Pål Thorvaldsen

Research Scientist

(+47) 406 21 869
pal.thorvaldsen@nibio.no

Place
Trondheim

Visiting address
Klæbuveien 153, bygg C 1.etasje, 7031 Trondheim

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Abstract

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Abstract

Questions During the winter of 2014, an intense drought combined with sub-zero temperatures resulted in a massive Calluna dieback in Norwegian heathlands. We studied the initial vegetation recovery under two management approaches: natural recovery and prescribed burning. We hypothesized that natural recovery will be slower in more drought-affected sites, whereas burning will facilitate post-fire recovery in all sites by effectively removing dead and damaged heath. Both natural recovery and post-fire succession will be slower in the north. Location Calluna heath in seven sites spanning an approx. 600-km latitudinal gradient along the coast of Norway (60.22–65.69° N). Methods After a natural drought, 10 permanent plots per site were either burnt or left for natural recovery. Vegetation data were recorded annually in 2016 (pre-fire) and 2017–2019 (post-fire) reflecting a factorial repeated-measures design (n = 280). The data were analyzed using mixed-effects models. Results Two years after the drought, we observed high but variable Calluna damage and mortality. Over the four years of study, damaged Calluna recovered, whereas dead Calluna showed little recovery. Both the extent of the damage and mortality, as well as the rate of natural recovery, are only weakly related to site climate or environmental factors. Fire efficiently removed dead and damaged Calluna and facilitated post-fire successional dynamics and recovery in a majority of sites. Conclusions Extreme winter drought resulted in substantial and often persistent damage and dieback on Calluna along the latitudinal gradient. In sites with high mortality, prescribed burning removed the dead biomass and, in some cases, facilitated vegetation recovery. Traditional heathland management, which uses burning to facilitate all-year grazing by Old Norse sheep in Atlantic coastal heathlands, can be an efficient tool to mitigate dieback events and more generally to increase resistance to and resilience after extreme drought events in the future.

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Abstract

In the last decade, several major dwarf-shrub dieback events have occurred in northern European coastal heathlands. These dieback events occur after extended periods with sub-zero temperatures under snow-free conditions and clear skies, suggesting that coastal heathlands have low resistance to winter drought. As climate projections forecast increased drought frequency, intensity, and duration, coastal heathlands are likely to experience more such diebacks in the future. There are, however, few empirical studies of drought impacts and responses on plant communities in humid oceanic ecosystems. We established a drought experiment with two distinct levels of intensified drought to identify responses and thresholds of drought resistance in coastal heathland vegetation. We repeated the experiment in two regions, separated by five degrees latitude, to represent different bioclimatic conditions within the coastal heathlands' wide latitudinal range in Europe. As coastal heathlands are semi-natural habitats managed by prescribed fire, and we repeated the experiment across three post-fire successional phases within each region. Plant community structure, annual primary production, and primary and secondary growth of the dominant dwarf-shrub Calluna vulgaris varied between climate regions. To our surprise, these wide-ranging vegetation- and plant-level response variables were largely unaffected by the drought treatments. Consequently, our results suggest that northern, coastal heathland vegetation is relatively resistant to substantial intensification in drought. This experiment represents the world's wettest (2200 mm year−1) and northernmost (65°8'N) drought experiment to date, thus filling important knowledge gaps on ecological drought responses in high-precipitation and high-latitude ecosystems across multiple phases of plant community succession.

Abstract

The combined impact of climate and land-use change poses increasing threats to nature and nature's benefit to people. The LandPress project makes use of the severe Norwegian winter-drought in 2014 as a case study; and combines geographical, ecological and social science approaches to explore the drivers of ecosystem resilience to drought die-back, the ecological processes and implications of drought responses, and management options for mitigating damage and costs. First, by means of remote sensing, we assess the role of climate, environment and land-use in regulating resilience of Calluna heaths to drought die-back locally and along a biogeographic gradient. We find that drought-damage in heather varies across landscapes, and can be quantified by aerial photos, allowing us to establish that both environment (slope) and land-use (prescribed fire) influence ecosystem resistance to drought. Second, we conduct a drought experiment to understand and assess the impacts of severe drought events on coastal heathland ecosystem dynamics and functioning. After the three first years we find only weak effects on plant communities, but distinct responses in plant functional traits suggesting that ecosystem resistance to drought decreases with time since the last prescribed fire. Third, we experimentally assess whether prescribed burning can be used to promote Calluna's resilience after severe drought, and find that prescribed burning efficiently removes damaged heather, stimulating post-fire vegetation development and restore ecosystem functioning after drought. Finally, we conduct a cost-benefit analysis to understand the contribution of land management to the provision of ecosystem services, with focus on securing low fire-risk landscapes. We find that management has more benefits than food production; land-use can reduce the extent of extreme drought, reduce fire risk and help us keep the ecosystem functioning. Our project demonstrates the importance of understanding how interactions between climate-change and land-use and is crucial in developing new management strategies.

Abstract

The open landscapes produced over centuries by small-scale farming in Norwegian coastal and fjord areas are threatened by agricultural abandonment, raising public concern for maintenance of the species-rich and valuable coastal grasslands. Semi-natural grasslands, traditionally grazed in the spring and fall and mown in summer, are most affected. Two linear programming models, one for small-scale sheep and one for small-scale mixed dairy and meat farms, both described in a separate method article, were developed. In the models is studied effects on production, grazing and land utilization, of altering government financial support among leys on arable land, enclosed farm pasture, grazing animals, and altering the (regulated) prices farmers pay for concentrate feed at the farm level. Sheep grazing can be expanded by intensification through increased fertilization and purchase of concentrate feed. Raising steers instead of bulls on dairy and beef farms with a milk quota would result in more mixed grazing by both sheep and steers, which is advantageous for the landscape. Steers are currently quite rare in Norway and their numbers can be increased with more subsidies for grazing, (Grazing Support (GS)) or by increasing the Regional Environmental Support (RES), a policy instrument targeting local projects for more grazing in specific areas. The current Agriculture and Cultural Landscape (ACL) subsidy payment places a higher value on arable land compared to the more biodiverse farm pastures, resulting in weaker incentives for keeping farm pasture in production. Raising the rate for farm pasture relative to that of arable land in the ACL scheme would result in stronger incentives for keeping such farm pasture in production, and likely increase biodiversity and landscape values. Increased GS for sheep might lead to more purchase of concentrate to keep more animals through the winter and eventually needs to be counteracted with higher prices for concentrated feedstuffs.

Abstract

Changes in land-use and climate represent major threats to Atlantic heathlands, and extreme climatic events, such as droughts, are likely to increase in frequency and intensity in the future. This is of particular relevance for nature management, and conservation, as extreme events are expected to have system-wide impacts on species and ecosystems. During the winter of 2014 an intense drought combined with low temperatures resulted in a massive dieback of Calluna vulgaris in the Norwegian heathlands, and two severe heathland wildfires occurred. With this as a background, a new Norwegian research project: Land use management to ensure ecosystem service delivery under new societal and environmental pressures in heathlands (LandPress) were initiated. LandPress combines observational data on ecosystem responses and resilience after the 2014 event with targeted experiments, one of them the International Drought Experiment, integrating our project into an international context. Drought impacts in mature Calluna-stands is investigated along a 650-km latitudinal gradient in Norway. Our first results indicate more drought damage in northern heathlands than in southern. Healthy Calluna was only observed in scattered patches with more suitable micro-climate, and, interestingly, in some areas regenerating after recent prescribed management burning. Moreover, drying experiments to learn how quickly Calluna plants dry up at 20°C and 50% relative humidity from rain-wet conditions showed that old Calluna stands represents a severe fire risk within two days. Young and more vigorous plants in the building phase (6–15 years old), as well as freeze drought damaged (typically some dead small branches), old but still live plants, showed different drying characteristics and dried more slowly. LandPress interlaces five work packages, exploring the impact of land-use change in combination with extreme climatic events in terms of vegetation change, ecosystem resilience, ecosystem services provisioning, sustainability, and evidence-based management and fire risk prevention.

Abstract

We have mapped the quality of pasture resources for sheep grazing outdoor all year on ten localities along the west coast of Norway, using a classification scheme developed for this purpose. The classes reflect fodder value throughout the year. We performed an accuracy assessment, and identified possible sources of error. The accuracy is relatively low, and like others, we found that separating heath classes is a challenge. However, most errors can be explained by special mislocation and temporal change. Our further work with exploring grazing habits and landscape use of Old Norse sheep will include a GPS study of sheep movements overlaid with our pasture maps. We will update the map on that locality through field visits to enhance its accuracy.