Global Change Biology

The increasing urbanization process is hypothesized to drastically alter (semi‐)natural environments with a concomitant major decline in species abundance and diversity. Yet, studies on this effect of urbanization, and the spatial scale at which it acts, are at present inconclusive due to the large heterogeneity in taxonomic groups and spatial scales at which this relationship has been investigated among studies. Comprehensive studies analysing this relationship across multiple animal groups and at multiple spatial scales are rare, hampering the assessment of how biodiversity generally responds to urbanization. We studied aquatic (cladocerans), limno‐terrestrial (bdelloid rotifers) and terrestrial (butterflies, ground beetles, ground‐ and web spiders, macro‐moths, orthopterans and snails) invertebrate groups using a hierarchical spatial design, wherein three local‐scale (200 m × 200 m) urbanization levels were repeatedly sampled across three landscape‐scale (3 km × 3 km) urbanization levels. We tested for local and landscape urbanization effects on abundance and species richness of each group, whereby total richness was partitioned into the average richness of local communities and the richness due to variation among local communities. Abundances of the terrestrial active dispersers declined in response to local urbanization, with reductions up to 85% for butterflies, while passive dispersers did not show any clear trend. Species richness also declined with increasing levels of urbanization, but responses were highly heterogeneous among the different groups with respect to the richness component and the spatial scale at which urbanization impacts richness. Depending on the group, species richness declined due to biotic homogenization and/or local species loss. This resulted in an overall decrease in total richness across groups in urban areas. These results provide strong support to the general negative impact of urbanization on abundance and species richness within habitat patches and highlight the importance of considering multiple spatial scales and taxa to assess the impacts of urbanization on biodiversity.

Urbanization is a major driver of land use change and biodiversity decline. While most of the ongoing and future urbanization hotspots are located in the Global South, the impact of urban expansion on agricultural biodiversity and associated functions and services in these regions has widely been neglected. Additionally, most studies assess biodiversity responses at local scale (α‐diversity), however, ecosystem functioning is strongly determined by compositional and functional turnover of communities (β‐diversity) at regional scales. We investigated taxonomic and functional β‐diversity of farmland birds across three seasons on 36 vegetable farms spread along a continuous urbanization gradient in Bangalore, a South Indian megacity. Increasing amount of grey area in the farm surroundings was the dominant driver affecting β‐diversity and resulting in taxonomic and functional homogenization of farmland bird communities. Functional diversity losses were higher than expected from species declines (i.e., urbanization acts as an environmental filter), with particular losses of functionally important groups such as insectivores of crop pests. Moreover, urbanization reduced functional redundancy of bird communities, which may further weaken ecosystems resilience to future perturbations. Our study underscores urbanization as a major driver of taxonomic and functional homogenization of species communities in agricultural systems, potentially threatening crucial ecosystem services for food production.

Urbanization is one of the most extreme forms of environmental alteration, posing a major threat to biodiversity. We studied the effects of urbanization on avian communities via a systematic review using hierarchical and categorical meta‐analyses. Altogether, we found 42 observations from 37 case studies for species richness and 23 observations from 20 case studies for abundance. Urbanization had an overall strong negative effect on bird species richness, whereas abundance increased marginally with urbanization. There was no evidence that city size played a role in influencing the relationship between urbanization and either species richness or abundance. Studies that examined long gradients (i.e. from urban to rural) were more likely to detect negative urbanization effects on species richness than studies that considered short gradients (i.e. urban vs. suburban or urban vs. rural areas). In contrast, we found little evidence that the effect of urbanization on abundance was influenced by gradient length. Effects of urbanization on species richness were more negative for studies including public green spaces (parks and other amenity areas) in the sampled landscapes. In contrast, studies performed solely in the urban matrix (i.e. no green spaces) revealed a strong positive effect on bird abundance. When performing subset analyses on urban–suburban, suburban–rural and suburban–natural comparisons, species richness decreased from natural to urban areas, but with a stronger decrease at the urban–suburban interface, whereas bird abundance showed a clear intermediate peak along the urban–rural gradient although abundance in natural areas was comparable to that in suburban areas. This suggests that species loss happens especially at the urban–suburban interface, and that the highest abundances occur in suburban areas compared to urban or rural areas. Thus, our study shows the importance of suburban areas, where the majority of birds occur with fairly high species richness.

The Luxury Effect hypothesizes a positive relationship between wealth and biodiversity within urban areas. Understanding how urban development, both in terms of socio‐economic status and the built environment, affects biodiversity can contribute to the sustainable development of cities, and may be especially important in the developing world where current growth in urban populations is most rapid. We tested the Luxury Effect by analysing bird species richness in relation to income levels, as well as human population density and urban cover, in landscapes along an urbanization gradient in South Africa. The Luxury Effect was supported in landscapes with lower urbanization levels in that species richness was positively correlated with income level where urban cover was relatively low. However, the effect was reversed in highly urbanized landscapes, where species richness was negatively associated with income level. Tree cover was also positively correlated with species richness, although it could not explain the Luxury Effect. Species richness was negatively related to urban cover, but there was no association with human population density. Our model suggests that maintaining green space in at least an equal proportion to the built environment is likely to provide a development strategy that will enhance urban biodiversity, and with it, the positive benefits that are manifest for urban dwellers. Our findings can form a key contribution to a wider strategy to expand urban settlements in a sustainable way to provide for the growing urban population in South Africa, including addressing imbalances in environmental justice across income levels and racial groups.

A strong relationship between dissolved organic carbon (DOC) and sulphate (SO₄²⁻) dynamics under drought conditions has been revealed from analysis of a 10‐year time series (1993–2002). Soil solution from a blanket peat at 10 cm depth and stream water were collected at biweekly and weekly intervals, respectively, by the Environmental Change Network at Moor House‐Upper Teesdale National Nature Reserve in the North Pennine uplands of Britain. DOC concentrations in soil solution and stream water were closely coupled, displaying a strong seasonal cycle with lowest concentrations in early spring and highest in late summer/early autumn. Soil solution DOC correlated strongly with seasonal variations in soil temperature at the same depth 4‐weeks prior to sampling. Deviation from this relationship was seen, however, in years with significant water table drawdown (>−25 cm), such that DOC concentrations were up to 60% lower than expected. Periods of drought also resulted in the release of SO₄²⁻, because of the oxidation of inorganic/organic sulphur stored in the peat, which was accompanied by a decrease in pH and increase in ionic strength. As both pH and ionic strength are known to control the solubility of DOC, inclusion of a function to account for DOC suppression because of drought‐induced acidification accounted for more of the variability of DOC in soil solution (R²=0.81) than temperature alone (R²=0.58). This statistical model of peat soil solution DOC at 10 cm depth was extended to reproduce 74% of the variation in stream DOC over this period. Analysis of annual budgets showed that the soil was the main source of SO₄²⁻during droughts, while atmospheric deposition was the main source in other years. Mass balance calculations also showed that most of the DOC originated from the peat. The DOC flux was also lower in the drought years of 1994 and 1995, reflecting low DOC concentrations in soil and stream water. The analysis presented in this paper suggests that lower concentrations of DOC in both soil and stream waters during drought years can be explained in terms of drought‐induced acidification. As future climate change scenarios suggest an increase in the magnitude and frequency of drought events, these results imply potential for a related increase in DOC suppression by episodic acidification.

Mối quan hệ giữa dòng nitơ oxit (N₂O) và sự sẵn có của nitơ trong các hệ sinh thái nông nghiệp thường được giả định là tuyến tính, với tỷ lệ nitơ mất như N₂O không đổi bất kể mức đầu vào. Chúng tôi đã thực hiện một nghiên cứu phản ứng phân bón nitơ có độ phân giải cao kéo dài 3 năm tại tây nam Michigan, Mỹ, để kiểm tra giả thuyết rằng dòng N₂O tăng chủ yếu là do sự bổ sung nitơ vượt quá nhu cầu của cây trồng. Chúng tôi đã thêm urê ammonium nitrate hoặc urê hạt tại chín mức khác nhau (0–292 kg N ha⁻¹) vào bốn ô lặp lại của ngô liên tục. Chúng tôi đo dòng N₂O và lượng nitơ sẵn có trong đất hai tuần một lần sau khi bón phân và năng suất hạt vào cuối mùa sinh trưởng. Từ năm 2001 đến 2003, dòng N₂O ở mức bổ sung nitơ đến 101 kg N ha⁻¹, nơi mà năng suất hạt được tối ưu hoá, vào khoảng (ca. 20 g N₂O-N ha⁻¹ ngày⁻¹), sau đó dòng này tăng hơn gấp đôi (lên >50 g N₂O-N ha⁻¹ ngày⁻¹). Phản ứng ngưỡng này của N₂O đối với việc bón phân nitơ gợi ý rằng việc giảm dòng N₂O nông nghiệp có thể đạt được mà không hoặc ít ảnh hưởng đến năng suất bằng cách giảm đầu vào phân bón nitơ xuống các mức chỉ đáp ứng nhu cầu của cây trồng.

Atmospheric concentrations of the greenhouse gas nitrous oxide (N₂O) have continued to rise since the advent of the industrial era, largely because of the increase in agricultural land use. The urine deposited by grazing ruminant animals is a major global source of agricultural N₂O. With the first commitment period for reducing greenhouse gas emissions under the Kyoto Protocol now underway, mitigation options for ruminant urine N₂O emissions are urgently needed. Recent studies showed that increasing the urinary concentration of the minor urine constituent hippuric acid resulted in reduced emissions of N₂O from a sandy soil treated with synthetic bovine urine, due to a reduction in denitrification. A similar effect was seen when benzoic acid, a product of hippuric acid hydrolysis, was used. This current laboratory experiment aimed to investigate these effects using real cow urine for the first time. Increased concentrations of hippuric acid or benzoic acid in the urine led to reduction of N₂O emissions by 65% (from 17% to <6% N applied), with no difference between the two acid treatments. Ammonia volatilization did not increase significantly with increased hippuric acid or benzoic acid concentrations in the urine applied. Therefore, there was a net reduction in gaseous N loss from the soil with higher urinary concentrations of both hippuric acid and benzoic acid. The results show that elevating hippuric acid in the urine had a marked negative effect on both nitrification and denitrification rates and on subsequent N₂O fluxes. This study indicates the potential for developing a novel mitigation strategy based on manipulation of urine composition through ruminant diet.

Grassland ecosystems worldwide not only provide many important ecosystem services but they also function as a major source of the greenhouse gas nitrous oxide (N₂O), especially in response to nitrogen deposition by grazing animals. To explore the role of plants as mediators of these emissions, we tested whether and how N₂O emissions are dependent on grass species richness and/or specific grass species composition in the absence and presence of urine deposition. We hypothesized that: (i) N₂O emissions relate negatively to plant productivity; (ii) four‐species mixtures have lower emissions than monocultures (as they are expected to be more productive); (iii) emissions are lowest in combinations of species with diverging root morphology and high root biomass; and (iv) the identity of the key species that reduce N₂O emissions is dependent on urine deposition. We established monocultures and two‐ and four‐species mixtures of common grass species with diverging functional traits: Lolium perenne L. (Lp), Festuca arundinacea Schreb. (Fa), Phleum pratense L. (Php) and Poa trivialis L. (Pt), and quantified N₂O emissions for 42 days. We found no relation between plant species richness and N₂O emissions. However, N₂O emissions were significantly reduced in specific plant species combinations. In the absence of urine, plant communities of Fa+Php acted as a sink for N₂O, whereas the monocultures of these species constituted a N₂O source. With urine application Lp+Pt plant communities reduced (P < 0.001) N₂O emissions by 44% compared to monocultures of Lp. Reductions in N₂O emissions by species mixtures could be explained by total biomass productivity and by complementarity in root morphology. This study shows that plant species composition is a key component underlying N₂O emissions from grassland ecosystems. Selection of specific grass species combinations in the context of the expected nitrogen deposition regimes may therefore provide a key for mitigation of N₂O emissions.

Vegetation forms a main component of the terrestrial biosphere and plays a crucial role in land‐cover and climate‐related studies. Activity of vegetation systems is commonly quantified using remotely sensed vegetation indices (VI). Extensive reports on temporal trends over the past decades in time series of such indices can be found in literature. However, little remains known about the processes underlying these changes at large spatial scales. In this study, we aimed at quantifying the spatial relationship between changes in potential climatic growth constraints (i.e. temperature, precipitation and incident solar radiation) and changes in vegetation activity (1982–2008). We demonstrate an additive spatial model with 0.5° resolution, consisting of a regression component representing climate‐associated effects and a spatially correlated field representing the combined influence of other factors, including land‐use change. Little over 50% of the spatial variance could be attributed to changes in climatologies; conspicuously, many greening trends and browning hotspots in Argentina and Australia. The nonassociated model component may contain large‐scale human interventions, feedback mechanisms or natural effects, which were not captured by the climatologies. Browning hotspots in this component were especially found in subequatorial Africa. On the scale of land‐cover types, strongest relationships between climatologies and vegetation activity were found in forests, including indications for browning under warming conditions (analogous to the divergence issue discussed in dendroclimatology).

Surface soil moisture dynamics is a key link between climate fluctuation and vegetation dynamics in space and time. In East Asia, precipitation is concentrated in the short monsoon season, which reduces plants water availability in the dry season. Furthermore, most forests are located in mountainous areas because of high demand for agricultural land, which results in increased lateral water flux and uneven distribution of plant available water. These climatic and topographic features of the forests make them more vulnerable to drought conditions. In this study, the eco‐hydrological model (Regional Hydro‐Ecological Simulation System) is validated with various water and carbon flux measurements in a small catchment in Korea. The model is then extended to the regional scale with fine‐resolution remote sensing data to evaluate the Moderate Resolution Imaging Radiometer (MODIS) leaf area index and gross primary productivity (GPP) products. Long‐term model runs simulated severe drought effect in 2001 well, which is clearly shown in the ring increment data. However, MODIS GPP does not capture this drought effect in 2001, which might be from a simplified treatment of water stress in the MODIS GPP algorithm. This study shows that the MODIS GPP products can potentially overestimate carbon uptake specifically during drought conditions driven by soil water stress.