Indagini ecologiche della tundra indagini ecologiche della tundra biome in Prudhoe Bay regione, Alaska . ecologicalinvest00brow Anno: 1975 184 CO 100 50 Q o c 20 - 10 Q,32e-o.3i5L^g8e-°0"'L I I I I I I I I 0 4 8 12 16 20 24 28 contenuto di lignina [L,g (lOOgr'] Fig. 13. La correlazione in vitro di digeribilità con contenuto di lignina di piante vascolari. 9, arbusti; O, carici; â , erbe; D , erbe; un , pellets commerciali. Le stime di biomassa per luglio, agosto e settembre (tabella 12) sono in generale in accordo con precedenti studi intensivi a Barrow, Alaska Tieszen (1972). Picco bi live

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Ecological investigations of the tundra Ecological investigations of the tundra biome in the Prudhoe Bay region, Alaska . ecologicalinvest00brow Year: 1975 184 CO 100 50 Q o c 20 - 10 Q, 32e-o.3i5L^g8e-°0'''L I I I I I I I I 0 4 8 12 16 20 24 28 Lignin Content [L, g (lOOgr'] Fig. 13. Correlation of in vitro digestibility with lignin content of vascular plants. 9, shrubs; O, sedges; â , grasses; D , herbs; A , commercial pellets. Biomass estimates for July, August, and September (Table 12) are in general agreement with previous intensive studies at Barrow, Alaska (Tieszen 1972). Peak live biomass is noted in the last week of July, and biomass declines marked- ly in most communities after this date. Chemical analyses are not complete; hence, no trend with age in the degree of lignification can be shown. However, preliminary evidence, again at Barrow, indicates an increase in lignin and a decrease in soluble (cell constituents) components of the plant during August (B. H. McCown, L. L. Ties- zen, and P. W. Flanagan, pers. comm.). At the start of the growing season, the effective produc- tivity of herbivores is limited by the available biomass and the rate of biomass increase. At the end of the season (early to mid-August), produc- tivity is also limited by the nutrient content of the available herbage. The amount of energy which is harvested by caribou and which becomes available for produc- tion depends on the maintenance energy require- ment of the animal. In turn, maintenance energy requirement is highly dependent on the activity pattern of the grazing animal. Insect harassment can increase substantially the daily heat production, the amount of the latter de- pending on the duration and intensity of harass- ment, the speed of movement, and the distance moved by the caribou. Following the present study, we are using simulation modeling (model ACTIVE) to give estimates of energy costs of insect harassment. Until this study is complete, we cannot calculate the lo

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