A Century of Plant Species Loss from an Isolated Fragment of Lowland Tropical Rain Forest

Abstract

An isolated 4‐ha fragment of lowland tropical rain forest has been preserved in the Singapore Botanic Gardens since their founding in 1859. The Botanic Gardens’Jungle has recently had enumerated all woody stems 5 cm diameter at breast height (dbh) and larger and the complete vascular plant flora inventoried. This inventory can be compared with the historic record of the flora of the Gardens’Jungle obtained from the extensive collection of herbarium specimens dating back to the 1890s. Of the 448 historically recorded native species, 220 are still present. Ninety‐four native species for which there were no historic records and 80 introduced species were also recorded in the recent inventory. The 50.9% loss of plant species richness over approximately the last century has not been distributed uniformly across plant life‐form groups. Tree species have been less likely to go extinct than shrubs, climbers, or epiphytes. But half of the tree species present in 1994 were represented by only one or two individuals ≥ 5 cm dbh and larger. Individual longevity may be the major correlate with persistence of plant species in isolated forest fragments. Shade‐tolerant understory shrubs (mostly Rubiaceae) and rattans (Palmae) have been particularly prone to extinction. Some species have probably proliferated during the period of isolation. The tree Calophyllum ferrugineum currently constitutes one quarter of all woody stems. A group of climbers has become very common and covers large areas, probably inhibiting tree regeneration. We conclude that tiny fragments will act as refuges for tropical rain‐forest plant species for decades, possibly even centuries after isolation but on their own they will not provide a permanent guarantee of the conservation of tropical biodiversity.

Análise da estrutura de fragmentos florestais no Planalto Paulistano - SP

“…Fragmentos florestais pequenos e isolados, originados por desmatamentos em uma paisagem originalmente coberta por floresta, apresentam uma tendência ao empobrecimento, devido à incapacidade de regeneração de muitas populações nessas condições (Turner et al 1996). A Reserva da CUASO não apenas é isolada hoje, como também o foi, em um grau provavelmente crescente ao longo do tempo, durante todo o processo de sucessão ecológica que deu origem à sua cobertura florestal atual.…”

Metapopulation Extinction Thresholds in Rain Forest Remnants

“…In particular, species with large local populations are regionally common (i.e., high probability of occurring at any given habitable site), whereas those characterized by small population sizes are regionally rare. Although several hypotheses, ranging from niche-breadth differences to sampling artifact, provide equally plausible explanations for this relationship (Gotelli and Simberloff 1987;Collins and Glenn 1997;Gaston et al 1997;van Rensberg et al 2000), only one hypothesis predicts how modifications to the regional distributional extent of a species assemblage is expected to alter both demographic and community-level processes.…”

Demography of the endangered tree species Ocotea porosa (Lauraceae) along a gradient of forest disturbance in southern Brazil

“…We also observed that O. porosa populations presented lower size hierarchy (i.e., less dominance of larger trees) in the more disturbed areas than in the undisturbed areas, suggesting that logging and fragmentation affect the structure of this species, possibly impacting the rates of reproduction and fecundity, which could lead to local extinction (Turner et al 1996;ArroyoRodríguez et al 2007).…”

“…For example, in fragments subjected to selective logging, tree removal creates gaps in which light intensity and ground humidity are modified, increasing the edge effects (Broadbent et al 2008) and affecting several ecological processes (Laurance et al 2011), including the survival of large trees (Laurance et al 2000). There is therefore potential synergism between selective logging and forest fragmentation affecting ecological processes, which in turn influences the distribution and structure of plant populations (Turner et al 1996;Hill & Curran 2003;Arroyo-Rodriguez et al 2007). …”