THE INFLUENCE OF SILVICULTURAL CLEANING ON MOOSE BROWSING IN YOUNG SCOTS PINE STANDS IN FINLAND

Abstract

Assessing the intensity of silvicultural cleaning in young stands of Scots pine (Pinus sylvestris), which are an important food source for moose (Alces alces), was studied in relation to the effects of feeding. Field data were collected in central Finland from 1990-96. The study area was divided into 13 silviculturally cleaned (1988-89) and seven untreated control stands. A second cleaning was done in all of the cleaned and untreated control stands in 1993-94. Six exclosures established in 1989 were also included in the study. White birch (Betula pubescens) was the main tree species removed by cleaning in both open areas and in exclosures. Total biomass consumed by moose in winter 1989-90, 1 year after the first cleaning, was significantly higher in untreated stands than in cleaned stands (33.3 kg/ha ± 3.7 SE vs. 12.0 kg/ha ± 3.7 SE, P < 0.01). Moose browsing on pine in silviculturally cleaned stands of pine was less intensive than in untreated ones. The total biomass consumed by moose in winter 1994-95, did not differ between cleaning treatments (10.4 kg/ha ± 2.2 SE vs. 11.0 kg/ha ± 5.1 SE, P = 0.90), nor did consumed pine biomass in winter 1995-95, 2 years after the second cleaning (4.6 kg/ha ± 1.3 SE vs. 9.0 kg/ha ± 3.8 SE, P = 0.20). Several factors were correlated with moose browsing on pine in winter 1994-95. Stepwise regression analysis revealed that total stem density and white birch density best explained moose browsing on pine. Significantly higher cumulative numbers of pine stem breakages and browsed pines occurred in sites cleaned once versus those cleaned twice during 1988-94. The neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents of pine twigs prior to the second cleaning in 1993-94 was higher in the untreated stands than in the cleaned ones. However, in vitro dry matter digestibility did not explain the difference in browsing between cleaning treatments. Total phenol content of pine twigs was slightly higher in the clean stands than in the untreated stands. the preferred species of trees, aspen (Populus tremula), rowan (Sorbus aucuparia), and willows (Salix spp.), were taller in exclosures then in open areas in 1995. The differences were evidently caused by browsing. Results indicated that moose browsing was not high enough to reduce the stem density of less-preferred white birch, which was strongly competing with pine especially in the single-cleaning treatment. Thus, relatively early cleaning is needed in conditions with excess birches because they can increase the risk of moose damage to pine. The importance of a mixture of tree species as well as the timing of silvicultural cleaning in relation to moose browsing has to be taken into account when combining moose management and forest practices.