Vegetation 
Type 
(Webber's 
Classification) 
Relative 
Insect 
Relief 60; am 
Availability 4 
(% of mt 
0 
In vitro 60 
Digestibility aof al = 
(%) 20 
Peak = — 
Biomass 60 
(g m-2) 40 || 
20 
Biomass 1.5 ee 
Ratio fi a 
(Live/Dead) .5 
49) 
Relative 12 77) 
Preference | | /// 
Index 4 ///\ 
(R) (0) 
= 
Increasing Wetness of Habitat 
[R=Availability x Digestibility* Biomass * (Live/Dead)] 
Fig. 14. Summary of relative characteristics of 
vegetation types which appear pertinent to cari- 
bou habitat at Prudhoe Bay. Relative degree of 
insect relief is a subjective assessment; avail- 
ability, see Table 8; in vitro digestibility, see 
Table 19; peak biomass, see Table 12 (live 
biomass); biomass ratio, calculated as ratio of 
live/dead, including litter at peak live biomass, 
see Table 12); relative preference index of 
herbage was calculated as the product of avail- 
ability of community type, in vitro digestibility, 
peak biomass and ratio of live/dead. 
when energy is available for growth and fatten- 
ing, low survival might be expected. Late July 
and August productivity would be higher if 
caribou followed the phenologic and primary 
production progression in vegetation types from 
south of the Prudhoe Bay study area into the 
foothills of the Brooks Range. This strategy 
might explain the adaptive significance of ob- 
served migration patterns of caribou, but why a 
small herd remains resident in the Prudhoe Bay 
area is less easily explained. 
185 
Acknowledgements 
This project was supported by Grant No. 
GB-29342 to the University of Alaska under the 
auspices of the U.S. Tundra Biome Program 
from the Office of Polar Programs and the 
International Biological Program of the National 
Science Foundation. Logistic support at Prud- 
hoe Bay was made available through the Tundra 
Biome Center, University of Alaska, from funds 
provided by the Prudhoe Bay Environmental 
Subcommittee; the Naval Arctic Research 
Laboratory, Barrow, Alaska, assisted in the 
transport of reindeer. Additional support was 
provided through contract with the U. S. Atom- 
ic Energy Commission (AEC _ Contract 
[(45-1)-2229-TA3] ). The authors are grateful to 
the late Scott Parrish for his assistance in logis- 
tics as site coordinator at Prudhoe Bay. The 
skilled technical assistance of A.M. Gau, P. 
Frelier, and Sandra White is gratefully acknowl- 
edged. 
R.G. White and J. R. Luick acknowledge 
international cooperation with the Grazing Pro- 
gramme of the Norwegian IBP Committee 
through exchange of data and personnel. The 
models ACTIVE and GRAZE were developed in 
cooperation with Dr. Fred Bunnell, Faculty of 
Forestry, University of British Columbia. 
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