Fig 1.
TMCF species adaptations reflect persistent cloud immersion.
In Puerto Rico, for example, high lichen diversity is illustrated for stunted, ridgetop “elfin” cloud forest (photos by Joel A. Mercardo-Díaz and María Rivera).
Fig 2.
Many páramo species are adapted to frost and scavenge fog water.
(A) Large rosette plants (Espeletia sp.) characteristic of much páramo vegetation and (B) a closeup of an Espeletia sp. showing its dense pubescence (photos by Mike and Lara Wolf (A) and Felipe Rodríguez (B)).
Fig 3.
A simple model mapped and projected cloud forest minimum elevation (CFmin).
The model parameters include maximum watershed elevation (ELEVmax), to gauge the mass elevation effect; average annual hourly relative humidity (RH) from 100–150 m elevation within a watershed (RH150), to account for differences in the humidity of the rising air; and region (Region), to help account for other factors that affect cloud formation. All else equal, the mass elevation effect causes CFmin to be at a lower elevation on smaller mountains compared with larger ones. Also, on larger mountains, frost or atmospheric inversions occur that cause colder or drier conditions that define cloud forest upper limits, though fast-draining soils, land use, microclimate, or other factors may also define cloud forest upper limits.
Fig 4.
The CFmin model explained 86% of point variation without having bias.
(A) A 1:1 line (thick black line) compared with log(CFmin) plotted as a function of CFmin predicted by the mapping model: Log(CFmin) = 8.480*** − 0.0305ELEVmax2*** + 0.317ELEVmax*** − 0.0233RH150*** − Region. Region = [0 if Region = Inland Tropics; else 0.676*** if Region = Dry Coastal; else 0.472*** if Region = Caribbean Coastal; else 0.324** if Region = Pacific Coastal; else 0.239*** if Region = Outer Tropics] (N = 79; Parameter estimate Pr > F: <0.0001 = ***, <0.01 = **), and (B) Modeling regions (Region). Light grey = areas with no CFmin estimates. Black circles = CFmin locations.
Fig 5.
Current Neotropical montane cloud forests and páramo.
The mapping algorithm, based on CFmin, minimum annual relative humidity (RH min) and Frost, detected TMCF across the Neotropics, including (A) Mesoamerica and the Caribbean islands, and (B) South America. “Other vegetation” includes other tropical alpine vegetation or non-TMCF forest (see Thresholds for frost).
Fig 6.
The approach detected TMCF on coasts and islands.
A closeup example of coastal and island TMCF zones for the island of Puerto Rico for current (A) and projected future conditions (B). Under a moderate greenhouse gas emissions scenario (RCP-4.5), in <45–65 yr (~2070) all of Puerto Rico’s cloud forest zones would either be below CFmin, suffer RH declines of 3% or more or to below RHmin. Although not depicted in this figure, all of Puerto Rico’s TMCF zones would suffer RH drops of more than 3%, and these RH declines are largest in Western and Central Puerto Rico.
Fig 7.
Cloud immersion changes in Neotropical cloud forests.
Existing Neotropical TMCF zone area (in km2, top line, 250-m cell size) and percent of this area (bars) by Region, TMCF upper limit and category of change in cloud immersion. TMCF would experience cloud immersion declines of nearly 60 to 90% with (A) moderate climate change as soon as around 2040 (57% decline, RCP 4.5, average year 2050), to (B) a worst-case scenario as soon as around 2060 (86% decline, RCP 8.5, ~2070). The remaining area with a TMCF climate is 43% Left, plus 6.8% Added, ≈ 50% for (A) and 14% plus 4.8% ≈ 19% for (B). Most added TMCF comes at the expense of páramo. The total lost includes these categories of change in cloud immersion: Below CFmin (= CFmin rises above this area—other categories remain above CFmin); RHd ≤ -3% or < RHmin (= RH falls severely); -3% < RHd < 0% (= RH falls by up to 3%). The percent Left includes the category RHd ≥ 0% (= RH is stable or increases slightly). The percent Added comes from CFmin lowering, RH increases, or frost declines at TMCF upper limits. Types of TMCF at upper limits: No Subalpine = montane TMCF where no subalpine TMCF occurs; Mixed = montane TMCF + mixed TMCF); Subalpine 1 = montane TMCF + subalpine 1 TMCF (TMCF transitions to páramo); Subalpine 2 = montane + subalpine 2 TMCF (Subalpine 2 TMCF transitions to puna). Regions: S. America = South America, Mesoamerica = Mexico + Central America, Caribbean = Caribbean Islands, Neotropics combines the three regions.
Fig 8.
Cloud immersion changes by protection for RCP 4.5, ~2070.
Existing Neotropical TMCF zone area (in km2, top line, 250-m cell size) and percent of this area (bars) by Region, TMCF upper limit, protection status and category of change in cloud immersion. In the Caribbean and Mesoamerica, unprotected and usually less-studied TMCF would experience greater cloud immersion declines. Protection status: UPR = Unprotected, PR = Protected. Types of TMCF at upper limits: Fig 7 legend defines cloud immersion change categories and other chart abbreviations.
Fig 9.
Transitions to páramo start at 1–1.5 d yr-1 of frost.
Transitions to páramo from TMCF began at frost frequencies of 1 to 1.5 d yr-1, highlighting frost as a major factor delimiting equatorial Andean tree lines. (A) a Landsat image composite in which páramo appears in dark pink to magenta-green shades, subalpine TMCF appears in green-violet to green shades, and montane to lower montane TMCF is green; (B) areas exceeding minimum frost frequency thresholds for subalpine (i.e., transitional) or páramo zones; (C) how the frost frequency thresholds were used to map subalpine cloud forest and páramo zones. A frost day is any day that temperatures fall to ≤ 0° C.
Fig 10.
Ecoregional changes in páramo cloud immersion and frost frequency.
Categories of change are shown as a percent of current páramo zone area for average year 2070 by Representative Concentration Pathway including: (A) RCP-4.5; (B) RCP-8.5. Páramo ecoregions: Santa Marta = Cordillera de Santa Marta; Talamanca = Cordillera de Talamanca (Costa Rica, Panama); N Oriental 1 = Colombian Cordillera Oriental north of 5° N; N Oriental 2 = Colombian Cordillera Oriental from 2° N to 5° N; N Central/Occid = Colombian Cordilleras Central and Occidental); Real = Ecuadorian Cordillera Real; Central = Peruvian Cordillera Central. Frost change categories: Alpine = frost above Alpine Frostmin2; Subalpine = frost above Subalpine Frostmin1; Montane = frost below Subalpine Frostmin1. Cloud immersion change categories: Beneath CFmin = falls below CFmin; RHd ≤ -3% or < RHmin = RH falls 3% or more or below RHmin; -3% < RHd < 0% = RH falls up to 3%; RHd ≥ 0% = RH is stable or increases.
Fig 11.
Drying and contraction of TMCF and páramo zones example.
Páramo and TMCF zones of the northern Andes for current conditions (A), and for ~2070 under (B) RCP-4.5 and (C) RCP-8.5.
Table 1.
Regional and subregional TMCF zone areas by forest cover and protectiona.
Fig 12.
Deforestation is extensive in some places with stable cloud immersion.
(A) Páramo and TMCF zones of the north, north-central and northwest Andes for current conditions, (B)-(C) remaining TMCF zones with RHd ≥ 0% with areas currently deforested indicated by color for ~2070 under (B) RCP-4.5 and (C) RCP-8.5.