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

TY - JOUR

T1 - The influence of trees, shrubs, and grasses on microclimate, soil carbon, nitrogen, and CO2 efflux

T2 - Potential implications of shrub encroachment for Kalahari rangelands

AU - Thomas, Andrew David

AU - Elliott, David R.

AU - Dougill, Andrew John

AU - Stringer, Lindsay Carman

AU - Hoon, Stephen Robert

AU - Sen, Robin

N1 - Funding Information: Research was funded by a Leverhulme Trust standard grant and a NERC facilities grant and conducted under Government of Botswana permit EWT8/36/4 VIII(4). We thank three anonymous reviewers for their constructive criticism which has helped improve the manuscript, and Dr Andrew Stott who undertook the isotope analyses. Stringer was supported by the Wolfson Foundation and Royal Society in her position as a Royal Society Wolfson Research Merit Award holder. We are indebted to Jill Thomas who provided access to her land and logistical support for which we are very grateful. This paper is dedicated to her memory. The authors declare no conflicts of interest. Publisher Copyright: © 2018 The Authors Land Degradation & Development Published by John Wiley & Sons Ltd.

PY - 2018/5/15

Y1 - 2018/5/15

N2 - 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.

AB - 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.

KW - dryland carbon cycles

KW - microclimate

KW - shrub encroachment

KW - soil-vegetation feedbacks

KW - vegetation change

UR - http://www.scopus.com/inward/record.url?scp=85044513143&partnerID=8YFLogxK

U2 - 10.1002/ldr.2918

DO - 10.1002/ldr.2918

M3 - Article

AN - SCOPUS:85044513143

SN - 1085-3278

VL - 29

SP - 1306

EP - 1316

JO - Land Degradation and Development

JF - Land Degradation and Development

IS - 5

ER -