Climate warming is altering carbon cycling in arctic tundra ecosystems. The presence of animals that consume, trample, excrete, and build structures on the tundra can alter carbon and nutrient (nitrogen & phosphorous) cycling. By studying how mammal herbivores (e.g., rodents such as voles & lemmings; ungulates such as moose, caribou & muskox) influence carbon and nutrient cycling in tundra in northern Alaska, our study contributes new insights into the roles animals may play in exacerbating or mitigating warming. To date, the main findings of our study are that:

(1) Rodents build structures (e.g., hay piles, nests, latrines) that alter carbon and nutrient cycling to different degrees, in different directions, and that are regionally-specific.

(2)   By selectively consuming certain plant species and changing micro-environmental conditions through various activities, mammalian herbivores can alter plant composition and cycling in ways that cause some tundra types to switch from being a sink to a source of atmospheric carbon during mid-summer.

(3)  The presence of herbivores can create canopies with higher 3D complexity in which foliage is more often shaded thus receiving less light and leading to lower daily photosynthetic rates.

(4)   Relative to unburned tundra, locations recovering from a wildfire that occurred 12 yrs ago had ten times as many rodents because of fire-induced increases in habitat suitability, which in turn led to two orders of magnitude higher mortality on preferred plants (sedges). Post-fire increases in herbivory  might lead to an increase in previously non-dominant plants (shrubs).

(5)   Lush, green tundra vegetation switches from being a sink to a source of carbon at higher temperatures and under low light conditions than does less lush vegetation (from greater herbivore activity), although the ability of lush vegetation to sequester carbon under warm conditions levels out once temperatures reach 25-30°C and light levels are high, suggesting continued warming of the tundra might eventually have a negative effect on the tundra’s net carbon uptake.

(6)   When tundra voles consume their preferred plant species, the plant has difficulty regrowing for several years. However, when soil nutrient availability is greater, such as is occurring with climate warming, the plant is more likely  to recover, assuming herbivory does not occur each year. This highlights how animal activity is interacting with warming to affect carbon cycling.

(7)   Herbivore pressure by tundra voles varies through 3-5 year “boom bust” population cycles. However, vole diet is consistent year to year, suggesting availability of preferred forage is not a factor driving population cycles in this system.  

(8)   Brown lemmings also experience multi-year “boom bust” population cycles. Analysis of stress hormone levels suggests weak support for stress as an intrinsic driver of population cycles. Stress hormone levels did however increase as winter temperatures decreased, a trend also evident in historical samples (1950-1960s) from the same location. Modern stress hormone levels fell within the natural range of variability in the historical sample, however, the variation in the modern population is greater. 

(9)   Our numerical modeling study indicates that in future climate scenarios of elevated CO2 concentrations and warming, rodent activity might stimulate nutrient cycling by amplifying the transfer of nitrogen from soil to vegetation thereby increasing carbon uptake via photosynthesis.

During this project, we broadened participation in the scientific enterprise by engaging many personnel in the research. We trained 17 undergraduates and partially or fully supported 9 graduate students (4 MS and 5 Ph.D.) in field research, engaging them in multiple disciplines pertinent to this project. In addition, we engaged 22 research assistants who sampled plants, soils, gases, and rodents. Of these students and research assistants, close to 2/3 were women and approximately 30% were from groups under-represented in ecology (primarily Black and Hispanic).

Our findings are being disseminated in the scientific community, to the general public,at our home institutions, and in Utqiagvik, one of our field sites. Multiple papers (many with student co-authors) have been published in a variety of journals, datasets have been made available, and both oral and poster presentations have been given at regional and national conferences. Several presentations and workshops have been given at K-12 schools near home institutions and at Hopson Middle School in Utquiagvik. Also in Utqiagvik, graduate students participated in the Barrow Arctic Research Center’s Science Fair in multiple years as well as the Fourth of July parade in 2019. In addition, voucher specimens of small mammals have been deposited at the University of Alaska Museum where they are publicly available to support future studies in ecology and evolution.

Combining the findings from these studies offers a comprehensive understanding of the complex interactions among herbivores, carbon and nutrient dynamics, and ecosystem responses in rapidly changing arctic tundra environments and the mechanisms whereby they might influence global warming. This research will assist ecologists, wildlife biologists, and residents of the tundra in understanding the role of herbivores in these ecosystems.

Last Modified: 08/14/2024
Modified by: Rebecca Rowe