Regeneration patterns after intermediate wind disturbance in an old-growth Fagus-Abies forest in southeastern Slovenia

We studied patterns of tree regeneration in relation to canopy structure in a 1-ha plot damaged by an intermediate windstorm in 1983 and a 1-ha control plot regulated by small-scale canopy gaps in an old-growth Fagus sylvatica-Abies alba forest, southeastern Slovenia. In the windthrow plot, a maze of interconnected gaps covered 55% of the plot, while more discrete canopy openings covered 27% of the control plot. The different canopy structures resulted in marked differences in the density and spatial patterns of tree regeneration in the two plots. Fagus dominated the regeneration layer in both plots, while Abies occurred infrequently. For Fagus, there were nearly six-fold less seedlings, but twice as many saplings and understory trees in the windthrow plot compared to the control plot. Overall, the spatial patterns of Fagus seedlings, saplings, and understory trees were clumped in both plots, but only saplings and understory trees were aggregated under canopy gaps in the control plot, whereas saplings in the windthrow plot were distributed irrespective of canopy gaps. Abies individuals also had an aggregated spatial distribution, but were growing under a closed canopy. We suggest that infrequent, intermediate windstorm disturbance plays an important role in the structure and dynamics of central European forests by creating more coarse-grained forest structures than in stands regulated by smaller-scale gap processes. (c) 2006 Elsevier B.V. All rights reserved.