Hydrometeorology of tropical montane cloud forests: emerging patterns

Abstract

Abstract:Tropical montane cloud forests (TMCF) typically experience conditions of frequent to persistent fog. On the basis of the altitudinal limits between which TMCF generally occur (800-3500 m.a.s.l. depending on mountain size and distance to coast) their current areal extent is estimated at ¾215 000 km 2 or 6Ð6% of all montane tropical forests. Alternatively, on the basis of remotely sensed frequencies of cloud occurrence, fog-affected forest may occupy as much as 2Ð21 Mkm 2 . Four hydrologically distinct montane forest types may be distinguished, viz. lower montane rain forest below the cloud belt (LMRF), tall lower montane cloud forest (LMCF), upper montane cloud forest (UMCF) of intermediate stature and a group that combines stunted sub-alpine cloud forest (SACF) and 'elfin' cloud forest (ECF). Average throughfall to precipitation ratios increase from 0Ð72 š 0Ð07 in LMRF (n D 15) to 0Ð81 š 0Ð11 in LMCF (n D 23), to 1Ð0 š 0Ð27 (n D 18) and 1Ð04 š 0Ð25 (n D 8) in UMCF and SACF-ECF, respectively. Average stemflow fractions increase from LMRF to UMCF and ECF, whereas leaf area index (LAI) and annual evapotranspiration (ET) decrease along the same sequence. Although the data sets for UMCF (n D 3) and ECF (n D 2) are very limited, the ET from UMCF (783 š 112 mm) and ECF (547 š 25 mm) is distinctly lower than that from LMCF (1188 š 239 mm, n D 9) and LMRF (1280 š 72 mm; n D 7). Field-measured annual 'cloud-water' interception (CWI) totals determined with the wet-canopy water budget method (WCWB) vary widely between locations and range between 22 and 1990 mm (n D 15). Field measured values also tend to be much larger than modelled amounts of fog interception, particularly at exposed sites. This is thought to reflect a combination of potential model limitations, a mismatch between the scale at which the model was applied (1 ð 1 km) and the scale of the measurements (small plots), as well as the inclusion of near-horizontal wind-driven precipitation in the WCWB-based estimate of CWI. Regional maps of modelled amounts of fog interception across the tropics are presented, showing major spatial variability. Modelled contributions by CWI make up less than 5% of total precipitation in wet areas to more than 75% in low-rainfall areas. Catchment water yields typically increase from LMRF to UMCF and SACF-ECF reflecting concurrent increases in incident precipitation and decreases in evaporative losses. The conversion of LMCF (or LMRF) to pasture likely results in substantial increases in water yield. Changes in water yield after UMCF conversion are probably modest due to trade-offs between concurrent changes in ET and CWI. General circulation model (GCM)-projected rates of climatic drying under SRES greenhouse gas scenarios to the year 2050 are considered to have a profound effect on TMCF hydrological functioning and ecology, although different GCMs produce different and sometimes opposing results. Whilst there have been substantial increases in our understanding of the hydrological processes operating in TMCF, additional re...

Interactions between payments for hydrologic services, landowner decisions, and ecohydrological consequences: synergies and disconnection in the cloud forest zone of central Veracruz, Mexico

“…We found that additional water inputs due to CWI were comparatively low (< 2% of 3180 mm yr -1 and 8% of dryseason rainfall of 640 mm), which was largely attributed to the relatively infrequent occurrence of dense fog and, especially, low wind speeds (Holwerda et al 2010, Alvarado-Barrientos et al 2014. Our cloud forest site falls at the low end of the global range for CWI, while the estimated ET (1325 mm yr -1 ) (Muñoz-Villers et al 2012) is at the higher end of the global range (Bruijnzeel et al 2011). These findings contrast with many other studies conducted in (foggier or windier) cloud forest sites that showed a much greater annual water recharge (i.e., CWI inputs minus ET losses) (Holwerda 2005, Holwerda et al 2006, McJannet et al 2007).…”

“…For example, some PHS schemes (Quintero et al 2009: Ecuador;Muñoz-Piña et al 2008: Mexico) attribute greater hydrologic value and, in turn, payment compensation to cloud forests because of their (presumably) higher water yield over other forests due to a combination of high rainfall, additional fog deposition inputs, and low evapotranspiration losses (cf. Bruijnzeel et al 2011). Other programs have attempted to identify areas of greater hydrologic priority based on recharge zones (Peñuela-Arévalo and Carrillo-Rivera 2013).…”

“…However, not all cloud forests are functionally equal , and their water yield varies as a function of geographic differences in, especially, climate and exposure to fog and wind (Jarvis and Mulligan 2011). For instance, observed annual amounts of CWI range from 22 mm to 1990 mm, and modeled contributions of CWI vary from 5% to > 75% of annual precipitation (P), while annual ET can range from < 550 mm to > 1280 mm (Bruijnzeel et al 2011 and references therein).…”

Edge Influence on Diversity of Orchids in Andean Cloud Forests

“…The CF world surface area consists of ca. 215,000 km 2 [5], constituting an average 6.6% of the world's tropical forests [6]. CF forests have scarce continuous vegetation cover and their restricted distribution makes them sensitive to isolation owing to the deforestation processes in recent years [7].…”

“…CF forests have scarce continuous vegetation cover and their restricted distribution makes them sensitive to isolation owing to the deforestation processes in recent years [7]. Since the 1990s, CF ecosystems have been classified amongst the most threatened terrestrial ecosystems [6], showing a deforestation rate during 1981-1990 much higher than that of lowland woods (1.1% vs. 0.8% yearly, respectively; [8]) causing a decrease in 19.3% of its original global cover [7], whilst a recent small scale study has shown a deforestation rate for 1986-2006 of 0.72% [9].…”