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Source: Data from Crittenden (1989).

Source: Data from Crittenden (1989).

In the Norwegian high arctic, Cooper and Wookey (2001) measured the rate of growth of the fruiticose lichens Cetraria spp., Cladonia spp., and Alectoria nigricans (Fig. 3.1) as between 2.4 and 10.6 mgg"1 per week or between 2.5 -11.2% of the original lichen biomass in one season (approximately 10 weeks). Similarly, Peck et al. (2000) showed that the arctic tumbleweed lichen Masonhalea richardsonii increased in biomass by about 10% per year in Alaska. These rates of growth are similar to those reported by Karenlampi (1971). These lichens provide a large amount of the winter feed of reindeer, and in the island of Svalbard, may become severely depleted in biomass due to the intense grazing pressure, low rates of growth, and the indirect effect of reindeer trampling on lichen survival.

In temperate forest ecosystems, epiphytic lichens can form a significant proportion of the net primary production of the ecosystem. Using tethered arboreal lichens, Sillett et al. (2000) showed that the colonization of experimental branches was highest in clear-cut and old-growth Douglas fir forests and lowest in young (10-year-old, 1.5-m-tall) forests (Fig. 3.2). In general there was improved lichen colonization and growth on rough branches compared to smooth branches,

Table 3.3 Accumulation and Loss of N in Two Mat-Forming Lichen Species During 82 Days of Growth

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