[show abstract][hide abstract] ABSTRACT: The effectiveness of agri-environment schemes (AES) in enhancing biodiversity in agricultural landscapes is still strongly debated. In the Netherlands, one of the most widely implemented AES is the management of ditch banks to enhance plant species diversity. Previous research has shown that this type of AES has not led to increases in plant diversity. However, this work also showed that the success of this type of AES may depend on the presence of source populations in the surrounding areas. In this study we investigated if species-rich nature reserves can act as seed sources for agricultural ditch banks under AES and whether this function of nature reserves differs among plant species with different dispersal capacities. We used data collected by farmers over a 10 year period to analyse trends in species richness of target plants and in different dispersal groups in ditch banks under AES at different distances from nature reserves.
Our results demonstrate that nature reserves can act as species rich sources in agricultural landscapes and that adjacent AES ditch banks can facilitate the colonisation of the surrounding agricultural landscape. However, the suitability of ditch banks as corridors depends on the dispersal capacity of a species. Particularly water-dispersed species clearly spread from nature reserves into the surrounding agricultural landscape along ditches. In contrast, species without adaptations to disperse over long distances do not show these spatiotemporal patterns.
[show abstract][hide abstract] ABSTRACT: It is generally known that managed, drained peatlands act as carbon
sources. In this study we examined how mitigation through the reduction
of management and through rewetting may affect the greenhouse gas (GHG)
emission and the carbon balance of intensively managed, drained,
agricultural peatlands. Carbon and GHG balances were determined for
three peatlands in the western part of the Netherlands from 2005 to 2008
by considering spatial and temporal variability of emissions
(CO2, CH4 and N2O). One area (Oukoop)
is an intensively managed grass-on-peatland, including a dairy farm,
with the ground water level at an average annual depth of 0.55 m below
the soil surface. The second area (Stein) is an extensively managed
grass-on-peatland, formerly intensively managed, with a dynamic ground
water level at an average annual depth of 0.45 m below the soil surface.
The third area is an (since 1998) rewetted former agricultural peatland
(Horstermeer), close to Oukoop and Stein, with the average annual ground
water level at a depth of 0.2 m below the soil surface. During the
measurement campaigns we found that both agriculturally managed sites
acted as carbon and GHG sources but the rewetted agricultural peatland
acted as a carbon and GHG sink. The terrestrial GHG source strength was
1.4 kg CO2-eq m-2 yr-1 for the
intensively managed area and 1.0 kg CO2-eq m-2
yr-1 for the extensively managed area; the unmanaged area
acted as a GHG sink of 0.7 kg CO2-eq m-2
yr-1. Water bodies contributed significantly to the
terrestrial GHG balance because of a high release of CH4 and
the loss of DOC only played a minor role. Adding the farm-based
CO2 and CH4 emissions increased the source
strength for the managed sites to 2.7 kg CO2-eq
m-2 yr-1 for Oukoop and 2.1 kg CO2-eq
m-2 yr-1 for Stein. Shifting from intensively
managed to extensively managed grass-on-peat reduced GHG emissions
mainly because N2O emission and farm-based CH4
emissions decreased. Overall, this study suggests that managed peatlands
are large sources of GHG and carbon, but, if appropriate measures are
taken they can be turned back into GHG and carbon sinks within 15 yr of
abandonment and rewetting.
[show abstract][hide abstract] ABSTRACT: Management of ditch banks of agricultural fields is considered to be a promising and
multifunctional application of agri-environment schemes (AES) on farmland. Our previous
esearch has shown that in the Netherlands, there is a small increase in the number of target
plant species of AES in ditch banks. However, the productivity and Ellenberg indicator value
or nitrogen also increased. This suggests a change in species composition towards more
competitive species. This is important, because management mainly focuses on restoring
disturbance tolerant species that used to be common in meadows, rather than competitive
dominants. In this study we use a large scale dataset of target species composition in ditch
banks of nature reserves and ditch banks with and without AES over 10 years to monitor
esults of functional plant species groups under these different management regimes. Our
analyses show that plant functional type composition in ditch banks of agricultural fields
ndeed shifted towards more competitive species over the last 10 years, independent of
AES. In nature reserves, a similar increase in competitive species was observed. The shift
owards more competitive species was reflected in the increase of the average height of
he vegetation and the increase in species with a leafy canopy structure, whereas species
with a semi-basal canopy structure were decreasing. We conclude that current AES does
not increase the number of targeted disturbance tolerant species and that more disturbance
such as more frequent mowing is required to obtain these species.
[show abstract][hide abstract] ABSTRACT: As biodiversity is declining at an unprecedented rate, an important current scientific challenge is to understand and predict the consequences of biodiversity loss. Here, we develop a theory that predicts the temporal variability of community biomass from the properties of individual component species in monoculture. Our theory shows that biodiversity stabilises ecosystems through three main mechanisms: (1) asynchrony in species' responses to environmental fluctuations, (2) reduced demographic stochasticity due to overyielding in species mixtures and (3) reduced observation error (including spatial and sampling variability). Parameterised with empirical data from four long-term grassland biodiversity experiments, our prediction explained 22-75% of the observed variability, and captured much of the effect of species richness. Richness stabilised communities mainly by increasing community biomass and reducing the strength of demographic stochasticity. Our approach calls for a re-evaluation of the mechanisms explaining the effects of biodiversity on ecosystem stability.
[show abstract][hide abstract] ABSTRACT: To comprehend the potential consequences of biodiversity loss on the leaf litter decomposition process, a better understanding of its underlying mechanisms is necessary. Here, we hypothesize that positive litter mixture effects occur via complementary resource use, when litter species complement each other in terms of resource quality for detritivores. To investigate this, monocultures and mixtures of two leaf litter species varying in quality were allowed to decompose with and without a single macro-detritivore species (the terrestrial woodlice Oniscus asellus). Resource quality of the mixture was assessed by the mean concentration, the dissimilarity in absolute and relative concentrations, and the covariance between nitrogen (N), phosphorus (P) and calcium (Ca) supply. Our results clearly show that litter mixing effects were driven by differences in their resource quality for detritivores. In particular, complementary supply of N and P was a major driver of litter mixing effects. Interestingly, litter mixing effects caused by the addition of woodlice were predominantly driven by N dissimilarity, whereas in their absence, increased P concentration was the main driver of litter mixing effects. These results show that ultimately, litter diversity effects on decomposition may be driven by complementary resource use of the whole decomposer community (i.e., microbes and macro-detritivores).
[show abstract][hide abstract] ABSTRACT: Many of the agri-environment schemes (AES) implemented in the Western Peat District of the Netherlands have as their objective the conservation of the diversity of ditch bank plants. We investigated the effects of AES on ditch bank species in this area, using a dataset collected by 377 farmers who managed and monitored ditch banks during a 10-year period. We found that species richness has increased minimally over the last 10 years in ditch banks. Yet, we found no differences in increases in time between ditch banks with and without AES. In both ditch bank types plant species composition changed to species with higher nitrogen tolerance. Furthermore, species that disperse over long distances by water increased, whereas species with no capacity to disperse over long distances declined in both ditch bank types. This indicates that changes in vegetation composition in ditch banks are affected by other factors than AES.ZusammenfassungViele der Naturschutzprogramme für die Agrarlandschaft (AES), die in den westlichen Torfmoorgebieten der Niederlande zum Einsatz kommen, setzen sich zum Ziel, die Diversität der Uferpflanzen in Gräben zu erhalten. Wir untersuchten die Auswirkungen der AES auf die Arten der Ufer von Gräben in diesem Gebiet, und nutzten dafür einen Datensatz, der während einer 10-Jahresperiode von 377 Landwirten gesammelt wurde, welche die Grabenufer managten und erfassten. Wir haben herausgefunden, dass der Artenreichtum an den Grabenufern in den letzten zehn Jahren minimal zunahm. Dennoch fanden wir keinen Unterschied in der Zunahme zwischen den Grabenufern mit und ohne AES. Bei beiden Grabenufertypen veränderte sich die Pflanzenartenzusammensetzung hin zu Arten mit einer höheren Stickstofftoleranz. Darüber hinaus nahmen die Arten zu, die sich über weite Distanzen mit dem Wasser verbreiten, während Arten, denen die Möglichkeit fehlt, sich über weite Distanzen auszubreiten, bei beiden Grabenufertypen abnahmen. Dies zeigt, dass die Veränderungen in der Vegetationszusammensetzung nicht durch die AES sondern durch andere Faktoren beeinflusst werden.
Basic and Applied Ecology 01/2013; 14:289-297. · 2.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: In recent decades, Skylark (Alauda arvensis) populations in Europe have declined sharply due to agricultural intensification. Insufficient reproduction rates are one reason. Increased winter mortality may also be important, but studies outside the breeding season are scarce and mostly limited to the UK. We studied habitat selection of wintering Skylarks in an agricultural area in the Netherlands. We monitored Skylarks between November 2008 and March 2009 on 10 survey plots including 77 different arable fields and permanent grasslands and covering in total 480 ha. We simultaneously measured food availability, vegetation structure and field boundary characteristics. We also analysed 158 faecal pellets collected on potato and cereal stubble fields to relate Skylark diet to seasonal changes in food availability and foraging habitat. We show that cereal stubble fields larger than 4.3 ha, surrounded by no or low boundary vegetation and a density of dietary seeds of more than 860 seeds m−2, were most suitable for wintering Skylarks. Skylark group densities were low on permanent grasslands and on maize stubble fields. Densities of dietary seeds were highest in soils of potato stubble fields followed by cereal stubble fields, grasslands and maize stubble fields. Skylarks showed a strong preference for cereal grains, but their proportion in the diet fell sharply at the end of November, indicating that cereal grains were depleted and birds had to switch to less profitable food sources, such as weed seeds and leaves. We conclude that Skylarks wintering in agricultural landscapes possibly suffer from a lack of energy-rich food sources and only a few fields provide sufficient food. Conservation measures should strive to improve the wintering situation by creating food-rich habitats such as over-winter stubble with a rich layer of weeds on large fields and localised in open areas.
[show abstract][hide abstract] ABSTRACT: European farmland bird populations have decreased dramatically in recent decades and agricultural
intensification has been identified as the main cause contributing to these declines. Identifying which
specific intensification pressures are driving those population trends seems vital for bird conservation
in European farmland.
We investigated the response of ground-nesting farmland birds to the multivariate process of agricultural
intensification in six European countries covering a bio-geographical and intensification gradient.
Supported by PCA analysis, two groups of factors, related to field management and landscape modification,
were considered, seeking to discriminate the relative importance of the effects of these main intensification
Variance partition analysis showed that landscape factors accounted for most of the variation of
ground-nesting farmland bird individual and breeding pair densities, as well as Skylark (i.e. our single
model species) individual densities. In the case of Skylark breeders, field factors were found to be more
important to explain their density. Our results suggest that in general farmland bird densities as well as
Skylark densities are higher in simple landscapes dominated by agriculture, but with smaller fields and
more different crops on the farms. In addition, high yields were negatively related to bird densities.
We conclude that while management actions aimed at farmland bird conservation taken at landscape
level may exert a strong positive effect on overall bird densities, those taken at field level are also relevant,
particularly for breeders and, therefore, may potentially influence the persistence of these species’
[show abstract][hide abstract] ABSTRACT: In eight European study sites (in Spain, Ireland, Netherlands, Germany, Poland, Estonia and Sweden), abundance of breeding farmland bird territories was obtained from 500 x 500 m survey plots (30 per area, N = 240) using the mapping method. Two analyses were performed: (I) a Canonical Correspondence Analysis of species abundance in relation to geographical location and variables measuring agricultural intensification at field and farm level to identify significant intensification variables and to estimate the fractions of total variance in bird abundance explained by geography and agricultural intensification; (II) several taxonomic and functional community indices were built and analysed using GLM in relation to the intensification variables found significant in the CCA. The geographical location of study sites alone explains nearly one fifth (19.5%) of total variation in species abundance. The fraction of variance explained by agricultural intensification alone is much smaller (4.3%), although significant. The intersectionexplains nearly two fifths (37.8%) of variance in species abundance. Community indices are negatively affected by correlates of intensification like farm size and yield, whereas correlates of habitat availability and quality have positive effects on taxonomic and functional diversity of assemblages. Most of the purely geographical variation in farmland bird assemblage composition is associated to Mediterranean steppe species, reflecting the bio-geographical singularity of that assemblage and reinforcing the need to preserve this community. Taxonomic and functional diversity of farmland bird communities are negatively affected by agricultural intensification and positively affected by increasing farmland habitat availability and quality.
Biodiversity and Conservation 09/2011; 20(14):3663-3681. · 2.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: Recently observed Arctic greening trends from normalized difference vegetation index (NDVI) data suggest that shrub growth is increasing in response to increasing summer temperature. An increase in shrub cover is expected to decrease summer albedo and thus positively feed back to climate warming. However, it is unknown how albedo and NDVI are affected by shrub cover and inter-annual variations in the summer climate. Here, we examine the relationship between deciduous shrub fractional cover, NDVI and albedo using field data collected at a tundra site in NE Siberia. Field data showed that NDVI increased and albedo decreased with increasing deciduous shrub cover. We then selected four Arctic tundra study areas and compiled annual growing season maximum NDVI and minimum albedo maps from MODIS satellite data (2000–10) and related these satellite products to tundra vegetation types (shrub, graminoid, barren and wetland tundra) and regional summer temperature. We observed that maximum NDVI was greatest in shrub tundra and that inter-annual variation was negatively related to summer minimum albedo but showed no consistent relationship with summer temperature. Shrub tundra showed higher albedo than wetland and barren tundra in all four study areas. These results suggest that a northwards shift of shrub tundra might not lead to a decrease in summer minimum albedo during the snow-free season when replacing wetland tundra. A fully integrative study is however needed to link results from satellite data with in situ observations across the Arctic to test the effect of increasing shrub cover on summer albedo in different tundra vegetation types.
Environmental Research Letters 09/2011; 6(3):035502. · 3.58 Impact Factor
[show abstract][hide abstract] ABSTRACT: Effects of agricultural intensification (AI) on biodiversity are often assessed on the plot scale, although processes determining diversity also operate on larger spatial scales. Here, we analyzed the diversity of vascular plants, carabid beetles, and birds in agricultural landscapes in cereal crop fields at the field (n = 1350), farm (n = 270), and European-region (n = 9) scale. We partitioned diversity into its additive components alpha, beta, and gamma, and assessed the relative contribution of beta diversity to total species richness at each spatial scale. AI was determined using pesticide and fertilizer inputs, as well as tillage operations and categorized into low, medium, and high levels. As AI was not significantly related to landscape complexity, we could disentangle potential AI effects on local vs. landscape community homogenization. AI negatively affected the species richness of plants and birds, but not carabid beetles, at all spatial scales. Hence, local AI was closely correlated to beta diversity on larger scales up to the farm and region level, and thereby was an indicator of farm- and region-wide biodiversity losses. At the scale of farms (12.83-20.52%) and regions (68.34-80.18%), beta diversity accounted for the major part of the total species richness for all three taxa, indicating great dissimilarity in environmental conditions on larger spatial scales. For plants, relative importance of alpha diversity decreased with AI, while relative importance of beta diversity on the farm scale increased with AI for carabids and birds. Hence, and in contrast to our expectations, AI does not necessarily homogenize local communities, presumably due to the heterogeneity of farming practices. In conclusion, a more detailed understanding of AI effects on diversity patterns of various taxa and at multiple spatial scales would contribute to more efficient agri-environmental schemes in agroecosystems.
[show abstract][hide abstract] ABSTRACT: Nutrient enrichment of habitats (eutrophication) is considered to be one of the main causes of plant diversity decline worldwide. Several experiments have shown a rapid loss of species in the first years after fertilization started. However, little is known about changes in species richness in the long term. Here, we use a 50-year-old field experiment with a range of fertilization treatments in grasslands that were mown twice each year in the center of The Netherlands. We show that species richness in all plots initially declined but started to recover after approximately 25 years of continued fertilization. This was also true for the heavily fertilized treatment (NPK). In NPK-fertilized plots, the decline was strongest and associated with a strong divergence of plant trait composition from the control, reflecting a shift to a plant community adapted to nutrient-rich conditions. During the subsequent period of increase in species richness, the trait composition remained stable. These results show that plant species richness can, at least partially, recover after an initial diversity decline caused by fertilization.
[show abstract][hide abstract] ABSTRACT: The importance of leaf litter diversity for decomposition, an important process in terrestrial ecosystems, is much debated. Previous leaf litter-mixing studies have shown that non-additive leaf litter diversity effects can occur, but it is not clear why they occurred in only half of the studies and which underlying mechanisms can explain these conflicting results. We hypothesized that incorporating the role of macro-detritivores could be important. Although often ignored, macro-detritivores are known to strongly influence decomposition. To better understand the importance of macro-detritivores for leaf litter mixing effects during decomposition, four common leaf litter species were added separately and in two and four species combinations to monocultures of three different macro-detritivores and a control without fauna. Our results clearly show that leaf litter-mixing effects occurred only in the presence of two macro-detritivores (earthworms and woodlice). Application of the additive partitioning method revealed that in the specific combination of woodlice and the presence of a slow-decomposing leaf litter species in the mixture, leaf litter mixing effects were strongly driven by a selection effect. This was caused by food preference of the isopod: the animals avoided the slow decomposing species when given the choice. However, most leaf litter mixing effects were caused by complementarity effects. The potential mechanisms underlying the complementarity effects are discussed. Our results clearly show that that both leaf litter and macro-detritivore identity can affect litter diversity. This may help to explain the conflicting results obtained in previous experiments.
[show abstract][hide abstract] ABSTRACT: 1. Organic farming in Europe has been shown to enhance biodiversity locally, but potential interactions with the surrounding landscape and the potential effects on ecosystem services are less well known.
2. In cereal fields on 153 farms in five European regions, we examined how the species richness and abundance of wild plants, ground beetles and breeding birds, and the biological control potential of the area, were affected by organic and conventional farming, and how these effects were modified by landscape complexity (percentage of arable crops within 1000 m of the study plots). Information on biodiversity was gathered from vegetation plots, pitfall traps and by bird territory mapping. The biological control potential was measured as the percentage of glued, live aphids removed from plastic labels exposed in cereal fields for 24 h.
3. Predation on aphids was highest in organic fields in complex landscapes, and declined with increasing landscape homogeneity. The biological control potential in conventional fields was not affected by landscape complexity, and in homogenous landscapes it was higher in conventional fields than in organic fields, as indicated by an interaction between farming practice and landscape complexity.
4. A simplification of the landscape, from 20% to 100% arable land, reduced plant species richness by about 16% and cover by 14% in organic fields, and 33% and 5·5% in conventional fields. For birds, landscape simplification reduced species richness and abundance by 34% and 32% in organic fields and by 45·5% and 39% in conventional fields. Ground beetles were more abundant in simple landscapes, but were unaffected by farming practice.
5. Synthesis and applications. This Europe-wide study shows that organic farming enhanced the biodiversity of plants and birds in all landscapes, but only improved the potential for biological control in heterogeneous landscapes. These mixed results stress the importance of taking both local management and regional landscape complexity into consideration when developing future agri-environment schemes, and suggest that local-regional interactions may affect other ecosystem services and functions. This study also shows that it is not enough to design and monitor agri-environment schemes on the basis of biodiversity, but that ecosystem services should be considered too.
[show abstract][hide abstract] ABSTRACT: Deciduous shrubs are expected to rapidly expand in the Arctic during the coming decades due to climate warming. A transition towards more shrub-dominated tundra may have large implications for the regional surface energy balance, permafrost stability and carbon storage capacity, with consequences for the global climate system. However, little information is available on the natural long-term shrub growth response to climatic variability. Our aim was to determine the climate factor and time period that are most important to annual shrub growth in our research site in NE-Siberia. Therefore, we determined annual radial growth rates in Salix pulchra and Betula nana shrubs by measuring ring widths. We constructed shrub ring width chronologies and compared growth rates to regional climate and remotely sensed greenness data. Early summer temperature was the most important factor influencing ring width of S. pulchra (Pearson's r=0.73, p<0.001) and B. nana (Pearson's r=0.46, p<0.001). No effect of winter precipitation on shrub growth was observed. In contrast, summer precipitation of the previous year correlated positively with B. nana ring width (r=0.42, p<0.01), suggesting that wet summers facilitate shrub growth in the following growing season. S. pulchra ring width correlated positively with peak summer NDVI, despite the small coverage of S. pulchra shrubs (<5% surface cover) in our research area. We provide the first climate-growth study on shrubs for Northeast Siberia, the largest tundra region in the world. We show that two deciduous shrub species with markedly different growth forms have a similar growth response to changes in climate. The obtained shrub growth response to climate variability in the past increases our understanding of the mechanisms underlying current shrub expansion, which is required to predict future climate-driven tundra vegetation shifts.
[show abstract][hide abstract] ABSTRACT: Effectiveness of European initiatives to restore populations of meadow breeding waders is heavily debated. We studied field preference of meadow birds throughout the breeding season in four areas of over 100ha each and related observed patterns of individual birds to in-field heterogeneity, sward height and management. Over the four areas, most waders were observed in the more heterogeneous fields at both the period of nest site selection and incubation. Additionally, fields grazed at relatively low-intensity for longer consecutive periods (on average 6cows/ha for 30d instead of 20cows/ha for 2d) were hosting high densities of lapwings but also black-tailed godwits. Our results suggest that in-field heterogeneity may be important for meadow breeding waders at the nest site selection and incubation stages. Conservation initiatives aimed at meadow breeding waders might improve their effectiveness when they increase the heterogeneity of fields. Grazing for longer consecutive periods at relatively low stocking rates might be a way to achieve this, if carried out at stocking rates low enough to allow waders to reproduce successfully.
[show abstract][hide abstract] ABSTRACT: Abstract Shallow fresh water bodies in peat areas are important contributors to greenhouse gas fluxes to the atmosphere. In this study we determined the magnitude of CH4 and CO2 fluxes from 12 water bodies in Dutch wetlands during the summer season and studied the factors that might regulate emissions of CH4 and CO2 from these lakes and ditches. The lakes and ditches acted as CO2 and CH4 sources of emissions to the atmosphere; the fluxes from the ditches were significantly larger than the fluxes from the lakes. The mean greenhouse gas flux from ditches and lakes amounted to 129.1 ± 8.2 (mean ± SE) and 61.5 ± 7.1 mg m−2 h−1 for CO2 and 33.7 ± 9.3 and 3.9 ± 1.6 mg m−2 h−1 for CH4, respectively. In most water bodies CH4 was the dominant greenhouse gas in terms of warming potential. Trophic status of the water and the sediment was an important factor regulating emissions. By using multiple linear regression 87% of the variation in CH4 could be explained by PO4 3− concentration in the sediment and Fe2+ concentration in the water, and 89% of the CO2 flux could be explained by depth, EC and pH of the water. Decreasing the nutrient loads and input of organic substrates to ditches and lakes by for example reducing application of fertilizers and manure within the catchments and decreasing upward seepage of nutrient rich water from the surrounding area will likely reduce summer emissions of CO2 and CH4 from these water bodies.
[show abstract][hide abstract] ABSTRACT: Arctic tundra vegetation composition is expected to undergo rapid changes during the coming decades because of changes in
climate. Higher air temperatures generally favor growth of deciduous shrubs, often at the cost of moss growth. Mosses are
considered to be very important to critical tundra ecosystem processes involved in water and energy exchange, but very little
empirical data are available. Here, we studied the effect of experimental moss removal on both understory evapotranspiration
and ground heat flux in plots with either a thin or a dense low shrub canopy in a tundra site with continuous permafrost in
Northeast Siberia. Understory evapotranspiration increased with removal of the green moss layer, suggesting that most of the
understory evapotranspiration originated from the organic soil layer underlying the green moss layer. Ground heat flux partitioning
also increased with green moss removal indicating the strong insulating effect of moss. No significant effect of shrub canopy
density on understory evapotranspiration was measured, but ground heat flux partitioning was reduced by a denser shrub canopy.
In summary, our results show that mosses may exert strong controls on understory water and heat fluxes. Changes in moss or
shrub cover may have important consequences for summer permafrost thaw and concomitant soil carbon release in Arctic tundra
Keywordsmoss–evaporation–ground heat flux–shrub–permafrost–tundra–Arctic–climate change
[show abstract][hide abstract] ABSTRACT: Background/Question/Methods The Siberian tundra is one of the key
permafrost regions in the Arctic because of its large spatial extent and
carbon-rich yedoma soils. Changes in permafrost thaw and concomitant
carbon losses to the atmosphere can have large impacts on the global
climate. Permafrost thaw is believed to strongly increase this century
as a result of predicted increasing air temperature. At the same time,
arctic vegetation growth and composition is predicted to respond to
future climate change, which can have large implications for the
stability of permafrost and can feedback to further vegetation changes.
Deciduous shrubs are expected to benefit from climate warming by
increasing growth and expanding their range to higher latitudes.
However, observational evidence for recent increases in deciduous shrub
cover in the arctic region is limited thus far to areas in Alaska. We
examined if deciduous shrubs at our research site in Northeastern
Siberia show a growth response to the main climate variables,
temperature and precipitation. We constructed dendrochronological
records for two key arctic deciduous shrub species, Betula nana and
Salix pulchra, dating back roughly 60 years. The ring-width records are
related to summer temperature and summer-precipitation data from the
closest climate station in order to identify the main climate factor
limiting shrub growth in this area. Remote sensing data are used to
assess changes in panarctic vegetation productivity by vegetation type
following the circumpolar arctic vegetation map (CAVM). Using a combined
approach of dendrochronology and remote sensing provides the opportunity
to study the vegetation response at different temporal and spatial
scales. Results/Conclusions Our results indicate that growth of both
Salix pulchra and Betula nana shrubs relates positively to summer
temperature at our research site in Northeast Siberia. Secondary growth
of both shrub species was most sensitive to early summer temperature
(mid-June to mid-July). Annual shrub growth correlated positively with
late-summer precipitation of the year preceding the ring formation.
Panarctic vegetation productivity of the last 25 years shows a
significant positive trend, especially in areas identified as
shrub-dominated plant communities in the CAVM. Most climate model
scenarios predict increasing summer temperature and precipitation in the
arctic region. This implies that shrub growth will further increase.
Finally, we present experimental evidence from a shrub removal
experiment showing that shrub cover is negatively correlated with active
layer thickness through shading of the soil surface. Expansion of
deciduous shrubs, triggered by climate warming, may thus reduce summer
permafrost thaw and partly offset the permafrost degradation expected to
result from the air temperature rise predicted for the coming decades.