Mesoclimatic Patterns Shape the Striking Vegetation Mosaic in the Cordillera Central, Dominican Republic

Abstract

A relationship between forest vegetation patterns and climate has been proposed for Caribbean mountains, but mesoscale temperature, precipitation (PPT), humidity, and cloud formation patterns are poorly documented. Half-hourly temperature and humidity observations were obtained from 2001 to 2011 from a network of 10 data-logging instruments ranging in elevation from 1500 to 2800 m on the windward slopes of the Cordillera Central, Dominican Republic. We report diurnal, seasonal, and annual patterns in temperature, PPT, humidity, and the trade wind inversion (TWI) along the elevation gradient. The elevational gradient in mean air temperature was non-linear during the dry season, with lapse rates decreasing to -0.5 °C km-1 between 1500 and 1900 m and -0.8 °C km-1 between 2100 and 2400 m. Relative humidity reached a maximum at 2100 m (mean of 91%), but remains above 85% over the entire gradient until 2600 m, above which it drops steeply. Relative humidity also showed marked seasonality but only at the highest elevations, dropping markedly above 2400 m and especially above 2600 m in the dry season, while remaining high at lower elevations throughout the year. PPT declined only slightly with elevation on windward slopes, but was markedly lower in leeward areas. Dry season PPT was lower on windward and leeward slopes at all elevations, except at ∼2400 m on windward slopes where it remained nearly as high as the rest of the year. Sub-zero temperatures occurred at elevations ≥2325 m and increased markedly in frequency ≥2600 m. These observations support the hypothesis that the discrete vegetation ecotone between the cloud forest and subalpine pine forest at ∼2200 m on windward slopes results from climatic discontinuities, especially during the dry season. In particular, the TWI effect on mesoclimatic patterns (especially moisture) regulates the elevational maximum of cloud forest flora and likely will represent a strong barrier to the future migration of cloud forest flora to higher elevations in response to warmer temperatures. Together with increased moisture stress due to higher temperatures, climate change in the high elevations of tropical mountains is therefore likely to disrupt the dynamics and distributions of tropical montane forests.