Applying a metapopulation framework to the management and conservation of a non-timber forest species

Abstract

The harvest of non-timber forest products (NTFPs) represents a significant source of income for hundreds of millions of people, and is promoted as a conservation and development strategy across the globe. Most research on NTFP management focuses on the dynamics of individuals within harvested populations, but the ways in which management may affect the dynamics of populations across a landscape and over time remain largely unexplored. Here, I use a metapopulation framework to assess the effects of management on populations of the fiber-harvested bromeliad, Aechmea magdalenae, in the Sierra Santa Marta, Mexico. Specifically, I quantify rates of colonization, extinction and growth as well as size structure of A. magdalenae populations from 1997 to 2003; and compare these variables between wild versus outplanted populations and between old-growth versus secondary forest populations. Over the 5-year study period, 42% of the 31 wild A. magdalenae populations went extinct due to anthropogenic fires and to ramet harvest for the creation of enrichment plantings. Significantly more secondary forest populations went extinct than old-growth forest populations. Sixty-two outplanted populations were created and in contrast to wild populations and despite harvest, these outplantings increased in size and none went extinct. The structure of wild populations shifted towards fewer populations with less rosettes but overall numbers and sizes of populations increased. These results illustrate the dynamic nature of A. magdalenae populations over both time and space and the ways in which the fates of populations depend on decisions made by harvesters at both the population and the landscape level. In this case, sustainable harvest of A. magdalenae does not necessarily ensure population persistence. Outplanting of A. magdelanae appears to be functioning as a very successful forest conservation strategy. Nonetheless, the conservation of at least some wild populations may be required to ensure long-term survival of this species in this region. Metapopulation approaches may provide an important compliment to demographic studies of A. magdalenae and other NTFP.