Vapor pressure deficit predicts epiphyte abundance across an elevational gradient in a tropical montane region

Gotsch, Sybil G.; Davidson, Kenneth; Murray, Jessica G.; Duarte, V.; Draguljić, Danel

doi:10.3732/ajb.1700247

Cited by 35 publications

(40 citation statements)

References 57 publications

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“…Canopy soil, meteorological and canopy hydrologic data are rarely collected together, but one ongoing study in the tropical montane cloud forest (TMCF) region in Monteverde, Costa Rica, is collecting such data. Researchers have established six canopy sites along an elevation gradient spanning from 1100 m on the Pacific side of the mountain range, which is a premontane rain forest, to 1600 m on the Atlantic side of the range, which is an exceedingly wet and relatively aseasonal cloud forest site [71]. We present, as an example, an analysis of the frequency of canopy soil dryness at multiple elevations for Monteverde's forest canopy ( Figure 6)-a site that represents conditions where the canopy saturation state is expected to be consistently saturated.…”

Section: Canopy Soilsmentioning

confidence: 99%

“…The uppermost site (1550 m asl) is in cloud forest, the mid-elevation (1400 m asl) site is just below the average current cloud base and the lowest site (1100 m) is in premontane rain forest. Further site details have been published previously [71], but each of these sites host canopy soils. Available canopy soil water storage varied with elevation, but a large portion of the maximum soil moisture content was often available to precipitation (and occult deposition) throughout the study period and many small rain events did not fill canopy soils to capacity ( Figure 6).…”

Section: Canopy Soilsmentioning

confidence: 99%

“…To determine the importance of the internal leaf "bucket" in canopy water cycling, a quantification of leaf water storage across species and habitats is necessary as well as the quantification of changes in leaf water stores with dehydration. In an ongoing study, Gotsch et al [22,71] have quantified functional traits in sites along an elevation gradient in the TMCF in Monteverde, Costa Rica. Since the cloud base is projected to rise in this region, concern is mounting regarding the vulnerability of the TMCF ecosystem and canopy plants in particular [22,[81][82][83].…”

Section: Vascular Epiphytes: Do Their Ecophysiological Mechanisms Keementioning

confidence: 99%

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Arboreal Epiphytes in the Soil-Atmosphere Interface: How Often Are the Biggest “Buckets” in the Canopy Empty?

et al. 2019

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Arboreal epiphytes (plants residing in forest canopies) are present across all major climate zones and play important roles in forest biogeochemistry. The substantial water storage capacity per unit area of the epiphyte "bucket" is a key attribute underlying their capability to influence forest hydrological processes and their related mass and energy flows. It is commonly assumed that the epiphyte bucket remains saturated, or near-saturated, most of the time; thus, epiphytes (particularly vascular epiphytes) can store little precipitation, limiting their impact on the forest canopy water budget. We present evidence that contradicts this common assumption from (i) an examination of past research; (ii) new datasets on vascular epiphyte and epi-soil water relations at a tropical montane cloud forest (Monteverde, Costa Rica); and (iii) a global evaluation of non-vascular epiphyte saturation state using a process-based vegetation model, LiBry. All analyses found that the external and internal water storage capacity of epiphyte communities is highly dynamic and frequently available to intercept precipitation. Globally, non-vascular epiphytes spend <20% of their time near saturation and regionally, including the humid tropics, model results found that non-vascular epiphytes spend~1/3 of their time in the dry state (0-10% of water storage capacity). Even data from Costa Rican cloud forest sites found the epiphyte community was saturated only 1/3 of the time and that internal leaf water storage was temporally dynamic enough to aid in precipitation interception. Analysis of the epi-soils associated with epiphytes further revealed the extent to which the epiphyte bucket emptied-as even the canopy soils were often <50% saturated (29-53% of all days observed). Results clearly show that the epiphyte bucket is more dynamic than currently assumed, meriting further research on epiphyte roles in precipitation interception, redistribution to the surface and chemical composition of "net" precipitation waters reaching the surface.

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Section: Canopy Soilsmentioning

confidence: 99%

Section: Canopy Soilsmentioning

confidence: 99%

Section: Vascular Epiphytes: Do Their Ecophysiological Mechanisms Keementioning

confidence: 99%

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Arboreal Epiphytes in the Soil-Atmosphere Interface: How Often Are the Biggest “Buckets” in the Canopy Empty?

et al. 2019

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“…The global average environmental lapse rate of 6.5°C/km (Thayyen & Dimri, ) applied to the rugged mountains underlying some tropical forests indicates that steep gradients in temperature and relative humidity occur over relatively short horizontal distances. These changes in microclimate with elevation appear to be strong drivers of variation in vascular epiphyte biomass and species richness (Bussmann, ; Ding et al, ; Gehrig‐Downie, Marquardt, Obregón, Bendix, & Gradstein, ; Gotsch, Davidson, Murray, Duarte, & Draguljić, ; Hietz & Hietz‐Seifert, ; Wolf & Flamenco‐S, ), and may explain the mid‐elevation peak in vascular epiphyte species richness that has been documented in montane forests (Cardelús, Colwell, & Watkins, ; Hietz & Hietz‐Seifert, ; Krömer, Kessler, Gradstein, & Acebey, ).…”

Section: Introductionmentioning

confidence: 99%

“…Such changes will likely cause physiological stress in epiphyte communities that could influence patterns of biomass and diversity (Darby, Draguljić, Glunk, & Gotsch, ; Pounds, Fogden, & Campbell, ; Still et al, ). For example, epiphytes exposed to experimental drought and warming experienced declines in leaf thickness, stomatal conductance, and sap flow (Darby et al, ), and the absorption of cloud water directly through the leaf surfaces of some species suggests that cloud immersion may be important for maintaining adequate hydration (Darby et al, ; Gotsch et al, , ). Understanding epiphyte patterns across multiple spatial scales can indicate at which scales taxa may be most vulnerable to changes in climate and landscape.…”

Section: Introductionmentioning

confidence: 99%

Differences in epiphyte biomass and community composition along landscape and within‐crown spatial scales

et al. 2019

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Vascular epiphytes contribute to the structural, compositional, and functional complexity of tropical montane cloud forests because of their high biomass, diversity, and ability to intercept and retain water and nutrients from atmospheric sources. However, human‐caused climate change and forest‐to‐pasture conversion are rapidly altering tropical montane cloud forests. Epiphyte communities may be particularly vulnerable to these changes because of their dependence on direct atmospheric inputs and host trees for survival. In Monteverde, Costa Rica, we measured vascular epiphyte biomass, community composition, and richness at two spatial scales: (1) along an elevation gradient spanning premontane forests to montane cloud forests and (2) within trees along branches from inner to outer crown positions. We also compared epiphyte biomass and distribution at these scales between two different land‐cover types, comparing trees in closed canopy forest to isolated trees in pastures. An ordination of epiphyte communities at the level of trees grouped forested sites above versus below the cloud base, and separated forest versus pasture trees. Species richness increased with increasing elevation and decreased from inner to outer branch positions. Although richness did not differ between land‐cover types, there were significant differences in community composition. The variability in epiphyte community organization between the two spatial scales and between land‐cover types underscores the potential complexity of epiphyte responses to climate and land‐cover changes. Abstract in Spanish is available with online material.

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Drought response strategies of vascular epiphytes in isolated pasture trees in a Costa Rican tropical montane landscape

Vaughan,

Williams,

Nadkarni

et al. 2024

American J of Botany

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PremiseVascular epiphytes of tropical montane cloud forests are vulnerable to climate change, particularly as cloud bases elevate and reduce atmospheric inputs to the system. However, studies have generally focused on epiphytes in contiguous forests, with little research being done on epiphytes on isolated pasture trees. We investigated water relations of pasture‐tree epiphytes at three sites located below and above the elevation of the average cloud base in Monteverde, Costa Rica.MethodsWe measured sap velocity and four microclimate variables in both the dry and wet season of 2018. We also measured functional traits, including pressure volume (PV) curves, predawn/midday water potential, and various lab‐based water relations traits. We used linear mixed models to assess the correlation between microclimate and sap velocity in both seasons and ANOVA to assess the variation in PV curve and water potential variables.ResultsThe turgor loss point generally increased from the wettest to driest site. However, this trend was driven primarily by the increasing prevalence of leaf succulence at drier sites. Microclimatic variables correlated strongly with sap velocity in the wet season, but low soil moisture availability caused this correlation to break down during the dry season.ConclusionsOur results emphasize the vulnerability of cloud forest epiphytes to rising cloud bases. This vulnerability may be more severe in pasture trees that lack the potential buffer of surrounding forest, but additional research that directly compares the canopy microclimate conditions between forest and pasture trees is needed to confirm this possibility.

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Vapor pressure deficit predicts epiphyte abundance across an elevational gradient in a tropical montane region

Cited by 35 publications

References 57 publications

Arboreal Epiphytes in the Soil-Atmosphere Interface: How Often Are the Biggest “Buckets” in the Canopy Empty?

Arboreal Epiphytes in the Soil-Atmosphere Interface: How Often Are the Biggest “Buckets” in the Canopy Empty?

Differences in epiphyte biomass and community composition along landscape and within‐crown spatial scales

Drought response strategies of vascular epiphytes in isolated pasture trees in a Costa Rican tropical montane landscape

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