Use of δ¹³C as water stress indicator and potential silvicultural decision support tool in Pinus radiata stand management in South Africa
Date
2018-11-15
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Italian Society of Silviculture and Forest Ecology
Abstract
ENGLISH ABSTRACT: In this study, the carbon isotope ratio in tree rings was investigated as a potential
measure of water availability and drought stress in Pinus radiata stands in
South Africa. An understanding of water availability and its variation in space
is fundamental to the implementation of increasingly site-specific management
regimes that have the potential to improve stand productivity. Fourteen plantation
compartments, situated on water shedding (convex) terrain were identified
where reliable weather data existed and a water balance model could be
run. This output was used to derive water stress indicators: (a) relative canopy
conductance (gc/gcmax) and (b) the ratio of actual to potential evapotranspiration
(ETa/ETp). The water stress indicators (calculated per year of growth)
were related to δ¹³C values in five tree rings formed in the five years before
mid-rotation thinning took place. The water balance model used adequately
described soil water availability throughout each growing season and indicated
that most severe stand water stress occurred during the summer months of
the study period (November to April). The ETa/ETp ratio for this period as well
as the relative canopy conductance proved to be good measures of water
stress. The 5-year averages of the ETa/ETp ratios (taken over the driest 6
month period) ranged from 0.17 to 0.32 (winter rainfall zone) and 0.44 to
0.70 (all-year rainfall zone). The 5-year averages of ETa/ETp ratios could be
accurately predicted (p< 0.0001; adjusted r2 = 0.83) with multiple regression
using δ¹³C values in whole-wood samples (i.e., earlywood and latewood) and
the site index of stands (where site index is the average height of the dominant
20% trees in the stand at base age 20). The δ¹³C values in tree rings
across the planted range of P. radiata in South Africa can therefore be used to
identify broad categories of water availability for purposes of increasingly sitespecific
silvicultural management.
Description
CITATION: Fischer, P. M. & Du Toit, B. 2019. Use of δ¹³C as water stress indicator and potential silvicultural decision support tool in Pinus radiata stand management in South Africa. iForest: Biogeosciences and Forestry, 12(1):51-60, doi:10.3832/ifor2628-011.
The original publication is available at http://iforest.sisef.org
The original publication is available at http://iforest.sisef.org
Keywords
Soil water, Stable Carbon Isotope, Isotopes, Forest management areas, Management of droughts, Monterey Pine
Citation
Fischer, P. M. & Du Toit, B. 2019. Use of δ¹³C as water stress indicator and potential silvicultural decision support tool in Pinus radiata stand management in South Africa. iForest: Biogeosciences and Forestry, 12(1):51-60, doi:10.3832/ifor2628-011