Spatial Variability In Species Composition In Neotropical Montane Tree Communities

Author : Christopher Heider
Publisher :
ISBN 13 :
Total Pages : 252 pages
Book Rating : 4.:/5 (519 download)

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Download or read book Landscape Level Patterns in Biodiversity written by Christopher Heider and published by . This book was released on 2001 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the tropics, widespread deforestation and conversion of primary forests to agricultural and pasture lands has resulted in losses of composition, structure, and functions of forest landscapes. Deforestation in the tropics is typically preformed via slash-and-burn practices; the byproducts from combustion have been identified as the second-highest form of anthropogenically derived 'greenhouse-gases' (such as carbon dioxide) to the atmosphere, and have been linked to the warming of the earth. Landscape-scale measures of species composition and biomass structure of primary forests are important for two reasons: (i) they provide accurate, land-based measures to predict what has been lost due to land-uses, and (ii) they aid in the discovery of key factors which explain patterns in compositional and structural diversity that are useful for defining conservation objectives. In this thesis, I enumerate the landscape-level patterns in species composition and biomass and C structure for 20-0.79 ha primary tropical forest stands within the region of "Los Tuxtlas", Veracruz, Mexico. These 20 sites were selected to capture the variability in composition and structure with respect to an array of environmental variables. These variables included a wide elevational range (15-1280 m.a.s.l.), variable slopes (Range: 3-41% slope), 3 soil-types (ash derived, lava flows, and weathered soils), a gradient of mean annual temperatures (~19.5-25.7°C), a broad precipitation range (2500 - 4000 mm year−1), a rainfall frequency range (i.e. max rainfall in 24 hours; ranged 30->100 mm day−1), and 3 Holdridge Life Zones (Tropical Moist Forest, Subtropical Wet Forest, and Subtropical Lower Montane Rain Forest). Species composition was highly correlated with the environmental variables, particularly elevation. In general for plants ≥10 cm dbh, site species richness declined at a rate of ~2 species per 100 m rise in elevation. Forest sites located at similar elevations were most similar in their species compositions as compared with sites separated by large elevational differences. Despite the gradual change in species richness and composition, four sub-regions, or forest environments, within Los Tuxtlas were identified that had different species compositions and distinct combinations of elevation, soil-types, and climates. These four sub-regions were described as community-types according to their geographic location: Lowland-Reserve (LR), La Perla Plateau (LP), Volcanic Upslope (VU), and Cloud Forests (CF). The LR, LP, and VU community-types were coarsely described as Tropical Evergreen Forests (TEF's; INEGI 2001). All community-types corresponded with classifications within the Holdridge Life Zone System; the LR community-type was classified as Tropical (transition to Subtropical) Moist Forest; LP and VU community-types were classified as Subtropical Wet Forest, and the Cloud Forest community-type was classified as Subtropical Lower Montane Rain Forest. These community-types and Life Zones are useful tools for conservation, as they represent unique forests that collectively capture much of the variation in the species richness and compositional diversity of the Los Tuxtlas region. Unlike species composition, the variability in forest structure among the 18 TEF sites was not associated with the environmental variables of the Los Tuxtlas landscape. On average, TEF's had a total aboveground biomass (TAGB) of 422 ± 17 Mg ha−1 and 205 ± 8 Mg ha−1 total aboveground carbon (C). The TAGB and C pools for Cloud Forests was ~18% lower than TEF's, and averaged 346 ± 1 and 168 ± 1 Mg ha−1, respectively. The majority of this biomass difference was due to large trees within the forest structure. Cloud Forests had generally fewer trees ≥70 cm dbh, and a more even distribution of trees 30-70 cm dbh than TEF's. The biomass contribution of large trees (≥70 cm dbh) accounted for most, if not all, of the variation in TAGB and C for these tropical forests. The relatively high TAGB and C pools implicates Los Tuxtlas forests as a significant pool of aboveground biomass and C within the Neotropics.