Part III - Plant case studies

Summary

There has been generally less research on the response of plants to habitat loss and fragmentation, at either the community or population level, than there has been on animals. This is surprising as the sessile growth habit of plants disposes them to direct and immediate changes in population size and structure that might be expected to influence both demographic and genetic population processes. Furthermore plants themselves often represent habitat, so effects on them provide avenues of secondary influence of fragmentation on other organisms.

Early work by Levenson (1981) and colleagues on temperate forest fragments, and subsequently by Kapos (1989) in the tropics, emphasised the influence of fragment size on species diversity and the importance of microclimate edges and their impact on population demography (see Murcia, 1995 for a review). This began to provide useful management guidelines in terms of minimum patch sizes for maintenance of plant community structure. This work was extended by Menges (1991a, b) and others (e.g. Lamont et al., 1993; Aizen & Feinsinger, 1994a, b) to direct examination of effects of population size on fecundity.

More recently, the research focus has shifted to assessment of the genetic implications of fragmentation. This has principally involved assessing the importance of genetic erosion and inbreeding in reducing fitness and population viability (e.g. van Treuren et al., 1991; Young et al., 1993; Prober & Brown, 1994; Oostermeijer et al., 1994a). Results are now available from a diverse range of species (see Young et al., 1996 for a review), and it has become clear that commonalities of response are hard to pick, other than a generally positive relationship between population size and genetic variation.