Fog Water and Ecosystem Function: Heterogeneity in a California Redwood Forest

Abstract

Fog is thought to influence ecological function in coastal forests worldwide, yet few data are available that illuminate the mechanisms underlying this influence. In a California redwood forest we measured water and nitrogen (N) fluxes from horizontally moving fog and vertically delivered rain as well as redwood tree function. The spatial heterogeneity of water and N fluxes, water availability, tree water use, and canopy N processing varied greatly across seasons. Water and N fluxes to soil (annual average of 98% and 89%, respectively) across the whole forest occurred primarily in the rain season and was relatively even across the whole forest. In contrast, below-canopy flux of fog water and N declined exponentially from the windward edge to the forest interior. Following large fog events, soil moisture was greater at the windward edge than anywhere else in the forest. Physiological activity in redwoods reflected these differences in inputs across seasons: tree physiological responses did not vary spatially in the rain season, but in the fog season, water use was greater, yet water stress was less, in trees at the windward edge of the forest versus the interior. In both seasons, vertical passage through the forest changed the amount of water and form and concentration of N, revealing the role of the tree canopy in processing atmospheric inputs. Although total fog water inputs were comparatively small, they may have important ecosystem functions, including relief of canopy water stress and, where there is fog drip, functional coupling of above-and belowground processes.

Climatic context and ecological implications of summer fog decline in the coast redwood region

“…Synoptic conditions in these areas are conducive to the development of low-level stratocumulus clouds, which form just below the inversion base, typically several hundred meters above the sea surface (2,3). The advection of marine stratus over land profoundly moderates the coastal terrestrial climate by reducing insolation and temperatures, raising humidity, and supplying water directly to the landscape (4)(5)(6)(7)(8)(9)(10)(11)(12). The last effect is particularly notable along the active tectonic margin defining the Pacific coast of the Americas, where uplifted relief intercepts marine air and cloud moisture and blocks its inland penetration.…”

“…This behavior highlights redwood sensitivity to ambient humidity and, consequently, the presence or absence of clouds. In coastally exposed sites, the marine stratus also provides significant quantities of water to coastal California forests (4,7,9,10,22) and grasslands (13), obtained primarily by drip from the canopy to the root zone (6) and to a lesser extent by direct foliar uptake (5,23). Intraannual variations in δ 18 O and δ 13 C of redwood tree rings show significant correlations to summer low-cloud frequency over recent years (24), reflecting an integrated effect on redwood physiology.…”

Proceedings of the coast redwood forests in a changing California: A symposium for scientists and managers

“…The high organic matter contents (and associated high water holding capacity) and the presence of fog (which reduces evapotranspiration) can both contribute to this characteristic. Decreases in fog water inputs could, however, lead to drier soils (Ewing et al 2009) In contrast to gross nitrification, rates of gross N mineralization in coast redwood forests were relatively insensitive to any variable measured, edaphic or climatic. Other studies have reported a direct relationship between gross N mineralization and substrate availability (Booth et al 2005), and a significant relationship between gross N mineralization and concentrations of soluble organic nitrogen was previously found for two northern redwood sites (Bradbury 2011).…”

Aerosol Deposition and Behavior on Leaves in Cool-temperate Deciduous Forests. Part 2: Characteristics of Fog Water Chemistry and Fog Deposition in Northern Japan

“…Such acid fog deposits on vegetative surfaces and is harmful to plants (Schaberg et al, 2000;Jacobson et al, 1989;Schemenauer, 1986). In addition, fog water deposition significantly contributes to hydrological, nutrient and pollutant inputs to forest ecosystems (Ewing et al, 2009;Fenn et al, 2000;Dawson, 1998), and it may affect the woodland along the somma of Lake Mashu. Nevertheless, the fog water deposition on the woodland in the area, which can cause supply considerable amounts of pollutants and nutrients, has still not been investigated.…”