There is extensive evidence of flowering time shifts over the past 50 years in temperate regions, but far less is known about tropical regions where seasonality is less temperature driven. In particular, few studies have addressed potential shifts in phenology for tropical species that are mutualistically interdependent but may respond differently to climate change leading to increased asynchrony (e.g. flowering plants and their pollinators). We combined recent phenological observations with historical datasets of flowering patterns in two guilds of ornithophilous plants in the montane cloud forests of Monteverde, Costa Rica to compare recent phenological patterns to those in the 1980s. Our goals were to 1) determine if flowering patterns have changed over 36 years of changing climate and 2) identify environmental cues for flowering in nine species of plant that are important resources for hummingbirds. Bimonthly censuses of flower production along standardized transects were used to quantify flower production during three sampling periods:1981-1983, 1986-1991 and 2017-2018. Model selection was used as an analytical approach to identifying environmental correlates and cues for flowering patterns.
Results/Conclusions
Considerable variance in flowering patterns over time for the majority of the species studied provided little evidence of a consistent shift in flowering patterns over time as has been seen in temperate latitudes. In contrast, to temperate plants the species studied here appear to cue flowering patterns to either accumulated drought units or a combination of accumulated drought units and chill units prior to flowering. However, recent patterns of warmer minimum temperatures and reduced accumulation of chill units have led to a poor fit of observed and expected flower production. These results suggest that flower production may have decreased over time and with it an important nectar resource available to hummingbirds.