Major Land Cover Changes Research Articles

Land Use and Land Cover Change in the Bale Mountain Eco-Region of Ethiopia during 1985 to 2015

Anthropogenic factors are responsible for major land use and land cover changes (LULCC). Bale Mountain Eco-Region in Ethiopia is a biodiversity-rich ecosystem where such LULCC have occurred. The specific objectives of this study were to: (i) determine which LULC types gained or lost most as a result of the observed LULCC; (ii) identify the major drivers of the LULCC/deforestation; and (iii) assess the approximate amount of carbon stock removed as a result of deforestation during the study period. Remote sensing and GIS were used to analyze LULCC. Landsat images acquired in 1985, 1995, 2005, and 2015 were used. Additionally, data from the Central Statistics Agency on cropland expansion, and human and livestock population growth were analyzed and correlations were made. The results showed that forest lost 123,751 ha while farmland gained 292,294 ha. Farmland and urban settlement expansion were found to be major drivers of LULCC. Aboveground carbon stock removed from forest and shrubland was more than 24 million tons. In the future, allocation of land to different uses must be based on appropriate land use policies. Integrating biodiversity and ecosystem values for each land cover as per the UN Sustainable Development Goal (UN-SDG) 15.9 may be one of the mechanisms to limit unplanned expansion or invasion of one sector at the expense of another.

A River Basin over the Course of Time: Multi-Temporal Analyses of Land Surface Dynamics in the Yellow River Basin (China) Based on Medium Resolution Remote Sensing Data

The Yellow River Basin is one of China’s most densely-populated, fastest growing and most dynamic regions, with abundant natural resources and intense agricultural production. Major land policies have recently resulted in remarkable landscape modifications throughout the basin. The availability of precise regional land cover change information is crucial to better understand the prevailing dynamics and underlying factors influencing the current processes in such a complex system and can additionally serve as a valuable component for modeling and decision making. Such comprehensive and detailed information is lacking for the Yellow River Basin so far. In this study, we derived land cover characteristics and dynamics from the complete last decade based on optical high-temporal MODIS Normalized Differenced Vegetation Index (NDVI) time series for the whole Yellow River Basin. After filtering and smoothing for noise reduction with the use of the adaptive Savitzky–Golay filter, the processed time series was used to derive a large variety of phenological and annual metrics. The final classifications for the basin (2003 and 2013) were based on a random forest classifier, trained by reference samples from very high-resolution imagery. The accuracy assessment for all 18 thematic classes, which was based on a 30% reference data split, yielded an overall accuracy of 87% and 84% for 2003 and 2013, respectively. Major land cover and land use changes during the last decade have occurred on the Loess Plateau, where land and conservation reforms triggered large-scale recovery of grassland and shrubland habitat that had been previously covered by agriculture or sparse vegetation. Agricultural encroachment and urban area expansion are other processes influencing the dynamics in the basin. The necessity for regionally-adapted land cover maps becomes obvious when our land cover products are compared to existing global products, where thematic accuracy remains low, particularly in a heterogeneous landscape, such as the Yellow River Basin. The basin-wide novel land cover and land use products of the Yellow River Basin hold a large potential for climate, hydrology and biodiversity modelers, as well as river basin and regional governmental authorities and will be shared upon request.

Land cover and landscape changes in Shaanxi Province during China’s Grain for Green Program (2000–2010)

This study examines landscape changes in the context of China's national Grain for Green (GFG) policy, one of the world's largest "payment for environmental/ecosystem services" (PES) programs. We explored landscape structures and dynamics between 2000 and 2010 in Shaanxi Province, the Chinese province with the greatest amount of cropland conversion and reforestation in recent decades. We used Landsat Thematic Mapper (TM)-derived data and landscape metrics for six land cover classes to determine (1) the major land cover changes during enforcement of the policy, (2) the spatial and temporal variations in these changes, and (3) the effects of land cover changes on landscape structure and dynamics. The results suggested that provincial-level land cover changes modestly reflected the goals of the GFG. Over the 10-year study period, the forest and grassland coverages expanded from 95,737.9 to 97,017.4km(2) and from 37,235.9 to 40,613.1km(2), respectively, while the cropland coverage decreased from 59,222.8 to 54,007.6km(2). The conversion direction differed regionally: the targeted croplands in Shanbei, namely, types III and IV, were mainly transformed into grassland while those in Shannan were mainly transformed into forestland. Reforestation was associated with increased inter-landscape aggregation and connection. Despite this large-scale reforestation trend, we found notable and significant differences in the land cover changes at the subprovincial level.

Mapping rice paddy extent and intensification in the Vietnamese Mekong River Delta with dense time stacks of Landsat data

Rice is a staple food crop for the majority of the world's population, yet paddy fields are threatened by urban expansion, climate change, and degraded agricultural land. Vietnam, one of the largest exporters of rice globally, grows most of its rice in the Mekong River Delta, but this low-lying and heavily populated area is susceptible to major land cover changes. To properly monitor and manage rice crops in this region, remote sensing with satellite imagery has been particularly useful; however, most efforts to map regional paddy area utilize coarse resolution MODIS or AVHRR data due to their high temporal frequency. Because the average size of a rice paddy field in the region is smaller than a coarse resolution pixel, we map the Mekong study area using finer-scale Landsat data collected across multiple growing seasons. First, we exploit dense Landsat time stacks for circa 2000 and circa 2010 to map rice paddy extent using vegetation trajectories, then combine these pixel-based rice maps with image-based segments to generate a polygon-based rice map. The results show that this method can map rice paddies with over 90% overall accuracy (and errors of omission and commission ranging from 6 to 25%) at a finer spatial resolution than previous efforts. Next, we differentiate between single-, double-, and triple-cropped rice paddies in the delta using a supervised classification based on exemplars of these different cropping trends. From circa 2000 to circa 2010, we find that triple-cropped rice fields have nearly doubled in area from one-third to nearly two-thirds of paddy area. Our work also highlights the importance of scenes that capture flooded fields, and the utility of cloud-covered scenes within the dense time stacks of data, to achieve higher classification accuracies. Methods to map rice paddies are vital to understanding the sustainability of these agricultural systems, and the work presented here makes strides toward routine monitoring at a field-level resolution.

Technology or policy? Drivers of land cover change in northwestern Spain before and after the accession to European Economic Community

Major changes in land cover can result from distant political, social, and environmental forces. Over the last 50 years, many technological innovations and political changes have transformed agriculture in Europe, resulting in substantial decrease of farmland area in many parts of the continent that potentially signify a shift in European land use systems. However, the relative importance of technological advances and agricultural policy to these changes is not well understood, and our goal here was to disentangle them. Because of its unique political context, Spain offers an ideal laboratory to investigate the impacts of technological and political innovations to regime change in land systems. During the time when agricultural innovation was at its peak (1960–1980) Spain was not part of the European Economic Community (EEC). The Spanish agricultural sector then experienced a shock after joining the EEC in 1986. Using historical aerial photographs, land use maps, and Farm Structure Surveys as our reference data, we compared changes in land cover in Terra Chá, a district of Northwest Spain from 1956–1984 and 1984–2005, i.e., approximately before and after the EEC accession in 1986, using spatially explicit multinomial logit models to quantify the relative impacts of technological innovation and political change on agriculture and forest lands. In our study area much more substantial shifts in agricultural and forest land took place after EEC accession than before. The dominant shift was a substantial increase in forest cover (from 7% to 31% of the landscape) and concurrent loss of agriculture (from 45% to 38%) and shrubland (from 46% to 27%). The role of drivers acting at parcel level was constant between time periods, which suggests that accession to EEC was a strong driver of change.

Functional diversity enhances the resistance of ecosystem multifunctionality to aridity in Mediterranean drylands.

We used a functional trait-based approach to assess the impacts of aridity and shrub encroachment on the functional structure of Mediterranean dryland communities (functional diversity (FD) and community-weighted mean trait values (CWM)), and to evaluate how these functional attributes ultimately affect multifunctionality (i.e. the provision of several ecosystem functions simultaneously). Shrub encroachment (the increase in the abundance/cover of shrubs) is a major land cover change that is taking place in grasslands worldwide. Studies conducted on drylands have reported positive or negative impacts of shrub encroachment depending on the functions and the traits of the sprouting or nonsprouting shrub species considered. FD and CWM were equally important as drivers of multifunctionality responses to both aridity and shrub encroachment. Size traits (e.g. vegetative height or lateral spread) and leaf traits (e.g. specific leaf area and leaf dry matter content) captured the effect of shrub encroachment on multifunctionality with a relative high accuracy (r(2) =0.63). FD also improved the resistance of multifunctionality along the aridity gradient studied. Maintaining and enhancing FD in plant communities may help to buffer negative effects of ongoing global environmental change on dryland multifunctionality.

Water Resources Response to Climate and Land-Cover Changes in a Semi-Arid Watershed, New Mexico, USA

This research evaluates a climate-land cover-water resources interconnected system in a semi-arid watershed with minimal human impact from 1970-2009. We found 0.9℃ increase in temperature and 10.9% decrease in precipitation. The temperature exhibited a lower increase trend and precipitation showed a similar decrease trend compared to previous studies. The dominant land-cover change trend was grass and forest conversion into bush/shrub and developed land and crop land into barren and grass land. These alterations indicate that changes in temperature and precipitation in the study area may be linked to changes in land cover, although human intervention is recognized as the major land-cover change contributor for the short term. These alterations also suggest that decreasing human activity in the study area leads to developed land and crop land conversion into barren and grass land. Hydrological responses to climate and land-cover changes for surface runoff, groundwater discharge, soil water content and evapotranspiration decreased by 10.2, 10.0, 4.1, and 10.5%, respectively. Hydrological parameters generally follow similar trends to that of precipitation in semi-arid watersheds with minimal human development. Soil water content is sensitive to land-cover change and offset relatively by the changes in precipitation.

The relative importance of climate change and shrub encroachment on nocturnal warming in the southwestern United States

ABSTRACTMany regions of the world are affected by a major land cover change resulting from the encroachment of woody plants and the conversion of grasslands into shrublands. In the southwestern United States, such a change in vegetation cover has been found to increase the winter nighttime temperature, thereby contributing to a positive feedback between shrub encroachment and microclimate in areas encroached by cold‐sensitive shrubs. Temperature measurements show that winter minimum temperatures are on average ∼2 K higher in shrubland than in adjacent grassland sites. It is unclear how the nighttime warming induced by shrub encroachment compares with regional climate trends. We address this question by analysing both the historical and future regional temperature trends in central New Mexico. The estimated regional increase in minimum winter temperature ranges from 1 to 4 K per century using observations and climate models. Thus, the warming resulting from shrub encroachment is equivalent to a change in regional climate over a time period of century scale, which suggests that shrub encroachment has an overall important effect on the regional climate.

Impact of the Human Activities on the Local Climate and Environment of the Suez City in Egypt

Surface temperature and vegetation are the major land cover changes that significantly affect on the thermal environment. In the present study, remote sensing techniques were applied to identify the relationship between anthropogenic activities and the thermal environment in the North Gulf of Suez area. Results have indicated that the urbanization and agricultural expansion have been increased during the last 25 years. Although urban areas increased from 49 km2 in 1987 to 57 km2 in 2012, the urban heat island-range declined from very high and high, to moderate and low. An expansion in cultivated areas from 3 km2 in 1987 to 26 km2 in 2012 was responsible for the decline. The results of this study provided valuable information for understanding the local thermal changes that associate rapid urbanization and expansion of cultivated areas. Consequently, this work recommends that proper planning and management regimes for land use and cover changes associated with rapid urbanization will result in positive impacts on the local climate and environment.

GIS based mapping of land cover changes utilizing multi-temporal remotely sensed image data in Lake Hawassa Watershed, Ethiopia

Classifying multi-temporal image data to produce thematic maps and quantify land cover changes is one of the most common applications of remote sensing. Mapping land cover changes at the regional level is essential for a wide range of applications including land use planning, decision making, land cover database generation, and as a source of information for sustainable management of natural resources. Land cover changes in Lake Hawassa Watershed, Southern Ethiopia, were investigated using Landsat MSS image data of 1973, and Landsat TM images of 1985, 1995, and 2011, covering a period of nearly four decades. Each image was partitioned in a GIS environment, and classified using an unsupervised algorithm followed by a supervised classification method. A hybrid approach was employed in order to reduce spectral confusion due to high variability of land cover. Classification of satellite image data was performed integrating field data, aerial photographs, topographical maps, medium resolution satellite image (SPOT 20m), and visual image interpretation. The image data were classified into nine land cover types: water, built-up, cropland, woody vegetation, forest, grassland, swamp, bare land, and scrub. The overall accuracy of the LULC maps ranged from 82.5 to 85.0%. The achieved accuracies were reasonable, and the observed classification errors were attributable to coarse spatial resolution and pixels containing a mixture of cover types. Land cover change statistics were extracted and tabulated using the ERDAS Imagine software. The results indicated an increase in built-up area, cropland, and bare land areas, and a reduction in the six other land cover classes. Predominant land cover is cropland changing from 43.6% in 1973 to 56.4% in 2011. A significant portion of land cover was converted into cropland. Woody vegetation and forest cover which occupied 21.0 and 10.3% in 1973, respectively, diminished to 13.6 and 5.6% in 2011. The change in water body was very peculiar in that the area of Lake Hawassa increased from 91.9km(2) in 1973 to 95.2km(2) in 2011, while that of Lake Cheleleka whose area was 11.3km(2) in 1973 totally vanished in 2011 and transformed into mud-flat and grass dominated swamp. The "change and no change" analysis revealed that more than one third (548.0km(2)) of the total area was exposed to change between 1973 and 2011. This study was useful in identifying the major land cover changes, and the analysis pursued provided a valuable insight into the ongoing changes in the area under investigation.

Land-cover change in the Paraguayan Chaco: 2000–2011

Land-use and land-cover change has been a topic that has called the attention of the scientific community for decades. Because of the importance of tropical and subtropical forest ecosystems, investigations into the causes and processes (e.g., underlying and proximate causation) that drive land use and land-cover change have typically concentrated on these regions. Consequently, little work has been done to understand the proximate and underlying drivers of land use and land-cover change in one of the least disturbed forests worldwide, the Paraguayan dry Chaco in South America. This article attempts to fill this gap in the literature by focusing on the processes and drivers behind land-cover change in the Paraguayan Chaco. More specifically, this article links underlying and proximate causes to regional land-cover change. To accomplish this task the study makes use of Moderate Resolution Imaging Spectroradiometer (MODIS) data and census data. Results show major land-cover changes. Different from other dry regions in South America where soybean expansion has been pointed out as main driver of land-cover change, in the Paraguayan Chaco, cattle ranching is a major driver of forest loss.

Calibración y aplicación de un modelo de erosión y dinámica del carbono (SPEROS-C) a doce pequeñas cuencas del sureste español

This paper presents a new methodology to assess sediment connectivity at the catchment scale. The proposed index CCI (Catchment Connectivity Index) is based on a combination of factors in a GIS environment that determine the connectivity of sediment in different elements (slopes, basins, channels) of the river system. The factors evaluated are the transport capacity on hillslopes (TC), check-dams’ trap efficiency (TE), the presence of geomorphological barriers (GF), flow conditions (FC) and the sediment transport capacity in channels (SP). This index was applied to estimate connectivity in the Upper Taibilla catchment (314 km2) (SE Spain) for different land use (1956 and 2006) and management (check-dams) scenarios. This catchment has suffered major land use and land cover changes over the last 50 years. The intense agricultural abandonment process and the implementation of soil erosion control measures (reforestation and check-dams) have strongly affected sediment dynamics of the basin. Calculation of the CCI allows identifying which landscape elements have most impact on the sediment (dis)connectivity at catchment scale. The results show a significant reduction in the connectivity of 76% between 1956 and 2006. However, it is observed that the check-dams contribute only 3% to this reduction. Land use changes had a much higher impact on reducing sediment connectivity, except in some areas with steep slopes, or with the development of agriculture along the main channels of the drainage network. Altogether, CCI showed to be a relatively easy and effective method that can be used for spatio-temporal sediment connectivity analyses in areas with natural and human disturbances.

Desarrollo y aplicación de un índice multifactorial de conectividad de sedimentos a escala de cuenca

This paper presents a new methodology to assess sediment connectivity at the catchment scale. The proposed index CCI (Catchment Connectivity Index) is based on a combination of factors in a GIS environment that determine the connectivity of sediment in different elements (slopes, basins, channels) of the river system. The factors evaluated are the transport capacity on hillslopes (TC), check-dams’ trap efficiency (TE), the presence of geomorphological barriers (GF), flow conditions (FC) and the sediment transport capacity in channels (SP). This index was applied to estimate connectivity in the Upper Taibilla catchment (314 km2) (SE Spain) for different land use (1956 and 2006) and management (check-dams) scenarios. This catchment has suffered major land use and land cover changes over the last 50 years. The intense agricultural abandonment process and the implementation of soil erosion control measures (reforestation and check-dams) have strongly affected sediment dynamics of the basin. Calculation of the CCI allows identifying which landscape elements have most impact on the sediment (dis)connectivity at catchment scale. The results show a significant reduction in the connectivity of 76% between 1956 and 2006. However, it is observed that the check-dams contribute only 3% to this reduction. Land use changes had a much higher impact on reducing sediment connectivity, except in some areas with steep slopes, or with the development of agriculture along the main channels of the drainage network. Altogether, CCI showed to be a relatively easy and effective method that can be used for spatio-temporal sediment connectivity analyses in areas with natural and human disturbances.

Three centuries of land cover changes in the largest French Atlantic wetland provide new insights for wetland conservation

Grassland to cropland conversion has been a major land cover change in wetlands during recent decades. Many conservation strategies have therefore focused on the protection or restoration of grasslands considered the remnant fragments of nature in wetlands before agricultural development. Through the example of the largest French Atlantic wetland (the Marais Poitevin) and using high-resolution historical records documenting landscape changes since the beginning of the 18th century, we propose the first long-term analysis of a wetland conversion at a large spatial scale. We demonstrate that, although the last land cover changes corresponded to significant grassland to cropland conversions, the mid-20th century was characterized by an exceptional grassland cover (90% of the area). We also show that current surface areas covered by grasslands are similar to those of the 18th and 19th centuries, and that grassland to cropland conversion followed a massive decline in the most natural habitats of the wetland such as marshes, salt-marshes and other marine habitats. From a long-term perspective, grassland to cropland conversion is rather a recent change and grasslands can be viewed as the result of agricultural development in this wetland rather than pristine habitats. In contrast, marshes, salt-marshes and other marine habitats can be considered the remnant fragments of nature of conservation interest, although they are neglected in current conservation plans. We discuss the problem of the time-span and the reference state to be considered when analyzing land cover changes and assessing wetland conservation issues at large spatial scales.

Land use/cover changes and vulnerability to flooding in the Harts catchment, South Africa

The purpose of this study is to determine the hydrological impacts of land use/land cover (LULC) change in the Harts catchment from 1990 to 2010 using an integration of remote sensing, geographic information system and statistical methods. Hydrological data of rainfall and river discharge were statistically analysed to reveal the alterations and trends from 1990 to 2010. Changes in year-to-year relationships between precipitation and discharge suggested that discharge was relatively higher in the second half than in the first half of the study period. In fact, an overall weak correlation of 0.39 was found between precipitation and river discharge during the study period. The positive trend in discharge in the Harts River coincides with major changes in land cover over the study area. The LULC changes showed a decrease of vegetation cover from 758,345 ha in 1990 to 736,879.4 ha in 2008, while barren land increased from 226,670 ha in 1990 to 324,321.49 ha in 2008 (an increase of 97,651.49 ha). The modifications of natural vegetation cover have lead to modified runoff production and consequently to changing flow regimes in the Harts catchment. The coupling of surface observations, remote sensing and statistical analysis demonstrated the impacts of changes in LULC on peak river discharge, hence flooding behaviour on the Harts catchment.

Land cover change detection of Hatiya Island, Bangladesh, using remote sensing techniques

Land cover change is a significant issue for environmental managers for sustainable management. Remote sensing techniques have been shown to have a high probability of recognizing land cover patterns and change detection due to periodic coverage, data integrity, and provision of data in a broad range of the electromagnetic spectrum. We evaluate the applicability of remote sensing techniques for land cover pattern recognition, as well as land cover change detection of the Hatiya Island, Bangladesh, and quantify land cover changes from 1977 to 1999. A supervised classification approach was used to classify Landsat Enhanced Thematic Mapper (ETM), Thematic Mapper (TM), and Multispectral Scanner (MSS) images into eight major land cover categories. We detected major land cover changes over the 22-year study period. During this period, marshy land, mud, mud with small grass, and bare soil had decreased by 85%, 46%, 44%, and 24%, respectively, while agricultural land, medium forest, forest, and settlement had positive changes of 26%, 45%, 363%, and 59%, respectively. The primary drivers of such landscape change were erosion and accretion processes, human pressure, and the reforestation and land reclamation programs of the Bangladesh Government.

Complex land cover change processes in semiarid Mediterranean regions: An approach using Landsat images in northeast Spain

In this study we used Landsat images to analyze land cover change processes since 1984 in the middle Ebro valley (Spain). The purpose was to identify abrupt changes suggesting modification of the land cover category, and gradual changes not associated with a change in the land cover type but potentially indicative of significant changes in natural areas. The results showed that: i) in analysis of land cover change the seasonality of vegetation cover is an important factor that must be taken into account in identifying the various change processes that may affect a region; ii) the major land cover changes in the study area were related to very diverse processes including urban expansion, industrial activities, the establishment of land irrigation, land extensification, natural revegetation following rural abandonment, forest fires, and changes in natural vegetated areas related to global warming and drought. With the exception of the occurrence of forest fires, the changes in natural areas (forest, shrubs and steppes) tended to be gradual with respect to both positive (forest colonization following rural abandonment and land extensification) and negative (land degradation and forest decline) processes. These areas showed rates of change that were lower in magnitude than those directly transformed by human activities. We found that time series of high spatial resolution satellite images and the application of change statistics provided a useful approach to the identification of abrupt changes, and gradual land cover change processes that are not commonly revealed using classical analytical approaches.

Remote sensing land-cover change in Port Elizabeth during South Africa’s democratic transition

Urban population increase has caused significant urban landscape transformation globally. Before 1994, South Africa’s highly regulated urban growth was shaped by the restrictive Prevention of Illegal Squatters Act of 1951. After the abolishment of the act in the 1980s, the period of transition to democracy in the 1990s was characterised by an unprecedented urban population influx that caused a myriad of socio-economic and environmental challenges. These challenges have consequently compounded the need to monitor urban growth for the planning and optimisation of urban spaces. The limitations of traditional mapping methods, such as surveying and photogrammetry, in urban mapping are well documented. In the recent past, satellite remote sensing has emerged as one of the most viable urban mapping tools. Using post-classification comparisons, we sought to monitor major land use and land cover (LULC) changes in the city of Port Elizabeth during South Africa’s democratic transition (1990–2000). Images for 1990, 1995 and 2000 were acquired, geo-rectified and atmospherically corrected. An iterative self-organising data analysis (ISODATA) was then used to generate existing LULCs. Classes generated using ISODATA were then amalgamated to the city’s major LULCs and resultant classes were validated using aerial photographs and field visits. Results showed that ‘Built-up’ and ‘Bare surface’ LULC classes had the highest increase and decrease, respectively. There was no change in the ‘Beach or dune’ LULC, whereas ‘Green vegetation’ and ‘Water’ classes had minimal changes. This study illustrates the efficacy of remote sensing in monitoring urban change and the potential of remote sensing to aid decision-making in rapidly changing urban landscapes.

Historical landscape photographs for calibration of Landsat land use/cover in the northern Ethiopian highlands

ABSTRACTThe combined effects of erosive rains, steep slopes and human land use have caused severe land degradation in the Ethiopian Highlands for several thousand years, but since the 1970s, however, land rehabilitation programmes have been established to try to reverse deterioration. In order to characterize and quantify the transformations in the north Ethiopian Highlands, a study was carried out over 8884 km2 of the Tigray Highlands of northern Ethiopia. Using Landsat Multispectral Scanner and later Thematic Mapper imagery (1972, 1984/1986 and 2000), historical terrestrial photographs (1974–1975) and fieldwork (2008), we prepared land use and cover maps. For assessing the use of the historical terrestrial photographs, Landsat images from 1972 were classified using two different methods, namely conventional change detection (image differencing) and ground truthing (using the historical photographs of 1974–1975). Results show that the use of terrestrial photographs is promising, as the classification accuracy based on this method (Kappa coefficient 0·54) is better than the classification accuracy of the method based on image differencing (Kappa coefficient 0·46). Major land use and cover changes indicate the following: (1) a gradual but significant decline in bare ground (32 per cent in 1972 to 8 per cent in 2000); (2) a significant increase of bushland (25 to 43 per cent) and total forest area (including eucalypt plantations, 2·6 to 6·3 per cent); and (3) creation of numerous lakes and ponds. The dominant change trajectory (27 per cent of the study area) indicates a gradual or recent vegetation increase. These changes can be linked to the population growth and the introduction of land rehabilitation initiatives, complemented by growing awareness of land holders. Copyright © 2012 John Wiley & Sons, Ltd.

Response of dominant grass and shrub species to water manipulation: an ecophysiological basis for shrub invasion in a Chihuahuan Desert Grassland

Increases in woody vegetation and declines in grasses in arid and semi-arid ecosystems have occurred globally since the 1800s, but the mechanisms driving this major land-cover change remain uncertain and controversial. Working in a shrub-encroached grassland in the northern Chihuahuan Desert where grasses and shrubs typically differ in leaf-level nitrogen allocation, photosynthetic pathway, and root distribution, we asked if differences in leaf-level ecophysiology could help explain shrub proliferation. We predicted that the relative performance of grasses and shrubs would vary with soil moisture due to the different morphological and physiological characteristics of the two life-forms. In a 2-year experiment with ambient, reduced, and enhanced precipitation during the monsoon season, respectively, the encroaching C(3) shrub (honey mesquite Prosopis glandulosa) consistently and substantially outperformed the historically dominant C(4) grass (black grama Bouteloua eriopoda) in terms of photosynthetic rates while also maintaining a more favorable leaf water status. These differences persisted across a wide range of soil moisture conditions, across which mesquite photosynthesis was decoupled from leaf water status and moisture in the upper 50 cm of the soil profile. Mesquite's ability to maintain physiologically active leaves for a greater fraction of the growing season than black grama potentially amplifies and extends the importance of physiological differences. These physiological and phenological differences may help account for grass displacement by shrubs in drylands. Furthermore, the greater sensitivity of the grass to low soil moisture suggests that grasslands may be increasingly susceptible to shrub encroachment in the face of the predicted increases in drought intensity and frequency in the desert of the southwestern USA.