The response of plant species to burial in three types of Alaskan wetlands

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At 15 freshwater lowland, 7 coastal, and 6 alpine sites, a burial experiment was set up with four treatments (0, 5, 10, or 15 cm of sediment). Species in alpine wetlands were damaged most by burial and their average shoot density in the 5-, 10-, and 15-cm treatments was reduced 35, 72, and 93% in 1979 and 28, 54, and 81% in 1980, respectively. In coastal wetlands, the average shoot density was 33, 65, and 76% lower in 1979 and 21, 37, and 53% in 1980 in the 5-, 10-, and 15-cm treatments. Species in freshwater lowland wetlands were the least damaged by burial: average shoot density was 17, 33, and 47% lower in 1979 and 10, 7, and 39% lower in 1980 in the 5-, 10-, and 15-cm treatments. The responses of three common species (Carex aquatilis, Carex lyngbyaei, and Equisetum fluviatile) to burial varied from site to site. For example, Equisetum fluviatile responded to burial with a significant increase in shoot density at two permanently flooded sites and with no change in shoot density or with a significant decrease in shoot density at sites flooded seasonally. Only eight species at five sites (mostly alpine sites) were eradicated and only in the 10- and (or) 15-cm treatments at any site. In seed traps in 1979 an average of 2.7, 3.6, and 5.9 species became established at alpine, coastal, and freshwater lowland sites, respectively. In 1980, there were 1.2, 4.1, and 7.3 species, on the average, represented in the seed traps in these three types of wetlands. Average seedling density was lowest in the alpine seed traps (6/m2 in 1979 and 7/m2 in 1980) and highest in coastal wetlands (362/m2 in 1979 and 270/m2 in 1980). In freshwater lowland wetlands, those with permanent standing water averaged 2.2 and 3.0 species in their seed traps in 1979 and 1980, respectively, while those only seasonally flooded averaged 8.8 species in 1979 and 9.0 in 1980. Permanently flooded freshwater lowland wetlands had 7 seedlings per square metre in 1979 and 25 in 1980, while those flooded seasonally had 122 seedlings per square metre in 1979 and 69 in 1980. On the average, slightly more than 40% of the taxa in the seed traps at a site in 1980 were taxa that had not been present in 1979, and slightly less than 40% of the taxa present in 1979 were not present in the seed traps at the same site in 1980. Only a few individuals of four species present in the seed traps of coastal wetlands in 1979 were still present in 1980.