Airborne laser scanning reveals increased growth and complexity of boreal forest canopies across a network of ungulate exclosures in Norway

Large herbivores are often classed as ecosystem engineers, and when they become scarce or overabundant, this can alter ecosystem states and influence climate forcing potentials. This realization has spurred a call to integrate large herbivores in earth system models. However, we lack a good understanding of their net effects on climate forcing, including carbon and energy exchange. A possible solution to this lies in harmonizing data across the myriad of large herbivore exclosure experiments around the world. This is challenging due to differences in experimental designs and field protocols. We used airborne laser scanning (ALS) to describe the effect of herbivore removal across 43 young boreal forest stands in Norway and found that exclusion caused the canopy height to increase from 1.7 0.2 to 2.5 0.2 m (means SE), and also causing a marked increase in vertical complexity and above-ground biomass. We then go on to discuss some of the issues with using ALS; we propose ALS as an approach for studying the effects of multiple large herbivore exclosure experiments simultaneously, and producing area-based estimates on canopy structure and forest biomass in a cheap, efficient, standardized and reproducible way. We suggest that this is a vital next step towards generating biome-wide predictions for the effects of large herbivores on forest ecosystem structure which can both inform both local management goals and earth system models biomass, herbivory, large herbivores, LiDAR, moose, remote sensingpublishedVersio

Integrative taxonomy reveals a new species, Nephroma orvoi, in the N. parile species complex (lichenized Ascomycota)

Our knowledge of the diversity and distribution of many groups of lichens remains poor due to unclear species boundaries and challenging species identification. We have studied the medium sized to large foliose lichen Nephroma parile, which is known to be heterogeneous in chemistry and genetics. Our aim has been to assess the potential presence of evolutionary significant units within the Nephroma parile species complex that may be worthy of recognition at species level. Using phylogenetic analysis of the fungal DNA-barcode marker (ITS) in combination with studies of morphology and chemistry, we discover two distinct lineages in the N. parile species complex. For the strongly supported clade that corresponds to chemotype II, we describe the new species Nephroma orvoi. The new species is known from Norway, Sweden, Finland, Switzerland, Canada (Alberta and British Columbia), USA (Washington), and Greenland.publishedVersio

Functional traits of alpine plant communities show long-term resistance to changing herbivore densities

Herbivores shape vegetation by suppressing certain plant species while benefitting others. By thus modifying plant species functional composition, herbivores affect carbon cycling, albedo, vegetation structure and species' interactions. These effects have been suggested to be able to counteract the effects of increasing temperatures on vegetation in alpine environments. Managing the dominant large ungulates in these ecosystems could thus provide a tool to mitigate climate change effects. However, it is possible that legacy effects of past grazing will dampen ungulate impacts on vegetation. We shed a light on this topic by investigating the short- and long-term effects of varying sheep densities on the plant trait composition in the Norwegian alpine tundra with centuries-long of intensive grazing history. In the first part of our study, we quantified the effects of sheep on the plant community functional trait composition at different elevations and under moderate and low productivity in. We combined data from two long-term (14 and 19 yr) sheep fence experiments and showed that differences in sheep densities did not affect plant trait composition, irrespective of productivity. However, in the second part of our study, we showed that the plant trait composition in mainland (that has been grazed for centuries) differed from vegetation on islands which have been herbivore-free. Taken together, these results suggest that sheep have an effect on the alpine plant communities on historical time scales covering centuries, but that the resulting sheep grazing resistant/tolerant communities may not respond to shorter-term (14 and 19 yr) changes in sheep densities, that is, at temporal scales relevant for ecosystem management. Furthermore, we showed that the plant trait composition at the site with low productivity had gone through a temporal trait change independent of sheep treatment, potentially due to increased temperatures and precipitation, suggesting that sheep may not be able to counteract climatic impacts in the areas with centuries-long grazing history.publishedVersio

Integrative taxonomy reveals a new species, Nephroma orvoi, in the N. parile species complex (lichenized Ascomycota)

Our knowledge of the diversity and distribution of many groups of lichens remains poor due to unclear species boundaries and challenging species identification. We have studied the medium sized to large foliose lichen Nephroma parile, which is known to be heterogeneous in chemistry and genetics. Our aim has been to assess the potential presence of evolutionary significant units within the Nephroma parile species complex that may be worthy of recognition at species level. Using phylogenetic analysis of the fungal DNA-barcode marker (ITS) in combination with studies of morphology and chemistry, we discover two distinct lineages in the N. parile species complex. For the strongly supported clade that corresponds to chemotype II, we describe the new species Nephroma orvoi. The new species is known from Norway, Sweden, Finland, Switzerland, Canada (Alberta and British Columbia), USA (Washington), and Greenland.publishedVersio

Will borealization of Arctic tundra herbivore communities be driven by climate warming or vegetation change?

Poleward shifts in species distributions are expected and frequently observed with a warming climate. In Arctic ecosystems, the strong warming trends are associated with increasing greenness and shrubification. Vertebrate herbivores have the potential to limit greening and shrub advance and expansion on the tundra, posing the question of whether changes in herbivore communities could partly mediate the impacts of climate warming on Arctic tundra. Therefore, future changes in the herbivore community in the Arctic tundra will depend on whether the community tracks the changing climates directly (i.e. occurs in response to temperature) or indirectly, in response to vegetation changes (which can be modified by trophic interactions). In this study, we used biogeographic and remotely sensed data to quantify spatial variation in vertebrate herbivore communities across the boreal forest and Arctic tundra biomes. We then tested whether present-day herbivore community structure is determined primarily by temperature or vegetation. We demonstrate that vertebrate herbivore communities are significantly more diverse in the boreal forest than in the Arctic tundra in terms of species richness, phylogenetic diversity and functional diversity. A clear shift in community structure was observed at the biome boundary, with stronger northward declines in diversity in the Arctic tundra. Interestingly, important functional traits characterizing the role of herbivores in limiting tundra vegetation change, such as body mass and woody plant feeding, did not show threshold changes across the biome boundary. Temperature was a more important determinant of herbivore community structure across these biomes than vegetation productivity or woody plant cover. Thus, our study does not support the premise that herbivore-driven limitation of Arctic tundra shrubification or greening would limit herbivore community change in the tundra. Instead, borealization of tundra herbivore communities is likely to result from the direct effect of climate warming

Natural and cultural heritage in mountain landscapes: towards an integrated valuation

Mountain areas of Europe have been managed by humans for a long time, leading to a prevalence of semi-natural habitats in mountain landscapes today. These landscapes contain both natural and cultural heritage; however, natural and cultural heritage are rarely considered together when valuing landscapes and developing management plans in protected areas. Here we present a case study of seven protected areas in the mountains of Great Britain and Norway. We take a long-term perspective on landscape and land-use change and propose an integrated model of landscape valuation on the basis of combined natural and cultural heritage. Our model plots indicators of natural and cultural heritage along a gradient of land-use intensity, allowing simultaneous assessment and highlighting how valuation depends on what type of heritage is considered. We show that while contemporary land-use changes follow similar trajectories in Norway and Britain, different land-use histories mean that the loss of heritage differs between the regions. The model presented here thus allows for the consolidation of valuation based on both cultural and natural heritage in landscapes.publishedVersio

Airborne laser scanning reveals uniform responses of forest structure to moose (Alces alces) across the boreal forest biome

1. The moose Alces alces is the largest herbivore in the boreal forest biome, where it can have dramatic impacts on ecosystem structure and dynamics. Despite the importance of the boreal forest biome in global carbon cycling, the impacts of moose have only been studied in disparate regional exclosure experiments, leading to calls for common analyses across a biome-wide network of moose exclosures. 2. In this study, we use airborne laser scanning (ALS) to analyse forest canopy re-sponses to moose across 100 paired exclosure-control experimental plots dis-tributed across the boreal biome, including sites in the United States (Isle Royale), Canada (Quebec, Newfoundland), Norway, Sweden and Finland. 3. We test the hypotheses that canopy height, vertical complexity and above- ground biomass (AGB) are all reduced by moose and that the impacts vary with moose density, productivity, temperature and pulse disturbances such as logging and insect outbreaks. 4. We find a surprising convergence in forest canopy response to moose. Moose had negative impacts on canopy height, complexity and AGB as expected. The responses of canopy complexity and AGB were consistent across regions and did not vary along environmental gradients. The difference in canopy height be-tween exclosures and open plots was on average 6 cm per year since the start of exclosure treatment (±2.1 SD). This rate increased with temperature, but only when moose density was high. 5. The difference in AGB between moose exclosures and open plots was 0.306 Mg ha−1 year−1 (±0.079). In browsed plots, stand AGB was 32% of that in the exclosures, a difference of 2.09 Mg ha−1. The uniform response allows scaling of the estimate to a biome-wide impact of moose of the loss of 448 (±115) Tg per year, or 224 Tg of carbon. 6. Synthesis: Analysis of ALS data from distributed exclosure experiments identified a largely uniform response of forest canopies to moose across regions, facilitat-ing scaling of moose impacts across the whole biome. This is an important step towards incorporating the effect of the largest boreal herbivore on the carbon cycling of one of the world's largest terrestrial biomes.publishedVersio

A regionally coherent ecological fingerprint of climate change, evidenced from natural history collections

publishedVersio

Developing common protocols to measure tundra herbivory across spatial scales

Understanding and predicting large-scale ecological responses to global environmental change requires comparative studies across geographic scales with coordinated efforts and standardized methodologies. We designed, applied, and assessed standardized protocols to measure tundra herbivory at three spatial scales: plot, site (habitat), and study area (landscape). The plot- and site-level protocols were tested in the field during summers 2014–2015 at 11 sites, nine of them consisting of warming experimental plots included in the International Tundra Experiment (ITEX). The study area protocols were assessed during 2014–2018 at 24 study areas across the Arctic. Our protocols provide comparable and easy to implement methods for assessing the intensity of invertebrate herbivory within ITEX plots and for characterizing vertebrate herbivore communities at larger spatial scales. We discuss methodological constraints and make recommendations for how these protocols can be used and how sampling effort can be optimized to obtain comparable estimates of herbivory, both at ITEX sites and at large landscape scales. The application of these protocols across the tundra biome will allow characterizing and comparing herbivore communities across tundra sites and at ecologically relevant spatial scales, providing an important step towards a better understanding of tundra ecosystem responses to large-scale environmental change

Location of studies and evidence of effects of herbivory on Arctic vegetation: a systematic map

Herbivores modify the structure and function of tundra ecosystems. Understanding their impacts is necessary to assess the responses of these ecosystems to ongoing environmental changes. However, the effects of herbivores on plants and ecosystem structure and function vary across the Arctic. Strong spatial variation in herbivore effects implies that the results of individual studies on herbivory depend on local conditions, i.e., their ecological context. An important first step in assessing whether generalizable conclusions can be produced is to identify the existing studies and assess how well they cover the underlying environmental conditions across the Arctic. This systematic map aims to identify the ecological contexts in which herbivore impacts on vegetation have been studied in the Arctic. Specifically, the primary question of the systematic map was: “What evidence exists on the effects of herbivores on Arctic vegetation?”