Abstract
Soil moisture content (SMC) is a limiting factor to ecosystem productivity in semiarid shrublands. Long-term droughts due to climatic changes may increase the water stress imposed on these lands. Recent observations demonstrate positive relations between geodiversity—expressed by the degree of soil stoniness—and SMC in the upper soil layers. This suggests that areas of high geodiversity can potentially provide a haven for plant survival under water scarcity conditions. The objective of this study was to assess the effect of geodiversity on the dynamics of SMC in semiarid environments, which so far has not been fully investigated. The optical trapezoid model (OPTRAM) applied to six-year time series data (November 2013–July 2018), obtained from LANDSAT 8 and highly correlated with field measurements (R2 = 0.96), shows here that the SMC in hillslopes with high geodiversity is consistently greater than that in hillslopes with low geodiversity. During winter periods (December–March), the difference between the two hillslope types was ~7%, while during summer periods (June–September) it reduced to ~4%. By using the high-resolution spectral-spatiotemporal VENµS data, we further studied the geodiversity mechanism during summertime, and at a smaller spatial scale. The VENµS-based Crop Water Content Index (CWCI) was compared with the OPTRAM measurements (R2 = 0.71). The Augmented Dickey–Fuller test showed that water loss in the high-geodiversity areas during summers was very small (p-value > 0.1). Furthermore, the biocrust index based on the VENµS data showed that biological crust activity in the high-geodiversity hillslopes during summers is high and almost stationary (ADF p-value > 0.1). We suggest that the mechanism responsible for the high SMC in the high-geodiversity areas may be related to lower evaporation rates in the dry season and high runoff rates in the wet season, both of which are the combined result of the greater presence of developed biocrusts and stoniness in the areas of higher geodiversity.
Highlights
Decreases in rainfall rates and increases in surface temperatures due to global warming processes may cause severe water deficits in semiarid ecosystems [1,2,3]
Soil patches with relatively high soil moisture content (SMC) can become a haven for vegetation species, and they have drawn the attention of researchers in the current literature [58,61]
Field observations revealed that areas with high geodiversity are characterized by Semiarid shrublands experience consistent water scarcity, which affects vegetation productivity [3,8]
Summary
Decreases in rainfall rates and increases in surface temperatures due to global warming processes may cause severe water deficits in semiarid ecosystems [1,2,3] These ecosystems are composed of mosaics of self-organized patches of shrubs, bare soil, and herbaceous vegetation [4,5,6,7]. The bare soil areas, known as the inter-patch spaces, play a critical role in regulating SMC in semiarid environments These spaces are often covered by biological and physical crusts, which may limit water infiltration, increasing the overland water flow that accumulates in the downslope vegetation patches [9,10,11]. These interactions play a major role in the durability and resilience of semiarid shrubland ecosystems to prolonged droughts and climatic changes [12,14,15]
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