Thursday, August 6, 2009

PS 64-59: Bog vegetation from oceanic to continental climate zone

Anna M. Laine1, Edgar Karofeld2, Jari Oksanen1, Pirita O. Oksanen3, ‹lle Sillasoo4, Minna Všliranta5, and Eeva-Stiina Tuittila5. (1) University of Oulu, (2) University of Tartu, (3) University of Bristol, (4) Tallinn University, (5) University of Helsinki

Background/Question/Methods

Peatland research community generally considers ombrotrophic mires, or bogs, as climax ecosystems that have developed via autogenic processes. While the term climax ecosystem has been widely criticized, it quite well describes bogs, which can persist for thousands of years. In addition to persistence, the bog vegetation and hummock-hollow surface structure related to water table is surprisingly similar in different parts of the world. In this study our objective is to quantify the importance of autogenic development and allogenic forcing of climate for bog vegetation. We study the vegetation of seven European bogs along a climatic gradient from highly maritime Ireland to continental Russia. We compare the variation in vegetation within each bog explained by the water table gradient and the residual variation between the bogs. In each site we surveyed the vegetation along microtopographical transect from highest hummocks to hollows, in a manner that the internal variation was caught. We measured the water table level from each sample plot. We used multivariate analysis (non-metric multidimensional scaling (NMDS) and partition of variation in RDA) to test and visualize our objectives.

Results/Conclusions

We observed two trends of variation in vegetation. Firstly, there was an east – west trend, which separated the study sites from each other, especially the two Irish bogs differed from the rest. This trend describes the allogenic forcing of climate for bog vegetation. Secondly, the internal variation within the study sites was largely explained by the water table level, implying the autogenic development. The partition of variation showed that 17% of the variation in vegetation was explained by the differences between the study sites, while 12% was explained by the water table, the interaction of those two explained 7%. The average distance to the centroid (describing the amount of variation within the study site) was largest (0.50) in the two concentric raised bogs located in southern Finland and Estonia, and lowest (0.34) in the eccentric raised bogs in more northern areas of Finland. In addition, the vegetation of the Irish raised bog varied less than that of the Irish blanket bog. We conclude that both autogenic development and allogenic forcing of climate are important for the development of bog vegetation. While the vegetation between the sites varied to certain extent, comparable microtopographical plant communities were found from all sites.