Opinion
On the hope for biodiversity-friendly tropical landscapes

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With the decreasing affordability of protecting large blocks of pristine tropical forests, ecologists have staked their hopes on the management of human-modified landscapes (HMLs) to conserve tropical biodiversity. Here, we examine key forces affecting the dynamics of HMLs, and propose a framework connecting human disturbances, land use, and prospects for both tropical biodiversity and ecosystem services. We question the forest transition as a worldwide source of new secondary forest; the role played by regenerating (secondary) forest for biodiversity conservation, and the resilience of HMLs. We then offer a conceptual model describing potential successional trajectories among four major landscape types (natural, conservation, functional, and degraded) and highlight the potential implications of our model in terms of research agendas and conservation planning.

Section snippets

Conservation out of the wild

To date, conservation strategies for tropical biodiversity have often been based on safeguarding large ‘intact’ tropical forest reserves. Although recommended [1], this conservation target is proving to be increasingly challenging [2]. Creation of new mega-reserves will soon be severely constrained because most tropical regions already lack large blocks of pristine forest available for conversion into conservation areas [3]. Therefore, the management of HMLs (see Figure I in Box 1) has emerged

Forest transition questioned

Economic growth, rural exodus, and urbanization are often correlated and represent a widespread and historical phenomenon that results in the abandonment of agricultural lands, particularly those considered marginally productive [29]. In this context, a huge amount of land has been predicted to be available for natural forest regeneration in many tropical countries as long as their economies become increasingly industrialized [30]. This phenomenon, known as ‘forest transition’ (i.e., the

Context matters

HMLs typically contain patches of regenerating or secondary forests [49], which globally account for more than 50% of remaining tropical moist forest 50, 51. This figure, plus the assumption of ongoing forest transition, has led scientists to ask whether regeneration or secondary forest patches are able to guarantee long-term biodiversity persistence as regrowth forests expand their coverage across HMLs [52]. Whereas some studies have recorded significant portions of the original biota in

Disturbance and conservation thresholds

Ecosystem services, such as carbon storage, soil protection, water cycling, and provision of forest products, are positively correlated with forest aboveground biomass [62]. As disturbance proceeds and harvest of forest products intensifies, forest biomass in a landscape will cross a threshold, thus greatly reducing the services and products provided by that forest [64]. This connection between human disturbance, forest biomass, and provision of ecosystem services implies that a maximum level

Multiple pathways for HMLs

Based on the evidence discussed so far, we propose a conceptual model describing potential trajectories for tropical forest landscapes (Figure 1). Initially, deforestation converts ‘natural landscapes’ into ‘conservation landscapes’ (Figure 1; flow 1), which retain a high old-growth:secondary forest ratio and low coverage of edge-affected habitats. Following further forest loss and fragmentation, conservation landscapes move towards ‘functional landscapes’, with intermediate

Theoretical and applied implications

Although our trajectory model represents a simplification of the real world, it makes at least two important contributions. First, it identifies, classifies, and establishes causal connections between the major forces determining shifts among tropical HMLs. Here, it is important to mention that global climatic change can also affect HML trajectories, because current models of climate change predict a reduction in precipitation in many tropical forests over the next few decades [69]. This could

Acknowledgments

We thank Bill Laurance and John Vandermeer for helpful comments on early versions of this manuscript. Thanks to CI-Brasil, Cepan, CNPq, Capes, CONACyT, Universidade Federal de Pernambuco, Universidad Nacional Autónoma de México, and Carleton University for funding this study.

References (70)

  • N.S. Sodhi

    Conserving Southeast Asian forest biodiversity in human-modified landscapes

    Biol. Conserv.

    (2010)
  • M. Quesada

    Succession and management of tropical dry forests in the Americas: review and new perspectives

    Forest Ecol. Manag.

    (2009)
  • M. Tabarelli

    The ‘few winners and many losers’ paradigm revisited: emerging prospects for tropical forest biodiversity

    Biol. Conserv.

    (2012)
  • N.S. Sodhi

    Conservation successes at micro-, meso- and macroscales

    Trends Ecol. Evol.

    (2011)
  • W.F. Laurance

    The fate of Amazonian forest fragments: a 32-year investigation

    Biol. Conserv.

    (2011)
  • W.F. Laurance

    Averting biodiversity collapse in tropical forest protected areas

    Nature

    (2012)
  • M.W. Schwartz

    Choosing the appropriate scale of reserves for conservation

    Annu. Rev. Ecol. Syst.

    (1999)
  • D. Tilman

    Global food demand and the sustainable intensification of agriculture

    Proc. Natl. Acad. Sci. U.S.A.

    (2011)
  • I. Perfecto et al.

    The agroecological matrix as alternative to the land-sparing/agriculture intensification model

    Proc. Natl. Acad. Sci. U.S.A.

    (2010)
  • I. Perfecto et al.

    Biodiversity conservation in tropical agroecosystems: a new conservation paradigm

    Ann. N. Y. Acad. Sci.

    (2008)
  • J. Fischer

    Limits of land sparing

    Science

    (2011)
  • J. Fischer

    Should agricultural policies encourage land sparing or wildlife-friendly farming?

    Front. Ecol. Environ.

    (2008)
  • D.P. Edwards

    Degraded lands worth protecting: the biological importance of Southeast Asia's repeatedly logged forests

    Proc. R. Soc. B

    (2011)
  • S.J. Wright et al.

    The uncertain future of tropical forest species

    Biotropica

    (2006)
  • M.J. Chappell

    Wildlife-friendly farming vs land sparing

    Front. Ecol. Environ.

    (2009)
  • T.A. Gardner

    Prospects for tropical forest biodiversity in a human-modified world

    Ecol. Lett.

    (2009)
  • J. Ranganathan

    Sustaining biodiversity in ancient tropical countryside

    Proc. Natl. Acad. Sci. U.S.A.

    (2008)
  • D.H. Thornton

    The relative influence of habitat loss and fragmentation: do tropical mammals meet the temperate paradigm?

    Ecol. Appl.

    (2011)
  • N. Norden

    Resilience of tropical rain forests: tree community reassembly in secondary forests

    Ecol. Lett.

    (2009)
  • J. Cavender-Bares

    The merging of community ecology and phylogenetic biology

    Ecol. Lett.

    (2009)
  • V. Arroyo-Rodríguez

    Maintenance of tree phylogenetic diversity in a highly fragmented rain forest

    J. Ecol.

    (2012)
  • E. Marris

    Ecology: ragamuffin Earth

    Nature

    (2009)
  • M. Hirota

    Global resilience of tropical forest and savanna to critical transitions

    Science

    (2011)
  • L. Gibson

    Primary forests are irreplaceable for sustaining tropical biodiversity

    Nature

    (2011)
  • D.S. Karp

    Intensive agriculture erodes β-diversity at large scales

    Ecol. Lett.

    (2012)
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