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Post-harvest forest herb layer demography : general patterns are driven by pre-disturbance conditions
Janez Kermavnar, Klemen Eler, Aleksander Marinšek, Lado Kutnar, 2021, original scientific article

Abstract: Timber harvesting constitutes extensive anthropogenic disturbance in temperate forests, producing a broad range of ecological impacts that most often enhance the demographic processes of vegetation. This study monitored post-harvest herb layer demography over a 6-year period in mesic Dinaric fir-beech forests (Slovenia), a vascular plant diversity hotspot among European forests. Three experimental harvesting intensities, i.e. full harvest (FH), partial harvest (PH) and a control treatment (NH), were each applied over a circular area of 4000 m2 and replicated three times at each of three study sites. Vegetation sampling was conducted before harvesting (in 2012), and two (2014) and six (2018) years following it, in a 400 m2 circular plot positioned in the centre of each treatment area. We focused on identifying general demographic patterns and evaluating the effects of various pre-disturbance abiotic and biotic predictors on compositional responses to disturbance. Two years after harvest (2012-2014), compositional shifts were larger than those in the next 4-year period (2014-2018), confirming the general theoretical prediction that species turnover rate decreases along a successional gradient. The degree of compositional shifts in gaps (FH) and thinned stands (PH) was affected by local abiotic factors (geomorphology of karst sinkholes) and community attributes, such as pre-harvest species richness. Our results indicate that compositional stability is positively associated with pre-disturbance species richness. Over the whole study period, increases in plot-level species richness (alpha diversity) and overall enrichment of the species pool (gamma diversity) were accompanied by compositional convergence, i.e. a decline in floristic dissimilarity (beta diversity) between and within study sites. However, the observed tendency towards homogenization was rather weak and would have been even more pronounced if the demographic type of persistent resident species had not shown a high degree of resistance, thus leaving a strong imprint on post-harvest vegetation development by preserving the forest characteristics of the herb layer community.
Keywords: forest succession, demographic types, community assembly, pre-disturbance factors, floristic convergence, fir-beech forests
Published in DiRROS: 22.07.2022; Views: 38; Downloads: 30
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Early-warning signals of individual tree mortality based on annual radial growth
Maxime Cailleret, Vasilis Dakos, Steven Jansen, Elisabeth M.R. Robert, Tuomas Aakala, Mariano M. Amoroso, Joe A. Antos, Christof Bigler, Harald Bugmann, Marco Caccianaga, Katarina Čufar, Tom Levanič, 2019, original scientific article

Abstract: Tree mortality is a key driver of forest dynamics and its occurrence is projected to increase in the future due to climate change. Despite recent advances in our understanding of the physiological mechanisms leading to death, we still lack robust indicators of mortality risk that could be applied at the individual tree scale. Here, we build on a previous contribution exploring the differences in growth level between trees that died and survived a given mortality event to assess whether changes in temporal autocorrelation, variance, and synchrony in time-series of annual radial growth data can be used as early warning signals of mortality risk. Taking advantage of a unique global ring-width database of 3065 dead trees and 4389 living trees growing together at 198 sites (belonging to 36 gymnosperm and angiosperm species), we analyzed temporal changes in autocorrelation, variance, and synchrony before tree death (diachronic analysis), and also compared these metrics between trees that died and trees that survived a given mortality event (synchronic analysis). Changes in autocorrelation were a poor indicator of mortality risk. However, we found a gradual increase in interannual growth variability and a decrease in growth synchrony in the last %20 years before mortality of gymnosperms, irrespective of the cause of mortality. These changes could be associated with drought-induced alterations in carbon economy and allocation patterns. In angiosperms, we did not find any consistent changes in any metric. Such lack of any signal might be explained by the relatively high capacity of angiosperms to recover after a stress-induced growth decline. Our analysis provides a robust method for estimating early-warning signals of tree mortality based on annual growth data. In addition to the frequently reported decrease in growth rates, an increase in inter-annual growth variability and a decrease in growth synchrony may be powerful predictors of gymnosperm mortality risk, but not necessarily so for angiosperms.
Keywords: tree mortality, ring-width, forest, growth, resilience indicators, drought, biotic agents, variance
Published in DiRROS: 20.07.2022; Views: 66; Downloads: 54
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River distance, stand basal area, and climatic conditions are the main drivers influencing lying deadwood in riparian forests
Janine Oettel, Martin Braun, Marcus Sallmannshofer, Maarten De Groot, Silvio Schueler, Charlotte Virgillito, Marjana Westergren, Gregor Božič, Laszlo Nagy, Srdjan Stojnić, Katharina Lapin, 2022, original scientific article

Abstract: Riparian forests are among the most diverse terrestrial ecosystems, yet their biodiversity is increasingly threatened by habitat degradation, climate change, river regulation and invasive species. We investigated deadwood, widely recognized as an indicator for forest biodiversity, in riparian forests of the Mura-Drava-Danube Transboundary Biosphere Reserve. The Biosphere Reserve is a conservation area that spans five countries and three rivers located in south-eastern Europe. In detail, we analyzed the drivers of lying deadwood volume, occurrence and decay related to floodplain type, silvicultural management, and climatic conditions using regression models. Lying deadwood occurrence and volume significantly decreased as distance from the river edge increased, indicating that river dynamics likely play a role in deadwood accumulation in riparian forests. Deadwood volume was also positively influenced by stand basal area, a parameter that can be directly addressed by silvicultural management. Deadwood decay was affected positively by temperature and negatively by precipitation, highlighting the importance of climatic conditions on decay progression. However, in order to draw more accurate conclusions about the drivers and dynamics of deadwood in riparian forests, further monitoring efforts that consider river flooding and flow regime, deadwood transport and saproxylic organism activity in addition to forest management and site conditions, are needed.
Keywords: alluvial forest, hardwood floodplain, deadwood decay, Mura-Drava-Danube transboundary biosphere, reserve, riparian area, softwood floodplain, UNESCO biosphere reserve, wetlands
Published in DiRROS: 18.07.2022; Views: 42; Downloads: 36
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Good survival of broadleaf tree species in a four-year-old plantation in the Slovenian Karst
Nina Škrk, Kristjan Jarni, Robert Brus, 2022, original scientific article

Abstract: Six broadleaf tree species (Celtis australis L. – Mediterranean hackberry, Quercus petraea (Matt.) Liebl. – sessile oak, Fagus sylvatica L. – European beech, Prunus avium L. – wild cherry, Juglans regia L. – Persian walnut and Acer pseudoplatanus L. – sycamore maple) were planted in 2012 in a trial in the Slovenian Karst on two sites differing in productivity to test their suitability for use in the conversion of old pine stands into ecologically more stable broadleaf forests and to investigate their possible response to the harsher growth conditions predicted in the future. The selected economically interesting tree species have higher timber quality than broadleaves which regenerate naturally (e.g., Ostrya carpinifolia, Fraxinus ornus, Quercus cerris). Measurements were taken in 2017, after four growth seasons. All planted species except Fagus sylvatica had a high survival rate. In total, 70% of all seedlings survived, which shows promising potential. The survival rate was higher at the site on flat terrain than at the site on a slope. Prunus avium was the most successful of all planted species in terms of survival rate, at 83%, and other measured parameters (height, height increment, stem diameter, vitality and quality), and Fagus sylvatica was the least successful, with a survival rate of only 20%. Celtis australis had the highest survival rate, at 87%. Acer pseudoplatanus had the largest differences in measured parameters between the more and less productive sites among all planted species. Quercus petraea showed high resistance to xeric conditions and is expected to be the most successful in conversions. All planted species except Fagus sylvatica show favourable initial potential for the future conversion of Karst pine forests.
Keywords: forest conversion, broadleaves, survival rate, seedlings quality, climate change
Published in DiRROS: 28.06.2022; Views: 386; Downloads: 165
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Artificial neural networks as an alternative method to nonlinear mixed-effects models for tree height predictions
Mitja Skudnik, Jernej Jevšenak, 2022, original scientific article

Abstract: Tree heights are one of the most important aspects of forest mensuration, but data are often unavailable due to costly and time-consuming field measurements. Therefore, various types of models have been developed for the imputation of tree heights for unmeasured trees, with mixed-effects models being one of the most commonly applied approaches. The disadvantage here is the need of sufficient sample size per tree species for each plot, which is often not met, especially in mixed forests. To avoid this limitation, we used principal component analysis (PCA) for the grouping of similar plots based on the most relevant site descriptors. Next, we compared mixed-effects models with height-diameter models based on artificial neural networks (ANN). In terms of root mean square error (RMSE), mixed-effects models provided the most accurate tree height predictions at the plot level, especially for tree species with a smaller number of tree height measurements. When plots were grouped using the PCA and the number of observations per category increased, ANN predictions improved and became more accurate than those provided by mixed-effects models. The performance of ANN also increased when the competition index was included as an additional explanatory variable. Our results show that in the pursuit of the most accurate modelling approach for tree height predictions, ANN should be seriously considered, especially when the number of tree measurements and their distribution is sufficient.
Keywords: height-diameter models, national forest inventory, permanent sample plot, mixed forests, model comparison, principal component analysis
Published in DiRROS: 08.06.2022; Views: 83; Downloads: 15
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Environmental impacts of boom-corridor and selectively thinned small-diameter-tree forests
Teresa de la Fuente, Dan Bergström, Raul Fernandez-Lacruz, Teppo Hujala, Nike Krajnc, Ruben Laina, Tomas Nordfjell, Matevž Triplat, Eduardo Tolosana, 2022, original scientific article

Abstract: European forest stands of small-diameter trees can provide industries with biomass as an alternative to fossil use. Small-tree harvesting is costly using conventional methods but using accumulating felling heads (AFH) in combination with a novel boom-corridor thinning (BCT) technique can increase harvester productivity and supply cost efficiency. This method has great potential to reduce costs, but its environmental impact compared with selective thinning (ST) needs to be determined. The objectives of this study were therefore to quantify and compare tree and soil damage as well as air, water and soil emissions for both BCT and ST in various European small-diameter-tree forests. Trials were performed in 84 study units (42 replications per thinning technique) across four countries. Damaged trees (with a diameter at breast height ≥ 7 cm) were measured after thinning and after forwarding. Harvesting emissions were calculated from a life cycle assessment. The percentage of remaining trees that had been damaged by the harvesting processes was 13% and 19% for BCT and ST, respectively, and the difference was significant. BCT exhibited the lowest emissions in all environmental impact categories considered, in all countries. Greenhouse gas emissions were on average 17% lower for BCT. BCT in small-diameter-tree stands therefore reduces the environmental impact of thinning operations compared with conventional methods, and results in less damage to the remaining trees.
Keywords: first thinning, harvesting damages, GHG emissions, forest biomass, forest operations
Published in DiRROS: 17.05.2022; Views: 131; Downloads: 107
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Private forest owner's cooperation in the machinery ring : is it a solution for wood mobilization from small-scale private forests?
Špela Pezdevšek Malovrh, Nike Krajnc, Matevž Triplat, 2022, original scientific article

Abstract: Legislation and policy makers have recognized private forest owners cooperation in machinery ring as an instrument to support wood mobilization through efficient use of machinery. The study analyzes private forest owner’s cooperation in the machinery ring in Slovenia and determines whether this cooperation contributes to wood mobilization from small-scale private forests. The research was conducted in two phases. In the first phase, the survey was conducted among the members of machinery rings at their annual general meetings (24 machinery rings participated in the survey, representing 64.9% of the total number of machinery rings). The questionnaire was distributed to all members present at the annual general meetings (n=529) and only those who were private forest owner or provided services within machinery rings were eligible to complete the questionnaire (n=438). In the second phase, data on the amount of service provided by machinery ring members were compared with the amount of felling in private forests for 2019 to gain insight into the extend of forestry work (timber harvesting) carried out in a private forest under neighbourhood assistance.The results show that machinery rings members are predominantly male, on average 50 years old, mainly with high school education and occupation in agriculture, owning on average 15.2 ha of forest. Regardless of forest management activities, machinery ring members perform forest management activities in their forest by themselves or with the help of family members. Only a small proportion of members use neighbourhood assistance to carry out the work. This most often occurs in the transport of timber. A very small proportion of members provide forest services through the machinery ring, but their scope of services is not insignificant. In 2019, machinery ring members most often performed harvesting activities with the chain saw, followed by timber skidding as a service. Equipment with machinery for providing services is good among members – about three quarters of them have a chainsaw and an adapted agricultural tractor, but this machinery is quite old, showing that machinery is insufficiently used for forestry operations. The results show that machinery rings are nowadays an essential part of strategic (operational) management in Slovenian agriculture and forestry, and provide important insights into the possibilities to improve forestry operations and the future development cooperation between private forest owners in machinery rings to support wood mobilization from small-scale private forests.
Keywords: private forest management, harvesting intensity, cooperation, machinery cooperation, neighbourhood assistance
Published in DiRROS: 25.04.2022; Views: 155; Downloads: 123
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