Four decades of fragmentation

27 09 2017

fragmented

I’ve recently read perhaps the most comprehensive treatise of forest fragmentation research ever compiled, and I personally view this rather readable and succinct review by Bill Laurance and colleagues as something every ecology and conservation student should read.

The ‘Biological Dynamics of Forest Fragments Project‘ (BDFFP) is unquestionably one of the most important landscape-scale experiments ever conceived and implemented, now having run 38 years since its inception in 1979. Indeed, it was way ahead of its time.

Experimental studies in ecology are comparatively rare, namely because it is difficult, expensive, and challenging in the extreme to manipulate entire ecosystems to test specific hypotheses relating to the response of biodiversity to environmental change. Thus, we ecologists tend to rely more on mensurative designs that use existing variation in the landscape (or over time) to infer mechanisms of community change. Of course, such experiments have to be large to be meaningful, which is one reason why the 1000 km2 BDFFP has been so successful as the gold standard for determining the effects of forest fragmentation on biodiversity.

And successful it has been. A quick search for ‘BDFFP’ in the Web of Knowledge database identifies > 40 peer-reviewed articles and a slew of books and book chapters arising from the project, some of which are highly cited classics in conservation ecology (e.g., doi:10.1046/j.1523-1739.2002.01025.x cited > 900 times; doi:10.1073/pnas.2336195100 cited > 200 times; doi:10.1016/j.biocon.2010.09.021 cited > 400 times; and doi:10.1111/j.1461-0248.2009.01294.x cited nearly 600 times). In fact, if we are to claim any ecological ‘laws’ at all, our understanding of fragmentation on biodiversity could be labelled as one of the few, thanks principally to the BDFFP.

Laurance and colleagues nicely summarise the vast amount of results that have been generated over nearly 40 years, and as you can imagine, they collectively describe a set of phenomena that are far from simple. Indeed, the role of the BDFFP over time has evolved, not least because the environment in which the experiment is situated has evolved itself.

Yes, the experiment has undeniably determined that the animal species most vulnerable to fragmentation are those with broad ranges and narrow ecological tolerances, and that the most vulnerable plants are those demonstrating high sensitivity to edge effects and/or needing animal assistance for pollination and seed dispersal. Indeed, the concept of ‘edge effects‘ itself can owe its ubiquity in the ecological literature in part to the BDFFP, which has clearly identified how the edges of fragments lead to microclimatic changes, increase tree mortality, alter carbon-storage dynamics, and modify fauna diversity.

We can also attribute our general understanding of how population dynamics respond to fragment instability to the BDFFP, for we now know that population fluctuations within them lead to greater variability from extreme weather events or other stochastic phenomena, thus increasing the probability of populations dipping below minimum viable sizes and becoming locally extinct.

These ‘classic’ responses are, however, not the only concepts solidified by the BDFFP, for it has revealed that local-site attributes are not the only processes that dictate the responses of their dependent biota. In fact, secondary regrowth in the disturbed ‘matrix’ surrounding the forest fragments has altered how some species respond, with some benefiting and others waning, and often in unexpected ways.

Another change probably not anticipated in the late 1970s was anthropogenic climate disruption, which has caused an increase in forest productivity in the region (possibly in response to higher atmospheric CO2 concentrations and altered climate dynamics), as well as shifts in tree community composition, and the rising abundance of lianas (woody vines). These changes synergise in sometimes complex ways with the particulars of each fragment, leading to unpredictable outcomes for any given species.

However, because most species are in fact rare within this important forest system, this synergistic uncertainty means that forest reserves have to be huge — a minimum of 10,000 km2 (about the size of Cyprus or Jamaica) to have any hope of stemming the tide of extinctions resulting from anthropogenic disturbances to the environment. The review therefore also provides a practical guide to conservation management that is based on four decades of research.

If we only that much information for other systems in need of positive intervention.

CJA Bradshaw


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27 09 2017
nigel64

Thanks for posting this – I hadn’t heard of BDFFP and am always looking out for long-term ecol. projects. I’ll attempt to absorb this over the coming days – I was pleased to see Didham’s beetle work referred to as he’s recently done beetle research here in NZ’s Fiordland looking at beetle responses to edge effects (Pervasive impact of large-scale edge effects on a beetle community – PNAS 2008 vol. 105 no. 14). The conclusion was troubling in “kilometer-scale edge effects” observed.

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