Ring Width Index Research Articles

Variación en los patrones de crecimiento previo a la muerte de individuos de Austrocedrus chilensis a lo largo de un gradiente pluviométrico en el norte de la Patagonia Andina

Fil: Vega, Leticia Maria. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias. Departamento de Economia, Politica y Administracion Rural.; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mendoza. Instituto Argentino de Nivologia, Glaciologia y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivologia, Glaciologia y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivologia, Glaciologia y Ciencias Ambientales; Argentina

Reconstruction of June–July Temperatures Based on a 233 Year Tree-Ring of Picea jezoensis var. microsperma

In this study, ring-width chronology of Picea jezoensis var. microsperma from the Changbai Mountain (CBM) area, Northeast China, was constructed. Growth/climate responses suggested that mean maximum temperature (Tmax) was the limiting factor affecting radial growth of PJ trees in the study region. According to the correlation analysis between the ring-width index and meteorological data, a June–July mean maximum temperature (Tmax6–7) series between 1772 and 2004 was reconstructed by using the standard chronology. For the calibration period (1959–2004), the explained variance of the reconstruction was 41.6%. During the last 233 years, there were 36 warm years and 34 cold years, accounting for 15.5% and 14.7% of the total reconstruction years, respectively. Cold periods occurred in 1899–1913, 1955–1970, and 1975–1989, while warm periods occurred in 1881–1888. The reconstructed temperature series corresponded to the historical disaster records of extreme climatic events (e.g., drought and flood disasters) in this area. Comparisons with other temperature reconstructions from surrounding areas and spatial correlation analysis between the gridded temperature data and reconstruction series indicated that the regional climatic variations were well captured by the reconstruction. In addition, multi-taper method spectral analysis indicated the existence of significant periodicities in the reconstructed series. The significant spatial correlations between the reconstructed temperature series and the El Niño–Southern Oscillation (ENSO), solar activity, and Pacific Decadal Oscillation (PDO) suggested that the temperature in the CBM area indicated both local-regional climate signals and global-scale climate changes.

Lowering Stand Density Enhances Resiliency of Ponderosa Pine Forests to Disturbances and Climate Change

AbstractStand density affects not only structure and growth, but also the health of forests and, subsequently, the functions of forest ecosystems. Here, we integrated dendrochronology and repeated inventories for ponderosa pine research plots to determine whether long-term growth and mortality responded to climate trends and how varying stand density influenced the responses. The plots were established prior to 1975 on existing stands throughout northern California. Although annual temperature increased consistently for the last 65 years, ring-width indices produced by eliminating age and thinning effects failed to detect radial trend regardless of site quality. However, interannual variation for the indices was substantial, reflecting a strong influence of climate on tree growth. Plot-level basal area increments were significantly affected by tree mortality. Stand density index explained most variation of mortality. Lowering stand density enhanced remaining tree growth, reduced mortality, and increased stand resiliency to disturbances and climate change. Besides higher climate moisture indices or lower vapor pressure deficits, any treatments that improve tree vigor and reduce stress will have a similar effect to reducing stand density. Although neither biotic disturbances nor abiotic conditions can be controlled, forest managers can manage stand density appropriately to enhance resilience to climate change and disturbances.

Linking tree growth rate, damage repair, and susceptibility to a genus-specific pest infestation

Pest preference and subsequent susceptibility of a host individual is likely related to previous growth patterns in that host. Emerald ash borer (Agrilus planipennis Fairmaire) is a pestiferous beetle introduced to North America from Asia. While all species of ash are susceptible to attack, some individual trees appear to survive infestation. We selected ash trees in southeastern Michigan, collected cores and categorized trees as high tolerance to emerald ash borer attack (high overall health, low crown dieback), low tolerance (low overall health, high crown dieback) and intermediate tolerance (in-between the other categories). We artificially wounded trees and measured wound closure after 3 years. Ring width indices were not correlated between high and low tolerance trees. Regression slopes comparing growth and years were significantly different between the three tolerance categories, with high tolerance trees having the steepest slope. Wound closure was greatest in high tolerance trees. High tolerance trees demonstrating more rapid (steeper regression slope), consistent (lower variance), and effective (greater wound closure) growth. Those vigorously growing trees likely had more capacity to repair damage caused by emerald ash borer, leading to healthier trees in our categorization. Linking previous host growth patterns to health may have implications related to identifying individual trees potentially tolerant to attack.

Forest type and height are important in shaping the altitudinal change of radial growth response to climate change

Tree radial growth is widely found to respond differently to climate change across altitudinal gradients, but the relative roles of biotic factors (e.g. forest type, height and density) vs. climate gradient remain unclear. We sampled tree rings from 15 plots along a large altitudinal gradient in northeast China, and examined how climate gradient, forest type, height, tree size and density affect: (1) temporal growth variability [mean sensitivity (MS) and standard deviation (SD) of the chronologies], and (2) the relationship of ring width indices (RWI) with historical climate. We used BIC based model selection and variable importance to explore the major drivers of their altitudinal patterns. The results showed that: both growth variability and RWI-climate relationships changed significantly with altitude. Forest height was the most important predictor for altitudinal changes of MS and SD. For RWI-climate relationships, forest type was more important than climate gradient, while height and stem density were weak but necessary predictors. We showed that the altitudinal difference in growth response to climate change cannot be explained by climate gradient alone, and highlight the necessity to examine the influence of biotic factors (which covary with climate across geographic gradient) to better understand forest response to climate change.

Linking Remote Sensing and Dendrochronology to Quantify Climate‐Induced Shifts in High‐Elevation Forests Over Space and Time

AbstractIt is well known that tree growth is strongly affected by climate at high elevations, but it is still unclear how climate variability influences the distribution of montane forest ecosystems, particularly tree line species. To advance knowledge in this field, we combined temporal (tree ring measurements) and spatial data (remotely sensed variables), to quantify how forests responded to climatic variability across altitudinal gradients in Central Mexico. Normalized difference vegetation index (NDVI), tree‐ring chronologies, and site‐level climatic data were used in a vegetation trend analysis of greenness and browning and to reconstruct canopy vigor for the last century. Although a common ring width chronology was developed, we found significant site‐dependent forest growth response, where young trees (<100 years) exhibited heterogeneous growth trends, without an altitudinal pattern. However, mature trees (100–200 years) showed a common growth decline during the middle twentieth century, regardless of their altitude. Annual maximum NDVI anomalies did not show a general greening effect at high‐elevations. The forest showed both greening and browning zones denoting spatial variability in tree vigor. Furthermore, temperature from the previous year had a positive effect on both NDVI and ring width index but negative at beginning of the growing season. The significant relationship between winter‐spring NDVI (December to March) and ring width index (r = 0.64, p < 0.05), was useful to reconstruct the canopy vigor for the last 151 years. Thus, the greening effect derived from NDVI should be carefully interpreted as a direct forest growth increase. These results highlight the potential of integrating remotely sensed and dendrochronological methods to improve predictions of forest ecosystem responses.

Comparison of elevational changes in relationships of blue intensity and ring width index in <i>Picea jezoensis</i> with climatic responses in Laobai Mountain of Jilin, China

Comparison of elevational changes in relationships of blue intensity and ring width index in <i>Picea jezoensis</i> with climatic responses in Laobai Mountain of Jilin, China

Linking functional traits and climate-growth relationships in Mediterranean species through wood density

ABSTRACTFunctional traits are considered to influence the performance of woody plants. However, few field studies have tested this idea by using radial-growth data. Here, I test if five major traits of the leafand wood-economics spectra (height, leaf area, specific leaf area – SLA, wood density – WD and hydraulic diameter) explain climate-growth relationships in 14 Mediterranean trees and shrubs. Traits were measured for both gymnosperm (four Juniperus species plus three Pinus species) and angiosperm species (two Quercus species, two Pistacia species, Arbutus unedo, Celtis australis, and one Tamarix species). Climategrowth relationships were calculated relating ring-width indices (RWIs) and local climate data. Leaf area and SLA were high in broadleaf deciduous species (e.g., C. australis), and low in junipers. WD reached minimum and maximum values in pine and oak species, respectively. WD explained 45 % of the variation of the association observed between RWI and April precipitation, one of the main climatic variables driving radial growth. Therefore, WD is a relevant functional trait useful to predict the performance of Mediterranean woody plant species, specifically concerning their growth responses to climate. Functional traits as WD should be further explored to explain growth variability between and within woody species, and to link this variability with responsiveness to climate and ecosystem productivity.

Changes in Sensitivity of Tree-Ring Widths to Climate in a Tropical Moist Forest Tree in Bangladesh

Tree growth in the tropics is strongly influenced by climate. However, reported tree growth responses to climate are largely inconsistent, varying with geographic location, forest type, and tree species. It is thus important to study the growth responses of tropical trees in sites and species that are under-represented so far. Bangladesh, a country influenced by the Asian monsoon climate, is understudied in terms of tree growth response to climate. In the present study, we developed a 121-year-long regional ring-width index chronology of Chukrasia tabularis A. Juss. sampled in two moist forest sites in Bangladesh to investigate tree growth responses to climate in monsoon South Asia. Standard dendrochronological methods were used to produce the ring-width chronologies. The climate sensitivity of C. tabularis was assessed through bootstrap correlation analysis and the stationarity and consistency of climate–growth relationships was evaluated using moving correlation functions and comparing the regression slopes of two sub-periods (1950–1985 and 1986–2015). Tree growth was negatively correlated with the mean, minimum, and maximum temperatures, particularly during the early growing season (March). Likewise, precipitation negatively influenced tree growth in the later growing season (October). Besides, radial growth of Chukrasia sharply ceased in years following strong and moderate El Niño events. In parallel with a significant positive trend in local temperatures, tree growth sensitivity to early growing season (March–April) mean temperatures and July minimum temperatures increased in recent decades. Tree growth sensitivity to October precipitation and April vapor pressure deficit also increased. Overall, climate–growth relationships were stronger during the period 1986–2015 than during 1950–1985. Changes in climate sensitivity might be linked to a warming trend that induced an increase in the dry season length during recent decades. With a further predicted temperature increase at our study sites, our results suggest that radial growth of C. tabularis will further decline in response to climate warming.

Dendroecology of Macrolobium acaciifolium (Fabaceae) in Central Amazonian floodplain forests

ABSTRACT The forest dynamics in the Amazonian floodplains is strongly triggered by the flood pulse. Trees respond to unfavorable growth conditions during the flood period by cambial dormancy, which results in the formation of annual growth rings. We determined tree age and compared the mean annual rates of increase in the diameter of Macrolobium acaciifolium with hydrological and climatic factors in three regions of central Amazonian floodplain forest. A wood sample was obtained from each tree using an increment borer. Ring growth was assessed by marginal parenchyma bands to determine tree age and the mean diameter increment. Ring widths were indexed to construct cross-dating chronologies and correlated with climatic and hydrological variables. The analyses demonstrate that the mean annual diameter increment did not differ between the three study sites. The chronologies correlated significantly with the terrestrial phase. There was no significant difference in the ring-width index between El Niño years and other years, and between La Niña and other years. These results show that the hydrological variables can be considered crucial to the rates of tree growth and diameter increment in floodplains, and El Niño signals were not detected in the tree-ring chronologies.

Recent rising temperatures drive younger and southern Korean pine growth decline

The Earth has experienced an unequivocal warming, with the warmest period of the past 150 years occurring in the last three decades. Korean pine (Pinus koraiensis), a key tree species in northeast Asia, is predicted to be particularly vulnerable to climate change. Here, we use dendrochronological methods to test whether the observed growth decline of Korean pine in northeast China is related to climate warming and whether climate-growth responses varied with age. A total of 628 cores from 401 trees across 16 sites were sampled over the entire distribution area of Korean pine in China. Samples were divided into three age classes: younger (50–130 years), middle (131–210 years), and older trees (>210 years), and measured by the ring-width index and basal area increment (BAI). Results showed a significant decline in BAI in most sites coinciding with an increase of temperature in the growing season and a decrease in precipitation since the 1980s. Meanwhile, we found that temperature-induced growth decline was significantly related to tree age. The BAI of younger trees decreased significantly and sharply (0.44 cm2 year−1, P < 0.0001), while old trees either decreased slightly or stabilized (0.04 cm2 year−1, P = 0.33). Tree growth in the southernmost locations was more likely to decline, what was most likely a result of forest-stand age. The age-related growth decline induced by climate warming might be explained by tree species traits, differences in growth rates between age classes and their relation to stress, changes in root system, competition/stand structure or physiological mechanisms. Our results might also predict that early stand process-thinning is exacerbated by warming and drying. This research informs that the age effect of growth response to rising temperature should be considered in forest management under climate change, and particularly models of future carbon cycle patterns and forest dynamics.

Tree radial growth is projected to decline in South Asian moist forest trees under climate change

Abstract Global climate change has been reported to affect tree growth around the world and such impacts are predicted to be intensified under future climate change particularly in the tropics. It is therefore important to study the climate-growth relationships of tropical trees to understand how they have responded to the past climate variability and to predict how they will respond to future climatic changes. We investigated tree radial growth responses to regional climatic changes in Bangladeshi moist tropical forests. We selected three species based on their distinct growth-ring boundaries and their wide distribution around the tropics. First, we simulated growth responses to climate for the past 66 years (1950–2015) based on the climate-growth relationships. Next, we projected tree-growth until the end of current century (2016–2100) under different climate change scenarios (Representative Concentration Pathways, RCP). All the three species produced statistically robust ring-width index chronologies covering the current and the past century. Climate-growth analysis revealed that temperature (monthly, annual and seasonal) significantly negatively affected tree radial growth in all three species. Precipitation prior to the current growing season negatively and current year post monsoon precipitation positively influenced radial growth. Tree radial growth was also influenced by Nino 3.4 region Sea Surface Temperature (SST) anomalies mainly through the modulation of local climate. We projected tree radial growth to be declined in all three species by 20% under high concentration scenario (RCP 8.5) followed by 11.3% and 9% under medium (RCP 6.0) and low-medium concentration scenarios (RCP 4.5). If these species show similar growth responses to climatic changes in other native ranges across the tropics, this could have severe consequences for the carbon balance of tropical forests.

Climatic drivers of tree growth at tree line in Southwest Yukon change over time and vary between landscapes

Growth of trees at their altitudinal and latitudinal range limits is expected to increase as climate warms, but trees often exhibit unexplained spatial and temporal variation in climate-growth responses, particularly in alpine regions. Until this variability is explained, predictions of future tree growth are unlikely to be accurate. We sampled Picea glauca (white spruce) growing at forest and tree line on north and south aspects in two mountain ranges of southwest Yukon to determine how and why ring-width patterns vary between topographic settings, and over time. We used multivariate statistical analysis to characterize variation in ring-width patterns between topographic factors and time periods, and calculated correlations between ring-width indices and climate variables to explain this variation. Ring-width patterns varied more between mountain ranges than elevations or aspects, particularly in recent decades when ring-widths increased in one mountain range but not the other. Growth responses to summer temperature were notably weaker during warmer time periods, but growth was not positively correlated to summer precipitation, suggesting trees may not be suffering from temperature-induced drought stress. Rather, ring-width indices began responding positively to spring snow depth after 1976. We conclude that tree growth is unlikely to increase in synchrony with rising air temperatures across subarctic tree lines in southwest Yukon. Instead, they may decline in areas that are prone to thin snowpacks or rapid spring runoff due to the negative influence warming springs will have on snow depth and, consequently, early growing season soil moisture.

Tree-Ring Carbon Isotope Records from the Western Oregon Cascade Mountains Primarily Record Summer Maximum Temperatures

Abstract Here we examine climatic influences on inter-annual variation in latewood tree growth (i.e. ring-width indices, RWILW) and stable-carbon isotope discrimination (Δ13CLW) from 1950 to 2013 at two SNOTEL snowpack monitoring sites in the Oregon Cascade Mountains. Douglas-fir and mountain hemlock trees were sampled at the lower and upper elevation sites where annual peak snow water equivalent (SWE) averaged 467 and 1128 mm, respectively. RWILW chronologies were poorly correlated among sites/species (r = 0.23, P = 0.063) and neither exhibited strong correlations with monthly or seasonal climate variables. By contrast, Δ13CLW chronologies were significantly correlated (r = 0.69, P < 0.001) and exhibited stronger climate responses. Multiple regression analyses identified summertime maximum temperature (Tmax) and/or vapor pressure deficit (VPD) as the primary drivers of Δ13CLW. Secondary influences included summertime precipitation, specific humidity, cloud cover, and SWE from the previous fall and winter...

Reconstruction of July NDVI over 172 years based on tree-ring width of Larix chinensis in Taibai Mountain Nature Reserve, China.

We used the correlation analysis of Larix chinensis tree-ring width chronologies, meteorological data as well as regional NDVI data to reconstruct the NDVI sequence variation of the north and south aspects of Taibai Mountain Nature Reserve in the recent 172 years. The results showed that the NDVI variation of Taibai Mountain Nature Reserve was consistent with plant growth dyna-mics. Hydrothermal condition in growing season was the dominant factor controlling NDVI changes. Tree-ring width was significantly positively correlated with NDVI in growing season. The strongest correlation occurred in July. Thus, we used the long time series of tree ring width index in July to reconstruct the regional historical period variation of NDVI sequence. The results demonstrated that historical changes of July NDVI sequence existed five dense periods and five sparse periods. Further analysis indicated that these periods corresponded with the climate change trends and drought events. The reconstructed July NDVI sequence of both northern and southern slopes of Taibai Mountain Nature Reserve highlighted the existence of quasi periodic variation of 60 years.

Increasing temperature sensitivity caused by climate warming, evidence from Northeastern China

The “Divergence Problem” in northern forests has been confirmed in a large number of empirical studies, especially in North America and Europe, climate warming having been identified as a cause for reduced sensitivity of recent tree-growth and increased tree mortality. However, according to other studies, tree growth patterns are keeping pace with climate warming. Covariation between rising temperatures and tree growth varies regionally. Therefore, extensive evidence is still needed across more geographic areas around the world. In the present study, we examined the sensitivity of Manchurian ash forest growth, which is one of the dominant species in the mixed coniferous and broad-leaved forests in the area around Changbai Mountain in Northeastern China. Five Manchurian ash tree-ring width chronologies were constructed from sites ranging along the elevational gradients of 750 m, 800 m, 900 m, 1000 m and 1100 m. We analyzed climate-growth relationships using Pearson correlation coefficients between ring-width indices and climate variables in two separate periods (before 1984 and after 1984), because instrumental temperature data have increased sharply after 1984. Along all of the elevational gradients, the sampled Manchurian ash forests show a higher growth rate and more sensitivity to climatic factors due to climate warming since the beginning of the 1984s. Comparatively, the forest growth at low elevation sites has increased faster than that at high elevation sites. If climate warming continues in northeastern China, further continuous and substantial increase in tree growth would substantially raise forest productivity in mixed coniferous and broad-leaved forests.

Forest drought resistance distinguished by canopy height

How are the survival and growth of trees under severe drought affected by their size? While some studies have shown that large trees are more vulnerable to drought than smaller trees, others found that small trees are the more vulnerable. We explored the potential relationships between canopy height and forest responses to drought indicated by tree mortality, tree ring width index (RWI), and normalized difference vegetation index (NDVI) in the southwestern United States (SWUS) in 2002. In that year many trees had zero tree ring growth due to mortality and dieback, presumably related to drought-stress. With RWI data from a tree ring data base and climate data co-located with the field measurements, we found size-dependent linear correlations between these forest responses and canopy height in SWUS under severe drought condition. During that drought period, both trunk growth (RWI) and leaf growth (NDVI) were positively correlated with canopy height of the smaller trees (less than 18 m) and negatively correlated with canopy height of greater than 18 m. Tree mortality was negatively correlated with canopy height up to 15 m. Both local-scale and regional-scale data are consistent in showing that forests with medium canopy height (around 18 meters) showed the greatest resistance to severe drought. We suggest that negative impacts of severe drought on forests could be modified with active management of canopy structure.

Red dendrocronológica de pino triste (Pinus lumholtzii B.L. Rob. &amp; Fernald) en la Sierra Madre Occidental para reconstrucción de lluvia estacional

Se desarrolló una red de siete cronologías de Pinus lumholtzii en la Sierra Madre Occidental para el desarrollo de reconstrucciones históricas de precipitación estacional. Los valores de los parámetros dendrocronológicos en general fueron similares a los de series de crecimiento desarrolladas con otras coníferas en esta región: sensibilidad media (0.25 - 0.38), inter-correlación entre series (0.52 - 0.66), relación señal/ruido (1.16 - 18.51) y autocorrelación de primer orden (0.01 - 0.30). El primer componente (PC1) que incluyó las cronologías involucradas se utilizó para realizar una reconstrucción de precipitación acumulada noviembre-junio en el período común de las series (1890-2001), donde el crecimiento anual explicó más de 80% de la precipitación ocurrida en dicho período; asimismo, se utilizó la cronología residual del sitio Sauz para reconstruir la precipitación acumulada de los últimos 346 años (1668-2013), la cual detectó períodos extremadamente secos (1665-1688, 1695-1718, 1767-1778, 1890-1896, 1948-1963). La respuesta de las cronologías de esta especie a fenómenos atmosféricos de circulación general, como El Niño Oscilación del Sur (ENSO, por sus siglas en ingles), también fue similar a la obtenida con cronologías de especies con probado potencial dendroclimático. La ventaja de extender la red dendrocronológica de P. lumholtzii se fundamenta en que su potencial dendroclimático es equiparable con el de especies tradicionalmente usadas con este fin; su amplia distribución y el poco disturbio antropogénico que han sufrido sus poblaciones favorece la posibilidad de encontrar individuos longevos. Por su excelente sensibilidad climática, la red dendroclimática de P. lumholtzii es fundamental para estudios dendroclimáticos, particularmente en regiones donde se carece de registros climáticos instrumentales.

Drought timing influences the legacy of tree growth recovery.

Whether and how the timing of extreme events affects the direction and magnitude of legacy effects on tree growth is poorly understood. In this study, we use a global database of Ring-Width Index (RWI) from 2,500 sites to examine the impact and legacy effects (the departure of observed RWI from expected RWI) of extreme drought events during 1948-2008, with a particular focus on the influence of drought timing. We assessed the recovery of stem radial growth in the years following severe drought events with separate groupings designed to characterize the timing of the drought. We found that legacies from extreme droughts during the dry season (DS droughts) lasted longer and had larger impacts in each of the 3years post drought than those from extreme droughts during the wet season (WS droughts). At the global scale, the average integrated legacy from DS droughts (0.18) was about nine times that from WS droughts (0.02). Site-level comparisons also suggest stronger negative impacts or weaker positive impacts of DS droughts on tree growth than WS droughts. Our results, therefore, highlight that the timing of drought is a crucial factor determining drought impacts on tree recovery. Further increases in baseline aridity could therefore exacerbate the impact of punctuated droughts on terrestrial ecosystems.

Inconsistent relationships between annual tree ring-widths and satellite-measured NDVI in a mountainous subarctic environment

Recent climate warming has intensified efforts to understand patterns of vegetation productivity at northern high latitudes. Remotely-sensed and dendrochronological measurements have indicated significant changes in aboveground vegetation production in these regions, but the relationship between the two indicators remains unclear. We examined the relationship between remotely-sensed data, using the normalized difference vegetation index (NDVI), and annual ring-width indices obtained from trees and shrubs in the boreal mountains of southwest Yukon. A 24-year (1990–2013) trend in annual maximum NDVI was generated from two Advanced Very High Resolution Radiometer (AVHRR) datasets: the Alaska Composite NDVI (1 km), and the third generation Global Inventory Modeling and Mapping Studies (GIMMS3g) NDVI (8 km). Twenty sites were systematically selected for dendrochronological sampling and chronologies were developed for the dominant coniferous (Picea glauca and Picea mariana) and deciduous (Salix glauca, Alnus crispa, and Populus tremuloides) species at each site. NDVI trends indicated low-level greening across much of the region during the 24-year period. However, ring-width trends varied in direction and magnitude and the agreement with annual maximum NDVI was low. Correlations between annual ring-width indices and biweekly NDVI values were also low, although eight coniferous chronologies did show significant positive correlations with GIMMS3g biweekly data, suggesting that radial growth may be reflected in NDVI at some point during the growing season. Reasons for the inconsistent relationships between ring-width and NDVI remain unclear. Future studies should examine the role of climatic variables on the ring-width-NDVI relationship, especially when multiple datasets and various resolutions are being used. Investigating the relative contributions of plant growth, establishment of new plants, and changes in plant resource allocation to NDVI trends are critical to achieve a more functional understanding of the changes occurring in mountainous boreal ecosystems.