Plant responses to fertilization and exclusion of grazers on an arctic tundra heath

Abstract

This study investigated the impacts of fertilization and grazing by Norwegian lemmings (Lemmus lemmus), grey‐sided voles (Clethrionomys rufocanus), and reindeer (Rangifer tarandus) on a diverse tundra plant community dominated by deciduous shrubs. Four out of eight study areas, having a size of 2500 m2 each, were fertilized with a N‐P‐K fertilizer and four areas served as unfertilized controls. Two types of exclosures were used within each study area, one to exclude solely reindeer, and one to exclude both rodents and reindeer. Open, grazed plots served as controls. During 5 years following the fertilization event the changes in vegetation inside and outside the exclosures were monitored using a point frequency method. The densities of rodents on the fertilized and unfertilized areas were investigated by live trapping and by counting nests of overwintering individuals. Reindeer do not graze on the study area during the growing season but migrate through this area in autumn and spring. Fertilization increased the abundance of vascular plants while grazing by reindeer and rodents decreased the abundance of vascular plants significantly on both fertilized and unfertilized areas. Rodents preferred clearly the fertilized areas during winter, decreasing the abundance of Vaccinium myrtillus and Vaccinium vitis‐idaea, while very little grazing occurred during summer. Graminoids showed the strongest positive response to fertilization and dominated the plant community on ungrazed plots, while winter grazing by both reindeer and rodents significantly decreased the abundance of graminoids. Deciduous shrubs (Betula nana, Vaccinium myrtillus) increased slightly but significantly due to fertilization and evergreen dwarf shrubs showed no response to fertilization. However, the use of functional growth forms for predicting the responses of nutrient enrichment and grazing must be questioned, as responses to fertilization as well as preferences by herbivores were shown to be species‐specific rather than uniform within functional groups based on plant growth forms.

Effects of Simulated Grazing in Ungrazed Wet Sedge Tundra in the High Arctic

“…Nonetheless, the nitrogen relocation by muskoxen is likely to have large qualitative effects on the plant communities. Numerous studies have shown enhanced primary productivity in arctic plant communities after nitrogen addition (Chapin and Shaver, 1996;Jonasson et al, 1996;Grellmann, 2002), and recently Barthelemy et al (2015) reported a strong plant response in a longterm reindeer feces experiment. Here reindeer feces were added to two different arctic vegetation types, graminoid-dominated meadow and shrubdominated heath.…”

Experimental approaches to predicting the future of tundra plant communities

“…This is undoubtedly the case for large herbivores, although lemmings and voles will not be excluded from OTCs, and reduced pollination has not been identified as a problem to date. The exclusion of large herbivores from OTC plots and not from control plots is an experimental artefact which is likely to become cumulatively more important as experiments progress (see Grellmann 2002;Olofsson et al 2004;Bråthen et al 2007;Ims et al 2007). An uncoupling between the magnitudes of air and soil warming is also likely to have cumulative effects on plantsoil interactions (Bardgett et al 2005), nutrient recycling and ecosystem C flux.…”

Fertilization and irrigation effects on the Geranium-Hedysarum Meadows, Northwestern Caucasus, Russia

“…Ïî äàííûì çà ïÿòûé ãîä, ìàñ-ñà ãåíåðàòèâíîãî ïîáåãà óâåëè÷èëàñü íà N. Ïî âñåì ãîäàì íàáëþäåíèé ñóììàðíàÿ ÷èñëåííîñòü ïîáåãîâ ñíèçèëàñü íà N, Ð, NP, à íà äåñÿòûé ãîä ýêñïåðè-ìåíòà îíà òàêaeå ñíèçèëàñü íà Ñà. Óìåíüøåíèå ÷èñ-ëåííîñòè ïîáåãîâ ïîäòâåðaeäàåò òîò ôàêò, ÷òî íà áî-ãàòûõ ïî÷âàõ Anthoxanthum odoratum ïîäàâëÿåòñÿ áîëåå ñèëüíûìè êîíêóðåíòàìè [12] èëè aeå ñèëüíåå ïîäâåðaeåí âëèÿíèþ ôèòîôàãîâ [26]. Èíòåðåñíî îò-ìåòèòü, ÷òî è â ýêñïåðèìåíòàõ ñ óäàëåíèåì ñîñåä-íèõ ðàñòåíèé [27] Anthoxanthum odoratum ðåàãèðîâàë óâåëè÷åíèåì ÷èñëåííîñòè ïîáåãîâ, à ìàññà îòäåëü-íûõ ïîáåãîâ ïðè ýòîì íå èçìåíÿëàñü.…”

“… ñâÿçè ñ ýòèì ìîaeíî ïðåä-ïîëîaeèòü, ÷òî íà ðåçóëüòàòû íàøåãî ýêñïåðèìåíòà çíà÷èòåëüíîå âëèÿíèå ìîãëî îêàçàòü âîçäåéñòâèå ôè-òîôàãîâ, òàê êàê áûëî ïîêàçàíî, ÷òî ýòîò âèä õî-ðîøî ïîåäàåòñÿ âñåìè çëàêîÿäíûìè ïðÿìîêðûëû-ìè [30]. Ýêñïåðèìåíò, ïðîâåäåííûé â Ñåâåðíîé Íîð-âåãèè [26], ïîäòâåðäèë íàøó ãèïîòåçó. Deschampsia flexuosa óâåëè÷èâàë ñâîå ó÷àñòèå íà óäîáðåííûõ âàðèàíòàõ òîëüêî ïðè óñëîâèè èçîëèðîâàííîñòè îò ôèòîôàãîâ.…”