Summarises recent information on the nature of gap-understorey environments, paying particular attention to the role of light amount and duration, soil nutrient availability and soil moisture and gap dynamics (focusing on gap-size frequency distributions and forest turnover rates). Patterns of growth and mortality are noted. Evidence is considered regarding habitat specialisation by tropical trees, reviewing data on the distribution of adult and juvenile trees, and on the relative performances of similar species along gap-understorey gradients. Discussion centres on life history attributes in a gap-understorey mosaic.-P.J.Jarvis
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"This suggests that local light availability plays a critical role on determining biodiversity patterns (Grubb, 1977; Denslow, 1987). Local disturbances, such as gaps formed by treefall and standing dead alders, increase heterogeneity in light conditions and may promote the coexistence of species by providing opportunities for niche differentiation (Denslow, 1987). Rüger et al. (2009) evaluated the influence of light gap disturbances on tree recruitment in a 50-ha tropical forest plot in Barro Colorado Island, which was the first established plot of the CTFS-ForestGEO network, concluding that nearly all species increased in recruitment with increasing light. "
"We conducted a canopy reduction treatment 4 years after planting in order to study the growth response to increased light availability, and examine how the responses varied with tree species' traits. The canopy reduction treatment was conducted to imitate the gap dynamics of a tropical rainforest (Denslow, 1987), and this sort of treatment is applicable for practical enrichment planting projects. We used traits to predict the tree species' responses in height growth to treatment (Table 1). "
[Show abstract][Hide abstract]ABSTRACT: Rainforest restoration is an important application in today's multipurpose management of secondary forest. However, our knowledge of tree species' traits and responses to treatment is insufficient for foresters to make good decisions for sustainable management. The aim of our study was to see whether it is possible to predict tree species' responses to increased light based on species' traits, and to relate these responses to a possible pioneer-climax continuum of life history traits, also among species with presumed climax properties. We examined 33 taxa (including 19 from the dipterocarp family) replicated 20 times and randomly planted in lines over a 3. ha area in the interior of Sabah, Borneo. Four years after establishment we performed a canopy reduction treatment to increase the light conditions up to levels present in tree gaps in the forest. We created a PLS (Partial Least Square Regressions) model with the two predicted variables HGR (height growth response) and Q3 HGR (the 75 percentile of a species' HGR, interpreted as the potential HGR). The model captured 47% of the variation for the predicted variables. We found significant tree species' responses in height growth to the increased light. High specific leaf area, strong early height growth, high foliar N content, high leaved stem length and large crown were linked to fast growth, while high wood density and high foliar K content were associated with slow growth. We also found a trade-off between growth response and survival among the species. We conclude that climax tree species have specific life history adaptations along a pioneer-climax continuum, which can be predicted from species' traits. The importance of easily observed or extracted traits such as initial growth rate, specific leaf area and wood density for predicting growth suggests the possibility of fast screening of species with unknown characteristics, which could be of great value in practical forest management.
No preview · Article · Feb 2016 · Forest Ecology and Management
"The latter hypothesis claims that " diversity is highest when disturbances are intermediate in intensity or size and lower when disturbances are at either extreme " (Connell 1978). Over time, confirming evidence has been presented for both hypotheses: the gap partitioning hypothesis (e.g., Brokaw 1985; Denslow 1987; Abe et al. 1995; Sipe and Bazzaz 1995) and the intermediate disturbance hypothesis (Sheil 2001). However, there is also a remaining debate about the validity of either hypothesis (e.g., Brokaw and Busing 2000; Fox 2013). "