Key Tree Research Articles

Long-term human influence on the demography and genetic diversity of the hyperdominant Bertholletia excelsa in the Amazon Basin.

The Amazon rainforest is characterized by a limited number of hyperdominant trees that play an oversized role in its ecosystems, nutrient cycle, and rainfall production. Some of these, such as the Brazil nut, appear to have been intensively exploited and dispersed by Indigenous populations since their earliest arrival in this part of South America around 13,000 years ago. However, the genetic diversity-and geographic structure-of these species remains poorly understood, as does their exact relationship with past human land use. We use a new genome assembly for Brazil nut to analyze 270 individuals sampled at areas with varying intensities of archaeological evidence. We demonstrate that overall low genetic diversity, with a notable decrease since the Late Pleistocene, is accompanied by significant geographic structure, where evidence for improved gene flow and regeneration by long-term traditional human management is linked to increased genetic diversity. We argue that historical perspectives on the genetic diversity of key tree species, such as the Brazil nut, can support the development of more active management strategies today.

Impacts of African elephants and other environmental drivers on trees nested in by critically endangered white‐backed vultures

The decline of white‐backed vultures Gyps africanus (hereafter termed vultures) across Africa highlights the need to understand their habitat and nesting requirements, especially in protected areas where African elephants Loxodonta africana can impact the trees in which vultures build their nests. Our study aimed to assess the impact that elephants have on trees containing vulture nests in the Associated Private Nature Reserves (APNR) of South Africa's savanna system through three separate but interlinked assessments. We first assessed the tree species used by vultures for nesting and compared their size and elephant impact scores between riparian and woodland habitats. We assessed how elephant presence or absence affects the size of Senegalia nigrescens, a key tree species, and compared vulture nests in an adjacent elephant‐free area. Lastly, we modeled environmental factors influencing vulture nest and tree persistence using data from 2008–2020. Vultures utilised 10 tree species, with riparian trees supporting nests being significantly taller, with larger DBHs, and experienced lower elephant impact compared to woodland trees, which were more heavily impacted by elephants. Less robust species like S. nigrescens were more vulnerable to elephant damage, primarily bark‐stripping, and less likely to host vulture nests. Our results show that vultures prefer the largest, least impacted trees for nesting, favouring those with greater stability and longevity. We suggest that although elephants influence the overall height range of trees to vultures, strong gusts of wind have a strong negative contribution on vulture nest persistence and that only a relatively small number of trees died during the 12‐year study in comparison to fallen nests. We recommend further research into elephant impact thresholds on trees and vulture nest selection. Monitoring treefall and regeneration rates will help predict when vultures may face a shortage of suitable nesting trees.

Willow above, changes below: Seedless tree invader impacts riparian seed bank in the Patagonian ecotone

AbstractAimThe soil seed bank, an ecosystem component with a crucial role in the natural regeneration of plant communities, can be impacted by invasive non‐native plants. The impact of non‐native plants can be direct with the production of their own seeds or indirect without producing seeds, which has been less investigated. We determined the impact of an invasive seedless tree, non‐native willow (Salix × rubens), on the soil seed bank in a riparian ecosystem.LocationNorthwestern Patagonia, Argentina.MethodsIn autumn and spring 2022, we collected soil samples and estimated understorey cover, respectively, in plant communities invaded by willow and in uninvaded communities with a canopy dominated by native species. Over a year, we recorded the seedling emergence of soil samples to estimate the abundance, richness, and composition of the seed bank. We also compared the composition between the seed bank and understorey.ResultsTotal seed abundance and native woody species seed abundance decreased twofold and fourfold, respectively, in invaded plant communities in comparison with uninvaded communities. The most affected woody species was Ochetophila trinervis, a key tree species, because of its dominance in the canopy and understorey, and its role in various ecological processes (nitrogen cycling). In addition, willow invasion moderately changed the seed bank species composition producing species turnover. For both the seed bank and the understorey, species composition was more similar between invaded and uninvaded communities than between the seed bank and understorey. Willow invasion had more impact on understorey composition than on the seed bank.ConclusionsAlthough willows do not produce seeds regionally, their invasion negatively impacts the soil seed bank by replacing native woody canopy species that supply seeds to the seed bank. These impacts could result in notable changes in the structure of the plant communities and the ecosystem dynamics of riparian areas.

A traceable and revocable decentralized attribute-based encryption scheme with fully hidden access policy for cloud-based smart healthcare

Smart healthcare is an emerging technology for enabling interaction between patients and medical personnel, medical institutions, and medical devices utilizing advanced Internet of Things (IoT) technologies. It has attracted significant attention from researchers because of the convenience of storing and sharing electronic medical records (EMRs) in the cloud. Given that a patient’s EMR contains sensitive individual information, it must be encrypted before uploading it to the cloud. As a solution for data confidentiality and fine-grained access control, the Ciphertext Policy Attribute-Based Encryption (CP-ABE) technique is proposed, which helps manipulate private personal data without explicit authorization. However, most CP-ABE schemes use a centralized mechanism which may lead to performance bottlenecks and single-point-of-failure issues. They will also be at risk of key abuse and privacy breaches in smart healthcare applications. To this end, in this paper, we investigate a traceable and revocable decentralized attribute-based encryption scheme with a fully hidden access policy (TR-HP-DABE). Firstly, to overcome the issues of user privacy leakage and single-point-of-failure, a fully hidden access policy is established for multiple attribute authorities. Secondly, to prevent key abuse, the proposed TR-HP-DABE can achieve the tracking and revocation of malicious users by using Key Encryption Key (KEK) trees and updating the partial ciphertext. Furthermore, the online/offline encryption and verifiable outsourced decryption are applied to improve its efficiency in practical smart healthcare. According to our analysis, the security and traceability of TR-HP-DABE can be proved. Finally, the performance evaluation of TR-HP-DABE is more effective than some existing typical ones.

Site-based climate-smart tree species selection for forestation under climate change

Global climate change threatens ecosystem functions and resilience, prompting large-scale planting initiatives to mitigate its impacts. To ensure new plantations are adaptive to future climates, it is crucial to consider climate mismatches resulting from climate change when selecting tree species. However, current research is all species-based, which is not effective for species selection across species at specific plantation sites. Our research developed a novel site-based approach that can identify optimal tree species for specific planting sites under projected future climates. We evaluated the feasibility and effectiveness of this method across 10 representative sites in diverse climatic zones in China based on climate niche projections for 100 key tree species. Our findings demonstrated the necessity and effectiveness of this approach, which can select a suit of suitable tree species tailored for any potential planting site across China under different climate change scenarios. For instance, at Tibet Dongjiu Forest farm, Aibes densa and Quercus pannosa currently showed high suitability scores above 0.8 (on a scale of 0–1). However, by the 2080s, Aibes densa's suitability was projected to drop to 0.25, while Quercus pannosa was expected to maintain its suitability. Conversely, Quercus aquifolioides currently had a low suitability of 0.08, but it was projected to increase to 0.74 by the 2080s. These findings demonstrate the importance of using this approach to avoid selecting the wrong species or overlooking potentially suitable species. In addition, our simulation analysis suggests that a dataset of 40–50 species is necessary to ensure that most planting sites can identify 2–3 suitable species. This advancement significantly enhances the precision and effectiveness of tree species selection strategies for local practitioners, offering vital insights for forestry, conservation, and ecological restoration projects. These results highlight the tremendous potential and practical applicability of our site-based approach in enhancing forestry adaptation and ecological functions in response to global climate change.

The linkage between functional traits and drone-derived phenology of 74 Northern Hemisphere tree species

Tree phenology is a major component of the global carbon and water cycle, serving as a fingerprint of climate change, and exhibiting significant variability both within and between species. In the emerging field of drone monitoring, it remains unclear whether this phenological variability can be effectively captured across numerous tree species. Additionally, the drivers behind interspecific variations in the phenology of deciduous trees are poorly understood, although they may be linked to plant functional traits. In this study, we derived the start of season (SOS), end of season (EOS), and length of season (LOS) for 3099 individuals from 74 deciduous tree species of the Northern Hemisphere at a unique study site in southeast Germany using drone imagery. We validated these phenological metrics with in-situ data and analyzed the interspecific variability in terms of plant functional traits. The drone-derived SOS and EOS showed high agreement with ground observations of leaf unfolding (R2 = 0.49) and leaf discoloration (R2 = 0.79), indicating that this methodology robustly captures phenology at the individual level with low temporal and human effort. Both intra- and interspecific phenological variability were high in spring and autumn, leading to differences in the LOS of up to two months under almost identical environmental conditions. Functional traits such as seed dry mass, chromosome number, and continent of origin played significant roles in explaining interspecific phenological differences in SOS, EOS, and LOS, respectively. In total, 55 %, 39 %, and 45 % of interspecific variation in SOS, EOS, and LOS could be explained by the Boosted Regression Tree (BRT) models based on functional traits. Our findings encourage new research avenues in tree phenology and advance our understanding of the growth strategies of key tree species in the Northern Hemisphere.

What we know about Turkey oak (Quercus cerris L.) — from evolutionary history to species ecology

Abstract Turkey oak (Quercus cerris L.) is a deciduous tree species of the genus Quercus section Cerris (Fagaceae), widely distributed in Europe and Asia Minor. Throughout its vast distribution range, the species carries high phenotypic and genetic variability. Due to its high drought tolerance, Turkey oak may have great potential to be a key tree species in Central and Western Europe under climate change conditions. However, more detailed information on its phylogeny, phylogeography, phenotypic, and genetic variability is still needed for a more careful and reliable assessment of the species’ adaptation potential. To this end, based on 41 reviewed articles, we collected detailed information to support the evaluation of Turkey oak’s adaptation potential under climate change. In the reviewed articles, we observed a significantly lower number of genetic studies of the members of the section Cerris (especially the Euro-Mediterranean species) relative to the subgenus Quercus. We also identified research gaps with respect to the functional and population genetics of the species that should be addressed in the future. Nevertheless, the different evolutionary background and adaptation strategies of Turkey oak as compared to Central European white oaks, as well as its high phenotypic and genetic variability, may indeed represent a great potential for this species to support the climate adaptation of forestry in Central and Western Europe.

Quaternary Tree Group Diffie- Hellman Based Group Key Management Protocol for Dynamic Peer Groups

Diffie-Hellman (DH) protocol for 2-party has made the key exchange to be simple yet powerful. It is widely used in many communication-oriented protocols for establishing the keys in public communication channels. With millions of internet users connected globally and using various group oriented applications, communication among them has to be in a secured manner. Due to its simplicity, DH has been further extended to group setting and number of protocols are developed. Establishing Group Key and regenerating it during membership changes is a challenging task in communication among large groups. This paper proposes a quaternary tree method that uses the key tree concept and Group Diffie Hellman protocol, GDH.3 to establish the common key. GDH.3, an extension of DH for n parties is best suited for large dynamic groups. Quaternary tree reduces the height almost by half as against binary trees, making the rekeying much easier. As the group size increases, GDH.3 outperforms other existing group protocols based on DH, since it requires much lesser number of exponentiations.

Use of a Consumer-Grade UAV Laser Scanner to Identify Trees and Estimate Key Tree Attributes across a Point Density Range

The management of plantation forests using precision forestry requires advanced inventory methods. Unmanned aerial vehicle laser scanning (ULS) offers a cost-effective approach to accurately estimate forest structural attributes at both plot and individual tree levels. We examined the utility of ULS data collected from a radiata pine stand for tree detection and prediction of diameter at breast height (DBH) and stem volume, using data thinned to 13-point densities (ranging from 10–12,200 points/m2). These datasets were created using a DTM with the highest pulse density and DTMs that used the native decimated point clouds. Models of DBH were constructed using partial least squares (PLS) and random forest (RF) from seven classes of metrics that characterized the horizontal and vertical structure of the canopy. Individual tree segmentation was consistently accurate across the 13-point densities and was insensitive to DTM type (F1 scores > 0.96). Predictions of DBH using PLS models were consistently more accurate than RF models and accuracy was insensitive to the DTM type. Using data from the native DTMs, DBH estimation using PLS had the lowest RMSE of 1.624 cm (R2 of 0.756) at a point density of 12,200 points/m2. Stem volume predictions made using PLS predictions of DBH and height from the ULS had the lowest RMSE of 0.0418 m3 (R2 of 0.792) at 12,200 points/m2. The RMSE values for DBH and volume remained relatively stable from 12,200 to between 750 and 400 points/m2, with reductions in accuracy occurring as point density declined below this threshold. Overall, these findings have significant implications, particularly for the precise estimation of DBH and stem volume at the individual tree level. They demonstrate the potential of cost-effective ULS sensors for rapid and frequent plantation forest assessment, thereby enhancing the application of light detection and ranging (LiDAR) technology in plantation forest management.

Vegetation trends and dynamics in Shada Mountain, Saudi Arabia, (1984–2023): insights from Google Earth Engine and R analysis

This research analyses the long-term vegetation trends in Shada Mountain across six elevation zones, utilizing Landsat 5, 7, 8, and 9 imageries processed via Google Earth Engine and R. The study managed differences in images resolution through meticulous calibration and image processing techniques. The study is structured around two objectives: examining the relationship between vegetation and its proximity to streams and land surface temperature and analyzing trends in the Normalized Difference Vegetation Index (NDVI). Regression analysis revealed a negative correlation between vegetation and proximity to streams in lower zones (1–3), with no significant effect in higher zones (4–6). NDVI trend analysis indicated an overall increase in vegetation across most zones, with the exception of zone 5, which displayed a negative trend (slope −0.0025). The findings reveal that the decline is particularly pronounced among key tree species such as Ficus cordata subsp. salicifolia and Acacia asak, suggesting potential impacts from climate change and land use alterations. These zone-specific insights deepen our understanding of the dynamic ecological processes in semi-arid environments and guide targeted environmental management and conservation efforts.

Growth of Nordic container forest tree seedlings in some peatless and peat-reduced growing media

Carbon emissions and environmental concerns have led to the aspiration to reduce peat extraction and its use as a growing medium (GM). In Nordic Forest tree seedling production, Sphagnum peat has been almost exclusively used as a GM in seedling containers due to its good properties and availability. This study examined the feasibility of several peat-reduced and peat-free GM in container tree seedling production of the key tree species in Nordic forestry (Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L. Karst.) and silver birch (Betula pendula Roth) as well as Russian larch (Larix archangelica P. Lawson & C. Lawson ex Trautv.) and common alder (Alnus glutinosa (L.) Gaertn.). Pure or mixed GM, consisting of low-humified Sphagnum peat (pure as a control), harvested Sphagnum moss, wood fiber, cow manure digestate from a biogas plant, and a common reed compost were tested. Seedlings were grown in controlled conditions in greenhouse experiments and also in larger-scale commercial tree nurseries. Peat-reduced media containing peat of at least 50 vol% provided growth that is similar to pure Sphagnum peat for the tested species and container types. All the studied alternative media can yield marketable seedlings, although commonly of reduced size and requiring special adjustments in growing management. The studied media have a potential to reduce or replace peat in seedling production, but adjustments of their physical and chemical properties, as well as of seedling fertigation and management procedures, are required. The economic feasibility and environmental sustainability of these GM, as well as the outplanting success of seedlings grown in these media, remain to be studied.

Climate-affected multi-decadal variations of biogenic volatile organic compounds in Pinus tabuliformis growth rings

Long-term dynamics of biogenic volatile organic compounds (BVOCs) in trees are rarely reported, despite environmental factors (such as climate change) influencing their growth and the subsequent chemical accumulation. For this, tree growth rings provide a promising biological proxy for the long-time variation and correlation with environmental changes. Therefore, tree rings from Pinus tabuliformis (two stem disks and 40 tree cores) were collected in the Taihang Mountain Macaque National Nature Reserve of China. These samples were divided into seven 5-year resolutions over the 34-year period 1985 to 2018. This enabled analysis of multi-decadal variations of compounds and their correlation with climate variability. A total of 292 BVOCs were detected; however, only 18 compounds were found together across all the 7 growth-periods. Temporal analyses showed decreasing trends for monoterpenes (0.026%/yr) and diterpenes (0.120%/yr), whereas alcohols and oxygenated monoterpenes showed increasing trends at 0.031%/yr and 0.042%/yr, respectively. Correlation analyses showed no obvious link to yearly precipitation, while seasonal temperature had a negative effect on monoterpenes and diterpenes but positive effects on alcohols and oxygenated monoterpenes (all P < 0.05). The present study showed that dendrochronology is a suitable method for re-establishing the biological effects from historical climate variability on key tree species.

Inter-provenance variability and phenotypic plasticity of wood and leaf traits related to hydraulic safety and efficiency in seven European beech (Fagus sylvatica L.) provenances differing in yield

Abstract Key message Seven European beech provenances differing largely in growth performance were grown at two common garden sites in Germany and Slovakia. The intra-specific variability of most traits was explained more by phenotypic plasticity than inter-provenance variability, and efficiency-related traits showed a higher phenotypic plasticity than safety-related traits. Context To maintain climate-resilient future forests, replicated common-garden experiments are suited for developing assisted migration strategies for key tree species. Aims We analysed the magnitude of inter-provenance variability and phenotypic plasticity for 12 functional traits of European beech (Fagus sylvatica L.) and analysed whether the climate at the place of origin left an imprint. Moreover, we asked whether growth is unrelated to xylem safety and to what extent the foliar, xylem and growth-related traits are coordinated. Methods Terminal branches were collected from 19-year-old and 22-year-old trees of seven European beech provenances planted at two common garden sites in Germany and Slovakia, respectively. Three hydraulic, three wood anatomical and four foliar traits were measured and related to two growth-related variables. Results At the two sites, the same pair of provenances showed the highest and lowest growth. Nevertheless, a high degree of phenotypic plasticity was observed, as all traits differed significantly between sites after accounting for provenance effects, with hydraulic safety-related traits showing the lowest and efficiency-related traits the highest plasticity. There was no evidence for inter-provenance variability in xylem embolism resistance (P50) or the foliar carbon isotope signature (δ13C), a proxy for intrinsic water use efficiency (iWUE), and both were unrelated to growth. P50 was positively correlated with the lumen-to-sapwood area ratio and vessel density. Conclusions Because of the lacking trade-off between embolism resistance and growth, highly productive provenances can be selected without reducing the drought tolerance of the branch xylem. However, as xylem safety is only one element of a trees’ drought response, it may be beneficial to select provenances with other more conservative drought adaptations such as smaller vessel lumen areas for increasing xylem safety and small supported total leaf areas for reduction of total transpiration.

Adaptation Strategies of Populus euphratica to Arid Environments Based on Leaf Trait Network Analysis in the Mainstream of the Tarim River

Populus euphratica, a key tree species in the ecologically fragile area of the Tarim River Basin, plays a crucial role in maintaining the ecological balance of the desert. In order to explore the response of Populus euphratica leaves to river water resources and drought climate change, the complex topological relationship between the leaf traits of Populus euphratica was comprehensively analyzed by establishing the leaf trait network of the mainstream of the Tarim River, and the central traits that play a key role in regulating the phenotype of Populus euphratica were identified. The adaptation strategies of Populus euphratica to different environments were clarified from the perspective of the overall leaf trait network. The results show that, with a decrease in river water flow, the internal coordination of the leaf traits weakened, forming a looser network structure. In the hyper-arid region, the leaf traits were more independent, the network was simpler, and it was easier for the leaf to coordinate the aggregation of specific traits. Leaf thickness and the related photosynthetic traits are the key to adaptive strategies, particularly the cuticle thickness and midvein vascular bundle area. Leaf anatomical traits are more critical than stoichiometry traits in drought resistance. Leaves tend to give priority to the relationship between structural traits. Populus euphratica leaves adjust their trait modularization through a trait substitution strategy to manage different drought conditions.

A quantitative systematic review on the scientific knowledge, uses and management of Genipa americana: a key tree crop for tropical agroecosystems

A quantitative systematic review on the scientific knowledge, uses and management of Genipa americana: a key tree crop for tropical agroecosystems

Advancing tree genomics to future proof next generation orchard production.

The challenges facing tree orchard production in the coming years will be largely driven by changes in the climate affecting the sustainability of farming practices in specific geographical regions. Identifying key traits that enable tree crops to modify their growth to varying environmental conditions and taking advantage of new crop improvement opportunities and technologies will ensure the tree crop industry remains viable and profitable into the future. In this review article we 1) outline climate and sustainability challenges relevant to horticultural tree crop industries, 2) describe key tree crop traits targeted for improvement in agroecosystem productivity and resilience to environmental change, and 3) discuss existing and emerging genomic technologies that provide opportunities for industries to future proof the next generation of orchards.

Potential of hydrogel treatment in forest regeneration: impact on growth and vitality of Central European tree species

IntroductionDrought negatively affects the growth and yield of plants. Several measures have been employed to improve the drought tolerance of plants, including the application of superabsorbent hydrogel (SAH) to soil. However, studies on the effect of SAH on trees in Central Europe, which has a temperate climate, are scarce.MethodsHere, the effects of SAH treatment on the cultivation of four key tree species in Central European forest ecosystems—European beech, sessile oak, Scots pine, and Norway spruce—were evaluated. Field and greenhouse experiments were conducted; the greenhouse conditions served as the reference for the absence of water stress.Results and DiscussionSAH treatment reduced seedling mortality by 1%–9% in the field experiment. The morphological parameters of the control and SAH-treated seedlings did not significantly differ. Among the tree species, oak seedlings exhibited a positive response to SAH treatment. Spruce, pine, and beech did not respond to SAH treatment; the proline content of SAH-treated conifer leaves was three times higher than that of oak leaves but still very low, revealing no drought stress. The results highlight the significance of employing an individual approach in the application of SAH in forestry, rather than relying on generic measures.

The breeding systems and floral visitors of two widespread African dry forest species of ethnobotanical significance.

Forest products derived from woody trees, such as fruits, seeds, honey, wood and others, are important resources for supporting rural livelihoods. However, little is known about the breeding systems or floral visitors of trees that provide these resources, often due to the difficulty of accessing tree canopies. This study addresses key knowledge gaps from a data poor region, providing information on the breeding systems and contribution of biotic pollination to two trees abundant in south-central Africa, that provide forest product supports for rural livelihoods: Julbernardia paniculata (Benth.) Troupin and Syzygium guineense (Willd.) subsp. barotsense F. White (Fabaceae and Myrtaceae respectively). The breeding systems of these species were assessed by conducting controlled pollination experiments, and then measuring the effects on reproductive success to determine the degree of self-compatibility and pollen limitation. Floral visitors and their behaviour were observed to provide preliminary information on possible pollinator groups. S. guineense appeared to be self-compatible, while J. paniculata showed signs of both self-incompatibility and pollen limitation. Floral visitors of both species were dominated by bees, with native honeybees (Apis mellifera) providing the highest visitation rates. These insights provide the first steps for understanding the reproductive ecology of these key tree species and can help to inform sustained management and conservation aimed at protecting forests and supporting rural livelihoods, as well as broaden the understanding of the floral visitors, and contribution of biotic pollination to forest tree reproductive success.

Future Reductions in Suitable Habitat for Key Tree Species Result in Declining Boreal Forest Aboveground Biomass Carbon in China

China’s forest ecosystem plays a crucial role in carbon sequestration, serving as a cornerstone in China’s journey toward achieving carbon neutrality by 2060. Yet, previous research primarily emphasized climate change’s influence on forest carbon sequestration, neglecting tree species’ suitable area changes. This study combinates the Lund–Potsdam–Jena model (LPJ) and the maximum entropy model (MaxENT) to reveal the coupling impacts of climate and tree species’ suitable area changes on forest aboveground biomass carbon (ABC) in China. Key findings include the following: (1) China’s forests are distributed unevenly, with the northeastern (temperate coniferous broad-leaved mixed forest, TCBMF), southwestern, and southeastern regions (subtropical evergreen broad-leaved forest, SEBF) as primary hubs. Notably, forest ABC rates in TCBMF exhibited a worrisome decline, whereas those in SEBF showed an increasing trend from 1993 to 2012 based on satellite observation and LPJ simulation. (2) Under different future scenarios, the forest ABC in TCBMF is projected to decline steadily from 2015 to 2060, with the SSP5-8.5 scenario recording the greatest decline (−4.6 Mg/ha/10a). Conversely, the forest ABC in SEBF is expected to increase under all scenarios (2015–2060), peaking at 1.3 Mg/ha/10a in SSP5-8.5. (3) Changes in forest ABC are highly attributed to climate and changes in tree species’ highly suitable area. By 2060, the suitable area for Larix gmelinii in TCBMF will significantly reduce to a peak of 65.71 × 104 km2 under SSP5-8.5, while Schima superba Gardner & Champ and Camphora officinarum in SEBF will expand to peaks of 94.07 × 104 km2 and 104.22 × 104 km2, respectively. The geographic detector’s results indicated that the climate and tree species’ suitable area changes showed bi-variate and nonlinear enhanced effects on forest ABC change. These findings would offer effective strategies for achieving carbon neutrality.

Effects of Douglas fir cultivation in German forests on soil seepage water quantity and quality

Norway spruce (Picea abies L.) has been a key tree species and timber source in European forests the last centuries and is increasingly suffering from drought and bark beetle infestations due to climate warming. Current management options include replacing of Norway spruce monocultures with pure and mixed stands of European beech (Fagus sylvatica) that is the naturally dominating tree species in Central Europe. Additionally, Douglas fir (Psudotsuga menziesii), a tree species with high water use efficiency and drought tolerance, is being increasingly cultivated to increase the resilience of European forests and meet the future demand of conifer timber in a warming climate. We studied the seepage water quantity and quality with a particular focus on the nitrate (NO3–) concentration and N leaching under pure and mixed stands of Douglas fir, Norway spruce, and European beech at seven sites in Germany. Additionally, we investigated seepage water concentrations of SO4-S, Ca, Mg, K, Al and hydrological variables (interception, canopy throughfall, transpiration). Looking at the seepage water quantity and quality, the best management option is the cultivation of pure beech stands. However, this is associated with the well-known risk of monocultures concerning ecosystem disturbance. Beech stands showed the highest seepage water quantities and the lowest seepage water concentrations of major cations and anions, including NO3–. Seepage water quantity was the smallest under pure Douglas fir compared to spruce and beech stands. The composition effects of stand tree species on seepage water quality and nutrient leaching were site-dependent. At N-rich sites, pure Douglas fir stands showed higher seepage water NO3– concentrations than spruce and beech stands, whereas the tree species effects were small at N-poor sites. With respect to seepage water quantity and quality, cultivation of mixed Douglas fir–beech stands is a promising option for producing conifer timber and at the same time avoiding increased disturbance risks of mono-species forests under a warmer climate. Our results support the recommendation of mixed Douglas fir–beech stands based on soil quality, ecosystem resilience, and forest economic studies.