TY - JOUR
T1 - Stand density effects on carbon and water fluxes in a semi-arid forest, from leaf to stand-scale
AU - Tsamir, Mor
AU - Gottlieb, Sagi
AU - Preisler, Yakir
AU - Rotenberg, Eyal
AU - Tatarinov, Fyodor
AU - Yakir, Dan
AU - Tague, Christina
AU - Klein, Tamir
PY - 2019/12/1
Y1 - 2019/12/1
N2 - Drought-induced productivity reductions and tree mortality have been increasing in recent decades in forests around the globe. Prescribed reduction in stand density, i.e. thinning, has been proposed as a management tool to improve forest sustainability in face of a warmer, drier future. Thinning should potentially reduce net stand water use and improve water-availability for remaining trees, thus reducing their subsequent drought vulnerability. However, few studies have directly measured these effects.In 2009 we established a large-scale thinning experiment in a semi-arid, 40-years-old pine afforestation. Study plots (70 x 70 m) were thinned to 100,200, and 300 trees ha(-1), and compared with unthinned control plots (210-400 trees ha(-1)), each at five replications. Stem and needle growth, and needle gas exchange were measured along 3-9 consecutive years at seasonal to annual temporal resolution. Measurements at the tree-scale were further up-scaled using both simple upscaling relationships and using an ecosystem model of coupled carbon, energy and hydrology (Regional Hydro Ecologic Simulation System, RHESSys).At the needle scale, photosynthesis was 70% higher at the 100 trees ha(-1) than at 300 trees ha(-1), whereas transpiration was merely 10% higher. Consequently, stem and needle growth increased by 100% and 20%, respectively. For most parameters, there was little change between 200 and 100 trees ha(-1). Applying RHESSys at the stand-scale, these effects on tree physiology translated into 35% reduction in CO2 uptake and a 47% reduction in tree water-use, which was compensated for by increased evaporation from exposed soil.Our long-term measurements at the dry timberline highlight the role of thinning in enhancing the activity and growth of remaining trees, with increased water-use efficiency. Unexpectedly, this density reduction was associated with a relatively small decrease in forest carbon uptake. Light availability was a limiting factor in the higher density plots, even in our light-abundant forest.
AB - Drought-induced productivity reductions and tree mortality have been increasing in recent decades in forests around the globe. Prescribed reduction in stand density, i.e. thinning, has been proposed as a management tool to improve forest sustainability in face of a warmer, drier future. Thinning should potentially reduce net stand water use and improve water-availability for remaining trees, thus reducing their subsequent drought vulnerability. However, few studies have directly measured these effects.In 2009 we established a large-scale thinning experiment in a semi-arid, 40-years-old pine afforestation. Study plots (70 x 70 m) were thinned to 100,200, and 300 trees ha(-1), and compared with unthinned control plots (210-400 trees ha(-1)), each at five replications. Stem and needle growth, and needle gas exchange were measured along 3-9 consecutive years at seasonal to annual temporal resolution. Measurements at the tree-scale were further up-scaled using both simple upscaling relationships and using an ecosystem model of coupled carbon, energy and hydrology (Regional Hydro Ecologic Simulation System, RHESSys).At the needle scale, photosynthesis was 70% higher at the 100 trees ha(-1) than at 300 trees ha(-1), whereas transpiration was merely 10% higher. Consequently, stem and needle growth increased by 100% and 20%, respectively. For most parameters, there was little change between 200 and 100 trees ha(-1). Applying RHESSys at the stand-scale, these effects on tree physiology translated into 35% reduction in CO2 uptake and a 47% reduction in tree water-use, which was compensated for by increased evaporation from exposed soil.Our long-term measurements at the dry timberline highlight the role of thinning in enhancing the activity and growth of remaining trees, with increased water-use efficiency. Unexpectedly, this density reduction was associated with a relatively small decrease in forest carbon uptake. Light availability was a limiting factor in the higher density plots, even in our light-abundant forest.
UR - http://www.scopus.com/inward/record.url?scp=85072191743&partnerID=8YFLogxK
U2 - 10.1016/j.foreco.2019.117573
DO - 10.1016/j.foreco.2019.117573
M3 - مقالة
SN - 0378-1127
VL - 453
JO - Forest Ecology and Management
JF - Forest Ecology and Management
M1 - 117573
ER -