Research in global change ecology relies heavily on global climatic grids derived from estimates ... more Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids thus fail to reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions are controlled and most terrestrial species reside. Here we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0–5 and 5–15 cm depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all of the world’s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding 2 m gridded air tempe...
& Key message Annual radial growth and latewood formation increase during the period 1966-2015 in... more & Key message Annual radial growth and latewood formation increase during the period 1966-2015 in Larix cajanderi Mayr. and Pinus sylvestris L. along a latitudinal gradient on Siberian permafrost. Warmer temperatures and precipitation at the onset of the growth season favor growth in both species. & Context A vast area of Siberian boreal forest is covered by continuous permafrost, where tree radial growth is strongly limited by low temperatures. Understanding how climate controls Siberian conifer growth is critical in order to predict their response to ongoing climate change. & Aims To explore variations in the radial growth and earlywood/latewood formation of Pinus sylvestris L. and Larix cajanderi Mayr. trees along a climate gradient within the continuous permafrost zone in Central Yakutia (Russia), a region experiencing accelerated warming. & Methods We evaluated spatiotemporal differences in tree-ring and latewood width among sites by using generalized additive mixed models. Pearson's correlations were used to analyze the effect of local climate (temperature, precipitation) and drought (SPEI) on the formation of earlywood and latewood. & Results Both conifers showed increased radial growth in recent decades. Radial growth was controlled by temperature and precipitation in both species along the gradient, with earlier precipitation events being critical for the formation of wide rings. & Conclusion Although temperature is considered as the main limiting factor triggering tree growth in the continuous permafrost zone, our results showed that water availability also plays a key role in radial tree growth even in the coldest sites.
Climate affects wood formation with consequences for the functioning and survival of trees. Since... more Climate affects wood formation with consequences for the functioning and survival of trees. Since tree-rings tissues (i.e., earlywood and latewood) are formed at different time in the season, the impact of climate change might differently affect their functions. In this study, we combine quantitative tracheid anatomy with the Vaganov-Shashkin growth model (VS-model) to investigate how summer drought affected the annual ring structure of Pinus sylvestris L. from a forest-steppe zone in Southern Siberia. In particular, we used climate-growth relationships over a 50-year period to identify the timing of climatic signal of early-, transition-, and late-wood tracheid's diameters (D EW , D TW and D LW). Corresponding daily growth rates (Gr) obtained by the VS-model were applied to calculate the changes in the width of the relative tree-ring sectors considering different levels of aridity. Results indicate that tracheid size is sensitive to drought with temporal shifts among the climatic signal of D EW (in May), D TW (June) and D LW (July). A comparison of modeled daily-growth rate cumulated over the climatic window of each ring sector and grouped by years with different level of aridity, indicated that a release of summer drought mostly affected the widths of the transition (+ 28.1%) and (+ 48.6%) latewood sectors, thus matching observations performed on the same cores. These results suggest that current changes in climate seasonality, as occurring in the selected area, are positively impacting both the hydraulic efficiency (by increasing the diameter of the earlywood cells) and the latewood width of the wood produced in the area.
The title and author names are listed on this sheet as they will be published, both on your paper... more The title and author names are listed on this sheet as they will be published, both on your paper and on the Table of Contents. Please review and ensure the information is correct and advise us if any changes need to be made. In addition, please review your paper as a whole for typographical and essential corrections. Your PDF proof has been enabled so that you can comment on the proof directly using Adobe Acrobat. For further information on marking corrections using Acrobat, please visit http://journalauthors.tandf.co.uk/production/acrobat.asp; https://authorservices.taylorandfrancis.com/how-to-correct-proofs-with-adobe/ The CrossRef database (www.crossref.org/) has been used to validate the references. Changes resulting from mismatches are tracked in red font. AUTHOR QUERIES Q1 Please note that the ORCID for Alberto Arzac has been created from information provided through CATS. Please correct if this is inaccurate. Q2 Please provide missing Department for the affiliation.
In order to understand the impact of drought and intrinsic water-use efficiency (iWUE) on tree gr... more In order to understand the impact of drought and intrinsic water-use efficiency (iWUE) on tree growth, we evaluated the relative importance of direct and indirect effects of water availability on secondary growth and xylem anatomy of Juniperus thurifera, a Mediterranean anisohydric conifer. Dendrochronological techniques, quantitative xylem anatomy, and 13C/12C isotopic ratio were combined to develop standardized chronologies for iWUE, BA I (basal area increment), and anatomical variables on a 40-year long annually resolved series for 20 trees. We tested the relationship between iWUE and secondary growth at short-term (annual) and long-term (decadal) temporal scales to evaluate whether gains in iWUE may lead to increases in secondary growth. We obtained a positive long-term correlation between iWUE and BA I, simultaneously with a negative short-term correlation between them. Furthermore, BA I and iWUE were correlated with anatomical traits related to carbon sink or storage (tracheid wall thickness and ray parenchyma amount), but no significant correlation with conductive traits (tracheid lumen) was found. Water availability during the growing season significantly modulated tree growth at the xylem level, where growth rates and wood anatomical traits were affected by June precipitation. Our results are consistent with a drought-induced limitation of tree growth response to rising CO2, despite the trend of rising iWUE being maintained. We also remark the usefulness of exploring this relationship at different temporal scales to fully understand the actual links between iWUE and secondary growth dynamics.
standing plant responses to different climatic drivers along altitudinal gradients is necessary i... more standing plant responses to different climatic drivers along altitudinal gradients is necessary in order topredict the response of Mediterranean mountain systems to the ongoing increase in drought intensity andseverity. We selected the prostrate shrub Juniperus sabina L. as a model species and explored its growthresponse to climatic variability over the last six decades through dendrochronological methods at foursites along a 750 m altitudinal gradient. Secondary growth was maximal at lower altitudes, where grow-ing seasons are longer. Water availability was the main factor controlling secondary growth variabilityalong the whole gradient, although the timing and strength of climatic variables affecting growth shiftedwith altitude. Earlier and stronger signals were detected in lower sites, where a combination with latesummer signals suggested the existence of a second growth pulse in response to longer growing seasons.J. sabina adjusted its secondary growth to the changing climatic conditions by shifting the timing of itsclimatic response to favorable climatic windows, with earlier responses to spring rainfall in lower sitesand an expanded growing season at the highest site during the second half of the study period. Our resultsshow that at least some Mediterranean plants can grow faster at the drier edge of their range even underintense climate pressure, indicating that the response to drought stress may be highly idiosyncratic. Theplastic nature of J. sabina secondary growth combined with its role as a nurse plant in Mediterraneanmountains may be key to maintaining the high diversity levels of these particular ecosystems.
Ray parenchyma is an essential tissue for tree functioning and survival. This living tissue plays... more Ray parenchyma is an essential tissue for tree functioning and survival. This living tissue plays a major role for storage and transport of water, nutrients, and non-structural carbohydrates (NSC), thus regulating xylem hydraulics and growth. However, despite the importance of rays for tree carbon and water relations, methodological challenges hamper knowledge about ray intra- and inter-tree variability and its ecological meaning. In this study we provide a methodological toolbox for soundly quantifying spatial and temporal variability of different ray features. Anatomical ray features were surveyed in different cutting planes (cross-sectional, tangential, and radial) using quantitative image analysis on stem-wood micro-sections sampled from 41 mature Scots pines (Pinus sylvestris). The percentage of ray surface (PERPAR), a proxy for ray volume, was compared among cutting planes and between early- and latewood to assess measurement-induced variability. Different tangential ray metrics were correlated to assess their similarities. The accuracy of cross-sectional and tangential measurements for PERPAR estimates as a function of number of samples and the measured wood surface was assessed using bootstrapping statistical technique. Tangential sections offered the best 3D insight of ray integration into the xylem and provided the most accurate estimates of PERPAR, with 10 samples of 4 mm(2) showing an estimate within ±6.0% of the true mean PERPAR (relative 95% confidence interval, CI95), and 20 samples of 4 mm(2) showing a CI95 of ±4.3%. Cross-sections were most efficient for establishment of time series, and facilitated comparisons with other widely used xylem anatomical features. Earlywood had significantly lower PERPAR (5.77 vs. 6.18%) and marginally fewer initiating rays than latewood. In comparison to tangential sections, PERPAR was systematically overestimated (6.50 vs. 4.92%) and required approximately twice the sample area for similar accuracy. Radial cuttings provided the least accurate PERPAR estimates. This evaluation of ray parenchyma in conifers and the presented guidelines regarding data accuracy as a function of measured wood surface and number of samples represent an important methodological reference for ray quantification, which will ultimately improve the understanding of the fundamental role of ray parenchyma tissue for the performance and survival of trees growing in stressed environments.
ABSTRACT Divergent evolutionary pressures associated with differential reproductive costs in dioe... more ABSTRACT Divergent evolutionary pressures associated with differential reproductive costs in dioecious trees may lead to sex-related variation in non-reproductive functions. Sex-related differences may be site-dependent, with different outcomes depending on environmental conditions. We explored the effects of sex and environmental conditions on the climatic control of annual secondary growth and intra-annual wood density fluctuations (IADF) of a dioecious conifer (Juniperus thurifera L.) growing in two sites with contrasting hydrological conditions under a continental Mediterranean climate. Different sex-related strategies had variable effects on relative secondary growth, with females outperforming males under more favorable hydrological conditions, and males outperforming females under water-limited conditions. Ring width and IADF formation were driven by climatic factors occurring at different temporal scales. Tree-ring growth depended on factors acting prior to the initiation of the xylogenesis and to conditions directly affecting the duration and pace of cambial activity, and ring width, therefore, integrated a complex signal of factors occurring over a relatively long period, and on an annual cycle. In contrast, IADFs responded to singular short-term events that alleviated drought and promoted cambial reactivation during the summer arrest. Female trees showed a more opportunistic water use, displayed in the stronger ring-width response to June–July conditions. Enhanced cambial sensitivity in females set a lower threshold for IADF occurrence, leading to a higher frequency of IADFs irrespective of site. Intra-annual and inter-annual female growth patterns reflect an opportunistic strategy to benefit from favorable climatic windows.
Tree-ring anatomy reflects the year-by-year impact of environmental factors on tree growth. Up to... more Tree-ring anatomy reflects the year-by-year impact of environmental factors on tree growth. Up to now, research in this field has mainly focused on the hydraulic architecture, with ray parenchyma neglected despite the growing recognition of its relevance for xylem function. Our aim was to address this gap by exploring the potential of the annual patterns of xylem parenchyma as a climate proxy. We constructed ring-width and ray-parenchyma chronologies from 1965 to 2004 for 20 Juniperus thurifera trees growing in a Mediterranean continental climate. Chronologies were related to climate records by means of correlation, multiple regression and partial correlation analyses. Ray parenchyma responded to climatic conditions at critical stages during the xylogenetic process; namely, at the end of the previous year's xylogenesis (October) and at the onset of earlywood (May) and latewood formation (August). Ray parenchyma-based chronologies have potential to complement ring-width chronologies as a tool for climate reconstructions. Furthermore, medium- and low-frequency signals in the variation of ray parenchyma may improve our understanding of how trees respond to environmental fluctuations and to global change.
En este trabajo analizamos el efecto de la altitud, exposición y pendiente sobre la distribución ... more En este trabajo analizamos el efecto de la altitud, exposición y pendiente sobre la distribución de formas de vida de plantas en páramos ubicados inmediatamente sobre el límite del bosque en la Sierra Nevada de Mérida. A partir de una ampliación del sistema de clasificación propuesto por Hedberg (1964) para la alta montaña tropical, se definieron 14 formas de vida en esta zona ecotonal. Se observaron patrones claros de cambio en la cobertura de las formas de vida en función de la altitud y la exposición. Los árboles y los helechos disminuyeron drásticamente su cobertura con el aumento en la altitud y la distancia al bosque contínuo. Las rosetas caulescentes pubescentes y los arbustos esclerófilos con láminas foliares más pequeñas (leptófilos) presentaron coberturas más altas en las zonas de mayor elevación y en las laderas de exposición oeste, donde las condiciones ambientales pudieran ser más limitantes en términos del balance energético foliar. Para el desarrollo de modelos más mecanísticos de la dinámica del límite forestal en escenarios de cambio climático, nuestros resultados enfatizan la importancia de profundizar la comprensión de la diversidad de respuestas funcionales de las formas de vida presentes en la alta montaña tropical y de analizar los efectos de la interacción de la altitud con otras variables como la exposición sobre determinantes ambientales clave como la radiación incidente y la temperatura.
Research in global change ecology relies heavily on global climatic grids derived from estimates ... more Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids thus fail to reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions are controlled and most terrestrial species reside. Here we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0–5 and 5–15 cm depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all of the world’s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding 2 m gridded air tempe...
& Key message Annual radial growth and latewood formation increase during the period 1966-2015 in... more & Key message Annual radial growth and latewood formation increase during the period 1966-2015 in Larix cajanderi Mayr. and Pinus sylvestris L. along a latitudinal gradient on Siberian permafrost. Warmer temperatures and precipitation at the onset of the growth season favor growth in both species. & Context A vast area of Siberian boreal forest is covered by continuous permafrost, where tree radial growth is strongly limited by low temperatures. Understanding how climate controls Siberian conifer growth is critical in order to predict their response to ongoing climate change. & Aims To explore variations in the radial growth and earlywood/latewood formation of Pinus sylvestris L. and Larix cajanderi Mayr. trees along a climate gradient within the continuous permafrost zone in Central Yakutia (Russia), a region experiencing accelerated warming. & Methods We evaluated spatiotemporal differences in tree-ring and latewood width among sites by using generalized additive mixed models. Pearson's correlations were used to analyze the effect of local climate (temperature, precipitation) and drought (SPEI) on the formation of earlywood and latewood. & Results Both conifers showed increased radial growth in recent decades. Radial growth was controlled by temperature and precipitation in both species along the gradient, with earlier precipitation events being critical for the formation of wide rings. & Conclusion Although temperature is considered as the main limiting factor triggering tree growth in the continuous permafrost zone, our results showed that water availability also plays a key role in radial tree growth even in the coldest sites.
Climate affects wood formation with consequences for the functioning and survival of trees. Since... more Climate affects wood formation with consequences for the functioning and survival of trees. Since tree-rings tissues (i.e., earlywood and latewood) are formed at different time in the season, the impact of climate change might differently affect their functions. In this study, we combine quantitative tracheid anatomy with the Vaganov-Shashkin growth model (VS-model) to investigate how summer drought affected the annual ring structure of Pinus sylvestris L. from a forest-steppe zone in Southern Siberia. In particular, we used climate-growth relationships over a 50-year period to identify the timing of climatic signal of early-, transition-, and late-wood tracheid's diameters (D EW , D TW and D LW). Corresponding daily growth rates (Gr) obtained by the VS-model were applied to calculate the changes in the width of the relative tree-ring sectors considering different levels of aridity. Results indicate that tracheid size is sensitive to drought with temporal shifts among the climatic signal of D EW (in May), D TW (June) and D LW (July). A comparison of modeled daily-growth rate cumulated over the climatic window of each ring sector and grouped by years with different level of aridity, indicated that a release of summer drought mostly affected the widths of the transition (+ 28.1%) and (+ 48.6%) latewood sectors, thus matching observations performed on the same cores. These results suggest that current changes in climate seasonality, as occurring in the selected area, are positively impacting both the hydraulic efficiency (by increasing the diameter of the earlywood cells) and the latewood width of the wood produced in the area.
The title and author names are listed on this sheet as they will be published, both on your paper... more The title and author names are listed on this sheet as they will be published, both on your paper and on the Table of Contents. Please review and ensure the information is correct and advise us if any changes need to be made. In addition, please review your paper as a whole for typographical and essential corrections. Your PDF proof has been enabled so that you can comment on the proof directly using Adobe Acrobat. For further information on marking corrections using Acrobat, please visit http://journalauthors.tandf.co.uk/production/acrobat.asp; https://authorservices.taylorandfrancis.com/how-to-correct-proofs-with-adobe/ The CrossRef database (www.crossref.org/) has been used to validate the references. Changes resulting from mismatches are tracked in red font. AUTHOR QUERIES Q1 Please note that the ORCID for Alberto Arzac has been created from information provided through CATS. Please correct if this is inaccurate. Q2 Please provide missing Department for the affiliation.
In order to understand the impact of drought and intrinsic water-use efficiency (iWUE) on tree gr... more In order to understand the impact of drought and intrinsic water-use efficiency (iWUE) on tree growth, we evaluated the relative importance of direct and indirect effects of water availability on secondary growth and xylem anatomy of Juniperus thurifera, a Mediterranean anisohydric conifer. Dendrochronological techniques, quantitative xylem anatomy, and 13C/12C isotopic ratio were combined to develop standardized chronologies for iWUE, BA I (basal area increment), and anatomical variables on a 40-year long annually resolved series for 20 trees. We tested the relationship between iWUE and secondary growth at short-term (annual) and long-term (decadal) temporal scales to evaluate whether gains in iWUE may lead to increases in secondary growth. We obtained a positive long-term correlation between iWUE and BA I, simultaneously with a negative short-term correlation between them. Furthermore, BA I and iWUE were correlated with anatomical traits related to carbon sink or storage (tracheid wall thickness and ray parenchyma amount), but no significant correlation with conductive traits (tracheid lumen) was found. Water availability during the growing season significantly modulated tree growth at the xylem level, where growth rates and wood anatomical traits were affected by June precipitation. Our results are consistent with a drought-induced limitation of tree growth response to rising CO2, despite the trend of rising iWUE being maintained. We also remark the usefulness of exploring this relationship at different temporal scales to fully understand the actual links between iWUE and secondary growth dynamics.
standing plant responses to different climatic drivers along altitudinal gradients is necessary i... more standing plant responses to different climatic drivers along altitudinal gradients is necessary in order topredict the response of Mediterranean mountain systems to the ongoing increase in drought intensity andseverity. We selected the prostrate shrub Juniperus sabina L. as a model species and explored its growthresponse to climatic variability over the last six decades through dendrochronological methods at foursites along a 750 m altitudinal gradient. Secondary growth was maximal at lower altitudes, where grow-ing seasons are longer. Water availability was the main factor controlling secondary growth variabilityalong the whole gradient, although the timing and strength of climatic variables affecting growth shiftedwith altitude. Earlier and stronger signals were detected in lower sites, where a combination with latesummer signals suggested the existence of a second growth pulse in response to longer growing seasons.J. sabina adjusted its secondary growth to the changing climatic conditions by shifting the timing of itsclimatic response to favorable climatic windows, with earlier responses to spring rainfall in lower sitesand an expanded growing season at the highest site during the second half of the study period. Our resultsshow that at least some Mediterranean plants can grow faster at the drier edge of their range even underintense climate pressure, indicating that the response to drought stress may be highly idiosyncratic. Theplastic nature of J. sabina secondary growth combined with its role as a nurse plant in Mediterraneanmountains may be key to maintaining the high diversity levels of these particular ecosystems.
Ray parenchyma is an essential tissue for tree functioning and survival. This living tissue plays... more Ray parenchyma is an essential tissue for tree functioning and survival. This living tissue plays a major role for storage and transport of water, nutrients, and non-structural carbohydrates (NSC), thus regulating xylem hydraulics and growth. However, despite the importance of rays for tree carbon and water relations, methodological challenges hamper knowledge about ray intra- and inter-tree variability and its ecological meaning. In this study we provide a methodological toolbox for soundly quantifying spatial and temporal variability of different ray features. Anatomical ray features were surveyed in different cutting planes (cross-sectional, tangential, and radial) using quantitative image analysis on stem-wood micro-sections sampled from 41 mature Scots pines (Pinus sylvestris). The percentage of ray surface (PERPAR), a proxy for ray volume, was compared among cutting planes and between early- and latewood to assess measurement-induced variability. Different tangential ray metrics were correlated to assess their similarities. The accuracy of cross-sectional and tangential measurements for PERPAR estimates as a function of number of samples and the measured wood surface was assessed using bootstrapping statistical technique. Tangential sections offered the best 3D insight of ray integration into the xylem and provided the most accurate estimates of PERPAR, with 10 samples of 4 mm(2) showing an estimate within ±6.0% of the true mean PERPAR (relative 95% confidence interval, CI95), and 20 samples of 4 mm(2) showing a CI95 of ±4.3%. Cross-sections were most efficient for establishment of time series, and facilitated comparisons with other widely used xylem anatomical features. Earlywood had significantly lower PERPAR (5.77 vs. 6.18%) and marginally fewer initiating rays than latewood. In comparison to tangential sections, PERPAR was systematically overestimated (6.50 vs. 4.92%) and required approximately twice the sample area for similar accuracy. Radial cuttings provided the least accurate PERPAR estimates. This evaluation of ray parenchyma in conifers and the presented guidelines regarding data accuracy as a function of measured wood surface and number of samples represent an important methodological reference for ray quantification, which will ultimately improve the understanding of the fundamental role of ray parenchyma tissue for the performance and survival of trees growing in stressed environments.
ABSTRACT Divergent evolutionary pressures associated with differential reproductive costs in dioe... more ABSTRACT Divergent evolutionary pressures associated with differential reproductive costs in dioecious trees may lead to sex-related variation in non-reproductive functions. Sex-related differences may be site-dependent, with different outcomes depending on environmental conditions. We explored the effects of sex and environmental conditions on the climatic control of annual secondary growth and intra-annual wood density fluctuations (IADF) of a dioecious conifer (Juniperus thurifera L.) growing in two sites with contrasting hydrological conditions under a continental Mediterranean climate. Different sex-related strategies had variable effects on relative secondary growth, with females outperforming males under more favorable hydrological conditions, and males outperforming females under water-limited conditions. Ring width and IADF formation were driven by climatic factors occurring at different temporal scales. Tree-ring growth depended on factors acting prior to the initiation of the xylogenesis and to conditions directly affecting the duration and pace of cambial activity, and ring width, therefore, integrated a complex signal of factors occurring over a relatively long period, and on an annual cycle. In contrast, IADFs responded to singular short-term events that alleviated drought and promoted cambial reactivation during the summer arrest. Female trees showed a more opportunistic water use, displayed in the stronger ring-width response to June–July conditions. Enhanced cambial sensitivity in females set a lower threshold for IADF occurrence, leading to a higher frequency of IADFs irrespective of site. Intra-annual and inter-annual female growth patterns reflect an opportunistic strategy to benefit from favorable climatic windows.
Tree-ring anatomy reflects the year-by-year impact of environmental factors on tree growth. Up to... more Tree-ring anatomy reflects the year-by-year impact of environmental factors on tree growth. Up to now, research in this field has mainly focused on the hydraulic architecture, with ray parenchyma neglected despite the growing recognition of its relevance for xylem function. Our aim was to address this gap by exploring the potential of the annual patterns of xylem parenchyma as a climate proxy. We constructed ring-width and ray-parenchyma chronologies from 1965 to 2004 for 20 Juniperus thurifera trees growing in a Mediterranean continental climate. Chronologies were related to climate records by means of correlation, multiple regression and partial correlation analyses. Ray parenchyma responded to climatic conditions at critical stages during the xylogenetic process; namely, at the end of the previous year's xylogenesis (October) and at the onset of earlywood (May) and latewood formation (August). Ray parenchyma-based chronologies have potential to complement ring-width chronologies as a tool for climate reconstructions. Furthermore, medium- and low-frequency signals in the variation of ray parenchyma may improve our understanding of how trees respond to environmental fluctuations and to global change.
En este trabajo analizamos el efecto de la altitud, exposición y pendiente sobre la distribución ... more En este trabajo analizamos el efecto de la altitud, exposición y pendiente sobre la distribución de formas de vida de plantas en páramos ubicados inmediatamente sobre el límite del bosque en la Sierra Nevada de Mérida. A partir de una ampliación del sistema de clasificación propuesto por Hedberg (1964) para la alta montaña tropical, se definieron 14 formas de vida en esta zona ecotonal. Se observaron patrones claros de cambio en la cobertura de las formas de vida en función de la altitud y la exposición. Los árboles y los helechos disminuyeron drásticamente su cobertura con el aumento en la altitud y la distancia al bosque contínuo. Las rosetas caulescentes pubescentes y los arbustos esclerófilos con láminas foliares más pequeñas (leptófilos) presentaron coberturas más altas en las zonas de mayor elevación y en las laderas de exposición oeste, donde las condiciones ambientales pudieran ser más limitantes en términos del balance energético foliar. Para el desarrollo de modelos más mecanísticos de la dinámica del límite forestal en escenarios de cambio climático, nuestros resultados enfatizan la importancia de profundizar la comprensión de la diversidad de respuestas funcionales de las formas de vida presentes en la alta montaña tropical y de analizar los efectos de la interacción de la altitud con otras variables como la exposición sobre determinantes ambientales clave como la radiación incidente y la temperatura.
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