Thinning effects on forest production and rainfall redistribution: Reduced soil water deficit and improved sustainability of semiarid plantation forestlands

Large-scale planted afforestation worldwide has exacerbated soil desiccation and led to a serious shortage of water resources for forests sustainability in semiarid areas. Consequently, thinning is discussed as an important management approach to conserve water resources and to maintain plantation forestland sustainability. Here, we explored the effects of thinning intensity on semiarid forest production and soil water supply. Three artificial forests of Populus cathayana with an age of 15 yr were selected and thinned with different intensities [1/3 amount of trees removed (T-1/3), 2/3 amount of trees removed (T-2/3), and using no thinning (NT) as a control]. Results showed that thinning presented a significant impact on the above-ground three-dimensional structure of planted forests and increased forest gaps. Meanwhile, the rainfall redistribution pattern changed significantly. Thinning increased throughfall (T-1/3, 43% +/- 9%; T-2/3, 79% +/- 18%), reduced stemflow (T-1/3,T- -44 +/- 2%; T-2/3, -71% +/- 2%), and increased the soil water replenishment (T-1/3, 34% +/- 7%; T-2/3, 64% +/- 19%) of forest land. Meanwhile, the dead root channel caused by thinning effectively increased the water infiltration rate and groundwater replenishment, and effectively reduced soil water deficit (T-1/3, 41% +/- 33%; T-2/3,T- 57% +/- 33%). Through trade-off analysis, we found that non-thinning aboveground biomass yields were the highest, and T-2/3 yields higher water yield, while T-1/3 can maintain acceptable aboveground biomass while keeping better soil water. We conclude that thinning increased soil water supply, reduced soil water deficit and maintained forestland sustainability, and there are synergies of thinning on forest production and soil water supply through rainfall redistribution for maintaining the sustainability of semiarid plantation forestlands.