Community and ecosystem ramifications of increasing lianas in neotropical forests

Abstract

L ianas (woody vines) are increasing in neotropical forests, representing one of the first large-scale structural changes documented for these important ecosystems. The potential ramifications of increasing lianas are huge, as lianas alter both tropical forest diversity and ecosystem functioning. At the community level, lianas affect tree species co-existence and diversity by competing more intensely with some tree species than others, and thus will likely alter tree species composition. At the ecosystem level, lianas affect forest carbon and nutrient storage and fluxes. A decrease in forest carbon storage and sequestration may be the most important ramification of liana increases. Lianas reduce tree growth and increase tree mortality-thus reducing forest-level carbon storage. The increase in lianas, which have much less wood than trees, compensates only partially for the amount of carbon lost in the displaced trees. Because tropical forests contribute approximately one-third of global terrestrial carbon stocks and net primary productivity, the effect of increasing lianas for tropical forest carbon cycles may have serious repercussions at the global scale.Tropical forests contain most of the earth's plant species and contribute more to carbon storage in the form of above ground biomass than any other terrestrial ecosystem. Temperate and boreal forests are changing rapidly in response to global anthropogenic drivers. Similar large-scale changes are now being detected in tropical forests. One of the largest contemporary changes

Liana Abundance, Diversity, and Distribution on Barro Colorado Island, Panama

“…For example, if liana increases are driven by increasing disturbance, we would expect more disturbance-adapted and highly clonal liana species to increase in abundance. In contrast, if other mechanisms such as increasing aridity, nitrogen deposition, hunting, or elevated atmospheric CO 2 are responsible for liana increases [27], [30], we may expect that both disturbance-adapted and highly shade-tolerant liana species will increase in abundance. If, as we hypothesize, the variation in stem size within aggregations is a good indicator of shade-tolerance, then species-specific patterns of liana stem-size distribution throughout the forest and within aggregations provide useful data for testing hypotheses to explain the observed increases in liana abundance and biomass in tropical forests.…”

“…Lianas in the BCI 50-ha plot are both abundant and diverse, and they are increasing in density and biomass, possibly due to global change [27], [30]. Lianas are spatially clumped throughout the BCI 50-ha plot – more so than trees – which may be due to the ability of lianas to rapidly colonize treefall gaps, particularly via clonal reproduction [1], [3], [17], [19].…”

“…In 1979, lianas were censused in ten 0.1 ha plots on the central plateau on BCI [1], in the area where the BCI 50-ha plot is now located, but until now we lacked comparable data to examine whether liana density has increased on BCI. An increase in liana density is likely to have significant consequences for community and ecosystem level processes in tropical forests [30].…”

The effect of seasonal spectral variation on species classification in the Panamanian tropical forest

“…In the context of this study, this implies that not only an understanding of within-species inter-seasonal variation, but the effects of environment (particularly the contrast between rainforest and dry tropical forests) are essential for the implementation of accurate automated classification on a broad scale. This issue is exacerbated by what appears to be increases in overall liana abundance in American tropical forests (Schnitzer et al, 2011).…”

“…More efficient resource allocation in these drier environments results in lower susceptibility to drought and a longer growing season than the surrounding trees. This has led to a general increase in liana load in tropical dry forests (Schnitzer et al, 2011). As well as registering at the leaf level, this syndrome potentially affects remote monitoring of forest phenology where a positive shift in the liana/tree ratio causes an apparent increase in greenness during the onset of the dry season.…”