Jørn-Frode Nordbakken
Forsker
(+47) 917 25 836
jorn-frode.nordbakken@nibio.no
Sted
Ås - Bygg O43
Besøksadresse
Oluf Thesens vei 43, 1433 Ås (Varelevering: Elizabeth Stephansens vei 23)
Sammendrag
Som del av et feltforsøk opprettet i en semi-naturlig blåbærgranskog i Gaupen (Ringsaker) i SØ-Norge i 2008, for å undersøke effekter av konvensjonell flatehogst og heltrehogst med GROT-uttak, ble det etablert 84 permanent merkete 1 m2 vegetasjonsruter for registrering av bakkevegetasjon. Tidligere er det gjort artsregistreringer én gang i intakt skog før hogst (2008) og tre ganger etter flatehogst (2010, 2012 og 2014). I denne rapporten utvider vi tidsserien med en re-analyse av vegetasjonsrutene i 2023, 15 år etter flatehogst. Flatehogsten førte til store endringer, særlig i artsdekning og artssammensetningen. For ingen av analyseårene var det forskjeller i artssammensetning (målt som posisjon langs ordinasjonsakser) mellom konvensjonell hogst og heltrehogst (med GROT-uttak). Mest i øyenfallende etter hogst var en redusert dekning av moser (alle artsgrupper: bladmoser, levermoser og torvmoser) og økt dekning av gras og halvgras, samt en tilstrømning av nye arter (hovedsakelig urter og moser). 11 arter registrert før hogst ble ikke gjenfunnet femten år etter hogst, mens 47 arter kun ble funnet etter hogst. Det totale artsmangfoldet av karplaner og moser økte over nivået før hogst. De viktigste suksesjonsendringene fra blåbær (Vaccinium myrtillus) og bladmose dominert vegetasjon før hogst var representert ved et stort skifte mot dominans av smyle (Avenella flexuosa) og et mindre skifte mot nitrofil vegetasjon på hogstavfall. Dekningen av graminider, som før hogst var henholdsvis 9 % og 14 % for konvensjonell og heltrehogst, økte til et maksimum på om lag 70 % dekning fire år etter hogst, hvorpå dekningen ble noe redusert, og femten år etter hogst var 50 %.
Forfattere
Sunil Mundra Dinesh Sanka Loganathachetti Håvard Kauserud Anna Maria Fiore-Donno Tonje Økland Jørn-Frode Nordbakken O. Janne KjønaasSammendrag
Large-scale replacements of native birch with spruce have been carried out in Western Norway for economic reasons. This tree species shift potentially affects biotic components such as the eucaryome, consisting of microscopic animals (Metazoa), protists and fungi, which are key players in the functioning of forest ecosystem. The impact on the belowground eukaryome and its interactions with vegetation and soil properties is not well assessed. We examined the impact of replacing native birch with Norway spruce plantations on the eukaryome of the boreal forest floor in Western Norway using 18S rDNA metabarcoding. The tree species shift from birch to spruce had significant impacts on the eukaryome at both taxonomic (Metazoa) and functional categories (phagotrophs, phototrophs, parasites and osmotrophs). The distinct differences in eukaryome communities were related to changes in understorey vegetation biomass and soil chemistry following the tree species shift. This had a negative effect on eukaryome richness, particularly affecting phagotrophs and parasites, while the opposite was observed for osmotroph richness. Our results indicated that the spruce plantations altered the eukaryome communities and their food-web patterns compared to what was found in the native birch forest soil. This information should be taken into consideration in forest management planning.
Sammendrag
Questions Observations in permanent forest vegetation plots in Norway and elsewhere indicate that complex changes have taken place over the period 1988–2020. These observations are summarised in the “climate-induced understorey change (CIUC)” hypothesis, i.e. that the understorey vegetation of old-growth boreal forests in Norway undergoes significant long-term changes and that these changes are consistent with the ongoing climate change as an important driver. Seven testable predictions were derived from the CIUC hypothesis. Location Norway. Methods Vegetation has been monitored in a total of 458 permanently marked plots, each 1 m2, in nine old-growth forest sites dominated by Picea abies at intervals of 5–8 years over the 32-year study period. For each of the 52 combinations of site and year, we obtained response variables for the abundance of single species, abundance and species density of taxonomic–ecological species groups and two size classes of cryptogams, and site species richness. All of these variables were subjected to linear regression modelling with site and year as predictors. Results Mean annual temperature, growing-season length and the number of days with precipitation were higher in the study period than in the preceding ca. 30-year period, resulting in increasingly favourable conditions for bryophyte growth. Site species richness decreased by 13% over the 32-year study period. On average, group abundance of vascular plants decreased by 24% (decrease in forbs: 38%). Patterns of group abundance change differed among cryptogam groups: although peat-moss abundance increased by 39%, the abundance of mosses, hepatics and lichens decreased by 13%, 49% and 67%, respectively. Group abundance of small cryptogams decreased by 61%, whereas a 13% increase was found for large cryptogams. Of 61 single species tested for abundance change, a significant decrease was found for 43 species, whereas a significant increase was found only for 6 species. Conclusions The major patterns of change in species richness, group species density and group abundance observed over the 32-year study period accord with most predictions from the CIUC hypothesis and are interpreted as direct and indirect responses to climate change, partly mediated through changes in the population dynamics of microtine rodents. The more favourable climate for bryophyte growth explains the observed increase for a few large bryophyte species, whereas the decrease observed for small mosses and hepatics is interpreted as an indirect amensalistic effect, brought about by shading and burial in mats of larger species and accelerated by reduced fine-scale disturbance by microtine rodents. Indirect effects of a thicker moss mat most likely drive the vascular plant decline although long-term effects of tree-stand dynamics and former logging cannot be completely ruled out. Our results suggest that the ongoing climate change has extensive, cascading effects on boreal forest ecosystems. The importance of long time-series of permanent vegetation plots for detecting and understanding the effects of climate change on boreal forests is emphasised.