Partitioning spatial,environmental, and community drivers of ecosystem functioning

Landscape Ecology - Community composition, environmental variation, and spatial structuring can influence ecosystem functioning, and ecosystem service delivery. While the role of space in...     

Urban agglomeration of Kunming and Yuxi cities in Yunnan,China: the relative importance of government policy drivers and environmental constraints

Landscape Ecology - Political decisions and policies, as well as bio-physical factors are very important drivers of urban agglomeration, yet studies researching links between those factors,...     

Landscape-scale patterns and drivers of novel mammal communities in a human-modified protected area

Landscape Ecology - The role of protected areas as biodiversity repositories has become increasingly important in face of increased deforestation. By adding free-living exotic mammals, removing...     

Quantifying spatiotemporal drivers of environmental heterogeneity in Kruger National Park,South Africa

Context

Environmental heterogeneity is considered an important mechanism of biodiversity. How environmental heterogeneity is characterised by the compositional, structural and functional variation of biotic and abiotic components is a central research theme in conservation.

Objectives

We explore how environmental heterogeneity relates to the underlying physical landscape template and how that relationship changes over space and time. We examine how, in some areas, environmental heterogeneity may also be driven by dynamic ecological processes, and how this relates to patterns of plant species richness.

Method

We use local geographically weighted regression to spatially partition environmental heterogeneity, measured as Landsat spectral variance, into the portion explained by stable physical landscape properties (R²) and the portion unexplained (1?R²) which we term landscape complexity. We explore how this relationship varies spatially and temporally as a function of dynamic ecological processes such as rainfall and season in Kruger National Park, as well as plant species richness at landscape scales.

Results

The significance and direction of relationships varied over space and time and as a function of rainfall and season. R² values generally decreased in higher rainfall summer months and revealed patterns describing the importance of known stable factors relative to unknown dynamic factors. Landscape complexity (1?R²) explained over 70 % of variation in species richness.

Conclusions

Rainfall and seasonality are important drivers of environmental heterogeneity. The spatial arrangement and magnitude of model agreement helped disentangle the relative influence of the physical landscape template on environmental heterogeneity. Given the high correlation with species richness, landscape complexity provides complementary guidance to biodiversity research and monitoring prioritization.

     

Irrigation induced change in vegetation and evapotranspiration in the Central Valley of California

Landscape changes in the Central Valley of California, USA, have been dramatic over the past 100 years. Irrigated agriculture has replaced natural communities of California prairie, riparian forest, tule marsh, valley oak savannah, and San Joaquin saltbrush. This paper addresses the implication of vegetation change on evapotranspiration as a consequence of these changes. It was found that an increase in irrigated agriculture and a 60% reduction in the aerial extent of native vegetation has not produced significant changes in the moisture transfer to the atmosphere. The apparent reason for this result is that irrigated agriculture has substituted one actively transpiring surface for another and, therefore, has not significantly altered the transpiration flux of the landscape.     

Evolving landscapes in the headwaters area of the Yellow River (China) and their ecological implications

The relationship and feedback between landscape pattern, function and process serve to describe the behavior of a regional landscape. Based on landscape function characteristics such as biological productivity, soil nutrient content, vegetative cover, etc., a quantitative method and digital model for analyzing evolving landscape functionality in the headwaters area of the Yellow River in the People's Republic of China were devised. Through the analysis of three-phase remote sensing data from 1975, 1985 and 1995 and based upon the well-defined characteristics of this region's evolving landscape over the past 30 years, the attendant ecology of the different functional landscape ecotypes was investigated. Between 1975 and 1995 the area of AC&S (alpine cold meadow and steppe) in the source area of the Yellow River has decreased by 27.25%, ACSW (alpine cold swamp meadow) has decreased by 27.04%, ALP (alpine steppe) by 38.18% and lakes by 9.78%. The grass biomass production decreased by 752.37 Gg, of which AC&S meadows accounted for 83.8% of these losses. The overall stock capacity of the headwaters area of the Yellow River decreased by 518.36 thousand sheep units. Soil nutrients showed a similar pattern, soil nutrient loss was greater from 1985–1995 than from 1975–1985. Changes in the overall ecological functionality of the area were not simply a result of a summation of the changes associated with individual evolving landscapes, but rather an integration of positive and negative influences. Landscape evolution occurs in two main directions: degradation and strengthening (expanding and improving). An understanding of the direction, force and integration of parameters influencing landscape evolution as it impacts the attending ecosystems can allow one to foresee how the landscape of the Yellow River source area will evolve in the coming years. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effects of environmental change on the spatial and environmental determinants of community-level traits

An advantage of trait-based approaches to ecology is the ability to predict the response of a species assemblage to environmental change through trait–environment relationships. Because species assemblages are also known to be affected by spatial processes, variation in community-level traits may be similarly affected by spatial structure. Furthermore, the importance of spatial structure may vary with changes to the environment. Using a dataset describing a local stream fish assemblage and environmental variables, we examine the relative contribution of environmental and spatial factors in explaining variation in community-level traits across seasons. We also test for any spatial structuring of community-level traits. For most traits, seasonal environmental change did not seem to alter the relative importance of environmental factors. Traits that did not vary consistently with environmental variables across seasons exhibited significant spatial structure. Overall, relationships between traits and environmental variables seemed to operate on a continuum with ‘environmental traits’ (those that were strongly correlated with environmental variables in response to environmental change) at one end to ‘spatial traits’ (those that did not correlate with environments, but exhibited spatial structure) at the other. We suggest that the distinction between these types of traits is important, as different modeling approaches would be appropriate in using community-level traits to predict the response of species assemblages to environmental change.     

Effects of vegetation structure and environmental characteristics on pollinator diversity in urban green spaces

With accelerating urbanization, insect pollinators in urban ecosystems face challenges such as reduced pollen sources, habitat fragmentation, and damage to the nesting environment. Urban green spaces (UGS) are essential for the stability of pollinator communities. However, little is known about the relationship between vertical layer heterogeneity and horizontal layer complexity of vegetation structure in UGS and pollinator communities. The present study aimed to assess how vegetation structure and environmental characteristics shape the insect pollinator community in UGS. To this end, this study was conducted with seven typical vegetation types which were selected according to the biotope mapping classification system (BMCS) in the ring parks around Hefei City, in Anhui province, China. A total of 11,401 pollinators belonging to 6 orders and 34 families were identified during the eight-month survey. Among the seven habitats under the BMCS, mainly successional short-cut shrub and partly open green space, trees two- or multi-layered broad-leaved mixed forest and partly closed green space, and mainly successional tall grass and partly open green space were identified as high-quality insect pollinator habitats. According to the results of the generalized linear regression, the explanatory power of the four best-fitting generalised linear models is relatively high (over 77%). In four optimal models, the effect of vegetation structure on pollinator community was greater than that of environmental characteristics. The redundancy discriminant analysis showed that the flowering abundance of nectar plants, herb richness, and shrub coverage rate were the three most important factors influencing insect pollinator communities, with a cumulative explanatory power of up to 78.8%. Pollinator abundance was positively influenced by spontaneous herbs and low-intensity management. However, high-intensity management, low diversity of plants, low nectar plant richness, ignoring seasonal nectar plant configuration, and dense tree distribution could limit pollinator reproduction and population growth. These results reflect the status of insect pollinator community in UGS in Hefei city and present a possible direction for improving urban green habitats and plant configurations.     

Fire regimes and forest resilience: alternative vegetation states in the West African tropics

Context

Terrestrial ecosystems, including tropical forests, are hypothesized to have tipping points beyond which environmental change triggers rapid and radical shifts to novel alternative states.

Objective

We explored the overarching hypothesis that fire-mediated alternative stable states exist in the semi-deciduous tropical forest zone of Ghana, and that increased fire activity has pushed some forests to a new state in which a novel ecosystem with low tree density is maintained by fire.

Methods

We combined a 30-year time series of remotely-sensed data with field measurements to assess land cover trends, the effects of fire on forest vegetation, and the reciprocal effects of vegetation change on fire regimes, in four forest reserves. We analyzed precipitation trends to determine if shifts in vegetation and fire regime reflected a shift to a drier climate.

Results

Two of the reserves experienced forest loss, were impacted by frequent fires, and transitioned to a vegetation community dominated by shrubs and grasses, which was maintained by fire–vegetation feedbacks. The other two reserves experienced less fire, retained higher levels of forest cover, and resisted fire encroachment from surrounding agricultural areas. Precipitation remained relatively stable, suggesting a hysteresis effect in which different vegetation states and fire regimes coexist within a similar climate.

Conclusion

There is potential for human land use and fire to create novel and persistent non-forest vegetation communities in areas that are climatically suitable for tropical forests. These disturbance-mediated regime shifts should be taken into account when assessing future trajectories of forest landscape change in West Africa.

     

Rates and patterns of landscape change between 1972 and 1988 in the Changbai Mountain area of China and North Korea

Satellite imagery was used to quantify rates and patterns oflandscape change between 1972 and 1988 in the Changbai MountainReserve and its adjacent areas in the Peoples Republic of Chinaand North Korea. The 190,000 ha Reserve was established as anInternational Biosphere Reserve by The United Nations Educational,Scientific and Cultural Organization (UNESCO) in 1979. It is themost important natural landscape remaining in Chinastemperate/boreal climate. The images used in this research cover atotal area of 967,847 ha, about three-fourths of which is in China.Imagery from 1972 and 1988 was classified into 2 broad cover types(forest and non-forest). Overall, forests covered 84.4% of thestudy area in 1972 and 74.5% in 1988. Changes in forest coverwithin the Reserve were minimal. The loss of forest cover outsidethe Reserve appears to be strongly associated with timberharvesting at lower elevations. Landscape patterns in 1988 weremore complex, more irregular, and more fragmented than in 1972.This is one of the few studies to assess landscape changes acrosstwo countries. The rates and patterns of forest-cover loss weredifferent in China and North Korea. In North Korea, extensivecutting appears to have occurred prior to 1972 and this hascontinued through 1988 while in China, most cutting appears to haveoccurred since 1972.     

Linking vegetation patterns to environmental gradients and human impacts in a mediterranean-type island ecosystem

Vegetation patterns at the landscape scale are shaped by myriad processes and historical events, and understanding the relative importance of these processes aids in predicting current and future plant distributions. To quantify the influence of different environmental and anthropogenic patterns on observed vegetation patterns, we used simultaneous autoregressive modeling to analyze data collected by the Carnegie Airborne Observatory over Santa Cruz Island (SCI; California, USA). SCI is a large continental island, and its limited suite of species and well documented land use history allowed us to consider many potential determinants of vegetation patterns, such as topography, substrate, and historical grazing intensity. As a metric of vegetation heterogeneity, we used the normalized difference vegetation index (NDVI) stratified into three vegetation height classes using LiDAR (short, medium, and tall). In the SAR models topography and substrate type were important controls, together explaining 8–15 % of the total variation in NDVI, but historical grazing and spatial autocorrelation were also key components of the models, together explaining 17–21 % of the variation in NDVI. Optimal spatial autocorrelation distances in the short and medium height vegetation models (600–700 m) were similar to the home range sizes of two crucial seed dispersers on the island– the island fox (Urocyon littoralis santacruzae) and the island scrub-jay (Aphelocoma insularis)—suggesting that these animals may be important drivers of the island’s vegetation patterns. This study highlights the importance of dynamic processes like dispersal limitation and disturbance history in determining present-day vegetation patterns.     

Coupled dynamics of urban landscape pattern and socioeconomic drivers in Shenzhen,China

The effects of land use policy and socioeconomic changes on urban landscape dynamics have been increasingly investigated around the world, but our knowledge of the underlying processes of these effects is still inadequate for sustainably managing urban ecosystems. Thus, the main goal of this study was to understand: (1) the changes in urban landscape, population, and economic conditions over a 36-year period, and (2) the coupled dynamics of land use policy, landscape structure, major demographic features, and three kinds of industries in one of the most dazzling modern cities of China—the Shenzhen special economic zone (SEZ). The landscape expansion index was used to explore the developed-land expansion under different land use policies while structural equation modeling (SEM) was used to analyze the relationship among three variables (Land Cover Change or LCC, Economy, and Population). We found that the urban expansion during the four periods (1973–1979, 1979–1995, 1995–2003, and 2003–2009) was not always at the expense of urban vegetation cover. The importance of each socioeconomic driver during the four periods was not consistent over time, with policy shifts as the primary driver. Our SEM showed that Economy played a more important role than Population in driving LCC in the Shenzhen SEZ. Meanwhile, the secondary and tertiary industries had a stronger influence than the primary industry; and the floating population had a greater effect than the registered permanent population.     

基于市场的华北高寒区洋葱生产分析

基于华北高寒区气候冷凉干燥、适宜洋葱生产的背景,为了丰富区域蔬菜种类、促进产业结构升级,通过调查分析以北京、甘肃、广州、武汉、辽宁为代表全国主要蔬菜批发市场的洋葱周年价格,结合坝上高寒区洋葱生产试验,探索华北高寒区洋葱生产的市场与经济适宜性。结果表明,全国主要市场的洋葱价格表现冬春季高、夏秋季低的时序同步变化特征,不同市场的洋葱淡旺季差价率在54.1%～203.3%,地区间差价率旺季为203.3%。华北坝上高寒区洋葱收获与上市期,洋葱价格处于低谷转向上升的初期,洋葱就近与即时销售不具经济优势。坝上洋葱"南苗北植"生产较当地育苗移栽成本降低了121.7元·667 m~(-2)元,经济效益提高16.7%～38.3%;按产地收购价计,比坝上主栽蔬菜经济收益提高74.6%～127.0%。洋葱可作为华北高寒区蔬菜生产结构调整的供选菜种,"南苗北植"方式可有效提高洋葱的经济效益。     

Effect of spatial image support in detecting long-term vegetation change from satellite time-series

Context

Arid rangelands have been severely degraded over the past century. Multi-temporal remote sensing techniques are ideally suited to detect significant changes in ecosystem state; however, considerable uncertainty exists regarding the effects of changing image resolution on their ability to detect ecologically meaningful change from satellite time-series.

Objectives

(1) Assess the effects of image resolution in detecting landscape spatial heterogeneity. (2) Compare and evaluate the efficacy of coarse (MODIS) and moderate (Landsat) resolution satellite time-series for detecting ecosystem change.

Methods

Using long-term (~12 year) vegetation monitoring data from grassland and shrubland sites in southern New Mexico, USA, we evaluated the effects of changing image support using MODIS (250-m) and Landsat (30-m) time-series in modeling and detecting significant changes in vegetation using time-series decomposition techniques.

Results

Within our study ecosystem, landscape-scale (>20-m) spatial heterogeneity was low, resulting in a similar ability to detect vegetation changes across both satellite sensors and levels of spatial image support. While both Landsat and MODIS imagery were effective in modeling temporal dynamics in vegetation structure and composition, MODIS was more strongly correlated to biomass due to its cleaner (i.e., fewer artifacts/data gaps) 16-day temporal signal.

Conclusions

The optimization of spatial/temporal scale is critical in ensuring adequate detection of change. While the results presented in this study are likely specific to arid shrub-grassland ecosystems, the approach presented here is generally applicable. Future analysis is needed in other ecosystems to assess how scaling relationships will change under different vegetation communities that range in their degree of landscape heterogeneity.

     

Longitudinal- and transverse-scale environmental influences on riparian vegetation across multiple levels of ecological organization

Riparian vegetation is distinct from adjacent upland terrestrial vegetation and its distribution is affected by various environmental controls operating at the longitudinal scale (along the river) or transverse scale (perpendicular to the river). Although several studies have shown how the relative importance of transverse or longitudinal influences varies with the scale of observation, few have examined how the influences of the two scales vary with the level of ecological organization. We modeled vegetation-environment relationships at three hierarchically nested levels of ecological organization: species, plant community, and vegetation type. Our hierarchically structured analyses differentiated the spatial extent of riparian zones from adjacent upland vegetation, the distribution of plant community types within the riparian zone, and the distribution of plant species within community types. Longitudinal gradients associated with climate and elevation exerted stronger effects at the species level than at the community level. Transverse gradients related to lateral surface water flux and groundwater availability distinguished riparian and upland vegetation types, although longitudinal gradients of variation better predicted species composition within either riparian or upland communities. We concur with other studies of riparian landscape ecology that the relative predictive power of environmental controls for modeling patterns of biodiversity is confounded with the spatial extent of the study area and sampling scheme. A hierarchical approach to spatial modeling of vegetation-environment relationships will yield substantial insights on riparian landscape patterns.     

The representation of landscapes in global scale assessments of environmental change

Landscape ecology has provided valuable insights in the relations between spatial structure and the functioning of landscapes. However, in most global scale environmental assessments the representation of landscapes is reduced to the dominant land cover within a 0.5 degree pixel, disregarding the insights about the role of structure, pattern and composition for the functioning of the landscape. This paper discusses the contributions landscape ecology can make to global scale environmental assessments. It proposes new directions for representing landscape characteristics at broad spatial scales. A contribution of landscape ecologists to the representation of landscape characteristics in global scale assessments will foster improved information and assessments for the design of sustainable earth system governance strategies.     

Spatial patterns and drivers of plant diversity in the tropical city of Sanya,China

Drivers of patterns in plant diversity remain poorly understood in tropical cities. Therefore, we investigated diversity within the tropical city of Sanya in Hainan Province of southern China by sampling one to three plots within 154 urban functional units (UFUs) based on six primary and 18 secondary UFUs. To measure diversity, we determined the number of vascular plants (species richness; SR) within each functional unit based on vegetation plots. We computed Faith's phylogenetic diversity (PD_Faith) using a large megatree of plant life. To assess the potential drivers of SR and PD_Faith, we performed multiple regressions using socioeconomic, biophysical, and vegetation management variables. The results showed significant differences in SR and PD_Faith among the six primary UFUs. PD_Faith of cultivated species was significantly higher than PD_Faith of spontaneous species in all UFUs except in the wasteland area. Management measures were better predictors of SR and PD_Faith than socioeconomic variables. The best predictor of SR and PD_Faith of spontaneous species was the management of the urban green space. Our results provide clear guidelines for improved management strategies in Sanya, especially by showing how spontaneous and/or cultivated plant diversity can be encouraged depending on environmental, ecological, and cultural needs. Our work also adds to the presently scarce literature on drivers of urban plant diversity in tropical cities worldwide.     

Landscape history,time lags and drivers of change: urban natural grassland remnants in Potchefstroom,South Africa

Context

The history of the landscape directly affects biotic assemblages, resulting in time lags in species response to disturbances. In highly fragmented environments, this phenomenon often causes extinction debts. However, few studies have been carried out in urban settings.

Objectives

To determine if there are time lags in the response of temperate natural grasslands to urbanization. Does it differ for indigenous species and for species indicative of disturbance and between woody and open grasslands? Do these time lags change over time? What are the potential landscape factors driving these changes? What are the corresponding vegetation changes?

Methods

In 1995 and 2012 vegetation sampling was carried out in 43 urban grassland sites. We calculated six urbanization and landscape measures in a 500 m buffer area surrounding each site for 1938, 1961, 1970, 1994, 1999, 2006, and 2010. We used generalized linear models and model selection to determine which time period best predicted the contemporary species richness patterns.

Results

Woody grasslands showed time lags of 20–40 years. Contemporary open grassland communities were, generally, associated with more contemporary landscapes. Altitude and road network density of natural areas were the most frequent predictors of species richness. The importance of the predictors changed between the different models. Species richness, specifically, indigenous herbaceous species, declined from 1995 to 2012.

Conclusions

The history of urbanization affects contemporary urban vegetation assemblages. This indicates potential extinction debts, which have important consequences for biodiversity conservation planning and sustainable future scenarios.