One yearlong analysis: The contribution of dewfall and distillation to rock- and cobble-inhabiting lichens in the Negev

Abstract

With rain providing only circa 20 rainy days a year, dewfall is regarded as the main water source for crustose lichens inhabiting rocks and cobbles in the Negev. Nevertheless, no attempt was yet done to evaluate the role played by dewfall or distillation (water vapor that originates from the soil and may condense on the cobbles i.e., indirect rain water, IRW) in providing water to lithic crustose lichens. For this end, one yearlong measurements of non-rainfall water (NRW), i.e. vapor, dewfall, and fog that originate from the atmosphere, and IRW were measured by the cloth-plate method (CPM) and on two pairs of rock slabs and cobbles between October 1st, 2021 and September 30th, 2022, along with periodic temperature measurements. A total of 79 days of NRW and 48 days of IRW were recorded by the CPM, but when adding the days during which measurements were not conducted, the total days with NRW and IRW amounted to 92 and 74 days, respectively. Whereas the daily average NRW for the cobbles and rocks was 0.095 and 0.044 mm, respectively, it was respectively 0.117 and 0.069 mm for IRW. Previous work allowed us to calculate the daylight wetness duration for NRW (230.9 and 149.7 h for the cobbles and rocks, respectively) and IRW (203.4 and 158.6 h for the cobbles and rocks, respectively). When considering also direct wetting by rain (additional 33 h), the dry period provided 49.4% and 43.9% of the daytime wetness duration for the cobbles and rock slabs, respectively. NRW may thus contribute an approximately equal amount of water to that of rain, with cobbles benefiting more than rock slabs from both water sources. Climate change which may result in increased drought frequency and nocturnal warming may respectively result in lower IRW and NRW, negatively impacting lithobiont distribution.