Influence of elevation on canopy transpiration of temperate deciduous forests in a complex mountainous terrain of South Korea

BACKGROUND AND AIMS: Variations in microclimate and soil characteristics on mountain slopes influence forest structure and function. Precipitation, incoming solar radiation and relative humidity change along a mountain slope. Equally, soil depth and the amount of stored soil moisture vary. The objective of this study was to examine the impacts of these factors on forest water use in mountainous terrains. METHODS: Transpiration of four temperate deciduous forest stands located at different elevations in South Korea was monitored with a sap flow technique throughout the growing season in 2010. The study sites were located on the north slope at 450 m (450 N), 650 m (650 N), and 950 m (950 N). To examine the effect of aspect, an additional site with a southern aspect was studied at 650 m (650S). All the sites were dominated by Quercus species, with leaf area index (L) ranging between 5 − 6 m² m⁻². RESULTS: Rainfall increased, while air temperature (T A) and daytime vapor pressure deficit (D) decreased with increasing elevation. We did not observe any gradients in solar radiation (R S), soil moisture and sap flux density of the individual trees (J ₛₜ) with an elevational gradient. Sapwood area (A S), i.e., hydro-active xylem area, and daily maximum tree water use (max TWU) increased non-linearly with increasing diameter at breast height (DBH). Neither A S nor max TWU varied among tree species or along the elevation. The total annual canopy transpiration (E C) was 175, 115, 110, and 90 mm for 450 N, 650 N, 650S, and 950 N, respectively. E C declined with increasing elevation as a result of decreasing length of the growing season, D, and T A along the elevation. Significantly (P < 0.001) higher stomatal sensitivity to changes in D was found at the 950 N, leading to lower annual E C and lower water use efficiency (WUE) at this elevation. CONCLUSIONS: We conclude that differences in E C exist along the mountain slope studied, corresponding to changing T A , D, length of the growing season, and stomatal sensitivity to D, which should be considered when establishing forest catchment water balances.