Forest fragmentation, one aspect of forest degradation, affects the distribution and abundance of species and subsequently the composition of communities.
Theoretical and empirial research provides strong evidence that fragmentation reduces biodiversity (Saunders et al. 1991. Conservation Biology; Ewers et al. 2009. Biological Conservation). Although overall effects will depend on species and detrimental effects of fragmentation may be obscured by variation in response of taxa and over time (Leidner et al. 2010. PlOS One).
Thus, righly so, fragmentation features in the Aichi targets for 2011 – 2020: ‘Trends in extent, condition and vulnerability of ecosystems, biomes and habitats’ is one of the strategic indicators which will be used to ac hieve the Aichi Biodiversity Targets (Strategic Goal B: reduce the direct pressures on biodiversity; Target 5: The rate of loss of all natural habitats at least halved), agreed in the Strategic Plan for Biodiversity 2011 – 2020 (Convention on Biological Diversity)
But, what is the most useful way to measure effects of forest fragmentation on biodiversity?
Selecting an appropriate indicator of fragmentation to reflect biological impacts rather than spatial pattern alone is a difficult task. Fragmentation is a combination of many, partly interdependent factors, and typical measures of fragmentation (landscape metrics) include habitat edges, patch shape and patch area, and the arrangement of these (in our case forest) patches in the landscape. The distance between patches (their isolation) can contribute signficantly to the way forest fragmentation impacts on ecological patterns such as demographic dynamics of species living within these patches (i.e. extinction) and subsequently biodiversity. Dispersal of species between patches plays a fundamental role for the functioning of natural populations facing fragmentation and can provide functional connectivity between physcially separated patches. Analysing impacts of fragmentation on ecological patterns and processes is challenging and thus far has been complicated by the diversity of measures used for a diversity of questions (i.e. which aspect of fragmentation to study in the landscape or which taxa to study). Species differ in their functional traits, including their ability to disperse and their ability to tolerate demographic fluctations) and thus they will respond differently to fragmentation.
BIOFRAG was proposed as a new measure that can combine the data gathered in the thousands of fragmentation studies to form a defensible estimate of the real impact that habitat fragmentation is having on biodiversity. The BIOFRAG index effectively scales up observational data (point-based) into a landscape-level statistic, either of the response of individual species to fragmentation or of the response of species communities. BIOFRAG can thus reflect the net biological impact of forest fragmentation (at species and community level), providing the basis for developing a widely applicable index.