. The Canadian field-naturalist. Natural history. 1997 Helm and Collins: Vegetation Succession and Disturbance 559 (A JS o .c TO I >16 8-16 4-8 2-4 1-2 0 Early Shrub Intermediate Alder Young Poplar Late Old Poplar Birch - Spruce. 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 IPoba HlfflPigl MBepa S Salix EZlForbs HH Grass lAlte &3 Late Shrub Cover(%) Figure 2. Scaled relative cover (%) (relative cover x total vascular plant cover) by major species or herba- ceous life form and height class in each successional stage. Shrubs between
. The Canadian field-naturalist. Natural history. 1997 Helm and Collins: Vegetation Succession and Disturbance 559 (A JS o .c TO I >16 8-16 4-8 2-4 1-2 0 Early Shrub Intermediate Alder Young Poplar Late Old Poplar Birch - Spruce. 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 IPoba HlfflPigl MBepa S Salix EZlForbs HH Grass lAlte &3 Late Shrub Cover(%) Figure 2. Scaled relative cover (%) (relative cover x total vascular plant cover) by major species or herba- ceous life form and height class in each successional stage. Shrubs between and 4 m tall are sub- ject to Moose browsing disturbance. Poba = Populus balsamifera, Bepa = Betula papyrifera, Pigl = Picea glauca, Salix = Salix alaxensis + Salix novae- angliae, Alte = Alnus tenuifolia, Late shrub = Rosa acicularis + Viburnum edule + Ribes triste. transects were plotted approximately every 4 cm (2 km) on aerial photographs (1:48 000 black- and- white taken in 1980). Points were systematically plotted approximately every 7 mm (350 m) along each transect from the base of slope on one side of the river to the base of first hill on the other side, which was considered the limit of the floodplain. The points were classified according to successional stage during a helicopter survey in June 1981. Results General Early Shrub sites were most common on the two lower reaches where the floodplain was wide with split and braided channels. Approximately 20 to 30% of available land in this reach was occupied by Barren or Early Shrub stages (Table 1). Above the Chulitna River confluence, the river was narrower with well-defined channels. Here the mature forests predominated and occupied almost three-fourths of the available land area. Similarly the intermediate stage only occupied 6% of the area compared to > 17% in the lower two reaches. Some Early Shrub sites have remained in early succession from 1951 (aerial photographs) to 1995 although they are periodically fl
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