Litter Fall of Alnus incana and Alnus glutinosa

1989

25 S.

15 Abb., 11 Tab., zahlr. Lit. Ang.

Bandaufführung

2628

37220

The aim of the present work was to provide long-term data concerning changes in the magnitude of the litter fall and proportins of the different litter components. The collection of material in the 1960's and early 1970's was carried out under the supervisin of the late professor Risto Sarvas. The amount of nutrients in the litter and the rate of litter decomposition are not examined in the study. The field experiments were located in six Alnus incana stands extending from southern Finland (Formel) to the artic fell region (Formel). The experiments in three of A. glutinosa stands were situated in southern Finland (Fig. 1). At four of the localities the litter fall was measured for a period of more than ten years; the longest period was 24 years (1963-1986) at Punkaharju (Table 1). The age of the stands varied between 14-103 years (Table 2). All the stands were even-aged, homogenous and consisted of one tree species only. On the sample plot at Enontekioe in Lapland, however, there was a slight admixture of Betula pubescens spp. tortuosa in the A. incana stand up until 1963 when the birches were felled. The size of the sample plots was 0.01-0.25 hectares (Table 2). Funnel-shaped traps with a collecting area of 0.05 m2 were sited randomly over the plots (Fig. 2). The number of traps/plot varied between 4- 20 (Table 3). The traps were emptied at monthly intervals during April- December. The litter trap material was allowed to dry at room temperature for a few days and then sorted into components such as leaves, male flowers and stamen remains, female floers, seeds, insect bodies and faeces, and other unsorted litter. A sieve (mesh size 0.59 mm) was used for sorting fine litter. All the fine material which passed through the sieve was included in the "insect bodies and faeces" component. Branches, twigs, lichens and leaves of other tree species were included in the "other unsorted litter" component. Only male flowers and stamen remains were oven-dried to a constant weight (16 hours at 106C). The litter components were weighted to an accuracy of 0.1 milligrams. The total annual litter fall in southern and central Finland varied between 1277-3766 kg/ha in the A. incana stands, and between 1468-3454 kg/ha in the A. glutinosa stands (Table 4). The mean annual total litter fall of both species was approximately 2300 kg/ha. The A. incana stand located in Enontekioe, Lapland, produced only 270 kg/ha/year of litter on the average. The total litter fall of A. incana on the Tuusula and Punkaharju sample plots increased slightly with stand age (Fig. 3). The annual amount of A. incana leaf fall ranged from 101 to 245 g/m2 in southern and central Finland. In Enontekioe, Lapland, the mean leaf litter fall was 23 g/m2/year. Leaves accounted for on average of 70-85% of the total litter fall. The range of the annual variation was 50-93%-units (Table 5).