Tree stomata conductance estimates of a wax myrtle-tree heath (fayal-brezal) cloud forest as affected by fog

- One-year measurements of sap flow and meteorological variables were studied.
- Stomata conductance estimates of two laurel forest tree species were investigated.
- Dependence of tree stomata conductance on meteorology was similar in both species.
- In the presence of fog meteorology and tree stomata conductance changed.

Direct transpiration measurements of tree species obtained with Granier's heat dissipation probes, combined with micrometeorological data were used to derive tree conductance estimates in a cloud-immersed wax myrtle-tree heath forest located in the Garajonay National Park (La Gomera, Canary Islands, Spain). The one-year period time series were analysed distinguishing between foggy and fog-free conditions in order to evaluate the vegetation response to fog. The presence of fog was found to reduce transpiration (T) in both species investigated (E. arborea and M. faya), such that the yearly medians of the hourly T values were 6-15.6 times higher when no fog was present as compared to cloud immersed periods. By contrast the gc estimates exhibit larger values in the afternoon during foggy conditions when compared in terms of the hourly gc medians at each time of the day, and were clearly greater on a daily basis. During foggy conditions, gc followed a monotonically increasing trend. Large variability of conductance estimates was observed across the ranges of micrometeorological conditions explored. The largest conductance values were associated with low solar radiations, air temperatures between 8 and 15 °C, low VPD (<0.5 kPa), and wind velocities of 2-4 m s−1. Laurel forest trees, previously referred as following a profligate water use strategy, may thus profit from the foggy environment by maintaining the stomata opened during the day without significant water losses, while benefiting with the associated carbon gain.