Effect of thinning-induced gap size on soil CO2 efflux in a reforested spruce forest in the eastern Tibetan Plateau

Published Date
15 April 2016, Vol.220:1–9, doi:10.1016/j.agrformet.2016.01.004

Author 

• Xueyong Pang ^a,b,,
• Bin Hu ^a,b
• Weikai Bao ^a,b,,
• Thiago de Oliveira Vargas ^c
• Guanglong Tian ^d,e

• aKey Laboratory of Mountain Ecological Restoration and Bioresource Utilization of Chinese Academy of Sciences, Chengdu Institute of Biology, Chinese Academy of Sciences, PO Box 416, Chengdu 610041, China
• bEcological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, PO Box 416, Chengdu 610041, China
• cDepartment of Environmental Studies, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
• dEnvironmental Monitoring and Research Division, Monitoring and Research Department, Metropolitan Water Reclamation District of Greater Chicago, Lue-Hing R&D Complex, 6001 W. Pershing Road, Cicero, IL 60804, USA
• eDepartment of Civil, Architectural & Environmental Engineering, Illinois Institute of Technology, 3201 S. Dearborn Street, Chicago, IL 60616, USA

Received 31 July 2015. Revised 24 December 2015. Accepted 6 January 2016. Available online 15 January 2016.

Highlights

• Change in soil temperature (T₁₀) and moisture depends on the time after thinning and gap size.
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  Gap formation decreases R_s in the forest, but such effect diminishes with time after thinning.
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  Decline in tree roots and soil labile C drives the decrease in R_s after thinning.
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  Positive effect of T₁₀ elevation under thinning on R_s is masked by other factors.

Abstract 

Understanding the effects of forest management practices (e.g. thinning) on soil respiration (R_s) is crucial for the accurate estimation of forest carbon budget. However, little is known about the response of R_s to forest thinning in the subalpine region and its linkage to changes in environmental factors induced by thinning. We aimed to quantify the response of R_s rate to various gap sizes following thinning treatments, and to explore the relationships between R_s and soil temperature and moisture and other biophysical factors in the different gap sizes. We applied the thinning by simulating gap formation (four gap sizes at 0, 74, 109 and 196 m²) in a 26-year old spruce plantation in the eastern Tibetan Plateau. We measured R_smonthly before (July to November 2008) and after (December 2008 to June 2012) thinning, as well as monthly soil temperature and moisture and other biophysical factors. Thinning tended to decrease fine root biomass, litterfall, soil extractable C, and increased soil temperature and soil moisture. The change in soil temperature and moisture depended on the time after thinning and the size of forest gap. We found that R_s showed an immediate decrease in initial stage after thinning, followed by a gradual increase with understory development towards the level at the control plot. Overall, thinning decreased R_s rate by 14.9%, 15.8% and 25.8% in the small, intermediate and large gap, respectively, as compared to the control. We concluded that the decrease in R_s rates by thinning in a spruce plantation was driven by the decline in tree root biomass and reduction in soil labile C. The positive effect of soil temperature elevation under thinning on R_s was masked by other factors, and the development of understory vegetation after thinning gradually offset the thinning-induced R_s reduction. Our results suggest the need to consider a set of abiotic and biotic factors induced by forest thinning intensity on R_s rates in modeling the response of soil C cycling to forest management practices.

Keywords

• Soil respiration
• Thinning
• Forest gap size
• Root biomass
• Understory
• Spruce plantation

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  Corresponding authors at: Chengdu Institute of Biology, Chinese Academy of Sciences, PO Box 416, No.9, Section 4, Renmin Nan Road, Chengdu 610041, China. Tel.: +86 28 82890528; fax: +86 28 82890288.
  
  

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