Abstract Crown dimensions such as diameter or crown projection area are important indicators for tree vigour, growing stage or production efficiency and can be used as proxies for the assessment of wood quality, leaf area and leaf biomass, biodiversity, wildlife habitat and disturbance risk to forest stability. Crown allometry can vary with site and competition conditions, but variation patterns are not still well understood. The main aim of this study was to analyze this allometry variation in the most common pine species along the aridity gradient of the Iberian Peninsula, studying the crown response to aridity and to competition, and determining whether the presence of inter-specific competition modifies crown allometry. A set of 40,402 sample trees from 12,283 sample plots, along with the Martonne aridity index as an indicator of climatic conditions, were used to develop allometric models, the parameters of which were generalized by including aridity and competition indicators. The plots were located in monospecific or mixed stands of Pinus sylvestris, Pinus nigra, Pinus pinaster, Pinus pinea and Pinus halepensis. According to our results, both aridity conditions and competition status are important factors modifying the crown allometry of the studied species. Moreover, we found that both size-symmetric competition and size-asymmetric competition should be taken into account when modelling the crown size, both types leading to smaller crown diameter. The crown plasticity of the studied pine species in response to competition presented a low range of variation, the greatest being that of maritime pine, while Scots pine and black pine showed the smallest. The way in which aridity and competition influence crown size differs among the studied species, indicating differences in crown plasticity patterns. Moreover, in humid sites, where competition for light is more important, the crown allometry response to changes in competition is greater, being most evident in P. pinea and P. halepensis. The species mixing effects had less influence on pine crown allometry than the total competition effect, although the effect was always significant. The effect of size-symmetric competition from admixed species was positive or neutral, except for the effect of P. sylvestris on P. nigra crowns. Size-asymmetric competition also plays an important role in the species mixing effects, these effects on intermediate or suppressed trees varying depending on the species mixture. The models developed reveal significant species-specific effects on crown allometry, pointing to the ability of pine species to adapt their crowns to different growing conditions.

中文翻译：

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响应干旱梯度竞争的五种松树树冠可塑性

摘要 直径或树冠投影面积等树冠尺寸是树木活力、生长阶段或生产效率的重要指标，可作为评估木材质量、叶面积和叶生物量、生物多样性、野生动物栖息地和森林干扰风险的替代指标。稳定。冠异速生长会因场地和比赛条件而异，但变异模式仍不清楚。本研究的主要目的是分析沿伊比利亚半岛干旱梯度的最常见松树物种的异速生长变化，研究树冠对干旱和竞争的反应，并确定种间竞争的存在是否会改变树冠异速生长. 一组来自 12,283 个样本地块的 40,402 个样本树，连同 Martonne 干旱指数作为气候条件的指标，被用来开发异速生长模型，其参数通过包括干旱和竞争指标进行概括。样地位于樟子松、黑松、松、松、松和黑松的单种或混交林中。根据我们的结果，干旱条件和竞争状态都是改变研究物种冠异速生长的重要因素。此外，我们发现在对牙冠尺寸建模时应同时考虑尺寸对称竞争和尺寸不对称竞争，这两种类型都会导致较小的牙冠直径。所研究的松树树种响应竞争的树冠可塑性呈现出低范围的变化，最大的是海松，而苏格兰松和黑松则最小。干旱和竞争影响树冠大小的方式在研究物种之间有所不同，表明树冠可塑性模式存在差异。此外，在对光的竞争更为重要的潮湿地区，对竞争变化的冠部异速生长反应更大，在 P. pinea 和 P. halepensis 中最为明显。与总竞争效应相比，物种混合效应对松树冠异速生长的影响较小，尽管这种效应总是显着的。除了 P. sylvestris 对 P. nigra 冠的影响外，来自混合物种的大小对称竞争的影响是积极的或中性的。大小不对称竞争在物种混合效应中也起着重要作用，这些对中间树或被抑制树的影响因物种混合物而异。开发的模型揭示了对树冠异速生长的显着物种特异性影响，表明松树物种能够使其树冠适应不同的生长条件。