Fog drip maintains dry season ecological function in a California coastal pine forest

Douglas T Fischer,Christopher J Still,A Park Williams,Sara A Baguskas,Colin M Ebert

doi:10.1002/ecs2.1364

Abstract

AbstractFog drip is recognized as an important source of water for many ecosystems that often harbor a disproportionate fraction of endemic species. Characterizing and quantifying the ecological importance of fog drip in these ecosystems requires a range of approaches. We report on a multi‐faceted study of Bishop pine (Pinus muricata D. Don) along a coastal‐inland transect on an island off Southern California. Hourly sampling included micrometeorology, sap flux, and soil moisture. Monthly measurements included changes in tree girth, plant water stress, and isotopic values of fogwater, rainwater, and xylem water. These data show that summertime fog drip clearly affected soil moisture and maintained aspects of tree function, including leaf water relations, sap flux dynamics, and growth rates. Although water from fog drip to the soil surface was occasionally taken up by pine trees, as quantified with isotopic measurements and a Bayesian mixing model, this utilization of fog drip was highly variable in space and time. The proportion of fogwater inferred to have been used is also much less than has been demonstrated in more mesic coastal forest ecosystems using isotopic methods. These results thus suggest high ecosystem sensitivity to even moderate amounts of fog drip, a finding with important implications as climate change differentially affects fog and rain patterns.

Highlights

Assessing and quantifying the ecological importance of fogwater to forest function has challenged researchers for more than a century (e.g., Marloth 1905, Scholl et al 2011)
Soil moisture data Soil moisture probes measuring water potential at Site 7 exhibit dynamic behaviors at different depths that are driven by soil drying following the last rains and regular light fog- drip to the soil surface (Fig. 2a)
Differences in the post-r ain dry-d own rate would be expected based on canopy cover affecting the amount of solar radiation reaching the soil surface, as well as differences in the rate of soil water withdrawal from active pine trees compared to senesced grasses

Summary

Introduction

Assessing and quantifying the ecological importance of fogwater to forest function has challenged researchers for more than a century (e.g., Marloth 1905, Scholl et al 2011). Fog drip has been shown to be an important source of water in a number of ecosystems, including tropical and temperate montane cloud forests and coastal ecosystems in the world’s five major Mediterranean climate zones. These ecosystems are recognized for high levels of biodiversity and species endemism (Olson and Dinerstein 1998). In Mediterranean climate regions like coastal California, water inputs are highly seasonal, with most rain falling in winter, followed by a long summer drought as stored soil moisture steadily v www.esajournals.org. The only significant summertime ecosystem water input is fog drip, and it can play a key role in maintaining some level of water availability through the summer (Carbone et al 2012)

Methods

Results

Conclusion