Tropical rainforest gaps and tree species diversity

Annual Review of Ecology and Systematics (Impact Factor: 10.97). 11/1987; 18:431-451. DOI: 10.1146/annurev.ecolsys.18.1.431
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    ABSTRACT: QuestionWhat are the conditions necessary for the establishment and development of seedlings and an early stage sapling community in an old-growth cloud forest? Cloud forests are one of the most threatened ecosystems in the world; however, recruitment patterns in these forests remain largely unknown.LocationCloud Forest, Northern Peruvian Andes.Methods We constructed a sapling community model through the unconstrained technique of non-metric multidimensional scaling. We related the distribution of saplings of each species to the distance from conspecific adult (potential parent) trees through a point pattern analysis. We also used zero-inflated Poisson models to investigate the relationship between sapling distributions and environmental conditions and forest structure.ResultsWe found that recruitment in woody plant species tends to be widely spread throughout the forest. The distribution of some sapling species was either positively or negatively related to the position of adult conspecific trees. Several species tended to occur within particular microhabitat conditions, with some differentiation between canopy and understorey species.Conclusions Cloud forest species recruitment may require the cover provided by the forest canopy. Under closed canopy conditions, both dispersal assembly and niche assembly mechanisms appear to simultaneously influence sapling distribution. The different strategies of various species may result in a trade-off between the importance of microhabitat conditions and distance mechanisms, with one prevailing over the other, depending on species and forest structure conditions.
    Journal of Vegetation Science 03/2015; DOI:10.1111/jvs.12287 · 3.37 Impact Factor
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    ABSTRACT: Reduced impact logging (RIL) has been promoted as a cornerstone in sustainable forest management in the tropics, although the ecological implications of RIL guidelines are poorly understood. This study aims to identify the impact of RIL on the regeneration of commercial timber species by comparing the regeneration dynamics of logging gaps with naturally occuring canopy gaps. In the concession of Consorcio Forestal Amazonico in the region of Ucayali in the Peruvian Amazon, a total of 210 circular sample plots were established in 35 gaps in unmanaged natural forest and 35 canopy gaps in forest managed according to RIL guidelines. The size of each canopy gap was estimated by establishing a polygon that followed the vertical projection of the edge of the gap. Three circular plots of 100 m(2) were established within each canopy gap. The center points of the plots were placed at the stump, mid-trunk and crown of the fallen tree. It appeared that the total abundance of seedlings did not differ significantly between logging gaps and natural canopy gaps. Instead the response to logging varied between species groups. The Clarisia sp. species group had a significant negative response to logging, while Ormosia sp., Aniba sp., Ocotea sp., Qualea sp. and Terminalia sp. were significantly more abundant in gaps of logged-over forest. A direct effect of seed tree retention on seedling abundance could not be detected statistically. Possible reasons for observed differences between untouched and logged forest and consequences of observed patterns for long-term forest development and management were discussed. It was concluded that issuing and enforcing strict guidelines on sustainable forest management is no guarantee for preserving species composition in tropical forests.
    Forest Ecology and Management 12/2013; 310:663-671. DOI:10.1016/j.foreco.2013.09.006 · 2.67 Impact Factor
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    ABSTRACT: Determining the impact of insect herbivores on forest tree seedlings and saplings is difficult without experimentation in the field. Moreover, this impact may be heterogeneous in time and space because of seasonal rainfall and canopy disturbances, or 'gaps', which can influence both insect abundance and plant performance. In this study we used fine netting to individually protect seedlings of Microberlinia bisulcata, Tetraberlinia bifoliolata and Tetraberlinia korupensis trees (Fabaceae = Leguminosae) from insects in 41 paired gap-understorey locations across 80 ha of primary rain forest (Korup, Cameroon). For all species, growth in height and leaf numbers was negligible in the understorey, where M. bisulcata had the lowest survival after c. 2 years. In gaps, however, all species responded positively with pronounced above-ground growth across seasons. When exposed to herbivores their seedling height growth was similar, but in the absence of herbivores, M. bisulcata significantly outgrew both Tetraberlinia species and matched their leaf numbers. This result suggests that insect herbivores might play an important role in maintaining species coexistence by mitigating sapling abundance of the more palatable M. bisulcata, which in gaps was eaten the most severely. The higher ratio in static leaf damage of control-to-caged M. bisulcata seedlings in gaps than understorey locations was consistent with the Plant Vigour Hypothesis. This result, however, did not apply to either Tetraberlinia species. For M. bisulcata and T. korupensis, but not T. bifoliolata (the most shade-tolerant species), caging improved relative seedling survival in the understory locations compared to gaps, providing restricted support for the Limiting Resource Model. Approximately 2.25 years after treatments were removed, the caged seedlings were taller and had more leaves than controls in all three species, and the effect remained strongest for M. bisulcata. We conclude that in this community the impact of leaf herbivory on seedling growth in gaps is strong for the dominant M. bisulcata, which coupled to a very low shade-tolerance contributes to limiting its regeneration. However, because gaps are common to most forests, insect herbivores may be having impacts upon functionally similar tree species that are also characterized by low sapling recruitment much more widely than currently appreciated. An implication for the restoration and management of M. bisulcata populations in forests outside of Korup is that physical protection from herbivores of new seedlings where the canopy is opened by gaps, or by harvesting, should substantially increase its subcanopy regeneration, and thus, too, its opportunities for adult recruitment.
    Forest Ecology and Management 12/2013; 310:555-566. DOI:10.1016/j.foreco.2013.08.029 · 2.67 Impact Factor