38 - Effects of fog on climatic conditions at a sub-tropical montane cloud forest site in northern Tenerife (Canary Islands, Spain)

Summary

ABSTRACT

This chapter discusses microclimatic conditions at a ridge crest site in northern Tenerife carrying an impoverished and stunted forest, locally called fayal–brezal. The site is characterized by persistent fog and low cloud brought in by the prevailing trade winds. Temperatures, relative humidity, and wind speed differed between times with and without fog, with lower temperatures and wind speeds, and increased humidity occurring during times of fog. Average rainfall was low (474 mm year⁻¹) with a long dry period in summer. Fog incidence as measured with “standard fog collectors” placed on the windward edge of the forest suggested potentially large amounts of fog water may be available for capturing by the vegetation during rain-free periods. This extra water is thought to explain the survival of an evergreen forest despite the low and strongly seasonal rainfall.

INTRODUCTION

Tenerife is the largest island within the Canaries with a surface area of 2065 km² (Figure 38.1). Despite an annual influx of 5 million tourists, nearly half of the island's area is protected as belonging to one of the six categories of environmental protection established under Spanish law (Martín et al., 1995). The steep relief and particular atmospheric conditions prevailing in this part of the Atlantic have produced a distinct altitudinal vegetation zonation that closely corresponds with changes in climatic conditions (Kämmer, 1974; Arozena, 1991; Fernández-Palacios, 1999).