Stand Structure and Spatial Pattern of Regeneration of Pinus sylvestris in a Natural Treed Mire in Latvia

摘要

We examined the regeneration patterns of Pinus sylvestris L. in a natural treed mire in the hemiboreal zone in Latvia. Data on tree stern age and size was collected in 207 fine-scale plots (10 m(2)) and 4 medium-scale plots (400 m(2)). Size structure of living and dead trees was also estimated on transects 180-m and 250-m length and 10-m width. In addition, the vegetation was described in 1-m(2) plots to determine preferred microsites for P. sylvestris establishment. Pinus sylvestris showed continuous regeneration by an inverse J-shaped age and size structure. Pulses of mortality induced by fire were also evident. Regeneration of P sylvestris was mostly on Sphagnum magellanicam Brid. hummocks free of competition from Ledum palustre L. and graminoids, which were found in small interspersed patches throughout the mire. The spatial pattern of tree cohorts differed, probably due to changing moisture conditions altering seedbed conditions and by fire-induced mortality in specific areas. Recent rapid invasion by Betula pubescens Ehrh. and Picea abies (L.) Karst. in a post-fire period since 1971 is probably associated with drier conditions.