Seeds integrate environmental cues that modulate their dormancy and germination. Although many mechanisms have been identified in laboratory experiments, their contribution to germination dynamics in ...existing communities and their involvement in defining species habitats remain elusive. By coupling mathematical models with ecological data we investigated the contribution of seed temperature responses to the dynamics of germination of three Nothofagus species that are sharply distributed across different altitudes in the Patagonian Andes. Seed responsiveness to temperature of the three Nothofagus species was linked to the thermal characteristics of their preferred ecological niche. In their natural distribution range, there was overlap in the timing of germination of the species, which was restricted to mid‐spring. By contrast, outside their species distribution range, germination was temporally uncoupled with altitude. This phenomenon was described mathematically by the interplay between interspecific differences in seed population thermal parameters and the range in soil thermic environments across different altitudes. The observed interspecific variations in seed responsiveness to temperature and its environmental regulation, constitute a major determinant of the dynamics of Nothofagus germination across elevations. This phenomenon likely contributes to the maintenance of patterns of species abundance across altitude by placing germinated seeds in a favorable environment for plant growth.
•Age, stem slenderness and site index as key determinants of modulus of elasticity.•At each site, the most slender trees, will have a greater modulus of elasticity.•Simple variables (ABH, SI, S and ...RH) allow to predict modulus of elasticity.
Using portable acoustic tools, measurements of dynamic modulus of elasticity (Ed) were made in standing ponderosa pine (Pinus ponderosa (Dougl. ex Laws)) trees (n = 437) growing in 22 stands encompassing the range of environmental site conditions and ages of the plantations that have been established in NW Patagonia, Argentina. The objectives of this research were to (i) identify the stand and tree-level factors associated with the variation in Ed and, with the most suitable variables (ii) develop a descriptive model to Ed for ponderosa pine grown in NW Patagonia Argentina as the first step of a predictive model.
Tree and stand variables showed a wide range of variation and Ed ranged ten-fold, from 2.13 GPa to 22.1 GPa, with a mean value of 11.2 Gpa. The cross-correlations analysis performed among Ed and independent tree and stand variables showed almost all variables to be significantly related to Ed. The main positive and significant correlation was found for total tree height (H, r = 0.78, p < 0.001), top height of the stand (H100, r = 0.78, p < 0.001) and basal area of the stand (G, r = 0.68, p < 0.001). Nevertheless, the most suitable independent variables for modelling Ed were two stand variables: age at breast height (ABH) and site index (SI20) and two tree variables: stem slenderness (S, tree height/diameter at breast height) and social status or relative height (RH = H/H100).
In combination, ABH, SI20, S and RH accounted for 68.4% of the variation in Ed within the sample population. This model could be readily applied by managers to estimate stand-level Ed, giving them greater understanding of how they can manipulate stands to achieve desired end product outcomes.
•Intense thinning decreases mean sensitivity of E. grandis to water availability.•High competition decreases mean growth and increases sensitivity of individual trees.•Low-density stands show higher ...resistance to an extreme drought event.•Two-stage thinning increases resistance and resilience to an extreme drought event.
Climate change has induced an increase in the frequency and intensity of droughts and heat waves, reducing growth and increasing the mortality risk of both natural and planted forests. Management practices are expected to affect the capacity of stands to tolerate these new and fluctuating environmental conditions. Particularly, the effect of thinning on growth and mortality responses to climatic variation is highly variable among species and environmental conditions, and very few studies have been carried out in broad-leaved species. The objectives of this study were to assess the effect of forest thinning on (1) the growth sensitivity of planted Eucalyptus grandis to typical interannual variation in water availability and (2) its response to extreme drought events. We analyzed data collected in the period 1999–2016 from three thinning trials installed in sites with normal growth conditions of the species in a subtropical, humid and warm region of South America (Mesopotamia region, Argentina), where it is the most planted Eucalyptus species. Different intensities (final densities between 300 and 1250 plants/ha) and modalities (single- versus two-stage) of thinning operations were applied in each trial. First, we used a hierarchical linear model to relate basal area increment to water balance, and from this analysis we obtained the mean growth and sensitivity to water balance at individual, treatment and site levels. Results at the treatment level show that the mean growth of E. grandis increases with thinning intensity while its sensitivity to water balance decreases, consistently across all sites. At the individual level, using Hegyi’s intraspecific competition index we observed that higher competition induces lower mean growth and higher sensitivity to water balance, regardless of the number of thinning stages. Second, we selected an extreme drought event at each site and computed resistance and resilience indices, as well as the probability of tree mortality associated with the event. Within the single-stage thinning treatments, those with the highest intensity showed the highest resistance (i.e. the lowest growth decrease during the drought event), while stand density did not affect their resilience (i.e. growth recovery after the drought event). The effect of thinning intensity on the probability of death due to the drought event was not conclusive. On the other hand, the two-stage treatments presented much higher resistance and resilience values than the other treatments, suggesting that this modality of treatment could be effective in improving the adaptability of E. grandis to extreme drought events. We conclude that high-intensity thinning interventions could increase the ability of this species to cope with climate change and benefit solid wood production, where the associated decrease in stand-level growth may be compensated by an increase in the individual-tree growth. For other industrial purposes, where final stand-level production is a key driver, medium intensity two-stage thinning is recommended, in particular when genetic materials selected for drought resistance are not available and there is high climatic risk.
Tree breeding programs and wood industries require simple, time- and cost-effective techniques to process large volumes of samples. In recent decades, near-infrared spectroscopy (NIRS) has been ...acknowledged as one of the most powerful techniques for wood analysis, making it the most used tool for high-throughput phenotyping. Previous studies have shown that a significant number of anatomical, physical, chemical and mechanical wood properties can be estimated through NIRS, both for angiosperm and gymnosperm species. However, the ability of this technique to predict functional traits related to drought resistance has been poorly explored, especially in angiosperm species. This is particularly relevant since determining xylem hydraulic properties by conventional techniques is complex and time-consuming, clearly limiting its use in studies and applications that demand large amounts of samples. In this study, we measured several wood anatomical and hydraulic traits and collected NIR spectra in branches of two Eucalyptus L'Hér species. We developed NIRS calibration models and discussed their ability to accurately predict the studied traits. The models generated allowed us to adequately calibrate the reference traits, with high R2 (≥0.75) for traits such as P12, P88, the slope of the vulnerability curves to xylem embolism or the fiber wall fraction, and with lower R2 (0.39-0.52) for P50, maximum hydraulic conductivity or frequency of ray parenchyma. We found that certain wavenumbers improve models' calibration, with those in the range of 4000-5500 cm-1 predicting the highest number of both anatomical and functional traits. We concluded that the use of NIRS allows calibrating models with potential predictive value not only for wood structural and chemical variables but also for anatomical and functional traits related to drought resistance in wood types with complex structure as eucalypts. These results are promising in light of the required knowledge about species and genotypes adaptability to global climatic change.
Why this research Matters
Phenotypic plasticity is a key mechanism for sedentary long‐living species to adjust to changing environment. Here, we use mature Larix decidua tree‐ring variables collected ...along an elevational transect in the French Alps to characterize the range of individual plastic responses to temperature. Stem cores from 821 mature Larix decidua trees have been collected from four plots distributed along a 1,000‐m elevational gradient in a natural forest to build up individual linear reaction norms of tree‐ring microdensity traits to temperature. The sign, magnitude and spread of variations of the slopes of the individual reaction norms were used to characterize variation of phenotypic plasticity among plots and traits. Results showed a large range of phenotypic plasticity (with positive and negative slopes) at each elevational plot and for each tree‐ring variable. Overall, phenotypic plasticity tends to be larger but positive at higher elevation, negative at the warmer lower sites, and more variable in the center of the elevation distribution. Individual inter‐ring reaction norm is a valuable tool to retrospectively characterize phenotypic plasticity of mature forest trees. This approach applied to Larix decidua tree‐ring micro‐density traits along an elevation gradient showed the existence of large inter‐individual variations that could support local adaptation to a fast‐changing climate.
Plot of the individual reactions norms, grouped by ring variable and elevation. Thick lines indicates the average slope for each elevation. All individual slopes are significantly different from zero. Only the average slopes of RW and LWD at 2000 and 2,300 m a.s.l. and of RD at 2,000 m a.s.l. are significantly different from zero.
In a global warming scenario, drought and heat waves like the one that occurred in 2003 in Europe are expected to become more intense and frequent. This extreme climate event strongly affected the ...hydraulic balance in many forest tree species including Douglas-fir, with symptoms ranging from partial crown necrosis to death. We studied a French Douglas-fir provenance trial, strongly affected by the 2003 drought and heat wave. Using wood X-ray microdensity profiles as a record of cambium response to environmental variations, we compared mean stem density and growth between dead and alive neighbouring trees and several microdensity characters measured over 17 growth rings previous to 2003. Special attention has been given to the sampling layout in order to minimize the micro-environmental effects. At tree level, surviving trees have a significantly higher mean stem density. At tree ring level, they have a significantly higher mean ring density, maximum ring density, latewood density and, to a lesser extent, latewood proportion. No significant difference was found for diameter growth. These results could have direct implications in the way to study and predict possible acclimation and adaptation of forest trees to climate change process. Wood could be used for the selection of genotypes with a desirable plasticity and resistance to drought induced-cavitation.
The genetic control of tree ring growth in Douglas-fir in response to the drought and heat-wave that occurred in 2003 in Europe was studied with microdensity profiles in three clonal experiments ...located in three different French regions. The drought and heat-wave significantly affected Douglas-fir wood formation. The Chassenoix site (Northeast of Massif-Central) was more severely affected that the other two: the 2003 year-ring was narrower and less dense than in the other sites and than the previous (2002) and following (2004) year-rings in the same site: ring growth stopped earlier and latewood did not develop completely. The year-rings 2004 and 2002 were very similar in this site. There was a significant genetic control for all ring parameters in the three sites and during the three years. The heritability was highly variable between years and among sites, without any clear pattern in this variability, except in Chassenoix where it was slightly lower in the 2003 year-ring. Variables measuring the response of trees to the 2003 event, i.e., the difference in ring width between 2002 and 2003, or between 2003 and 2004, showed a very variable degree of genetic control, from very low to relatively high. Douglas-fir seemed plastic enough to acclimate to the drought and heat-wave and then to recover during 2004. Furthermore the level of heritability estimated demonstrates that Douglas-fir has an adaptive potential that could be useful for multi-generation long-term response.
Microdensity profiles of Douglas-fir's clones and weather data were used to study phenotypic plasticity (dendroplasticity). Within-ring microdensity was interpreted as the variation of tree response ...to drought constraints during selected growing seasons. An original norm of reaction was obtained by pairing evident points of abrupt changes in tree-ring microdensity profiles and in weather indices. The coefficients of the non-linear models adjusted to the reaction norms were analysed as dendroplasticity variables. Dendroplasticity variables were significantly different between geographical locations, years and clones. Heritability of the dendroplasticity variables ranged from low to high and was similar to heritability values of microdensity variables such as mean ring density (MRD). Coefficients of genetic variation of dendroplasticity variables were intermediate between those of wood density and growth variables. Dendroplasticity variables were phenotypically and genetically related to ring microdensity variables, more strongly to latewood variables. Dendroplasticity provides retrospective, synthetic and easy-to-interpret information about tree response to the variation of the balance between water availability and water demand during the growing season. The proposed model of dendroplasticity is described by a number of parameters that are linked to a biological meaning. Our results suggest that there is a potential for adaptation to drought in Douglas-fir, with two mechanisms involved: at individual level, short-term plastic response during the growing season and, at population level, long-term, between-generation, evolution process.
Tree-ring datasets are used in a variety of circumstances, including archeology, climatology, forest ecology, and wood technology. These data are based on microdensity profiles and consist of a set ...of tree-ring descriptors, such as ring width or early/latewood density, measured for a set of individual trees. Because successive rings correspond to successive years, the resulting dataset is a ring variables × trees × time datacube. Multivariate statistical analyses, such as principal component analysis, have been widely used for extracting worthwhile information from ring datasets, but they typically address two-way matrices, such as ring variables × trees or ring variables × time. Here, we explore the potential of the partial triadic analysis (PTA), a multivariate method dedicated to the analysis of three-way datasets, to apprehend the space-time structure of tree-ring datasets. We analyzed a set of 11 tree-ring descriptors measured in 149 georeferenced individuals of European larch (Larix decidua Miller) during the period of 1967-2007. The processing of densitometry profiles led to a set of ring descriptors for each tree and for each year from 1967-2007. The resulting three-way data table was subjected to two distinct analyses in order to explore i) the temporal evolution of spatial structures and ii) the spatial structure of temporal dynamics. We report the presence of a spatial structure common to the different years, highlighting the inter-individual variability of the ring descriptors at the stand scale. We found a temporal trajectory common to the trees that could be separated into a high and low frequency signal, corresponding to inter-annual variations possibly related to defoliation events and a long-term trend possibly related to climate change. We conclude that PTA is a powerful tool to unravel and hierarchize the different sources of variation within tree-ring datasets.
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