Abstract
Surface soil moisture (SSM) is a key limiting factor for vegetation growth in alpine meadow on the Qinghai-Tibetan Plateau (QTP). Patches with various sizes and types may cause the redistribution of SSM by changing soil hydrological processes, and then trigger or accelerate alpine grassland degradation. Therefore, it is vital to understand the effects of patchiness on SSM at multi-scales to provide a reference for alpine grassland restoration. However, there is a lack of direct observational evidence concerning the role of the size and type of patches on SSM, and little is known about the effects of patches pattern on SSM at plot scale. Here, we first measured SSM of typical patches with different sizes and types at patch scale and investigated their patterns and SSM spatial distribution through unmanned aerial vehicle (UAV)-mounted multi-type cameras at plot scale. We then analyzed the role of the size and type of patchiness on SSM at both patch and plot scales. Results showed that: (1) in situ measured SSM of typical patches was significantly different (P < 0.01), original vegetation patch (OV) had the highest SSM, followed by isolate vegetation patch (IV), small bare patch (SP), medium bare patch (MP) and large bare patch (LP); (2) the proposed method based on UAV images was able to estimate SSM (0–40 cm) with a satisfactory accuracy (R2 = 0.89, P < 0.001); (3) all landscape indices of OV, with the exception of patch density, were positively correlated with SSM at plot scale, while most of the landscape indices of LP and IV showed negative correlations (P < 0.05). Our results indicated that patchiness intensified the spatial heterogeneity of SSM and potentially accelerated the alpine meadow degradation. Preventing the development of OV into IV and the expansion of LP is a critical task for alpine meadow management and restoration.
Highlights
The Qinghai-Tibetan Plateau (QTP) encompasses 83% of the Earth’s terrain above 4000 m [1], and alpine meadow is widely distributed on the QTP [2]
Aerial photogrammetry based on a unmanned aerial vehicle (UAV) with multi-type cameras performed well in investigating patch pattern and estimating surface soil moisture distribution
The original vegetation patch had the highest surface soil moisture at patch scale and its spatial pattern played a critical role in maintaining the stability of surface soil moisture in the alpine meadow area
Summary
The Qinghai-Tibetan Plateau (QTP) encompasses 83% of the Earth’s terrain above 4000 m [1], and alpine meadow is widely distributed on the QTP [2]. Permafrost degradation, rodent disturbance and overgrazing usually divide intact vegetation into archipelagos of small fragments [7,8] Various patches, such as original vegetation patches, isolated vegetation patches and bare patches with different sizes are common on the QTP [9–11]. These patches with various sizes and types intensify the spatial heterogeneous distribution of soil gravel content, root biomass, and soil-saturated hydraulic conductivity [11,12]. These differences will cause the vertical exchange of energy and water fluxes among atmosphere, ground surface and underneath the soil, and thereby alter surface soil moisture (SSM). The patch pattern (the spatial distribution of various patches) can affect SSM through horizontal exchange of soil waters [13]
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