The influence of trees, shrubs, and grasses on microclimate, soil carbon, nitrogen, and CO₂ efflux: Potential implications of shrub encroachment for Kalahari rangelands

Abstract

Shrub encroachment is a well‐documented phenomenon affecting many of the world's drylands. The alteration of vegetation structure and species composition can lead to changes in local microclimate and soil properties which in turn affect carbon cycling. The objectives of this paper were to quantify differences in air temperatures, soil carbon, nitrogen, and CO2 efflux under trees (Vachellia erioloba), shrubs (Grewia flava), and annual and perennial grasses (Schmidtia kalahariensis and Eragrostis lehmanniana) collected over three seasons at a site in Kgalagadi District, Botswana, in order to determine the vegetation‐soil feedback mechanism affecting the carbon cycle. Air temperatures were logged continuously, and soil CO2 efflux was determined throughout the day and evening using closed respiration chambers and an infrared gas analyser. There were significant differences in soil carbon, total nitrogen, CO2 efflux, light, and temperatures beneath the canopies of trees, shrubs, and grasses. Daytime air temperatures beneath shrubs and trees were cooler compared with grass sites, particularly in summer months. Night‐time air temperatures under shrubs and trees were, however, warmer than at the grass sites. There was also significantly more soil carbon, nitrogen, and CO2 efflux under shrubs and trees compared with grasses. Although the differences observed in soils and microclimate may reinforce the competitive dominance of shrubs and present challenges to strategies designed to manage encroachment, they should not be viewed as entirely negative. Our findings highlight some of the dichotomies and challenges to be addressed before interventions aiming to bring about more sustainable land management can be implemented.

Flora, Life-forms and Biological Spectrum of Muscat Governorate

“…Therophytes and chamaephytes were the dominate forms, the dominance of the therophytes and chamaephytes may be attributed to the hot dry climate, geological factors and the topography [33][34][35]. Therophytes are associated with a dry climate [36,37], and are characteristics vegetation type of desert flora, as influenced by microclimate and soil conditions [38]. The therochamaephytic spectrum has been assiociated with other desert climates observed in the neighbouring countries such as Taif, Saudi Arabia [39], Hail region of Saudi Arabia [40], Wadi Al-Jufair, Saudi Arabia [35], Toor Al-Baha District, Lahej Governorate, Yemen, [41].…”

Spatial and temporal variations in global soil respiration and their relationships with climate and land cover

“…R s change can be affected by many factors, and climate factors (e.g., air temperature and precipitation) have been commonly investigated because of their direct or indirect effects on R s metabolism (9)(10)(11)(12)(13)(14)(15). Land-cover change can also greatly affect R s by changing vegetation structure, plant species composition, local microclimate, and soil properties (24,25). For instance, global greening and the associated vegetation structural change could affect R s by altering biogeophysical processes (26,27).…”

Shrub encroachment is not always land degradation: Insights from ground‐dwelling beetle species niches along a shrub cover gradient in a semi‐arid Namibian savanna

“…The interacting causes of shrub encroachment include the increase in atmospheric CO 2 (Ward, Hoffman, & Collocott, ), annual variability of rainfall (Joubert, Smit, & Hoffman, ), suppression of natural fires (Van Wilgen, Govender, Biggs, Ntsala, & Funda, ), and unsustainable large herbivore management (e.g., Bakker et al, ; Rohde & Hoffman, ; Sankaran, Augustine, & Ratnam, ). Although an increase in shrub cover can improve abiotic conditions via the mitigation of microclimate extremes and the increase in soil C and N (Eldridge et al, ; Thomas et al, ), linked changes in biotic conditions have been shown to have negative effects. For example, reduced grass cover leads to a decrease in livestock production, and a change in structural diversity can cause loss of biodiversity (Archer et al, ; Blaum, Seymour, Rossmanith, Schwager, & Jeltsch, ; Chown, ).…”