Pine Canopy Research Articles

Multitemporal UAV study of phenolic compounds in slash pine canopies

Phenolic compounds (PC) are important secondary metabolites in plants, playing a crucial role in plant defense mechanisms against pathogens and other plants. Monitoring PC levels is important for understanding tree stress and implementing effective breeding programs. However, traditional methods for monitoring PC are time-consuming, prone to altering the phenolic composition, and mostly applicable only on a small scale. In this study, we evaluated the performance of Unoccupied Aerial Vehicles (UAV) multispectral imaging in estimating the canopy phenolic content in slash pine over an 11-month period in 2021 and a seven-month period in 2022. Three machine learning models including Partial least squares regression (PLSR), Random forest (RF) and Support Vector Machine (SVM) were compared to determine the optimal predictive model for canopy PC. The RF model provided the best predictive results, with R2 values of 0.82 for the validation set and 0.94 for the calibration set. Additionally, the study assesses the heritable variation in canopy PC over time, with the monthly heritability (h2) of PC ranging from 0 to 0.26 in 2021 and from 0 to 0.35 in 2022; The highest h2 levels were observed in July and September 2021and July 2022. The findings demonstrate significant genetic control over the variation of PC. Furthermore, we observed higher breeding values and genetic gains in July and November, which further supports the strong correlation between PC and environmental factors such as temperature and light intensity. To the best of our knowledge, this is the first study to employ time-series UAV multispectral imaging to predict secondary metabolites in pine trees and estimate their genetic variation over time. As a proof of concept, these findings provide more reliable information for tree breeding programs, ultimately enhancing their overall performance.

A Preliminary Study of Longleaf Pine Canopy Arthropods in Southwest Georgia

A Preliminary Study of Longleaf Pine Canopy Arthropods in Southwest Georgia

Oaks enhance early life stage longleaf pine growth and density in a subtropical xeric savanna.

The interplay of positive and negative species interactions controls species assembly in communities. Dryland plant communities, such as savannas, are important to global biodiversity and ecosystem functioning. Sandhill oaks in xeric savannas of the southeastern United States can facilitate longleaf pine by enhancing seedling survival, but the effects of oaks on recruitment and growth of longleaf pine have not been examined. We censused, mapped, and monitored nine contiguous hectares of longleaf pine in a xeric savanna to quantify oak-pine facilitation, and to examine other factors impacting recruitment, such as vegetation cover and longleaf pine tree density.We found that newly recruited seedlings and grass stage longleaf pines were more abundant in oak-dominated areas where densities were 230% (newly recruited seedlings) and 360% (grass stage) greater from lowest to highest oak neighborhood densities. Longleaf pine also grew faster under higher oak density. Longleaf pine recruitment was lowest under longleaf pine canopies. Mortality of grass stage and bolt stage longleaf pine was low (~1.0%yr-1) in the census interval without fire. Overall, our findings highlight the complex interactions between pines and oaks-two economically and ecologically important genera globally. Xeric oaks should be incorporated as a management option for conservation and restoration of longleaf pine ecosystems.

Radiation and temperature drive diurnal variation of aerobic methane emissions from Scots pine canopy.

Methane emissions from plant foliage may play an important role in the global methane cycle, but their size and the underlying source processes remain poorly understood. Here, we quantify methane fluxes from the shoots of Scots pine trees, a dominant tree species in boreal forests, to identify source processes and environmental drivers, and we evaluate whether these fluxes can be constrained at the ecosystem-level by eddy covariance flux measurements. We show that shoot-level measurements conducted in forest, garden, or greenhouse settings; on mature trees and saplings; manually and with an automated CO2-, temperature-, and water-controlled chamber system; and with multiple methane analyzers all resulted in comparable daytime fluxes (0.144 ± 0.019 to 0.375 ± 0.074 nmol CH4 g-1 foliar d.w. h-1). We further find that these emissions exhibit a pronounced diurnal cycle that closely follows photosynthetically active radiation and is further modulated by temperature. These diurnal patterns indicate that methane production is associated with diurnal cycle of sunlight, indicating that this production is either a byproduct of photosynthesis-associated biochemical reactions (e.g., the methionine cycle) or produced through nonenzymatic photochemical reactions in plant biomass. Moreover, we identified a light-dependent component in stand-level methane fluxes, which showed order-of-magnitude agreement with shoot-level measurements (0.968 ± 0.031 nmol CH4 g-1 h-1) and which provides an upper limit for shoot methane emissions.

The influence of vegetation on the microstructure and erosivity of precipitation

The process of precipitation interception, in which vegetation retains precipitation, has a major influence on natural processes such as soil erosion. Assessing this influence requires measurements of the microstructure of precipitation using modern instruments that allow measurements of the velocity, size, and number of raindrops. The precipitation microstructure data were obtained using 1-minute measurements from three optical disdrometers placed under the birch canopy, under the black pine canopy and above the canopies. In the period under consideration between 12 July 2022 and 16 February 2023, 48 rainfall events were recorded, for which the duration, the amount of precipitation, the average intensity of precipitation, and the characteristics of the raindrops (size, velocity, and number of drops) were calculated. Additionally, the kinetic energy (KE), the maximum 30-minute intensity (max I30), and the rainfall erosivity factor (R) were calculated. All these variables were calculated for measurements above and below the tree canopies. The results show that the proportion of intercepted precipitation decreases with the duration of the events for both birch and pine. Droplets increased on average during the leafed period, as they passed through the tree canopy, and decreased during the leafless period. During the entire period, the diameter of the droplets increased on average by 46% under birch and by 26% under black pine. The droplet velocity decreased on average by 38% under the pine, while it increased minimally under the birch by 1%, which is the result of an increase in the average velocity under the birch during the leafless period by 7%. The analysis of the results shows that the rainfall interception has a large impact on soil erosion, as, for example, the rainfall erosivity factor (R) under birch decreased by 43% and under pine by 90%.

Cooling streams with riparian trees: Thermal regime depends on total solar radiation penetrating the canopy

AbstractRiparian planting is often recommended for stream restoration, notably to mitigate solar heating of stream waters. However, plant leaves shade photosynthetically active radiation (PAR, 400–700 nm) more efficiently than the near‐infrared (NIR, 700–3000 nm) wavelengths that comprise about half of incident solar radiation and so contribute equally to water heating. Total solar radiation (NIR + PAR) exposure at the reach scale is needed to avoid bias when predicting the thermal response of streams. In this article, we alert stream ecologists and riparian restorers to the water heating contribution of NIR and provide a means to account for both NIR and PAR in total solar radiation penetrating riparian canopies. We used spectral pyranometers to simultaneously measure total solar radiation and its NIR component under different tree canopies over a wide range of shade conditions as indexed by PAR exposure. Measurements were made during full overcast (diffuse lighting) conditions so as to ‘sample’ transmission of radiation through the complete canopy. The NIR proportion of sub‐canopy solar radiation increased steadily with increasing shade and was appreciably greater under willow than pine canopies, while NZ native broadleaf rainforest had intermediate (rather variable) NIR content. Our trend lines for different tree canopies permit total sub‐canopy solar radiation to be estimated from PAR exposure for unbiased modelling of stream thermal regimes.

Aerobic methane emissions from the shoots of Scots pine

Plants are recognized sources of methane (CH4) but plant-mediated CH4 emissions have mostly been studied on herbaceous species, although also trees are known to emit CH4. Emissions from tree canopies likely mostly derive from an aerobic, abiotic process. Aerobic CH4 production from trees has not been thoroughly studied, leaving uncertainties to the global source strength estimates, which vary from 0 to 240 Tg yr-1. Even less is known about how aerobic emissions affect the CH4 cycles in boreal forest ecosystems, as the environmental and physiological drivers are not fully understood. In this study, shoot-level CH4 fluxes of boreal conifer trees were measured outdoors and in the greenhouse, to investigate the environmental and physiological drivers and regulators of shoot-level CH4 fluxes. Most of the measurements were done from saplings of Pinus sylvestris L. (Scots pine), one of the most important tree species of the boreal region of the Eurasian continent, by using chamber enclosure methods with spectral, online greenhouse gas analysers. The measurements were conducted either manually, or with an automated measurement system, developed to overcome issues related to manual measurement techniques. The shoots of Scots pine showed small but significant emissions of CH4 in all experimental setups, the emissions were driven by light, enhanced by elevated temperature, and occurred independently from drought and photosynthesis. Solar radiation was a more significant driver of these CH4 emissions than artificial light with UV-A. These results show that Scots pine canopies have the potential to produce CH4 in a similar process that has been described before for the foliage of herbaceous plants, but these emissions are smaller than the initial estimates of the aerobic CH4 source from vegetation. The boreal forest canopies are sources of CH4 and have the capacity to decrease the CH4 sink strength of boreal upland forests by ~ 5 %.

Predicting the impact of invasive trees from different measures of abundance

Biological invasions produce negative impacts worldwide, causing massive economic costs and ecological impacts. Knowing the relationship between invasive species abundance and the magnitude of their impacts (abundance-impact curves) is critical to designing prevention and management strategies that effectively tackle these impacts. However, different measures of abundance may produce different abundance-impact curves. Woody plants are among the most transformative invaders, especially in grassland ecosystems because of the introduction of hitherto absent life forms. In this study, our first goal was to assess the impact of a woody invader, Pinus contorta (hereafter pine), on native grassland productivity and livestock grazing in Patagonia (Argentina), building abundance-impact curves. Our second goal, was to compare different measure of pine abundance (density, basal area and canopy cover) as predictors of pine's impact on grassland productivity. Our third goal, was to compare abundance-impact curves among the mentioned measures of pine abundance and among different measures of impact: total grassland productivity, palatable productivity and sheep stocking rate (the number of sheep that the grassland can sustainably support). Pine canopy cover, closely followed by basal area, was the measure of abundance that best explained the impact on grassland productivity, but the shape of abundance impact curves differed between measures of abundance. While increases in pine density and basal area always reduced grassland productivity, pine canopy cover below 30% slightly increased grassland productivity and higher values caused an exponential decline. This increase in grassland productivity with low levels of pine canopy cover could be explained by the amelioration of stressful abiotic conditions for grassland species. Different measures of impact, namely total productivity, palatable productivity and sheep stocking rate, drew very similar results. Our abundance-impact curves are key to guide the management of invasive pines because a proper assessment of how many invasive individuals (per surface unit) are unacceptable, according to environmental or economic impact thresholds, is fundamental to define when to start management actions.

Homogenization of bryophyte species after alpine grassland restoration.

The causes of decreasing plant species richness include abandonment of traditional management and the spread of invasive species, even in alpine habitats. Studies on the restoration and management of alpine habitats are predominantly focused on vascular plants, although an important part of alpine vegetation and its diversity is formed by bryophytes. We used bryophytes to indicate changes that occur after the clearcutting of nonindigenous dwarf pine (Pinus mugo Turra) and attempted to reveal the community to which the development of bryophyte species structure was directed. We compared species richness and composition between surveys to test for changes in spatial heterogeneity bryophyte communities. We also tried to reveal the main ecological drivers of the restoration process. The study was performed in the (sub)alpine area of the Eastern High Sudetes Mts. (the Czech Republic). We estimated bryophyte species cover and compared the composition of the bryophyte community in autochthonous grassland areas, areas under the dwarf pine canopy, and clearcut areas to reveal the pattern of shifts 9 years after the treatment. We also measured soil characteristics to reveal the environmental habitat conditions. Evidence of taxonomic homogenization of habitat after dwarf pine removal was found. Light conditions and attributes of litter were the driving factors of successional changes in the bryophyte communities, which led to taxonomic homogenization. This finding explains the slow restoration process due to dwarf pine legacy on the clearcut area. The succession trends were also shaped by unobserved factors, such as climate change and environmental eutrophication. We highly recommended active management and long-term monitoring.

Ericaceous dwarf shrubs contribute a significant but drought‐sensitive fraction of soil respiration in a boreal pine forest

Abstract Boreal forests often have a dense understorey of ericaceous dwarf shrubs with ecological adaptations that contrast those of the canopy‐forming trees. It is therefore important to quantify contributions by understorey shrubs to ecosystem processes and disentangle shrub‐ and tree‐driven responses to climatic factors. We quantified soil respiration driven by the pine canopy and the ericaceous shrub understorey over 3 years, using a factorial pine root exclusion and shrub removal experiment in a mature Pinus sylvestris forest. Soil temperature and moisture‐related responses of respiration attributed to autotrophs (shrubs, pine roots) and heterotrophs were compared. Additionally, we assessed effects of interactions between these functional groups on soil nitrogen availability and respiration. Understorey shrubs accounted for 22% ± 10% of total autotrophic respiration, reflecting the ericaceous proportion of fine root production in the ecosystem. Heterotrophic respiration constituted about half of total soil respiration. Shrub‐driven respiration was more susceptible to drought than heterotrophic‐ and pine‐driven respiration. While the respiration attributed to canopy and understorey remained additive, indicating no competitive release, the plant guilds competed for soil N. Synthesis. Ericaceous understorey shrubs accounted for a small, yet significant, share of total growing season soil respiration. Overlooking understorey respiration may lead to erroneous partitioning and modelling of soil respiration mediated by functional guilds with contrasting responses to soil temperature and moisture. A larger contribution by heterotrophs and pine root‐associated organisms to soil respiration under drought conditions could have important implications for soil organic matter accumulation and decomposition as the climate changes in boreal forests.

Improved Coffee Management by Farmers in State Forest Plantations in Indonesia: An Experimental Platform

The Indonesian state forest managers have accepted farmer-managed coffee agroforestry in their estates as part of their social forestry program. Access by local farming communities to state-owned plantation forestry supports public motivation to maintain forest cover. However, balancing the expectations and needs of forest managers with those of the local farming communities is not easy. Coffee yields in Indonesia are lower than those of neighboring countries, suggesting that there is scope for improvement. Here we describe an experimental research platform developed through an international collaboration between the Universitas Brawijaya (UB), the UK Centre for Ecology and Hydrology (UKCEH), and smallholder coffee farmers to explore options for improving pine-coffee agroforestry systems within existing regulations. Located in a former state-owned pine production forest on the slopes of the stratovolcano, Mount Arjuna, in the Malang Regency of East Java, the research platform has seven instrumented research plots (40 × 60 m2), where agronomic practices can be trialed. The aim of the platform is to support the development of sustainable agronomic practices to improve the profitability of coffee agroforestry and thus the livelihood of low-income rural communities. Current trials are focused on improving coffee yields and include pine canopy trimming, fertilizers, and coffee pruning trials, with links to the development of socio-economic and environmental models. Whilst it is too early to assess the full impacts on yields, a survey of farmers demonstrated a positive attitude to canopy pruning, although with some concern over labor cost. The initial ecosystem modelling has highlighted the benefits of coffee agroforestry in balancing environmental and economic benefits. Here we provide a detailed description of the site, the current trials, and the modelling work, with the hope of highlighting opportunities for future collaboration and innovation.

Population and reproductive structure of an endangered juniper from coastal pine forests

Plant species adapted to coastal systems are suffering severe declines. This is the case of the critically endangered Juniperus navicularis, which colonizes fossil dunes in the southwestern Iberian Peninsula and grows in the understory of pine plantations. This endemic juniper presents low reproduction rates and a decreasing number of populations has been reported in its western distribution edge. However, age structure and the demographic situation of its easternmost populations, that have been recently discovered, remain unknown. We used dendrochronological procedures to estimate the age structure of the easternmost isolated population of J. navicularis, considering three subpopulations under contrasting management regimes and selecting plots under pine cover and in open areas. We also assessed sex ratio, age at maturity and reproductive effort. We observed the predominance of 20–40 years-old stems in all study plots and a remarkable lack of young stems in open areas. Stem density was higher under pine canopies. There, junipers were, on average, younger than pine trees, meaning that junipers had grown in already forested areas. Only one sex per plot was found in all study plots but one, in which no reproductive stems were recorded, suggesting the existence of clonal growth. Reproductive effort increased with age in females, but was independent in males. We hypothesize that clonal growth might occur as a survival strategy to endure the harsher conditions of distribution edges. These results will help to develop more effective management strategies to preserve this endangered species, contributing to our understanding of dynamics of coastal ecosystems and setting the basis for future genetic studies.

Temperature and precipitation affect seasonal changes in mite communities (Acari: Mesostigmata) in decomposing litter of broadleaved and coniferous temperate tree species

Key messageWe identified the effect of microclimatic conditions on soil mite communities (Mesostigmata) during the decomposition of broadleaved and coniferous litter. The abundance, species richness, and diversity of mite communities decreased from spring to autumn regardless of litter quality and was related to changes in temperature and precipitation.ContextLitter decomposition is one of the fundamental soil-supporting processes in terrestrial ecosystems. However, there is still a lack of knowledge on some general patterns of the relationships between litter quality (tree species), microclimate, and structure of soil mite assemblages.AimsThe study aimed to analyze the impact of climatic conditions (temperature and precipitation) on mesostigmatid mite communities in the litter of 11 tree species through the vegetation season.MethodsThe experiment tested litter decomposition of 11 different tree species (693 litterbags), for seven consecutive months (April-October) under homogenous Scots pine (Pinus sylvestris L.) canopy monocultures in common garden conditions. Soil mites were extracted in Tullgren funnels.ResultsMesostigmatid mite abundance was positively correlated with the temperature of the sampling month and negatively with the temperature of the previous month. Species richness depended on the sampling month temperature. Changes in litter mass loss in late autumn (after litterfall) and overwinter were important for colonization of litterbags by soil mesostigmatid mites in the following spring.ConclusionsChanges in climatic conditions, i.e., temperature and precipitation between the sampling months (during the following vegetation period), may cause significant changes in mesostigmatid mite abundance and thus may impact ecosystem functions. The winter period is important for mesostigmatid mite abundance in the following vegetation period.

Moderate pine cover maximizes 10-year survival and growth in late-successional species of contrasting functional strategies

Monospecific pine forests are widespread due to extensive afforestation efforts and natural colonization of abandoned croplands in the Mediterranean Basin. It was originally thought that pines would facilitate the natural colonization of native late-successional resprouter species (e.g., hardwoods), but these species can be compromised if competition with pines outweighs their facilitative effect on these hardwood species. Managing the density or canopy cover of these widespread pine forests can potentially provide some “optimum” balance between facilitation and competition to maximize success in the introduction of late successional species while maintaining a tree stratum. We tested the response (survival and growth across 10 years) of six resprouter species covering a wide range of plant functional strategies, from drought-tolerant sclerophyllous shrubs and trees to malacophyllous drought-sensitive trees, across an experimental gradient of Aleppo pine canopy cover. Seedling performance varied according to the functional strategy, pine cover and time. High pine cover generally enhanced seedling survival, whereas moderate pine cover generally enhanced seedling growth, although this response was modulated by the functional strategy of the seedling species. Interactions between pines and seedlings were only detectable 2–3 years after plantation, increasing in intensity with time. The latter highlights the need of medium to long-term studies to evaluate plant-plant interactions in these water-limited environments with slow successional trajectories. Our results could be attributed to the shade tolerance of most of the introduced trees, combined with their low tolerance to the combination of high sunlight radiation and drought. We found an optimal pine cover of ca. 50% (equivalent to 300–400 trees/ha) in which both survival and growth of late successional species can be maximized, which help to select best locations for more efficient reforestation programs and set a threshold value to decide whether or not to perform tree thinning to enhance ecosystem diversity and, subsequently, resilience.

Are northern German Scots pine plantations climate smart? The impact of large-scale conifer planting on climate, soil and the water cycle

Increasing temperatures and rising atmospheric vapor pressure deficits are exposing forests around the globe to increasing drought and heat stress, demanding a shift to climate-smart forestry for increasing the stress resistance and resilience of production forests and to enhance their climate change mitigation potential. Based on measurements in paired pine and beech forests and the review of literature data, we analyse the biophysical consequences and the carbon cycle impact of large-scale Scots pine (Pinus sylvestris L.) plantations in northern Germany in the face of a warming and aridifying climate. We quantified canopy surface albedo and surface temperature, evapotranspiration and deep seepage, carbon (C) storage in biomass and soil and annual C sequestration, and soil acidification of pine plantations in comparison to beech forests (Fagus sylvatica L.), the natural forest vegetation. We find that near-infrared (NIR, 700–3000 mn) canopy surface albedo is higher by 5.2 percentage points during summer over beech as compared to pine forest, resulting in a 9 % higher net radiation and a 0.6 K higher surface temperature of the pine canopy. Deep seepage is on average by 68 mm yr−1 smaller under pine than beech forest (66 mm yr−1 vs. 134 mm yr−1) due to the higher evapotranspiration of pine. C storage in biomass and soil is by ∼ 48 Mg C ha−1 higher in beech than pine forests, reflecting the higher productivity of beech, demonstrating an unfavorably low C sequestration potential of Scots pine plantations. We conclude that the large-scale Scots pine plantations in northern Germany (>1.7 million ha) are neither environmental-friendly nor climate smart, given their enhancement of climate-warming, low climate change mitigation potential, and negative effect on groundwater recharge. Replacing pine plantations by beech (or other hardwood) forests in northern Germany and adjacent regions is urgently needed for achieving the goals of climate-smart forestry.

Year-round multi-scale habitat selection by Crested Tit (Lophophanes cristatus) in lowland mixed forests (northern Italy)

Determining how animals respond to resource availability across spatial and temporal extents is crucial to understand ecological processes underpinning habitat selection. Here, we used a multi-scale approach to study the year-round habitat selection of the Crested Tit (Lophophanes cristatus) in a semi-natural lowland woodland of northern Italy, analysing different habitat features at each scale. We performed Crested Tit censuses at three different spatial scales. At the macrohabitat scale, we used geolocalized observations of individuals to compute Manly's habitat selection index, based on a detailed land-use map of the study area. At the microhabitat scale, the trees features were compared between presence and absence locations. At the foraging habitat scale, individual foraging birds and their specific position on trees were recorded using focal animal sampling. Censuses were performed during both the breeding (March to May) and wintering (December to January) seasons. At the macrohabitat scale, the Crested Tits significantly selected pure and mixed pine forests and avoided woods of alien plant species, farmlands and urban areas. At the microhabitat scale, old pine woods with dense cover were selected, with no significant difference in the features of tree selection between the two phenological phases. At the foraging habitat scale, the species was observed spending more time foraging in the canopies than in the understorey, using mostly the portion of Scots Pine (Pinus sylvestris) canopies closer to the trunk in winter, while during the breeding period, the whole canopy was visited. Overall, breeding and wintering habitats largely overlapped in the Crested Tit. Based on our findings, lowland Crested Tits can be well defined as true habitat specialists: they are strictly related to some specific coniferous woodland features. Noteworthily, compared to other tit species, which normally show generalist habits during winter, the Crested Tit behaves as a habitat specialist also out of the breeding season. Our study stressed the importance of considering multi-scale (both spatial and phenological) habitat selection in birds.

Forage yield and nutritive value of forest gap rangelands under differing Scotch pine canopy coverage

Forage yield and nutritive value of forest gap rangelands under differing Scotch pine canopy coverage

Wildland Fire Detection and Monitoring Using a Drone-Collected RGB/IR Image Dataset

Current forest monitoring technologies including satellite remote sensing, manned/piloted aircraft, and observation towers leave uncertainties about a wildfire’s extent, behavior, and conditions in the fire’s near environment, particularly during its early growth. Rapid mapping and real-time fire monitoring can inform in-time intervention or management solutions to maximize beneficial fire outcomes. Drone systems’ unique features of 3D mobility, low flight altitude, and fast and easy deployment make them a valuable tool for early detection and assessment of wildland fires, especially in remote forests that are not easily accessible by ground vehicles. In addition, the lack of abundant, well-annotated aerial datasets – in part due to unmanned aerial vehicles’ (UAVs’) flight restrictions during prescribed burns and wildfires – has limited research advances in reliable data-driven fire detection and modeling techniques. While existing wildland fire datasets often include either color or thermal fire images, here we present (1) a multi-modal UAV-collected dataset of dual-feed side-by-side videos including both RGB and thermal images of a prescribed fire in an open canopy pine forest in Northern Arizona and (2) a deep learning-based methodology for detecting fire and smoke pixels at accuracy much higher than the usual single-channel video feeds. The collected images are labeled to "fire" or "no-fire" frames by two human experts using side-by-side RGB and thermal images to determine the label. To provide context to the main dataset’s aerial imagery, the included supplementary dataset provides a georeferenced pre-burn point cloud, an RGB orthomosaic, weather information, a burn plan, and other burn information. By using and expanding on this guide dataset, research can develop new data-driven fire detection, fire segmentation, and fire modeling techniques.

Implications of mistletoe parasitism for the host metabolome: A new plant identity in the forest canopy.

Mistletoe-host systems exemplify an intimate and chronic relationship where mistletoes represent protracted stress for hosts, causing long-lasting impact. Although host changes in morphological and reproductive traits due to parasitism are well known, shifts in their physiological system, altering metabolite concentrations, are less known due to the difficulty of quantification. Here, we use ecometabolomic techniques in the plant-plant interaction, comparing the complete metabolome of the leaves from mistletoe (Viscum album) and needles from their host (Pinus nigra), both parasitized and unparasitized, to elucidate host responses to plant parasitism. Our results show that mistletoe acquires metabolites basically from the primary metabolism of its host and synthesizes its own defence compounds. In response to mistletoe parasitism, pines modify a quarter of their metabolome over the year, making the pine canopy metabolome more homogeneous by reducing the seasonal shifts in top-down stratification. Overall, host pines increase antioxidant metabolites, suggesting oxidative stress, and also increase part of the metabolites required by mistletoe, which act as a permanent sink of host resources. In conclusion, by exerting biotic stress and thereby causing permanent systemic change, mistletoe parasitism generates a new host-plant metabolic identity available in forest canopy, which could have notable ecological consequences in the forest ecosystem.

Allocation of Wood Density in European Oak (Quercus robur L.) Trees Grown under a Canopy of Scots Pine

The allocation of wood density in trees depends on many factors, but mainly on the tree species. A great number of studies have analysed wood density in dominant or codominant trees, but only a few have focused on trees grown under canopy. We examined the basic wood density and fresh wood density of natural origin oaks growing under canopy of artificially planted Scots pine. The major purpose of the work was to study the wood density allocation in different parts of the trees such as the trunk and branches. From a total of 80 oaks we selected eight model trees and measured biometric features of their trunks and crowns. Wood samples from different parts of the trunk and crown were collected after the trees were felled. We observed significant differences between the average basic wood density (595 kg·m−3) and the average fresh wood density (1031 kg·m−3). The central part of the trunk and heartwood shows much higher density than the outer part of the trunk and sapwood, which corresponds to the model of ring-porous trees. Both types of wood density (basic and fresh) were also higher in the trunk than in the branches. The wood density of the branches differed between two zones: A1, which was closer to the trunk and had higher density; and A2, which was farther away from the trunk with lower density. Wood density shows positive correlation with crown length but not with crown width, which was more connected with diameter at breast height. We found lower value of slenderness than the value reported by other authors in oaks planted without canopy. The allocation of wood density in trees is associated with the potential mechanical load.