.5 ha show no difference in disturbance level with distance from population center. Based on our findings, we recommend that local conservation strategies not only protect large forests, but also the small and highly used forests in South Gondar which are critical to the needs of local people, including preserving large trees for seed sources, removing exotic and weedy species from forests, and reducing clearings and trails within forests. [ABSTRACT FROM AUTHOR]

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