JALONEN, JYRKI A.* AND ILKKA VANHA-MAJAMAA. CW-405, Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada. - Understorey vegetation response to alternative forest harvesting methods in southern boreal forests.
New forestry practices are being implemented in the hope of achieving
ecological sustainability, but little is known of their effects on
biota. We investigated stand level effects of five different felling
methods on mature boreal Picea abies forest understorey
vegetation in southern Finland. We hypothesized that vegetation
response depends on the level of disturbance, i.e., intensity of the
felling method. There were eight one hectare sized replicates of the
five treatments, which were as follows: a) control, 100 % retention;
b) single-tree selection system felling, 70 % dispersed retention; c)
gap felling, with and without (n=3) site preparation, 50 % aggregated
retention in three patches/ha; d) retention felling, 10 % retention,
three clusters of trees/ha and d) clear felling, 0 % retention.
Vegetation was sampled before the treatments and during two following
years. The immediate response of the understorey vegetation to the
level of retention was linear. Bryophyte species richness decreased
significantly in selection system, 10 % retention and clear felling,
but remained at the pre-treatment level in gap fellings and control.
Bryophyte cover decreased significantly with all studied retention
levels except control, most prominently in clear and 10 % retention
felling. Vascular plant cover decreased significantly in all studied
retention levels, including control, but species richness only with 10
and 0 % retention levels. During the second post-treatment year, a
significant decrease in bryophyte cover was observed in gap felling
with site preparation, apparently due to the disturbance caused by the
preparation, while no further decrease was observed in the other
treatments. On the contrary, species number and cover of bryophytes
and vascular plants increased slightly in 10% retention felling and
clear felling due to the invasion of early successional species. The
10% retention and clear felling did not differ from each other in
terms of vegetation response. Apparently the residual tree groups were
too small to provide shelter for late successional vegetation in or
outside of residuals.
Key words: bryophytes, disturbance, diversity, forestry, vascular plants