Tree community change in Tropical Dry Forests
Specifically the role of impact of building/maintaining/using roads. [5].
Study area:
880 km2 in the Western Ghats of southern India Methods: The goal of this study was to “document tree death and tree community composition with respect to road, road width and road-associated exotic plants.” [5]. There were also comparisons included in the study between road bordering communities and inner forest. The road-associated exotic plants were accounted for in the variable for understory as it was separated into two categories: Native and Exotic. (i.e. The road-side exotic plants would be represented as exotic understory.) Road width also was represented as two categories: Wide Roads and Narrow Roads. There were ten experimental plots (each plot 10m2) at random locations (80 total plots) in each of the possible categories of forest type (narrow-native, narrow-exotic, wide-native, wide-exotic). In each plot, tree species numbers and the number of dead trees were noted for comparison. It is important to note that not all tree species were able to be accounted for because of the presence of burned specimens, as fire occurs often in these forests as part of a successional cycle between tropical dry forest and tropical savannah. Data collection: Oct. 2006 - Jan. 2007. |
Results:
Dead tree Density:
70% (56/80) plots contained at least one dead tree.
Highest dead tree density correlated with the lowest live tree density. These areas were defined as being the plots near wide roads with exotic understory. It is important to note that roadside plots showed a much higher tree death than interior plots (both wide and narrow roads). Plots that were defined as having exotic understory had a higher number (twice as many) of dead trees that ones with native understory. Statistical analysis shows an insignificant relationship between tree death and understory composition, though there is a significant relationship between road width and understory type when looking at the density of dead trees per plot.
Species Composition:
Total Tree Density:
3-17 individual trees, 1-16 of them being live per plot.
The study shows that actual species composition did not change much between roadside and interior plots, but rather that plots that were classified as having exotic understory had a significantly different species composition. Specific species were found more abundantly in native understories (Anogeissus latifolia and Terminalia alata) and in exotic understories (Tectona grandis and Phyllanthus emblica). Road width also showed a similar relation to species composition. Plots that were part of the wide road category contained less individuals of the aforementioned species than the plots that were in the narrow road category.
Conservation actions:
This study makes it clear that the creation/maintenance of roads directly influences/damages the tree communities of Tropical Dry Forests. While these roads are necessary to maintain the forests (and in the case of the study area: tourism) it is clear that the human activity associated with the roads have a massive impact on the forests. It is important to note that most of these forests occur in isolated patches and that the construction of roads could directly influence the biotic/abiotic factors occurring there.
Logging (in this case selective logging) is a destructive industry that takes place in tropical dry forests around the world, because the inhabitant tree species are sources for rare/valuable woods. Therefore, roads are constructed for use by logging trucks. These trucks bring in exotic grass species that lead to the effects outlined by exotic/invasive plant colonization on tree communities. Similar to the study area stated above, the tropical dry forests of Bolivia are undergoing a similar phenomenon. Exotic plant species (in this case exotic African grasses) are being brought into the forests via logging trucks. As it turns out, these trucks are the primary source of seed dispersal in these forests targeted by selective logging [10]. Abundance of exotic grasses increased with the increased severity of the logging taking place; therefore, a comparison can be made between the tropical dry forests of Bolivia and India [9]. Roads (i.e. pathways to selective logging sites) are a major pathway in the dispersal of exotic plant seeds. In the case of the Indian forests, the exotic species that colonize are destructive to the current tree/forest community (i.e dead tree density).
“Understanding the vegetation changes that result from human disturbances is important at both (local and global) scales to develop better forest management and improve vegetation dynamic models to predict the fates of tropical forests” [9]. Because of the fragile state of tropical dry forests, exotic plant influence is a strong driving force. In the case of Bolivia, selective logging changes the complete infrastructure of the forest communities, and in many cases, changes the logging plots into grasslands comprised of exotic grass species instead of native forest grass species. In India, fewer studies have been done to discover where/how the exotic species disperse, but it is safe to say that the presence of roads correlates with the presence of exotic species. Further studies should be done to evaluate the correlation between the two areas described here.
Dead tree Density:
70% (56/80) plots contained at least one dead tree.
Highest dead tree density correlated with the lowest live tree density. These areas were defined as being the plots near wide roads with exotic understory. It is important to note that roadside plots showed a much higher tree death than interior plots (both wide and narrow roads). Plots that were defined as having exotic understory had a higher number (twice as many) of dead trees that ones with native understory. Statistical analysis shows an insignificant relationship between tree death and understory composition, though there is a significant relationship between road width and understory type when looking at the density of dead trees per plot.
Species Composition:
Total Tree Density:
3-17 individual trees, 1-16 of them being live per plot.
The study shows that actual species composition did not change much between roadside and interior plots, but rather that plots that were classified as having exotic understory had a significantly different species composition. Specific species were found more abundantly in native understories (Anogeissus latifolia and Terminalia alata) and in exotic understories (Tectona grandis and Phyllanthus emblica). Road width also showed a similar relation to species composition. Plots that were part of the wide road category contained less individuals of the aforementioned species than the plots that were in the narrow road category.
Conservation actions:
This study makes it clear that the creation/maintenance of roads directly influences/damages the tree communities of Tropical Dry Forests. While these roads are necessary to maintain the forests (and in the case of the study area: tourism) it is clear that the human activity associated with the roads have a massive impact on the forests. It is important to note that most of these forests occur in isolated patches and that the construction of roads could directly influence the biotic/abiotic factors occurring there.
Logging (in this case selective logging) is a destructive industry that takes place in tropical dry forests around the world, because the inhabitant tree species are sources for rare/valuable woods. Therefore, roads are constructed for use by logging trucks. These trucks bring in exotic grass species that lead to the effects outlined by exotic/invasive plant colonization on tree communities. Similar to the study area stated above, the tropical dry forests of Bolivia are undergoing a similar phenomenon. Exotic plant species (in this case exotic African grasses) are being brought into the forests via logging trucks. As it turns out, these trucks are the primary source of seed dispersal in these forests targeted by selective logging [10]. Abundance of exotic grasses increased with the increased severity of the logging taking place; therefore, a comparison can be made between the tropical dry forests of Bolivia and India [9]. Roads (i.e. pathways to selective logging sites) are a major pathway in the dispersal of exotic plant seeds. In the case of the Indian forests, the exotic species that colonize are destructive to the current tree/forest community (i.e dead tree density).
“Understanding the vegetation changes that result from human disturbances is important at both (local and global) scales to develop better forest management and improve vegetation dynamic models to predict the fates of tropical forests” [9]. Because of the fragile state of tropical dry forests, exotic plant influence is a strong driving force. In the case of Bolivia, selective logging changes the complete infrastructure of the forest communities, and in many cases, changes the logging plots into grasslands comprised of exotic grass species instead of native forest grass species. In India, fewer studies have been done to discover where/how the exotic species disperse, but it is safe to say that the presence of roads correlates with the presence of exotic species. Further studies should be done to evaluate the correlation between the two areas described here.