Minimum and maximum wood density as proxies of water availability in two Mexican pine species coexisting in a seasonally dry area

摘要

Key message Minimum wood density is a proxy of soil moisture during the early growing season. Maximum wood density responds to late growing-season drought. Seasonally dry areas are ideal settings to refine our understanding of tree growth proxies of water availability. Despite recent methodological advances in quantitative wood anatomy and wood density, our knowledge of wood density responses to climate at intra-annual scales in seasonal drought-prone regions is still limited. The objective of this study is to elucidate how minimum (MnD) and maximum (MxD) wood density respond to hydroclimate variability of two coexisting conifers growing in a moisture-stressed environment. We prepared wood samples to obtain MnD and MxD values in Pinus lumholtzii and Pinus durangensis trees co-occurring in a drought-prone site located in northern Mexico. MnD and MxD were correlated with temperature, water balance and a drought index considering the period 1970-2013. The P. lumholtzii MnD negatively responded to growing-season water availability as indicated by the negative correlations with water balance, and considering short to mid-term droughts lasting from 2 to 8 months. Both species showed a decrease in MxD during the last 15 years associated to a rise in temperature and drier conditions. Winter-spring water balance was positively associated with MxD, but July water balance showed a negative correlation. Intra-annual density data can represent robust proxies of hydroclimate variability in similar seasonally dry areas. Specifically, MnD should be further investigated as a surrogate of water availability effects on earlywood during the early growing season.