Multiple successional pathways in human-modified tropical landscapes: new insights from forest succession, forest fragmentation and landscape ecology research

Abstract

Old-growth tropical forests are being extensively deforested and fragmented worldwide. Yet forest recovery through succession has led to an expansion of secondary forests in human-modified tropical landscapes (HMTLs). Secondary forests thus emerge as a potential repository for tropical biodiversity, and also as a source of essential ecosystem functions and services in HMTLs. Such critical roles are controversial, however, as they depend on successional, landscape and socio-economic dynamics, which can vary widely within and across landscapes and regions. Understanding the main drivers of successional pathways of disturbed tropical forests is critically needed for improving management, conservation, and restoration strategies. Here, we combine emerging knowledge from tropical forest succession, forest fragmentation and landscape ecology research to identify the main driving forces shaping successional pathways at different spatial scales. We also explore causal connections between land-use dynamics and the level of predictability of successional pathways, and examine potential implications of such connections to determine the importance of secondary forests for biodiversity conservation in HMTLs. We show that secondary succession (SS) in tropical landscapes is a multifactorial phenomenon affected by a myriad of forces operating at multiple spatio-temporal scales. SS is relatively fast and more predictable in recently modified landscapes and where well-preserved biodiversity-rich native forests are still present in the landscape. Yet the increasing variation in landscape spatial configuration and matrix heterogeneity in landscapes with intermediate levels of disturbance increases the uncertainty of successional pathways. In landscapes that have suffered extensive and intensive human disturbances, however, succession can be slow or arrested, with impoverished assemblages and reduced potential to deliver ecosystem functions and services. We conclude that: (i) succession must be examined using more comprehensive explanatory models, providing information about the forces affecting not only the presence but also the persistence of species and ecological groups, particularly of those taxa expected to be extirpated from HMTLs; (ii) SS research should integrate new aspects from forest fragmentation and landscape ecology research to address accurately the potential of secondary forests to serve as biodiversity repositories; and (iii) secondary forest stands, as a dynamic component of HMTLs, must be incorporated as key elements of conservation planning; i.e. secondary forest stands must be actively managed (e.g. using assisted forest restoration) according to conservation goals at broad spatial scales.

Scale sensitivity of the relationship between alpha and gamma diversity along an alpine elevation gradient in central Nepal

“…Although much is now known about the mechanisms shaping vegetation assemblages, uncertainties still exist regarding spatiotemporal variations in the drivers, in the underlying mechanisms and trajectories of secondary succession under different types of environmental perturbations, and in their cross-scale linkages (Zhou et al 2014;Meiners et al 2015;Arroyo-Rodríguez et al 2017). A long-standing debate concerns whether the assembly and spatiotemporal dynamics of communities are governed by deterministic or stochastic processes (e.g., Hubbell 2001;Tilman 2004;Chase & Myers 2011;Bhaskar et al 2014) or by a combination of both (e.g., Gravel et al 2006;Leibold & McPeek 2006;Adler et al 2007;Caruso et al 2011;Måren et al 2018).…”

“…A recent consensus is that both deterministic and stochastic processes operate simultaneously in the assembly of local communities (Leibold & McPeek 2006;Chase 2010;Caruso et al 2011;Chase & Myers 2011), and that the relative importance of stochastic (neutral) versus deterministic (niche-based) processes of temporal changes is a matter of scale (Fig. 1;Chase 2014;Arroyo-Rodríguez et al 2017). At a fine scale, stochastic processes such as birth and death rates, dispersal, disturbance, and biotic interactions become prominent, which moderate the influence of coarse-scale environmental factors on species composition (Connor & McCoy 1979;Levin 1992;Crawley & Harral 2001).…”

Tree species diversity and utilities in a contracting lowland hillside rainforest fragment in Central Vietnam

“…effects which may increase mortality of sensitive trees and seedlings, and simplify the vegetation by promoting generalist species (Laurance 1997;Benitez-Malvido and Martínez-Ramos 2003;Bennet and Saunders 2010;Cochard 2011). Edge-effects in small fragments are disproportionally higher than in large fragments; simultaneously, anthropogenic impacts may increase in smaller fragments (Arroyo-Rodríguez et al 2015).…”

Decision support tools for forest landscape restoration: Current status and future outlook

“…Apart from the importance of overall forest cover, species persistence may also depend on the quality and physical arrangement of forest cover and tree cover within landscapes (Arroyo-Rodriguez et al 2017). Agroforests, silvopastoral systems, single-species tree plantations, multi-species plantations and naturally regenerating forests vary widely in the number and types of plant and animal species they support (Barlow et al 2007;Scales and Marsden 2008;Gardner et al 2009;Chazdon 2014).…”