Abstract Thinning intensity is an important factor affecting forest structure and density and influencing tree growth. The main objective of the study is to evaluate how the different intensity of thinning can influence, in the short and long term, the productivity and intrinsic water use efficiency (WUEi) of Quercus robur L., a widespread European species. Three thinning types of different intensity were applied in 14-year mixed plantation of Quercus robur L. growing with Alnus glutinosa (L) Gaertn., a N-fixing species, with an initial density of 625 trees/ha. A multidisciplinary approach was applied, coupling the tree-ring analyses with the measurements of stable isotopes of carbon and oxygen. Findings highlighted how the different conditions of light and competition, determined by the type and intensity of thinning, triggered different responses of Q. robur species in terms of growth and WUEi. Data suggested that the moderate selective thinning (31% reduction of total biomass) was not able to reduce the high competition for resources among individuals: this condition negatively influenced the trees growth. The presence of the N-fixing species, left after the thinning, was not able to counteract the negative effect of competition. A negative effect on productivity was recorded with the geometric thinning (62% reduction of total biomass). Indeed, this treatment resulted in an increase of asymmetry of the canopy (0.90 vs 0.83, respectively in pre- and post-thinning period), due to the partial crown competition from one side and with a consequent limitation of the photosynthetic activity of the trees. Finally, the very high selective thinning (75% reduction of total biomass) resulted to be the most appropriate management practice, as it guarantees positive effects both in terms of growth and intrinsic water use efficiency. The post thinning conditions determined high photosynthesis rates, an increase of productivity and a limited water loss.

中文翻译：

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间伐强度对栎树生产力和水分利用效率的影响

摘要 间伐强度是影响森林结构和密度、影响树木生长的重要因素。该研究的主要目的是评估不同的间伐强度如何在短期和长期影响 Quercus robur L.（一种广泛分布的欧洲物种）的生产力和内在用水效率 (WUEi)。与固氮树桤木（Alnus glutinosa (L) Gaertn.）混合种植14年间，采用三种不同强度的间伐类型，初始密度为625棵树/公顷。应用了多学科方法，将树木年轮分析与碳和氧的稳定同位素测量相结合。研究结果强调了由稀疏的类型和强度决定的光照和竞争的不同条件，引发 Q. robur 物种在生长和 WUEi 方面的不同反应。数据表明，适度的选择性间伐（总生物量减少 31%）无法减少个体之间对资源的激烈竞争：这种情况对树木的生长产生了负面影响。变薄后留下的固氮物种的存在无法抵消竞争的负面影响。几何变薄（总生物量减少 62%）记录了对生产力的负面影响。事实上，由于来自一侧的部分树冠竞争以及随之而来的树木光合作用活动的限制，这种处理导致冠层的不对称性增加（在间伐前和间伐期分别为 0.90 和 0.83） . 最后，非常高的选择性间伐（总生物量减少 75%）是最合适的管理实践，因为它保证了在生长和内在用水效率方面的积极影响。间伐后的条件决定了高光合作用速率、生产力的提高和有限的水分流失。