Author: isabel

Finding sustainable grazing management in tundra ecosystems is becoming increasingly important for northern agriculture. In the Icelandic highlands, past grazing practices have played a major role in the extensive soil erosion, leaving many parts of this tundra rangeland in poor condition. However, following a reduction in sheep numbers, stricter grazing management policies, and a progressive turn to fertilisers for combating soil erosion, the current impacts of grazing practices are not well understood.

In this study we measured the short-term effect of current sheep grazing by comparing the amount of bare ground and aboveground biomass in grazed and ungrazed plots, with and without fertiliser application, in adjacent dwarf-shrub heaths and sparsely vegetated areas, at two sites within and outside the volcanic active zone.

After three years, grazing did not affect the amount of bare ground, but in the fertilised plots grazing consistently reduced plant biomass (mainly graminoids). Fertiliser application can increase grazing intensity, which can counteract the additional biomass accumulation. Consequently, the removal of biomass by sheep needs to be considered when fertilisers are used as part of a strategy to combat erosion.

The article is open access and you can find the full text here.

Reference: Mulloy, T.A., Barrio, I.C., Björnsdóttir, K., Jónsdóttir, I.S., Hik, D.S. (2019) Fertilisers mediate the short-term effects of sheep grazing in the Icelandic highlands. Icelandic Agricultural Sciences, 32: 75-85.

---

Text by Tara Mulloy, MSc student at Simon Fraser University

Picture: The study addressed the combined effects of fertiliser application and sheep grazing in the highlands of Iceland (photo: Tara Mulloy, Simon Fraser University, 2019)

Voles and lemmings are known for their high-amplitude population fluctuations and strong effects on dwarf shrub-dominated vegetation communities across the Fennoscandian tundra. Despite their key role in above-ground trophic interactions, there has been a dearth of research on how voles and lemmings affect ecosystem process rates, including ecosystem nutrient cycling and soil microbial activity. To address this gap, Maria Tuomi and colleagues studied how contrasting vole density regimes affect both vegetation and soil characteristics in a long-term island experiment located in West-Finnmark, Norway.

The study found that over the course of three population cycles, peak vole densities associated with increased abundance of palatable over non-palatable plants as well as increased nitrogen content in plant tissues. These changes in plant community characteristics link with increases in soil inorganic nitrogen content and microbial activity in litter. While these findings are in line with well-documented decimation of non-palatable shrubs during vole and lemming population peaks in Fennoscandia, they contrast predictions based on prevailing conceptual models on herbivore-plant-soil interactions. The study thus challenges the assumption that in low-productive ecosystems, herbivores slow down process rates by selectively eating nutritious plants, and proposes a new conceptual model with two alternative vole-plant-soil interaction pathways.

Reference: Tuomi, M., Stark, S., Hoset, K.S., Maria Väisänen, M., Oksanen, L., Murguzur, F.J.A., Tuomisto, H., Dahlgren, J., Bråthen, K.A. (2019) Herbivore effects on ecosystem process rates in a low-productive system. Ecosystems 22: 827-843

https://doi.org/10.1007/s10021-018-0307-4

---

Picture: In their study, high peak vole densities over multiple population cycles increased the relative abundance of forbs like Rubus chamaemorus (front) (photo: Maria Tuomi, University of Turku, 2018)

Shrubification of arctic tundra is a well-recognized phenomenon, and it can be particularly rapid in moist habitats. Reindeer grazing can inhibit shrubification, but grazing impacts on mire vegetation have been overlooked. We studied grazing effects on plant communities and Salix lapponum in oroarctic mires at the border of Finland and Norway. We compared plant community structure and S. lapponum abundance and traits between (1) grazed fens (Finland); (2) experimental exclosures (Finland), where reindeer have been kept out for 13 years; and (3) non-grazed fens (Norway). Grazing effect on shrubification was assessed using the Normalized Difference Vegetation Index (NDVI) and leaf area index (LAI).

We did not find a uniform direction of vegetation change connected to the exclosure treatment, and grazing treatments were overlapping in multivariate ordination. Neither NDVI nor LAI indicated clear differences. Instead, significant results were revealed in total abundance of species groups and in S. lapponum traits. The cover of bryophytes was significantly lower under free grazing. Reindeer grazing reduced the abundance, height, and flowering and increased leaf N concentration of S. lapponum. We conclude that reindeer grazing controls willows and affects total abundance of important species groups, and plant community structure is resistant to grazing effects in oroarctic mires. 

Reference: Kolari THM, Kumpula T, Verdonen M, Forbes BC, Tahvanainen T (2019) Reindeer grazing controls willows but has only minor effects on plant communities in Fennoscandian oroarctic mires. Arctic, Antarctic, and Alpine Research, 51(1):506-520

https://doi.org/10.1080/15230430.2019.1679940

---

Picture: Heidi Kitti, then PhD student, making ITEX-style tundra vegetation measurements in summer 2002 when the fenced reindeer exclosures were established in Näkkälä reindeer herding district, Finland (photo credit: Bruce Forbes, University of Lapland)

This new paper by David Anderson and collaborators reviews archaeological and palaeoecological evidence for the nature of occupation by humans (Nenets) and both wild and semi-domesticated reindeer at a low arctic tundra site on the Yamal Peninsula.

Yarte-6 on the Yuribei River is probably the most important Late Holocene archaeological site in West Siberia, which lies along the time continuum during the transition from hunting to herding reindeer. Yarte-6 is situated on a prominent headland overlooking the river valley and two large lakes. Although disused since the Middle Ages, the former camp site is covered by a lush grassy meadow, easily distinguished from the prevailing dwarf-shrub heath tundra vegetation.

When reindeer graze at modern Yamal tundra Nenets camps, their combined grazing and trampling creates a radial pattern. This has the effect of either killing or stunting the growth of shrubs within the grass/herb-rich area, while confining the growth of taller shrubs to the low-lying ravines encircling the site – which, as we will see, may have been an important feature for wild reindeer hunters. At low densities, Rangifer do not have a marked effect on either erect shrubs or ground-level vegetation. However, at higher densities, the negative impacts of more intensive grazing and trampling can become clear within as little as six years. While herbivores can help to preserve meadows by grazing the shrubs, their grazing is not essential when the graminoid-herb cover is so dense – as it is at Yarte-6 – that it prevents the germination of shrub seedlings. The establishment and long-term persistence of this grassy feature amongst well-grazed shrubs does indicate, however, that the activities of people and Rangifer had once been intense.

The question of what that shrub cover might have been like 1000 years ago is a key factor in interpreting past livelihoods. The Yarte promontory has few shrubs today, and indeed it would be hard to imagine how the existing willow copses could conceal a campsite or hide a hunter. However, the palynological evidence suggests that the shrub cover was thicker in the centuries after 800AD. During slightly warmer periods, willows grow taller and copses become more dense, as exemplified by the contemporary “shrubification” of Yamal, which is associated with the 21st-century warmer temperatures. The growth of shrubs during warm periods in the past might also have been encouraged by deeper snow cover, which also seems to be associated with warmer periods.

Reference: Anderson DG, Harrault L, Milek KB, Forbes BC, Kuoppamaa M, Plekhanov AV (2019) Animal domestication in the high Arctic: Hunting and holding reindeer on the I͡Amal peninsula, northwest Siberia. Journal of Anthropological Archaeology 55: 101079

https://doi.org/10.1016/j.jaa.2019.101079

---

Picture: The Yarte promontory in Yamal (photo: Bruce Forbes, University of Lapland)

In a recent paper published in Journal of Ecology, Maja Sundqvist, Jon Moen, Robert Björk, Tage Vowles, Minna-Maarit Kytöviita, Malcolm Parsons and Johan Olofsson studied the long-term effects of reindeer on vegetation in experimental sites across the Scandinavian mountains. They made use of a large network of study plots where reindeer have been excluded from vegetation for at least 15 years, spanning a latitudinal gradient including sites in Sweden, Finland and Norway.

The paper shows that reindeer reduced vegetation greenness, lichen and deciduous shrub abundances while increased soil mineral N, and the relative reductions in vegetation greenness in response to reindeer were not related to climate and soil properties. It also highlights the role of reindeer density for vegetation patterns at regional scales in the Arctic: reindeer density effects on plant species richness were related to productivity and reindeer density was positively related to the relative reduction in leaf area index and associated reductions of deciduous shrubs across the experimental sites.

Reference: Sundqvist, M.K., Moen, J., Björk, R.G., Vowles, T., Kytöviita, M.M., Parsons, M.A., Olofsson, J. (2019) Experimental evidence of the long‐term effects of reindeer on Arctic vegetation greenness and species richness at a larger landscape scale. Journal of Ecology

https://doi.org/10.1111/1365-2745.13201

---

Picture: One of the experimental exclosures used in this study, in Ritsem, Sweden (photo: Maja Sundqvist, SLU, 2019)

In a recent paper published in Ecosystems, Henni Ylänne and Sari Stark compare how key processes behind ecosystem carbon cycling depend on the time passed since reindeer have induced a vegetation shift. The study makes use of an area that had become dominated by graminoids due to a high reindeer grazing intensity within the past 14 years, and compares the processes on this to the processes in an area of decades old grazing-induced graminoid dominance and in an area of shrub dominance with little grazer influence.

The paper shows that ecosystem carbon sink was similar under both old and recent grassification. Yet the individual carbon fluxes varied depending on the time passed since the vegetation shift: ecosystem respiration and mid-season photosynthesis were higher under old than recent grassification. In contrast, the extracellular enzyme activities for carbon and phosphorus acquisition were similar regardless of the time elapsed since grazer-induced vegetation change. These results show that both autotrophic and heterotrophic ecosystem processes develop over time in response to changes in the intensity of herbivory with varying time-lags.

Reference: Ylänne, H., Stark, S. (2019) Distinguishing rapid and slow C cycling feedbacks to grazing in subarctic tundra. Ecosystems 22: 1145– 1159.

https://doi.org/10.1007/s10021-018-0329-y

---

Picture: Reindeer grazing in Reisa (photo: Henni Ylänne, Lund University, 2013)

Roger Ruess and colleagues have just published a very interesting paper in Ecosphere, on vegetation shifts mediated by geese. You can read the abstract below.

Along the coastal fringe of the Yukon–Kuskokwim River Delta in southwestern Alaska, geese maintain grazing lawns dominated by a rhizomatous sedge that, when ungrazed, transitions to a taller, less palatable growth form that is taxonomically described as a different species. Nutrients recycled in goose feces, in conjunction with grazing, are critical to the rapid, nutritious growth of grazing lawns, and selective foraging on lawns has positive life-history consequences for goslings. To examine whether bidirectional vegetation shifts were accompanied by parallel changes in N cycling, we studied how 15N-urea and 13C15N-glycine were processed through soils and plants of native and recently reverted vegetation states. Biomass and plant 15N uptake from plots reverted to the tall growth form using exclosures and from those shifted to grazing lawns by experimental clipping and then goose grazing were identical to their native counterparts. Total recovery of 15N within the tall vegetation types was significantly greater than within grazing lawns, although when expressed on a per-gram biomass basis, percentage of 15N recovery was significantly higher in grazing lawns compared with the tall vegetation state. Patterns of 13C enrichment in CO2 soil efflux showed rapid use of 13C-glycine as a respiratory substrate within the first hour following injection, with both the timing and magnitude of efflux occurring at similar time points for all four vegetation types. However, higher soil respiration rates and a shorter half-life for 13C-glycine in soils from tall meadows resulted in a greater proportional loss of 13CO2 compared with grazing lawns. Despite daily to-weekly tidal inundation, all of 15N from labeled substrates could be accounted for within 1 m of the injection grid from soils of both states after 30 d, with significant levels of 15N in soils and vegetation after one year. Geese have remarkably high fidelity to brood-rearing areas, returning as adults to the same grazing lawns where they were raised as goslings. Our data suggest that the role fecal-derived nutrients play in the positive feedback loop between geese and their food resources can provide a long-term legacy that spans generations.

You can also access the full text of the article here.

Reference: Ruess RW, McFarland JW, Person B, Sedinger JS (2019) Geese mediate vegetation state changes with parallel effects on N cycling that leave nutritional legacies for offspring. Ecosphere 10(8):e02850

---

Picture: Pacific black brant (Branta bernicla nigricans)
(photo: Roger Ruess, University of Alaska)