Wind drives nocturnal, but not diurnal, transpiration in Leucospermum conocarpodendron trees: implications for stilling on the Cape Peninsula

Surface winds have declined in many regions of the world over the past few decades, These trends are referred to as global stilling and have recently been observed in the Western Cape Province of South Africa. The potential consequences of such changes on ecosystem function and productivity are a particular concern for the highly diverse and endemic local flora, largely associated with the fynbos biome. Yet, few studies have directly examined the impact of wind in the region. In this study, we explored the importance of wind and other drivers of plant transpiration (E) in a stand of Leucospermum conocarpodendron (L.) Buek trees on the Cape Peninsula. Wind speeds can be high in the Cape and could play an important role in influencing the rate of E. Overall, the influence of wind appeared to be significantly greater at night than during the day. While daytime E responded most strongly to changes in solar radiation (R-2 = 0.79) and vapour pressure deficit (R-2 = 0.57-0.67), night-time E (En) was primarily driven by wind speed (R-2 = 0.30-0.59). These findings have important implications for stilling and other aspects of climate change. Since E-n was found to be a regular and significant (P < 0.00) component of total daily E (10-27%), plants may conserve water should stilling continue. Still, the extent of this could be offset by strong daytime drivers. As such, plant water consumption will most likely increase in response to a warmer and drier climate. Changes in other biophysical variables are, however, clearly important to consider in the current debate on the impact of climate change.