Sapwood to heartwood ratio affects whole-tree water use in dry forest legume and non-legume trees.

摘要

We investigated vegetation structure, seasonal water use and leaf deciduousness in a seasonally dry forest of Dzibilchaltun, Mexico. Legumes, species which tend to dominate these forests, have an array of water-saving traits. We explored whether legume species had reduced water use under similar growth conditions as other non-legume species of this seasonally dry forest. Sap flux and conductive sapwood area were measured for eight legume and 12 non-legume species. Species abundance, diameter at breast height (DBH), wood density and seasonal leaf cover were characterized in 16, 10x10 m2 plots. Seasonal stand water use was calculated using the sap flux and ecological data. As predicted, legumes presented lower whole-tree water use compared with sympatric non-legume species. This difference, however, was related to a higher allocation to non-conductive heartwood in legumes and not to differences in sap flux density. Differences in allocation were higher in wider stems (>10 cm DBH); legumes above 25 cm DBH presented nearly half the daily water use of non-legumes of similar size. Wet (July) and dry (March) season stand water use was 629,000 and 156,000 kg ha-1 month-1, respectively. During the wet season three non-legume species with high basal area dominated the stand water use, but due to early leaf fall in these species, dry season stand water use was dominated by the legumes.