European Journal of Forest Research

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Map of study sites in Lipusz State Forest Management Unit; SD, SCD, MD, MCD—severely and moderately disturbed stands without and with tree crowns lying on the ground; LD: least disturbed forests; 1–3: replications of treatments. Numbers in italics are the numbers of forest divisions
Average rarefied number of species (a), abundance (b) and proportion of individuals representing: forest species (c), generalist species (d), open-habitat species (e), large zoophages (f), small zoophages (g) and hemizoophages (h) in the least disturbed stands (LD), moderately disturbed stands (MD) and severely disturbed stands (SD) with tree crowns on the ground (MCD and SCD); lower-case letters above the bars indicate differences between data collected (at p < 0.01; Tukey’s test)
Redundancy analysis of carabid assemblages; data from 2018 (a), 2019 (b), 2020 (c) for severely (S), severely + tree crowns on the ground (SC), moderately (M), moderately + tree crowns on the ground (MC) and least (L) disturbed stands. Only significant habitat variables are shown: LAI: leaf area index; temperature: soil temperature; C: soil content of carbon; CO2: soil respiration and soil humidity—measured directly in soil. The abbreviations of the species names are shown in the table in Appendix B. RDA model calculated without data transformation, with interspecies correlation scaling, species scores divided by SD and centring by species
The usual practice following a windthrow event is salvage logging of all damaged trees. This study was carried out in a pine stand affected by storms with varying disturbance severities in which no salvage logging was performed. Epigeic carabids(Coleoptera) were the test taxon. How does windthrow severity and disturbance legacies affect the abundance, richness and life traits of carabid assemblages? Two hypotheses were formulated: (1) the more severe the disturbance, the higher the abun-dance and species richness, and the lower the proportion of late-successional fauna in carabid assemblages, and (2) pine tree crowns lying on the ground support a higher proportion of late-successional carabid species, the effect of which should be more pronounced in more severely disturbed stands but will decrease as needles fall off over the next 3 years. To test the first hypothesis, 3 degrees of stand disturbance were distinguished. Both hypotheses were partially supported. Simultaneously, it was demonstrated that the importance of the leaf area index for carabids decreased over the 3 years, while the significance of the soil respiration rate and soil humidity increased. During the 3 years, the percentage of carabid forest species living under the fallen tree crowns remained at the same level. The findings indicate that there is a rationale for leaving fallen trees in place together with their crowns, while in tree stands where salvage logging is performed, whole crowns should be leftcut-off from trunks to provide shelter for forest species (18) (PDF) Leaving windthrown stands unsalvaged as a management practice for facilitating late-successional carabid assemblages. Available from: https://www.researchgate.net/publication/367361151_Leaving_windthrown_stands_unsalvaged_as_a_management_practice_for_facilitating_late-successional_carabid_assemblages [accessed Jan 24 2023].
 
European Black Pine Mitotype distribution by natural population on the full area of natural distribution. In the top right corner (i.e., the large pie chart) is a summary of the observed relative total mitotype diversity
The neighbor-joining (NJ) agglomerative construction clustering method of the Goldstein (1995) genetic distance among principal geographic meta-populations (top left). The asterisks are for bootstrap support by minimum 67%. The similar results are obtained by UPGMA (unweighted pair-group method with arithmetic mean) hierarchical clustering method by same distance (fig not shown). The colored chart is the result from BAPS’s admixing Bayesian algorithm with spatial interference (K = 5 s) and nonspatial interference K = 5 and K = 6
The natural range of Pinus nigra according IUFRO (top left) and the principal five European Black Pine meta-population geographic interpolation determined by two different algorithms implemented in BAPS, BARRIER programs. The barrier range shown best support for barrier A&B (endemic region of Northern Turkey), flowed by C (western Greece endemic region), D (Italian- French barrier) and low support for E (French-Spain barrier)
Migration pattern from the Balkan Peninsulas to the Western Russia (at the top); and the migration pattern from the Balkan Peninsulas to the Crimea Peninsulas (at the bottom). The vertical colored bar limit is 15 thousand individuals; and the horizontal colored bar in the middle of the figure represents geological time grid as white color—Holocene epoch (up to 0.01 scanned units), blue light color—Pleistocene epoch (between 0.01 and 0.1 scanned units), yellow color—Pliocene epoch (between 0.1 and 0.3 scanned units), and orange color—Miocene epoch (≥ 0.3 scanned units). In the present manuscript, we have set the base of the Pleistocene (Quaternary Period) at 2.6 Ma. The traditionally used the Tertiary Period comprises the Pliocene epoch (2.6–5.3 Ma), the Miocene epoch (5.3–23.0 Ma) and the Paleogene epoch (23.0–65.5 Ma). For the reverse directions migration patterns see Appendix Fig. 1S and 2S
Comparative asymmetric migration pattern between the mitochondrial INDEL, chloroplast SSRs and nuclear SSRs from two Mediterranean Pines (P. nigra and P. pinaster). The red dashed line connected the red asterisk is the time mark of the Last Glacial Maximum (LGM ≈ 27,000 YBP). The horizontal colored bar in the middle of each chart represent geological time grid as white color—Holocene epoch (up to 0.0117 MY), blue light color—Pleistocene epoch (between 0.0117 and 1.806 MY), yellow color—Pliocene epoch (between 1.806 and 5.332 MY), and orange color—Miocene epoch (≥ 5.332 MY). The Pines seed radiation molecular markers as INDEL (top) and nuSSR (bottom) shown average low migration intensity of ≈ 10 thousand individuals per migration wave, but the pollen radiation marker as cpSSR (middle) average high migration intensity of ≈ 50 thousand individuals per migration wave. The used 3 molecular markers shown different phylogenetic memories: longest for mt-INDEL, following by cpSSR and shorten for nuSSR. Note: The horizontal axis for each chart is the time by mutation rate. The time units are different for the different molecular markers, respectively; average time span for each migration wave is different number of generations for each chart. The result from the middle and bottom charts is from Naydenov et al. (2014; 2017)
Here, from macrophylogeographic mtDNA empirical data, we propose a scenario for the evolution and speciation of two important forest trees, European black pine and Scotch pine, and their multiple subspecies and varieties. Molecular clock simulations revealed that INDEL variability in the Pinus mitochondrial genome is relatively old, i.e., from the Pliocene-Miocene epoch, and related to historical tectonic continental fluctuations rather than to climate change at a large geographic scale. For conservation and management biodiversity program recommendations, special attention is given to the relationships between different speciation models, historical migration patterns, and differences between peripheral and central populations. Species evolution involves the mixing of different speciation modes, and every speciation mode has different effects on different DNA types (e.g., mitochondrial vs. chloroplast vs. nuclear DNA). The misbalance between the contributions of different meta-population census sizes vs. effective population sizes to asymmetric migration patterns is the result of different genotypes (and subphylogenetic lines) responding to selection pressure and adaptive evolution. We propose initial minimal size of conservation unit (between 3 and 5 ha) from central and marginal natural area of distribution for both species in the dynamic management system for practical forest genetic diversity management. The proposed physical sizes was determine by the effective population size, effective radius of seed distribution data, forest density age dynamics, succession pattern, natural selection pressing and species biology [R-17].
 
This study develops a stochastic dynamic model to optimize site value from timber and non-timber benefits for a landowner in the southeast United States who integrates wildfire risk and fuel accumulation into forest management and fire prevention decisions. The derived model determines optimal fuel treatment frequencies, timing, and level simultaneously and as a function of fire risk and fuel biomass dynamics under a range of economic and biophysical conditions. The landowner’s optimal prevention decisions are highly dependent on the type of fuel biomass growth and the association between fire arrival rate and fuel accumulation, which can vary across a broad forest landscape. Results indicate that policymakers should develop their management strategies based on their long-run objectives and fuel accumulation patterns, and these strategies should vary in timing and effort level within each rotation.
 
The presented study focuses on the impact of deadwood on surface water run-off, which was examined under laboratory conditions. In total we performed 600 rainfall simulations with harvest residues (wood with maximum length of 1 m and maximum diameter of 7 cm) that were either fresh (collected immediately after the harvest) or old (3 years and 3 months after harvest). The research analysed the impact of different values of deadwood coverage (15%, 30%), direction of its spatial arrangement (along the contour line, along the slope, random), moisture and decay stage (fresh, old) of deadwood situated on the slope with different inclinations (1% and 25%) under different rainfall intensities (5, 20, 40, 80 and 150 mm/h) on water run-off. The obtained results confirmed the significant impact of terrain slope on water run-off. The run-off from 1% slope represented 32% of the run-off observed from 25% slope. From the point of deadwood coverage, we found the fastest run-off at the smaller coverage of 15%, while in the case of 30% deadwood coverage, the run-off was only 75% of the value for 15% coverage. Decay stage of deadwood had also a significant impact on water run-off, which was by one third lower in the case of old deadwood in comparison to fresh wood. The water run-off was the fastest in the case of the spatial arrangement of deadwood along the contour line, and the slowest in the case of randomly distributed deadwood in all directions.
 
We analyzed growth trajectories recorded in the tree-ring series of Norway spruce Picea abies (L.) H. Karst. and silver fir Abies alba Mill. co-occuring with European beech Fagus sylvatica L. in old-growth forests driven by natural stand dynamics. The study sites were localized in five old-growth stands in the Western Carpathians (Central Europe). We characterized the life histories of 218 individual trees by using 25 metrics which refer to the age of the trees, number of release events, reaction to releases, radial increment and basal area increment. We found a large variation in the dbh-age relationship. The life histories of most trees included two or three (in single cases up to seven) release events. We did not find tree age as an important factor in determining post-release growth response. The maximal basal area increment was frequently registered at the terminal stage of tree life. The life histories of spruces and firs did not significantly differ. We concluded that in natural forests driven by gap-phase dynamics, the history of release events is the primary driver of tree growth and that tree age plays a secondary role. After reaching the overstory, trees can continue growing without significant symptoms of aging until extrinsic forces cause their death. Our results indicate that in the studied ecosystem the persistence of less shade-tolerant spruce is not attributable to the niche differentiation and site partitioning mechanism. An alternative hypothesis based on shifts in stand densities, species composition and climatic factors is more probable.
 
Texture in the A horizons of the studied soils
Results of PCA carried out for all studied stands in the O and A horizons for the following variables: fractional composition Cdec, HAs, FAs and HUs expressed as a % of TOC, the E4/6 quotient, HAs components, i.e. C, H, N, O and NMR parameters Calip, Carom, Ccarb
Cluster analysis (Ward method, Euclidean distance) carried out for all studied stands in the O and A horizons for the following variables: fractional composition Cdec, HAs, FAs and HUs expressed as a % of TOC, the E4/6 quotient, HAs components, i.e. C, H, N, O and contents of Calip., Carom., Ccarb. based on ¹³C-NMR analysis
A chronosequence approach was applied to evaluate the effects of silver birch succession on soil organic matter (SOM). The studies covered five plots (arable field [AF], fallow [FA] and three birch stands aged 8, 33 and 40 years), and all located in the same complex of Brunic Arenosols in central Poland. The O and A horizons of the soils were sampled and analysed using the standard procedures in soil science. It was found that the birch succession was accompanied by dynamic changes in the stock and quality of the SOM. The transition from AF to FA soils did not significantly change the content or pool of SOM in the A horizon; however, it did modify its fractional composition and internal structure. This was reflected by an increase in the humic acids content and a decrease in the fulvic acid, as well as in the values of the elemental and ¹³C-NMR analyses. Rapid losses in the SOM content and stock in the A horizon were recorded after entering the silver birch. The soils under the young birches were characterised by lower contents of low-molecular humus fractions, which are more susceptible to microbial degradation, than the FA soils. In addition, the birch succession contributed to a lower internal oxidation of the humic acids and an increase in the content of aliphatic structures in their molecules. The next stages of succession were characterised by gradually increasing SOM contents and stocks, accompanied by the increasing internal oxidation and maturity of the humic acids.
 
Impacts of climate warming on forests vigour are forecasted to increase in magnitude. Yet it remains unclear how stand characteristics and competition modulate the relationship between tree growth and gross primary production with drought. Here, we studied how the spatial variation in stand density, basal area and height modulates tree growth (Basal Area Increment, BAI and stand growth), summer NDVI, as well as their responses to drought (Standardized Precipitation-Evapotranspiration Index, SPEI) in 56 Aleppo pine ( Pinus halepensis Mill.) planted forests located in Northeast Spain. Long-term BAI responses to SPEI were strongly determined by stand density, suggesting that competition modulates Aleppo pine growth responses to drought. Along this, summer NDVI also displayed strong associations with SPEI. NDVI was mostly related with stand growth, suggesting canopy densification drives NDVI pattern and trends. Short-term BAI and NDVI responses to severe droughts were mainly independent of stand characteristics. In the studied region, drought is a universal factor limiting Aleppo pine secondary growth and canopy greening. However, the results suggest that stand density modulates Aleppo pine growth responses to drought on the long-term, reducing the growth in densest stands. Denser stands with larger trees are the ones that present higher NDVI values, suggesting that canopy activity depends more on stand canopy coverage than on secondary growth rate and its response to drought. In these Mediterranean pines, canopy activity and secondary growth are temporally coupled but spatially decoupled.
 
Photodegradation can play a key role in litter decomposition under the context of climate change which hinders organic matter turnover because of available water scarcity. Here, we aimed at testing the effect of a two-month sunlight exposure with different radiation intensities (either in winter or summer) on the chemical signature of two typical Mediterranean species, i.e., Quercus ilex and Q. pubescens. We also tested whether the side of the leaf exposed mattered in the chemical modification observed. To do so, two holistic chemical approaches, FTIR-ATR (Fourier transform infrared–attenuated total reflectance) and solid-state NMR of ¹³C, were used. ANOVA from solid-state NMR of ¹³C revealed that after exposure in summer, certain markers of lignin (phenol and aromatics) decreased in leaves whatever the Quercus spp. and it depended on the side of the leaf exposed. Lignin transformation thus occurred via dearomatization and/or dephenolization. Moreover, for both species, when leaves were exposed at their topside, their NMR chemical signatures were negatively correlated with alkyl assigned to cutin and waxes, showing that the thin layer of cuticle was attacked by photodegradation. FTIR-ATR spectra and NMR data also highlighted that a weaker irradiation (winter vs summer exposure) strongly limited lignin content decrease. Finally, lignin, cutin and wax oxidation, by enhancing the availability of polysaccharides from lignocellulose, may favor further litter transformation when suitable climate conditions (mainly humidity) are recovered.
 
A Study area in the Jeseníky Mountains, northern Czech Republic, with sampling sites indicated on the background layer derived from regional forest development plans (forest areas in green), based on a digital shading model of the Czech Republic; PL = Poland; B location of the Czech Republic within Europe; C location of the study area in the Czech Republic; D example of sampling design within a forest stand
Vertical distribution of metals in the soil profile. Different uppercase letters indicate significant differences between forest types, while different lowercase letters indicate significant differences between sampling depths within a forest type; boxes represent quartiles, red crosses represent arithmetic means, points represent mean values at a site (differentiated by colour), with point size proportional to the in-site standard deviation (n = 7)
The objective of this study was to assess the influence of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst.) on the vertical distribution of Cd, Cu, Pb and Zn in forest soil. Soil samples were taken from six beech- and six spruce-dominated mature (80–100-year-old) forest stands. In total, 420 composite soil samples were collected from the organic horizons, and at depths of 0–2, 2–10, 10–20 and 20–30 cm in the mineral soil, of 84 plots in a hexagonal sampling design. A direct influence of forest type was confirmed for Zn, which showed increased soil accumulation under beech. In spruce stand soils, Zn is likely to have leached more due to lower pH levels. While a minor influence of tree species on the vertical distribution of Cd, Cu and Pb was also confirmed, particularly as regards accumulation in the F + H layer of spruce stands, the results suggest a more dominant effect of other site-specific conditions at the scale studied, such as topography and atmospheric deposition, despite homogenous forest stand conditions. Furthermore, the C:N ratio had a significant impact on both Cd and Cu content, regardless of forest type, highlighting the importance of specific site conditions for driving decomposition of organic matter, a primary factor affecting Cd and Cu mobility in soil.
 
With progressing climate change, increasing weather extremes will endanger tree regeneration. Canopy openings provide light for tree establishment, but also reduce the microclimatic buffering effect of forests. Thus, disturbances can have both positive and negative impacts on tree regeneration. In 2015, three years before an extreme drought episode hit Central Europe, we established a manipulation experiment with a factorial block design in European beech ( Fagus sylvatica L.)-dominated forests. At five sites located in southeastern Germany, we conducted three censuses of tree regeneration after implementing two different canopy disturbances (aggregated and distributed canopy openings), and four deadwood treatments (retaining downed, standing, downed + standing deadwood and removing all deadwood), as well as in one untreated control plot. In addition, we measured understory light levels and recorded local air temperature and humidity over five years. We (i) tested the effects of experimental disturbance and deadwood treatments on regeneration and (ii) identified the drivers of regeneration density as well as seedling species and structural diversity. Regeneration density increased over time. Aggregated canopy openings supported species and structural diversity, but reduced regeneration density. Tree regeneration was positively associated with understory light levels, while maximum vapor pressure deficit influenced tree regeneration negatively. Deadwood and browsing impacts on regeneration varied and were inconclusive. Our study indicates that despite the drought episode regeneration in beech-dominated forests persisted under moderately disturbed canopies. However, the positive effect of increased light availability on tree regeneration might have been offset by harsher microclimate after canopies have been disturbed.
 
Growth ring analysis of B. longifolia trees on the polluted and unpolluted sites. The horizontal line indicates the average MAI at the polluted site, while the vertical line represents a dry year
Anatomical characteristics of B. longifolia naturally growing in copper mining polluted [a] and unpolluted [b] environments
Changes in wood cell dimensions caused by copper mining pollution-induced heavy metal toxicities. Letters indicate statistically significant differences
Effect of wood cell characteristics and heavy metal concentration on wood density
Vulnerability of B. longifolia wood cells to copper mining pollution-induced metal toxicities. Letters indicate statistically significant differences
The soil in the area surrounding copper mines is often highly contaminated by mining-induced heavy metal pollution. This study investigated the effect of metal-induced stress on the anatomical characteristics of native Brachystegia longifolia Benth trees naturally growing in a polluted environment around Mufulira in northern Zambia. Annual growth rings, cell dimensions, wood density and vulnerability indices were assessed from wood extracted from trees growing in a contaminated and uncontaminated sites. Significant differences were observed between the study sites in the basic wood density and anatomical characteristics. Growth rings and cell dimensions were generally smaller at the Cu- and Fe-contaminated sites. The percentage reductions in cell dimensions at the polluted site accounted for 47% fibre wall thickness, 27% fibre length, 24% fibre diameter, 27% vessel length, 23% vessel diameter and 39% in axial parenchyma cells. An average wood density of 0.52 and 0.61 g/cm³ was recorded at the control and polluted site, respectively, representing a 17% increase in the heavy metal-contaminated environment. Furthermore, significantly lower vulnerability (47%), mesomorphic (54%) and fibre/vessel (40%) ratios were observed at the polluted site. These results confirm that copper mining pollution-induced heavy metal stress alters the anatomical characteristics of B. longifolia wood, which can affect the sustainable utilization of B. longifolia trees naturally growing in heavy metal-polluted environments.
 
Effect of thinning-derived deadwood on the soil organic carbon (SOC) content (A), total nitrogen (Total N) content (B), carbon to nitrogen ratio (C:N) (C), and extractable carbon fraction in soil organic carbon expressed in % (D) of the studied temperate spruce forest in Kulmbach, Bavaria, Germany (factorial ANOVA test at α = 0.05, n = 4). P-values ≤ 0.05 indicate a significant effect. Error bars show the standard error of the mean
Effect of thinning-derived deadwood on the soil extractable carbon (DOC) (A), β-glucosidase activity (Vmax) (B), chitinase activity (C), and cellobiosidase activity (D) of the studied temperate spruce forest in Kulmbach, Bavaria, Germany (factorial ANOVA test at α = 0.05, n = 4). P-values ≤ 0.05 indicate a significant effect. Error bars show the standard error of the mean
Effect of thinning-derived deadwood on the soil microbial biomass carbon (MBC) content (A), microbial biomass nitrogen (MBN) content (B), microbial biomass carbon to microbial biomass nitrogen ratio (MBC:MBN) (C), and microbial biomass carbon in soil organic carbon expressed in % (D) of the studied temperate spruce forest in Kulmbach, Bavaria, Germany (factorial ANOVA test at α = 0.05, n = 4). P-values ≤ 0.05 indicate a significant effect. Error bars show the standard error of the mean
The studied thinned spruce forest located in Kulmbach, Bavaria, Germany (A), the perpendicular position of the deadwood log and the organic soil layer underneath (B), and white-rot fungi on the deadwood log shown by the red ellipse (C)
Deadwood is a key component of forest ecosystems, but there is limited information on how it influences forest soils. Moreover , studies on the effect of thinning-derived deadwood logs on forest soil properties are lacking. This study aimed to investigate the impact of thinning-derived deadwood logs on the soil chemical and microbial properties of a managed spruce forest on a loamy sand Podzol in Bavaria, Germany, after about 15 years. Deadwood increased the soil organic carbon contents by 59% and 56% at 0-4 cm and 8-12 cm depths, respectively. Under deadwood, the soil dissolved organic carbon and carbon to nitrogen ratio increased by 66% and 15% at 0-4 cm depth and by 55% and 28% at 8-12 cm depth, respectively. Deadwood also induced 71% and 92% higher microbial biomass carbon, 106% and 125% higher microbial biomass nitrogen, and 136% and 44% higher β-glucosidase activity in the soil at 0-4 cm and 8-12 cm depths, respectively. Many of the measured variables significantly correlated with soil organic carbon suggesting that deadwood modified the soil biochemical processes by altering soil carbon storage. Our results indicate the potential of thinned spruce deadwood logs to sequester carbon and improve the fertility of Podzol soils. This could be associated with the slow decay rate of spruce deadwood logs and low biological activity of Podzols that promote the accumulation of soil carbon. We propose that leaving thinning-derived deadwood on the forest floor can support soil and forest sustainability as well as carbon sequestration.
 
In exotic coniferous plantations established in treeless environments, light availability is drastically reduced, limiting the development of the native herb–shrub layer and consequently ecosystem functions and services. However, plants exhibit different responses to deal with changes in the light environment. Aiming to contribute to management guidelines favoring understory vegetation persistence in forest plantations, we evaluated, under nursery trial, the growth of three representative species of the Patagonian steppe at 20, 60, and 100% irradiance. For each species, we compared, among treatments, total biomass, biomass allocation, and specific leaf area several times during two growing seasons, relative growth rate, net assimilation rate, and leaf area ratio at each time interval, and reproductive structures the second growing season. Berberis microphylla and Adesmia volckmannii maintained their total biomass at 60% irradiance, with A. volckmannii showing a tendency to increase it, whereas Poa ligularis tended to decrease total biomass at irradiances below 60%. For the three species, changes in biomass allocation, generally higher leaf mass fraction, and higher specific leaf area were detected at 20% and sometimes at 60% irradiance. Relative growth rate and net assimilation rate, in general, tended to be higher at 60 and 100% irradiance, whereas leaf area ratio was higher at 20% and sometimes at 60% irradiance. Adesmia volckmannii and P. ligularis had fewer reproductive structures at 20% irradiance. These results suggest that the analyzed species present a certain level of shade tolerance, at least up to 60% irradiance, that may benefit their development in forest plantations with appropriate management.
 
Forest fragmentation is one of the main factors leading to biodiversity loss and negatively affecting arthropod communities. We analyzed the effects of forest fragment size and habitat type (forest edge x interior) on the canopy arthropod diversity of Quercus deserticola in the Cuitzeo Basin in Mexico. Six forest fragments where Q. deserticola occurs were selected and classified as (i) small (≤ 10 ha); (ii) medium (≥ 25 ha); and (iii) large (≥ 65 ha). In each forest fragment, ten trees were randomly selected: five at the edge and five in the interior of the fragment to sampled canopy arthropods using fogging techniques. We collected 12,739 arthropods representing 716 morphospecies grouped into 155 families and 16 orders. Differences in canopy arthropod community and species diversity were detected between fragment sizes. Canopy arthropod diversity was greater in Q. deserticola individuals from small fragments and the edges of fragments than in larger fragments and in the interior of fragments. Small fragments had highest phytophages diversity and lowest parasitoids and predator's diversity. The opposite pattern was observed in large fragments. Our results confirm that fragment size and edge effects modify canopy arthropod diversity of Q. deserticola, disrupting interactions between guilds and trophic levels probably by bottom-up and top-down forces. We highlight the importance to conserving large fragments to maintain the unique arthropod community that is sensitive to the disruption of ecological interactions and functions in Mexican temperate ecosystems, which constitute the main center of diversification and endemism of oaks in the northern hemisphere.
 
Mixed-species plantation forests are of high interest both because of their potentially superior productivity and multi-functionality benefits over monocultures. However, how trees of different species interact at the canopy level in mixed forests remains unclear, even at young growth stages. We tested whether crown shape and size and stand-level canopy packing were affected by stand composition and how mixture effects varied with stand density and irrigation. We measured crown attributes in pure and mixed plots of two light-demanding species, silver birch (Betula pendula Roth) and maritime pine (Pinus pinaster Ait.), in a 10-year-old tree diversity experiment (ORPHEE). This allowed us to estimate tree-level crown volumes and stand-level canopy packing. We found that (i) at the tree level, stand composition influenced crown-stem allometric relationships in pine but not in birch, (ii) mixture led to greater crown and tree dimensions in pine, but to the opposite for birch, (iii) the changes in crown volume resulted in a higher canopy packing in mixed stands, only at high density and with no irrigation, i.e., under highest constraints for light availability but also soil water availability, contrary to initial expectations. This study sheds light on the effects of water constraints on the aboveground mechanistic processes that explain greater productivity in young mixed plantations, and improves our understanding of canopy packing in mixed stands.
 
Chinese pine (Pinus tabuliformis Carr.) is an important ecological and timber coniferous species endemic to China. In northern China, there are vast areas of plantations and natural forests of Chinese pine, but it is unclear the genetic diversity, genetic structure, and germplasm sources of artificial populations, as well as the genetic relationship between them. Here, using nine nuclear simple sequence repeats markers, we analyzed 1310 individuals representing 38 populations of main natural and artificial populations in northern China (Shanxi, Hebei, and Liaoning provinces). The results suggested that the population from “Taiyueshan” was the core of the natural populations of Shanxi Province. We found that there were geographical effects among Chinese pine populations, and there was a relatively stronger gene flow among Chinese pine populations with close distances (between natural and artificial populations). We confirmed that most of the germplasm of the plantation populations of Hebei and Liaoning probably came from the Shanxi natural populations, and the new adaptive variations and the strong gene flow “driving force” from local natural populations had brought the opportunity for Shanxi germplasm to invade Hebei and Liaoning provinces successfully. Our findings provide a theoretical basis for the scientific allocation, management, and utilization of Chinese pine germplasm resources and promote the efficient cultivation of artificial populations.
 
Crown width (CW) is an important individual tree variable commonly used to assess tree vigor and the production efficiency of stands. However, our understanding of the effects of climate and the combined effects of climate with competition on the variation of CW remains unknown. Therefore, this study developed CW models by nonlinear mixed-effects (NLME) to explore these effects. Data were obtained from Korean pine (Pinus koraiensis Siebold and Zucc.) plantations in five forestry agencies in northeastern China. The results showed that stand basal area (BA), height to crown base (HCB), isothermality (BIO3), and annual precipitation (BIO12) were significantly related to the variations of CW. CW increased with increasing BIO12, while decreased with increasing BA, HCB, and BIO3. The hierarchical partitioning (HP) analysis showed that the relative importance of BIO3 was larger than BA, HCB, and BIO12. In addition, we found that competition altered the variations of CW responses to climate. Competition, tree size, and climate CW model (CC-CWM) performed the best performance in model fitting and prediction accuracy. Therefore, CC-CWM was selected to predict CW under future climate change. By comparing the eleven sampling methods with eighteen sample sizes, it was reasonable to select six medium-trees to estimate the random effect parameters. Our study provides evidence of the effects of climate and the combined effects of competition and climate on the variations of CW, potentially useful for the development of rational and scientific forest management decisions under future climate changes.
 
Structure analysis: bar plots representing mean membership coefficients for the major modes for K = 2, K = 3 and K = 7 merged with CLUMPAK (Kopelman et al. 2015), drawn with STRUCTURE PLOT (Ramasamy et al. 2014). Populations: 1 = seed orchard Voigtsdorf (green); 2 = seed orchard Niederfinow (green); 3 = seed orchard Harsefeld (green); 4 = seed orchard Beerwalde (“grey”, see Pakull et al. (2021) for seed orchard description); 5 = mixed stand Mitterfels; 6 = mixed stand Mirow; 7 = seed stand Chorin (green), 8 = seed stand Morschen (green); 9 = seed stand Drebkau (green); 10 = seed stand Romrod (green, see Wojacki et al. (2019) for seed stand description). Cluster 2 corresponds to the blue variety and is shown in blue, Cluster 1 and 3–7 correspond to different subclusters of the green variety and are shown in different shades of green
Spatial positions of 240 trees of the stand Mirow. Each dot represents a tree. Dot size varies in relation to determined DBH (not to scale with tree distance). Dot colour indicates STRUCTURE cluster assignment at K = 3 (cluster 2: blue, cluster 1 and/or 3: green, unclear cluster assignment (P < 0.7): turquoise). Pollination partners of three trees used for seed harvest (104, 119, 132) are represented by lines drawn between seed and pollen parent. Thickness of the lines varies in relation to the number of observed pollinations
Spatial positions of 60 trees of the stand Mitterfels. Each dot represents a tree. Dot size varies in relation to determined DBH (not to scale with tree distance). Dot colour indicates STRUCTURE cluster assignment at K = 3 (cluster 2: blue, cluster 1 and/or 3: green, unclear cluster assignment (P < 0.7): turquoise)
Pollination distance, percentage of pollination events within a certain distance between seed and pollen parent
Adult individuals and seeds of two mixed stands of coastal and interior Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) were analysed for genetic differentiation between the two varieties and evidence of intervarietal pollination. Clear genetic discrimination between the two varieties was observed based on multilocus evaluation of nine microsatellite markers using other Douglas-fir stands of known variety composition for comparison. Analysis of pollination distances showed that 80% of pollinations took place within a distance of about 44–55 m. Analysis of stand structure showed clearly separated areas of mainly coastal or interior Douglas-fir within both stands. Together with short pollination distances this led to an apparent dominance of intravarietal pollinations. However, analysis of pollination partners of trees growing near the border of the variety specific areas, does not indicate the existence of reproductive barriers between trees of the two varieties growing in mixed stands. Therefore, commercial seed harvesting in mixed stands should be avoided if the production of seed lots of pure coastal or interior Douglas-fir is intended.
 
Map of Brazil with the remnants of the Atlantic Forest, highlighting the states and the spots where the populations of the tree species in this study were collected
Partition of genetic diversity components after analysis of molecular variance (AMOVA) for adult and juvenile stages of the tree species under study
Effect of the number of individuals sampled in the population on the number of alleles for the ontogenetic stage of adults (a) and juvenile (b) of the tree species under analysis. Black lines correspond to the best-fit model (see Table S2)
Understanding populational genetic diversity is crucial for making proper decisions about conservation and sustainable species management. In this work, we overviewed the conservation genetics of economically exploited tree species that are vulnerable to extinction in the Atlantic Forest of Brazil. For this, data on genetic parameters from research on 10 species of evergreen trees dwelling in that environment were compiled. Genetic variability differences between young and adults were assessed when data were available for both stages. Very low values observed for the probability of identity (PI) suggested that the SSR markers used had sufficient statistical power to consistently evaluate genetic variability of the populations. An innovative analytical approach using linear mixed-effect models revealed an integrated influence of the number of individuals sampled per population and the number of SSR markers on the output of the genetic estimators assessed. A large number of different alleles (NA) were observed in four out of the 10 species, indicating these populations may still hold unique and rare alleles. HO was smaller than HE for all but one of the studied species, suggesting higher numbers of homozygotes than expected. Comparison of data between ontogenic stages suggested that the time frame of habitat loss and fragmentation was not yet sufficient to cause significant loss of genetic diversity and differentiate populations. Our findings are discussed considering that intensity and duration of selective lodging and economic exploitation appear to be crucial for the underlying ecological patterns and for the definition of proper diversity conservation strategies.
 
Distribution of sampled populations of European white elm in Bavaria (codes on the map correspond to the codes in Table 1). The size of the circle corresponds to actual population size
The plot shows the inferred structure clusters (K = 2) (soft. STRUCTURE 2.3.3). In the CLUMPAK plot, every individual is represented by a thin vertical line divided into K = 2 colored segments that represent the individual’s estimated membership fractions in these two clusters. Black lines separate different populations. The first cluster (orange) displays the clear separation of the U. glabra (No. 19 seed orchard of wych elm) and U. minor (No. 20 field elm Landshut) groups, and the second cluster (blue) indicates the group of U. laevis
Histogram of the genetic structure of European white elm in Bavaria based on Bayesian clustering with STRUCTURE2.3.3 software (Evanno et al. 2005). The four colours represent different STRUCTURE clusters. Populations are separated by vertical lines and identified on the X-axis by numbers (each individual is a separate colour line). The column height of each colour in the Y-axis corresponds to the probability of individual assignment to a different cluster separated by the STRUCTURE software. Structuring performed based on 12 nSSR loci for K = 4
Population genetic structure based on Bayesian clustering (STRUCTURE2.3.3). The pie charts show the relative proportions of four STRUCTURE clusters
The relative migration network shows all relative migration rates (Nm). To test if migration is significantly higher in one direction than the other (i.e. asymmetric) 95% confidence intervals were calculated from 1000 bootstrap iterations (R-package diversity)
The ecological importance of scattered tree species such as elms (the European white elm, the wych elm and the field elm) is widely recognized in Europe. The European white elm, along with other elm species, is important as part of the traditional landscape and as a tree with multiple uses. In Germany, a total of more than 825 white elm populations numbering approximately 138,000 trees have been inventoried. Most of the largest populations are closely associated with the main rivers and concentrated mainly in the northeast of the country. However, to date there has been a lack of knowledge on the genetic structure and diversity of European white elm populations in Bavaria (southern Germany). The aim of this study was to assess genetic structure and diversity and to select putative seed stands and gene conservation units (GCU) for European white elm. Nuclear microsatellite loci (nSSR) were first selected for successful elm species discrimination. Next, in order to represent the distribution range of European white elms in Bavaria, 18 populations were selected and sampled for genetic analysis with 12 variable nSSR loci. AMOVA revealed that genetic variation is mainly distributed within populations (89%), while only 11% occurred between them (FST = 0.11). Bayesian clustering indicated the highest probability for the presence of four genetic clusters (Delta K = 19.954 at K4) within the dataset. However, spatial genetic structure indicates a close link to the two main river basins in Bavaria (Main River basin and the Danube River basin). Thus, our results fill existing gaps in sustainable use and conservation of rare and scattered tree species by providing insights into genetic variation and genetic structure of the species and allow us to better plan genetic conservation measures and to select GCU and seed stands in Bavaria. We, therefore, suggest that in the future all putative seed stands or gene conservation units should be assessed based on several aspects, one of them being the level of genetic diversity, before final selection and use as a source of forest reproductive material (FRM).
 
Linked to climate change, drivers such as increased temperatures and decreased water availability affect forest health in complex ways by simultaneously weakening tree vitality and promoting insect pest activity. One major beneficiary of climate-induced changes is the European spruce bark beetle (Ips typographus). To improve the mechanistic understanding of climate change impacts on long-term beetle infestation risks, individual-based simulation models (IBM) such as the bark beetle dispersion model IPS-SPREADS have been proven as effective tools. However, the computational costs of IBMs limit their spatial scale of application. While these tools are best suitable to simulate bark beetle dynamics on the plot level, upscaling the process to larger areas is challenging. The larger spatial scale is, nevertheless, often required to support the selection of adequate management intervention. Here, we introduce a novel two-step approach to address this challenge: (1) we use the IPS-SPREADS model to simulate the bark beetle dispersal at a local scale by dividing the research area into 250 × 250 m grid cells; and (2) we then apply a metamodel framework to upscale the results to the landscape level. The metamodel is based on Markov chains derived from the infestation probabilities of IPS-SPREADS results and extended by considering neighbor interaction and spruce dieback of each focal cell. We validated the metamodel by comparing its predictions with infestations observed in 2017 and 2018 in the Saxon Switzerland national park, Germany, and tested sanitation felling as a measure to prevent potential further outbreaks in the region. Validation showed an improvement in predictions by introducing the model extension of beetle spreading from one cell to another. The metamodel forecasts indicated an increase in the risk of infestation for adjacent forest areas. In case of a beetle mass outbreak, sanitation felling intensities of 80 percent and above seem to mitigate further outbreak progression.
 
Respiration in a oak-hornbeam litter at ambient and higher temperatures and b mixed pine-oak litter at ambient temperature in the control, nitrogen (N), phosphorus (P), sodium (Na), and potassium (K) treatments estimated by GLMMs. Note that the litter of each forest type was collected at different times. In general, respiration was higher with increased temperature in oak-hornbeam litter and decreased with time in both litter types. The graphs show means estimated from GLMMs
Cumulative CO2 emissions released during the experiment from a oak-hornbeam litter at ambient and increased temperatures and b from mixed pine-oak litter at ambient temperature in the control, nitrogen (N), phosphorus (P), sodium (Na), and potassium (K) treatments. Note that the litter of each forest type was collected at different times. The graphs show means with 95% confidence intervals estimated from GLMs. Cumulative CO2 emissions were higher at increased temperature for oak-hornbeam litter
Response ratios (mean ± CI) of respiration in oak-hornbeam litter a at ambient and b increased temperatures and c in mixed pine-oak litter at ambient temperature calculated for the nitrogen (N), phosphorus (P), sodium (Na), and potassium (K) treatments. “⁕” below a marker denotes a significant effect of nutrient addition on respiration in relation to the control (α = 0.05)
At present, ecosystems are facing changes caused by global warming and anthropogenic impacts on geochemical cycles. Both temperature and nutrient availability affect litter decomposition; however, little is known about their simultaneous effect on litter decomposition in temperate forests, especially for nutrients such as Na and K. To address this perspective, we investigated how changes in N, P, Na and K supply and increased temperature affect litter decomposition measured as respiration. Moreover, the study determines what changes can be expected in the functioning of two forest types of different fertility (deciduous and coniferous). The respiration measurements were conducted in the laboratory in mesocosms filled with litter from deciduous (oak-hornbeam) and coniferous (mixed pine-oak) forests fertilized by N, P, K, and Na. The experiment was conducted at ambient (14 °C; oak-hornbeam and mixed pine-oak litter) and increased temperatures (22 °C; oak-hornbeam litter). The respiration of oak-hornbeam litter increased with increasing temperature, with Q10 values ranging from 1.49 to 2.14. Our results showed different responses of respiration to nutrient addition between temperatures and litter types. In oak-hornbeam, at 14 °C, the addition of N, P and K decreased respiration, whereas at 22 °C, such an effect was noted only under N application, and P and Na addition increased respiration. In mixed pine-oak litter at 14 °C, respiration decreased after Na addition, and other nutrients had no effect. Together, our results suggest that forecasting the impact of nutrient deposition on ecosystem functioning should consider temperature rise as a factor altering ecosystem responses to fertilization in future research.
 
Survival probability of acorns, for different treatments in 2017 (total of 240 acorns), 2019 (total of 480 acorns) and 2020 (total of 460 acorns). Treatment with large-size acorns is represented by blue line, treatment with medium-size acorns by green line and treatment with mixed-size acorns by red line. Shaded area indicates 95% confidence intervals
Seeds produced by individual plants often vary substantially in size. Typically, larger seeds produce seedlings that have higher chances of establishment and survival relative to seedlings produced by smaller seeds. However, larger seeds are also preferred by granivores due to larger caloric content. While choosing the patch to forage, granivores might avoid the ones with smaller, less preferred seeds. We tested a novel hypothesis that the production of different size seeds by a plant may be a strategy to decrease predation by granivores. We conducted a 3-year seed removal experiment. We presented Quercus robur acorns in forests in three configurations: large acorns alone, medium acorns alone, and large acorns mixed with small ones. The impact of seed size on seed survival was inconsistent: in the first year of the study, survival probability for seeds in the mixed treatment was significantly higher than survival probability of large seeds alone, supporting our hypothesis. However, in the following years, results were non-significant, probably because of reduced granivore selectivity in poor seed crop years. Our study demonstrated that the impact of neighbourhood of different size seeds seed survival varied over time in Q. robur. This provides limited evidence that intraspecific variation in seed size could evolve to shift the interaction between trees and scatter hoarders away from predation and towards mutualism.
 
SNFI2 plot distribution of the four mixtures in Spain. aPinus sylvestris – Pinus nigra, bPinus sylvestris – Pinus pinaster, cPinus sylvestris – Fagus sylvatica,dPinus sylvestris – Quercus pyrenaica
Overview of Shared Socioeconomic Pathways (SSPs) representing combinations of mitigation and adaptation challenges related to climate change [Figure extracted from O’Neill et al. (2017)]
Total CO2 stock (Mg · ha.⁻¹) simulation for the 2000–2100 period in the most realistic SSP scenario (SSP2)
Mean CO2 accumulation rates (Mg · ha⁻¹·year.⁻¹) for the different studied mixtures and tree fractions for the 2000–2100 period based on the intermediate scenario (SSP2)
Adapting forests to climate change is a critical issue for forest management. It requires an understanding of climate effects on forest systems and the ability to forecast how these effects may change over time. We used Spanish Second National Forest Inventory data and the SIMANFOR platform to simulate the evolution of CO2 stock (CO2 Mg · ha⁻¹) and accumulation rates (CO2 Mg · ha⁻¹ · year⁻¹) for the 2000–2100 period in pure and mixed stands managed under different Shared Socioeconomic Pathways (SSPs) in Spain. We hypothesized that (1) the more optimistic climate scenarios (SSP1 > > SSP5) would have higher CO2 stock and accumulation rates; (2) mixed stands would have higher CO2 stock and accumulation rates than pure stands; and (3) the behavior of both variables would vary based on forest composition (conifer–conifer vs. conifer–broadleaf). We focused on Pinus sylvestris L., and its main mixtures with Pinus nigra, Pinus pinaster, Fagus sylvatica and Quercus pyrenaica. The SSP scenarios had correlating CO2 stock values in which SSP1 > SSP2 > SSP3 > SSP5, ranging from the most optimistic (SSP1) to the most pessimistic (SSP5). Though pure stands had higher CO2 stock at the beginning, differences with regard to mixed stands were drastically reduced at the end of the simulation period. We also found an increase in the aboveground CO2 proportion compared to belowground in conifer–broadleaf mixtures, while the opposite trend occurred in conifer–conifer mixtures. Overall CO2 accumulation rates decreased significantly from the beginning to the end of the simulation period, but our results indicated that this decline would be less drastic in mixed stands than in pure ones. At the end of the simulation period, CO2 accumulation rates were higher in mixed stands than in pure stands for all mixtures, fractions (aboveground and belowground) and SSPs. Knowing the evolution of mixed forests in different climate scenarios is relevant for developing useful silvicultural guidelines in the Mediterranean region and optimizing forestry adaptation strategies. Better understanding can also inform the design of management measures for transitioning from pure stands to more resource efficient, resistant and resilient mixed stands, in efforts to reduce forest vulnerability in the face of climate change. This work highlights the importance and benefits of mixed stands in terms of CO2 accumulation, stand productivity and species diversity.
 
Fir species have been threatened by extreme weather and climate conditions in many parts of the Mediterranean Basin. However, there are almost no studies focused on the mortality of Taurus fir in the Eastern Mediterranean basin and Turkey. This study aims to quantify the mortality pattern of Taurus fir stands in Hadim Forest Enterprise from 1971 to 2016 and to assess this pattern considering the long-term trends and fluctuations in the observed climate data. To this end, spatiotemporal changes in forest cover were analyzed using historical stand type maps in GIS. Statistical and graphical time-series analyses were performed on observed climate data. As a result, rapid areal losses were detected in pure fir stands, even though the annual rate of forestation is 0.5% for the entire forest. More than half of the stands transformed into pure or mixed stands dominated by black pine. Both fir stands and the entire forest became much more fragmented and drought-induced deadwood remarkably increased in almost all fir stands. Regarding the climatic analyses, statistically significant increased trends (p < 0.01) were detected particularly in annual, summer, and autumn mean and average maximum and minimum air temperatures of the Hadim station; strong decreased trends were observed in all relative humidity series; and rapid warming in the surrounding region along Hadim was observed. In addition, series of the Aridity Index and the Standardized Precipitation-Evapotranspiration Index revealed that more arid conditions and significant droughts have dominated the study district since the 1990s. This period has been characterized mostly by long-term agricultural and hydrological droughts. We conclude that selective tree mortality events in the Hadim’s forests are likely caused by adverse impacts of observed climate variations and long-term droughts in the sub-region.
 
Location of the study area
Relationship between the available light and aboveground and belowground biomass for Scots pine (SP), black pine (BP), and Oriental beech (OB)
Relationship between the available light and height and shoot: root (S:R) ratio for Scots pine (SP), black pine (BP), and Oriental beech (OB)
Seedling growth as well as aboveground and belowground biomass allocation is mostly influenced by Light Transmittance (LT) (%) through the canopy. The knowledge of how understory light conditions affect seedling growth and biomass of different species in mixed forests is not well documented. Thus, it is essential to quantify the effects of light on the growth and biomass of understory seedlings. Given their advantages over pure forests, these quantitative understandings are especially crucial in mixed forests with species whose light demand and shade tolerance vary. This research examined the growth responses of natural-origin Scots pine (Pinus sylvestris L.), black pine (Pinus nigra Arnold.) and Oriental beech (Fagus orientalis L.) seedlings to LT (%) through the canopy in their mixed stands. Linear mixed-effect models were utilized to examine the influence of LT (%) on the seedlings. Moreover, allometric equations for estimating the aboveground biomass and belowground biomass of seedlings were developed for each species. Seedling height, and aboveground and belowground biomass after five years of germination were most significantly affected by LT (%) and tree species in the mixed pine-beech stand (p < 0.001). Biomass models for each species included different variable combinations of seedling height, root-collar diameter, LT (%), and their interactions. This study demonstrates the importance of canopy structure and overstory disturbances for the maintenance of mixed pine-beech forests since canopy structure significantly contributes to the understory light environment.
 
An example of the research material used in our analysis
Characteristics of analyzed features of the needles and shoots of nine Scots pine populations (horizontal bars in graphs represent statistically homogeneous groups calculated using the Tukey's test at the level of α = 0.05)
Dendrogram of pine populations constructed by the Ward’s clustering method
Tree provenance trials are believed to be a valuable tool for assessing the adaptive potential of a population to a changing environment and ultimately for predicting the populations that are best adapted to global warming. Here, the phenotypic plasticity of morphometric traits of needles and lateral shoots of pines growing in a provenance plot in central Poland was examined to assess the inter- and intra-population variability. No significant differences were found in the measured and counted morphometric features, i.e., needle length (NL), cumulative needles length (CNL), thickness (ST), volume (SV) and shoot density (SD), number of needles per 5 cm fragment of shoot (NN), dry weight of needles (NDW) and shoot (SDW), thickness of bark (BT) and wood (WT), pith diameter (PD), and needle dry mass per area (LMA) among three pine populations while accounting for their region of origin (inter-population variability). In terms of the above-mentioned features, individual populations differed significantly from each other, except for NN and ST. We also noticed a positive, significant relationship between LMA and ST in all studied populations and based on Euclidean distances of measurable or counted traits, three population groups were identified. We concluded that LMA, which is commonly used to quantify leaf structure, is helpful in differentiating intra-population variability.
 
Visual representation of the sampling scheme. Left: locations of the 17 plots in the Białowieża Forest, Poland. Right: the sampling design within the plot. The dots denote the trees, with a different colour for each species and a size proportionate to the diameter at breast height. The crosses denote the sampling locations. In each of the 17 plots, two transects were laid out between two target trees (two of the same species in monocultures and two different species in mixtures). In each transect, we sampled at three locations: close to each target tree and once midway between the two target trees
Changes in concentration or ratio (C, C/N, Olsen P, pH-H2O, and base cations (BC)) in function of the distance (m) to the nearest tree within the transect. The lines show the model predictions of the concentration or ratio in function of the logarithmic distance and the shading shows the standard deviation. The dots show the observed concentration or ratio for each of the subplots with the colour denoting the location within the subplot (blue: close to a target tree; orange: midway between two target trees). Significance level of the distance-to-tree variable: p value =  < 0.001: ***; 0.001: **; 0.01: *; 0.05: n.s
Predicted percentage difference between the chemical composition (C, C/N, Olsen P, pH-H2O, and base cations (BC)) of the subplot close to a target tree (subplot of interest) and the subplot in the centre of that same transect. We predicted the percentage difference in function of the tree species of the target tree closest to the subplot of interest (near species: P = pine, O = oak, B = birch, H = hornbeam) and the other target tree (distant species) and their interaction effect and the logarithmic distance between the subplot of interest and the centre subplot. Note that the monoculture responses are plotted on the diagonal and have a larger linewidth. The predictions shown in the figure are of all species combinations in our study (note the absence of the combination birch and pine) and use the mean distance over all subplots. The hue denotes the direction of the difference with blue being positive and orange being negative. The intensity denotes the strength of the difference. Bottom-right: three of the species combinations are highlighted (monoculture of oak: (1), oak-birch mixture nearby oak: (2), and oak-birch mixture nearby birch: (3)). The concentration or ratio at the centre subplot is used as baseline, which makes the value 0% in the centre subplot. The slope denotes the difference in chemical composition between the subplot of interest (subplot closest to the near species and shown at the left-hand side of the graph) and the centre subplot (shown in the middle of the graph) and is dependent on the distant species (shown on the right-hand side of the graph) and the near species
Chemical variation in mixture transects. The grey violin plots and black dots show the observed concentration or ratio (C, C/N, Olsen P, pH-H2O, and base cations (BC)), where the left and right data points are observations of the subplots close to the target trees and the centre data points are observations in the centre subplot. The blue lines and the shaded area show the predicted mean and standard deviation based on the monoculture responses. We fitted the monoculture observations in function of the target species and the distance to the nearest target tree. Based on these model results, we predicted the expected mixture response using the proportion of the target species and the distance to the nearest tree of the respecting subplot
Trees have a large impact on the topsoil chemistry and the strength and direction of this impact depend on the identity of the tree species. Tree species with nutrient-poor litter have the potential to degrade soil fertility, which is characterized by high acidity, low availability of essential nutrients for plant growth, and high levels of available Al and Fe. In contrast, species with more easily decomposing, nutrient-rich litter can ameliorate the soil quality. In this study, we are investigating the effects of tree species identity on topsoil chemistry on a small spatial scale. Our study site, situated in Białowieża Forest in Poland, replicates mature monocultures and two-species mixtures, using a pool of four tree species. Soil was sampled at a metre distance to the base of a tree and in the centre along a transect between two trees. We found that the total C concentration, plant available P and base cation concentration, and C/N ratio were all larger close to the tree. The pH was unaffected by the distance. We identified clear species identity effects on this distance effect. In particular, we found that the pH and base cations were affected more negatively by the proximity to a tree nearby nutrient-poor trees in comparison with nutrient-rich trees. However, no non-additive diversity effects in mixtures could be distinguished. Our results highlight the ameliorating effects of admixing nutrient-rich species with nutrient-poor species and the importance of tree species choice in regard to the topsoil chemical composition on a small within-stand scale.
 
In the context of increasing heat periods and recurrence of droughts, and thus higher soil water depletion, we explored and quantified the role of understorey vegetation in ecosystem evapotranspiration in boreal and temperate forests. We reviewed and analysed about 200 papers that explicitly gave figures of understorey vegetation evapotranspiration relative to different stand features and traits. Understorey vegetation accounted on average for one-third of total ecosystem evapotranspiration during the growing season. Overstorey leaf area index (LAI) is the main variable that drives understorey evapotranspiration through radiation interception. Most data show that below an overstorey LAI of 2–3, the contribution of the understorey vegetation to ecosystem evapotranspiration increases exponentially, following the exponential increase of the climatic demand, i.e. potential evapotranspiration. Different factors have the potential to modulate this effect such as species composition and phenology, root distribution, and interaction with droughts. Consequently, managers must be aware that depending on understorey species present on site and stand structure, understorey vegetation can contribute significantly to a negative stand water balance.
 
Location of study area and distribution of sampling plots. Location of the Sant Llorenç del Munt i l’Obac Natural Park, with its border (orange line) in Catalonia (NE Iberian Peninsula), the 2003-burnt shape and size (grey), the historical (1970 and 1994) burnt areas (grated), and the forty 100 × 100 m plots, where black triangles correspond to unburnt forests, black circles to branches left on the ground, black squares to branches reduction, and white crosses to recurrent burnt areas (plots areas are out of scale). Burnt and protected perimeters was obtained from Sant Llorenç del Munt i l’Obac Natural Park managers (parcs.diba.cat/web/santllorenc)
Model predictions of plant production and habitat heterogeneity over time. Responses of a plant productivity (NDVI mean) and b habitat heterogeneity (NDVI standard deviation) to time since fire and each treatment (Unburnt forest, branches left on the ground, reduction of branches and recurrent fires). Marginal effects (i.e. measure the instantaneous rate of change) of the time since fire on the c plant productivity and d habitat heterogeneity. Trend line and standard error shown were obtained from model estimates
Model predictions of European wild rabbit abundance after fire and logging. Effects of the time since fire (short and long term) and treatment (Unburnt forest, branches left on the ground, branch reduction and recurrent fires) interaction on a European wild rabbit relative abundance (expressed as the density of pellets per m2 of transect). Marginal effects (measure the instantaneous rate of change) on b rabbit relative abundance by plant productivity (NDVI mean). Trend line and standard error shown were obtained from model estimates
of the selected generalized additive mixed models (GAMM), on plant productivity (NDVI mean), habitat heterogeneity (NDVI standard deviation) and European wild rabbit relative abundance (expressed as the density of pellets per m² of transect) in Sant Llorenç del Munt i l’Obac burnt area
Salvage logging treatments, a type of logging to economic returns after natural disturbance, are often applied in the aftermath of wildfires. Specialist or dependent species of open-habitat usually increase their populations in the short-term after wildfires and post-fire salvage logging. However, the long-term effects on threatened open-habitat species such as the European wild rabbit (Oryctolagus cuniculus L.) are still poorly known. Thus, plant productivity, habitat heterogeneity and rabbit abundance were studied in the north-east Iberian Peninsula in four type of post-fire treatment plots: (1) unburnt, (2) salvage logging with branches left on the ground, (3) salvage logging and manual removal of branches, and (4) recurrent fires. Both the time since the fire and the treatment affected plant productivity and habitat heterogeneity. Plant productivity was quicker in treatments when branches were left on the ground or when branches were removed than in recurrent fire plots. Rabbit relative abundance increased in the short term but dramatically declined over time after fires, especially in the plots where branches were left on the ground and with recurrent fires, in which rabbit abundances fell dramatically. In the long-term, the lack of food availability and adequate habitat structure are the main factors affecting the maintenance of the rabbit population. An appropriate moment for managing burnt areas to favour the persistence of rabbit is between the fifth and sixth year after the fire. These actions also benefit the reduction of environmental biomass and so help prevent future severe wildfires.
 
Natural regeneration and forest successional development are influenced by gap formation in forest stands. Nonetheless, there are limited studies that provide quantitative information on the influence of gaps on forest regeneration. We evaluated characteristics of inner and outer canopy gaps and their effects on natural regeneration in 40 canopy gaps in Sitapahar forest reserve of Bangladesh. A total of 50 individuals of 27 gapmaker tree species were found, of which 58% were formed by logging and the rest by natural damages. Elliptical shape represented 53% of the gaps followed by circular and rectangular gaps. The mean area of the outer and inner gaps was 50.1 ± 8.6 and 20.0 ± 3.0 m2, respectively. Gap formation types and shapes did not vary significantly between outer and inner gaps, while the mean gap area in older gaps was significantly higher than in new gaps. In comparison with outer gaps, mean densities of seedlings and saplings in the inner gaps were significantly higher, which is probably because of the closeness to seed trees. The diversity index of regenerating species and their height and collar diameter did not vary significantly between the inner and outer gaps. Positive, but weak relationships of gap area with subcanopy tree density and diversity were found. Since gaps were found dominated by few light-demanding tree species such as Brownlowia elata, Lithocarpus acuminata, Lithocarpus polystachya, and Macaranga denticulate, it is suggested that larger gaps need to be replanted with a combination of light-demanding and shade-tolerant native trees.
 
Relationship between tree species richness and soil organic carbon (SOC) stock in the study forest (n = 46). The shaded areas represent the 95% confidence intervals for the regression line
Structural equation modeling (SEM) analysis depicting the regulatory pathway of the controls of soil organic carbon (SOC) stock in the study forest (n = 46). The numbers adjacent to the arrows represent the standardized path coefficients. Solid lines indicate a significant positive (red) or negative (blue) piecewise relationship between variables (p < 0.05), and dotted lines indicate nonsignificant relationships between variables (p > 0.05). R.² indicates the total variation in the dependent variable explained by all independent variables. Fisher’s C statistic refers to the test of the overall model fit, where high p values indicate plausibility of the overall model. p < 0.05 (*), p < 0.01 (**), and p < 0.001 (***). (Color figure online)
Relationships between tree species richness and leaf litter biomass (a), fine root biomass (b), the relationships between fine root C/N ratio and tree species richness (c), soil organic carbon (SOC) stock (d), and the relationships between leaf litter C/N ratio and tree species richness (e), soil organic carbon (SOC) stock (f) in the study forest (n = 46). The shaded areas represent the 95% confidence intervals for the regression line
Canonical correspondence analysis (CCA) displaying the effect of environmental factors on the variance in the four chemical compositions of soil organic carbon (SOC) among eight tree species richness. Arrows represent environmental variables: litter alkyl C, litter aromatic C, fine root aromatic C, B_Chao. The symbols indicate a significant effect, p < 0.05 (*), p < 0.01 (**). The abbreviation of “B_Chao” represents the soil bacterial α-diversity
Relationships between the soil organic carbon (SOC) stock and SOC chemical compositions (O-alkyl C, aromatic C, carbonyl C, alkyl C/O-alkyl C ratio, and aromatic C/O-alkyl C ratio) in the study forest (n = 46). The shaded areas represent the 95% confidence intervals for the regression line
Despite recent evidence from inventories and experimental forests indicating that high species richness among trees increases productivity and further improves soil organic carbon (SOC) storage, the mechanisms controlling the richness–SOC relationship are inconsistent. Hence, the optimal tree species richness required to increase SOC stocks needs to be further explored. Based on field observations from a subtropical mixed-species planted forest, which was established 40 years ago through a mosaic pattern of afforestation and natural regeneration, we examined the effects of tree species richness on the SOC stock and the chemical composition of SOC in the topsoil (top 10 cm layer). We found a quadratic relationship between tree species richness and SOC stocks. The threshold of tree species richness appeared between four and five. Tree species richness affected the SOC stocks primarily by increasing the quantity of leaf litter, and while decreasing the quality of leaf litter and fine root. In addition, tree species richness changed the chemical composition of SOC by affecting the chemical composition of the plant carbon, and soil bacterial α-diversity, thereby affecting the SOC stock. The trade-off between leaf litter and fine root C sources contributed to the quadratic relationship between tree species richness and SOC stocks. These results show that the mixing of 4–5 tree species can achieve a higher SOC level than having fewer or more tree species in a planted subtropical forest.
 
A schematic drawing of the prototype CFDD
The machine at work in Western Slovakia
The two chain drums adapted for horizontal feeding
Delimbing quality obtained with a cut-to-length processor (left) and the prototype CFDD (right)
Results of the elemental time study
Small tree size represents a main challenge for single-tree handling techniques and caps harvesting productivity in short rotation poplar (SRP) plantations. That challenge is best met by a shift towards mass-handling. Chainflail delimbing is one of the best solutions for multi-tree processing, but commercially available equipment is often too heavy and expensive for European operations. Therefore, an Italian company developed a compact chainflail delimber-debarker (CFDD) specifically designed for small-scale SRP. The machine was tested in Western Slovakia in early March 2022. The test included a five-days endurance trial and a controlled experiment on 16 carefully measured wood piles representing “strong” and “weak” trees, i.e. trees with a mean diameter at breast height (DBH) of 12 and 10 cm, respectively. The endurance trial was quite successful since no mechanical problems were recorded during the five-days period. Delimbing and crosscutting quality were as good as those obtained with a standard processor head, while log yield was generally better, averaging 42% and 68% for the “weak” and the “strong” trees, respectively. Productivity was on a par with the alternative cut-to-length technology options and can be significantly increased once the prototype will be further developed. In general, the new compact CFDD may become the best option for handling the small trees offered by underdeveloped SRP plantations, which cannot be efficiently harvested with the cut-to-length system.
 
Model estimates for the impact of forest locations on the concentrations of cellulose and lignin in decaying logs (for details of the model’s results, see Table S1). The concentrations of cellulose and lignin were evaluated in different wood tissues under three different forest locations (canopy, edge and gap) for three subsequent years. Different lowercase letters indicate significant differences among forest locations (P < 0.05)
Effects of forest location on the relationship between cellulose and lignin concentrations in bark, sapwood, and heartwood. Different colored lines represent the regression lines between cellulose and lignin concentrations in different forest locations, with the equations being inserted
Effects of forest locations on the mass losses of cellulose and lignin in the decaying logs after the four years of decomposition. Different lowercase letters indicate significant differences among forest locations (P < 0.05)
Knowledge of the patterns in the degradation of cellulose and lignin in decaying logs under different climatic conditions is necessary to understand the carbon cycling in forest ecosystems since cellulose and lignin are the dominant carbon fractions in decaying logs. However, the effects of the environmental heterogeneity by variation in canopy cover on the degradation of cellulose and lignin in decaying logs remain unknown. To evaluate the effect of forest gaps, we measured the concentration and mass loss of cellulose and lignin in experimentally exposed decaying logs in gaps, at the edge of gaps, and under the closed canopy during a four-year in situ log incubation experiment in a subalpine Minjiang fir (Abies faxoniana) forest on the eastern Qinghai-Tibet Plateau, China. We found the lowest cellulose concentration in gaps for all wood tissues, while we observed the opposite for lignin except for bark. Based on the linear relationship between cellulose and lignin concentrations, the rate of lignin enrichment in bark and heartwood was slowest in gaps and fastest under closed canopy, while in sapwood gaps had almost no influence. The mass loss of cellulose was highest in gaps for all wood tissues in any decay classes. The gap effect on lignin mass loss in decaying logs showed high variability with wood tissues and decay classes. Our results show that forest gaps accelerate the degradation of cellulose and lignin during the decomposition of logs by increasing cellulose mass loss and slowing lignin enrichment. The observed gap effects were mediated by wood tissues but not by decay classes.
 
Geographical location of the 10 test plots in the Swiss canton of Grisons © swisstopo 2021. Coordinate System EPSG 21,781
The selected processing steps from the areas of data basis, filtering method and detection method. A total of 48 combinations of methods is possible
Each point shows the extraction rate and the commission error of one combination of methods averaged over all test plots once evaluated according to the data basis (A), the filtering method (B), the detection method (C), and the selection of the best method combinations (D)
(top panel) Each point represents the difference between the terrestrially measured tree height or position and the tree height or position derived from the canopy height model (CHM). The tree height differences and the distances between the detected trees and their assigned reference trees have been averaged over all test plots per combination of methods. (bottom panel) Each point represents the difference between the terrestrially measured tree height or DBH and the tree height or calculated DBH derived from the CHM. The differences between the measured and calculated tree heights, as well as between the measured and calculated DBH, are mostly positive
For the provision of various ecosystem services in steep terrain, such as protection against natural hazards, a forest must be managed, which often requires the use of cable yarders. The design of a cable road is a complex and demanding task that also includes the search for appropriate support and anchor trees. The aim of this study was to evaluate whether and with what reliability potential support trees for cable yarding can be detected using remote sensing data. The detection of potential support trees was tested using 48 method combinations on 10 test plots of the Experimental Forest Management project in cable yarder terrain in the Swiss Alps in the Canton of Grisons. The most suitable method combinations used a Gaussian filter and a local maxima algorithm. On average, they had an extraction rate of 108.9–124.5% (root mean square, RMS) and a mean commission error of 66.0–67.2% (RMS). The correctly detected trees deviated horizontally by an average of 1.8 to 1.9 m from the position of the reference trees. The difference in tree heights was 1.1 to 1.6 m. However, for the application of single tree detection to support cable road planning in steep and complex terrain, too few potential support trees were detected. Nonetheless, the accuracy of the extracted tree parameters would already be sufficient for cable road planning.
 
Retention of habitat trees is a common biodiversity conservation practice in continuous cover forests of temperate Europe. Commonly, living habitat trees are selected on the basis of their tree-related microhabitats (TreMs) such as cavities or crown deadwood. Owing to the increasing frequency and intensity of climate change-related disturbances, habitat trees in particular are expected to experience increased mortality rates. This may impact the long-term provisioning of TreMs. Here, we compared the TreM occurrence on living and dead trees to investigate whether dead trees support more and other TreMs than living trees. We also hypothesized that a combination of living and dead trees results in the most diverse stand-level TreM composition. We surveyed the TreM composition of living and dead habitat trees in 133 one-hectare plots in the Black Forest region managed according to a continuous cover approach. We fitted generalized linear mixed models to identify the main predictors of TreM occurrence to predict their abundance and richness. Tree identity (as a combination of species and vitality status) and diameter were the main drivers of TreM abundance and richness, which were highest on dead Abies alba. Even though dead A. alba and Picea abies supported TreM numbers similar to those provided by large living trees, their TreM composition was significantly different. This suggests that dead trees cannot substitute the habitat functions of living habitat trees, but they can complement them to increase the overall stand-level TreM diversity, in particular through decayed, large snags.
 
This study was conducted following the fires that took place in Rocallaura (Spain) between 23/06/2016 and 19/07/2017. The aim is to analyse the importance of soil on forest planning and management mechanisms to mitigate the impacts of forest fire re-ignitions on risk and management framework. The main factors found to influence the occurrence of re-ignitions in a forest ecosystem dominated by Pinus halepensis were weather conditions, possible future climatic changes, soil and subsoil biomass amount and the physico-chemical properties of the organic layer. The re-ignition dynamics were included in the study as a new parameter-fire persistence-to be considered in fire regimes. It is proposed that fire persistence should be included in strategic framework for integrating wildfire risk in forest planning. This will entail identifying and including the potential for re-ignition in fire risk maps and fire suppression policies and implementing forest management actions in areas vulnerable to re-ignition.
 
Slavonian oak ( Quercus robur subsp. slavonica (Gáyer) Mátyás) is currently gaining interest in forestry due to forest restructuring in Germany caused by climate change. Slavonian oaks originating from Croatia have been introduced into Germany mainly in the Münsterland region of North Rhine-Westphalia since the second half of the nineteenth century. They are characterized by their late bud burst, long clear bole, stem straightness and faster height and diameter growth compared to indigenous oaks in Germany. In this study, the genetic differentiation of adult trees and their respective progeny of two Slavonian and two indigenous stands in Hamm-Westtünnen, was evaluated. Genetic diversity and structure were estimated using 23 nuclear simple sequence repeat (SSRs) and 5 maternally inherited chloroplast microsatellite markers (cpSSRs). The mean expected heterozygosity of 0.545 and allelic richness of 6.23 indicate high genetic diversity in the studied populations. The group of progenies (A R = 8.40, H o = 0.524, H e = 0.559, F IS = 0.064) shows similar levels of genetic variation as the adult stands (A R = 8.37, H o = 0.513, H e = 0.554, F IS = 0.075). The genetic differentiation between adult stands and progeny was low (F ST = 0.013). Genetic assignment of individuals using STRUCTURE revealed that the studied populations were divided into two clusters. There was no evidence of extensive hybridization or gene flow between Slavonian and native populations, possibly due to the different timing of bud burst of the two taxa.
 
Variations in growth traits and climatic factors in different locations and ages. a and b: Box plots showing the differences between the three sites with pairwise comparisons by Wilcox test in the H (a) and DBH (b) groups. The whiskers mean 1.5 times the interquartile range above the upper quartile and below the lower quartile, but when there is no maximum or minimum value exceeding the upper and lower beard lines, the whiskers are the location of the maximum or minimum value. At each age, the same lowercase letter above the box plot means that there is no difference between two sites; otherwise, there is a difference at the 0.05 level. JDZ, JX and XS are the three tested sites in the text and are the same below. c: The heatmaps of different climatic indicators varied by age and site, and they included the annual average temperature (T), annual average daily maximum temperature (TM), average annual daily minimum temperature (Tm), average annual relative humidity (RH) and total annual rain precipitation (PP)
EBV ranking of families (left side for H, right side for DBH) at different ages (4, 5, 6, 7 and 8) and sites (JDZ, XS and JX). The small square in red indicates that its EBV value ranks high, and a darker shade indicates a higher or lower ranking
The additive genetic correlation (rA) between each pair of sites for the H (a) and DBH (b) varied with age
Scatter plots of HMRPGV of DBH vs. HMRPGV of H across ages. H4, H5, H6, H7 and H8 represent the H at ages 4, 5, 6, 7 and 8, respectively. DBH4, DBH5, DBH6, DBH7 and DBH8 also represent the DBH at ages 4, 5, 6, 7 and 8, respectively. The two dashed lines, which are separately perpendicular to the X and Y axes, represent the selection intensity of 30%. The red points located in the upper right part of the intersection of the two lines represent the families selected on both H and DBH by the value of the HMRPGV
GGE biplots of growth traits. The GGE biplots were created based on the adjusted phenotypic means by multiage-single-site analysis. AXIS1 and AXIS2 represent the first and second principal components (PCA 1 and PCA 2), respectively, and also indicate the variation explaining the proportion on each axis. The blue letters represent different sites, and the green letters represent the different families in each biplot. The blue and green lines with a small circle are average environmental vectors. a and d: “Which Won Where/What” biplots for H (a) and DBH (d). b and e: “Discriminativeness vs. representativeness” biplots for H (b) and DBH (e). c and f: “Mean vs. Stability” biplots for H (c) and DBH (f)
To select genotypes with stable growth in diverse environments, tree breeders use multisite trials to evaluate genotypic stability and adaptation. Since genotype-by-environment (G × E) interaction effects vary with age, most multisite trials focus only on site effects, ignoring age effects. Liriodendron tulipifera trees are valuable due to their rapid growth and high-quality wood. Currently, multisite trials involving L. tulipifera plants are rare and the lack of data on G × E interaction effects impedes its selection. In this study, to explore the better performance and G × E pattern of L. tulipifera across ages, the growth traits (tree height, H; and diameter at breast height, DBH) of trees that were of five consecutive ages and grown on progeny-testing plantations were studied for 27 open-pollinated families at three sites. The results showed that the heritability of DBH was greater than that of H at almost all ages, and the individual breeding value ranking differed across sites and ages. The additive genetic correlations (rA) between different site pairs were relatively small and varied with age, indicating an age trend for G × E, and showed a difference in traits. It was found that the absolute differences in some monthly average climatic indicators correlated with the G × E. Based on a comprehensive analysis considering stability and productivity, four elite families were identified. These results could aid in selecting stable, adaptable L. tulipifera genotypes and provide a reference for evaluating G × E interaction effects in multiage, multisite trials of other tree species.
 
The aim of the work was to quantify the mass of logging residues (branches and tops; t yr ⁻¹ dry matter, DM) for energy generation starting from Forest Management Plans (FMP) data. The methodology was applied to public stands of an Italian district (area: 3.60 × 10 ⁴ ha; period: 2009–2018). Compared to the previous preliminary analysis, the potentially available residues were computed considering forest accessibility and road traversability, by combining FMPs data with a geographic information system (GIS). New issues that were assessed here were: (i) representation of stands consisting of multiple disconnected parts; (ii) calculation of producible residues by using different values of biomass expansion factors (Scenario 1, S1; Scenario 2, S2). The potentially available residues computed for the analyzed period were used to quantify the current sustainable supply. Then, the potentially generated heat (thermal energy, TE; GJ yr ⁻¹ ) and electricity (EE; GJ yr ⁻¹ ), and the potentially avoided CO 2 emissions into the atmosphere (EM; t yr ⁻¹ CO 2 ) related to the final combustion process were computed by assuming that the current supply of residues was used as woodchips in a local centralized heating plant currently operating. For both S1 and S2, the large difference between the potentially producible and the potentially available residues demonstrated that geodata are essential for reliable estimations. Moreover, as the required information for the GIS analysis can be easily found in databases made available by forestry authorities, the proposed approach can be applied also to other areas; this could be helpful to support local decision-makers in defining sustainable practices for residues recovery.
 
Trade-offs between high stand productivity and good wood quality exist for chestnut coppices and related wood-based products. The main objective of this study was to determine the most suitable duration (in years) of cutting cycles that maximizes stand productivity and preserve wood quality of chestnut coppices in a Mediterranean setting. To this aim, a stand-level growth model was developed to verify if wood quality of chestnut coppices at different stand ages varies when the rotation period is modified. Wood quality and stand productivity were analysed, using a chronosequence approach, in coppice stands in Southern Italy characterized by four cutting cycles (15, 25, 30, and 50 years). Results implied that the culmination of the mean annual increment occurs at 28 years, while the current annual increment culminates 10 years earlier. The MOEd values revealed a negative correlation with shoot age; however, a cutting cycle between 25 and 30 years might represent the best compromise for balancing stand productivity and wood quality. Results are discussed in the context of adaptive forest management.
 
Seasonal variation in the (a) litterfall, (b) litter-C content, and (c) litter-C input under different litter treatments (mean ± SE, n = 3). LR, litter removal; CT, control; LA, litter addition. Different capital letters indicate significant differences among the seasons (p < 0.05). Different lowercase letters indicate significant differences among the litter treatments (p < 0.05)
Seasonal variation in the (a) fine root biomass and (b) C content under different litter treatments (mean ± SE, n = 3). LR, litter removal: CT, control; LA, litter addition
Seasonal variation in the root exudation of Pinus massoniana under different litter treatments (mean ± SE, n = 3). a Root exudation I (μg C g⁻¹ root biomass h⁻¹), b root exudation II (μg C cm⁻¹ root length⁻¹), and c root exudation III (μg C cm⁻² root area h⁻¹). LR, litter removal; CT, control; LA, litter addition. Different capital letters indicate significant differences among the seasons (p < 0.05). Different lowercase letters indicate significant differences among the litter treatments (p < 0.05)
Effects of litter treatments on plant-C inputs. The dark red, light red, and light gray arrows indicate a significant increase, significant decrease, and no significant difference in the C input among the different litter treatments, respectively
Redundancy analysis of the correlations between the plan-C inputs and soil properties under different litter treatments. LR, litter removal; CT, control; LA, litter addition. Black solid arrows represent plant-C inputs, and red hollow arrows represent soil properties. SOC, soil organic C; TP, total phosphorus; AP, available phosphorus; MBC, microbial biomass carbon; MBN, microbial biomass nitrogen
Plants are the main sources of soil organic carbon in forest ecosystems. Photosynthetic C assimilated by plants enters the soil through litter, root litter, and root exudates. However, it remains unclear how litter changes affect the plant-C input. We aimed to quantify the responses of C inputs via the litter, root litter, and root exudates to litter alteration. We conducted a 2 years litter manipulation (litter removal, litter addition, and control) experiment in a Pinus massoniana plantation and studied its impacts on plant-C inputs via litter, fine root litter, and root exudates. The results show that litter removal significantly increases the litterfall in summer and autumn and reduces root-C exudation rates in spring but has no effect on the C input by fine roots. The annual C inputs by litter, fine roots, and root exudates in the control plots were 348.28, 42.39, and 17.44 g C m⁻², respectively, accounting for 85.34%, 10.39%, and 4.27% of the total C input, respectively. Litter removal increases the plant annual total C input by 24.55% due to the decrease in the root exudate-C input by 30.50% and increase in the litter-C input by 31.12%. In contrast, litter addition insignificantly affects the C input through litter, fine roots, or root exudates. Increasing the litter-C input and decreasing the root exudate-C input by litter removal are a plant strategy based on which forest growth can be maximized in the short term. The increased plant-C input due to litter removal mitigates the effects of litter alteration. This study is of great significance for understanding plant growth strategies.
 
Box-plots showing the effects of the longhorn species (Cw: Cerambyx welensii and Cc: Cerambyx cerdo), year (2017–2020) and their interaction on catch number per trap per sex (ln [x + 1] transformed) obtained with feeding traps as a proxy of population density (abundance). The species × year interaction was significant (see GLMM1 statistics in text). Asterisks show significant differences between species within years (*: p < 0.05; ns: not significant) and lowercase/uppercase letters show significant differences between years within species (p < 0.05)
Box-plots showing the effects of the longhorn species (Cw: Cerambyx welensii and Cc: Cerambyx cerdo), sex, host oak tree (cork, holm and pyrenean oak) and their interactions on catch number per trap per year (ln [x + 1] transformed) obtained with feeding traps as a proxy of population density (abundance). All three efects and some interactions were significant (see GLMM2 statistics in text). Letters show significant differences between host oak trees within especies (p < 0.05, sexes pooled)
Relationships between abundance (mean catch number per trap per year in traps with at least one catch) and occupancy (proportion of traps with at least one catch) in Cerambyx cerdo (Cc) and Cerambyx welensii (Cw). The feeding traps used in this study (n = 1650, years 2017–2020) were arranged for occupancy estimates according to the 26 zones that make up the region of Extremadura (SW Spain) (see map). Occupancy-abundance regressions (log10-transformed data) were significant in both longhorn species. The effects of species, occupancy and species x occupancy were all significant (see LM statistics in text). Codes for the 26 zones are (trap number per zone between brackets), 1: Sierra de Gata (n = 73), 2: Las Hurdes (n = 31), 3: Trasierra-Tierras de Granadilla (n = 35), 4: Valle del Ambroz (n = 31), 5: Valle del Jerte (n = 29), 6: La Vera (n = 40), 7: Valle del Alagón (n = 57), 8: Plasencia (n = 14), 9: Tajo-Salor-Almonte (n = 50), 10: Monfragüe (n = 49), 11: Campo Arañuelo (n = 67), 12: Sierra de San Pedro-Los Baldíos (n = 90), 13: Llanos de Cáceres (n = 69), 14: Sierra de Montánchez-Tamuja (n = 53), 15: Llanos de Trujillo-Miajadas (n = 107), 16: Villuercas-Ibores-Jara (n = 190), 17: Tierra de Badajoz-Mérida-Vegas Bajas (n = 117), 18: Vegas Altas (n = 56), 19: La Siberia (n = 81), 20: Llanos de Olivenza (n = 60), 21: Sierra Grande-Tierra de Barros (n = 70), 22: La Serena (n = 61), 23: Sierra Suroeste (n = 50), 24: Zafra-Río Bodión (n = 30), 25: Tentudía (n = 77), 26: Campiña Sur (n = 63)
Probability maps in Extremadura (SW Spain) generated with the Kriging Indicator algorithm for either Cerambyx cerdo (Cc, a–d) or Cerambyx welensii (Cw, e–h) with capture data from four consecutive years: 2017 (a, e), 2018 (b, f), 2019 (c, g) and 2020 (d, h). All maps depict for each longhorn species the probability of capturing at least 1 adult per trap per year
Probability maps in Extremadura (SW Spain) generated with the Kriging Indicator algorithm for either Cerambyx cerdo (Cc, a–c) or Cerambyx welensii (Cw, d–f), by pooling the four studied years (2017–2020) after normalise capture data within years. Maps depict for each longhorn species the probability of capturing at least 1 adult (a, d), 10 adults (b, e) or 20 adults (c, f) per trap per year
Wood-boring insects are considered potential contributing/inciting factors to oak decline. Cerambyx cerdo (Cc) and C. welensii (Cw) are two sympatric oak-living large sapro-xylophagous longhorn beetles with different pest/legal status, whose larvae bore into living wood of healthy/decayed trees, and whose impact has increased alarmingly in recent years. We conducted a regional-scale multi-year (2017-2020) field study to model Cc and Cw distribution and to explore species-specific occupancy-abundance patterns. Records were obtained with 1650 feeding traps placed throughout the region of Extremadura (SW Spain) (41,634 km2) in holm, cork and pyrenean oak woodlands. Catch number (a proxy of abundance) was analysed through GLMMs, LMs and geostatistical interpolation (IK algorithm) to generate catch probability maps. Catch number was extremely variable between trees (traps), stands and years (Cc: 0-252, Cw: 0-219 adults/trap) with no repulsive interspecific association at the tree scale. Explanatory factors in the models (species, sex, year and host oak) and several interactions among them significantly affected catch number. As a whole, Cw was more abundant than Cc, but catch number greatly depended on host tree (Cw: cork > holm > pyrenean oak, Cc: holm > cork > pyrenean oak). Occupancy-abundance patterns were positive with significant occupancy x species interaction. Niche breadth was more than double in Cw (Levins' BA = 0.42) than in Cc (BA = 0.19) and niche overlap almost complete (Pianka's O = 0.98). Our large-scale pioneer study shows that Cc and Cw are widespread in SW Spain, but with huge host-mediated intra-and interspecific geographic variation in abundance, which has critical implications in population management/control strategies.
 
Mixed mountain forests with an uneven-aged structure are characterized by a high tree-growth variability making traditional age-dependent growth models inapplicable. Estimating site productivity is yet another impediment for modelling tree growth in such forests. Uneven-aged mixed-stand forests are known for their high resilience, resistance and productivity, and are being promoted as a suitable alternative to even-aged, pure plantations for climate change adaptation and mitigation. However, their growth must be accurately measured and predicted, but diameter at the breast height ( dbh ) increment models specifically designed for uneven-aged mixed mountain forests are still rare. Using permanent sampling network data and 465 increment cores, we built two age-independent dbh increment ( $${i}_{d}$$ i d ) models for the main species of the study area, namely Norway spruce ( Picea abies (L.) Karst.), silver fir ( Abies alba Mill.) and European beech ( Fagus sylvatica L.). Mixed effects models and the algebraic difference approach were employed to develop $${i}_{d}$$ i d models based on empirical and commonly used theoretical growth functions. A past growth index was further developed and introduced in the model in order to explain the $${i}_{d}$$ i d variability. Several mixed effects calibration strategies were assessed in order to obtain the most accurate localized curve for new plots. Tree size, competition and biogeoclimatic variables were found to explain the $${i}_{d}$$ i d through the empirical growth function, while the growth index significantly improved the theoretical growth function for Norway spruce. The optimization of the calibration strategy for the mixed effects modelling framework enables the growth index implementation in forest practice as an accurate method for estimating site productivity. The accuracy of the two $${i}_{d}$$ i d models was similar: the root mean squared error of the empirical growth function varied between 0.940 and 1.042 cm for spruce, beech and fir, while the root mean squared error obtained through the theoretical growth function for spruce only was 1.105 cm. The basal area increment prediction at the plot level based on the theoretical growth function reached a root mean squared error of 0.043 m ² while using the empirical growth function the root mean squared error is 0.047 m ² . The high accuracy obtained using age-independent models underlines their suitability for predicting growth in mixed uneven-aged forests. The developed models can be easily integrated into forest practice to accurately obtain $${i}_{d}$$ i d estimates.
 
On top is shown the location of the study area in Italy (Paneveggio-Pale di San Martino Natural Park, Trentino). Map shows the study areas (red line) and the relative N2000 boundary (green line). Black dots represent hazel grouse locations (i.e., faecal samples collected) while white dots represent randomly generated locations used in the habitat selection analysis collected over winter 2017-2018. Red areas represent forests of Community Interest (Illyrian beech forest - N2000 code: 91K0; Norway spruce forests - N2000 code: 9410) while those in blue represent forests of non-Community Interest of recent formation (10-60 years) following the abandonment of traditional agropastoral activities. Areas in yellow represent N2000 hay meadows (code: 6520, 6210, 6230)
Hazel grouse diet composition in winter (2015–2016 and 2017–2018) based on DNA metabarcoding: a plant component (trnL barcode region); b arthropod component (CO1 barcode region). The most frequent taxa are reported, based on their RRA (relative read abundance; expressed here as percentage) in the whole dataset (plant component) and in the faecal samples containing at least one arthropod taxon (arthropod component; 35/72, 48.61%)
Frequency comparison between hazel grouse droppings collected in winter 2015–2016 and 2017–2018 (n = 192) and an equal number of randomly created locations in respect of Natura 2000 Community Interest forest habitats and non-Community Interest forest habitat. Hazel grouse droppings were more abundant in non-Community Interest forest (χ² = 64.28 df = 1, p < 0.001) of recent formation (10–60 years old) following the abandonment of traditional agropastoral activities
Probability of hazel grouse occurrence (faecal sample n = 117; individuals n = 24) for the most supported variables describing winter microhabitat selection in 2017–2018 according to conditional regression models (clogit). Gray band indicates 95% confidence interval
In contrast to old-growth forests, early-successional stands remain understudied despite potentially harbouring species of conservation interest. With this work, focused on hazel grouse Tetrastes bonasia , a cryptic and indicator species known to select for close-to-natural forests, we evaluated winter densities, home range, microhabitat selection and diet, combining DNA-based mark-recapture and metabarcoding from faecal samples. In total, 216 droppings, collected over 2 years along forest transects in the Italian Alps, were successfully genotyped and 43 individuals were identified. Density estimates were similar to values reported by other studies in the Alps with an average of 4.5 and 2.4 individuals/km ² in the first and second study year, respectively, and mean home ranges estimated at 0.95 km ² . According to habitat selection models and eDNA-based diet analysis, hazel grouse selected early-succession secondary-growth forests formed after the abandonment of traditional agropastoral activities. These forests, mostly composed of hazel Corylus avellana, Norway spruce Picea abies and Sorbus spp., provided winter food resources and shelter. The diet analysis also highlighted forest arthropods as a non-negligible source of food. Birds avoided areas subject to intensive browsing by ungulates; small forest roads seasonally closed to traffic had positive influence on hazel grouse (i.e. higher abundance of droppings), while roads open to traffic had no effect. Importantly, despite the high coverage of mature forest habitats of Community Interest (53% of our study area), droppings were more abundant in non-listed early-succession secondary forests with similar plant composition. Our results suggest that forest succession after agropastoral abandonment may be beneficial for some forest birds of conservation interest, while acknowledging its negative effects on the previous grassland biodiversity. Graphical abstract
 
Study area (Namkhaneh and Gorazbon districts of Kheyrud forest) in northern Iran (a); the location of skid trails with different harvesting periods (6, 10, and 20 years since harvest) in the selected compartments after logging operations (b); beech litter (c), beech-hornbeam litter (d) and mixed beech litter (e) on the skid trail after logging operations
Mean (± SE; n = 18) contents of litter C, N, C/N ratio and litter thickness under litter treatments and time since harvest (years). *P < 0.05, **P < 0.01. B, beech; B-H, beech-hornbeam; B-H-O, mixed beech, and UND: undisturbed area. Different letters indicate a significant difference in mean by Duncan test (P < 0.05)
Principal component analysis (PCA) of litter properties and soil physio-chemical properties and enzyme activities at various treatments (Litter type: B, beech; B-H, beech-hornbeam; B-H-O, mixed beech; time since harvest: ST6; 6 years, ST10; 10 years, ST20; 20 years; Traffic intensity: HT, high traffic; MT, medium traffic; LT, low traffic; and UND, undisturbed area. Soil physical properties (BD, bulk density; TP, total porosity; SM, soil moisture). SMR, soil microbial respiration; MBC, microbial biomass carbon; MBN, microbial biomass nitrogen
Pearson correlation coefficients (Heat map) between of studied litter and soil properties (n = 18)
Changes in vegetation and forest floor are among the factors affecting the variability of ecological indicators of soil organic and mineral layers. Therefore, the present study was conducted to examine the effect of forest floor on soil microbial properties and enzyme activities of skid trails after skidding operations. A total of 216 soil samples were taken from three litter treatments (B; beech, B-H; beech-hornbeam, B-H-O; mixed beech with maple and alder species) on skid trails that were each assigned to three time periods (6, 10 and 20 years after harvesting). All combinations were replicated three times. 20-years since harvest, the values of TP, N, available nutrients, NH4⁺, NO3⁻, fulvic and humic acid were highest in the B-H-O treatment and then B-H > B. In contrast, BD, C and C/N ratio were at the lowest level in the B-H-O treatment followed by B-H < B. The highest value of soil microbial characteristics and enzyme activity belonged to B-H-O treatment followed by > B-H > B and 20-years since harvest followed by > 10 years > 6 years. Values of soil microbial respiration (15%), microbial biomass carbon (8.7%), microbial biomass nitrogen (15.4%), urease (10.2%), acid phosphatase (4.4%), arylsulfatase (8.8%) and invertase (6.9%) in the B-H-O treatment measured 20 years after harvesting were less than the values of the undisturbed area. According to the results, as an ecological response to soil disturbance after skidding operations in skid trails, planting a mixture of trees with proper litter quality improves soil properties.
 
Terrestrial laser scanning of conifer tree crowns is challenged by occlusion problems causing sparse point clouds for many trees. Automatic segmentation of conifer tree crowns from sparse point clouds is a task that has only recently been addressed and not solved in a way that all trees can be segmented automatically without assignment errors. We developed a new segmentation algorithm that is based on region growing from seeds in voxelized 3D laser point clouds. In our data, field measured tree positions and diameters were available as input data to estimate crown cores as seeds for the region growing. In other applications, these seeds can be derived from the laser point cloud. Segmentation success was judged visually in the 3D voxel clouds for 1294 tree crowns of Norway spruce and Scots pine on 24 plots in six mixed species stands. Only about half of the tree crowns had only minor or no segmentation errors allowing to fit concentric crown models. Segmentation errors were most often caused by unsegmented neighbors at the edge of the sample plots. Wrong assignments of crown parts were also more frequent in dense groups of trees and for understory trees. For some trees, point clouds were too sparse to describe the crown. Segmentation success rates were considerably higher for dominant trees in the plot center. Despite the incomplete automatic segmentation of tree crowns, metrics describing crown size and crown shape could be derived for a large number of sample trees. A description of the irregular shape of tree crowns was not possible for most trees due to the sparse point clouds in the upper crown of most trees.
 
Top-cited authors
Miren del Rio
  • Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria
Kamil Bielak
  • Warsaw University of Life Sciences - SGGW
Christian Ammer
  • Georg-August-Universität Göttingen
Felipe Bravo
  • Universidad de Valladolid
Maciej Pach
  • University of Agriculture in Krakow