Long-term impacts of logging on forest diversity in Madagascar

Abstract

Ecological perturbations can either be necessary for maintaining tropical forest diversity or responsible for its decline, depending on the scale, nature, and frequency of the disturbance. Anthropogenic disturbances such as logging and subsistence agriculture may promote the establishment of nonnative, invasive plant species, potentially affecting forest structure and diversity even long after the perturbation has ceased. We investigated the impacts of logging 50 and 150 years ago on tropical forest vegetation in Madagascar, a ''hotspot'' of biodiversity. Logging was the overriding factor influencing establishment of nonnative plants. Sites once logged never recovered native species diversity because of the dominance and persistence of invasive species.T emporal and spatial scales of disturbance affect forests differently. Disturbances over a range of scales are critical determinants of tropical forest composition, and the disturbance regime of tropical forests can be essential to maintaining native species diversity and community structure (1-4). Changes in disturbance type, frequency, scale, or intensity can also lead to the loss of species (5-10). The effect of selective logging on native tree diversity in tropical forests is a subject of speculation and of great current concern, but very limited data are available to assess its impact. Under some circumstances, logged tropical forests have been shown to contain as many tree species as unlogged forests (11,12). Some disturbances may also facilitate colonization and establishment of invasive, nonnative plants when dominant native trees are removed (13,14). The most critical questions about the establishment of invasive plants are not whether disturbance promotes establishment of nonnatives. Rather, it is essential to determine whether nonnative plant populations persist in tropical forests once established or are replaced by native species over time, and if persistent, whether the nonnative species have a negative impact on native tree diversity and forest community structure. Although the negative consequences of clear-cutting on the loss of biodiversity are well known, little is currently known about the long-term consequences for tropical forest diversity of selective logging and other more limited anthropogenic disturbances. The effects of colonization by nonnative species on native diversity under such conditions have rarely been considered, but may be important.We investigated the effects of limited logging on the presence, persistence, and impact of invasive species on forest composition in Ranomafana National Park in southeastern Madagascar. The forests of Madagascar are considered a global ''hotspot'' of biodiversity, with among the world's highest levels of plant diversity and endemism. However, they are severely threatened by anthropogenic disturbances (15)(16)(17)(18)(19). We compared stands that were clear-cut and abandoned in about 1855, Ϸ150 years before the study, those selectively logged and abandoned in 1947, a stand that was never logged but...

Logging Impacts in Tropical Lowland Humid Forest on Tree Species Diversity and Environmental Conservation

“…Regardless of how long trees were clear-cut or selectively removed, logging decreased species diversity (Brown and Gurevitch, 2004) . These researchers established the fact that logging affects tree species diversity and evenness.…”

Forest-bird Species Assemblages in the Lowland Rainforest of Madagascar: The Effects of Forest Fragmentation Revisited

“…lightweight trees for rafts, lianas to drag trees) [61][62][63]. In this respect, one interesting finding is the clustering of And (4,170 ha) with reference sites in the ordination plot (Fig.…”

Historique de l'introduction du genre <em>Eucalyptus</em> à Madagascar

“…Les eucalyptus sont parfois présentés en tant qu'espèces potentiellement invasives (Brown, Gurevitch, 2004 ;Richardson, 1998) ou néfastes par les écologistes ; mais, à Madagascar, ils occupent une place privilégiée dans les campagnes en rendant de nombreux services et en remplaçant progressivement les espèces forestières qui sont pourtant toujours disponibles. Les reboisements contribuent à améliorer les conditions de vie et de bien-être des communautés rurales mais, dans un contexte de crise, les revenus forestiers ne sont plus suffisants pour assurer leur survie.…”