Article

Tropical Rainforest Gaps And Tree Species Diversity

Annual Review of Ecology and Systematics (Impact Factor: 10.97). 11/1987; 18(1):431-451. DOI: 10.1146/annurev.ecolsys.18.1.431

ABSTRACT 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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    • "As in natural processes, forest management interventions such as thinning or timber harvesting generate gaps that change forest structure and may trigger natural regeneration (Lamprecht 1990) by influencing the germination and development of forest species in different ways (e.g. Denslow 1987; Alvarez-Buylla and Martinez-Ramos 1992; Dalling and Hubbell 2002). These changes in physical and biotic conditions, as well as the disturbance itself can be viewed as filters that may allow or prevent the entrance of new species in the community (Temperton and Hobbs 2004). "
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    ABSTRACT: Exotic species are used to trigger facilitation in restoration plantings, but this positive effect may not be permanent and these species may have negative effects later on. Since such species can provide a marketable product (firewood), their harvest may represent an advantageous strategy to achieve both ecological and economic benefits. In this study, we looked at the effect of removal of a non-native tree species (Mimosa caesalpiniifolia) on the understory of a semideciduous forest undergoing restoration. We assessed two 14-year-old plantation systems (modified "taungya" agroforestry system; and mixed plantation using commercial timber and firewood tree species) established at two sites with contrasting soil properties in São Paulo state, Brazil. The experimental design included randomized blocks with split plots. The natural regeneration of woody species (height ≥0.2 m) was compared between managed (all M. caesalpiniifolia trees removed) and unmanaged plots during the first year after the intervention. The removal of M. caesalpiniifolia increased species diversity but decreased stand basal area. Nevertheless, the basal area loss was recovered after 1 year. The management treatment affected tree species regeneration differently between species groups. The results of this study suggest that removal of M. caesalpiniifolia benefited the understory and possibly accelerated the succession process. Further monitoring studies are needed to evaluate the longer term effects on stand structure and composition. The lack of negative effects of tree removal on the natural regeneration indicates that such interventions can be recommended, especially considering the expectations of economic revenues from tree harvesting in restoration plantings.
    Environmental Management 06/2015; DOI:10.1007/s00267-015-0560-7 · 1.65 Impact Factor
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    • "Unless these aspects are given more attention, we suspect that a better understanding of the ' population-bridge ' between the mechanism and the community consequences of the JC hypothesis will remain elusive. Because most non-pioneer, overstory forest tree species have intermediate light requirements as seedlings and saplings , one or more gaps appear essential for their juveniles to recruit into the canopy, or at least for a new seedling to quickly grow into a sapling, even among more shadetolerant species (Hartshorn 1980, Denslow 1987, Canham 1989, Wright et al. 2003, R ü ger et al. 2009). Gaps, moreover, can form at variable distances from and amidst clusters of reproductive trees with size-dependent fecundity, and thus are likely critical for understanding the EV-2 "
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    ABSTRACT: The Janzen–Connell hypothesis proposes that specialized herbivores maintain high numbers of tree species in tropical forests by restricting adult recruitment so that host populations remain at low densities. We tested this prediction for the large timber tree species, Swietenia macrophylla, whose seeds and seedlings are preyed upon by small mammals and a host-specific moth caterpillar Steniscadia poliophaea, respectively. At a primary forest site, experimental seed additions to gaps – canopy-disturbed areas that enhance seedling growth into saplings – over three years revealed lower survival and seedling recruitment closer to conspecific trees and in higher basal area neighborhoods, as well as reduced subsequent seedling survival and height growth. When we included these Janzen–Connell effects in a spatially explicit individual-based population model, the caterpillar's impact was critical to limiting Swietenia's density, with a >10-fold reduction estimated at 300 years. Our research demonstrates the crucial but oft-ignored linkage between Janzen–Connell effects on offspring and population-level consequences for a long-lived, potentially dominant tree species.This article is protected by copyright. All rights reserved.
    Oikos 04/2015; DOI:10.1111/oik.02324 · 3.56 Impact Factor
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    • "Alternatively, the first four species to expand their leaves are herbs, whereas the two late leaf expansion species are canopy tree species. Canopy gaps are essential for growth and recruitment of most of canopy trees species (Pickett & White, 1985; Denslow, 1987). Thus, not only different leaf expansion phenologies but also different life forms may explain the different responses of leaf traits to canopy gaps. "
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