Floristic Composition and Edge-Induced Homogenization in Tree Communities in the Fragmented Atlantic Rainforest of Rio De Janeiro, Brazil

Abstract

This study investigates the changes of tree species composition and diversity along the gradient from fragment edge to interior, and between edge and interior habitats, on a regional scale, in nine Atlantic forest fragments (6-120 ha), in southeastern Brazil. A total of 1980 trees (dbh ≥ 5 cm) comprising 252 species, 156 genera and 57 families were surveyed using the point-centered quarter method. From the fragment edge towards the interior the proportion of shade-tolerant trees increased continuously. The majority of all trees within the first 100 m from the edge belonged to the pioneer-guild. Floristic dissimilarity was found to be higher among interior habitats of different fragments than among the corresponding edge areas or among different small fragments. Species diversity increased along the edge-interior gradient 1.5 times within the first 250 m. Our results support previous findings that the establishment of edge-affected habitats leads to tree species impoverishment and homogenization via the dominance and proliferation of pioneer species in the forest edges of severely fragmented tropical landscapes. We argue that conservation strategies which include the creation of buffer zones between forest edges and the matrix will be more efficient than the establishment of narrow corridors to connect fragments and protected areas.Keywords: Atlantic forest; biotic homogenization; pioneer species; forest fragmentation; edge effects ResumoO estudo investiga as mudanças na composição e diversidade das espécies arbóreas ao longo do gradiente bordainterior e entre habitats na borda e no interior a escala regional em nove fragmentos florestais da Mata Atlântica (6-120 ha) no sudeste do Brasil. Um total de 1980 árvores (dap ≥ 5 cm) pertencentes a 252 espécies, 156 gêneros e 57 famílias foram investigadas utilizando-se o método de ponto-quadrante. A proporção de árvores tolerantes à sombra aumenta continuamente ao longo do gradiente borda-interior. Dentro dos primeiros 100 metros a partir da borda florestal, a maioria das árvores pertence à guilda das pioneiras. A dissimilaridade florística foi maior entre as áreas do interior de diferentes fragmentos que entre as áreas de borda correspondentes ou entre diferentes fragmentos pequenos. Nos primeiros 250 metros, ao longo gradiente borda-interior, a diversidade de espécies aumentou 1.5 vezes. Nossos resultados sustentam conclusões prévias de que o estabelecimento de habitats afetados pelos efeitos de borda leva ao empobrecimento e homogeneização das espécies arbóreas através da dominância e proliferação das espécies pioneiras nas bordas florestais de paisagens tropicais severamente fragmentadas. Concluímos que estratégias de conservação que incluam o estabelecimento de zonas de amortecimento entre bordas florestais e a matriz poderiam ser mais eficientes do que o estabelecimento de corredores estreitos para conectar fragmentos e áreas protegidas.

Cross‐scale drivers of plant trait distributions in a fragmented forest landscape

“…At the local‐scale, we found that both the mean and range of leaf economic trait‐complex values increased from the patch interior toward the edge, implying that species (on average) have higher photosynthetic capacity and a more diverse range of light‐use strategies at edges. This pattern agrees with the observation that edges generally have higher light availability (Matlack , Gehlhausen et al ) and soil nutrients, such that edges tend to favour pioneer species with acquisitive light‐use strategies (Benchimol and Peres 2015, Thier and Wesenberg ). Moreover, high light environments are expected to allow the coexistence of species with diverse light‐use strategies (Ries et al , Shen et al ).…”

“…For the 18 small islands (≤ 1 ha), the whole island was gridded and surveyed, excluding the extreme peripheral zones of the island that were located in the inundation zone. For the 11 larger islands (1.16–1158.09 ha), one to four transects 40 m in width were sampled from the forest edge to forest interior (transect lengths varied from 40 to 210 m, depending on island size; Hu et al ). The FDPs were divided into 10 × 10 m subplots, then further divided into 5 × 5 m (projected area) quadrats.…”

“…ArcGIS ver. 10.4 (ESRI ) was used to estimate the LHL for each island at six different buffer radius distances (500, 1000, 1500, , 2500 and 3000 m).…”

“…Patch shape was quantified using the shape index, calculated as the perimeter length of the patch divided by the perimeter of a circle with equal area to that of the patch. Both variables were measured in ArcGIS 10.4 (ESRI ) and FRAGSTATS 4.2 (McGarigal et al ).…”

“…specific leaf area) that reflects variation from quick to slow return on leaf construction investment (Wright et al ). Plant size describes traits such as adult plant height and leaf size (Díaz et al ), and is related to tolerance to disturbance (i.e. climatic extremes) and hydraulic stress (Westoby et al 2002, Ryan et al ).…”