Species diversity in small old-growth forest fragments:
the effect of the time since isolation


This study focuses on the question how does the species composition change in small old-growth forest fragments as the time spent in isolation from larger forests increases? We test the hypothesis that an isolated forest fragment gradually loses specialized species, because of higher rate of local extinctions than the rate of colonizations, as the time spent in isolation increases. In particular, we examine the influence of isolation on the number of species and the abundance of species specialized on old-growth spruce forest.

Study design and organisms

We selected 5 small spruce-dominated old-growth forest fragments (3.5-13.5 ha in size and ca 150 y in age) in each of the following three isolation time classes for the study: 2-7, 12-18 and 25-32 years in isolation from larger (>100 ha) old growth forests. Isolation to the surrounding more extensive old-growth forests varied mostly between 1 and 3km. The selected fragments were fairly close to the natural stage of old-growth spruce forest with moderate to large quantity of dead and decaying wood available. We selected two kinds of control areas for the study: firstly 9 ha sample plots within large old-growth forests (150-6500 ha in size, n=5) with a presumably undisturbed composition of old-growth specialist species, and secondly small natural fragments of spruce forest (6-10 ha in size, n=3) surrounded by large bogs and open wetlands representing a species composition following several hundreds of years of isolation from large old growth forests.

The organisms studied included birds, small mammals, insects, polypores and lichens (SEE A SEPARATE PAGE FOR THE SAMPLING OF EACH GROUP, BELOW). For the analyses of the effect of isolation history on species composition, we measured several covariate variables: patch size and the degree of present isolation as well as several measures of habitat quality (e.g. amount and quality of decaying wood, species composition of living trees, forest age, amount of man-cut stumps, amount and size of canopy gaps and coverage of spruce swamp depressions). We will calculate a measure of spatio-temporal isolation based on the known history of forest fragmentation in the study area during the past 50 years.

Use this table as short-cut to see THE SAMPLING OF EACH GROUP
1 Insects - Mikko Kuussaari
2 Birds - Raimo Virkkala
3 Small mammals - Vesa Selonen
4 Polypores - Reijo Penttilä and Mariko Lindgren
5 Lichens - Laura Kivistö and Mikko Kuusinen