Dendrometer Bands Research Articles

Intra-annual dynamics of stem circumference variation and water status of four coniferous tree species (Pinus sylvestris, Picea abies, Larix decidua and Abies alba) under warmer and water-limited conditions

AbstractIn the paper, the intra-annual growth patterns and tree water balance of four different tree species (Pinus sylvestris, Picea abies, Larix decidua and Abies alba) were examined. Seasonal radial increment, tree water deficit (ΔW) and maximum daily shrinkage (MDS) were derived from the records obtained using high-resolution digital band dendrometers. The study area was located in Arboretum Borová hora (350 m a. s. l., Zvolen valley, Central Slovakia) characterised by a warmer climate (Picea abies) and warmer and drier climate (Abies alba, Larix decidua, Pinus sylvestris) compared to the sites of tree origins. Monitored species exhibited remarkably distinct growth and water balance patterns over the 2015 growing season characterised with the highly above normal temperature and uneven precipitation distribution. A. alba exhibited smooth continuous growth least affected by varying environmental conditions. Of all analysed species, only A. alba showed significant positive correlations of radial growth and ΔW with temperature and global radiation, despite environmental water limitations. The lowest cumulative growth, lower negative values of ΔW and greater MDS of L. decidua indicate a higher water limitation of this species. The results showed more pronounced sensitivity of P. sylvestris to increased temperature and drought. All monitored variables of environmental conditions, except precipitation, significantly influenced MDS values of all studied tree species. Based on 30 variables describing radial stem growth patterns and water status we identified large inter-species variability and discrete species-specific groups, while the indicators of growth and water status of L. decidua and P. sylvestris were similar and the most different patterns were observed between A. alba and L. decidua. The behaviour of P. abies was closer to A. alba than to the other two species.

The timing of wood formation in peatland trees as obtained with different approaches

Dendrometers offer valuable insights into how tree growth responds to climatic variables and physiological processes over the course of a year. Yet, their applicability to extremely slow-growing trees, such as those in peatlands, has been limited due to the intricate and slow nature of growth, therefore rendering interpretation of results complex. In this study, we conducted a comprehensive monitoring of tree wood formation in both peatland and mineral soil ecosystems in southern Sweden (58.37 N, 12.17 E, 75 m asl) in 2021 and 2022, using both band and point dendrometers. To verify and validate the dendrometer data, we also sampled microcores every two weeks during both growing seasons. We find that peatland trees grow at approximately 30 % the rate of their neighbors on mineral soils. The onset of growth among peatland trees typically occurs between mid-May and early June, consistently lagging the start of the growing season in trees on mineral soils by one to three weeks. Notably, growth peaks are synchronized across peatland trees and coincide with the summer solstice. Both types of dendrometers exhibit varying degrees of accuracy depending on the phenological stages measured. They perform well in identifying growth onset and peak but are less effective at detecting growth cessation. Point dendrometers demonstrate superior accuracy as they better capture daily irreversible growth increments. In the case of band dendrometers, growth increments are obscured by greater reversible fluctuations in dead bark tissues. However, they remain valuable for tracking the wood phenology of trees with growth rates exceeding 2 mm/year. Based on our results, for an effective tree monitoring in peatlands, we strongly recommend (1) using point dendrometers and (2) removing the dead bark tissues on monitored trees.

The metropolitan parks of Quito as important carbon sinks

Abstract Despite the importance of urban forests as important carbon sinks, studies in Ecuador have yet to assess their potential to store carbon. We assessed the carbon stored in the aboveground biomass (AGB) and annual rates of AGB accumulation in the Guangüiltagua Metropolitan Park (GMP) and the Southern Metropolitan Park (SMP). We installed 11 plots per park of 0.063 ha, where we surveyed all stems with a diameter at breast height (DBH) ≥2.5 cm. To estimate annual increments in AGB, we installed dendrometer bands on 10% of the total stems recorded in each plot (only in stems with ≥10 cm DBH). We measured the dendrometer band segment increase every 4 months from September 2019 to October 2020. Our results show that the GMP stores 171 ± 96 Mg C ha−1, significantly higher than the amount of carbon storage recorded in the SMP (100 ± 41 Mg C ha−1). In contrast, the GMP sequestered 3.30 ± 1.71 Mg C ha year−1, while the SMP sequestered an average of 4.45 ± 2.63 Mg C ha year−1. At the landscape scale, the SMP contains 0.072 Tg C (0.058–0.091, 95% CI), while the GMP contains a reservoir of 0.096 Tg C (0.067–0.13, 95% CI). Likewise, the AGB in the SMP 3,165 Mg C year−1 (2209–4297, 95% CI), while that in the GMP sequestered 1859 Mg year−1 (1361–2430, 95% CI). Our results show that the metropolitan parks of Quito are important carbon sinks and constitute essential elements in mitigating climate change in urban spaces.

Assessing intra-annual growth dynamics in climatically contrasting years, sites, and tree species using dendrometers and wood anatomical data

Detecting the intra-annual dynamics and courses of secondary tree growth enables the accurate identification of crucial steps in the forming of a new tree ring. Furthermore, comparing the high-resolution recordings of tree growth with environmental conditions allows assessment of the influence of weather on wood formation processes. This study investigates the intra-annual growth performance of conifer species and European beech at two high- and two low-elevation sites in Bavaria, southeast Germany. We measured stem circumference changes with electronic band dendrometers and cambial dynamics by collecting microcores at biweekly intervals. We analyzed growth variations between the consecutive years 2020 and 2021, which showed distinct climatic differences during the growing seasons. While warm and dry conditions prevailed in spring and summer in 2020, spring in 2021 was comparatively cold, and summer precipitation was high. Different tree growth patterns were observed in the contrasting years 2020 and 2021. Distinct growth reductions occurred in the drier year 2020 for most of the studied tree species, while trees showed wider tree rings in 2021 despite of low growth rates at the beginning of the growing season. Climate-growth correlations exposed the intraseasonal influence of climatic conditions, particularly available soil water, water vapor pressure deficit, and soil temperature, on short-term tree responses. Wood anatomical analysis and daily stem diameter variations proved to be valid monitoring methods to assess individual wood formation processes and to identify species-specific tree responses to the influence of climatic conditions. However, combining both methods represents the most reliable approach due to the mutual ability to compensate for each other’s deficiencies. While dendrometers provided a very accurate and high-resolution record of intra-annual tree growth, wood anatomical analyses were more reliable in determining the exact onset and cessation of wood formation. For this reason, combining both is recommended for assessing prospective tree growth performance in the context of climate change.

Growth rate of Clethra mexicana, Juglans pyriformis, Liquidambar styraciflua, and Trema micrantha in secondary cloud forest

Secondary cloud forests (SCF) play a valuable role in regulating the hydrological cycle, providing habitat for biodiversity and resources for local livelihoods in cloud forest landscapes. At present, there is limited information on the potential of SCF for timber production. In this study, we determined the growth rates of 4 common SCF tree species, relative to tree size, crown exposure to light, and basal area of neighbouring trees. We used dendrometric bands to measure annual diameter growth in 375 individuals for 2 years, in SCF in Veracruz, Mexico. Average diameter growth rates were: Clethra mexicana = 0.53 ± 0.04 cm y-1, Juglans pyriformis = 0.41 ± 0.03 cm y-1, Liquidambar styraciflua = 0.41 ± 0.03 cm y-1, and Trema micrantha = 0.22 ± 0.04 cm y-1. Tree size was a significant predictor of diameter growth rate; diameter growth rate increased with tree size in all 4 species. Trees with crown laterally illuminated showed higher growth than trees without direct illumination in L. styraciflua. The basal area of neighbouring trees did not affect diameter growth in any species. The results indicate that young trees have high growth potential.

Radial increment dynamics of Maritime pine (Pinus pinaster Ait.) in pure and mixed stands with Scots pine (Pinus sylvestris L.) under changing environmental conditions

Forest dynamics are undergoing profound alteration due to the fact that climate change is increasing the frequency and severity of abiotic and biotic forest disturbances. Because of the unpredictable nature of the drought periods and the variation in their severity, Mediterranean forests are typically more vulnerable. Mediterranean Pinus pinaster forests are showing decay symptoms linked to climate change. There is clear evidence that promoting mixtures can serve as an effective forest adaptation strategy. In this regard, we sought to better understand the responses of P. pinaster radial growth dynamics to various factors, in both mixed and pure forest stands, and provide valuable insights into P. pinaster dynamics when mixed with P. sylvestris. In this study, we examined the variation of intra-annual cumulative radial increment patterns in response to the climate of P. pinaster between pure and mixed stands with P. sylvestris. Using data from band dendrometers collected over five consecutive climatically distinct years (2016–2020), a nonlinear mixed-effect model approach was used to analyze the differences in intra-annual cumulative radial increment patterns for P. pinaster between years in mixed and pure stands. The intra-annual radial increment pattern of P. pinaster showed significant year-to-year variation and varied with tree size, with greater increment in larger trees. Trees in mixed stands had a higher mean radial increment compared to corresponding ones in pure stands. Increased summer maximum temperatures negatively affected tree cumulative annual increment regardless of composition, but with a lower impact on trees in pure stands. Spring precipitation increased the length of the growing season, while higher spring maximum temperatures triggered an earlier inflection point. Our results highlight the high plasticity of P. pinaster in adapting to varying intra- and inter-annual environmental conditions and competition with other species and suggest that promoting mixtures with P. sylvestris may be an interesting management strategy for adaptation to climate change.

Effects of fertilization on radial growth of Pinus pinea explored hourly using dendrometers

BackgroundStone pine (Pinus pinea), a drought-resistant species, has significant socio-economic benefits and increasing interest for the establishment of productive plantations in several countries, especially in a climate change context. Monitoring hourly stem diameter variations contributes to the understanding of the tree-growth response to changes in environmental conditions and management. By monitoring the diameter expansion of tree stems, high-resolution band dendrometers were used to study the development of adult trees growing in a semi-arid coastal environment of central Chile under fertilized and non-fertilized soil conditions through the span of a year.ResultsShort cycles (< 21 h) were few in fertilized and non-fertilized trees (6 and 4, respectively), whereas long cycles (> 28 h) occurred at a higher frequency in fertilized trees (16 vs 6). Most of the circadian cycles were regular (24 ± 3 h). The longest cycle duration (59 h) was observed in fertilized trees during spring. In all seasons, each phase of the circadian cycle, especially during the stem diameter increment phase (P3, irreversible growth), started earlier in fertilized than in control trees. P3 duration was significantly longer in fertilized than in control trees in springtime. The maximum shrinkage (P1) was observed in summer for both treatments. Stem diameter increased faster in fertilized than in control trees throughout the year, with the highest accumulation occurring in spring and the lowest in autumn. The daily variability pattern showed lower growth under high temperature across seasons.ConclusionsThis study highlights the importance of fertilization in enhancing stone pine diameter growth. This cultural practice should be further explored to contribute to the mitigation of climate change effects in semi-arid environments.

Short-term effect of thinning on inter- and intra-annual radial increment in Mediterranean Scots pine-oak mixed forests

Thinning treatments along with the establishment of mixed forest stands have been put forward as possible adaptation strategies to cope with climate change, although the effectiveness of combining these two measures has scarcely been studied and may vary depending on stand conditions and the thinning regime employed. The aim of this study was to better understand the effect of commercial thinning and of the different growth behavior of two coexisting species on their inter- and intra-annual cumulative radial increment patterns. For this purpose, we studied radial increment in a Scots pine-Pyrenean oak (Pinus sylvestris L.-Quercus pyrenaica Willd.) Mediterranean mixed forest in north-west Spain over two climatically contrasting years (2016–2017). The data came from a thinning trial consisting of a randomized latin square design with a control and two commercial thinning treatments from below; one moderate and the other heavy, removing 25% and 50 % of initial basal area, respectively, of both species. The radial increment was analyzed based on bi-weekly readings from band dendrometers installed on 90 oak and pine trees. A non-linear mixed model based on double-Richards curve was fitted to explore the differences between thinning treatments and species response in the intra-annual cumulative radial increment patterns. Inter-annual basal area increments for each species at stand level were quantified by aggregating the tree estimates obtained from the model fitted in the first step. Tree and stand level growth were greater in Scots pine, which also showed a greater growth response to early spring droughts than the Pyrenean oak. Heavy thinning increased radial increment in trees of both species at the expense of decreased total stand basal area. At species level, basal area growth in Scots pine decreased through thinning, whereas for Pyrenean oak, the heavy thinning intensity resulted in the same basal area growth as the control. Thus, heavy thinning induced a trade-off between total stand growth and tree-level response to climatic conditions for Scots pine but with no loss in productivity in the case of the Pyrenean oak. Hence, heavy thinning may be an appropriate measure to attain productive stability of the oak coppice in the studied mixed forest as well as to adapt tree growth to future droughts associated with climate change.

Close-to-nature management effects on tree growth and soil moisture in Mediterranean mixed forests

Given the rising frequency of drought events, close-to-nature principles appear to be a suitable management option for promoting more adapted forests by increasing diversity and vitality (e.g., enhancing tree growth), while preserving soil moisture. In this study, we evaluate individual tree growth from selected trees (including future crop trees) and soil moisture responses to close-to-nature silvicultural treatments in sub-humid Mediterranean mixed forests in Catalonia (Northeastern Spain). We relied on 18 permanent sample plots (i.e., 9 paired-plots: managed / control) representing a competition intensity gradient and different forest types (dominated by either Quercus ilex, Castanea sativa, Quercus pubescens/petraea, Pinus pinea and Pinus sylvestris). From them, 8 plots were subject to intense monitoring in terms of intra-annual tree radial growth, monitored by manual band dendrometers, and hourly soil water content. Basal area increment, and annual and seasonal (May, June, July) radial increment rates were computed as a proxy of tree growth for all plots and for those plots with dendrometers, respectively. We conducted Spearman correlation analyses between tree growth, competition intensity, soil water content and climatic variables to detect significant relations between forest management and variables of interest (e.g., basal area increment, radial increment rates, soil water content). To investigate further into the effect of this silviculture on tree growth, we used mixed-effects models using as predictors variables related to competition intensity and forest management (dummy variable) in combination with monthly soil water content variables. We observed that basal area increment and radial increment rates had a positive (albeit weak) correlation with forest management, while competition intensity had a negative correlation with both variables. The models were not capable of detecting clear species-specific tree growth responses to competition. Compared to control plots, on average, the treatments boosted soil water content by about a 10% in managed plots in Q. ilex, P. sylvestris and P. pinea stands, and this increase was particularly significant during the growing season. Moreover, the best-fitted model predicted seasonal radial increment rates using not only forest management and competition variables, but also monthly soil water content factors. Our results suggest that close-to-nature-forest management may reduce the vulnerability to drought by increasing tree vitality and soil moisture, at least in the short term (<3 years).

Assessing water stress in a high-density apple orchard using trunk circumference variation, sap flow index and stem water potential.

Automated plant-based measurements of water stress have the potential to advance precision irrigation in orchard crops. Previous studies have shown correlations between sap flow, line variable differential transform (LVDT) dendrometers and fruit tree drought response. Here we report season-long automated measurement of maximum daily change in trunk diameter using band dendrometers and heated needles to measure a simplified sap flow index (SFI). Measurements were made on two apple cultivars that were stressed at 7 to 12 day intervals by withholding irrigation until the average stem water potential (ΨStem) dropped below -1.5 MPa, after which irrigation was restored and the drought cycle repeated. Dendrometer measurements of maximum daily trunk shrinkage (MDS) were highly correlated (r² = 0.85) with pressure chamber measurements of stem water potential. The SFI measurements were less correlated with stem water potential but were highly correlated with evaporative demand (r² = 0.82) as determined by the Penman-Monteith equation (ETr). The high correlation of SFI to ETr suggests that high-density orchards resemble a continuous surface, unlike orchards with widely spaced trees. The correlations of MDS and SFI to ΨStem were higher during the early season than the late season growth. Band dendrometers are less labor intensive to install than LVDT dendrometers and are non-invasive so are well suited to commercialization.

Using homemade stainless steel dendrometer band for long term tree growth measurements

Dendrometer bands have been proposed as an accurate method for measuring tree growth. However, the constrained observation window and the material used in them hamper long-term tree growth monitoring. This study devised a dendrometer band made from stainless steel and primarily extended the extension length of the band spring to yield ample space to monitor diameter increments long-term. A total of more than 500 individual trees, including both coniferous and broadleaf trees, were examined. We compared the dendrometer band’s long-term performance with diameter tape for 5- and 10-year measurements. The results showed that the measurements of the two methods were highly correlated (R > 0.89) in both measuring periods. Differences between the two measurements for individual trees were typically less than 5 mm, and the mean differences at a stand level were less than 2 mm. These consistent observations suggested that the dendrometer band measurements were reliable for long-term measurement. Using the dendrometer bands, we further demonstrated the annual tree growths of diameter at breast height (DBH) and basal area (BA) for ten years of measurements. The size-dependent relationships between DBH/BA growth and initial DBH were also presented. Owing to their simple installation, low cost, and reliable measurement, these dendrometer bands would be helpful in forestry and forest ecology research.

Effect of Provenance and Environmental Factors on Tree Growth and Tree Water Status of Norway Spruce

Changes in temperature regime, and a higher frequency of extreme weather conditions due to global warming are considered great risks for forest stands worldwide because of their negative impact on tree growth and vitality. We examined tree growth and water balance of two provenances of Norway spruce growing in Arboretum Borová hora (350 m a.s.l., Zvolen, central Slovakia) that originated from climatologically cooler conditions. The research was performed during three meteorologically different years from 2017 to 2019. We evaluated the impact of climatic and soil factors on intra-species variability in radial stem growth and tree water status that were characterised by seasonal radial increment, stem water deficit and maximum daily shrinkage derived from the records of stem circumference changes obtained from band dendrometers installed on five mature trees of each provenance. The impact of environmental factors on the characteristics was evaluated using the univariate factor analysis and four machine learning models (random forest, support vector machine, gradient boosting machine and neural network). The responses to climatic conditions differed between the provenances. Seasonal radial increments of the provenance from cooler conditions were greater than those of the provenance originating from cooler and wetter conditions due to the long-term shortage of water the latter provenance had to cope with in the current environment, while the provenance from the cooler region was more sensitive to short-term changes in environmental conditions.

Potassium fertilization enhances xylem plasticity and growth recovery of Eucalyptus grandis trees in response to drastic changes in water availability

Most Eucalyptus plantations in Brazil are located in regions currently experiencing periods of water shortage, where fertilizers such as potassium (K) are intensively used to achieve high productivity. In a changing environment, improving our understanding of the effects of K nutrition on tree growth rates and xylem plasticity across tree ages as a function of climate is crucial for forest management. The objective of this study was to gain insight into the interactive effects of K fertilization, water availability, and tree age on stem growth and changes in xylem traits of E. grandis trees over a full rotation. Changes in growth and xylem traits in response to a severe drought that occurred in 2014 were also studied. An experimental plantation of E. grandis trees was established in São Paulo, Brazil and monitored over a full 6-year rotation period. The experiment consisted of a split-plot design with two water supply regimes (37 % throughfall reduction vs undisturbed throughfall) and two fertilization regimes (K supply vs control). Basal area increment (BAI) was monitored using band dendrometers at 14-day intervals from 1 to 6 years after planting. Xylem traits including wood density (WD), cell wall fraction (CWF), cell density (CDen), theoretical xylem specific hydraulic conductivity (Kst), vessel diameter (VD), vessel density (VDen), vessel area (VA), and the vulnerability index (VI) were measured in 6-month periods (rainy and dry seasons) throughout the rotation. K fertilization increased BAI by a factor of 3 in plots where throughfall was not disturbed but led to an interruption of tree growth during the severe drought in 2014. The growth patterns showed a positive effect of K for growth recovery following drought. Throughfall reduction affected growth only in K-fertilized trees and up to 30 months of age. K fertilization also increased changes in xylem traits in response to drought in E. grandis trees. The main changes occurred in vessel traits, with a 53 % decrease in Kst during the drought but recovery was rapid after the first rainfall events. High plasticity was also observed for WD, CWF, CDen, and VI.

Implementing GitHub Actions continuous integration to reduce error rates in ecological data collection

Abstract Accurate field data are essential to understanding ecological systems and forecasting their responses to global change. Yet, data collection errors are common, and data analysis often lags far enough behind its collection that many errors can no longer be corrected, nor can anomalous observations be revisited. Needed is a system in which data quality assurance and control (QA/QC), along with the production of basic data summaries, can be automated immediately following data collection. Here, we implement and test a system to satisfy these needs. For two annual tree mortality censuses and a dendrometer band survey at two forest research sites, we used GitHub Actions continuous integration (CI) to automate data QA/QC and run routine data wrangling scripts to produce cleaned datasets ready for analysis. This system automation had numerous benefits, including (1) the production of near real‐time information on data collection status and errors requiring correction, resulting in final datasets free of detectable errors, (2) an apparent learning effect among field technicians, wherein original error rates in field data collection declined significantly following implementation of the system, and (3) an assurance of computational reproducibility—that is, robustness of the system to changes in code, data and software. By implementing CI, researchers can ensure that datasets are free of any errors for which a test can be coded. The result is dramatically improved data quality, increased skill among field technicians, and reduced need for expert oversight. Furthermore, we view CI implementation as a first step towards a data collection and analysis pipeline that is also more responsive to rapidly changing ecological dynamics, making it better suited to study ecological systems in the current era of rapid environmental change.

Warm springs alter timing but not total growth of temperate deciduous trees.

As the climate changes, warmer spring temperatures are causing earlier leaf-out1-3 and commencement of CO2 uptake1,3 in temperate deciduous forests, resulting in a tendency towards increased growing season length3 and annual CO2 uptake1,3-7. However, less is known about how spring temperatures affect tree stem growth8,9, which sequesters carbon in wood that has a long residence time in the ecosystem10,11. Here we show that warmer spring temperatures shifted stem diameter growth of deciduous trees earlier but had no consistent effect on peak growing season length, maximum growth rates, or annual growth, using dendrometer band measurements from 440 trees across two forests. The latter finding was confirmed on the centennial scale by 207 tree-ring chronologies from 108 forests across eastern North America, where annual ring width was far more sensitive to temperatures during the peak growing season than in the spring. These findings imply that any extra CO2 uptake in years with warmer spring temperatures4,5 does not significantly contribute to increased sequestration in long-lived woody stem biomass. Rather, contradicting projections from global carbon cycle models1,12, our empirical results imply that warming spring temperatures are unlikely to increase woody productivity enough to strengthen the long-term CO2 sink of temperate deciduous forests.

The Impact of Climate and Adaptative Forest Management on the Intra-Annual Growth of Pinus halepensis Based on Long-Term Dendrometer Recordings

Future climate predictions for the Mediterranean area include prolonged droughts and an increase in the frequency of extreme events. Silvicultural modification of stand density can buffer the response of tree growth to changes in climate by enhancing soil water availability. We analyzed the stem growth dynamics of Pinus halepensis, including the days of the year when 25%, 50% and 75% of the intra-annual basal growth was achieved, considering two different social statuses (suppressed and dominant) under four different thinning intensities (15%, 30% and 45% removal of the basal area) for 8 years, based on biweekly band dendrometer recordings. The moment the trees reached 25% of the intra-annual basal growth was significantly influenced by the amount of precipitation accumulated during the previous winter. On the other hand, the moment the trees reached 75% of the intra-annual basal growth was significantly influenced by water availability in a shorter term, which also affected the length of the growing period. Modification of competition through thinning showed a significantly positive impact on growth, causing a delayed attainment of 50% of the intra-annual basal growth. These results imply valuable information about forest dynamics that will support forest managers’ decisions dealing with low water-availability in forests.

Trunk growth rate frequencies as water stress indicator in almond trees

The continuous monitoring of water stress will increase the accuracy of the deficit irrigation scheduling. Almonds are very sensitive to water stress conditions and an important water consumer. Recently, a novel approach to the use of trunk growth rate (TGR) data has been proposed for olive trees. These works suggested the use of TGR frequencies to evaluate water status of the trees. The aim of the current work was to compare the seasonal pattern of three different indicators derived from the daily curves of trunk diameter fluctuations with midday stem water potential. During three consecutive seasons (2017–2019), an irrigation experiment was carried out in a mature almond orchard (cv Vairo) at Dos Hermanas (Seville, Spain). Four irrigation treatments replicated in four blocks were evaluated using the daily curves of midday stem water potential and trunk diameter fluctuations. The different irrigation treatments were: Control, full irrigated conditions; RDI-1 (irrigation scheduling based on midday stem water potential with a deficit irrigation during kernel filling [values around −1.2 MPa]); RDI-2(similar to RDI-1 but with a more severe water stress [−2 MPa]) and incomplete recovery after harvest due to limitation of the seasonal amount of water (around 100 mm); SDI, sustained deficit irrigation with a seasonal applied water equal to RDI-2. Trunk diameter fluctuations were measured with a wireless band dendrometer. The daily curves were processed to obtain three different indicators. Maximum daily shrinkage (MDS) was the difference between the daily maximum and minimum. Trunk growth rate (TGR) was the difference between two consecutive daily maximums. The frequencies of several ranges of TGR were compared with the midday stem water potential. Weekly frequencies of values greater than 0.3 mm day−1 decreased with the reduction of midday stem water potential, but the pattern changed greatly in different seasons. The weekly frequency of values between − 0.1 and 0 and between 0 and 0.1 mm day−1 were steadier in different seasons. Differences between seasons were related to growth pattern and yield.

A methodological framework to optimize models predicting critical dates of xylem phenology based on dendrometer data

Dendrometer measurements are a frequently used alternative to the laborious and time consuming microcoring to investigate intra-annual growth dynamics of trees. However, since dendrometer data not only comprise cambial growth, but also hydrological fluctuations, both signals need to be disentangled to derive critical dates of xylem phenology from dendrometer data. For this purpose, various approaches can be found in the literature, however a systematic comparison of the different options is still missing. In this study we present a methodological framework to evaluate the accuracy of different mathematical fittings to derive tree-ring phenology from dendrometer data and apply this approach to a data set comprised of three conifer species where high-resolution band dendrometer measurements and microcore sampling have been done in parallel. Based on our study we provide evidence that the most common approaches to derive onset and cessation of xylem cell enlargement from dendrometer data, i.e. applying absolute and relative thresholds to deterministic models fitted to dendrometer data, caused systematic deviations from the reference of xylogenesis observations, but could be improved by small adaptations. The most precise and unbiased predictions of xylem growth phenology were obtained by fitting the three-parameter Gompertz model to the dendrometer data and applying a relative threshold of 3.5% of annual increment to the model predictions for growth onset and an absolute threshold of 4.5 µm day-1 based on the first model derivative for growth cessation. Our framework enables an improved usage of dendrometer data for the prediction of the onset and cessation of xylem cell enlargement, which are important ecological indicators to quantify the effects environmental changes on forest growth and the terrestrial carbon cycle.

Intra- and Inter-Annual Growth Patterns of a Mixed Pine-Oak Forest under Mediterranean Climate

Temperature and precipitation variability throughout the year control the intra-annual dynamics of tree-ring formation. Physiological adaptation of trees to climate change is among the key issues to better understand and predict future forest performance and composition. In this study, we investigated the species’ coexistence and performance of Scots pine and pubescent oak growing in a mixed sub-Mediterranean forest in the northeast of the Iberian Peninsula. We assessed intra-annual cumulative growth patterns derived from band dendrometers during four consecutive growing seasons and long-term changes in basal area increment for the period 1950–2014. Our results revealed that Scots pine followed an intra-annual bimodal growth pattern. Scots pine growth was mainly limited by water availability at intra-annual, interannual and decadal time scales, which resulted in a negative long-term growth trend. Conversely, oak displayed a unimodal growth pattern, which was less climatically constrained. A significant increase in basal area of oak denotes an overall better potential acclimation to prevailing climatic conditions at the expenses of a higher risk of physiological failure during extreme climate events.

Tree growth responses to climate variation in upland and seasonally flooded forests and woodlands of the Cerrado-Pantanal transition of Brazil

Tropical forest trees are sensitive to climate variations, especially during anomalously warm and dry years that occur during El Niño. However, species growth responses are poorly understood. We measured annual stem growth of 27 different tree species from upland and seasonally flooded forests and woodlands in the Cuiaba Basin and Northern Pantanal of Mato Grosso, Brazil. Stem growth increment was measured using plastic, spring-loaded dendrometer bands installed on 344 trees. Measurements were made between 2015 and 2019, which encompassed the 2015–16 El Niño that was one of the warmest and driest on record. Relative stem growth rates (RGR) at both sites increased with higher rainfall and declined with an increase in maximum temperature, but the RGR of trees in the Cuiaba Basin also declined as the length of the dry season increased. RGR, and the response of RGR to climate variation, varied substantially across species. Some species only exhibited a significant RGR response to variations in rainfall, maximum temperature, or dry season length, other species responded to more than one climate variable, and a subset were insensitive to the variation in all three climate variables studied. Rainfall appeared to be a stronger control on RGR in the predominately upland Cuiaba Basin (87% of species exhibited a significant RGR response to rainfall in the Cuiaba Basin vs. 39% in the Pantanal) while temperature was a stronger control on RGR in the seasonally flooded Pantanal (67% of species exhibited a significant RGR response to temperature in the Pantanal vs. 53% in the Cuiaba Basin). While our study period was short, and measurements were done on a small subset of available species, our data indicate that variations in climate affect the growth of tropical forest and woodland tree species differently. These species-specific responses have the potential to alter community diversity and productivity as climate change ensues.