Abstract Wood density is one of the main functional traits affecting demographic rates of tropical trees. However, little is known about how this translates into abundance of trees in local assemblages. I hypothesized that: (1) higher wood density would generally result in better adaptation to prevailing environmental conditions in seasonally dry semideciduous forests, which would translate into numerical dominance of denser-wood species; (2 and 3, respectively) as drought severity and disturbance intensity scale, the performance of individuals of denser-wood species would drop, so that the numerical dominance of those species would decline. A community-level functional measure (ΔMWD) was used to access the role played by wood density in shaping numerical dominance in assemblages. I obtained the value of ΔMWD for 30 local assemblages by computing the difference between wood density mean value of two species groups in each assemblage: dominant and rare. The proportion of ΔMWD positive values was significantly greater than 0.5, thus supporting hypothesis 1. This finding may be explained by the possible ability of denser-wood species to continue growing under drought conditions due to greater resistance to drought-induced cavitation of vessels associated with higher wood density. Pearson correlation coefficients between ΔMWD and drought severity and between ΔMWD and disturbance intensity were negative and statistically significant, supporting hypotheses 2 and 3, respectively. Also supporting these hypotheses, Glm fitting showed that drought severity and disturbance intensity had significant negative effects on ΔMWD; and the median values of ΔMWD of the subsets of assemblages showing higher levels of drought severity and disturbance intensity were significantly smaller than that of their respective counterparts. These findings may be explained by shifts of adaptive advantages from denser-wood drought tolerant strategists to softer-wood drought avoidance strategists, and from denser-wood resource conservative strategists to softer-wood resource acquisitive strategists, as drought severity and disturbance intensity increase, respectively.

中文翻译：

---

巴西季节性干旱半落叶林优势树种和稀有树种的干旱程度、干扰强度和木材密度

摘要 木材密度是影响热带树木人口率的主要功能性状之一。然而，人们对这如何转化为当地组合中丰富的树木知之甚少。我假设：（1）较高的木材密度通常会导致更好地适应季节性干燥的半落叶林中的普遍环境条件，这将转化为密度较大的木材物种的数量优势；（分别为 2 和 3）作为干旱严重程度和干扰强度尺度，密度较大的木材物种的个体表现将下降，从而使这些物种的数量优势下降。使用社区级功能测量 (ΔMWD) 来了解木材密度在塑造组合中的数量优势方面所起的作用。我通过计算每个组合中两个物种组的木材密度平均值之间的差异，获得了 30 个局部组合的 ΔMWD 值：优势和稀有。ΔMWD 正值的比例显着大于 0.5，因此支持假设 1。这一发现可能是由于密度较大的木材物种在干旱条件下继续生长的可能能力，因为对干旱引起的血管空化具有更强的抵抗力较高的木材密度。ΔMWD 与干旱严重程度之间以及 ΔMWD 与干扰强度之间的 Pearson 相关系数为负且具有统计学意义，分别支持假设 2 和 3。同样支持这些假设的是，Glm 拟合表明干旱严重程度和干扰强度对 ΔMWD 有显着的负面影响；干旱严重程度和干扰强度较高的组合子集的ΔMWD中值显着小于各自对应的组合子集。这些发现可能是由于适应性优势从较密木材耐旱策略师向较软木材抗旱策略师以及从较密木材资源保守策略师转向较软木材资源获取策略师的转变，分别是干旱严重程度和干扰强度增加.