Journal of Ecology1996, 84, 905-914 The growth response ofgraminoid plants to goose grazing in a HighArctic environment JULIEN BEAULIEU, GILLES GAUTHIER and LINE ROCHEFORT* Departement de biologie & Centre d'etudes nordiques, Universite Laval, Ste-Foy, Quebec,Canada GIK 7P4 and *Departement dephytologie, Universite Laval, Ste-Foy, Quebec,Canada GIK 7P4 Summary 1 The response of plantsto herbivory usually varies with thegrazing regime experi- enced. We investigated (i) if the timing and frequency ofgrazing affected plant growth, (ii) if faecesdeposition by herbivores stimulated plant growth, and (iii) if grazing affected the total nonstructural carbohydrate (TNC) reserves in the below-ground vegetation of twoarctic graminoids, Dupontiafisheri and Eriophorum scheuchzeri. 2 This study was conducted in polygon fens exposed to intense summer grazing by greater snow geese (Chen caerulescens atlantica) on BylotIsland (73?N) in theCan- adian HighArctic. We manipulated the frequency (once or three times) and the timing (early, midor latein the season) ofgrazing and faeces deposition incontrolled grazing trials using captive goslings. 3 Although ungrazed plantsweretaller thangrazed ones at theend of the season, data on cumulative tiller elongation (net above-ground height production) showed that plants grazedonce or three times produced newfoliage after each defoliation in both species. However, neither grazing (presence orabsence)norits frequency affected thenetabove-ground primary production (NAPP) or thenumber oftillers at theend of the summer. Nitrogen concentration was highest in plants grazed threetimes, intermediate in thosegrazedonce,and lowest in ungrazed plants. 4 Timingof grazing and presence of goose faeceswithor without grazing had no effect on plantgrowth. 5 Eriophorum plantsgrazedthree times had less TNC in their below-ground tissues thanungrazed plants, and thetrend was similar in Dupontia. 6 Dupontiaand Eriophorum wereable to compensate forleaves lost to grazing and to maintain production at a level similar to ungrazed plants, butat somecost(reduced below-ground reserves). The absence of an effect of faeces on plant growth may explaintheabsenceof a positive effect of grazing on NAPP (i.e. overcompensation) in this ecosystem. Keywords: Arctic, below-ground reserve, Dupontia, Eriophorum, production, snow geese Journal ofEcology(1996) 84, 905-914 Introduction Theconsumption of living plant tissues by herbivores impacts directly upon plant production, growth and reproduction (Batzli et al. 1980) and, intuitively, we would expect these impactsto be deleterious. However, according to the model developed by McNaughton (1983), moderate grazing onplants can sometimes be followed byan increase in net above- ground primary production (NAPP). Although this model hasbeen investigated inmany plant-herbivore studies, it still remains the subject of controversy (Belsky1986, 1987; Belsky et al. 1993; McNaughton 1979, 1983, 1993). Most studies of plant-herbivoreinteractions involving vertebrates havecentred on mammals. Few birds are herbivorous (exceptions include grouse and geese)and their distribution and/or impact on plants are usually morepatchy thanmammals (Batzli et al. 1980). However,over the last 20 years, manygoose populationsworldwide have increased considerably (Reed 1990; Cooch & Cooke 1991; Ebbinge 1992; Owen & Black 1992).The potential impact ofgrazing by geese has thus increasedin several plant com- munities where they havebecome one ofthe dominant grazers (Kerbesetal. 1990).Hence,goose-plant inter- actions have received much attention lately(Hik & ? 1996British Ecological Society