On the hope for biodiversity-friendly tropical landscapes

Melo, F.P.; Arroyo-Rodríguez, V.; Fahrig, L.; Martínez-Ramos, M.; Tabarelli, M. 2013, Trends in Ecology and Evolution.

 

Loss of biodiversity, forest fragmentation and habitat degradation are common features in tropical biotas, primarily as a result of human activity. In the past, conservation efforts have been based on preserving large intact areas of pristine rainforest, however this is becoming increasingly challenging (Melo et al., 2013). The management of human-modified-landscapes (HML) has been identified as an opportunity to conserve biodiversity, whereby productive non-degradable agricultural landscapes coexist with natural tropical forest (Chazdon et al., 2009; Melo et al., 2013). Secondary (regenerating) forests, as a part of the HML model, have been suggested by some as a ‘Noah’s Ark' for biodiversity. As a result, the primary goal is a somewhat favourable situation for both economy and the conservation of biodiversity. 
 

This article was written for the purpose to provide a conceptual model, which examines four possible successional trajectories (natural, conservation, functional and degraded) and examines the fundamental forces affecting the dynamics of HML’s. For example, Melo et al. (2013) identified that there is no guarantee that forest transition (net loss to net gain) driven by urbanisation and land abandonment will ultimately lead to further forest regeneration. Whether or not secondary forests will support the original suite of taxa, or retain improvised fractions of biodiversity will be influenced by processes, such as anthropogenic disturbance in the surrounding landscape.

The actual potential for maintaining biodiversity in HML’s remains controversial and uncertain, considering the current land uses such as extensive logging and more commonly slash-and-burn agriculture. Within the last the last 50 years alone, the expansion of agriculture has occurred at the expense of mature and regenerating forests, with less than 30% of the original forest cover remaining in developing tropical countries. Furthermore, the potential for secondary forests to become a target for land clearance in the future was identified as problematic (Melo et al., 2013). However, Hawes et al. (2008) reported that small patches of regenerating forest are able to retain high levels of biodiversity of several taxa, while supporting valuable ecosystem services such as carbon sequestration and a sustainable hydrological supply (Chazdon et al., 2009). Melo et al. (2013) concluded that whether or not these landscapes shift towards sustainable or unsustainable systems will largely depend on agricultural practices.

Discussion group reception

One of the key points raised by the EcoEvo group is that the authors took an optimistic approach on HML’s, which was interpreted as HML’s may be the best alternative conservation option. While conserving pristine forest is ideal, regenerating secondary forest is better than no forest at all. In developing tropical countries, economic growth and productivity are often prioritised above conservation values; therefore an integrated landscape approach seems the only way to move forward, while maintaining biodiversity, ecosystem services and sustainability of rural livelihoods (Chazdon et al., 2009). As developing countries become more affluent, farming could possibly become intensified, resulting in higher productivity while allowing marginally productive areas to be valued as conservation remnants.  This approach would require inter-disciplinary co-operation and extensive management to ensure sustainability, in rapidly changing tropical landscapes (Chazdon et al., 2009). 

As acknowledged in the article, the context of the surrounding landscape is both important and influential. Secondary forests are likely to retain higher levels of biodiversity if surrounded by other forest remnants in contrast to agricultural land and unsustainable practices. As Melo et al. (2013) discussed in the article, landscape context is key;  therefore it will be important to creatively clear land, so that representatives from each ecosystem are maintained and biodiversity is retained in the long-term.

There may be lessons that tropical countries could learn from developed western societies such as New Zealand. It was mentioned that if the Canterbury plains resembled the HML’s in the tropics, it would be a vast improvement of the current landscape.  In New Zealand, a large proportion of the fertile land has been cleared for agriculture, and remnant patches of native forest are few and far between. However, some areas such as along rivers, steep slopes and gullies are not generally productive, and are now being valued for their restoration potential. It seems that rarity is valued. In temperate countries large efforts are being made to restore the landscape, while conservation is often traded-off for productivity in tropical landscapes. 

Questions

Is landscape restoration possible for abandoned and degraded farmland on such a large scale?

How important are conceptual models for identifying conservation priorities and are there limitations to their practicality and relevance?

Could channelling limited resources into conserving secondary forest achieve better outcomes than using them solely to conserve primary rainforest?

References

Chazdon, R.L.; Harvey, C.A.; Komar, O.; Griffith, D.M.; Ferguson, B.G.; Martínez-Ramos, M.; Morales, H.; Nigh, R.; Soto-Pinto, L.; Van Breugel, M.; Philpott, S.M. 2009. Beyond Reserves: A Research Agenda for Conserving Biodiversity in Human-modified Tropical Landscapes. Biotropica 41: 142-153.

Hawes, J.; Barlow, J.; Gardner, T.A.; Peres, C.A. 2008. The value of forest strips for understorey birds in an Amazonian plantation landscape. Biological Conservation 141: 2262-2278.

Melo, F.P.; Arroyo-Rodríguez, V.; Fahrig, L.; Martínez-Ramos, M.; Tabarelli, M. 2013. On the hope for biodiversity-friendly tropical landscapes. Trends in ecology & evolution.