Hans Van Calster

EXTINCTION DEBT OF FOREST PLANTS PERSISTS FOR MORE THAN A CENTURY FOLLOWING HABITAT FRAGMENTATION

Following habitat fragmentation individual habitat patches may lose species over time as they pay off their extinction debt. Species with relatively low rates of population extinction and colonization (slow species) may maintain extinction debts for particularly prolonged periods, but few data are available to test this prediction. We analyzed two unusually detailed data sets on forest plant distributions and land-use history from Lincolnshire, United Kingdom, and Vlaams-Brabant, Belgium, to test for an extinction debt in relation to species-specific extinction and colonization rates. Logistic regression models predicting the presence-absence of 36 plant species were first parameterized using data from Lincolnshire, where forest cover has been relatively low (approximately 5-8%) for the past 1000 years. Consistent with extinction debt theory, for relatively slow species (but not fast species) these models systematically underpredicted levels of patch occupancy in Vlaams-Brabant, where forest cover was reduced from approximately 25% to <10% between 1775 and 1900 (it is presently 6.5%). As a consequence, the ability of the Lincolnshire models to predict patch occupancy in Vlaams-Brabant was worse for slow than for fast species. Thus, more than a century after forest fragmentation reached its current level an extinction debt persists for species with low rates of population turnover.

METAPOPULATION DYNAMICS IN CHANGING LANDSCAPES: A NEW SPATIALLY REALISTIC MODEL FOR FOREST PLANTS

In fragmented landscapes, habitat patches are often destroyed and created through time, though most metapopulation models treat patch networks as static. Here we present a generally applicable, modified version of Hanskis Incidence Function Model (IFM) that incorporates landscape dynamics (i.e., habitat patch turnover), and we param- eterize the model with data on patch occupancy patterns for forest plants in central Lin- colnshire, UK. The modified IFM provided a better, or equally good, fit to species patch occupancy patterns than logistic regression. Estimated colonization and extinction rates, and the results of logistic regression analyses, varied significantly among species with different life history traits. For example, species with low seed production and predomi- nantly short-distance seed dispersal showed lower rates of colonization and extinction and were more likely to show effects of patch age and connectivity on patch-level presence than species with the opposite set of traits. Model simulations demonstrate a profound negative influence of habitat turnover rate on metapopulation dynamics and persistence, particularly for slow-colonizing species. The incorporation of temporal habitat dynamics into the metapopulation paradigm will permit its application to organisms in a much wider range of real landscapes.

Long-term seed bank dynamics in a temperate forest under conversion from coppice-with-standards to high forest management

ABSTRACT Questions: How do changes in forest management, i.e. in disturbance type and frequency, influence species diversity, abundance and composition of the seed bank? How does the relationship between seed bank and vegetation change? What are the implications for seed bank dynamics? Location: An ancient Quercus petraea - Carpinus betulus forest in conversion from coppice-with-standards to regular Quercus high forest near Montargis, France. Methods: Seed bank and vegetation were sampled in six replicated stand types, forming a chronosequence along the conversion pathway. The stand types represented mid-successional stages of stands in transition from coppice-with-standards (to high forest (16 plots) and early- and mid-successional high forest stands (32 plots). Results: Seed bank density and species richness decreased with time since last disturbance. Adjusting for seed density effects obscured species richness differences between stand types, but species of later seres were nested subsets of earlier seres, implying concomitant shifts in species richness and composition with time since disturbance. Later seres were characterized by species with low seed weight and high seed longevity. Seed banks of early seres were more similar to vegetation than to later seres. Conclusions: Abandonment of the coppice-with-standards regime altered the seed bank characteristics, as well as its relationship with vegetation. Longer management cycles under high forest yield impoverished seed banks. For their persistence, seed bank species will increasingly rely on management of permanently open areas in the forest landscape. Thus, revegetation at the beginning of new high-forest cycles may increasingly depend on inflow from seed sources. Nomenclature: Lambinon et al. (1998).