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In order to estimate how much population extinction risk may be affected by local fragmentation, population viability analyses were performed in six populations of the endangered grassland herb Gentianella campestris in Sweden. The populations had been experimentally reintroduced to grasslands that were locally fragmented by juniper shrubs. The sites represented three sizes of grassland and two levels of grassland abundance in the landscape. Five years' demographic data were evaluated in a stochastic matrix population model, and studies of seed set, pollinator abundance, and inbreeding depression were performed in order to examine possible links between population viability and pollination. In all six sites, plants with reduced capacity of self-pollination (due to herkogamy) showed strongly reduced population viability in locally fragmented grassland habit, with pronounced extinction thresholds at certain levels of local fragmentation. Population viability was reduced because of inbreeding depression and reduced seed production in combination, both caused by pollinator deficit in locally fragmented grasslands. Plants with high selfing capacity had low population viability over the entire local fragmentation gradients. Selfing yielded high seed set in the absence of pollinators and was advantageous in fragmented parts of the grasslands. However, selfing had negative effects in nonfragmented parts of the grasslands, because it decreased the chances of cross-pollination and because selfed progeny had reduced fitness compared to outcrossed offspring. A comparison among the six sites indicated that the negative effects of local fragmentation were amplified by reduced size of the grassland sites and by reduced abundance of grassland habitat in the landscape. To my knowledge, this is the first quantitative estimate of increased extinction risk in fragmented plant populations.

We present field evidence for the induction of overcompensation, or increased fruit and seed yield as a consequence of damage, in the grassland biennial field gentian,

Summary1 Transition matrix models were used to evaluate the effects of environmental stochasticity and four different methods of grassland management on dynamics and viability of a population of the biennial Gentianella campestris (Gentianaceae) in species-rich grassland. Data were collected between 1990 and 1995. 2 Continuous summer grazing, the prevailing management strategy in Scandinavian grasslands, resulted in high recruitment of new plants, mainly because litter accumulation was prevented and gaps were created by trampling. Trampling and repeated grazing, however, caused damage which reduced seed production. Lambda for the average matrix was c . 0.77, and a stochastic matrix model yielded an extinction probability for the total population of c. 0.08 within 50 years. 3 Mowing in mid-July (used as a conservation tool) increased seed production, but litter accumulation following re-growth of the vegetation prevented establishment. Lambda and extinction risk were similar to continuous grazing. 4 Mowing in October (another conservation tool) promoted recruitment because of low litter accumulation, but the seed output decreased because plant growth was impaired by tall vegetation. Lambda was 0.64, while the extinction probability was very high ( c. 0.98 within 50 years). 5 Mid-July mowing followed by autumn grazing (the historical management regime) yielded high values for both seed production and establishment of rosettes. Lambda was 0.94 and the probability of extinction within 50 years was below detection level. 6 Log-linear analysis showed that the matrices differed significantly both between treatments and between years. The latter indicates environmental stochasticity, here caused by summer drought that increased the extinction risk. Lambda may be slightly underestimated because drought occurred in one out of five summers during the study period, which is high compared with the natural frequency. 7 We conclude that traditional grassland management is more favourable for G. campestris than the methods that prevail in Scandinavia today. This indicates a serious conservation problem, because grazing has replaced traditional management in many of the remaining semi-natural grasslands throughout Europe.