The effect of moose browsing on the height structure of Scots pine saplings in a mixed stand

Abstract

We studied long-term effect of moose ( Alces alces) browsing on the height distribution of Scots pine ( Pinus sylvestris L.) saplings in mixed stands in central Finland. The experiment, established in 1988–1989 in an area of dense moose population, consisted of six 6-year-old pine stands, each including a moose-fenced exclosure and adjacent non-fenced study plots in similar initial conditions, including standard cleaning in 1993. Browsing on preferred species was shown as decreased mean height and tree density. Differences in height distributions, observed in 2000, were caused by moose browsing on the competing broadleaved species and browsing on the leader shoots of the non-fenced pine saplings. We constructed models for the 50th and 97th sample percentiles of the height distribution and used them to estimate the parameters of the two-parameter Weibull distribution. According to the models, the height distribution of pine became increasingly skewed to the right, i.e. longer tail towards taller trees, due to increasing proportion of the leader shoot damage of pine saplings. Intensive browsing of competing broadleaved trees shifted the height distribution to the right, towards taller trees. The results may not be generalized widely. In the future, among with other more widely located corresponding experiments, the results can be used to evaluate the effects of dense moose population in relation to pre-commercial thinning of young pine stands.