Identifying Water Use Strategies in Mediterranean Tree Species Combining Sap Flow and Dendrometer Data

Drought stress is known to limit tree patterns of water use and radial growth in Mediterranean-type ecosystems. However, both processes are rarely dealt with in combination in multi-species studies. Here, we combine sap flow measurements with automatic band dendrometers in order to assess year-round water use strategies and stem radius growth of four co-existing Mediterranean woody species growing under natural conditions: Pinus halepensis Mill., Quercus pubescens Willd., Quercus ilex L. and Arbutus unedo L. Sap flow per unit sapwood area showed strong seasonality associated with species-specific leaf habit and drought responses. A water-spender behaviour was found for Q. pubescens in response to depleted soil water supply and high atmospheric demand, as opposed to P. halepensis, which showed the most conservative water use. For Q. ilex and A. unedo, intermediate water use strategies were found. P. halepensis and Q. pubescens showed the highest water use efficiency for growth (WUEG), calculated as the annually-integrated water use per unit of radial growth. Our results thus show the diversity of water use and growth responses to seasonal variations of water availability in Mediterranean forests.