Question: How do we distinguish between concurrent allogenic and autogenic forcings behind changing patterns in plant community structures during mire development?

Location: Lakkasuo raised bog, southern Finland.

Methods: Two radiometrically dated peat profiles were studied using high resolution plant macrofossil analysis. A combination of partial direct and indirect gradient analyses (CCA and DCA) was applied to quantify the role of different drivers of vegetation changes.

Results: Autogenic hydroseral succession explained 16% of the compositional variation in the vegetation. Disturbance successions initiated by fire explained 15% of the variation in the hummock, but only 9% in the wetter lawn. The early post-disturbance successional stages were characterized by Eriophorum vaginatum. After partialling out the effects of peat depth and time since fire, a moisture gradient explained 29% of variation in the hummock core and 26% in the lawn. The analyses also indicated alternation between species with a similar niche. This interaction gradient explained 26% and 31% of the compositional variation in the hummock and lawn, respectively. The similar order of species replacement from both cores supported the existence of general directional succession in mire vegetation, both during the mire development and after fire events. The autogenic succession was slow and gradual while the disturbance successions were episodic and fast.

Conclusion: Our results support the paradigm of the complex nature of mire vegetation dynamics where several interlinked agents have simultaneous effects. The approach of combining partial ordinations developed here appeared to be a useful tool to assess the role of different environmental factors in controlling the vegetation succession.

Nomenclature: Hämet-Ahti et al. (1998) for vascular plants and Koponen et al. (1977) for bryophytes.