Abstract
Rangelands provide significant socioeconomic and environmental benefits to humans. However, climate variability and anthropogenic drivers can negatively impact rangeland productivity. The main goal of this study was to investigate structural and productivity changes in rangeland ecosystems in New Mexico (NM), in the southwestern United States of America during the 1984–2015 period. This goal was achieved by applying the time series segmented residual trend analysis (TSS-RESTREND) method, using datasets of the normalized difference vegetation index (NDVI) from the Global Inventory Modeling and Mapping Studies and precipitation from Parameter elevation Regressions on Independent Slopes Model (PRISM), and developing an assessment framework. The results indicated that about 17.6% and 12.8% of NM experienced a decrease and an increase in productivity, respectively. More than half of the state (55.6%) had insignificant change productivity, 10.8% was classified as indeterminant, and 3.2% was considered as agriculture. A decrease in productivity was observed in 2.2%, 4.5%, and 1.7% of NM’s grassland, shrubland, and ever green forest land cover classes, respectively. Significant decrease in productivity was observed in the northeastern and southeastern quadrants of NM while significant increase was observed in northwestern, southwestern, and a small portion of the southeastern quadrants. The timing of detected breakpoints coincided with some of NM’s drought events as indicated by the self-calibrated Palmar Drought Severity Index as their number increased since 2000s following a similar increase in drought severity. Some breakpoints were concurrent with some fire events. The combination of these two types of disturbances can partly explain the emergence of breakpoints with degradation in productivity. Using the breakpoint assessment framework developed in this study, the observed degradation based on the TSS-RESTREND showed only 55% agreement with the Rangeland Productivity Monitoring Service (RPMS) data. There was an agreement between the TSS-RESTREND and RPMS on the occurrence of significant degradation in productivity over the grasslands and shrublands within the Arizona/NM Tablelands and in the Chihuahua Desert ecoregions, respectively. This assessment of NM’s vegetation productivity is critical to support the decision-making process for rangeland management; address challenges related to the sustainability of forage supply and livestock production; conserve the biodiversity of rangelands ecosystems; and increase their resilience. Future analysis should consider the effects of rising temperatures and drought on rangeland degradation and productivity.
Highlights
Land degradation affects ecosystem productivity and threatens its capacity to sustain human, livestock, and wildlife population specially in dryland environments
From all pixels that showed increased productivity (12.8% or 570 pixels, 34,816 km2 ), 5.7% (16,320 km2 ) were identified using the Segmented vegetation- precipitation relationships (VPR) method, 4.6% (12,992 km2 ) were identified using the RESTREND method, and the remaining 2.5% (7168 km2 ) were identified using the Segmented RESTREND method
This study evaluated the degradation of New Mexico’s rangelands during the 1984 period with respect to climate using an normalized difference vegetation index (NDVI) timeseries—as a surrogate of net primary production (NPP)—
Summary
Land degradation affects ecosystem productivity and threatens its capacity to sustain human, livestock, and wildlife population specially in dryland environments. Sever land degradation is prevalent in over. Understanding the rate, expansion, and severity of drylands degradation has received (and will continue to receive) considerable attention, due to their pivotal role in food production and water availability for more than 2 billion people in the world [3,8,9,10,11]. The main causes of drylands degradation are principally associated with population growth, overgrazing, inappropriate land and water use practices, and climate change impacts [1,11,12]. Future predictions showed that climate change impacts (i.e., increase in surface air temperature and evapotranspiration, and decrease in precipitation) are expected to worsen poverty and inequality in developing countries [15,16]
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