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

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

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?”

Moose browsing effects on boreal production forests – implications for ecosystems and human society

Sammendrag: Den viktige elgen Utmarkbeite er trolig den mest utbredte arealbruken i Norge, som i verden forøvrig. Etter at mengden beitende husdyr begynte å ned på midten av forrige århundre har ville hjortedyr tatt over deres plass i naturen. Disse ville populasjonene reguleres tett og forvaltes faktisk av landbruks- og matdepartementet. Så på mange måter kan man si at elgen er den nye kua. Hva betyr så elgen for oss? For naturen rundt oss? For samfunnet? Vi snakker om verdens største hjortedyr, en spisemaskin som kan omsette så mye som 40 kg plantemateriale om dagen. I Norge er det rekordmange elg om dagen – ofte 2 dyr per kvadratkilometer flere steder. Dette tilsier at elgen kan ha virkelig mye å si for skogen der den bor, og skal vi nå bærekraftsmålene til FN, og skal vi klare å reversere klimaendringene, ja da kan vi faktisk ikke la være å tenke på elgen. Mitt doktorgradsarbeid har bekreftet at dagens beitetrykk fra elgen går hardt utover løvtrærne som den lever av. Men at det i hele studieområdet vårt ikke skulle finnes en eneste rogn som hadde unnsluppet elgens kjever, det var allikevel dystert nytt. I hvert fall for oss som ønsker å se løvtrær og artsmangfold i skogene. Jeg har også studert hvordan endringene forplanter seg i jordsmonnet og i undervegetasjonen. Ja elgen er viktig for hele økosystemet. Men elgen er også en del av mangfoldet. Og den er jakt, den er kultur og den er tradisjon. Så hvordan veier vi opp alle disse positive og negative sidene ved elg? Avhandlingen min rundes av med oppstarten på noe nytt – ett nettbasert samarbeids og -læringsverktøy for å forstå elgens mange roller i naturen og i samfunnet. Gjennom tverrfaglig samarbeid og med tettere kontakt mellom forskere og samfunnet for øvrig, legger vi grunnlaget for å mer bærekraftig fremtid

Soil charcoal addition affected biochemistry but not growth in European beech and Norway spruce seedlings

Climate change is projected to result in European beech (Fagus sylvatica) expanding northwards into Norway spruce (Picea abies) forests where, in addition to climate, numerous local factors will determine the relative success of these two species. Among these are soil related factors, including charcoal from previous forest fires, which is present in soils in considerable amounts and exerts largely unknown and species-specific effects on plant growth and metabolism. Here I show that glasshouse grown beech and spruce seedlings responded differently to laboratory-produced charcoal addition and that the effect was dependent on plant organ, charcoal origin (beech- or spruce wood), and soil type (beech- or spruce forest). Charcoal addition had no effect on plant biomass, but caused several compound specific changes to the concentrations of low molecular weight phenolics assumed important in plant defences. Shoot:root ratios, specific leaf area, condensed tannin concentrations, and C:N ratios were also affected, but in such a way that the overall positive versus negative effect of charcoal addition could not easily be determined. This was largely due to the organ specific responses that complicates interpretations of the whole-plant response. Overall, the effects of charcoal addition fades in comparison to the effect imposed by soil origin. Results further indicate an uncoupling between growth and phenolic synthesis, contrary to predictions from the protein competition model. The common consensus that soil charcoal has unequivocally beneficial effects on plant growth is challenged. Sammendrag Klimaendringene er sagt å føre til at bøk (Fagus sylvatica) sprer seg nordover inn i områder med granskog, hvor i tillegg til klima, flere lokale faktorer vil påvirke dominansforholdet mellom gran (Picea abies) og bøk. Blant disse er flere jord-aspekter, bl.a. effekten av trekull fra tidligere skogbranner. Trekull finnes i jorda, ofte i betydelige mengder, hvor det har en stort sett ukjent og artsspesifikk effekt på plantevekst og -metabolisme. Her viser jeg hvordan drivhusdyrkede småplanter av gran og bøk reagerte ulikt på tilsetning av laboratorieprodusert trekull til vekstjorda og at effekten av kullbehandlingen var avhengig av opphavet til jorda (bøk- eller granskog) og trekullet (bøk- eller granved), i tillegg til at den ofte var ulik for forskjellige plantedeler. Trekull hadde ingen påvirkning på vekst (biomasse), men induserte flere endringer i konsentrasjonene av ulike lav-molekylvekt-fenoler som man antar er viktige i det kjemiske forsvaret hos planter. Tilsetning av trekull påvirket også skudd:rot forholdet, SLA (bladareal/tørrvekt), konsentrasjonen av kondenserte tanniner, samt karbon:nitrogen forholdet, men pga. kontrasterende resultater i de ulike plantedelene er det vanskelig å fastslå om den totale effekten var overveiende positiv eller negativ. Effekten av trekulltilsetning var veldig liten sammenlignet med påvirkningen av jordtype. Resultatene indikerer videre at det ikke eksisterer en enten-eller dynamikk mellom vekst og fenolsyntese, i strid med prediksjonene fra proteinkonkurransemodellen (en: protein competition model). Den rådende tanken om at trekull har en utelukkende positiv effekt på planter blir herved utfordret

Uttak av fremmede treslag i verneområder. Etablering av overvåking

Det er et uttalt mål i Norge å hindre spredning og etablering av fremmede arter siden dette blir sett på som en av de største truslene mot det biologiske mangfoldet. Spesielt gjelder dette for verneområder hvor viktige naturverdier står i fare for å bli erstattet av ikke-hjemlig vegetasjon. Derfor brukes det i dag betydelige ressurser, ikke bare på å hindre spredning og etablering, men også på å fjerne allerede etablerte bestand av fremmede arter innenfor verneområder i Norge. Dette gjøres selv om det er manglende kunnskap om effekten av ulike tiltak, og i hvor stor grad man lykkes med restaureringsarbeidet. Målet med dette prosjektet er å utvikle et opplegg for å overvåke effekten av å fjerne fremmede bartrær fra verneområder, og å gjennomføre innsamling av basisdata fra tre ulike lokaliteter. Disse lokalitetene er: Brenslefjellet naturreservat, et variert edelløvskogområde i Molde kommune, Møre og Romsdal; øya Borgan (dyrelivsfredning) med mye kystlynghei i Nærøysund kommune, Trøndelag; og øya Seløya (naturreservat) i Hadsel kommune, Nordland, som er vernet hovedsakelig for å beskytte hekkende sjøfugl. Vi valgte hierarkisk arrangering av permanente overvåkningsarealer med flere blokker som metode, der hver blokk består av fem 1 m² ruter inne i en 250 m² sirkel. I de tre lokalitetene ble det etablert opp til fem blokker i plantasjene, og fem blokker i omkringliggende referanseområder. Analyser av effekten av innsamlingsinnsatsen viser at metodikken fanger opp en stor del av naturvariasjonen. Feltprotokollen er lagt nær opptil metodikken i det nasjonale overvåkningsprogrammet «Arealrepresentativ naturovervåking» (ANO). Dette vil gjøre dataene i dette prosjektet sammenlignbare med dette mye større, landsdekkende datasettet, og det øker mulighetene for å få vitenskapelig utbytte av prosjektet. Innsamlet data inkluderer prosent dekning av karplanter og moser, kronedekke i ulike sjikt, en rekke jordparametere, samt utvalgte ANO-variabler for å beskrive økologisk tilstand. Tidsbruken i felt var tre til fire dager per lokalitet, og det er om lag slik vi hadde anslått på forhånd. Dette anser vi som gjennomførbart, også med tanke på oppfølging framover. De innsamlede dataene er anvendelige i statistiske analyser, slik som ordinasjonsanalyser, som vi også viser i denne rapporten. Til slutt gir vi råd om oppfølging, og diskuterer hva de innsamlede dataene kan brukes til

Long-term changes in northern large-herbivore communities reveal differential rewilding rates in space and time.

Herbivores have important impacts on ecological and ecosystem dynamics. Population density and species composition are both important determinants of these impacts. Large herbivore communities are shifting in many parts of the world driven by changes in livestock management and exploitation of wild populations. In this study, we analyse changes in large herbivore community structure over 66 years in Norway, with a focus on the contribution of wildlife and livestock. We calculate metabolic biomass of all large-herbivore species across the whole region between 1949 and 2015. Temporal and spatial patterns in herbivore community change are investigated and we test hypotheses that changes in wildlife biomass are driven by competition with livestock. We find that total herbivore biomass decreased from 1949 to a minimum in 1969 due to decreases in livestock biomass. Increasing wild herbivore populations lead to an increase in total herbivore biomass by 2009. Herbivore communities have thus reverted from a livestock dominated state in 1949 (2% of large herbivore metabolic biomass comprised of wildlife species) to a state with roughly equal wildlife and livestock (48% of metabolic biomass comprised of wildlife species). Declines in livestock biomass were a modest predictor of wildlife increases, suggesting that competition with livestock has not been a major limiting factor of wild herbivore populations over the past decades. Instead there was strong geographic variation in herbivore community change, with milder lowland regions becoming more dominated by wild species, but colder mountain and northern regions remaining dominated by livestock. Our findings indicate that there has been notable rewilding of herbivore communities and herbivore-ecosystem interactions in Norway, particularly in milder lowland regions. However, Norwegian herbivores remain mostly regulated by management, and our findings call for integrated management of wild and domestic herbivores

Long-term changes in northern large-herbivore communities reveal differential rewilding rates in space and time

Herbivores have important impacts on ecological and ecosystem dynamics. Population density and species composition are both important determinants of these impacts. Large herbivore communities are shifting in many parts of the world driven by changes in livestock management and exploitation of wild populations. In this study, we analyse changes in large herbivore community structure over 66 years in Norway, with a focus on the contribution of wildlife and livestock. We calculate metabolic biomass of all large-herbivore species across the whole region between 1949 and 2015. Temporal and spatial patterns in herbivore community change are investigated and we test hypotheses that changes in wildlife biomass are driven by competition with livestock. We find that total herbivore biomass decreased from 1949 to a minimum in 1969 due to decreases in livestock biomass. Increasing wild herbivore populations lead to an increase in total herbivore biomass by 2009. Herbivore communities have thus reverted from a livestock dominated state in 1949 (2% of large herbivore metabolic biomass comprised of wildlife species) to a state with roughly equal wildlife and livestock (48% of metabolic biomass comprised of wildlife species). Declines in livestock biomass were a modest predictor of wildlife increases, suggesting that competition with livestock has not been a major limiting factor of wild herbivore populations over the past decades. Instead there was strong geographic variation in herbivore community change, with milder lowland regions becoming more dominated by wild species, but colder mountain and northern regions remaining dominated by livestock. Our findings indicate that there has been notable rewilding of herbivore communities and herbivore-ecosystem interactions in Norway, particularly in milder lowland regions. However, Norwegian herbivores remain mostly regulated by management, and our findings call for integrated management of wild and domestic herbivores

Increasing Cervidae populations have variable impacts on habitat suitability for threatened forest plant and lichen species

Large herbivores play a key role in temperate and boreal forest ecosystems. Cervidae (deer) population densities and community structure have undergone drastic changes in many parts of the world over the past decades, often with deer populations increasing. Many studies show impacts of Cervidae on multiple ecosystem properties, including vegetation and biodiversity, at local spatial scales. At larger spatial scales, however, impacts of changing Cervidae populations on forest ecosystems are less known. Although both abiotic and biotic dimensions contribute to shaping species’ niches, abiotic variables are generally given prominence when modelling species habitats and ranges. This is despite biotic changes, including changes in trophic structure, being an important component of global environmental change. In this study, we examined the potential contribution of Cervidae densities to the habitat suitability for rare plant and lichen species across the temperate and boreal forests of Norway, where cervid densities have increased over the past 60 years. We also examined how these changes in herbivore communities may have shaped habitat suitability for rare lichens and plants and discuss the results in light of continuing shifts in herbivore assemblages. We ran habitat suitability models for 47 species of rare plants and lichens, which were selected based on herbivory reported as a criterion for placement on the national red list for species. Climate (temperature and precipitation), forest (forest type and productivity), soil pH and Cervidae densities (moose Alces alces, red deer Cervus elaphus and roe deer Capreolus capreolus) were used as independent variables. Densities of one or more of the three Cervidae species were inferred to be associated with the distribution of 14 (ten lichen, one bryophyte and three vascular plant species) of these 47 species. We found a range of habitat suitability associations with Cervidae densities, including positive, negative and hump-backed responses. Increases in Cervidae densities over the past 60 years may have led to different spatial trends in habitat suitability across the 14 species. Our results suggest that Cervidae densities are associated with the distribution of rare forest plant and lichen species differently at large spatial scales; experimental studies should test the causality of these associations. If causal, this implies that Cervidae management should find a balance between high and low densities to conserve several plant and lichen species. The preponderance of epiphytic lichens species, for which habitat suitability was associated with Cervidae densities, calls for field studies to focus on Cervidae impacts on forest lichens