Epiphytes

• Epiphytes are essential to the viability of tropical cloud forest ecosystems. Arboreal flora controls a number of systemic cycles and serves as nesting and breeding area for many of the unique cloud forest fauna. The high density of epiphytes greatly influences the light cycle, and is responsible for both decreased UV radiation in the understory and increased leaf area index (7). The unusual hydrologic cycle of cloud forests is greatly influenced by the abilities of epiphytes to both capture and store large quantities of water (1). The average water storage volume of arboreal flora is approximately 3000 liters per hectare (1). Water that is captured by epiphytes via horizontal precipitation typically contains concentrations of nutrient ions several times greater than normal rainfall (1). Consequentially, epiphytes and their associated humus are also key players in the nutrient cycle, sometimes holding up to half of the entire nutrient pool of the canopy (7).

• Epiphytes are tightly coupled with climate, particularly with regard to moisture supply. Cloud forest epiphytes in particular, require a strict set of growing conditions including cool temperatures, dim light, and a continuous supply of moisture (1). Such a close association with climate suggests a heightened sensitivity to the potential impacts of climate change (1). To test the potential effects of reduced cloud warter, Nadkarni and Solano (2002) transplanted epiphytes from cloud forests to slightly lower elevations with less available moisture from cloud immersion. The study revealed higher leaf mortality, reduced longevity, and lower leaf production in the experimental plants in comparison to controls. Furthermore, after the transplanted epiphytes died, gap-colonizing tree species established themselves in the newly formed canopy openings, germinating from the existing seed banks within the residual mats of the arboreal soil. Based on their findings, Nadkarni and Solano concluded that death of epiphytes resultant from decreased cloud immersion could potentially result in radical changes to the composition of canopy communities.

Amphibians, lizards, and birds

• Amphibians are notoriously vulnerable to environmental changes due to their permeable skin and eggs. Due to this sensitivity, amphibian populations have been declining worldwide, sometimes in seemingly undisturbed habitats (17).

The last sighting of the Golden Toad (Bufo periglenes) in 1989; it is thought to be extinct

• Climate change may be at least partly to blame. In cloud forest systems, climate change can kill amphibians directly by desiccation from increased water stress. Additionally, climate change may indirectly affect populations by decreasing suitable egg-laying locations, drying ponds before tadpoles hatch, and drying the eggs of leaf-laying frogs (6). A study at the Monte-Verde cloud forest in Costa Rica documented the disappearance of 20 of the 50 anuran (frog and toad) species from a 30 km study site. These disappearances followed large-scale population crashes in 1987, which are thought to have severely altered the bird, reptile, and amphibian communities in the region. The population crashes and subsequent disappearances are likely associated with recent climate warming (17). The same study found that the best predictor of upslope movements for both amphibians and anoline lizard populations was the total number of dry days in the preceding year’s dry season (17).

Declines in populations of anoline lizards and anurans. (a) Correlations of abundance with number of dry days in the preceding dry season for anoles; (b) % change in abundance and relative abundance of several Anuran species corresponding to the number of dry days. Note the three major population crashes. The maximum probability that these three demographic events could be explained by chance alone was calculated to be 0.008. (Pounds et al. 1999)