Abstract
Understorey vegetation changes between 1997 and 2005 were studied using 100 permanent plots (1 m2) in four boreal spruce forest stands situated within a National Nature Reserve in SE Norway. The stands differed with respect to former forest management performed 70–80 years prior to the study: natural old-growth forest, minor selectively cut forest, major selectively cut forest and clear cut forest. Based on repeated recording of species composition (vegetation gradients acquired by ordination axes) and tree-stand properties, as well as several environmental variables recorded in 1997, my aim was to assess if previous logging affected the understorey species composition and/or species abundance.
No general patterns in species abundance change across stands were observed that could be directly ascribed to former management. Most of the change in abundance was interpreted as stochastic inter-annual fluctuations. Previous logging was a poor predictor of change in species composition, and the average positions of plots from a given stand along the tree influence gradient in species composition did not reflect average tree influence at stand scale. This was interpreted as an indication that the influence of trees on understorey species composition is local, at the scale of individual trees rather than stand-scale tree stand properties (including logging history). The vegetation in the major selectively cut stand (highly significant), the clear cut and the natural stand had, however, changed in direction of one typical of more open and moist forest in spite of the forest becoming generally denser. This was attributed to increased amounts of precipitation in the period prior to 2005 compared to the years preceding 1997, which favours spread of species typical of moist microsites and between trees towards tree bases.
Some convergence in species composition changes towards that of the old-growth forest was observed for all formerly managed stands, along the two first ordination axes. This exemplifies the long-term nature of forest floor-successions, which evidently last for many decades after logging. A slight time-lag was also found (though, not significant) in the response of vegetation to tree influence, and in the response of species composition in 2005 to its’ surrounding environment relative to the species composition in 1997 and the environmental variables recorded the same year.
Apparently, previous logging does not directly influence today's species abundances or species composition per se, although indirect effects via tree-layer properties seem to be traceable. Further insight into the complex dynamics of understorey vegetation in boreal post-logged forest require continued long-term monitoring of permanent plots.