Simulation of Vegetation Cover Based on the Theory of Ecohydrological Optimality in the Yongding River Watershed, China

Yixuan Zhang,Tingning Zhao,Changqing Shi,Qiang Ma

doi:10.3390/f12101377

Abstract

During ecological restoration, it is necessary to comprehensively consider the state of vegetation in climate–soil–vegetation systems. The theory of ecohydrological optimality assumes that this state tends to reach long-term dynamic equilibrium between the available water supply of the system and the water demand of vegetation, which is driven by the maximization of productivity. This study aimed to understand the factors that affect the spatial distribution of vegetation and simulate the ideal vegetation coverage (M0) that a specific climate and soil can maintain under an equilibrium state. The ecohydrological optimality model was applied based on meteorological, soil, and vegetation data during the 2000–2018 growing seasons, and the sensitivity of the simulated results to input data under distinct vegetation and soil conditions was also considered in the Yongding River watershed, China. The results revealed that the average observed vegetation coverage (M) was affected by precipitation characteristic factors, followed by wind speed and relative humidity. The M, as a whole, exhibited horizontal zonal changes from a spatial perspective, with an average value of 0.502, whereas the average M0 was 0.475. The ecohydrological optimality theory ignores the drought resistance measures evolved by vegetation in high vegetation coverage areas and is applicable to simulate the long-term average vegetation coverage that minimizes water stress and maximizes productivity. The differences between M and M0 increased from the northwest to the southeast of this area, with a maximum value exceeding 0.3. Meteorological factors were the most sensitive factors of this model, and the M0 of the steppe was most sensitive to the stem fraction, mean storm depth, and air temperature. Whether soil factors are sensitive depends on soil texture. Overall, the study of the carrying capacity of vegetation in the natural environment contributes to providing new insights into vegetation restoration and the conservation of water resources.

Highlights

Vegetation, as the primary component of terrestrial ecosystems, interacts with hydrological processes [1,2]
The soil texture is responsible for the differences in the hydraulic properties of the root zone soil and further impacts the spatial distribution of soil moisture [9]
The theory of ecohydrological optimality focuses on the long-term average status of the growing season rather than dynamic trends

Summary

Introduction

Vegetation, as the primary component of terrestrial ecosystems, interacts with hydrological processes [1,2]. The spatiotemporal responses of vegetation to water circulation mainly depend on the climate, soil, and physiological characteristics of the vegetation [3,4,5]. Precipitation is linked to vegetation through soil moisture [6]. The uncertainty of both the frequency and amount of precipitation promotes vegetation to optimize productivity [7,8]. The water available for use by vegetation in the soil increases from coarse sand, fine sand, sandy soil, loam to clay [10]. The physiological responses of plant species to moisture changes are related to their own structure and strategies for adaptation to drought, such as the crown shape, xylem structures, size and depth of roots, and leaf traits [12,13,14,15]

Objectives

Methods

Discussion

Conclusion