Utskrift
Forskningsdelen av Miljøregistrering i skog (MiS) har som mål å bedre kunnskapen om biologisk mangfold i skog, og dermed bidra til en bedre registrering, overvåking og forvaltning av miljøverdiene i skog.
Ivar Gjerde
Seniorforsker
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Divisjon for skog og utmark
(+47) 915 15 139 ivar.gjerde@nibio.no Kontorsted: Bergen
NIBIO har ansvar for forskning og utvikling, formidling og rådgiving knyttet til skogbrukets sektoransvar for bevaring av miljøverdier i skog. Dette arbeidet er finansiert av Landbruks- og matdepartementet.
Landbruksdirektoratet er fagmyndighet for bruken av MiS-metoden for praktiske registreringer, les mer på direktoratets sider. Statsforvalter har ansvar for planlegging og koordinering av registreringene.
Skogbrukets andelslag (skogeierforeninger) gjennomfører MiS-registreringer som en del av miljøsertifiseringen. Registreringene gjennomføres vanligvis i forbindelse med skogbruksplanlegging, og utføres etter en detaljert instruks av personell som har opplæring i metoden. For spørsmål om konkrete arealer i forbindelse med MiS-registreringer, ta kontakt med de som har gjennomført registreringene.
Accurately determining the age of individual trees is important for understanding forest dynamics, tree growth, site productivity and describing ecological processes. Traditional methods, such as dendrochronological coring, are invasive, labor-intensive, and costly. This study investigates the use of deep learning (DL) to predict tree age from high-density laser scanning data as a scalable, non-invasive alternative. The dataset includes approximately 1700 tree point clouds from approx. 1 K trees across Norway, Sweden, and Finland, encompassing Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) and a broad range of tree age and developmental stages, from young seedlings (1 year) to old trees (∼350 years). Data were collected using terrestrial, mobile, and high-density airborne laser scanning platforms, enabling the development of sensor-agnostic models. We evaluated multiple modelling approaches, from linear regression to transformer architectures, using both training-from-scratch and fine-tuning strategies. Models fine-tuned starting from pre-trained weights from ForestFormer3D's U-Net as well as the transformer architecture (PointTransformerV3) trained from scratch, proved effective for age regression (RMSE ≤23 years). Although our analysis was limited to two tree species, we demonstrated that a single joint age-estimation model can be successfully trained for both species. We demonstrate that models trained on high-resolution data can generalize to lower-resolution, less costly inputs, provided that data augmentations that mimic reduced resolutions are included during training. This study presents a data-driven framework for estimating tree age without destructive sampling. The findings support the potential for AI-based methods to complement or replace traditional age estimation techniques in forest inventory and monitoring.
Guiden viser et utvalg av visuelle kjennetegn som kan brukes i felt når gamle bartrær skal vurderes.
1. The results of nature restoration efforts have been characterized as notoriously unpredictable. Many variables impact the trajectory of species communities towards recovery, and ecological theory that takes traits, habitat configuration and scale into account, can improve models. However, the most important questions regarding the predictability of species community restoration may be related to stochasticity. 2. We investigated the assembly of a cyanolichen community in a chronosequence consisting of 88 new forest patches (30–140+ years old) comprising today 0.4% of a 170 km2 former treeless heathland area in south-western Norway. Two complete inventories were carried out 12 years apart, and we (1) tested inferences on colonization status and recovery time based on the first inventory only; (2) investigated the recovery of the lichen community by changes in species richness, species density and composition at three different spatial scales; and (3) discussed how dispersal capacity and stochasticity affect community recovery in general. 3. Colonization of sites by lichen species exceeded extinctions in young sites but not in old sites, and in the second inventory, the richness of species weighed by occurrences no longer differed significantly between young and old sites at landscape scale. However, the differences between old and young sites depended on the spatial scale and method of measurement. 4. In accordance with inferences based only on the first inventory, colonization and extinction dynamics indicated that recovery of species richness in our study system will take 90–120 years at the landscape scale, whereas recovery of species composition was difficult to determine due to idiosyncratic development among sites. 5. Synthesis and applications. Using species composition as a template for the evaluation of restoration recovery in systems with a high degree of stochastic colonization and extinction is problematic, particularly at finer scales. Ideally, comparisons of restoration and reference communities should therefore be at large enough spatial scale to cancel out the major effects of stochasticity at finer scales. Furthermore, we suggest that a complete recovery of species numbers may not be needed as an indicator of restoration success if species richness measurements indicate that communities are en route to recovery.
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Multiple ecological drivers, along with forest age, determine the species composition of boreal forest ecosystems. However, the role of age in successional changes in forests cannot be understood without taking site conditions, the disturbance regime and forest structure into account. In this study, we ask two research questions: 1. What is the relationship between forest age and overall species composition in older near-natural spruce forests, i.e. forests of age beyond harvest maturity? 2. Do species associated with different forest habitats respond similarly to variation in forest age? Data were collected in 257 Norway spruce dominated 0.25 ha plots from three study areas in Southeastern and Central Norway. Species inventories were conducted for lichens and bryophytes on trees and rocks, vascular plants on the forest floor, and for deadwood-associated bryophytes and polypore fungi. Although NMDS ordination analyses of the total species composition identified a main axis related to the age of the oldest trees in two of the study areas, variation partitioning analyses showed that age explained a small fraction of variation of the species composition compared to site conditions, logging history, forest structure, and differences between the sites in all habitats. The unique variation explained by forest age species was, however, significant for all habitats. The fraction of variation in species composition explained by forest age was the largest for lichens and bryophytes on trees, and for deadwood-associated bryophytes and polypore fungi. Our results suggest that practical mapping of near-natural forests for management purposes inventories should include site conditions, forest structure and between site differences in addition to forest age.
1. Persistence of standing dead trees (snags) is an important determinant for their role for biodiversity and dead wood associated carbon fluxes. How fast snags fall varies widely among species and regions and is further influenced by a variety of stand- and tree-level factors. However, our understanding of this variation is fragmentary at best, partly due to lack of empirical data. 2. Here, we took advantage of the accruing time series of snag observations in the Finnish, Norwegian and Swedish National Forest Inventories that have been followed in these programs since the mid-1990s. We first harmonized observations from slightly different inventory protocols and then, using this harmonized dataset of ca. 43,000 observations that had a consistent 5-year census interval, we modelled the probability of snags of the main boreal tree species Pinus sylvestris, Picea abies and Betula spp. falling, as a function of tree- and stand-level variables, using Bayesian logistic regression modelling. 3. The models were moderately good at predicting snags remaining standing or falling, with a correct classification rate ranging from 68% to 75% among species. 4. In general, snag persistence increased with tree size and climatic wetness, and decreased with temperature sum, advancing stage of decay, site productivity and disturbance intensity (mainly harvesting). 5. Synthesis and applications: The effect of harvesting demonstrates that an efficient avenue to increase the amount of snags in managed forests is protecting them during silvicultural operations. In the warmer future, negative relationship between snag persistence and temperature suggests decreasing the time snags remain standing and hence decreasing habitat availability for associated species. As decomposition rates generally increase after fall, decreasing snag persistence also implies substantially faster release of carbon from dead wood.
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The pine-dominated forests of Western Norway have been found to harbour viable populations of woodpeckers, including the highly specialized White-backed Woodpecker Dendrocopos leucotos. The aim of this study was to investigate to what extent there were any changes in frequencies of woodpeckers, in particular the White-backed Woodpecker and the Grey-headed Woodpecker Picus canus, by resurveying 60 plots (each 1 km2 ) originally surveyed during 1994/1995. The resurvey was performed in 2013/2014. The White-backed Woodpecker was found to be the most common woodpecker species in both time periods. The Grey-headed Woodpecker was found to have a statistically significant decline from 27% of the 60 plots in 1994/95 to only 12% in 2013/14. The other four species all increased in frequency; although none of those increased frequencies were found to be statistically significant. We discuss possible explanations to why pine forests in Western Norway constitute a valuable habitat for the White-backed Woodpecker at the same time as it has drastically declined in other parts of Norway and Western Europe. In general, the reduced frequency of Grey-headed Woodpecker is not fully understood, although we suggest that cold winters during the years prior to the surveys in 2013/14 may be an important factor.
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Knowing the historical variation in fire regimes is instrumental in managing forests today and in predicting what may happen in the future. By cross-dating 745 fire scars in 378 samples of remnant Scots pines, we delineated 254 individual forest fires during the past 700 years in a 74-km2 section of Trillemarka-Rollagsfjell Nature Reserve in south-central Norway. Fire sizes, numbers, burn rates, and frequencies were compared with historical climate proxies, vegetation maps, and written sources. The results revealed patterns consistent with a predominantly climate-driven fire regime up to 1625, followed by periods of strong anthropogenic influence that increased fire frequency during 1600–1700s and diminished fires during 1800–1900s. This was documented by an abrupt increase in number of small fires from the early 1600s that markedly shortened fire intervals from a median of 73 to 37 yr. This shift in fire frequency coincided with a sudden appearance of early-season fires from 1625 and onward. Whereas late-season burn rate increased with summer temperature, no such relationship was found for early-season fires. These results were corroborated by written sources that describe anthropogenic forest fires and slash-and-burn cultivation expanding with the increasing population from the late 1500s and subsequently diminishing due to increasing timber values during 1700–1800s. Whereas human activity strongly influenced the fire regime at multidecadal to centennial scales, it was the interannual variability in climate that triggered large fire events, especially during the pre-1625 period. Prior to 1625, the percentage of years with fire tripled from 7% during cold summers (10–12°C) to 21% during warm summers (14–16°C). Burn rate increased even more, from 0.01% to 1.3% for the same temperature intervals. Ecologically, the post-1625 period is remarkable in such a way that human activity, first by greatly increasing fire frequency and subsequently almost eradicating fires, possibly influenced the fire regime to such an extent that it may be unprecedented for millennia.
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Skogen har vært, er og vil være en viktig ressurs i Norge. Skogen leverer biomasse til produksjon av en mengde forskjellige varer: bioenergi i mange former, treprodukter til bygningsindustri, papir og papp, og avanserte produkter fra bioraffineringsprosesser. I fremtiden vil trolig trebaserte produkter dekke et enda bredere produktspekter. Tilgangen på biomasse er imidlertid begrenset, selv om bevisst forvaltning kan øke tilgangen utover dagens nivå. Skogen leverer også andre økosystemtjenester, som biodiversitet og friluftsliv, og kan ikke minst spille en rolle i det grønne skiftet. Men optimal forvaltning for klima og næring kan stå i motsetning til optimal forvaltning for andre økosystemtjenester.
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Usnea longissima Ach. is a circumboreal epiphytic lichen draping tree canopies in moist coastal and mountainous forests. It is extinct from many European and North-American localities, presumably due to industrial forestry and air pollution, but still has a stronghold in parts of Scandinavia and U.S. and Canadian Pacific Northwest. In 2005/06 we used a comparative and retrospective approach to evaluate how present and historic tree and stand characteristics influenced the occurrence and abundance of the lichen (Storaunet et al. 2008). In 2012, we re-inventoried ten Norway spruce forest stands with 401 U. longissima-bearing trees and recorded changes in the number of U. longissima thalli. Seven of the stands had been experimentally, selectively logged 5–8 years before, where the lichen-bearing trees had been marked in the field and were avoided during the logging operation. Total number of lichen-bearing trees decreased slightly (2.9%), whereas the number of thalli had increased with 34%. Number of thalli increased more where the forest was open (low basal area, m2ha-1) whether or not the low tree density was caused by the logging events. At high tree densities the change in number of thalli was negligible. We suggest that selective logging, securing lichen-bearing trees, may be a viable management option to keep tree density from becoming too dense, thereby enhancing growth and establishment of U. longissima.
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This study combines tree-ring and charcoal data to explore possible drivers of the charcoal record and its spatial variation in a boreal Norwegian forest landscape. Peat and mineral soil samples were collected in a multiple site sampling approach and the amount of charcoal in the peat is related to fire history, Holocene climate variation, major shifts in the vegetation composition, and fuel availability. Dendrochronologic dating was used to reveal the fire history over the last 600 years with spatial and temporal accuracy, and AMS radiocarbon dating of 20 peat columns and their charcoal records from four peatlands was used to elucidate the fire history over the Holocene. The average amount of charcoal was about 2.5 times higher in the mineral soil than in the peat (270 versus 100 g/m², respectively), and there were considerable between- and within-site variations. There was no relationship between the age of a given peatland and its content of charcoal, nor between the amount of charcoal in a given peatland and in the neighboring mineral soil. Although most of the charcoal mass in the peatlands was found in parts of the peat columns originating from relatively warm climatic periods and from the period before the local establishment of Norway spruce (Picea abies), charcoal accumulation rates (per 1000 yr) were higher during cold climatic periods and similar before and after spruce establishment. Recent fires showed up to a low degree in the peat columns. On fine spatial scales (1–10 m), fuel quality and distribution together with fire behaviour throughout millennia are likely to be responsible for variations in the charcoal record. On the landscape scale (100–1000 m), the charcoal records were site-specifically idiosyncratic, presumably due to topography, distribution of fire breaks and fuel types, and human land use, coupled with long-term variations inherent in these factors.
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To better understand the historic range of variability in the fire regime of Fennoscandian boreal forests we cross-dated 736 fire scars of remnant Scots pine (Pinus sylvestris L.) wood samples in a 3.6 km2 section of the Trillemarka-Rollagsfjell Reserve of south-central Norway. Using a kernel range application in GIS we spatially delineated 57 individual forest fires between 1350 and the present. We found a strong anthropogenic signal in the fire regime from 1600 and onwards: (i) infrequent variably sized fires prior to 1600 shifted to frequent fires gradually decreasing in size during the 1600s and 1700s, with only a few small fires after 1800; (ii) time intervals between fires and the hazard of burning showed substantial differences pre- and post-1600; (iii) fire seasonality changed from late- to early-season fires from the 1626 fire and onwards; and (iv) fire severity decreased gradually over time. Written sources corroborated our results, narrating a history where anthropogenic forest fires and slash-and-burn cultivation expanded with the increasing population from the late 1500s. Concurrently, timber resources increased in value, gradually forcing slash-and-burn cultivators to abandon fires on forest land. Our results strengthen and expand previous Fennoscandian findings on the anthropogenic influence of historic fire regimes.
North European epiphytic lichens are often genetically impoverished compared with their North American counterparts. This has been hypothesized to impede sexual reproduction due to reduced chances of finding compatible mating type partners. We compared genetic variation and reproductive mode in two threatened Scandinavian lichens, Evernia divaricata and Usnea longissima, with more viable populations in North America to see (i) if these species also show genetical depletion in northern Europe and (ii) if the occurrence of sexual propagules (ascospores in apothecia) is more prevalent in genetically diverse populations. Genetic variation of the fungal component was assessed by sequencing two nuclear rDNA gene regions (ITS and IGS) in 1005 and 1477 thalli, collected from 92 and 160 localities of E. divaricata and U. longissima, respectively. Scandinavian populations of both species were almost devoid of genetic variation compared with much higher genetic diversity in North America.We found no support for the proposed relationship between genetic diversity and fertility. Fertile thalli were found in several genetically invariable populations. Fertility increased with population size and regional abundance in E. divaricata, but not in U. longissima. In Scandinavia, E. divaricata was more fertile than previously recorded, whereas all sampled populations of U. longissima were sterile and possibly clonal.
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Det internasjonale biomangfoldåret er på hell. Norge har, i likhet med flere andre land, satt 2010 som frist for å ”stoppe tapet av det biologiske mangfoldet”. Som en del av dette arbeidet fikk Norge i 2009 ny Naturmangfoldlov (Lov om forvaltning av naturens mangfold). I §23 i loven heter det at ”Kongen i statsråd kan ved forskrift utpeke nærmere angitte arter som prioritert.” Dette åpner for særskilte tiltak, og skal være et virkemiddel for å ta vare på arter som har problemer med å overleve. Men hvilke av de rundt 40.000 naturlig forekommende arter av dyr, planter og sopp i Norge skal prioriteres, og hvilke kriterier skal legges til grunn for utvelgelsen av disse artene?
Rasmarker, berg og bekkekløfter utgjør særegne levesteder med et stort biologisk mangfold, på grunn av variasjon i miljøforhold og gunstige kombinasjoner av miljøfaktorer. Både blant moser, lav, sopp og karplanter finnes mange rødlistearter i disse naturtypene, og rasmarkene er særlig viktige for insektene. Ustabile naturforhold og vanskelig tilgjengelig terreng gjør disse områdene lite tilgjengelige for inngrep. Likevel påvirkes artssamfunnene negativt av vassdragsregulering, skogbruk og gjengroing.
Effekter av skogbruk på biologisk mangfold er i dag et viktig tema innen skogforskningen. Vi vet en hel del om artenes biologi, og hvilken type skog og habitater de finnes i. Dette har blant annet gitt mulighet for å registrere og ta vare på arealtyper som er spesielt viktige for biologisk mangfold. Det vi vet mindre om er hvordan bestandsskogbruket påvirker artenes populasjoner over tid.
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Arthropods were collected by fogging the canopy of Scots pine Pinus sylvestris selected from a 2 km2 boreal forest area in Sigdal, Norway with the overall purpose to examine whether there were faunal differences in the representation of arthropods among mature and old trees, and specifically for this paper, the biting midges (Ceratopogonidae). Target trees were chosen as pairs, one mature (70-110 years) and one old (250 years or older) tree from six different stands. All knock-down treatments were performed in June and July 1999, before dawn and after a dry and windless night. Knocked-down arthropods were collected in plastic funnels placed systematically on the ground. Funnels remained in place for circa one hour after treatment. Among the 61 species records new to Norway, the most frequently encountered taxon of invertebrates was Diptera, and the family of biting midges, Ceratopogonidae, comprised 30 of 61 (49%) of all new records, compared with the overall species numbers showing 40 biting midges of 193 recorded species (21%). Among the Ceratopogonidae new to Norway, two species new to science and two first records from Europe were found. Coleman rarefaction curves were constructed by running 500 iterations without replacements using EstimateS and showed that there were significantly more new records of Diptera in old trees in comparison with mature trees. A similar pattern of significance (by comparing standard deviations estimated by EstimateS) was found for Diptera when Ceratopogonidae was excluded. New species records of Ceratopogonidae were more common in old trees than in mature trees, although not significantly so. No predominance of new records in old trees was found for arthropods other than Diptera. Old trees are rare and may provide a variety of resources (e.g. resting sites, places to over-winter, hiding places, sites for oviposition, larval habitat, etc.) that are rarely found in younger trees. Thus, the high number of new species records probably result from studying a whole arthropod taxon (Diptera) in a part of a forest ecosystem (canopies) with a suite of microhabitats (old pine trees) that in combination has been poorly investigated earlier.
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Huldrestry er en epifyttisk lavart som står på den norske rødlista som sterkt truet (EN). Arten synes å være i sterk tilbakegang i mange av de kjente lokalitetene i hele Norge. Det er mangelfull kunnskap om artens økologiske krav og toleranse for hogst. En av flere grunner til tilbakegangen antas å være at skogen i noen lokaliteter er blitt for tett. Mjøsen Skog har en betydelig andel av huldrestryforekomstene i landet i sitt område og har dermed et ansvar for å bidra til å ivareta lavarten. Mjøsen har derfor gjennom prosjektet tatt initiativ til å skaffe fram et bedre grunnlag for å forvalte arten. Prosjektet har gått over 3 år, 2005 – 2007. Huldrestryforekomstene i Lillehammer ble registrert under kartlegging av biologisk viktige områder (MiSregistreringer) i 2003. Huldrestry er her mest tallrik i hogstmoden granskog i produktive skoglier. Historisk utvikling Forskere ved Norsk institutt for skog og landskap har gjennomført undersøkelser av huldrestry og skoghistorie. I forsøksområdet, Saksumdalen og Korsåsen i Lillehammer, ble tidligere tiders plukkhogst erstattet av flatehogst og kulturskogbruk fra 1950tallet. Den eldre skogen i dag framstår som rester etter de gamle hogstene...
Whereas lichen growth rates have received considerable attention, comparatively few detailed studies of growth patterns have been carried out. Generally, most lichens seem to grow apically, with pseudomeristomatic tissue confined to lobe margins and branch tips. However, some species appear to retain the capacity to expand throughout the thallus. Such intercalary growth processes have proved difficult to confirm in the field for two- and three-dimensionally growing folious and fruticose forms. Using transplants of the conspicuous, one-dimensionally growing Usnea longissima Ach., we document that intercalary growth actually does occur, with thalli expanding geometrically in length with a doubling time of less than a year under favorable conditions.
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In recent years attention has focused on the consequences of modern forestry on biological diversity. Additionally, past forest management has reduced the structural heterogeneity of forest landscapes, increasing the interest in assessing forest naturalness. General forest history of Norway shows that single-tree and selective logging was the main silvicultural method up to the mid-twentieth century when clearcutting practice took over as the dominating logging regime. Thus, regenerating forests on former clearcut areas have barely reached the stages of maturity, implying that mature forests of today for the most part are remnants from the period of selective logging. This thesis has been part of a comprehensive research project where one of the general objectives was to gain knowledge on the distribution and abundance of rare and threatened species in Norwegian forests....
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We investigated the relationship between site productivity and diversity of vascular plants, bryophytes, lichens, and polypore fungi in forests based on species richness data in 0.25 ha forest plots (grain size), selected from six 150-200 ha study areas (focus), and spanning over a latitudinal distance of 1350 km (extent) in Norway. We (1) searched for prevailing productivity-diversity relationships (PDRs), (2) compared PDRs among taxonomic groups and species found in different micro-habitats, and (3) investigated the effect of increasing plot (grain) size on PDRs. Using vegetation types as a surrogate for site productivity, we found a general pattern of increasing species richness with site productivity. On average total species richness doubled with a ten-fold increase in productivity. Lichens PDRs stood out as less pronounced and more variable than for other species groups investigated. PDRs of species associated with downed logs tended to level off at high-productive sites, a pattern interpreted as an effect of disturbance. Increasing the grain size >10-fold did not change the proportional difference in species richness between sites with high and low productivity.
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The potential as indicators of species richness were investigated for 178 species belonging to six ecologically defined species groups (epiphytic bryophytes on nutrient-rich bark, epiphytic macrolichens on nutrient rich bark, pendant lichens on conifer trees, bryophytes on siliceous rocks, bryophytes on dead conifer wood, and polypore fungi on dead conifer wood), using species data from 0.25 ha plots from three different coniferous forest areas (ca. 200 ha each). A species was defined as a potential indicator species for a species group within a study area if its distribution was statistically significantly nested within the species-plot matrix ranked according to species richness, and if the plot frequency of the species was less than 25%. Only two species were identified as potential indicators within all three areas and on average ≈80% of the potential indicator species were lost from one area to another. The results indicate that inconsistency between areas in the species’ frequency distributions and their position in nested hierarchies may strongly reduce the general predictive power of indicator species of species richness, even if significantly nested patterns are found at the community level. We suggest that indicators related to amount and quality of habitats may be an alternative to lists of indicator species of species richness.
Vascular plants were investigated as a potential surrogate group in complementary small scale site selection, such as woodland key habitats in Scandinavia. We compared the response of vascular plants to environmental gradients to that of seven other plant, fungal and animal groups within a forest reserve in western Norway using data from 59 plots of 0.25 ha. We also examined whether the spatial changes in species (beta-2 index) of vascular plants matched that of the other groups. All seven groups responded to the same gradients in nutrient richness and humidity as the vascular plants. Furthermore, changes in species composition of vascular plants were reflected in comparable degrees of change among the “target“ groups. The lower the degree of change in species composition between plots in the “target“ groups relative to that of vascular plants, the higher the percentage “target“ species encompassed in a complementary selection of sites based on vascular plants. We conclude that in practical site selection of small scale sites of conservation value, such as woodland key habitats, vascular plants may be used in combination with an inventory of important habitats for rare and/or redlisted forest species, such as dead wood, old trees, deciduous trees, and cliffs.
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Number of years since death was estimated by dendrochronological cross-dating of 107 standing dead trees (snags) of Norway spruce [Picea abies (L.) Karst.] in a submountainous old-growth forest in south-central Norway. Snag characteristics (size, bark cover, branch order present and variables derived from tree-ring analyses) were used in stepwise linear regression procedures to identify variables that explained time since death.Number of branch orders present (where branches growing directly on the stem were branch order 1, branches growing on order 1 branches were order 2, and so on) explained two-thirds of the variation in time since death. Adding other significant variables, such as diameter, relative height of snags, percentage bark cover and average tree-ring width in the final years before death, increased model precision only moderately.The models were validated by the PRESS statistic, which showed that new observations were predicted fairly well with 65-69% of the variation explained.
We estimated time from death to fall (standing time) of Norway spruce (Picea abies (L.) Karst.) snags in a submountainous old-growth forest in south-central Norway, applying four calculation methods to 124 dendrochronologically cross-dated still-standing snags and 64 fallen logs. The calculation methods consistently estimated expected standing time of snags at 26–34 years, with a median of 16–21 years and 20% of snags standing for >48–58 years. The survival function from all methods took the approximate form of a negative exponential, with a 3%–4% annual fall rate for snags. In the distribution of time since death, a small peak in dead trees 20–30 years ago (late 1970s) coincides with a historic epidemic of bark beetles. The method using only time since death of still-standing snags appears to be the most feasible for estimating total standing time of snags in old-growth forests with constant tree mortality.
We fogged trees in two pine dominated forests in Norway with a synthetic pyrethroid in order to compare the canopy-dwelling fauna of arthropods between costal (Kvam) and boreal (Sigdal) sites and between old (250-330 years) and mature (60-120 years) trees at Sigdal. Almost 30,000 specimens were assigned to 510 species; only 93 species were present at both sites. Species diversity, as established by rarefaction, was similar in old and mature trees. However, the number of species new to Norway (including nine species new to science) was significantly higher in the old trees. We suggest that the scarcity of old trees, habitat heterogeneity and structural differences between old and mature trees may explain these patterns. Productivity and topographic position at the site of growth explained the between-tree variation in species occurrence for the more abundant species, which were mainly Collembola and Oribatida. Species diversity was similar at the boreal and coastal sites, but there were clear differences in species composition
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We studied four south-facing and three north-facing boreal spruce forest stands (ca. 0.1ha each) in SE Norway with the aim of testing the hypothesis that former logging has long-term effects on boreal forest-floor vegetation. The stand series comprised unlogged natural forests and forests that were selectively or clear cut 6070 years prior to our study. Each stand was described with respect to history of forestry impact and tree-stand structure.Environmental, species number, species abundance and species composition (vegetation gradients obtained as ordination axes) variables obtained for 25 m1m plots in each stand were tested for among-stand differences. Significant among-stand differences were found, partly related to former forest management and partly due to among-stand differences in topography.Differences among stands related to management were found for tree stand density, highest in managed stands, and for Dryopteris expansa agg. and Luzula pilosa abundances, peaking in formerly clear-cut stands. Species number (at plot or stand scales) was weakly related to former management.On southerly as well as northerly aspects, gradients in species composition were found that separated plots according to former management. Differences among stand conditioned on topography resulted in opposite patterns in the two series of stands because among southerly stands the clear cut was the least while among northerly the clear cut was the most strongly sloping. Low-inclination sites tended more strongly to be paludified and to have high Sphagnum cover, and to have low abundance of specific microsites with small mosses and hepatics. Vegetation gradients related to soil moisture and microtopography were found for both aspects.A strong gradient in species composition related to tree influence at within-stand scales was found, with variation in species number. Existence of such a gradient should provide for significant biotic effects (of short or long duration) of the environmental changes that take place during forest re-growth: (1) the immediate creation of small or large tree-layer gaps by tree felling; and (2) the closing of the tree layer during the regeneration phase.Most notably, the phases at which the tree layer reaches minimum and maximum cover, respectively, may act as `bottlenecks\" for survival of forest-floor species. We conclude that forestry impacts understorey vegetation by way of changes in tree-layer structure and, to a lesser extent, substrate availability and the local environment, during forest regrowth. The extent and duration of this impact will depend on a complex set of factors.Our results are consistent with the view that if maintenance of species diversity is aimed at, environmental considerations should be built into forest management practices, preferably by mimicking the natural structural dynamics of the tree layer.
Previous studies point at biogeographic (i.e. evolutionary and demographic) and ecological (i.e. habitat differentiation and disturbance) processes as the most important causes of spatial variation in species richness and species composition. We examined patterns of variation in similarity of vascular plant and bryophyte species composition among 150 1-m2 plots distributed semi-randomly over 11 Norwegian boreal swamp-forest localities that were species-rich islands in an otherwise species-poor forest landscape. For each plot, 53 environmental variables were recorded. By using CCA analyses, we found that c. 20% of the explainable variation in species composition was due to swamp-forest affiliation, in addition to the c. 35% that was due to environmental differences between swamp-forest localities. The unique component of the species composition of each swamp forest was also emphasised by analyses of floristic dissimilarity: plots were significantly more floristically dissimilar if situated in different than if situated in the same swamp forest, even after environmental differences had been corrected for. The lack of any significant relationship between floristic dissimilarity and geographical distance or swamp-forest area indicated that this pattern was not mainly due to demographic processes. We argue that the floristic distinctness of swamp forests, in particular those richer in species and soil nutrients, is due to a combination of factors among which randomness in establishment in infrequently occurring gaps ( ‘windows of opportunity’) are likely to be important. The unique combination of important determinants of the species composition found for boreal swamp forests supports the view that there exists a diversity of explanations for diversity and that these, to a large extent, are system- and/or area-specific.
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Historical reconstructions of past forest dynamics and stand structures have been used to establish reference conditions for managing present forest ecosystems. In this study we (1) developed and combined a suite of stand reconstruction techniques to describe past stand characteristics, and (2) applied these stand histories to evaluate the relationship between wood-decay fungi and forest continuity. Ten previous selectively logged stands of Norway spruce (<i>Picea abies</i> (L.) Karst.), in the middle boreal zone of southeastern Norway, were studied. We reconstructed stand structures during the 20th century using tree-ring series, growth patterns, age structures, and decay classification and datings of stumps and logs. All stands were selectively logged between 1890 and 1965, with a mean logging interval of 25 years. Harvested volumes (1900-1965) constituted 25-99% of present standing volumes and present volumes were 2.6-21 (median 4) times higher than the lowest estimated historic volumes. Dead wood was categorized into eight decay classes, where one is recently fallen, and eight is almost completely decayed. Six fungus species, assumed to indicate dead-wood continuity, were found on logs in decay classes 2-4, all of which were estimated to be<30 years old. Logs in decay classes 1-4 constituted 85% of logs >=20 cm. Expectedly, fungus abundance increased linearly with increasing number of available logs, but we failed to find a positive correlation between fungi abundance and number of old logs present (decay classes 5-8), when the effect of younger logs (2-4) was accounted for. This finding, together with the stand histories, does not lend support to the hypothesis that a continuous supply of dead wood, at the scale of forest stands, is crucial for the occurrence of the surveyed wood-decay fungi. We propose forest stand reconstructions to hold promise as a tool to assess the role of structural continuity for the occurrence of late-successional and old-growth species
To estimate the age of Norway spruce (Picea abies (L.) Karst.) logs by means of decay classes, and to assess how long it takes for downed logs to decompose, we dated logs dendrochronologically by applying 5- and 8-grade decay classification systems. Study sites were chosen in old-growth and previously selectively cut forest stands in boreal south-central Scandinavia; 113 logs were dated to the number of years since death, 120 were dated to the number of years since fall, and 61 logs were dated to both. The number of years from death to fall showed a negative exponential distribution, with a mean of 22 years and a range of 0–91 years. Decay classes of logs (8-grade scale) reflected time since fall (R2 = 0.58) better than time since death (R2 = 0.27) in a linear regression model. This result is due to the lower decomposition rate of standing snags. Therefore, the decomposition time of logs should be divided into two periods: time from death to fall, which varies considerably, and time after fall, which appears to follow a linear relationship with decay class. The model predicted that it takes 100 years after fall for downed logs to decompose completely (reaching decay class 8) in old-growth stands. Logs in selectively cut stands appeared to decompose faster (64 years), which is explained by a sample shortage of old logs resulting from previous cuttings. We conclude that the decomposition time of downed logs may be severely underestimated when data is retrospectively compiled from previously logged forest stands.
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Epiphytic lichens (and some non-lichenized fungi) on 34 coppices (204 stems) of Corylus avellana were investigated in a 140 ha study area in south-western Norway. A total of 65 species were recorded on a total bark area of 63 m2. Corylus in broad-leaved deciduous forest supported more species of macrolichens, and fewer species of icrolichens, than Corylus in pine forest. The macrolichen flora of the deciduous forest differed from that of the pine forest by having a rich flora of species belonging to the Lobarion alliance. Old Corylus coppices with tall stems (>8 m), large girth (>8 cm diameter at breast height) and a noticeable cover of macrolichens (>10% of bark area) supported the highest number of rare species, and overall, species of mcrolichens. More than 50% cover of icrolichens indicated richness and rarity of microlichens on Corylus
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Undervegetasjonens artssammensetning er undersøkt i 150 prøveflater á 1 m2 i 11 gransumpskogslokaliteter i Østmarka naturreservat, Akershus. 53 miljøvariabler er registrert i tilknytning til hver prøveflate. Det ble funnet to hovedgradienter i artssammensetning i sumpskogene. Begge kunne relateres til økologiske hovedkompleksgradienter; jordas (og grunnvannets) nærings- og surhetsstatus, og dybden til det mediane grunnvannsspeilet. En rekke arter har klare fordelingsmønstre langs disse gradientene og kan derfor nyttes som indikatorer på ulike voksestedsforhold. Variasjonen langs de to hovedkompleksgradientene blir lagt til grunn for beskrivelse av seks voksestedstyper i gransumpskog.. Det blir vist at grensa mellom sumpskog og granskog på fastmark er relativt skarp, og at artsmangfoldet i sumpskoger er høyt, både på grunn av høyt nisjemangfold og på grunn av høyt antall mindre vanlige arter. Fordi artsinventaret i sumpskogene bare i begrenset grad kan forutsies på grunnlag av økologiske forhold anbefales at man, dersom man ønsker å ta vare på det biologiske mangfoldet i skog, sikrer alle intakte sumpskoger på næringsrik grunn og et representativt utvalg av øvrige sumpskoger mot grøfting og andre irreversible inngrep.
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I de senere årene har det blitt gjennomført registreringer av såkalte nøkkelbiotoper (Haugset m.fl. 1996), som vanligvis er mindre flekker av skog som anses for å være særlig viktig for mangfoldet av arter i skog. Metoden ble opprinnelig utviklet av feltbiologer i Nord-Sverige (Karström 1992) som igjen var inspirert av britiske undersøkelser (f.eks Peterken 1974, Rose 1976). Den bygger i stor grad på registrering av såkalte indikatorarter eller signalarter (særlig av lav og vedboende sopp), som skal indikere spesielle skogtilstander og forekomst av sjeldne og truete arter (rødlistearter). Interessen for slike registreringer har vært stor i skogbruket, ikke minst fordi næringen er inne i en prosess med miljøsertifisering, der hensyn til biologisk mangfold i utøvelsen av praktisk skogbruket står sentralt. I skogbruksmiljøene har man naturlig nok også funnet det interessant at man mener å kunne bevare en stor andel av mangfoldet gjennom å bevare en liten andel av skogen som nøkkelbiotoper (ca1% i Sverige, Skogsstyrelsen 1999 ). MiS-prosjektet har lagt ned et betydelig arbeid for å undersøke de faglige forutsetningene for bevaring av biologisk mangfold i skog, og for å videreutvikle en registreringsmetodikk for norske forhold. Arbeidet med å publisere resultatene er nå igang. I denne artikkelen skal jeg ta for meg noen grunnleggende prinsipper for hvordan MiS-registreringene er bygget opp, og hvordan de er knyttet til viktige resultater fra prosjektet.
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Arthothelillm lirellans and A. orbilliferum are reported new to Scandinavia. Both species were found in Hordaland, western Norway. Their ecology and European distribution are discussed, and distribution maps presented.
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