. The Canadian field-naturalist. . Figure L Seed trap with aspen seedlings in early July. Toothpicks mark seedling locations. Populus and summer-dispersing Salix under opti- mum conditions of temperature and moisture (Zasada and Viereck 1975). Seeds of these two genera must germinate shortly after landing on the seedbed or they die (Schreiner 1974; Brinkman 1974). Our trap is a 1- X 1-m wooden frame (5 cm deep) covered on the underside with one layer of 4-mil plastic sheeting (Figure 1). The trap is filled with a standard potting soil, such as Jiffy-Mix,' that is kept wet. If flooding from hea
. The Canadian field-naturalist. . Figure L Seed trap with aspen seedlings in early July. Toothpicks mark seedling locations. Populus and summer-dispersing Salix under opti- mum conditions of temperature and moisture (Zasada and Viereck 1975). Seeds of these two genera must germinate shortly after landing on the seedbed or they die (Schreiner 1974; Brinkman 1974). Our trap is a 1- X 1-m wooden frame (5 cm deep) covered on the underside with one layer of 4-mil plastic sheeting (Figure 1). The trap is filled with a standard potting soil, such as Jiffy-Mix,' that is kept wet. If flooding from heavy rains is a problem, holes should be cut in the frame just below soil level. So that soil stays wet, holes should not be punched in the sheeting. It is important that the commercial potting mixes not have an inhibitory effect on germination of these species. We have not observed any effect from Jiffy- Mix' or Jiffy-Mix Plus' in growth chamber studies. Traps should be placed in the field prior to seed dispersal. Germinants are counted periodically and left to develop until they can be identified. Seed collected from identified willows and poplars and germinated on trap soils can be used as an aid to identify unknown germinants. We have used the traps on upland and floodplain sites in interior Alaska. On a birch ( ha) and aspen ( ha) clearcut we used four traps in each area to measure seedfall. Aspen seedfall was estimated to be 383 seeds/m- in the aspen clearcut and 376 seeds/m- in the birch clearcuts (coefficients of variation 25% and 19%, respectively). The first seed dispersal was observed on 10 June, the first germinants between 12 and 16 June, and the last germinants on 14 July (Table 1). Only aspen seedlings were observed in these traps. Figure 1 shows traps in early July. Four traps placed on a floodplain produced seedlings of a number of species (Table 2). The traps were set out after dispersal of Salix alaxensis. They were within an 8-yr-old stand (traps 1 and 2
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