| Summary: | Short and long term recovery of plant communities following intensive grazing by
caribou (Rangifer tarandus) and muskoxen (Ovibos moschatus) were examined in the Low
Arctic of Nunavut, Canada. Animals stranded on small islands resulted in intensively grazed
the plant communities, creating natural grazing "experiments." Field work was conducted
during July and August of 1997, at four locations. Islands intensively grazed by muskoxen
(in 1980, 1984, 1996 and 1997) and by caribou (in 1987) were measured for plant cover and
biomass, and current grazing intensity.
Regression was used to detect correlations between plant cover and biomass. For
most species, cover was a poor predictor of biomass.
Detrended Correspondence Analysis (DCA) clearly separated sites by latitude.
Direct gradient ordination (Redundancy Analysis) of each location showed the
importance of soil moisture and slope position to vascular plant cover, and current
grazing pressure and previous intensive grazing to biomass. Intensive grazing affected
cover and biomass for at least one year. After thirteen years recovery of vascular plants
was complete.
Analysis of Variance (ANOVA) of all locations showed that cover of all species
and functional groups (forbs, graminoids, lichens, shrubs) differed significantly between
intensively grazed island and adjacent mainland sites. Cover of all species differed
significantly by location and by site. There was no evidence of overcompensation, rather
equal or undercompensatory growth occurred.
Significant differences were found among intensively grazed islands, adjacent
islands and mainland sites. There were significant differences between the islands and
between the adjacent island and the mainland sites, but no significant differences between
the intensively grazed island and the mainland. Mainland sites had levels of grazing
similar to those of the recently, intensively grazed islands. Thus, it is necessary to
compare islands, rather than island and mainland sites, to detect grazing effects. No
significant differences were found between locations after thirteen years recovery from
intensive grazing by muskoxen.
Intensive grazing by caribou had longer-term effects than that by muskoxen.
Caribou eat lichen whereas muskoxen trample and leave thalli in situ. Ten years after
grazing by caribou, non-crustose lichen cover on the intensively grazed island was lower
than the mainland, whereas 1 month, 13 and 17 years after grazing by muskoxen, cover
was equal or greater than adjacent sites.
The fertilization effect of decomposing muskoxen carcasses was evident 13 years
after 27 muskoxen were killed at Merkeley Lake. Growth in some species was nutrient
limited; cover and biomass of surrounding graminoids and Dryas integrifolia and cover
of mosses were greatly increased. Salix spp. were not nutrient limited, and their growth
was unaffected by nutrient addition.
Without stranded grazers, small islands were protected from summer grazing by
ungulates, and grazing levels were lower than on the mainland. With stranded caribou or
muskox, however, grazing impacts were greatest on these islands, intermediate on
mainland sites, and least on adjacent islands. Upland sites experienced greatest grazing
pressure. The recently, intensively grazed sites had temporarily lower species richness.
Discrete episodes of intensive grazing on small islands do not appear to cause permanent
plant community change. === Arts, Faculty of === Geography, Department of === Graduate
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