Publications

The role of land-use history in driving successional pathways and its implications for the restoration of tropical forests  

Catarina C. Jakovac, André B. Junqueira, Renato Crouzeilles, Marielos Peña-Claros, Rita C. G. Mesquita and Frans Bongers 

Biological Reviews, 2021, doi: 10.1111/brv.12694 

Secondary forests are increasingly important components of human-modified landscapes in the tropics. Successional pathways, however, can vary enormously across and within landscapes, with divergent regrowth rates, vegetation structure and species composition. 

We review the literature aiming to provide a comprehensive understanding of the mechanisms underlying the long-lasting effects of land use on tropical forest succession and to discuss its implications for forest restoration. We organize it following a framework based on the hierarchical model of succession and ecological filtering theory.  

This review shows that our knowledge is mostly derived from studies in Neotropical forests regenerating after abandonment of shifting cultivation or pasture systems. The literature shows that (i) species availability to succession is affected by transformations in the landscape that affect dispersal, and by management practices and seed predation. Species establishment and performance are dependent on resistance to management practices, tolerance to (modified) soil conditions, herbivory, competition with weeds and invasive species, and facilitation by remnant trees. (ii) Structural and compositional divergences at early stages of succession remain for decades, suggesting that early communities play an important role in governing further ecosystem functioning and processes during succession. Management interventions at early stages could help enhance recovery rates and manipulate successional pathways. (iii) The combination of local and landscape conditions defines the limitations to succession and therefore the potential for natural regeneration to restore ecosystem properties effectively. 

The interaction between landscape integrity and previous land-use history defines the limitations to succession (A), and restoration requirements (B). Here landscape integrity represents the amount and quality of sources of propagules, meaning that higher landscape integrity involves higher forest cover, lower forest fragmentation and higher tree cover in agricultural fields. The axis of intensity of previous land use summarizes an increase in the spatial extent, frequency, duration and intensity of management practices. (A) Species availability for succession is strongly reduced by reduction in landscape integrity as well as by intensive, extensive and long-term land use. Limitations to species performance increases with land-use intensity due to reduced resource availability and increased competition with invaders, for example. As a response to these driving factors, succession follows different pathways with varying rates of biomass regrowth and species turnover. (B) Along the gradients of landscape integrity and intensity of previous land use within and across human-modified landscapes, different restoration strategies will be required: unassisted natural regeneration (NR), assisted natural regeneration (ANR) or tree planting (TP). In each quadrant we provide examples of management practices that can help to overcome the limitations to succession (A) for effective restoration of ecosystem functions.

Forest structure drives changes in light heterogeneity during tropical secondary forest succession   

Tomonari Matsuo, Miguel Martínez-Ramos, Frans Bongers, Masha T. van der Sande, Lourens Poorter   

Journal of Ecology, 2021

The rationale. Light is a key resource for tree performance and hence, tree species partition spatial and temporal gradients in light availability. Although light distribution drives tree performance and species replacement during secondary forest succession, we yet lack understanding how light distribution changes with tropical forest development.

Aims. This study aims to evaluate how changes in forest structure lead to changes in the vertical- and horizontal light heterogeneity during tropical forest succession.

Approach. We described successional patterns in light using a chronosequence approach in which we compared 14 Mexican secondary forest stands that differ in age (8-32 years) since agricultural abandonment. For each stand, we measured vertical light profiles in 16 grid cells, and structural parameters (diameter at breast height, height, and crown dimensions) for each tree.

Findings.

  • During succession, the inflection points of the vertical light gradient (i.e., the absolute height at which 50% relative light intensity is attained) rapidly moved towards higher heights in the first 20 years, indicating that larger amounts of light are intercepted by canopy trees.
  • Light attenuation rate (i.e., the rate of light extinction) decreased during succession due to slower accumulation of the crown area with height.
  • Understory light intensity and heterogeneity slightly decreased during succession because of an increase in crown size and a decrease in lateral gap frequency.
  • Understory relative light intensity was 1.56% at 32 years after abandonment.
  • These changes in light conditions are largely driven by the successional changes in forest structure, as basal area strongly determines the height where most light is absorbed, whereas crown area, and to a lesser extent crown length, determine light distribution. 

Implications. The fast forest development during tropical secondary forest succession leads to the fast changes in light conditions and more light heterogeneity, which can increase the proportion of shade-tolerant late-successional species over time, and hence tree species diversity.

Forest structural changes during secondary succession in Marqués de Comillas, southeastern Mexico. Panels in (a) and (b) show three-dimensional images of forest structure and those in (c) and (d) corresponding vertical light profiles for a stand of 9 years old (left panels) and a stand of 32 years old (right panels). Height, crown size, and tree position are drawn based on actual measurements using Forest Window (2.24). Grey lines represent the light profiles of each of the 16 sub-plots, and black lines represent the average light profile across the 16 sub-plots.