Hans Meltofte

Rapid advancement of spring in the High Arctic

Summary Despite uncertainties in the magnitude of expected global warming over the next century, one consistent feature of extant and projected changes is that Arctic environments are and will be exposed to the greatest warming [1]. Concomitant with such large abiotic changes, biological responses to warming at high northern latitudes are also expected to outpace those at lower latitudes. One of the clearest and most rapid signals of biological response to rising temperatures across an array of biomes has been shifts in species phenology [2–4], yet to date evidence for phenological responses to climate change has been presented from most biomes except the High Arctic [3]. Given the well-established consequences for population dynamics of shifts in the timing of life history events [5,6], it is essential that the High Arctic be represented in assessments of phenological response to climate change. Using the most comprehensive data set available from this region, we document extremely rapid climate-induced advancement of flowering, emergence and egg-laying in a wide array of species in a high-arctic ecosystem. The strong responses and the large variability within species and taxa illustrate how easily biological interactions may be disrupted by abiotic forcing, and how dramatic responses to climatic changes can be for arctic ecosystems.

Climate change and the ecology and evolution of Arctic vertebrates

Climate change is taking place more rapidly and severely in the Arctic than anywhere on the globe, exposing Arctic vertebrates to a host of impacts. Changes in the cryosphere dominate the physical changes that already affect these animals, but increasing air temperatures, changes in precipitation, and ocean acidification will also affect Arctic ecosystems in the future. Adaptation via natural selection is problematic in such a rapidly changing environment. Adjustment via phenotypic plasticity is therefore likely to dominate Arctic vertebrate responses in the short term, and many such adjustments have already been documented. Changes in phenology and range will occur for most species but will only partly mitigate climate change impacts, which are particularly difficult to forecast due to the many interactions within and between trophic levels. Even though Arctic species richness is increasing via immigration from the South, many Arctic vertebrates are expected to become increasingly threatened during this century.

Differences in food abundance cause inter-annual variation in the breeding phenology of High Arctic waders

Previous work has shown that High Arctic waders in Greenland are “income breeders”, i.e. the resources used for egg formation are based almost entirely on biomass obtained on the breeding grounds. Thus, their breeding phenology is expected to be highly sensitive to inter-annual variation in food abundance during the pre-laying period. Early spring snow-cover may also influence timing of egg-laying either directly or mediated through food resources. Here, we report on the inter-annual variation in clutch initiation of three wader species breeding in High Arctic Greenland, Sanderling (Calidris alba), Dunlin (Calidris alpina) and Ruddy Turnstone (Arenaria interpres), in relation to spring snow-cover and spring arthropod abundance over ten breeding seasons at Zackenberg Research Station 1995–2005. Food abundance had the strongest effect on timing of clutch initiation, while the proportion of snow-free land had a weaker but still significant effect, i.e. more food and more snow-free land both result in earlier egg-laying. We hypothesize that food is most important when there is sufficient snow-free land to nest on, while snow-cover is of increasing importance in years with late snowmelt.

Effects of Food Availability, Snow and Predation on Breeding Performance of Waders at Zackenberg

Publisher Summary Arctic waders depend on rich feeding grounds on their final staging areas in temperate climates to be able to carry out thousands of kilometers of nonstop flight to their arctic breeding grounds. In a study discussed in the chapter, early spring food availability turned out to be the most important determinant of timing of egg laying, followed by snow cover in years with less than average snow-free land in early June. Mean clutch size decreased during June–July, and the total length of the laying period was shortened in years of late snowmelt, meaning that the chances for re-laying in case of failure were limited in such years. All this led to reduced breeding success in late breeding seasons. Events of inclement weather and predation, including the availability of alternative prey for the predators, had little effect on breeding success in most years. Densities of breeding waders in high-arctic Greenland are low both in the desert-like north and in the snow-rich south, while higher densities are found in central Northeast Greenland. The balance between spring snow cover and vegetation cover available for the waders during the critical prelaying period is more favorable. Hence, densities at Zackenberg are among the highest recorded in Northeast Greenland, and the populations show relatively limited year-to-year variation.

Vertebrate Predator—Prey Interactions in a Seasonal Environment

Publisher Summary This chapter describes and analyzes the predator–prey dynamics representative of the terrestrial ecosystem in Zackenbergdalen. By using comprehensive, temporally replicated data on the collared lemming and its predators, the chapter focuses on the predator–lemming dynamics embracing a period of 10 years. The chapter discusses the predator–lemming model, specifically modified to reflect the observed predator–lemming system in Zackenbergdalen. In spring and summer, predation pressure is heavy, and the lemming predators are capable of reducing the density of collared lemmings in most summers. In winter, however, stoat predation alone is insufficient to regulate the collared lemming population. These marked effects of predators are also visible in the behavior of collared lemmings in summer. Collared lemmings spend most of their time belowground, and aboveground, they divide their time almost equally between foraging and being vigilant. Climate not only contributes to the shaping of the seasonal dynamics of the lemming population but also affects the pattern of fluctuations. Earlier onset of winter has no impact on the periodicity, whereas the later the onset of winter the longer the periodicity of the lemming fluctuations, moving toward less stable population fluctuations.

The Study Area at Zackenberg

Publisher Summary The Zackenberg Research Station is situated in central Northeast Greenland and is open during June–August. The climate is high arctic, and the study area is mountainous with deep valleys and fjords. The study area for the terrestrial monitoring and research within the framework of Zackenberg Ecological Research Operations (ZERO) comprises the drainage basin of the river Zackenbergelven. Zackenbergdalen was selected as the main study area because of its great diversity in physical landscape features, plant communities, and other biota. Almost all of Greenlands high-arctic landforms and biodiversity are represented in the valley, including moraines, scree slopes, rock glaciers, gently sloping rock faces, river beds, alluvial fans, a raised delta, beach terraces, permanent and perennial snow beds and glaciers, several types of ponds and lakes, fens, heath and barren lands, together with most known species of plants and animals. Research, monitoring, and logistics at Zackenberg are coordinated by the research program ZERO. Research and monitoring within the Zackenberg research area are managed to secure appropriate coordination among individual research projects and between research and monitoring.

Circumpolar Arctic vegetation: a hierarchic review and roadmap toward an internationally consistent approach to survey, archive and classify tundra plot data

Satellite-derived remote-sensing products are providing a modern circumpolar perspective of Arctic vegetation and its changes, but this new view is dependent on a long heritage of ground-based observations in the Arctic. Several products of the Conservation of Arctic Flora and Fauna are key to our current understanding. We review aspects of the PanArctic Flora, the Circumpolar Arctic Vegetation Map, the Arctic Biodiversity Assessment, and the Arctic Vegetation Archive (AVA) as they relate to efforts to describe and map the vegetation, plant biomass, and biodiversity of the Arctic at circumpolar, regional, landscape and plot scales. Cornerstones for all these tools are ground-based plant-species and plant-community surveys. The AVA is in progress and will store plot-based vegetation observations in a public-accessible database for vegetation classification, modeling, diversity studies, and other applications. We present the current status of the Alaska Arctic Vegetation Archive (AVA-AK), as a regional example for the panarctic archive, and with a roadmap for a coordinated international approach to survey, archive and classify Arctic vegetation. We note the need for more consistent standards of plot-based observations, and make several recommendations to improve the linkage between plot-based observations biodiversity studies and satellite-based observations of Arctic vegetation.

Zackenberg in a circumpolar context

Throughout the Northern Hemisphere, changes in local and regional climate conditions are coupled to the recurring and persistent large-scale patterns of pressure and circulation anomalies spanning vast geographical areas, the so-called teleconnection patterns. Indeed, the atmospheric fluctuations described by the North Atlantic Oscillation (NAO) are closely associated with the last four decades of inter-annual variability in local snow and ice conditions observed in the Arctic. Since the NAO has also been connected with changes in the global climate, the behaviour of species, communities and other ecosystem elements at Zackenberg in relation to the NAO enables us to view these in circumpolar and global contexts. Large-scale systems like the NAO constitute the link between the global change and local climate variability to which ecosystem components respond. Here, we place selected ecosystem elements from the monitoring programme Zackenberg Basic presented in previous chapters in a circumpolar context related to NAO-mediated climatic changes. We begin by linking the local variability in winter weather conditions at Zackenberg to fluctuations in the NAO. We then proceed by linking the observed intra- and inter-annual behaviour of selected ecosystem elements to changes in the NAO. The functional ecosystem characteristics in focus are landscape gas exchange dynamics phenological patterns at different trophic levels, consumer-resource dynamics and community stability. The influence of the NAO is presented and discussed in a broader perspective based on information obtained from other arctic localities. The relation between the NAO and the Zackenberg winter weather, is nonlinear, reflecting differential effects of the NAO as the index moves between high and low phases. The inverse hyperbolic relationship found between the NAO and the amount of winter snow was also evident as non-linear response in organisms and systems to inter-annual changes in the NAO. Responses investigated included growth and reproduction in plants and animals, population dynamics and synchrony, inter-trophic interactions and community stability together with system feedback dynamics. (Less)

Interaction webs in arctic ecosystems: Determinants of arctic change?

How species interact modulate their dynamics, their response to environmental change, and ultimately the functioning and stability of entire communities. Work conducted at Zackenberg, Northeast Greenland, has changed our view on how networks of arctic biotic interactions are structured, how they vary in time, and how they are changing with current environmental change: firstly, the high arctic interaction webs are much more complex than previously envisaged, and with a structure mainly dictated by its arthropod component. Secondly, the dynamics of species within these webs reflect changes in environmental conditions. Thirdly, biotic interactions within a trophic level may affect other trophic levels, in some cases ultimately affecting land–atmosphere feedbacks. Finally, differential responses to environmental change may decouple interacting species. These insights form Zackenberg emphasize that the combination of long-term, ecosystem-based monitoring, and targeted research projects offers the most fruitful basis for understanding and predicting the future of arctic ecosystems.

Trends in breeding phenology across ten decades show varying adjustments to environmental changes in four wader species

ABSTRACT Capsule: During 1928–2016, initiation of egg-laying advanced in two wader species, remained unchanged in one, and was delayed in one species. The changes across years and variation among species can be explained by climatic variables and differences in migratory strategies. Aims: To document possible changes in initiation of egg-laying in common Danish wader species since the early part of the 20th century and seek possible correlations between egg-laying, timing of arrival and environmental factors. Methods: Annual records of the first eggs and chicks found on the scientific reserve of Tipperne in western Denmark 1928–2016 were analysed using linear regression to determine patterns in timing of egg-laying, pre-breeding length and influence of climate factors. Results: Two short/medium-distance migrant wader species, Northern Lapwing Vanellus vanellus and Common Redshank Tringa totanus advanced breeding initiation by about one week, with winter North Atlantic oscillation Index and spring temperature as important predictors. By contrast, two long-distance migrants, Black-tailed Godwit Limosa limosa and Ruff Calidris pugnax, did not advance egg-laying, and Ruff actually delaying it. As a result, the pre-laying period was significantly prolonged in both Black-tailed Godwit (21 days) and Ruff (52 days), while there was no significant change for Common Redshank. Conclusion: Long-distance migrants are able to adjust spring arrival but unlike short/medium-distance migrants, do not necessarily adjust breeding initiation.