Flowering Phenology of Werauhia sintenisii, a Bromeliad from the Dwarf Montane Forest in Puerto Rico: an Indicator of Climate Change?

Abstract

Tropical montane cloud forests are experiencing climatic change that may alter their sensitive biota and ecosystem processes. We studied the relationship between several environmental factors and the flowering phenology of Werauhia sintenisii, an epiphytic bromeliad from the dwarf montane cloud forest in Puerto Rico, to infer responsiveness of this species to climate and to suggest how useful its phenology may be in monitoring climatic change. We applied a cross-correlation analysis to the number of open flowers per month to eight different environmental variables for 1999-2000. After determining the lag-time at which the environmental factor was best correlated with the number of open flowers, we performed a stepwise regression with the environmental factor shifted by the number of months indicated by the cross-correlation analysis and the number of open flowers per month. Differences were observed between years in the timing of flowering, which began one month earlier in 2000 than in 1999. The production of flowers was related to the monthly mean minimum temperature three months previous and to the monthly mean daily irradiance two months earlier. Together both variables explained 66% of the variation. The flowering of W. sintenisii, which appears to be susceptible to nocturnal temperatures and solar irradiance, may be useful as a biotic indicator of climate change in cloud forests.