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BackgroundTropical montane cloud forests (TMCFs) are characterized by a unique set of biological and hydroclimatic features, including frequent and/or persistent fog, cool temperatures, and high biodiversity and endemism. These forests are one of the most vulnerable ecosystems to climate change given their small geographic range, high endemism and dependence on a rare microclimatic envelope. The frequency of atmospheric water deficits for some TMCFs is likely to increase in the future, but the consequences for the integrity and distribution of these ecosystems are uncertain. In order to investigate plant and ecosystem responses to climate change, we need to know how TMCF species function in response to current climate, which factors shape function and ecology most and how these will change into the future.ScopeThis review focuses on recent advances in ecophysiological research of TMCF plants to establish a link between TMCF hydrometeorological conditions and vegetation distribution, functioning and survival. The hydraulic characteristics of TMCF trees are discussed, together with the prevalence and ecological consequences of foliar uptake of fog water (FWU) in TMCFs, a key process that allows efficient acquisition of water during cloud immersion periods, minimizing water deficits and favouring survival of species prone to drought-induced hydraulic failure.ConclusionsFog occurrence is the single most important microclimatic feature affecting the distribution and function of TMCF plants. Plants in TMCFs are very vulnerable to drought (possessing a small hydraulic safety margin), and the presence of fog and FWU minimizes the occurrence of tree water deficits and thus favours the survival of TMCF trees where such deficits may occur. Characterizing the interplay between microclimatic dynamics and plant water relations is key to foster more realistic projections about climate change effects on TMCF functioning and distribution.

Tropical forest restoration is increasingly seen as an activity that may counteract or reduce biodiversity loss. However, few studies monitor fauna or consider measures of functional diversity to assess restoration success. We assessed the effect of a tropical montane forest restoration program on species and functional diversity, using amphibians as the target group. We compared amphibian assemblages in three types of land use: restoration areas, tropical montane cloud forest (TMCF; reference ecosystem) and cattle pastures (degraded ecosystem) in southern Mexico. We also described microclimate, microhabitat heterogeneity, woody vegetation structure and diversity for each type of land use, and their relationship to amphibian species and functional diversity. Compared to TMCF, restoration areas had similar environmental conditions. However, amphibian species richness was similar in the three types of land use and abundance was lower in the restoration areas. In TMCF, the amphibian assemblage was dominated by forest-specialist species, the pastures by generalist species, and the restoration areas by a combination of both species types. Interestingly, functional richness, functional evenness and functional divergence did not vary with land use, though the number of functional groups in restoration areas and TMCF was slightly higher. Overall, the results suggest that after seven years, active restoration provided habitat heterogeneity and recovered woody vegetation capable of maintaining amphibian species and functional groups similar to those inhabiting TMCF. Forest fragments adjacent to restoration areas seem to facilitate fauna recolonization and this emphasizes the importance of the conservation of the reference ecosystems to achieving restoration success.

Epiphyte communities comprise important components of many forest ecosystems in terms of biomass and diversity, but little is known regarding trade-offs that underlie diversity and structure in these communities or the impact that microclimate has on epiphyte trait allocation. We measured 22 functional traits in vascular epiphyte communities across six sites that span a microclimatic gradient in a tropical montane cloud forest region in Costa Rica. We quantified traits that relate to carbon and nitrogen allocation, gas exchange, water storage, and drought tolerance. Functional diversity was high in all but the lowest elevation site where drought likely limits the success of certain species with particular trait combinations. For most traits, variation was explained by relationships with other traits, rather than differences in microclimate across sites. Although there were significant differences in microclimate, epiphyte abundance, and diversity, we found substantial overlap in multivariate trait space across five of the sites. We found significant correlations between functional traits, many of which related to water storage (leaf water content, leaf thickness, hydrenchymal thickness), drought tolerance (turgor loss point), and carbon allocation (specific leaf area, leaf dry matter content). This suite of trait correlations suggests that the epiphyte community has evolved functional strategies along with a drought avoidance versus drought tolerance continuum where leaf succulence emerged as a pivotal overall trait.

Many tropical montane cloud forest (TMCF) trees are capable of foliar water uptake (FWU) during leaf-wetting events. In this study, we tested the hypothesis that maintenance of leaf turgor during periods of fog exposure and soil drought is related to species’ FWU capacity. We conducted several experiments using apoplastic tracers, deuterium labeling and leaf immersion in water to evaluate differences in FWU among three common TMCF tree species. We also measured the effect of regular fog exposure on the leaf water potential of plants subjected to soil drought and used these data to model species’ response to long-term drought. All species were able to absorb water through their leaf cuticles and/or trichomes, although the capacity to do so differed between species. During the drought experiment, the species with higher FWU capacity maintained leaf turgor for a longer period when exposed to fog, whereas the species with lower FWU exerted tighter stomatal regulation to maintain leaf turgor. Model results suggest that without fog, species with high FWU are more likely to lose turgor during seasonal droughts. We show that leaf-wetting events are essential for trees with high FWU, which tend to be more anisohydric, maintaining leaf turgor during seasonal droughts.

Questions: What is the role of microclimate relative to easily obtainable measures of forest structure in explaining epiphyte abundance? Do these roles differ between epiphytic plant groups? Location: Tropical pre-montane cloud forests. Alto Mayo watershed, northern Peru. Methods: We recorded vascular epiphyte abundance, epiphytic bryophyte cover and forest structural features in 36 plots (20 m × 20 m), and measured air temperature and humidity in a subset of 17 plots. We modelled bryophyte cover, total vascular epiphyte abundance and the abundances of the main vascular epiphyte groups separately (bromeliads, aroids, ferns), as a function of forest structure and microclimate using spatial autoregressive models. Three forest structural variables (basal area, tree height and canopy openness) and two microclimatic variables (minimum humidity and maximum temperature) were considered. We constructed all possible combinations of maximum two-variable models from the five explanatory variables and carried out AIC-based model selection and variable importance tests with these as input models. Results: Canopy openness was the most important variable explaining the abundance of the main epiphytic plant groups. It was also strongly correlated with stand microclimate. Therefore, predictions of epiphyte abundance did not improve with the inclusion of microclimatic data in the models. There were some differences among the epiphytic plant groups in their response to microclimate and forest structural features. Conclusions: Forest stand microclimate, reflected through canopy openness in particular, was a main determinant of the distributions of all epiphytic plant groups. This implies that easily measurable forest structural variables alone can be used as good predictors of epiphyte abundance. Taxon-specific differences in responses to microclimate imply that these taxa may also differ in their sensitivity to predicted future changes in temperature and rainfall.

Planted forests contribute to maximizing timber production but their role as valuable habitat for diversity is of increasing concern, particularly in tropical montane cloud forest (TMCF) landscapes, which present extremely high diversity and endemism. We compared tree diversity, potential timber productivity and estimated net revenues in planted forests of Pinus patula and mixed TMCF species in southern Mexico. These planted forests were 21 years-old and established under similar environmental conditions in abandoned pastures previously occupied by TMCF. Adult tree height and density were similar between planted forests, but sapling and seedling density were reduced in P. patula in comparison to the mixed forest (0.05 and 0.28 sapling m−2 and 0.08 and 0.56 seedling m−2, respectively). The diversity of adults was similar, but that of saplings and seedlings was lower in P. patula than in the mixed forest (saplings: 3.39 and 9.14 effective species; seedlings: 2.85 and 9.59, respectively). Timber volume was similar between planted forests; however, due to higher establishment costs and lower market price, the net present value (NPV) of the mixed forest was considerably lower than that of P. patula. The mixed forest only achieved a positive NPV with subsidies and an interest rate < 5% under a 30% harvesting intensity. To ameliorate biobiodiversity loss, TMCF landscapes require alternative measures; e.g., a supply of a diverse mix of native seedlings, stimulation of the market for native species, compensatory mechanisms for mixed plantations of native species and landscape approaches that combine economically profitable and ecologically desirable species.

Epiphytes are common in tropical montane cloud forests (TMCFs) and play many important ecological roles, but the degree to which these unique plants will be affected by changes in climate is unknown. We investigated the drought responses of three vascular epiphyte communities bracketing the cloud base during a severe, El Niño-impacted dry season. Epiphytes were instrumented with sap flow probes in each site. Leaf water potential and pressure–volume curve parameters were also measured before and during the drought. We monitored the canopy microclimate in each site to determine the drivers of sap velocity across the sites. All plants greatly reduced their water use during the drought, but recovery occurred more quickly for plants in the lower and drier sites. Plants in drier sites also exhibited the greatest shifts in the osmotic potential at full saturation and the turgor loss point. Although all individuals survived this intense drought, epiphytes in the cloud forest experienced the slowest recovery, suggesting that plants in the TMCF are particularly sensitive to severe drought. Although vapor pressure deficit was an important driver of sap velocity in the highest elevation site, other factors, such as the volumetric water content of the canopy soil, were more important at lower (and warmer) sites.

Bryophytes play key roles in the ecological function of a number of major world biomes but remain understudied compared with vascular plants. Little is known about bryophyte responses to different aspects of predicted changes in moisture dynamics with climate change. In this study, CO₂ fluxes and photosynthetic light responses were measured within bryophyte mesocosms, being subjected to different amounts, frequencies, and types (mist or rainfall) of water addition, both before and after different periods of complete desiccation. Bryophyte carbon fluxes and photosynthetic light response were generally affected by the magnitude and type, but not frequency, of watering events. Desiccation suppressed bryophyte carbon uptake even after rehydration, and the degree of uptake suppression progressively increased with desiccation duration. Estimated ecosystem-level bryophyte respiration and net carbon uptake were c. 58% and c. 3%, respectively, of corresponding fluxes from tree foliage at the site. Our results suggest that a simplified representation of precipitation processes may be sufficient to accurately model bryophyte carbon cycling under future climate scenarios. Further, we find that projected increases in drought could have strong negative impacts on bryophyte and ecosystem carbon storage, with major consequences for a wide range of ecosystem processes.

The protection of natural areas is considered an essential strategy for environment conservation. The objective of this work was to determine the level of vulnerability, considering the characterization and identification of the risk zones and ecological protection of the Pagaibamba Protection Forest (PPF, Peru). To determine the vulnerable areas, Landsat ETM satellite images, topographic, geological, ecological, and vegetation cover maps were used. Geological, physiographic, edaphological, vegetation cover, and land use potential characteristics, were analyzed. Three Ecological Protection and Risk Zones were identified, with the largest extension of the PPF corresponding to lands of very high and high vulnerability and high ecological risk, which include >85% of Protected Natural Areas (PNA) and 54% of the Buffer Zone (BZ). Moderate risk areas represent 30% of the Buffer Zone (BZ) and 13% of the PNA, and the low-risk areas (represent 15% of the BZ and 2% of the PNA). Biogeographically, the PPF was related to the Cloudy Montane Forests Ecoregion of the Andes Mountains, standing out the Tropical Montane Cloud Forest (TMCF) and the Tropical Lower Montane Cloud Forest (TLMCF). These forests are a global conservation priority due to their great biodiversity, high level of endemicity of flora and fauna, and the crucial hydrological function they fulfill.

Key messageThe Mexican beech undergoes masting events, on average, every 5.5 years. These events depend directly on precipitation.Climate change has considerably impacted the protective functions of tropical montane cloud forests, possibly influencing the synchronicity of phenological processes and the distribution and physiology of plants. In particular, climatic fluctuations cause changes in the distribution of tree species. Mexican beech (Fagus grandifolia subsp. mexicana) is considered an endangered species, due to its restricted distribution and its being a Miocene relict, limited to tropical montane cloud forests in the mountains of the Sierra Madre Oriental in eastern Mexico. We analyzed the influence of temperature and precipitation in prompting changes to tree-ring width, as well as vessel frequency and diameter, of Mexican beech in eastern Mexico. We used growth rings and xylem vessels traits to infer the historical masting events of Mexican beech over the last 128 years. We obtained independent chronologies for Mexican beech in each of the studied sites, dating back 152–178 years. Precipitation was strongly associated with differences in tree-ring width between masting and non-masting years. Our study highlights the use of dendroecological research to detect climate-induced modifications in the vessel frequency and diameter of tree species inhabiting tropical montane cloud forests. This association also explained differences in vessel frequency and diameter recorded before, during, and after masting events. Our results revealed that Mexican beech undergoes masting events every 5.5 years on average, and that these events directly depend on minimum annual precipitation. In conclusion, our results advance our understanding on the plasticity of growth rings and vessels traits (frequency and diameter) in response to fluctuation in precipitation.