Does physiology alone explain Betula pendula recovery from drought?

Increasing drought intensity, duration and frequency worldwide challenges tree health. In addition to the importance of drought resistance, post-drought recovery capacity is a vital determinant in tree growth and survival. However, the capacity of trees to recover from different types of drought stress remains largely unquantified. In this study, we applied three different drought treatments (short-term drought, long-term drought, and repeated drought) and a well-watered control to 3-year-old silver birch (Betula pendula) saplings growing in a greenhouse. Ecophysiological traits regarding key water- and carbon-relation processes such as sap flow, stem radial variation, leaf gas exchange, water potential, and leaf phenology were continuously measured throughout the drought-recovery process. The preliminary results indicate that water consumption, photosynthesis and tree growth were greatly diminished in all drought treatments, though their recovery capabilities and timing differed. None of the stressed treatments recovered to pre-drought status after re-watering, which might be attributed to their limited ability to repair xylem embolism and restore leaf area. The adjustment of tree-level leaf area emerged as a key strategy to cope with the drought, shedding light on traits other than physiology requiring consideration when studying drought resistance and resilience.