Global patterns of tree wood density.

Wood density is a fundamental property related to tree biomechanics and hydraulic function while playing a crucial role in assessing vegetation carbon stocks by linking volumetric retrieval and a mass estimate. This study provides a high-resolution map of the global distribution of tree wood density at the 0.01° (~1 km) spatial resolution, derived from four decision trees machine learning models using a global database of 28,822 tree-level wood density measurements. An ensemble of four top-performing models combined with eight cross-validation strategies shows great consistency, providing wood density patterns with pronounced spatial heterogeneity. The global pattern shows lower wood density values in northern and northwestern Europe, Canadian forest regions and slightly higher values in Siberia forests, western United States, and southern China. In contrast, tropical regions, especially wet tropical areas, exhibit high wood density. Climatic predictors explain 49%-63% of spatial variations, followed by vegetation characteristics (25%-31%) and edaphic properties (11%-16%). Notably, leaf type (evergreen vs. deciduous) and leaf habit type (broadleaved vs. needleleaved) are the most dominant individual features among all selected predictive covariates. Wood density tends to be higher for angiosperm broadleaf trees compared to gymnosperm needleleaf trees, particularly for evergreen species. The distributions of wood density categorized by leaf types and leaf habit types have good agreement with the features observed in wood density measurements. This global map quantifying wood density distribution can help improve accurate predictions of forest carbon stocks, providing deeper insights into ecosystem functioning and carbon cycling such as forest vulnerability to hydraulic and thermal stresses in the context of future climate change.

An assessment of the habitat preferences of European bison with airborne laser scanning data in forest ecosystem.

Research on habitat preferences is an important part of contemporary ecology. For the European bison, the classic approach to distinguishing habitat features is still being followed, but the limitations of this approach cannot provide the standard features of optimal habitats for this species. The study consisted in comparing analyses of the habitat preferences of European bison that were based on either classic forest typology (habitat types) or airborne laser scanning data. The data for these analyses were collected from telemetry collars on European bison in Bialowieza Forest. The model based on airborne laser scanning features presented better parameters (percent of correctly classified cases and ROC) than the model based on habitat types. The results show that it is possible to find universal indicators of European bison's preferences that are independent of local forest classification methodology. The indicators used suggest that European bison have a preference for forest habitats with low canopy cover and a small share of woody plants in the lower parts of the forest. Low canopy cover itself is not necessarily beneficial for European bison. Our study also indicates that airborne laser scanning is also useful in the assessment of habitat suitability for European bison in forest ecosystems.

Integration of remote sensing in spatial ecology: assessing the interspecific interactions of two plant species in a semi-arid woodland using unmanned aerial vehicle (UAV) photogrammetric data.

The spatial structure of plant communities in semi-arid regions is mostly derived by plant-plant interactions and environmental heterogeneity. In this study, we investigated the intra- and interspecific interactions and their contribution to growth inhibition in the patches of Pistacia trees and Amygdalus shrubs in semi-arid woodland communities through the implementation of photogrammetric data provided by unmanned aerial vehicle (UAV). This study was conducted in a part of Wild Pistachio Natural Reserve covered by Pistacia-Amygdalus stands in Zagros Mountains, western Iran. We used univariate and bivariate forms of pair- and mark correlation functions and Analytical Global Envelopes under inhomogeneous Poisson process which allow detection of the interactions of the species within the 45-ha study area. Our results indicated that the UAV-derived photogrammetric data proved to be efficient in identification of the plant individuals (F-score ≈ 0.92 for both species). Additionally, strong coefficients of determination (R2 = 0.98 and 0.94 for Pistacia and Amygdalus, respectively) supported prediction of crown area. We observed the aggregation of the species individuals in clusters of conspecifics and heterospecifics at small spatial scales, most likely as a result of aggregation in favourable parts of the study area. The aggregation of the species within patches had a marked effect on their size (i.e., crown area, height) inferred as growth inhibition, probably due to intra- and interspecific competition. Our findings demonstrated that promising UAV photogrammetric data can be effectively utilized by ecologists for investigation of plant associations, hence increasing the potentiality of remote sensing in spatial ecology of vegetation patches in semi-arid environments.

Factors influencing the accuracy of ground-based tree-height measurements for major European tree species.

Tree height is one of the most important forest characteristics and is one of the crucial measurements taken for either practical or scientific reasons. However, the accuracy of a tree-height measurement may vary in relation to many factors. The work described here thus sought to evaluate the accuracy of ground-based tree-height measurements for major forest-forming tree species of the temperate and boreal zones. The focus was on the importance of factors affecting accuracy of the measurements in question at larger geographical scales. In line with the above research goals, data were gathered from 299 stands throughout Poland and heights of 2388 sample trees of eight species, growing in different stands and site conditions, were measured; heights were then compared with measured lengths of felled trees as a reference. In total, 10 variables to determine factors that may influence ground-based tree-height measurement accuracy were used. We merged them into 4 groups: measurements, topography, stand and biometric-related factors. Results showed that biometric and topographic factors had the greatest relative influence on the accuracy of measurements of tree height. Tree length and species, followed by the slope of the terrain, tree age, and height above sea level were the most important factors found to affect accuracy. In most of the cases studied the terrestrial tree-height measurements were underestimated when set against definitive measurements of length. This was true for all species studied except oak, for which height measurements were typically overestimated. Notwithstanding the broad geographical scope of the work, the particular device used and the team factor were only found to have a marginal influence on measurement accuracy.

What do we expect from forests? The European view of public demands.

The paper constitutes an overview of the hitherto prevailing knowledge of the factors which influence the attractiveness of forests. What is more, it shows, in a cross-sectoral manner, the study methods and general preferences of people in the context of recreational use of forests. 109 papers published in the years 2000-2016 have been analyzed. In the work, five main issues were discussed, which constitute the study subject i.e.: a) the preferred forest type and function; b) expenses incurred by people to reach a forest (time and distance); c) the society's demand for technical infrastructure and forest management; d) factors disturbing the recreation in forest areas; e) reasons and frequency of visits to forests for recreation purposes. The results indicate that the following have an impact on the perception of forests: tree stand factors (age, species composition, etc.), social factors (age, material status, interests, etc.), and factors related to human activity (the extent of forest operations, noise, littering, etc.). Based on the literature, it is possible to indicate a model forest, which in view of respondents, is described as the one that is preferred for recreation purposes. The model differs depending on the analyzed part of Europe.

The Role of Topography in the Distribution and Intensity of Damage Caused by Deer in Polish Mountain Forests.

The increase in the deer population observed in recent decades has strongly impacted forest regeneration and the forest itself. The reduction in the quality of raw wood material, as a consequence of deer-mediated damage, constitutes a significant burden on forest owners. The basis for the commencement of preventive actions in this setting is the understanding of the populations and behaviors of deer in their natural environment. Although multiple studies have been carried out regarding this subject, only a few suggested topography as an important factor that may influence the distribution and intensity of deer-mediated damage. The detailed terrain models based on LiDAR data as well as the data on damage caused by deer from the State Forests database enabled thorough analyses of the distribution and intensity of damage in relation to land form in this study. These analyses were performed on three mountain regions in Poland: the Western Sudety Mountains, the Eastern Sudety Mountains, and the Beskidy Mountains. Even though these three regions are located several dozen to several hundred kilometers apart from each other, not all evaluated factors appeared common among them, and therefore, these regions have been analyzed separately. The obtained results indicated that the forest damage caused by deer increased with increasing altitude above 1000 m ASL. However, much larger areas of damage by deer were observed at elevations ranging from 401 to 1000 m ASL than at elevations below 400 m ASL. Moreover, the locations of damage (forest thickets and old stands) indicated that red deer is the species that exerts the strongest pressure on forest ecosystems. Our results show the importance of deer foraging behavior to the structure of the environment.