Three decades of vegetation changes in peatlands isolated in an agricultural landscape

Questions : What vegetation changes occurred over three decades on two large temperate peatlands (1115 ha) isolated in an agricultural landscape and affected by a human-ignited fire? Location : Southwest Québec, Canada. Methods : In 2012, we revisited 103 plots first sampled in 1984–85. Changes in species composition were evaluated using the Sørensen dissimilarity index, in species frequency with Chi-square goodness-of-fit tests, and in species cover using one-sample t-tests. Tree encroachment was evaluated using aerial photographs and satellite imagery. We used linear discriminant analyses (LDA) and ANOVA to evaluate the impact of tree encroachment on species composition. Results : We found a floristic dissimilarity of 35% between 1984 and 1985 and 2012. Most species whose frequency and mean cover increased were peatland species, while most species with lower frequency and mean cover in 2012 were non-peatland species. The total area occupied by forest increased from 26% to 51%, an overall gain of 280 ha of forest. The species composition of old and new forests as well as of open sectors was highly distinct, as shown by the LDA that correctly assigned 97% of the sampling plots to these groups. Non-peatland species were 15 and five times more abundant than peatland species in old and new forests than open habitats, respectively. Conclusions : Gradual drying of the peatland margins due to drainage of the surrounding catchment, as well as post-fire succession are likely the main drivers of the changes observed. Overall, our study showed that peatlands isolated in an anthropogenic landscape are dynamic ecosystems where vegetation communities can experience substantial changes in a short time frame. The broader implication is that peatland conservation in highly modified landscapes must be linked to restoration