Excessive livestock grazing overrides the positive effects of trees on infiltration capacity and modifies preferential flow in dry miombo woodlands

Abstract

The increase in livestock grazing in African drylands such as miombo woodlands threatens land productivity and ecosystem functioning. Trees have positive effects on soil hydraulic properties, but few studies have looked at grazing intensity and hydrological functioning in different land uses. Therefore, we conducted a biophysical survey in Morogoro Rural District, Tanzania, where we identified four main land uses and land cover types, that is, Forest reserve, open-access forest, cropland under fallow, and active cropland. We assessed grazing intensity, measured infiltration capacity, and conducted dye tracer experiments to assess the degree of preferential flow in 64 plots. We also tested the effect of grazing exclusion on infiltration capacity in 12-year-old fenced plots. Our results show that irrespective of land use or cover type, soil bulk density increased by 10% from low to high grazing intensity, whereas infiltration capacity and soil organic carbon decreased by 55% and 28%, respectively.We found a positive relationship between infiltration capacity and tree basal area in plots with lowest grazing intensities. However, at higher grazing, the infiltration capacity remained low independently of the basal area. Preferential flow in deeper soils was six-times higher in areas with no grazing, indicating higher deep soil and groundwater recharge potential at low grazing intensities. We conclude that the negative impacts on soil hydrological functioning of excessive livestock grazing override the positive effect of trees, but restricting grazing can reverse the impact.

The size of clearings for charcoal production in miombo woodlands affects soil hydrological properties and soil organic carbon

“…Furthermore, the activity of soil fauna and roots enhances soil aggregation and macroporosity, leading to improved soil water conductivity and drainage (Belsky et al, 1993;Benegas, 2013). Our findings support previous studies which have shown increased soil infiltration capacity with tree cover in various tropical ecosystems (Bargués-Tobella et al, 2014;Benegas, 2013Benegas, & 2018Ilstedt et al, 2016;Lulandala et al, 2021). Tree removal typically reduces the quantity and quality of organic matter input and increases soil surface exposure to rainfall and sunlight (Bhuyan & Laskar, 2020), which can result in higher impact from raindrops and crust formation at the soil surface, leading to lower infiltration and increased surface runoff and erosion (Aber et al, 2010).…”

“…In our study area, forest roads are mainly used by people, motorcycles, livestock, and sometimes tractors coming and going from the forest to transport charcoal and timber. The decrease in infiltration capacity near the road could be explained by loss of tree cover, which may be due to illegal tree cutting for building material (poles) or firewood collection (Manyanda et al, 2021), frequent movement of livestock, and grazing (Lulandala et al, 2021). Both illegal cutting and livestock grazing lead to biomass removal, which may, in turn, decrease soil organic matter and SOC stock (Devi, 2021).…”

“…However, there is less understanding of the implications of forest clearings that do not involve crop cultivation, such as those for charcoal production, or are not located within protected areas and are hence open to other uses such as livestock grazing. Heavy livestock grazing in miombo woodlands has a negative influence on the physical and hydrological properties of soils, including bulk density, infiltration capacity, and preferential flow (Lulandala et al, 2021). This influence can vary spatially depending on forest accessibility, which itself depends on factors such as the presence of forest roads that serve as pathways for the livestock en route to different grazing lands.…”

Flow variability in the Araguaia River Hydrographic Basin influenced by precipitation in extreme years and deforestation

“…The increase in river discharge may be the effect of replacing the Amazon forest and cerrado for pasture expansion, with possible longterm consequences for the regional hydrological cycle. Such hydro-environmental relationships are due to the fact that the soil of the areas destined for the activities usually becomes more compact, hindering the process of water infiltration and, consequently, increasing the surface runoff (Lulandala et al, 2021). The urban area × flow (r = 0.46) has a low direct and positive correlation, in which the increase in flow consists of a decrease in soil infiltration conditions.…”

Impact on local sustainability of the northward expansion of human activities into protected areas in northern Tibet

“…According to the theoretical framework of sustainable livelihood and sustainable development, humans' livelihood assets are the natural ecology within the scope of human activities (Huq et al, 2020; Lusseau & Mancini, 2019), and their livelihood strategy is to highly develop and utilize natural assets. Due to its low economic benefits, this approach can only meet the livelihood needs and cannot restore and build natural ecology, leading to the reduction of ecological assets (Barbier & Hochard, 2018; Lulandala et al, 2022). If there is no other livelihood strategy and livelihood needs continue to increase, utilizing more natural assets becomes the only means of survival.…”