Structural Changes of Desertified and Managed Shrubland Landscapes in Response to Drought: Spectral, Spatial and Temporal Analyses

Tarin Paz-Kagan,Eli Zaady,Natalya Panov,Moshe Shachak,Arnon Karnieli

doi:10.3390/rs6098134

Tarin Paz-Kagan, Eli Zaady + Show 3 more

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https://doi.org/10.3390/rs6098134

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Abstract

Drought events cause changes in ecosystem function and structure by reducing the shrub abundance and expanding the biological soil crusts (biocrusts). This change increases the leakage of nutrient resources and water into the river streams in semi-arid areas. A common management solution for decreasing this loss of resources is to create a runoff-harvesting system (RHS). The objective of the current research is to apply geo-information techniques, including remote sensing and geographic information systems (GIS), on the watershed scale, to monitor and analyze the spatial and temporal changes in response to drought of two source-sink systems, the natural shrubland and the human-made RHSs in the semi-arid area of the northern Negev Desert, Israel. This was done by evaluating the changes in soil, vegetation and landscape cover. The spatial changes were evaluated by three spectral indices: Normalized Difference Vegetation Index (NDVI), Crust Index (CI) and landscape classification change between 2003 and 2010. In addition, we examined the effects of environmental factors on NDVI, CI and their clustering after successive drought years. The results show that vegetation cover indicates a negative ∆NDVI change due to a reduction in the abundance of woody vegetation. On the other hand, the soil cover change data indicate a positive ∆CI change due to the expansion of the biocrusts. These two trends are evidence for degradation processes in terms of resource conservation and bio-production. A considerable part of the changed area (39%) represents transitions between redistribution processes of resources, such as water, sediments, nutrients and seeds, on the watershed scale. In the pre-drought period, resource redistribution mainly occurred on the slope scale, while in the post-drought period, resource redistribution occurred on the whole watershed scale. However, the RHS management is effective in reducing leakage, since these systems are located on the slopes where the magnitude of runoff pulses is low.

Highlights

Shrublands in arid and semi-arid areas, on a small spatial scale, are characterized by a structure of a “two-phase landscape mosaic” of woody vegetated patches and bare or soil-crusted patches [1].Water, sediments, nutrients and seeds flow across the system, between the components of the landscape mosaic, creating a functional “sink-source” relationship
The study site is located within the Shaked Park near Beer-Sheva in the northern Negev Desert of Israel (31°17ʹN, 34°37ʹE, 190–200 m a.m.s.l.), which is a long-term ecological research (LTER) site (Figure 1)
Previous studies have shown that runoff-harvesting system (RHS) enhance ecosystem function by increasing soil organic matter accumulation in the pits [4,25,77], increasing active carbon rates and nutrient accumulation, reducing the leakage of resources by accumulating runoff water and nutrients and preventing soil erosion [4,25]

Summary

Introduction

Shrublands in arid and semi-arid areas, on a small spatial scale, are characterized by a structure of a “two-phase landscape mosaic” of woody vegetated patches and bare or soil-crusted patches [1].Water, sediments, nutrients and seeds flow across the system, between the components of the landscape mosaic, creating a functional “sink-source” relationship. A decrease in precipitation and higher temperatures are drivers of woody vegetation mortality [19,20,21,22], and on the other hand, stronger rainfall intensities increase the susceptibility of soil to erosion and flash floods [23] These changes disturb the function of the present ecosystem source-sink relationship by reducing the shrub cover, which decreases the sink function, resulting in a reduction in resource conservation and an expansion of the biocrust areas that increase the source function of that system, resulting in the leakage of resources [24,25,26]. Land-use practices, such as livestock grazing and clear cutting, cause a reduction in the abundance of shrub patches and an increase in the biological soil crust cover [27] Both climate and land-use changes reduce the sink function of the landscape, resulting in the resource leakage of water, organic matter and nutrients and, in low ecosystem productivity and biodiversity [4,11,25]

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