Logging, exotic plant invasions, and native plant reassembly in a lowland tropical rain forest

Abstract

Habitat modification and biological invasions are key drivers of global environmental change. However, the extent and impact of exotic plant invasions in modified tropical landscapes remain poorly understood. We examined whether logging drives exotic plant invasions and whether their combined influences alter understory plant community composition in lowland rain forests in Borneo. We tested the relationship between understory communities and local‐ and landscape‐scale logging intensity, using leaf area index (LAI) and aboveground biomass (AGB) data from 192 plots across a logging‐intensity gradient from primary to repeatedly logged forests. Overall, we found relatively low levels of exotic plant invasions, despite an intensive logging history. Exotic species were more speciose, had greater cover, and more biomass in sites with more local‐scale canopy loss. Surprisingly, though, exotic species invasion was not related to either landscape‐scale canopy loss or road configuration. Moreover, logging and invasion did not seem to be acting synergistically on native plant composition, except that seedlings of the canopy‐dominant Dipterocarpaceae family were less abundant in areas with higher exotic plant biomass. Current low levels of invasion, and limited association with native understory community change, suggest there is a window of opportunity to manage invasive impacts. We caution about potential lag effects and the possibly severe negative impacts of exotic plant invasions on the long‐term quality of tropical forest, particularly where agricultural plantations function as permanent seed sources for recurrent dispersal along logging roads. We therefore urge prioritization of strategic management plans to counter the growing threat of exotic plant invasions in modified tropical landscapes.

Trait filtering during exotic plant invasion of tropical rainforest remnants along a disturbance gradient

“…As with the species composition analyses, distance to forest edge had no significant effect on the mean functional trait value of forest communities for any trait (Appendix S1). Our study also supported previous findings that closed canopy rainforest have low levels of invasion (Dawson, Burslem, & Hulme, 2015;Döbert et al, 2017a;Teo et al, 2003), and provided the first evidence of this result in conservation set-asides embedded within oil palm plantations. Despite most remnants being small in size (<100 ha; no.…”

“…logging; Broadbent et al., 2008; Laurance et al., 2011; Lôbo, Leão, Melo, Santos, & Tabarelli, 2011). These disturbances result in physical gaps in the canopy, which increase light levels and thus facilitate the establishment of introduced exotic propagules (Döbert, Webber, Sugau, Dickinson, & Didham, 2017a; Peters, 2001; Teo, Tan, Corlett, Wong, & Lum, 2003; Waddell, Banin, et al., 2020). Many exotic species are not well adapted to closed canopy, intact forests, however, and habitat filtering may mean that only a few shade‐tolerant species present in the landscape can establish and persist in these environments (Dawson, Burslem, & Hulme, 2009; Koike, 2001; Martin & Marks, 2006).…”

Land-use change and propagule pressure promote plant invasions in tropical rainforest remnants

“…high seed number, fast growth rate, early age of reproduction, asexual reproduction, fruits produced year round and very large seed bank), allowing for rapid population growth (Rejmánek and Richardson 1996;Singhakumara et al 2000;Daehler 2003), making it a highly invasive species and a pest throughout most of its introduced range (Wester and Wood 1977;Gerlach 1993). Similar patterns have been observed in temperate forests with dominant invasive species disrupting native seedling growth (Gorchov and Trisel 2003;Stinson et al 2006), and in selectively logged Malaysian tropical rainforests, Döbert et al (2017) found fewer Dipterocarpaceae seedlings where exotic biomass was higher. Therefore, high niche overlap may lead to strong competition between young trees and exotic shrubs for resources such as light.…”

“…Voucher specimens and photographs of plants in the quadrats were used to identify individuals by a botanist at Danum Valley Field Centre (co-author BBO) and the herbarium at the Forest Research Centre, Sepilok. Exotic species were identified based on lists and guides of Sabah's known exotic plants prepared prior to fieldwork (see Pallewatta et al 2003;Bakar, 2004;Peh, 2010;Döbert et al 2017;Fee et al 2017;CABI 2017) and confirmed by botanists from vouchers. The observed number of exotic species and number of exotic stems per plot were used as measurements of invasion within a plot.…”

“…Gradients from forest edge to interior have been recorded for temperature, humidity, wind intensity and soil erosion, with the most extreme differentiation seen at forest edges, known as edge effects (Laurance et al 2002). In disturbed tropical forests, more exotic plants have been recorded at forest edges, driven by a combination of increased propagule pressure and increased canopy openness and soil disturbance associated with forest edge conditions and anthropogenic influence (Peters 2001;Harper et al 2005;Edward et al 2009;Dawson et al 2014;Döbert et al 2017). However, these studies only looked at a few forest sites, only one studied a gradient of disturbance (Döbert et al 2017) and none have considered gradients in landscape fragmentation.…”