Different climate response of three tree ring proxies of Pinus sylvestris from the Eastern Carpathians,Romania

The aim of this study was to compare the climatic responses of three tree rings proxies: tree ring width (TRW), maximum latewood density (MXD), and blue intensity (BI). For this study, 20 cores of Pinus sylvestris covering the period 1886–2015 were extracted from living non-damaged trees from the Eastern Carpathian Mountains (Romania). Each chronology was compared to monthly and daily climate data. All tree ring proxies had a stronger correlation with the daily climate data compared to monthly data. The highest correlation coefficient was obtained between the MXD chronology and daily maximum temperature over the period beginning with the end of July and ending in the middle of September (r = 0.64). The optimal intervals for the temperature signature were 01 Aug – 24 Sept for the MXD chronology, 05 Aug – 25 Aug for the BI chronology, and both 16 Nov of the previous year – 16 March of the current year and 15 Apr – 05 May for the TRW chronology. The results from our study indicate that MXD can be used as a proxy indicator for summer maximum temperature, while TRW can be used as a proxy indicator for just March maximum temperature. The weak and unstable relationship between BI and maximum temperature indicates that BI is not a good proxy indicator for climate reconstructions over the analysed region.     

A Pinus cembra L. tree-ring record for late spring to late summer temperature in the Rhaetian Alps,Italy

Ongoing climate change strongly affects high-elevation environments in the European Alps, influencing the cryosphere and the biosphere and causing widespread retreat of glaciers and changes in biomes. Nevertheless, high-elevation areas often lack long meteorological series, and global datasets cannot represent local variations well. Thus, proxy data, such as tree rings, provide information on past climatic variations from these remote sites. Although maximum latewood density (MXD) chronologies provide better temperature information than those based on tree-ring width (TRW), MXD series from the European Alps are lacking. To derive high-quality temperature information for the Rhaetian Alps, Pinus cembra L. trees sampled at approximately 2000 m a.s.l. were used to build one MXD chronology spanning from 1647 to 2015. The MXD data were significantly and highly correlated with seasonal May-September mean temperatures. The MXD chronology showed a generally positive trend since the middle of the 19^th century, interrupted by short phases of climatic deterioration in the beginning of the 20^th century and in the 1970s, conforming with the temperature trends. Our results underline the potential for using Pinus cembra L. MXD to reconstruct mean temperature variations, especially during the onset and latter part of the growing season, providing additional information on parts of the growing season not inferred from TRW. Future studies on MXD for this species will increase the availability of temporal and spatial data, allowing detailed climate reconstructions.     

A lonely dot on the map: Exploring the climate signal in tree-ring density and stable isotopes of clanwilliam cedar,South Africa

Clanwilliam cedar (Widdringtonia cedarbergensis; WICE), a long-lived conifer with distinct tree rings in Cape Province, South Africa, has potential to provide a unique high-resolution climate proxy for southern Africa. However, the climate signal in WICE tree-ring width (TRW) is weak and the dendroclimatic potential of other WICE tree-ring parameters therefore needs to be explored. Here, we investigate the climatic signal in various tree-ring parameters, including TRW, Minimum Density (MND), Maximum Latewood Density (MXD), Maximum Latewood Blue Intensity (MXBI), and stable carbon and oxygen isotopes (δ¹⁸O and δ¹³C) measured in WICE samples collected in 1978. MND was negatively influenced by early spring (October-November) precipitation whereas TRW was positively influenced by spring November-December precipitation. MXD was negatively influenced by autumn (April-May) temperature whereas MXBI was not influenced by temperature. Both MXD and MXBI were negatively influenced by January-March and January-May precipitation respectively. We did not find a significant climate signal in either of the stable isotope time series, which were measured on a limited number of samples. WICE can live to be at least 356 years old and the current TRW chronology extends back to 1564 CE. The development of full-length chronologies of alternative tree-ring parameters, particularly MND, would allow for an annually resolved, multi-century spring precipitation reconstruction for this region in southern Africa, where vulnerability to future climate change is high.     

Separating the climatic signal from tree-ring width and maximum latewood density records

We propose a technique for separating the climatic signal which is contained in two tree-ring parameters widely used in dendroclimatology. The method is based on the removal of the relationship between tree-ring width (TRW) and maximum latewood density (MXD) observed for narrow tree rings from high latitudes. The new technique is tested on data from three larch stands located along the northern timberline in Eurasia. Correlations were calculated between the temperatures of pentads (five consecutive days), TRW chronologies and MXD chronologies calculated according to the standard and proposed methods. The analysis confirms the great importance of summer temperature for tree radial growth and tree-ring formation. TRW is positively correlated with the temperature of four to eight pentads (depending on the region) at the beginning of the growth season, but MXD as obtained by the standard technique is correlated with temperature over a much longer period. For maximum density series from which the relationship between MXD and TRW has been removed (MXD′), there is a clear correlation with temperatures in the second part of the growing season. These results are consistent with the known dynamics of tree-ring growth in high latitudes and mechanisms of tree-ring formation.     

用西伯利亚落叶松年轮最大密度重建和布克赛尔5—8月份平均最高温度

利用采自和布克塞尔铁布克山二号沟的西伯利亚落叶松树轮样本,研制出树轮最大密度年表(MXD)和年轮宽度年表(TRW),分析了其年表特征和气候响应特点。结果表明,该样点的落叶松树轮最大密度年表与和布克塞尔气象站5-8月份平均温度和平均最高温度度均具有很好的正相关关系,最高单相关系数为0.660。用铁布克山二号沟的最大密度差值年表序列,可较好地重建和布克塞尔地区1795-2007年来春夏季平均最高温度距平,47 a重建值对实测值的解释方差达43.5%,且方程稳定。重建结果揭示,在和布克赛尔地区,20世纪平均最高温度距平要高于20世纪以前的平均最高温度距平,20世纪前中期平均最高温度距平出现了明显的上升,并且在重建的时段的末期,5-8月份平均最高温度距平表现出上升趋势。     

Assessing non-linearity in European temperature-sensitive tree-ring data

We test the application of parametric, non-parametric, and semi-parametric calibration models for reconstructing summer (June–August) temperature from a set of tree-ring width and density data on the same dendro samples from 40 sites across Europe. By comparing the performance of the three calibration models on pairs” of tree-ring width (TRW) and maximum density (MXD) or maximum blue intensity (MXBI), we test whether a non-linear temperature response is more prevalent in TRW or MXD (MXBI) data, and whether it is associated with the temperature sensitivity and/or autocorrelation structure of the dendro parameters. We note that MXD (MXBI) data have a significantly stronger temperature response than TRW data as well as a lower autocorrelation that is more similar to that of the instrumental temperature data, whereas TRW exhibits a redder” variability continuum. This study shows that the use of non-parametric calibration models is more suitable for TRW data, while parametric calibration is sufficient for both MXD and MXBI data – that is, we show that TRW is by far the more non-linear proxy.     

Diverse climate sensitivity of Mediterranean tree-ring width and density

Understanding long-term environmental controls on the formation of tree-ring width (TRW) and maximum latewood density (MXD) is fundamental for evaluating parameter-specific growth characteristics and climate reconstruction skills. This is of particular interest for mid-latitudinal environments where future rates of climate change are expected to be most rapid. Here we present a network of 28 TRW and 21 MXD chronologies from living and relict conifers. Data cover an area from the Atlantic Ocean in the west to the Mediterranean Sea in the east and an altitudinal gradient from 1,000 to 2,500 m asl. Age trends, spatial autocorrelation functions, carry-over effects, variance changes, and climate responses were analyzed for the individual sites and two parameter-specific regional means. Variations in warm season (May–September) temperature mainly control MXD formation (r = 0.58 to 0.87 from inter-annual to decadal time-scales), whereas lower TRW sensitivity to temperature remains unstable over space and time.     

The temperature sensitivity along elevational gradients is more stable in maximum latewood density than tree-ring width

Tree ring-based temperature reconstructions are preferably derived from maximum latewood density (MXD) compared to tree-ring width (TRW). Although temperature signals in MXD are less dependent on site ecology, systematic analyses of the effects of elevation and slope aspect on ring formation are still lacking. Here, we assess the climate sensitivity of MXD and TRW chronologies from six larch (Larix decidua Mill.) sites across the Simplon valley in the southwestern Swiss Alps, representing elevations from 1400 to 2150 m asl on both north- and south-facing slopes. We find decreasing temperature signals with decreasing elevation in MXD and TRW, though correlation coefficients are generally higher for MXD and on the warmer and dryer south exposed slopes. While the greatest temperature signals are found for MJJA at highest elevations with r = 0.71 for MXD and r = 0.57 for TRW (both p < 0.05 and for the 1928–2009 common period), MXD still correlates significantly positive at the lowest elevation site that is ~750 m below the treeline. Our findings indicate the suitability of MXD over TRW for temperature reconstructions when using historical wood sources of unknown origin.     

Comparing Scots pine tree-ring proxies and detrending methods among sites in Jämtland,west-central Scandinavia

Scots pine tree-ring width (TRW) data from Jämtland in the Central Scandinavian Mountains has been used to reconstruct summer temperatures back to 1630 BC. However, it was recently shown that this reconstruction was of limited spatial importance. In this paper, we aim to explain this limitation in the TRW data as a temperature proxy, as well as assess the temperature information from new maximum latewood density (MXD) data. Furthermore, the effect of two standardization methods is evaluated: regional curve standardization (RCS) and a more traditional standardization, termed “non-RCS” standardization. Three TRW and two MXD sites were analyzed. Our results showed that despite the proximity to the Norwegian Sea, the MXD data is a powerful temperature proxy. Difference among sites in TRW data, especially on decadal timescales, together with a lower temperature association, suggests that other factors, such as changes in the local climate regimes, weakens the temperature signal. In general the RCS method overestimates pine growth trends in the latter half of the twentieth century, a feature not seen when using “non-RCS” standardization. This is likely due to an age-bias of older trees in most recent parts of the tree-ring chronologies. This effect will have consequences when reconstructing climate with tree-ring data. To overcome this problem, all age-classes should be represented throughout a chronology. If this is not possible, the use of “non-RCS” standardization is recommended, although this method results in a loss of low-frequency variability.     

Temperature sensitivity of blue intensity,maximum latewood density,and ring width data of living black spruce trees in the eastern Canadian taiga

The blue intensity (BI) technique provides opportunities to obtain surrogates to tree-ring density for reconstructing summer temperatures in high-latitude regions. In this study, we compare latewood BI (LBI) and delta BI (DBI), with the conventional X-ray maximum latewood density (MXD) and tree-ring width (TRW) data using 178 living trees of black spruce (Picea mariana (Mill.) B.S.P.), one of the most dominant species of conifers in the Northern Hemisphere, from 17 sites across the eastern Canadian taiga. The regional LBI and DBI chronologies are highly correlated to that of MXD (Pearson’s r = 0.97 and 0.92, respectively), while DBI is also similar to TRW (Pearson’s r = 0.67). Both LBI and DBI exhibit stronger responses to the May–August temperatures than TRW over larger time and spatial scales. However, only DBI is comparable to MXD data from inter-annual to decadal timescales. Low-frequency components of LBI data are likely distorted by color biases even if no obvious discoloration is present, as well as by the potentially low measurement resolution, leading to an overall weaker temperature sensitivity compared to the MXD data. Resampling experiments suggest that a minimum replication of 10 trees is needed to retain ≥90 % of the optimal temperature signal for MXD, LBI, and DBI data, and a minimum of 20 trees is required for TRW data.     

First measurements of Blue intensity from Pinus peuce and Pinus heldreichii tree rings and potential for climate reconstructions

Climate changes, their regional patterns, origin, and prediction are currently one of the most important scientific challenges. Tree-rings are among the most widely used proxies for past climate variation. However tree-ring width (TRW) from certain tree species and regions often do not contain robust climate signal. Other parameters such as Maximum latewood density (MXD) of conifer tree rings are more sensitive to summer temperatures, but the measurements have high costs. A potential surrogate for MXD is blue intensity (BI), which is based on the measurements of high-resolution images of the wood. The method has been tested and applied for several species. However it has not been tested up to now for Pinus heldreichii Christ (PIHE) and Pinus peuce Griseb. (PIPE). Those species are with limited distribution on the Balkan Peninsula and due to their longevity (frequently more than 500 years with potential to more than 1000 years) may serve as one of the best proxies for past climate variation in SE Europe.We composed BI chronologies following standard procedures from PIHE and PIPE trees from subalpine locations in the Pirin Mts, Bulgaria. The correlation analysis with climate parameters revealed strong and significant positive correlations of PIHE BI (ΔBI and Latewood BI (LwBI) series) and summer temperatures. The highest were 0.74 (p < 0.05) with July-August average temperatures for the period 1933–1983. The correlation values of ΔBI remained higher than 0.6 for the whole period (1933–2014) and sub-periods both for average monthly and average maximum temperatures. LwBI values of the PIHE chronology had correlation coefficients above 0.52 (highest 0.64) with August and August-July temperatures. The PIPE BI chronologies were also positively correlated with summer temperatures, but showed lower values than PIHE with lower temporal stability. The most stable were the correlations with LwBI average August temperatures, which were above 0.52. Delta BI series displayed high correlations for the 1933–1983 period, but then decreased and this caused overall lower correlations with August temperatures. Our data shows that there is potential to develop long BI chronologies and proxy climate reconstructions from the studied species and in this way complement the knowledge of the past climate of SE Europe.     

Stationarity of climate-growth response is only marginally influenced by the soil moisture regime in Western Siberia

Stationary (time-stable) relationships between a tree-ring proxy and climatic drivers are a prerequisite for using tree rings as paleo-climatological archives, but non-stationarity has been detected worldwide. Here we use a classical, temperature-sensitive treeline site in Western Siberia to specifically test the influence of micro-site conditions (wet versus dry) on the stationarity of climate-growth relationships in three co-existing conifer species: Larix sibirica Ledeb., Picea obovata Ledeb., and Pinus sibirica DuTour. We test two commonly used tree-ring proxies, annual tree-ring width (TRW) and maximum latewood density (MXD), using moving windows and the bootstrapped transfer function stability test (BTFS). Summer temperature is the main driver of tree growth in all three species, but non-stationarities exist in all species and both tree-ring proxies. For TRW, we found stationarity only for larch from both micro-sites, while for MXD, we found stationarity for spruce from both micro-sites, and for pine from the wet micro-site. Micro-site variability did not seem to affect stationarity in any systematic way. We highlight the necessity to systematically test the influence of different methods of stationarity tests, since BTFS was more sensitive than moving-window analysis. Taken together, our results underscore the importance of testing the assumption of stationarity for diverse micro-sites, different species and proxies at all sites prior to any tree-ring based temperature reconstruction, since even within one site results can be drastically different.     

Pre-1930 unstable relationship between climate and tree-ring width of Pinus taiwanensis hayata in southeastern China

Although it has been widely recognized that tree-ring response to climate drivers may change over recent decades, often due to anthropogenic environment changes, there are fewer reports of such changes in earlier pre-warming periods. In this paper we report on the pre-1930 unstable relationship between climate and tree-ring width (TRW) of Pinus taiwanensis Hayata in southeastern China based on reliable long-term temperature data. TRW of P. taiwanensis is strongly controlled by temperatures in two seasons, previous spring to summer (March to August, mainly June to July) and previous winter to current spring (December to March). However, TRW are insensitive to previous spring to summer temperature between 1890 and 1930. Reduced summer temperature variability, changing regimes of spring-summer temperature and precipitation, and complicated tree physiological processes behind the complex growth-climate relationship are the more likely causes of this phenomenon. This study adds to the body of knowledge that lower climate sensitivity of tree rings is not specific to the most recent decades.     

Multi-proxy crossdating extends the longest high-elevation tree-ring chronology from the Mediterranean

Annually precise dating is the cornerstone of dendrochronology. The accurate crossdating of relict wood is, however, frequently challenged during early chronology periods when sample replication is typically low. Here we present a multi-proxy approach in which stable carbon (δ¹³C) and radiocarbon (¹⁴C) isotope data are used to evaluate and correct dating errors in the early period of the longest high-elevation tree-ring chronology from the Mediterranean Basin. The record was initially developed using 878 tree-ring width (TRW) and 192 maximum latewood density (MXD) series from living and relict Bosnian pines (Pinus heldreichii) from Mt. Smolikas in Greece to reconstruct hydroclimate and temperature variability back to the 8th century. New annually resolved and non-pooled δ¹³C series now suggest a re-dating of first millennium relict pine samples during a period when sample replication was too low for proper TRW and/or MXD crossdating. The associated correction shifts the start of the Mt. Smolikas chronology from 575 back to 468 CE, a change independently confirmed by wiggle-matching annual ¹⁴C data along the 774/775 CE cosmic event. Our study demonstrates the importance of independent age validation for robust chronology development and shows how multi-proxy crossdating can improve dating success during periods of low sample replication.     

Determinants of mountain birch growth in situ: effects of temperature and herbivory

Variation in in situ growth performance of the mountain birch as indicated by the widths of annual rings was analysed and related mainly to temperature and herbivory using ring width series from five heath forest sites in the Lake Torneträsk area, northern Sweden. Climate explained 48–64% of the variation in age-corrected mean ring width series. In general, the effect of current year July followed by June temperature was most important at all sites. A warm May resulted in wider rings due to an earlier budburst. Short-term (inter-annual) responses to increased temperature were in most cases not reflected into long-term responses (decades). A large proportion of the variation in stem mean ring width was due to variation among stems within trees (81%) in these polycormic trees, while variation among sites was marginal (0.4%). Within trees, main stems grew faster and were more responsive to climate variation than subordinate stems. No effect of insect herbivory on ring width was found at low defoliation levels (≤12%). At a defoliation level of ca 84% a one-year reduction in stem growth was observed while the growth reduction (ca 50% reduction in ring width) lasted for 4 yr after ca 93% defoliation. After outbreaks resulting in complete defoliation and some stem mortality, ring widths of surviving stems mainly responded with increased growth. Basal sprouts, emerging just after a severe insect outbreak with a high mortality of old stems, grew faster than sprouts occurring during other periods. It is concluded that the mountain birch is well adapted to recover from Epirrita outbreaks; the ability to produce basal sprouts, that can benefit from an existing root system for fast initial growth, is one important mechanism for this.     

El Niño-Southern Oscillation modulates insect outbreaks in humid subtropical China: Evidences from tree rings and carbon isotopes

Insect outbreaks are key disturbances triggering decline episodes in humid subtropical evergreen forests in eastern China. However, their long-term variability and linkages to climate are still unclear largely due to the shortness of records reporting forest damage. A retrospective approach would improve our understanding of long-term outbreak variability and its dependence on climate and relevant atmospheric circulation patterns such as the El Niño-Southern Oscillation (ENSO). This study provides a dendrochronological reconstruction of Dendrolimus punctatus outbreaks affecting Pinus massoniana in humid subtropical eastern China. We used tree-ring width and carbon isotope data from sites where outbreaks were or not were reported for the past fifty years, here considered as host and non-host sites, respectively. The results showed that inter-annual changes in carbon isotope discrimination are more sensitive to outbreaks than changes in tree-ring width. Based on carbon isotopes, we inferred that photosynthetic rates increased as a compensatory mechanism in response to insect defoliation. We reconstructed eleven insect outbreaks since 1915, which corresponded to ENSO positive phases and below-average sea surface temperatures in the central and eastern tropical Pacific Ocean. These conditions correspond to “La Niña” episodes which induce hot and dry climate conditions across the study region and these may facilitate the occurrence of D. punctatus outbreaks.     

Influence of climate on multiple tree-ring parameters of Pinus kesiya from Manipur,Northeast India

Tree-rings of Pinus kesiya from southern region of Manipur, Northeast India were used to develop chronologies of multiple tree-ring parameters that are: total-ring width (TRW), earlywood width (EW), latewood width (LW) and adjusted latewood (LWadj). The time span of these chronologies is 39 years (1980–2018 C.E.) and we compared their growth responses with monthly and daily climatic records. The comparison revealed a broadly consistent pattern of climate sensitivity with daily climate exhibiting higher correlation. The climate signals during pre-monsoon (March–May) were recorded in TRW and EW, whereas late-monsoon to post-monsoon climate signals were recorded in LW and LWadj. The spatial correlation analysis of tree-ring parameters and global sea surface temperature (SST) showed a positive relationship between tree growth with tropical Pacific Ocean and Indian Ocean during winter (December–February) and pre-monsoon (March–May) seasons. The LW and LWadj were also correlated with peak summer monsoon (July–August) SST over the tropical Pacific Ocean. IADFs observed in EW (E-IADF) were caused by dry and warm conditions during March–April. IADFs in LW (L-IADF) occurred due to a combination of enhanced rainfall and temperature during post-monsoon (October–November) season. Evidence of stand-specific micro-climatic conditions in the formation IADFs in this species was also found. This study showed that multiple parameters of P. kesiya provides a lucid understanding of climate response on its growth and can be considered as a proxy for studying sub-seasonal changes in past environmental conditions in longer records.     

A statistical model for the prediction of the number of sapwood rings in Scots pine (Pinus sylvestris L.)

Dendrochronology is a well-established dating method for wooden objects, but due to surface processing of construction timber or natural degradation the dating of historical wood often relies on a prediction of the number of missing rings based on sapwood statistics. Since Scots pine (Pinus sylvestris L.) is one of the most common tree species in north-western Europe, the absence of reliable sapwood statistics and models for the prediction of missing sapwood rings for pine samples is remarkable. We have therefore produced sapwood statistics based on data from 776 pine trees with ages from 15 to 345 years. The material consists of both living trees and historical timber, with varying growth rates, geographic settings, and from different soil types. When the whole material is considered, the average age of the trees is 103 years, and the number of sapwood rings is 54 ± 15 (1 SD), but range from 18 to 129. Trees less than 100-years in age contained 46 ± 11 (1 SD) sapwood rings and had an average tree-ring width (TRW) of 1.76 mm. With increasing age, the average TRW decreased while the number of sapwood rings increased. The average TRW of 101–200-year-old trees is 0.99 mm while the samples contained 63 ± 12 (1 SD) sapwood rings. For trees older than 201 years, the average TRW is 0.64 mm while the number of sapwood rings increased to 85 ± 16 (1 SD). The two most important factors in determining the number of sapwood rings for a given tree when only heartwood statistics are available proved to be (i) the number of heartwood rings and (ii) the average TRW of the heartwood rings. For incomplete samples, we have therefore developed a statistical model based on the sample’s heartwood rings (number and average width) to compute a prediction interval for the total number of rings. The sapwood and heartwood statistics suggest a statistical model for the number of sapwood rings with mean that increase with the number of heartwood rings. Furthermore, the average number of sapwood rings decreases with the mean width of the heartwood rings. However, the predictive power of the mean width is limited when the number of heartwood rings has already been taken into account. Thus, we suggest making predictions for the number of sapwood rings using only the number of heartwood rings. Predictions of the number of sapwood rings based on the statistical model where convincing in the case of the three different datasets that were analysed. The certainty in these predictions was such that the width of the 80% and 95% prediction intervals ranged 28–34 and 45–52 sapwood rings, respectively. Additionally, we demonstrate how make predictions when there is information about the number of remaining sapwood rings in a given sample. To make the sapwood model available, we present a free online R package for fitting our models and an online software dashboard.     

Revealing Polylepis microphylla as a suitable tree species for dendrochronology and quantitative wood anatomy in the Andean montane forests

In the tropical Andes climate change is expected to increase temperatures and change precipitation patterns. To overcome the lack of systematic weather records that limits the performance of climate models in this region, the use of the environmental information contained in tree rings from tropical Andean species have been found useful to reconstruct spatio-temporal climate variability. Because classical dendrochronology based on ring-width patterns is often challenging in the tropics, alternative approaches such as Quantitative Wood Anatomy (QWA) based on the measurement and quantification of anatomical traits within tree rings can be a significant advance in the field. Here we assess the dendrochronological potential of Polylepis microphylla and its climate sensitivity by using i) classic dendrochronological methods to generate the first Tree-ring Width (TRW) chronology for this tree species spanning from 1965 to 2018; ii) radiocarbon (¹⁴C) analyses as an independent validation method to assess the annual periodicity of the tree growth layers; and iii) QWA to generate tree-ring annual records of the number (VN) and size (VS) of vessels to investigate the climate sensitivity of these anatomical traits. The annual periodicity in P. microphylla radial growth was confirmed by both dendrochronological and ¹⁴C analyses. We found that VN and VS are promising new proxies to reconstruct climate variability in this region and that they provide different information than TRW. While TRW provides information at inter-annual resolution (i.e., year-to-year variability), VN and VS generated with sectorial QWA provide intra-annual resolution for each stage of the growing process. The TRW and the anatomical traits (i.e., VN and VS) showed strong positive correlation with maximum temperature for different periods of the growing season: while VS is higher with warmer conditions prior to the growing season onset, tree-rings are wider and present higher number of vessels when warmer conditions occur during the current growing season. Our findings pointed out the suitability of P. microphylla for dendrochronological studies and may suggest a good performance of this species under the significant warming expected according to future projections for the tropical Andes.