Boreal Grasslands Research Articles

Simulating Soil-Plant-Climate Interactions and Greenhouse Gas Exchange in Boreal Grasslands Using the DNDC Model

With global warming, arable land in boreal regions is tending to expand into high latitude regions in the northern hemisphere. This entails certain risks; such that inappropriate management could result in previously stable carbon sinks becoming sources. Agroecological models are an important tool for assessing the sustainability of long-term management, yet applications of such models in boreal zones are scarce. We collated eddy-covariance, soil climate and biomass data to evaluate the simulation of GHG emissions from grassland in eastern Finland using the process-based model DNDC. We simulated gross primary production (GPP), net ecosystem exchange (NEE) and ecosystem respiration (Reco) with fair performance. Soil climate, soil temperature and soil moisture at 5 cm were excellent, and soil moisture at 20 cm was good. However, the model overestimated NEE and Reco following crop termination and tillage events. These results indicate that DNDC can satisfactorily simulate GHG fluxes in a boreal grassland setting, but further work is needed, particularly in simulated second biomass cuts, the (>20 cm) soil layers and model response to management transitions between crop types, cultivation, and land use change.

Climate change simulations in Alpine summer pastures suggest a disruption of current vegetation zonation

Alpine summer grazing areas (high-altitude pastures) represent hotspots of biodiversity and high cultural heritage values. Low density forests (Alpine Larix decidua and/or Pinus cembra forests) and species-rich open land (Alpine and boreal heaths, siliceous Alpine and boreal grasslands) are protected according to the Flora-Fauna-Habitat-directive of the European Union. These habitats are threatened by the accelerated mountain climate warming and the expected upslope shift of vegetation zones. With climate change, tree growth accelerates and montane species spread to higher altitudes. The fate of low density larch forests, alpine heathlands and grasslands is unclear. We used the process-based wooded pasture model WoodPaM to simulate large-scale and long-term dynamics of the forest and tree line under several land-use scenarios and climate change. The simulation results for the central Alpine summer grazing area Furggtal (Canton Valais, Switzerland) showed a plausible projection of the upslope migration of vegetation zones due to climate warming in the very long-term. For the upcoming centuries however, the existing vegetation zonation was disrupted by the intermixing of tree species during the migration process. This unexpected result emerged from the process-based modelling of tree species specific dispersal and establishment in interaction with livestock grazing. This effect was most pronounced in simulations of grazing abandonment and current low intensity grazing of free ranging livestock, which failed to buffer climate change effects. The establishment of paddocks and thereby intensified grazing on the current pastures on the valley floor promised the conservation of valuable open habitats. We conclude that the ongoing rapid upslope shift of climate zones in mountain regions might not be followed by a similar shift of vegetation zones. Widespread colonisation processes might lead to a period dominated by very dynamic vegetation communities that might not zone along climatic gradients as it was in the past of comparable stable climate. Climate change may therefore impact more like disturbance on alpine ecosystems rather than to drive continuous range shifts. During this disruptive transformation, adapted grazing management in summer pastures can help to maintain continuity for valuable habitats but would require subsidies to establish infrastructure and to increase livestock numbers. • Rapid warming disturbs the ecological balance among larch forests, Alpine grasslands, and livestock grazing. • The upslope shift of climate zones in mountain regions might not be followed by a continuous shift of vegetation zones. • During a disruptive transformation period, colonisation processes might be dominated by dynamic vegetation communities. • Climate change might therefore impact like disturbance on Alpine ecosystems. • Adapted grazing management in summer pastures can help to maintain continuity for valuable habitats.

Nitrogen effects on grassland biomass production and biodiversity are stronger than those of phosphorus

Human-induced nitrogen (N) and phosphorus (P) enrichment have profound effects on grassland net primary production (NPP) and species richness. However, a comprehensive understanding of the relative contribution of N vs. P addition and their interaction on grassland NPP increase and species loss remains elusive. We compiled data from 80 field manipulative studies and conducted a meta-analysis (2107 observations world-wide) to evaluate the individual and combined effects of N and P addition on grassland NPP and species richness. We found that both N addition and P addition significantly enhanced grassland above-ground NPP (ANPP; 33.2% and 14.2%, respectively), but did not affect total NPP, below-ground NPP (BNPP), and species evenness. Species richness significantly decreased with N addition (11.7%; by decreasing forbs) probably due to strong decreased soil pH, but not with P addition. The combined effects of N and P addition were generally stronger than the individual effects of N or P addition, and we found the synergistic effects on ANPP, and additive effects on total NPP, BNPP, species richness, and evenness within the combinations of N and P addition. In addition, N and P addition effects were strongly affected by moderator variables (e.g. climate and fertilization type, duration and amount of fertilizer addition). These results demonstrate a higher relative contribution of N than P addition to grassland NPP increase and species loss, although the effects varied across climate and fertilization types. The existing data also reveals that more long-term (≥5 years) experimental studies that combine N and P and test multifactor effects in different climate zones (particularly in boreal grasslands) are needed to provide a more solid basis for forecasting grassland community response and C sequestration response to nutrient enrichment at the global scale.

Topographic and vegetation drivers of thermal heterogeneity along the boreal-grassland transition zone in western Canada: Implications for climate change refugia.

Climate change refugia are areas that are relatively buffered from contemporary climate change and may be important safe havens for wildlife and plants under anthropogenic climate change. Topographic variation is an important driver of thermal heterogeneity, but it is limited in relatively flat landscapes, such as the boreal plain and prairie regions of western Canada. Topographic variation within this region is mostly restricted to river valleys and hill systems, and their effects on local climates are not well documented. We sought to quantify thermal heterogeneity as a function of topography and vegetation cover within major valleys and hill systems across the boreal–grassland transition zone.Using iButton data loggers, we monitored local temperature at four hills and 12 river valley systems that comprised a wide range of habitats and ecosystems in Alberta, Canada (N = 240), between 2014 and 2020. We then modeled monthly temperature by season as a function of topography and different vegetation cover types using general linear mixed effect models.Summer maximum temperatures (T max) varied nearly 6°C across the elevation gradient sampled. Local summer mean (T mean) and maximum (T max) temperatures on steep, north‐facing slopes (i.e., low levels of potential solar radiation) were up to 0.70°C and 2.90°C cooler than highly exposed areas, respectively. T max in incised valleys was between 0.26 and 0.28°C cooler than other landforms, whereas areas with greater terrain roughness experienced maximum temperatures that were up to 1.62°C cooler. We also found that forest cover buffered temperatures locally, with coniferous and mixedwood forests decreasing summer T mean from 0.23 to 0.72°C and increasing winter T min by up to 2°C, relative to non‐forested areas.Spatial predictions of temperatures from iButton data loggers were similar to a gridded climate product (ClimateNA), but the difference between them increased with potential solar radiation, vegetation cover, and terrain roughness.Species that can track their climate niche may be able to compensate for regional climate warming through local migrations to cooler microsites. Topographic and vegetation characteristics that are related to cooler local climates should be considered in the evaluation of future climate change impacts and to identify potential refugia from climate change.

Long-term leaf C:N ratio change under elevated CO2 and nitrogen deposition in China: Evidence from observations and process-based modeling

Climate change, elevating atmosphere CO2 (eCO2) and increased nitrogen deposition (iNDEP) are altering the biogeochemical interactions between plants, microbes and soils, which further modify plant leaf carbon‑nitrogen (C:N) stoichiometry and their carbon assimilation capability. Many field experiments have observed large sensitivity of leaf C:N ratio to eCO2 and iNDEP. However, the large-scale pattern of this sensitivity is still unclear, because eCO2 and iNDEP drive leaf C:N ratio toward opposite directions, which are further compounded by the complex processes of nitrogen acquisition and plant-and-microbial nitrogen competition. Here, we attempt to map the leaf C:N ratio spatial variation in the past 5 decades in China with a combination of data-driven model and process-based modeling. These two approaches showed consistent results. Over different regions, we found that leaf C:N ratio had significant but uneven changes between 2 time periods (1960-1989 and 1990-2015): a 5% ± 8% increase for temperate grasslands in northern China, a 3% ± 6% increase for boreal grasslands in western China, and by contrast, a 7% ± 6% decrease for temperate forests in southern China, and a 3% ± 5% decrease for boreal forests in northeastern China. Additionally, the structural equation models indicated that the leaf C:N change was sensitive to ΔNDEP, ΔCO2 and ΔMAT rather than ΔMAP and ecosystem types. Process-based modeling suggested that iNDEP was the main source of soil mineral nitrogen change, dominating leaf C:N ratio change in most areas in China, while eCO2 led to leaf C:N ratio increase in low iNDEP area. This study also indicates that the long-term leaf C:N ratio acclimation was dominated by climate constraint, especially temperature, but was constrained by soil N availability over decade scale.

Summer Climatic Moisture Balances for Yukon Xerophytic Grassland Slopes and Their Late-Wisconsinan Counterparts: Are Present-Day Grasslands Beringian Relicts?

Summer climatic moisture balances (precipitation vs. potential evapotranspiration) for topographic slopes favored by present-day xerophytic boreal grasslands (SSW aspects with 61% – 65% gradients) in southwest Yukon were compared to their unglaciated late-Wisconsinan (14 000 – 12 000 cal yr BP) Beringian counterparts. The purpose was to determine whether present-day grasslands are ecologically plausible Beringian relicts or analogues. The Beringian climate was represented by meteorological stations with average July temperatures 4˚C colder than those of present-day grassland areas; all were from Arctic locations. The most commonly occupied grassland slopes received maximum local solar radiation and likely represented the warmest topographic positions in the landscape. Their summer evapotranspiration demands exceeded the 200 mm moisture supply by 189 mm. The same slopes had late-Wisconsinan summer moisture balances of −57 to −101 mm because of colder and shorter growing seasons. Moisture balances for late-Wisconsinan SSW slopes were similar to those of present-day WNW – NW aspects, which do not support grasslands. Differences in moisture deficits indicated present-day xerophytic grasslands were improbable Beringian in situ relicts or analogues. Alternatively, it was hypothesized that present-day Calamagrostis purpurascens communities developed during the Holocene Thermal Maximum (11 000 – 9000 cal yr BP), whereas Hesperostipa comata communities formed less than 3000 years ago after postglacial migration of the species from central North America.

Environmental performance of manure co-digestion with natural and cultivated grass – A consequential life cycle assessment

The aim of this study was to assess the environmental consequences of increased manure-based biogas production relying on grass as a co-substrate (from both unused and cultivated boreal grasslands). Through consequential life cycle assessment, three biogas scenarios were investigated: i) mono-digestion of dairy cow manure, ii) manure co-digestion with reed canary grass cultivated specifically for bioenergy production and iii) manure co-digestion with unused grass from semi-natural grasslands. A full balance of biogenic carbon was considered including soil carbon changes and indirect land use changes. Mono-digestion of manure showed a potential for an improved environmental performance for global warming and phosphorus-eutrophication, in comparison to conventional manure management, but yielded more than 2 times lower energy production compared to co-digestion. Co-digestion with grass from semi-natural grasslands showed an even 41% better potential to reduce global warming and resulted 2 times lower phosphorus-eutrophication compared to mono-digestion, provided that the grass would have otherwise been left un-harvested on land. Because of the indirect land use change associated with an additional demand for land, and the need for additional fertilizers, co-digestion with cultivated grass showed a 26% worse global warming, 2 times higher acidification, 4 times higher nitrogen-eutrophication and 36% worse phosphorus-eutrophication performance compared to natural grass. Results highlighted that grass co-digestion with manure does lead to an enhanced performance of the global warming and phosphorus-induced eutrophication impacts. This conclusion, however, did not apply for nitrogen-related impacts categories (acidification and nitrogen-induced eutrophication). Results were strongly affected by the choice of the indirect land use change factor for modelling and the energy source displaced. In a nutshell, this study highlighted the environmental relevance of considering energy grass and in particular semi-natural grasslands for the production of manure-based biogas, though it showed the necessity to improve the nitrogen balance of the supply chain of these scenarios, and to carefully consider the counterfactual use of the grass stream.

The Importance of Biotic vs. Abiotic Drivers of Local Plant Community Composition Along Regional Bioclimatic Gradients.

We assessed if the relative importance of biotic and abiotic factors for plant community composition differs along environmental gradients and between functional groups, and asked which implications this may have in a warmer and wetter future. The study location is a unique grid of sites spanning regional-scale temperature and precipitation gradients in boreal and alpine grasslands in southern Norway. Within each site we sampled vegetation and associated biotic and abiotic factors, and combined broad- and fine-scale ordination analyses to assess the relative explanatory power of these factors for species composition. Although the community responses to biotic and abiotic factors did not consistently change as predicted along the bioclimatic gradients, abiotic variables tended to explain a larger proportion of the variation in species composition towards colder sites, whereas biotic variables explained more towards warmer sites, supporting the stress gradient hypothesis. Significant interactions with precipitation suggest that biotic variables explained more towards wetter climates in the sub alpine and boreal sites, but more towards drier climates in the colder alpine. Thus, we predict that biotic interactions may become more important in alpine and boreal grasslands in a warmer future, although more winter precipitation may counteract this trend in oceanic alpine climates. Our results show that both local and regional scales analyses are needed to disentangle the local vegetation-environment relationships and their regional-scale drivers, and biotic interactions and precipitation must be included when predicting future species assemblages.

High-Latitude Yukon Boreal-Cordilleran Grassland Plant Communities

High-latitude (61.9˚ – 62.8˚ N) graminoid plant communities located near the northern limit of boreal forest occurrence in the Carmacks – Pelly Crossing area of Yukon were sampled and classified, and four sociations were recognized: Calamagrostis purpurascens (purple reedgrass), Hesperostipa comata (needle-and-thread grass), Poa glauca – Artemisia frigida (glaucous bluegrass – pasture sagewort), and Pseudoroegneria spicata – Artemisia frigida (bluebunch wheatgrass – pasture sagewort). These plant communities occurred primarily on south – southwest slopes (180˚ – 230˚) with 45% – 75% gradients. Relative to southern Canada mixedgrass prairie, Yukon grasslands were likely species poor, had less total canopy cover, and produced less than half as much aboveground herb biomass (typically 200 – 300 kg/ha). The distribution of the sociations appeared limited to ~60˚ – 65˚ N latitude in the Yukon-Alaska region. Calamagrostis was the most abundant and widespread grassland sociation in the study area. The four sociations occupied less than 4% of the Carmacks – Pelly Crossing landscape, although they represented the most extensive high-latitude boreal grassland vegetation in Canada (≥ 2600 ha) and they were among the most northerly in North America.

Geoarchaeology and paleoenvironmental context of the Beacon Island site, an Agate Basin (Paleoindian) bison kill in northwestern North Dakota, USA

A geoarchaeological investigation that included soil-stratigraphic and paleoecological analyses was conducted at Beacon Island, located in the flood pool of Lake Sakakawea in northwestern North Dakota. Beacon Island is a multi-component archaeological site that includes an Agate Basin (Paleoindian) component consisting of the butchered remains of at least 29 Bison antiquus, along with projectile point fragments and other artifacts. The bison bonebed is a product of a single kill at ca. 10,300 B.P. and is buried in a shallow kettle basin. The basin formed around 16,000–15,000 B.P. and initially trapped loess comprising the Mallard Island Member of the Oahe Formation; other members of the Oahe Formation subsequently filled the basin. Conditions probably were relatively dry when the Mallard Island Member aggraded, but by ca. 10,300 B.P. paludal deposits comprising the Aggie Brown Member began to accumulate in the basin, indicating a shift to wetter conditions. Based on phytolith and stable carbon isotope data, cool-season C3 prairie species dominated the site at the time of the bison kill, and the micromammal faunal assemblage suggests that this boreal grassland may have been punctuated by stands of shrubby vegetation. Slight warming and drying occurred soon after ca. 10,300 B.P., indicated by relatively higher δ13C values determined on soil organic matter and a significant increase in concentrations of microscopic particulate charcoal and drought-resistant Stipa-type phytoliths, but paludal deposits continued to aggrade, resulting in deep burial of the bonebed. Sedimentation was relatively slow in the basin, allowing soil development to keep up with deposition. This cumulization process resulted in the formation of an overthickened A horizon in the Aggie Brown Member, typical of the Leonard Paleosol. Aggradation of the Aggie Brown Member ceased by ca. 8000 B.P., and loess comprising the Pick City Member began accumulating soon after that time, likely marking the initiation of the warm, dry Altithermal climatic episode. Isotope and phytolith data also point to a warmer and probably drier climate after 8000 B.P., indicated by higher δ13C values and the appearance of warm-season C4 chloridoids at the site. Hence the Agate Basin occupation coincided with the coolest and perhaps the wettest climatic episode recorded in the sampled deposits. However, it is likely that the people associated with the Agate Basin culture at Beacon Island did not experience environmental conditions dramatically different from the modern conditions at the site.

Short-term changes in soil Munsell colour value, organic matter content and soil water repellency after a spring grassland fire in Lithuania

Abstract. Fire is a natural phenomenon with important implications on soil properties. The degree of this impact depends upon fire severity, the ecosystem affected, topography of the burned area and post-fire meteorological conditions. The study of fire effects on soil properties is fundamental to understand the impacts of this disturbance on ecosystems. The aim of this work was to study the short-term effects immediately after the fire (IAF), 2, 5, 7 and 9 months after a low-severity spring boreal grassland fire on soil colour value (assessed with the Munsell colour chart), soil organic matter content (SOM) and soil water repellency (SWR) in Lithuania. Four days after the fire a 400 m2 plot was delineated in an unburned and burned area with the same topographical characteristics. Soil samples were collected at 0–5 cm depth in a 20 m × 20 m grid, with 5 m space between sampling points. In each plot 25 samples were collected (50 each sampling date) for a total of 250 samples for the whole study. SWR was assessed in fine earth (< 2 mm) and sieve fractions of 2–1, 1–0.5, 0.5–0.25 and < 0.25 mm from the 250 soil samples using the water drop penetration time (WDPT) method. The results showed that significant differences were only identified in the burned area. Fire darkened the soil significantly during the entire study period due to the incorporation of ash/charcoal into the topsoil (significant differences were found among plots for all sampling dates). SOM was only significantly different among samples from the unburned area. The comparison between plots revealed that SOM was significantly higher in the first 2 months after the fire in the burned plot, compared to the unburned plot. SWR of the fine earth was significantly different in the burned and unburned plot among all sampling dates. SWR was significantly more severe only IAF and 2 months after the fire. In the unburned area SWR was significantly higher IAF, 2, 5 and 7 months later after than 9 months later. The comparison between plots showed that SWR was more severe in the burned plot during the first 2 months after the fire in relation to the unburned plot. Considering the different sieve fractions studied, in the burned plot SWR was significantly more severe in the first 7 months after the fire in the coarser fractions (2–1 and 1–0.5 mm) and 9 months after in the finer fractions (0.5–0.25 and < 0.25 mm). In relation to the unburned plot, SWR was significantly more severe in the size fractions 2–1 and < 0.25 mm, IAF, 5 and 7 months after the fire than 2 and 9 months later. In the 1–0.5- and 0.5–0.25 mm-size fractions, SWR was significantly higher IAF, 2, 5 and 7 months after the fire than in the last sampling date. Significant differences in SWR were observed among the different sieve fractions in each plot, with exception of 2 and 9 months after the fire in the unburned plot. In most cases the finer fraction (< 0.25 mm) was more water repellent than the others. The comparison between plots for each sieve fraction showed significant differences in all cases IAF, 2 and 5 months after the fire. Seven months after the fire significant differences were only observed in the finer fractions (0.5–0.25 and < 0.25 mm) and after 9 months no significant differences were identified. The correlations between soil Munsell colour value and SOM were negatively significant in the burned and unburned areas. The correlations between Munsell colour value and SWR were only significant in the burned plot IAF, 2 and 7 months after the fire. In the case of the correlations between SOM and SWR, significant differences were only identified IAF and 2 months after the fire. The partial correlations (controlling for the effect of SOM) revealed that SOM had an important influence on the correlation between soil Munsell colour value and SWR in the burned plot IAF, 2 and 7 months after the fire.

Insights for lake management gained when paleolimnological and water column monitoring studies are combined: A case study from Baptiste Lake

Many lakes within the Boreal Plain and Grassland regions of Canada are currently eutrophic to hypereutrophic. Limited paleolimnological work has been conducted to define water quality trajectories of lakes within this region. A 25-year intermittent monitoring and a ∼150-year paleolimnological time series from Baptiste Lake, Alberta, were analyzed using a combination of trend, correlation, and multivariate analyses. The temporal overlap between the monitoring and paleolimnological time series provides an opportunity to assess coherence between the data sources. Diatom assemblages in the sediment core show that eutrophic conditions were present for at least 150 years. Monitored water chemistry data since the early 1980s show that total Kjeldahl nitrogen (TKN) has increased by approximately 50% since the early 1990s, whereas concentrations of total phosphorus (TP) have remained stable. Further, measured TKN is significantly correlated to measurements of chlorophyll a over the monitoring period and to diatom-inferred TKN values, suggesting nitrogen limitation in Baptiste Lake. In contrast, measured TP was not correlated to chlorophyll a or diatom-inferred TP. Changes in land use over the past 100 years is the most parsimonious explanation for the nutrient changes. No statistical support for climatic change as a linear predictor of nutrient dynamics was found. Our contemporary and paleolimnological analysis provides an important perspective on the timing and magnitude of nutrient dynamics over ∼150 years. Future government and community decisions on Baptiste Lake management would benefit from testing nutrient limitation and detailed modeling of nutrient runoff from the watershed.

Culturing and direct PCR suggest prevalent host generalism among diverse fungal endophytes of tropical forest grasses

Most studies examining endophytic fungi associated with grasses (Poaceae) have focused on agronomically important species in managed ecosystems or on wild grasses in subtropical, temperate and boreal grasslands. However grasses first arose in tropical forests, where they remain a significant and diverse component of understory and forest-edge communities. To provide a broader context for understanding grass-endophyte associations we characterized fungal endophyte communities inhabiting foliage of 11 species of phylogenetically diverse C3 grasses in the understory of a lowland tropical forest at Barro Colorado Island, Panama. Our sample included members of early-arising subfamilies of Poaceae that are endemic to forests, as well as more recently arising subfamilies that transitioned to open environments. Isolation on culture media and direct PCR and cloning revealed that these grasses harbor species-rich and phylogenetically diverse communities that lack the endophytic Clavicipitaceae known from diverse woodland and pasture grasses in the temperate zone. Both the incidence and diversity of endophytes was consistent among grass species regardless of subfamily, clade affiliation or ancestral habitat use. Genotype and phylogenetic analyses suggest that these endophytic fungi are predominantly host generalists, shared not only among distinctive lineages of Poaceae but also with non-grass plants at the same site.

Loss of density-dependence and incomplete control by dominant breeders in a territorial species with density outbreaks

BackgroundA territory as a prerequisite for breeding limits the maximum number of breeders in a given area, and thus lowers the proportion of breeders if population size increases. However, some territorially breeding animals can have dramatic density fluctuations and little is known about the change from density-dependent processes to density-independence of breeding during a population increase or an outbreak. We suggest that territoriality, breeding suppression and its break-down can be understood with an incomplete-control model, developed for social breeders and social suppression.ResultsWe studied density dependence in an arvicoline species, the bank vole, known as a territorial breeder with cyclic and non-cyclic density fluctuations and periodically high densities in different parts of its range. Our long-term data base from 38 experimental populations in large enclosures in boreal grassland confirms that breeding rates are density-regulated at moderate densities, probably by social suppression of subordinate potential breeders. We conducted an experiment, were we doubled and tripled this moderate density under otherwise the same conditions and measured space use, mortality, reproduction and faecal stress hormone levels (FGM) of adult females. We found that mortality did not differ among the densities, but the regulation of the breeding rate broke down: at double and triple densities all females were breeding, while at the low density the breeding rate was regulated as observed before. Spatial overlap among females increased with density, while a minimum territory size was maintained. Mean stress hormone levels were higher in double and triple densities than at moderate density.ConclusionsAt low and moderate densities, breeding suppression by the dominant breeders, But above a density-threshold (similar to a competition point), the dominance of breeders could not be sustained (incomplete control). In our experiment, this point was reached after territories could not shrink any further, while the number of intruders continued to increase with increasing density. Probably suppression becomes too costly for the dominants, and increasing number of other breeders reduces the effectiveness of threats. In wild populations, crossing this threshold would allow for a rapid density increase or population outbreaks, enabling territorial species to escape density-dependency.

Improving the treatment of the vertical snow burial fraction over short vegetation in the NCAR CLM3

One deficiency of the NCAR Community Land Model (CLM3) is the disappearance of the simulated snow even in the middle of winter over a boreal grassland site due to unrealistically modeled high downward turbulent fluxes. This is caused by the inappropriate treatment of the vertical snow burial fraction for short vegetation. A new snow burial fraction formulation for short vegetation is then proposed and validated using in situ observations. This modification in the CLM3 largely removes the unrealistic surface turbulent fluxes, leading to a more reasonable snowmelt process, and improves the snow water equivalent (SWE) simulation. Moreover, global offline simulations show that the proposed formulation decreases sensible and latent heat fluxes as well as the ground temperature during the snowmelt season over short vegetation dominant regions. Correspondingly, the SWE is enhanced, leading to the increase in snowmelt-induced runoff during the same period. Furthermore, sensitivity tests indicate that these improvements are insensitive to the exact functional form or parameter values in the proposed formulation.

Field-scale spatial variation in yields and nitrogen fixation of clover-grass leys and in soil nutrients

Biological nitrogen fixation (BNF) plays a crucial role in organic farming and red clover (Trifolium pratense) is cultivated widely in boreal grasslands for BNF. A geostatistical method, model-based kriging, was used to determine the spatial variation in yield, clover content and BNF of clover-grass leys as well as soil chemical properties throughout two fields in 2004-2006. Based on this variation, principal component analysis (PCA) was used to determine the similar patterns of variation. On one location, total dry matter yields of the leys decreased over three production years from 9 700 to 4 100 kg ha-1, clover content from 53 to 26% and BNF from 150 to 40 kg N ha-1, whereas on the other location the yields increased from 6 500 to 7 100 kg ha-1, clover content from 52 to 62% and BNF from 100 to 120 kg N ha-1. Nutrient concentrations in soil also varied greatly within the fields, although this depended on the nutrient species. Kriging combined with PCA described the spatial variation of ley parameters very informatively, but was not as powerful for describing the pattern of nutrients. Based on the spatial dependence determined in the two fields investigated, it seems that the sampling distance should be 80 m for soil nutrients, 100 m for yield and 60 m for clover content and BNF determination, respectively.;

Comparison of carbon and water vapor exchange of forest and grassland in permafrost regions, Central Yakutia, Russia

Boreal grasslands have been largely neglected in carbon and water vapor flux models despite being originated by past global climate changes. Therefore in this study, meteorological conditions, water vapor and CO 2 fluxes were measured by the eddy correlation technique simultaneously in a larch forest and alas ecosystem (grassland thermokarst depression) in Central Yakutia, eastern Siberia, during the growing season of 2006 (approximately 100 days, May 23rd–August 31st). The alas ecosystem was a carbon sink (−1.38 tC ha −1) but had a 60% lower carbon sequestration capacity than the surrounding larch forest (−3.44 tC ha −1) during the study period. Despite this large difference in carbon exchange, water loss from the alas ecosystem (118 mm) was only 13% lower than that from the forest ecosystem (136 mm). Water vapor flux measured in the alas was higher under similar environmental conditions when the source was the lake water than when the source was the grassland. This supports the theory that lake evaporation contributes significantly to the evaporation from the alas as indicated also by the lake water level constant decrease during the growing season. Mid-summer forest and alas mean evapotranspiration was 1.4 and 1.2 mm d −1 respectively. Mean daily canopy conductance was higher in the forest than in the alas (3.8 and 2.4 mm s −1, respectively) as expected due to differences in canopy architecture at each site. In this study a rough estimate of the NEE of grassland in Central Yakutia shows an underestimation of 0.9 × 10 −3 Pg if this area is considered as forested, as most regional models do. Our results suggest that a more detail analysis of distinctive areas within the territory of eastern Siberia is needed in order to obtain a better understanding of carbon and water fluxes from this immense boreal region. Furthermore, if the present global warming evokes landscape change from forest to grassland, the carbon sink capacity of this boreal region could be significantly reduced.

Importance of boreal grasslands in Sweden for butterfly diversity and effects of local and landscape habitat factors

A widespread decline in biodiversity in agro-ecosystems has been reported for several groups of organisms in Western Europe. The butterfly fauna was studied in 60 selected semi-natural grasslands in a coniferous-dominated boreal landscape in south-eastern Sweden. The aim was to investigate how butterfly assemblages were affected by the amount of semi-natural grasslands in the surrounding landscape. Furthermore, we wanted to determine if semi-natural grasslands in boreal landscapes harboured species otherwise declining in other parts of Europe. For each study site, the amounts of semi-natural grasslands in the landscape within radii of 500, 2,000 and 5,000 m were studied. Nine local habitat factors were also recorded. Only the amount of semi-natural grasslands within a 5,000 m radius could explain a significant part of the variation in butterfly composition, but there was no clear relationship between the amount of semi-natural grassland and butterfly diversity. Instead, this study showed that local habitat quality was very important for butterfly diversity at individual sites. Flower abundance, sward height and herb composition were the most important local factors. Patches surrounded by a small amount of semi-natural grasslands had high butterfly diversity, contrary to expectations. This may be explained by the fact that forest habitat provides a matrix with several features suitable for butterflies. The butterfly fauna was rich in species representative of low-productivity grasslands, species that are declining in other countries in Western Europe.

Simulation and quantification of pasture condition and animal performance on boreal grasslands in Alberta

We developed a computer model (PASTURE) to simulate both condition of pastures grazed by farmed wildlife and animal performance as dual measures of system performance. For representative habitat types (e.g., aspen forest and open grasslands), the model simulates herbage growth, maturation and senescence, habitat and diet selection, and nutrient intake of several wild ruminant species. The model generated seasonal patterns of pasture productivity and animal behavior expected for Bromus-Poa pastures in aspen boreal ecosystems. Model calibration was conducted using data collected from studies conducted within the aspen boreal ecosystems at the Ministik Research Station in 1997 and 1998, and Elk Island National Park and the University of Alberta greenhouse in 1999 and parameters adjusted until the predicted and observed results were visibly close. Evaluation of the model was conducted using statistical criteria of calculating average error, root mean square, root mean square error, coefficient of residual mass and modeling efficiency and comparing these statistics against optimal values. Statistical tests indicated a good fit between predicted and observed values for cumulative phytomass, herbage use and animal performance.

Quantification and Simulation of Grazing Impacts on Soil Water in Boreal Grasslands

AbstractWe conducted a 2‐year study in central Alberta to quantify and simulate the soil water status of boreal grasslands under three grazing systems using wapiti (Cervus elaphus Canadensis), viz. (1) ungrazed control (UNG), (2) high intensity [4.16 animal unit month per ha (AUM) ha−1 ] short‐duration grazing (SDG) and (3) moderate intensity (2.08 AUM ha−1) continuous grazing (CG). Soil water was measured from May 1997 to September 1998 to a depth of 15 cm. Total annual precipitation in 1997 and 1998 was 494 and 429 mm respectively. In both years grazing treatments reduced soil water. Soil water content under SDG was significantly (P < 0.05) lower than CG. Simulation of soil water on each grazing system was conducted using PASTURE, a simple compartmental system dynamics model. Evaluation of the model was conducted using statistical criteria that included calculation of average error, root mean square, coefficient of residual mass and modelling efficiency and comparing these statistics against optimal values. Although the model under‐predicted soil water, simulations of soil water for grazing treatments in both years were closest to measured values with modelling efficiency (how well observed values are close to simulated values) up to 68 %.