Ecosystem-scale spatial heterogeneity of stable isotopes of soil nitrogen in African savannas

Soil ¹⁵N is a natural tracer of nitrogen (N) cycling. Its spatial distribution is a good indicator of processes that are critical to N cycling and of their controlling factors integrated both in time and space. The spatial distribution of soil δ¹⁵N and its underlying drivers at sub-kilometer scales are rarely investigated. This study utilizes two sites (dry vs. wet) from a megatransect in southern Africa encompassing locations with similar soil substrate but different rainfall and vegetation, to explore the effects of soil moisture and vegetation distribution on ecosystem-scale patterns of soil δ¹⁵N. A 300-m long transect was set up at each site and surface soil samples were randomly collected for analyses of δ¹⁵N, %N and nitrate content. At each soil sampling location the presence of grasses, woody plants, Acacia species (potential N fixer) as well as soil moisture levels were recorded. A spatial pattern of soil δ¹⁵N existed at the dry site, but not at the wet site. Woody cover distribution determined the soil δ¹⁵N spatial pattern at ecosystem-scale; however, the two Acacia species did not contribute to the spatial pattern of soil δ¹⁵N. Grass cover was negatively correlated with soil δ¹⁵N at both sites owing to the lower foliar δ¹⁵N values of grasses. Soil moisture did not play a role in the spatial pattern of soil δ¹⁵N at either site. These results suggest that vegetation distribution, directly, and water availability, indirectly, affect the spatial patterns of soil δ¹⁵N through their effects on woody plant and grass distributions.     

Estimating regional forest productivity and water yield using an ecosystem model linked to a GIS

We used the PnET-II model of forest carbon and water balances to estimate regional forest productivity and runoff for the northeastern United States. The model was run at 30 arc sec resolution (approximately 1 km) in conjunction with a Geographic Information System that contained monthly climate data and a satellite-derived land cover map. Predicted net primary production (NPP) ranged from 700 to 1450 g m² yr¹ with a regional mean of 1084 g m² yr¹. Validation at a number of locations within the region showed close agreement between predicted and observed values. Disagreement at two sites was proportional to differences between measured foliar N concentrations and values used in the model. Predicted runoff ranged from 24 to 150 cm yr¹with a regional mean of 63 cm yr¹. Predictions agreed well with observed values from U.S. Geologic Survey watersheds across the region although there was a slight bias towards overprediction at high elevations and underprediction at lower elevations.Spatial patterns in NPP followed patterns of precipitation and growing degree days, depending on the degree of predicted water versus energy limitation within each forest type. Randomized sensitivity analyses indicated that NPP within hardwood and pine forests was limited by variables controlling water availability (precipitation and soil water holding capacity) to a greater extent than foliar nitrogen, suggesting greater limitations by water than nitrogen for these forest types. In contrast, spruce-fir NPP was not sensitive to water availability and was highly sensitivity to foliar N, indicating greater limitation by available nitrogen. Although more work is needed to fully understand the relative importance of water versus nitrogen limitation in northeastern forests, these results suggests that spatial patterns of NPP for hardwoods and pines can be largely captured using currently available data sets, while substantial uncertainties exist for spruce-fir.     

Plant productivity and nitrogen gas fluxes in a tallgrass prairie landscape

We explored relationships between plant productivity and annual fluxes of nitrogen (N₂) and nitrous oxide (N₂O) in a tallgrass prairie landscape in central Kansas. Our objective was to develop predictive relationships between these variables that could be used in conjunction with remote sensing information on plant productivity to produce large-area estimates of N gas fluxes. Our hypothesis was that there are inherent relationships between plant productivity and N gas fluxes in tallgrass prairie because both are controlled by water and N availability. The research was carried out as part of a multi-investigator project, the First ISLSCP Field Experiment (FIFE, ISLSCP = International Satellite Land Surface Climatology Program), directed toward the use of remote sensing to characterize land-atmosphere interactions. Fluxes of N₂ (denitrification) and N₂O were measured using soil core techniques. Estimates of annual flux were produced by temporal extrapolation of measured rates. Annual aboveground net primary productivity (ANPP) was estimated from measurements of the maximum standing crop of plant biomass. There were strong relationships between ANPP and N gas fluxes, and between a satellite remote sensing-based index of plant productivity (normalized difference vegetation index, NDVI) and gas fluxes. We used these relationships to convert images of NDVI into images of N gas fluxes for one 83 ha watershed and for the entire 15 by 15 km FIFE site. These images were used to compute mean landscape gas fluxes (0.62 g N m^-2 y^-1 for N₂, 0.66 g N m^-2 y^-1 for N₂O) and total N gas production for the two areas. Our flux and production values are useful for comparison with values produced by simulation models and site-specific studies, and for assessing the significance of N gas production to ecosystem and landscape scale processes related to nutrient cycling, water quality and atmospheric chemistry.     

Scaling up ecosystem productivity from patch to landscape: a case study of Changbai Mountain Nature Reserve,China

Scaling up ecosystem processes from plots to landscapes is essential for understanding landscape structure and functioning as well as for assessing ecological impacts of land use and climate change. This study illustrates an upscaling approach to studying the spatiotemporal pattern of ecosystem processes in the Changbai Mountain Nature Reserve in northeastern China by integrating simulation modeling, GIS, remote sensing data, and field-based observations. The ecosystem model incorporated processes of energy transfer, plant physiology, carbon dynamics, and water cycling. Using a direct extrapolation scheme, the patch-level ecosystem model was scaled up to quantify the landscape-level pattern of primary productivity and the carbon source-sink relationship. The simulated net primary productivity (NPP) for the entire landscape, consisting of several ecosystem types, was 0.680 kg C m⁻² yr⁻¹. The most widely distributed ecosystem type in this region was the mixed broad-leaved and Korean pine (Pinus koraiensis) forest, which had the highest NPP (1.084 kg C m⁻² yr⁻¹). The total annual NPP for all ecosystem types combined was estimated to be 1.332 Mt C yr⁻¹. These results suggest that the Changbai Mountain landscape as a whole was a carbon sink, with a net carbon sequestration rate of about 0.884 Mt C yr⁻¹ for the study period. The simulated NPP agreed reasonably well with available field measurements at a number of locations within the study landscape. Our study provides new insight into the relationship between landscape pattern and ecosystem processes, and useful information for improving management practices in the Changbai Mountain Nature Reserve, which is one of the most important forested landscapes in China. Several research needs are discussed to further refine the modeling approach and reduce prediction uncertainties.     

果园生草试验及适生草种评价

试验以自然生草和自然生草＋人工生草（紫花苜蓿、白三叶、红三叶、早熟禾、高羊茅和黑麦草）的‘寒富’苹果园为研究对象,以清耕为对照,研究了自然生草对土壤理化性质、微生物数量和酶活性的影响,并对自然生草条件下的人工草种进行了初步评价。结果表明,与对照相比,自然生草处理土壤pH值、有机质、全氮、全磷、碱解氮、速效磷、速效钾、细菌、真菌、放线菌、脲酶和磷酸酶明显升高,全钾增幅较小,但含水量降低了。通过适宜草种评价的初步研究可知,以生草覆盖为目的、刈割次数少的可选择白三叶、高羊茅和黑麦草等品种;为增加土壤有机质、提高土壤肥力,需要刈割用于覆盖的则应选择紫花苜蓿、红三叶等产草量较高的草种。     

Estimating primary productivity of forested wetland communities in different hydrologic landscapes

Five forested wetland sites in western Kentucky with hydrologic regimes varying from seasonally to continuously flooded were investigated for net above-ground biomass productivity (litterfall plus biomass growth) and for possible indicators of that productivity, including abiotic (flooding frequency and depth, phosphorus concentrations in water and sediments) and biotic (biomass, tree density, basal area, structural complexity, and mean height) indices. Net biomass productivity ranged from 205 g m^-2y^-1 for a stagnant semipermanently flooded Taxodium swamp to 1,334 g m^-2y^-1 in a bottomland forest along the Ohio River. Productivity was highest in wetlands with pulsing hydroperiods, intermediate with slowly flowing systems, and lowest with stagnant conditions. Surface water flooding of the wetlands during the growing season ranged from 17 to 100 percent of the year and did not predict productivity. Phosphorus concentrations in water and in sediments were not correlated to one another and did not, by themselves, predict productivity. No single abiotic variable predicted the exact ranking of productivity of the sites. Of the biotic variables, average tree diameter was inversely related to productivity.     

Human appropriated net primary productivity as a metric for land use planning: a case study in the US Great Lakes region

Context

Human appropriation of net primary productivity (HANPP) is employed as a measure of human pressures on biodiversity, though largely at global and national scales rather than landscape to regional scales where many conservation decisions take place. Though gaining in familiarity, HANPP is not widely utilized by conservation professionals.

Objectives

This study, encompassing the US side of the Great Lakes basin, examines how regional distributions of HANPP relate to landscape-based biodiversity proxy metrics used by conservation professionals. Our objectives were (1) to quantify the HANPP of managed lands at the county scale; and (2) to assess spatial patterns of HANPP in comparison to landscape diversity and local habitat connectedness to determine if the metric can provide useful information to conservation professionals.

Methods

We aggregated forest and cropland NPP data between 2005 and 2015 and coupled it with previously published potential vegetation maps to quantify the HANPP of each county in the study region. We mapped the outputs at 500 m resolution to analyze spatial relationships between HANPP and landscape metrics of biodiversity potential.

Results

Area-weighted HANPP across our study region averaged 45% of NPP, down to 4.9% in forest-dominated counties. Greater HANPP correlated with reduced landscape diversity (p?<?0.001, r²?=?0.28) and reduced local habitat connectedness (p?<?0.001, r²?=?0.36).

Conclusion

HANPP could be used as an additional tool for conservation professionals during regional-scale land use planning or conservation decision-making, particularly in mixed-use landscapes that both support important biodiversity and have high levels of primary production harvest.

     

Relationships between canopy size,light interception and productivity in conventional avocado planting systems

Avocado (Persea americana Mill.) is a relatively under-developed tree crop, grown commercially in climates ranging from tropical to temperate. Orchard productivity across a broad range of tree crops has been demonstrated to be related to total light interception. However, little information is currently available for avocado. Here we document the relationships between canopy volume per hectare, total orchard light interception and yield per ha for avocados of cultivar ‘Hass’ grown in low density planting systems. Total orchard light interception increased with canopy volume, with increases in light interception per unit canopy volume becoming smaller at the higher levels of canopy volume/ha. Yield/ha increased with light interception and canopy volume up to approximately 80–84% total light interception and 30,000–35,000 m³ canopy volume/ha. It is unclear whether the trend in yield/ ha at the very highest measured levels of orchard light interception and canopy volume should be described as plateauing or declining. Mean fruit weight decreased as light interception increased, although the relationship varied between seasons. For these conventional planting systems there is no yield benefit from increasing canopy light interception above 80–84%, and there may be yield decline at higher levels of orchard light interception.     

Small-scale patch structure in North American and South African grasslands responds differently to fire and grazing

Fire and grazing significantly impact small-scale patch structure and dynamics in savanna grasslands. We assessed small-scale grass-forb associations in long-term fire and grazing experiments in North America (NA) and Southern Africa (SA). Transects of 128 0.25 m² contiguous quadrats were sampled in areas with different combinations of grazing (ungrazed, single grazer, or multiple grazers) and fire frequency (unburned or annually burned). We predicted that (1) the patch structure of each of the dominant grasses in NA and SA would respond similarly to fire and grazing, and (2) that forb richness would be correlated to grass patch structure. Semi-variance analysis was used to determine patch structure of dominant grasses and forb cover. Community structure responded similarly in NA and SA to fire, grazing, and fire-grazing interactions. Species richness, diversity, and community heterogeneity were significantly higher in unburned-grazed sites. Grazing significantly increased forb cover and decreased cover of the dominant grasses, and the effects of fire on community structure depended on the grazing regime. Contrary to our prediction, we found that small-scale patch structure of the dominant grass species in NA and SA responded differently to grazing and fire. We found strong grass patch structure in unburned-ungrazed grasslands in both sites; however, grazing and fire reduced patch structure in NA but not SA, and in no instance did grass patch structure influence forb community structure. We conclude that fire and grazing have larger impacts on small-scale patch structure in NA than they do in SA even though overall community structure responded similarly on both continents.     

Microclimate influences on vegetation water availability and net primary production in coastal ecosystems of Central California

Field sampling and satellite remote sensing were used to test the hypothesis that site microclimate variability leading to divergent soil water use by vegetation types is closely associated with variability in annual net primary productivity (NPP) at the landscape scale. A simulation model based on satellite observations of seasonal phenology was used to estimate NPP of grassland, shrubland, and conifer forest vegetation types on the Central California coast near Big Sur. Daily microclimate at the soil surface was monitored over 4 years (2008–2011) for each vegetation type to infer soil moisture controls on plant production. Grassland soils were found to have lower soil organic matter content and were subjected to extreme radiation and wind events, and thereby dry-down faster with daily spring–summer warming than do shrubland or redwood forest soils. This reduced moisture microclimate affected the water stress on grassland plants to reduce NPP fluxes from April to October each year on the Central Coast far sooner than for shrubland or redwood stands. Results from this study suggested that the satellite-observed canopy greenness variations represented can be used to quantify plant production in coastal ecosystems at the landscape scale of defined microclimate variation.     

Alternative spatial resolutions and estimation of carbon flux over a managed forest landscape in Western Oregon

Spatially-distributed estimates of biologically-driven CO₂ flux are of interest in relation to understanding the global carbon cycle. Global coverage by satellite sensors offers an opportunity to assess terrestrial carbon (C) flux using a variety of approaches and corresponding spatial resolutions. An important consideration in evaluating the approaches concerns the scale of the spatial heterogeneity in land cover over the domain being studied. In the Pacific Northwest region of the United States, forests are highly fragmented with respect to stand age class and hence C flux. In this study, the effects of spatial resolution on estimates of total annual net primary production (NPP) and net ecosystem production (NEP) for a 96 km² area in the central Cascades Mountains of western Oregon were examined. The scaling approach was a simple `measure and multiply' algorithm. At the highest spatial resolution (25 m), a stand age map derived from Landsat Thematic Mapper imagery provided the area for each of six forest age classes. The products of area for each age class and its respective NPP or NEP were summed for the area wide estimates. In order to evaluate potential errors at coarser resolutions, the stand age map was resampled to grain sizes of 100, 250, 500 and 1000 m using a majority filter reclassification. Local variance in near-infrared (NIR) band digital number at successively coarser grain sizes was also examined to characterize the scale of the heterogeneity in the scene. For this managed forest landscape, proportional estimation error in land cover classification at the coarsest resolution varied from –1.0 to +0.6 depending on the initial representation and the spatial distribution of the age class. The overall accuracy of the 1000 m resolution map was 42% with respect to the 25 m map. Analysis of local variance in NIR digital number suggested a patch size on the order of 100–500 m on a side. Total estimated NPP was 12% lower and total estimated NEP was 4% lower at 1000 m compared to 25 m. Carbon flux estimates based on quantifying differences in total biomass stored on the landscape at two points in time might be affected more strongly by a coarse resolution analysis because the differences among classes in biomass are more extreme than the differences in C flux and because the additional steps in the flux algorithm would contribute to error propagation. Scaling exercises involving reclassification of fine scale imagery over a range of grain sizes may be a useful screening tool for stratifying regions of the terrestrial surface relative to optimizing the spatial resolution for C flux estimation purposes.     

In the bleak mid-winter: The value of brownfield sites for birds during the winter

Brownfield sites (e.g., wastelands, disused industrial grounds and power stations) are valuable refuges for urban birds during the breeding season. This owes to the presence of vegetation in different stages of succession, which provide a high diversity of food and breeding resources. However, insufficient research has explored their winter value, when temperatures are lower and food is scarcer. Accordingly, 342 bird and habitat surveys were conducted in brownfield sites, and other land-uses, across Greater Manchester. Bird density estimates were then calculated using Distance software and bird-habitat associations were analysed using Canonical Correspondence Analysis (CCA). Moreover, the impact of brownfield site development on winter bird density from 2000 to 2009 in Greater Manchester was explored using the bird density estimates, and historical image function in Google Earth. In brownfield sites, Pica pica had the highest density estimate (142 per km²), although four species had estimated densities > 100 per km² (Turdus merula; Cyanistes caeruleus; Passer domesticus; Aegithalos caudatus). The CCA indicated that Aegithalos caudatus, Cyanistes caeruleus, Parus major, Prunella modularis were associated with Fagus sylvatica, Betula pendula, and Buddleja davidii on brownfield sites, which during the winter 1) produce seeds 2) support overwintering insects, providing a valuable food source. Nevertheless, across land-uses, most species favoured green space and pre-2000 housing. Brownfield sites were most replaced between 2000 and 2009, with 17.8 km², 14.9 km², and 12 km² replaced by commercial, industrial, and post-2000 housing respectively. This is likely to have had a negative impact on the winter density of most bird species, owing to 1) the removal of brownfield site vegetation 2) increases in impervious land cover. Future declines in winter bird abundance could be mitigated by retaining brownfield site vegetation and setting aside brownfield sites in close proximity to green space and pre-2000 housing.     

Scale-Dependent Influence of Topography-Based Hydrologic Features on Patterns of Woody Plant Encroachment in Savanna Landscapes

Rainfall in drylands is erratic. Topographic features of landscapes can dampen or amplify temporal variability by spatially influencing patterns of water loss and accumulation. The extent to which portions of a landscape may differentially capture or retain scarce water and nutrient resources is an important determinant of vegetation patterns, particularly with respect to the distribution of woody plants. We therefore hypothesized that historic changes in woody cover on landscapes experiencing similar climate and disturbance regimes would vary with catena-to-catena (hillslope-to-hillslope) variation in topography-based hydrologic features. We tested this hypothesis by comparing topographic wetness index (TWI) values on replicate landscapes where woody plant abundance has increased over the past 100 yr. These landscapes are characterized by savanna parklands on coarse-textured upland portions of catenas that grade (1–3% slopes) into closed-canopy woodlands on fine-textured (lowland) portions of catenas. TWI values for woody and herbaceous communities were comparable within uplands, suggesting factors unrelated to surface/subsurface hydrology determine patterns of woody cover in these catena locations. TWI values for upland savanna parklands were significantly lower than those of closed-canopy woodlands occupying catena footslopes. Furthermore, uplands adjoining historically static woodland boundaries had lower TWI values than those where woodland boundaries had moved upslope 2.1 m yr⁻¹ from 1976 to 1995. Results suggest runoff–runon relationships influence patterns of woody plant cover and change at the catena scale and may override constraints imposed by soil texture. As a result, changes in woody cover potentially accompanying changes in disturbance regimes, climate or atmospheric chemistry are likely to be constrained by topoedaphic settings. Models of vegetation dynamics may therefore need to explicitly account for rainfall–topography–soil texture relationships and associated scale-dependent mechanisms to accurately predict rates and patterns of change in woody and herbaceous plant abundance.     

Net primary productivity (NPP) dynamics and associated urbanization driving forces in metropolitan areas: a case study in Beijing City,China

Context

Eco-environmental effects of urbanization are a focus in landscape ecology.

Objective

The influences of population, economic and spatial development during the urbanization process in Beijing City, China on net primary productivity (NPP) were analyzed. The responding mechanism of NPP in different urbanization stages was also examined to develop advice about eco-environmental sustainability of urban development.

Methods

Using the Carnegie Ames Stanford Approach model, we estimated NPP. Using linear regression and polynomial regression analysis, we analyzed NPP responses to stages of urbanization.

Results

High NPP areas were located in northeast Yanqing, northwest Miyun, northern Huairou and Pinggu. The distribution of NPP generally occurred in the following order from high NPP to low NPP: outer suburbs, inner suburbs, encircled city center, and inner city. Because of the heat island effect in winter, the estimated NPP in the encircled city center and inner city was higher in 2009 than in 2001. There was a negative correlation between NPP and both economic and spatial urbanization, but an increase in population did not necessarily lead to an immediate decrease in NPP. An analysis of NPP dynamics in five kinds of urban development zones showed that urbanization resulted in a lasting and observable loss of NPP over time and space, although there was some promotion of NPP in highly urbanized zones.

Conclusion

There are three stages in the response of NPP to urbanization: damage stage, antagonistic stage, and coordination stage. The stage threshold depends on local eco-environmental management and urban planning interventions.

     

Human-scale structural heterogeneity induced by grazing in a Mediterranean woodland landscape

A set of structural criteria to differentiate among types of a heterogeneous woodland landscape that are shaped by goat and cattle grazing was studied in northern Israel. The landscape was described with relation to the “human scale” of the observer, by mapping the dimensions, basic shapes, and distribution of gaps between individual plants on sites with various grazing management systems. The shapes of the trees and the bushes were drawn in situ and the ratio between plant height and the width of the adjacent open space was measured in order to define the various structural profiles of the vegetation. All the structural criteria clearly and significantly differentiated among grazing systems that created closed (no grazing), half-open (cattle and modern goat grazing) and open (traditional goat grazing) landscapes. The diversity of plant shapes was highest under the cattle and modern goat grazing management systems. In the ungrazed treatment, more than 60% of the gaps were defined as ‘inaccessible’ compared with only 10–15% under cattle grazing and modern goat grazing. The diversity of gap proportions was high, but their absolute number was low. Under traditional heavy goat grazing, there were only wide and open gaps. Under cattle grazing and modern goat-grazing management systems, a relatively large number of wide and open gaps were found, with small numbers of narrow and closed gaps. Overall, the various grazing systems were differentiated most clearly according to their transparency, accessibility, height of Quercus calliprinos, and gap distribution. We conclude that structural criteria provide an efficient and objective methodology for evaluating the effects of grazing on different components of Mediterranean woodland mosaic landscapes. Nomenclature follows Feinbrun-Dothan and Danin (1991)     

Tree-grass coexistence in a flood-disturbed, semi-arid savanna system

The coexistence of trees and grasses in savanna ecosystems is a contentious phenomenon. Fire and herbivory disturbances are often cited as major structuring forces that create a sustainable tree–grass relationship. However, periodic flooding of savanna patches may also enable coexistence. The aim of this study was to investigate the effects of flood-disturbance on the recruitment patterns of Acacia karroo trees in a semi-arid savanna system in South Africa. We analysed the spatial coincidence of A. karroo seedlings with tussocks of the tall spiny grass Stipagrostis namaquensis in the riverbed and related herbivory intensity to spatial position. The data showed that A. karroo seedlings were significantly positively associated with S. namaquensis (Chi-square test, $ \chi_{1}^{2} = 4 5. 20 $ , n = 118, P < 0.001); A. karroo seedlings growing inside of tussocks experienced less browsing pressure than those growing in the floodplain (Kruskal–Wallis test, H = 11.90, n = 118, P < 0.01); and recruitment success of A. karroo trees was spatially discrete (K–S test, D = 0.78, n = 196, P < 0.01). We suggest that floods create an enemy-free zone, which S. namaquensis colonises and then facilitates successful A. karroo establishment. High levels of A. karroo recruitment in the riverbed may replenish the woodlands fringing the river, which appear to be sink areas for A. karroo seedlings. Thus, the interaction between disturbances at different spatial and temporal scales (flooding versus herbivory) seems to maintain the inherently unstable coexistence of tree and grass species in this ecosystem. These findings also suggested that flood disturbances alter the tree–grass relationship.     

Primary productivity in cities and their influence over subtropical bird assemblages

Changes in ecosystem structure caused by urbanization produce a reduction in photosynthetic productivity, which can lead to reductions in resource availability for birds. Here, we analyzed the relation between photosynthetic productivity and bird assemblages in a subtropical urban ecosystem, in North-Western Argentina. We used Generalized Linear Models to assess the responses of bird abundance, richness and diversity to photosynthetic productivity, vegetation cover and distance to main natural forest. We found higher bird richness and diversity with increasing photosynthetic productivity and vegetation cover, and with decreasing distance to forests; while total bird abundance was positively related to vegetation cover. When we classified bird species in different groups, based on their use of the environment, we found that species adapted to urban environments were more dependent on photosynthetic productivity, while species related to native forests were more dependent on the distance to source forests. Understanding the factors that affect bird assemblages in cities is important for the development of strategies for urban planning and conservation.     

The influence of spatial configuration of green areas on microclimate and thermal comfort

It has been shown that the spatial configuration of a green area can strongly influence its cooling effect. However, the specific correlation has not been sufficiently studied. To systematically clarify the correlation between the spatial configuration and the cooling effect of green areas, 25 idealized scenarios are designed and simulated using the microclimate model ENVI-met. These 25 scenarios represent green areas with five different spatial configurations (integrated green area, sparse dotted green areas, dense dotted green areas, belt-shaped green areas parallel to wind direction, and belt-shaped green areas vertical to wind direction) and five vegetation types (trees with big canopies, trees with small canopies, hedges and shrubs, 50 cm grass, and 10 cm grass). The human thermal comfort of each scenario is evaluated by means of physiologically equivalent temperature (PET) using Rayman. The results reveal the influence of the fragmentation degree (quantified by the patch density and edge density), shape complexity (quantified by the land shape index), orientation of green belt, and vegetation type on the cooling effect of a green area. The spatial configuration and the vegetation type of green areas were found jointly affecting the efficiency of the green areas’ cooling effect. The highest cooling effect appears at 2 pm, reaching 6.3 K in the scenario of belt-shaped green areas parallel to the wind direction and with big canopy trees. The conclusions of this paper can provide suggestions for the climate-adaptive design and planning of urban green areas in the future.     

Drivers of the dynamics in net primary productivity across ecological zones on the Mongolian Plateau

Understanding the drivers and mechanisms of the dynamics in grassland productivity is prerequisite for studying effective resource institutions and policies that can be used to govern grassland resources sustainably. We present a diagnostic analysis of the major drivers of the dynamics in grassland net primary productivity (NPP) across ecological zones on the Mongolian Plateau. We estimated a spatial panel data model for NPP (1986–2009) as a function of climatic and socioeconomic variables. Static and dynamic spatial panel models were estimated in each of the sub-regions, which were classified based on rural livelihoods and ecological models of grassland dynamics, to identify the major drivers of NPP dynamics. The statistical modeling results indicated that the major drivers of NPP dynamics vary across the six sub-regions. Grain output was the major predictor of NPP dynamics in the farming and farming-grazing zones of Inner Mongolia. Precipitation and livestock populations both had significantly positive relationships with NPP in the two grazing zones of Inner Mongolia. However, in Mongolia, livestock populations was the only significant predictor of NPP in the grazing zone with relatively stable climate, and precipitation was the only significant predictor of NPP in the grazing zone with highly variable climate. Human land-use activities and livestock management behaviors and the bidirectional causal relationships between livestock populations and NPP could explain the positive relationships between livestock population and grassland NPP. The heterogeneous drivers of NPP dynamics across space indicated the necessity of diverse resource polices and institutions for sustainable governance of grassland resources.     

Spatial attenuation of ambient particulate matter air pollution within an urbanised native forest patch

Of interest to researchers and urban planners is the effect of urban forests on concentrations of ambient air pollution. Although estimates of the attenuation effect of urban vegetation on levels of air pollution have been put forward, there have been few monitored data on small-scale changes within forests, especially in urban forest patches. This study explores the spatial attenuation of particulate matter air pollution less than 10 μ in diameter (PM₁₀) within the confines of an evergreen broadleaved urban forest patch in Christchurch, New Zealand, a city with high levels of PM₁₀ winter air pollution. The monitoring network consisted of eight monitoring sites at various distances from the edge of the canopy and was operated on 13 winter nights when conditions were conducive for high pollution events. A negative gradient of particulate concentration was found, moving from higher mean PM10 concentrations outside the forest (mean=31.5 μg m^?3) to lower concentrations deep within the forest (mean=22.4 μg m^?3). A mixed-effects model applied to monitor meteorological, spatial and pollution data indicated temperature and an interaction between wind speed and temperature were also significant (P?0.05) predictors of particulate concentration. These results provide evidence of the potential role that urban forest patches may play in mitigating particulate matter air pollution and should be considered in plans for improving urban air quality.