Morphological response of soil surface cracks to the microclimate induced by planted Tamarix shrubs

Document Type : Scientific article

Authors

1 Ph.D. Student of Forestry, Department of Forestry, Faculty of Natural Resources, Urmia University, Urmia, I.R. Iran

2 Professor, Department of Forestry, Faculty of Natural Resources, Urmia University, Urmia, I.R. Iran

3 Associate Professor, Department of Watershed and Rangeland, Faculty of Natural Resources, Urmia University, Urmia, I.R. Iran

Abstract

Background and Objective: The desiccation of lakes and wetlands in arid and semi-arid regions, such as Lake Urmia, is driven by climate change and anthropogenic pressures, leading to the formation of unstable saline playas that serve as major sources of harmful dust. Establishing salt-tolerant shrubs like Tamarix ramosissima (tamarisk) is an effective strategy for soil stabilization and microclimate modulation. The microclimate created beneath shrub canopies reduces temperature, buffers thermal fluctuations, increases relative humidity, and limits evaporation, thereby influencing surface crack morphology in saline-clay soils. Such cracks not only disrupt water infiltration, gas exchange, and root growth but also provide pathways for wind erosion. However, knowledge of how plant-induced microclimates affect crack patterns in these ecosystems remains limited, hindering the optimization of ecological restoration efforts.
Material and Methods: This study assessed the impact of microclimates generated by hand-planted tamarisk shrubs on surface soil crack morphology in the western dried bed of Lake Urmia. Sixty shrubs, planted since 2015, were systematically selected based on uniformity in height, canopy dimensions, and spacing to minimize confounding factors. Prevailing wind directions were determined using synoptic station wind-rose data (1949-2021). From 15 shrubs, high-resolution vertical digital images (n= 120) were acquired at two sampling positions per shrub, beneath the canopy (at half-canopy radius) and outside the canopy (5-8 m from the stem base, in inter-canopy gaps), across four cardinal directions (N, S, E, W). Images were processed using PCAS (Pores and Cracks Analysis System) to extract key morphological indices: crack density (Dc), area-to-perimeter ratio (AWMARP), weighted mean fractal dimension (AWMFRAC), and morphological connectivity (r). Statistical analyses (two-way ANOVA, Tukey’s HSD, independent t-tests) compared indices across canopy conditions and directions.
Results: Shrub microclimates significantly altered crack morphology. Under canopies, mean Dc was 1.99% versus 0.70% in open areas; AWMARP was >2× higher (0.0375 vs. 0.014); AWMFRAC was ~12× greater (1.40 vs. 0.122); and r increased by ~83% (0.293 vs. 0.160). Two-way ANOVA confirmed highly significant effects of canopy position on all indices (p< 0.01), while direction alone significantly affected only r (p< 0.01). Interaction effects (position × direction) were significant for AWMARP and r, indicating directional dependence of microclimate impacts. Maximum Dc and AWMFRAC occurred in the NE and NW directions beneath canopies. Independent t-tests revealed highly significant differences (p< 0.01): Dc (+65%), AWMARP (+>60%), AWMFRAC (+~91%), and r (+~43%) were all higher under canopy. Visual PCAS outputs confirmed denser, more uniform, semi-regular polygonal crack networks beneath canopies, versus sparse, irregular, fragmented patterns in open areas, highlighting the efficacy of tamarisk-induced microclimate in modulating soil physical processes.
Conclusion: Hand-planted tamarisk shrubs substantially enhance surface crack morphology in the western playa of Lake Urmia by fostering structured, dense, interconnected crack networks, thereby improving soil hydraulic and biological functionality. Greatest effects occurred in NE and NW aspects, likely due to interactions between microclimate, prevailing winds, and solar radiation. Functionally, tamarisk acts as an ecosystem engineer, offering more than physical stabilization, by enabling ecological restoration and dust mitigation. Moreover, crack morphological indices serve as valuable quantitative indicators for evaluating restoration effectiveness in arid degraded lands.

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References

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Forest Research and Development
Volume 12, Issue 1
June 2026
Pages 65-86

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