•Coastal Douglas-fir provenances are most productive at the northern range limits.•Drought tolerances generally increases towards south.•Productive AND drought tolerant provenances originate from the ...Olympic Peninsula.•Latewood/earlywood ratio will be strongly reduced in the expected future climate.•Winter photosynthesis might compensate for summer limitations in some provenances.
Forests of the future should be resistant to exacerbating climatic conditions, especially to increasing drought, but at the same time provide a sufficient amount and quality of timber. In this context coastal Douglas-fir (Pseudotsuga menziesii (Mirb.)) is a promising species since it remains productive even under chronic drought. By choosing suitable provenances within the range of Douglas-fir (P. menziesii (Mirb.)) for a given site we can further optimise tree fitness under dry conditions or even increase timber yield.
Eighteen coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) var. menziesii) provenances were tested for seedling survival, yield, wood quality, and drought tolerance by taking advantage of a Dutch provenance trial, established in 1971 within the framework of the 1966/1967 IUFRO seed collection program. The site of the Dutch trial is representative for many sites in Central Europe and is characterised by a moderate precipitation and temperature regime. Measurements on height and diameter growth were combined with a dendrochronological study on growth response to drought years.
We found a clear latitudinal trend indicating that Douglas-fir provenances from the northern part of the species-distribution range are generally more productive than provenances from the south. In contrast, drought tolerance increased towards the south. This suggests that it is impossible to identify provenances combining maximum productivity with lowest susceptibility towards drought. However, based on the results from the trial we can give recommendations on suitable provenances that are expected to perform best under future conditions in Central Europe. On sites where severe drought events are unlikely to occur in future, fast growing provenances from the north, like Nimkish, should be planted. These provenances respond plastically to drought years, but the strong reduction of tree growth in the drought year itself indicates that these provenances will be harmed by an increasing frequency of drought events. However, on sites where water availability is likely to decrease, provenances from the Olympic Peninsula like Forks and Matlock are very promising since they showed still relatively high yield in combination with a high potential to cope with drought.
If summer drought increases in frequency and severity as expected, the latewood/earlywood ratio will be drastically reduced with negative consequences for wood quality and cavitation resistance. However, some provenances, like Marblemount or Matlock, might compensate for the negative effect of summer drought on latewood/earlywood ratio by the contribution of photosynthesis in winter to whole-year carbon stock.
•Dead wood varies greatly in quality as dependent on tree species and decay stage.•Differences in dead wood quality contribute greatly to forest invertebrate diversity.•Total invertebrate richness ...depends on specific tree species-decay stage combinations.•These findings can be used to optimize invertebrate diversity in managed forests.
Dead wood availability and the variability in dead wood quality, i.e. tree species and decay stages, are often low in managed forests, which negatively affects biodiversity of invertebrate species. Leaving more (coarse) dead wood can increase invertebrate richness, but it remains unclear how many and which combinations of tree taxa and decay stages are required to optimize niche heterogeneity in managed forests. We investigated the diversity of the main arthropod groups associated with dead wood, i.e. millipedes, centipedes, isopods and beetles, through the first four years of decomposition of logs of twenty common temperate tree species placed in the “common garden” experiment LOGLIFE. We hypothesized that (1) invertebrate richness for combinations of a given number of tree species would be promoted by mixing both tree species and decay period and that (2) invertebrate richness increases up to a saturation point with more tree species at different decay stages added. We also hypothesized that (3) an increase in phylogenetic distance among the tree species in combinations would promote their overall invertebrate diversity. We found that the better combinations, in terms of invertebrate richness, after one and two years of decay, but not after four years, consisted of a mix of gymnosperms and angiosperms, indicating that variation in tree species is especially important during the initial decomposition period. The best combinations in terms of invertebrate richness consisted of at least one tree species from each decay period, indicating that also variation in the decay stage of the tree is important to promote invertebrate diversity. We observed that at least four wood types were required to approach the 95% saturation point for species richness. The third hypothesis, that dissimilarity in phylogenetic position could be a predictive tool for increasing invertebrate richness in combinations of tree species, was not supported by our results. Thus, in order to maintain diversity of dead wood invertebrates in forests we recommend not only to provide richness in tree species, but also to plant particular combinations of trees (preferably angiosperm-gymnosperm combinations) that differ in the invertebrate communities they typically host and to temporally spread the logging of trees. This way the logging residues cover different resources and habitats at each moment in time, which is likely to result in a large diversity of dead wood invertebrates.
Dead wood provides a huge terrestrial carbon stock and a habitat to wide-ranging organisms during its decay. Our brief review highlights that, in order to understand environmental change impacts on ...these functions, we need to quantify the contributions of different interacting biotic and abiotic drivers to wood decomposition. LOGLIFE is a new long-term ‘common-garden’ experiment to disentangle the effects of species’ wood traits and site-related environmental drivers on wood decomposition dynamics and its associated diversity of microbial and invertebrate communities. This experiment is firmly rooted in pioneering experiments under the directorship of Terry Callaghan at Abisko Research Station, Sweden. LOGLIFE features two contrasting forest sites in the Netherlands, each hosting a similar set of coarse logs and branches of 10 tree species. LOGLIFE welcomes other researchers to test further questions concerning coarse wood decay that will also help to optimise forest management in view of carbon sequestration and biodiversity conservation.
•B. papyrifera forms annual growth rings.•The average radial growth rate of B. papyrifera is 1.15mm.•Individual trees of B. papyrifera show persistent growth difference.•Age and diameter of B. ...papyrifera trees are significantly related.•The current B. papyrifera populations lack successful recruitment since 1955.
Boswellia papyrifera (Burseraceae) trees grow in dry woodlands south of the Sahara and produce frankincense, the economically important olio-gum resin used for cultural and religious ceremonies throughout the world and as raw material in several industries. Across its distribution area, this species is threatened by farmland expansion, fire, improper tapping and overgrazing. Most of its populations lack saplings and small-sized trees (e.g. <10cm). It is unknown whether the older, adult trees represent a single or several cohorts, representing single or plural regeneration and survival waves. To understand such long-term population dynamics, it is imperative to evaluate the age structure of the current populations. We used tree ring analysis to determine the age-diameter relationship. This study, (1) determines radial growth dynamics and age-diameter relationship of B. papyrifera, including verification of annual growth-ring formation, and (2) constructs the population age structure and discusses consequences thereof for population maintenance and long-term frankincense production. We could prove that B. papyrifera forms annual growth rings. The average radial annual growth rate of B. papyrifera is 1.15mm (s.d.=0.22) and varies significantly among the sampled trees. Age and diameter of B. papyrifera trees are significantly correlated. From the population-age structure, it becomes obvious that the current B. papyrifera populations lack successful recruitment since 1955, which we attribute to intensive grazing and fire associated with the escalating increase of human settlement in the area. Lack of recruitment leads to rapidly declining populations resulting in strongly reduced frankincense production. Management aimed at seedling survival and sustainable use of relic trees is urgent.
The increase in length and severity of drought events predicted for South-Eastern Europe are expected to engender important changes to remaining native forests. To make informed management decisions ...promoting their conservation, it is important to better understand their responses to climate and environmental disturbances.
In this study, we analyze growth responses over a network of 15 sites of Serbian spruce (Picea omorika), an endemic relict conifer species of the Balkan region — with a natural range restricted to the canyon of the Drina river at the border between Serbia and Bosnia Herzegovina — that has already shown signs of decline and dieback likely induced by increasing temperature and drought.
Tree-ring analyses spanning the common period from 1974 to 2016 have shown a strong growth reduction and highlighted an increasing negative growth response to summer drought over the last 30–40 years. The strength of the response differed among individuals and sites, where younger trees and those growing at lower altitude suffered more from drought.
Management practices oriented at reducing drought impact, such as thinning to reduce competition for water resources and enhance survival of seedlings, together with assisted natural regeneration and migration to more suitable habitats, are recommended for the conservation of this relict species. The measures are even more necessary considering that this species is more vulnerable than others due to its weak capacity to naturally regenerate and compete.
Forensic methods to independently trace timber origin are essential to combat illegal timber trade. Tracing product origin by analysing their multi-element composition has been successfully applied ...in several commodities, but its potential for timber is not yet known. To evaluate this potential the drivers of wood multi-elemental composition need to be studied. Here we report on the first study relating wood multi-elemental composition of forest trees to soil chemical and physical properties.
We studied the reactive soil element pools and the multi-elemental composition in sapwood and heartwood for 37 Azobé (Lophira alata) trees at two forest sites in Cameroon. A total of 46 elements were measured using ICP-MS. We also measured three potential drivers of soil and wood elemental composition: clay content, soil organic matter and pH. We tested associations between soil and wood using multiple regressions and multivariate analyses (Mantel test, db-RDA). Finally, we performed a Random Forest analysis of heartwood elemental composition to check site assignment accuracy.
We found elemental compositions of soil, sapwood and heartwood to be significantly associated. Soil clay content and organic matter positively influenced individual element concentrations (for 13 and 9 elements out of 46 respectively) as well as the multi-elemental composition in wood. However, associations between wood and topsoil elemental concentrations were only significant for one element. We found close associations between element concentrations and composition in sapwood and heartwood. Lastly, the Random Forest assignment success was 97.3 %.
Our findings indicate that wood elemental composition is associated with that in the topsoil and its variation is related to soil clay and organic matter content. These associations suggests that the multi-elemental composition of wood can yield chemical fingerprints obtained from sites that differ in soil properties. This finding in addition to the high assignment accuracy shows potential of multi-element analysis for tracing wood origin.
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•Multi-elemental composition can provide a chemical fingerprint for timber tracing.•Insight into what drives elemental variation is needed to apply the method in wood.•Our results show variation in soil clay content and organic matter are important.•Heartwood formation further affects individual elements but not composition.•Elemental tracing accuracy was 97.3 % for our study species at two sites in Cameroon.
Abstract
Reactivation of axial water flow in ring-porous species is a complex process related to stem water content and developmental stage of both earlywood-vessel and leaf formation. Yet empirical ...evidence with non-destructive methods on the dynamics of water flow resumption in relation to these mechanisms is lacking. Here we combined in vivo magnetic resonance imaging and wood-anatomical observations to monitor the dynamic changes in stem water content and flow during spring reactivation in 4-year-old pedunculate oaks (Quercus robur L.) saplings. We found that previous year latewood vessels and current year developing earlywood vessels form a functional unit for water flow during growth resumption. During spring reactivation, water flow shifted from latewood towards the new earlywood, paralleling the formation of earlywood vessels and leaves. At leaves' full expansion, volumetric water content of previous rings drastically decreased due to the near-absence of water in fibre tissue. We conclude (i) that in ring-porous oak, latewood vessels play an important hydraulic role for bridging the transition between old and new water-conducting vessels and (ii) that fibre and parenchyma provides a place for water storage.
Leaf specific conductivity (LSC; the ratio of stem conductivity (KP) to leaf area (AL)), a measure of the hydraulic capacity of the stem to supply leaves with water, varies with soil water content. ...Empirical evidence for LSC responses to drought is ambiguous, because previously published results were subject to many confounding factors. We tested how LSC of similar-sized trees of the same population, under similar climatic conditions, responds to persistently wet or dry soil. Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) trees were compared between a dry site and a wet site in the Valais, an inner alpine valley in Switzerland. Soil water strongly influenced AL and KP and the plant components affecting KP, such as conduit radius, conduit density and functional sapwood area. Trees at the dry site had lower LSC than trees with the same stem diameter at the wet site. Low LSC in trees at the dry site was associated with a smaller functional sapwood area and narrower conduits, resulting in a stronger reduction in KP than in AL. These observations support the hypothesis that trees maintain a homeostatic water pressure gradient. An alternative hypothesis is that relatively high investments in leaves compared with sapwood contribute to carbon gain over an entire season by enabling rapid whole-plant photosynthesis during periods of high water availability (e.g., in spring, after rain events and during morning hours when leaf-to-air vapor pressure deficit is small). Dynamic data and a hydraulic plant growth model are needed to test how investments in leaves versus sapwood and roots contribute to transpiration and to maximizing carbon gain throughout entire growth seasons.
•Local variation in wood stable isotope ratios was high in Central Africa.•This resulted in low accuracy when assigning sites of origin based on stable isotopes.•High local variation also resulted in ...high uncertainty in isoscapes.•Isotopic variation was sufficiently high for assignment at country level.•Species-specific reference datasets are needed because of interspecific differences.
Origin verification of timber is essential to expose origin fraud and reduce illegal timber trade. A promising forensic method for origin verification is based on stable isotope ratios in wood, but large-scale studies that test local and regional variation to apply the method at a sub-country scale are lacking.
We investigated the isotopic variation in wood in Central Africa for two economically important timbers (Azobé and Tali). We measured wood δ18O, δ2H, δ13C and δ34S at 17 locations in the main timber exporting countries (Cameroon, Republic of the Congo, Gabon). This is the first study to quantify both local and regional variation as well as species differences. We applied a novel statistical technique, Quantile Regression Forests, to develop spatial predictions of isotopic composition based on gridded covariables (isoscapes). This is a powerful method to develop isoscapes based on non-normally distributed and correlating covariables.
We found limited potential for origin assignment with stable isotope ratios in Central Africa, because the local variability of values for all four studied isotopes was generally higher than regional variation. This led to low site classification success (Azobé: 32.1%, Tali: 20.5%) and large uncertainty in the isoscapes. The limited origin signal can be attributed to low variation in the driving environmental factors in the region. The isotope ratios did differ between the three countries, country-level assignment was good (Azobé: 79.4%, Tali: 61.7%) and considerably higher than site-level values. Lastly, we found a significant species and site effect, stressing species-specific reference datasets might be needed for future isotope tracing studies.
These results show that the four isotopes applied here have limited potential for sub-country origin assignment of timber in this region (Cameroon, Republic of the Congo, Gabon). Nevertheless, the variation at large spatial scales resulted in promising accuracy of country-level assignment. These findings contribute to our understanding of forensic timber tracing methods and can help to identify the most appropriate method for a tracing question at hand.
Quantitative wood anatomy (QWA) is a dynamic research approach of increasing interest that can provide answers to a wide range of research questions across different disciplines. However, the lack of ...common protocols and knowledge gaps hinder the realisation of the full potential of QWA. Therefore, we established the new community-based network Q-NET to provide an open interdisciplinary platform for exchange and research around QWA. Q-NET (https://qwa-net.com) combines an online knowledge and exchange base with virtual workshops. The first two workshops each attracted more than 125 participants from around the world, demonstrating the community's interest in QWA and this virtual way of networking and collaborating. Indeed, virtual networks such as Q-NET could increase the inclusiveness, efficiency and sustainability of scientific collaboration while providing additional training and teaching opportunities for early career scientists, both of which complement in-person conferences and workshops.
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