Herbivore impacts to the moss layer determine tundra ecosystem response to grazing and warming.
Herbivory and climate are key environmental drivers, shaping ecosystems at high latitudes. Here, we focus on how these two drivers act in concert, influencing the high arctic tundra. We aim to investigate mechanisms through which herbivory by geese influences vegetation and soil processes in tundra ecosystems under ambient and warmed conditions. To achieve this, two grazing treatments, clipping plus faecal additions and moss removal, were implemented in conjunction with passive warming. Our key finding was that, in many cases, the tundra ecosystem response was determined by treatment impacts on the moss layer. Moss removal reduced the remaining moss layer depth by 30% and increased peak grass biomass by 27%. These impacts were probably due to observed higher soil temperatures and decomposition rates associated with moss removal. The positive impact of moss removal on grass biomass was even greater with warming, further supporting this conclusion. In contrast, moss removal reduced dwarf shrub biomass possibly resulting from increased exposure to desiccating winds. An intact moss layer buffered the soil to increased air temperature and as a result there was no response of vascular plant productivity to warming over the course of this study. In fact, moss removal impacts on soil temperature were nearly double those of warming, suggesting that the moss layer is a key component in controlling soil conditions. The moss layer also absorbed nutrients from faeces, promoting moss growth. We conclude that both herbivory and warming influence this high arctic ecosystem but that herbivory is the stronger driver of the two. Disturbance to the moss layer resulted in a shift towards a more grass-dominated system with less abundant mosses and shrubs, a trend that was further enhanced by warming. Thus herbivore impacts to the moss layer are key to understanding arctic ecosystem response to grazing and warming.
Gornall
Jemma L
JL
Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 3UU, Scotland. jemma.gornall@metoffice.gov.uk
Woodin
Sarah J
SJ
Jónsdóttir
Ingibjörg S
IS
Van der Wal
Rene
R
D000818:Animals; D001110:Arctic Regions; D018533:Biomass; D044002:Bryophyta / Q000502:physiology*; D003081:Cold Climate; D017753:Ecosystem; D005247:Feeding Behavior / Q000502:physiology*; D005777:Geese / Q000502:physiology*; D057232:Global Warming; D006109:Poaceae / Q000254:growth & development / Q000502:physiology; D012987:Soil / Q000032:analysis
D012987:Soil
Nature. 2001 May 31;411(6837):546-7
11385559
Trends Ecol Evol. 1997 Aug;12(9):352-6
21238102
Oecologia. 2003 May;135(4):583-92
12684865
Proc Natl Acad Sci U S A. 2006 Jan 31;103(5):1342-6
16428292
Oecologia. 2007 Oct;153(4):931-41
17618466
Proc Natl Acad Sci U S A. 2008 Aug 26;105(34):12353-8
18719116
Oecologia. 2002 Feb;130(4):600-608
28547263
Oecologia. 2005 Jan;142(2):159-68
15490246
Oecologia. 1998 Aug;116(1-2):202-206
28308527