Ecohydrology of a seasonal cloud forest in Dhofar: 1. Field experiment

Abstract

[1] We describe the ecohydrology of a unique semiarid broadleaf deciduous forest in Dhofar (Oman). The forest is surrounded by desert and is confined to a coastal area, where the summer wet season is characterized by a persistent dense cloud immersion. Using field observations, we show how clouds render the ecosystem particularly water conserving and therefore create a niche for a moist forest biome in a semiarid area in three ways. First, horizontal precipitation (collection of cloud droplets on tree canopies) added valuable water, such that about two times as much water was received below the canopy (net precipitation) compared to above (rainfall). Second, high stemflow, of about 30% to net precipitation, led to concentrated water input around the stems. Third, transpiration was suppressed during the cloudy summer season, which allowed for storage of the received water. It was only used after the end of the wet season and lasted for the following 3 months, which roughly doubled the length of the growing season. Our results demonstrate that cloud immersion may shape ecosystem hydrology in significant ways, particularly in semiarid environments.

Induced precipitation recycling (IPR): A proposed concept for increasing precipitation through natural vegetation feedback mechanisms

“…Surrounding slopes may also be immersed in clouds, making it possible to replicate conditions like those that support cloud forests in other semi-arid regions (Dawson 1998;Pepin et al, 2010;Hildebrandt et al, 2007), enabling trees on slopes and hills to acquire moisture through "fog harvesting".…”

Pseudo-hysteretic double-front hiatus-stage soil water parcels supplying a plant–root continuum: the Green-Ampt-Youngs model revisited

“…We assume that transpiration is relatively small during the monsoon period and the water uptake from the saturated zone is negligible (Hildebrandt et al 2007). Then the position of the front y i (t) during the time interval 0 < t < T is described by the classical GA analytical solution (PolubarinovaKochina 1962).…”

“…Due to the high intensity of their rainfall, and the prevalence of runoff, it seems not to penetrate the deep soil as thoroughly as the precipitation during the monsoon. Hildebrandt et al (2007) estimated that water received below the tree crowns consists of about onethird rainfall and two-thirds intercepted cloud water. This leads to a pattern where more soil water infiltrates below the tree crowns compared to further away (i.e.…”

“…For comparison, the most common fruiting tree in the region, the date palm, consumes 30 000-50 000 L of water through regular irrigation. Most of the water uptake in the Dhofar forest occurs after the end of the monsoon until the time when water becomes limiting and transpiration declines (Hildebrandt et al 2007). It is noteworthy that irrigation of date palms and other crops requires thorough scheduling over the season with watering in the range of 50-150 L/d (winter-summer) that is time-, labour-and instrumentally-consuming.…”

“…Annual precipitation over the canopy projection is 300 mm/year (Hildebrandt et al 2007). In computations based on Hildebrandt et al (2007), we assumed that 85% of precipitation in both zones (canopy-covered and bare) is used in transpiration. For the selected crown radius, this gives 1750 L/year per tree under the canopy.…”