René van der Wal

Ecological Dynamics Across the Arctic Associated with Recent Climate Change

Assessing the Arctic The Arctic is experiencing some of the most rapid climate change currently under way across the globe, but consequent ecological responses have not been widely reported. At the close of the Fourth International Polar Year, Post et al. (p. 1355) review observations on ecological impacts in this sensitive region. The widespread changes occurring in terrestrial, freshwater, and marine systems, presage changes at lower latitudes that will affect natural resources, food production, and future climate buffering. At the close of the Fourth International Polar Year, we take stock of the ecological consequences of recent climate change in the Arctic, focusing on effects at population, community, and ecosystem scales. Despite the buffering effect of landscape heterogeneity, Arctic ecosystems and the trophic relationships that structure them have been severely perturbed. These rapid changes may be a bellwether of changes to come at lower latitudes and have the potential to affect ecosystem services related to natural resources, food production, climate regulation, and cultural integrity. We highlight areas of ecological research that deserve priority as the Arctic continues to warm.

Effects of nitrogen deposition on growth and survival of montane Racomitrium lanuginosum heath

Montane heaths dominated by the moss Racomitrium lanuginosum are in decline, for which increased atmospheric nitrogen (N) deposition may be partially responsible. To test this, field plots in northeast Scotland were treated with either low or high (10 or 40 kg N ha−1year−1) doses of nitrogen (as NO3− or NH4+) for 2 years. Although Racomitrium tissue N increased after treatment, with greater response for low than high N application, activity of the enzyme nitrate reductase and Racomitrium growth were severely inhibited by increasing N addition. Racomitrium cover declined following N addition and graminoid cover increased, also with greatest effect at high doses. Of all measurements, only nitrate reductase showed a distinction between NO3− and NH4+ application. The results demonstrate the detrimental effects of even low increases in nitrogen deposition on the moss heath, suggesting that loss of Racomitrium and its replacement by graminoids is strongly linked to increased levels of anthropogenic N pollution.

Differential effects of reindeer on high Arctic lichens

We studied the effects of Svalbard reindeer on the abundance of lichens in Spitsbergen. A survey was carried out in 14 areas with contrasting reindeer densities. Separate cover estimates for crustose, fructose and foliose lichens were taken in each area, and related to the density of reindeer pellet groups, a measure of reindeer density. Dominant macrolichen families were identified in 10 areas, and a full record of macrolichen species was taken in four additional areas. Varia- tion in reindeer density is partially due to past overhunting, and subsequent incomplete recovery, releasing some areas from reindeer grazing for 100-200 yr. The cover of fruticose lichens was negatively related to reindeer pellet group density, indicating suppression by Svalbard reindeer. This makes their impact comparable to other members of the Rangifer genus around the northern hemisphere. The generally recorded low abundance of lichens in the diet of Svalbard reindeer compared to other Rangifer species, therefore, was interpreted as the depletion of fruticose lichens in Spitsbergen, and a subsequent switch to alternative foods. Of all fruticose lichens, Stereocaulon spp. appeared least sensitive to grazing. Crustose and foliose lichen cover was independent of reindeer pellet group density. The cover of crustose lichens was significantly related to latitude, with greater cover in more northern areas. Foliose lichens were more abundant in places where moss cover was high. We conclude that the impact of Svalbard reindeer on lichens is dependent on growth form, with fruticose lichens suffering from grazing, whereas foliose lichens might indirectly benefit from higher densities of reindeer or, like crustose lichens, be controlled by other factors.

The Enigma of Soil Animal Species Diversity Revisited: The Role of Small-Scale Heterogeneity

Background “The enigma of soil animal species diversity” was the title of a popular article by J. M. Anderson published in 1975. In that paper, Anderson provided insights on the great richness of species found in soils, but emphasized that the mechanisms contributing to the high species richness belowground were largely unknown. Yet, exploration of the mechanisms driving species richness has focused, almost exclusively, on above-ground plant and animal communities, and nearly 35 years later we have several new hypotheses but are not much closer to revealing why soils are so rich in species. One persistent but untested hypothesis is that species richness is promoted by small-scale environmental heterogeneity. Methodology/Principal Findings To test this hypothesis we manipulated small-scale heterogeneity in soil properties in a one-year field experiment and investigated the impacts on the richness of soil fauna and evenness of the microbial communities. We found that heterogeneity substantially increased the species richness of oribatid mites, collembolans and nematodes, whereas heterogeneity had no direct influence on the evenness of either the fungal, bacterial or archaeal communities or on species richness of the large and mobile mesostigmatid mites. These results suggest that the heterogeneity-species richness relationship is scale dependent. Conclusions Our results provide direct evidence for the hypothesis that small-scale heterogeneity in soils increase species richness of intermediate-sized soil fauna. The concordance of mechanisms between above and belowground communities suggests that the relationship between environmental heterogeneity and species richness may be a general property of ecological communities.

HABITAT TYPE DETERMINES HERBIVORY CONTROLS OVER CO2 FLUXES IN A WARMER ARCTIC

High-latitude ecosystems store large amounts of carbon (C); however, the C storage of these ecosystems is under threat from both climate warming and increased levels of herbivory. In this study we examined the combined role of herbivores and climate warming as drivers of CO2 fluxes in two typical high-latitude habitats (mesic heath and wet meadow). We hypothesized that both herbivory and climate warming would reduce the C sink strength of Arctic tundra through their combined effects on plant biomass and gross ecosystem photosynthesis and on decomposition rates and the abiotic environment. To test this hypothesis we employed experimental warming (via International Tundra Experiment [ITEX] chambers) and grazing (via captive Barnacle Geese) in a three-year factorial field experiment. Ecosystem CO2 fluxes (net ecosystem exchange of CO2, ecosystem respiration, and gross ecosystem photosynthesis) were measured in all treatments at varying intensity over the three growing seasons to capture the impact of the treatments on a range of temporal scales (diurnal, seasonal, and interannual). Grazing and warming treatments had markedly different effects on CO2 fluxes in the two tundra habitats. Grazing caused a strong reduction in CO2 assimilation in the wet meadow, while warming reduced CO2 efflux from the mesic heath. Treatment effects on net ecosystem exchange largely derived from the modification of gross ecosystem photosynthesis rather than ecosystem respiration. In this study we have demonstrated that on the habitat scale, grazing by geese is a strong driver of net ecosystem exchange of CO2, with the potential to reduce the CO2 sink strength of Arctic ecosystems. Our results highlight that the large reduction in plant biomass due to goose grazing in the Arctic noted in several studies can alter the C balance of wet tundra ecosystems. We conclude that herbivory will modulate direct climate warming responses of Arctic tundra with implications for the ecosystem C balance; however, the magnitude and direction of the response will be habitat-specific.

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.

Digital technology and the conservation of nature.

Digital technology is changing nature conservation in increasingly profound ways. We describe this impact and its significance through the concept of ‘digital conservation’, which we found to comprise five pivotal dimensions: data on nature, data on people, data integration and analysis, communication and experience, and participatory governance. Examining digital innovation in nature conservation and addressing how its development, implementation and diffusion may be steered, we warn against hypes, techno-fix thinking, good news narratives and unverified assumptions. We identify a need for rigorous evaluation, more comprehensive consideration of social exclusion, frameworks for regulation and increased multi-sector as well as multi-discipline awareness and cooperation. Along the way, digital technology may best be reconceptualised by conservationists from something that is either good or bad, to a dual-faced force in need of guidance.

Can soil temperature direct the composition of high arctic plant communities

Low temperatures exert a primary constraint on the growth of high arctic vascular plants. However, investigations into the impact of temperature on high arctic plants rarely separate out the role of air and soil temperatures, and few data exist to indicate whether soil temperatures alone can significantly influence the growth of high arctic vascular plants in a manner that might direct community composition. We examined the response of high arctic plants of three functional types (grasses, sedges/rushes and non-graminoids) to manipulated soil temperature under common air temperature conditions. Target plants, within intact soil cores, were placed in water baths at a range of temperatures between 4.9 and 15.3 oC for one growing season. Grasses responded most rapidly to increased soil temperature, with increased total live plant mass, above-ground live mass and total below-ground live mass, with non-graminoids having the lowest, and sedges/ rushes an intermediate degree of response. The ratio of aboveground live mass to total live mass increased in all growth forms. Grasses, in particular, responded to enhanced soil temperatures by increasing shoot size rather than shoot number. In all growth forms the mass of root tissue beneath the moss layer increased significantly and to a similar extent with increasing soil temperature. These results clearly indicate that different growth forms, although collected from the same plant community, respond differently to changes in soil temperature. As a consequence, factors influencing soil temperature in high arctic ecosystems, such as global climate change or herbivory (which leads to reduced moss depth and increased soil temperatures), may also direct changes in vascular plant community composition.

High‐arctic plants like it hot: a long‐term investigation of between‐year variability in plant biomass

The Arctic is viewed as most sensitive to climate warming and subject to a general greening. Yet, summer weather conditions, which differ greatly among years, are believed to have little direct effect on arctic plant productivity. The dominant view is that between-year variation in aboveground plant biomass is small and poorly related to weather conditions in the same year in the Arctic. Here, we test this view based on a 12-year investigation of peak plant biomass among habitats, plant functional types, and species in high-arctic Svalbard. Our study revealed twofold variation (range 23–46 g/m2) in plant biomass between years, this being strongly related to summer temperature (r = 0.92). Importantly, we found strong plant biomass–summer temperature relationships across habitats, plant functional types, and species, and little evidence for a lagged effect of previous years biomass. Responses were of similar orders of magnitude, indicating that summer weather conditions were the key driver of plant productivity at all three levels of investigation. We propose three key factors behind such tight relationships between summer temperature and plant biomass in the same year. First, our methodological approach, a combination of nondestructive shoot density estimates in small, permanent plots and destructive shoot mass estimates outside these plots, allowed us to overcome the otherwise overwhelming small-scale spatial heterogeneity in aboveground plant biomass typical for high-arctic tundra vegetation. Second, the high-latitude location (78° N) makes the vegetation most susceptible to temperature differences due to their influence on process rates. Third, Svalbards oceanic nature dictates prevalent cloud cover, making summer temperature a good proxy for light availability and thus an index of photosynthetic activity required for plants to produce biomass. The present study challenges the prevailing notion that relationships between summer weather and vascular plant performance in the Arctic are weak and highly variable among plant species. This has important implications for our understanding of how and at which temporal scales future climate change will shape arctic plant productivity and, in turn, the dynamics of other ecosystem components in the low-productivity, bottom-up regulated ecosystems of the High Arctic.

Exploring beliefs behind support for and opposition to wildlife management methods: a qualitative study

Wildlife management methods such as culling (lethal control) and fencing can be controversial in some circumstances. Such controversy can be problematic for decision-makers or those managing decision-making processes and can lead to management delays or inertia. Understanding the reasons why people support or oppose specific management methods is therefore an important objective for researchers. Attitudes towards methods are in part based on individual beliefs about those methods, the species of wildlife being managed and other associated phenomena. This paper adopts a qualitative approach to develop understanding of these beliefs. We conducted 17 focus-groups on wild deer management at two locations in Britain, with both ‘professional’ land manager and ‘public’ participants (n = 103). We identified a number of individual beliefs which are grouped into five categories: naturalness, overabundance, impacts, effectiveness and animal welfare. Our findings suggest that potentially controversial management methods will receive most support where the objective is to maintain a ‘natural’ environment, at sites where impacts are evident, and when using targeted and effective methods.