Significant increase in natural disturbance impacts on European forests since 1950

Over the last decades, the natural disturbance is increasingly putting pressure on European forests. Shifts in disturbance regimes may compromise forest functioning and the continuous provisioning of ecosystem services to society, including their climate change mitigation potential. Although forests are central to many European policies, we lack the long-term empirical data needed for thoroughly understanding disturbance dynamics, modeling them, and developing adaptive management strategies. Here, we present a unique database of >170,000 records of ground-based natural disturbance observations in European forests from 1950 to 2019. Reported data confirm a significant increase in forest disturbance in 34 European countries, causing on an average of 43.8 million m3 of disturbed timber volume per year over the 70-year study period. This value is likely a conservative estimate due to under-reporting, especially of small-scale disturbances. We used machine learning techniques for assessing the magnitude of unreported disturbances, which are estimated to be between 8.6 and 18.3 million m3/year. In the last 20 years, disturbances on average accounted for 16% of the mean annual harvest in Europe. Wind was the most important disturbance agent over the study period (46% of total damage), followed by fire (24%) and bark beetles (17%). Bark beetle disturbance doubled its share of the total damage in the last 20 years. Forest disturbances can profoundly impact ecosystem services (e.g., climate change mitigation), affect regional forest resource provisioning and consequently disrupt long-term management planning objectives and timber markets. We conclude that adaptation to changing disturbance regimes must be placed at the core of the European forest management and policy debate. Furthermore, a coherent and homogeneous monitoring system of natural disturbances is urgently needed in Europe, to better observe and respond to the ongoing changes in forest disturbance regimes

Presoja varovalnega učinka gozda pred drobirskimi tokovi ob Savi Bohinjki v Soteski

Varovalni gozdovi imajo pomembno vlogo pri zmanjševanju učinka različnih naravnih nevarnosti. V Sloveniji imamo 10 % varovalnih gozdov, 30 % teh gozdovima zaščitno funkcijo. Preučili smo učinkovitost varovalnih gozdov na severozahodu Slovenije, v Soteski med Bledom in Bohinjem, kjer sta ogroženi državna cesta in železnica. Na podlagi geološke karte in karte podvrženosti drobirskim tokovom smo ugotovili vplivno območje drobirskih tokov. Pri modeliranju njihovega širjenja smo uporabili program TopRunDF. Podatke o gozdu smo zbrali na 47 vzorčnih ploskvah, kjer smo izmerili vsa živa drevesa s prsnim premerom ? 10 cm. Podrobno smo opisali sestoje in jih ovrednotili po metodi NaiS. Ugotovili smo, da ima gozd ključno vlogo pri zaščiti infrastrukturnih objektov. Za trajno zaščitno vlogo v enomernih sestojih je potrebno gojenje mozaično raznomernega gozda. V sestojih, kjer gozdnogojitveni ukrepi ne zadostujejo, je potrebno uporabiti tehnične ukrepe. Ker s sestoji niso gospodarili več desetletij so motnje (najpogosteje v obliki vetrolomov) pogoste. Izsledki kažejo, da je potrebno ovrednotenje varovalne in zaščitne funkcije teh gozdov. Priporočamo tudi aktivno nego, kar je v nasprotju z dosedanjo prakso negospodarjenja teh gozdov.Protection forests have an important role of mitigating the influence of various natural hazards. Only 10% of all forests in Slovenia have an indirect protection function, while 30% of them perform a direct protection role. Studyof protection efficiency of beech dominated forests in the Soteska gorge in NW Slovenia, where a main state road and railway are endangered was done. We assessed the starting impacts of the debris-flow natural hazard based on a small-scale geological survey of the terrain characteristics and local debris flow susceptibillity map. For determination of the run-out zones we used the TopRunDF model. Forest structure data was obtained from 47 sample plots where all trees with DBH ? 10 cm were measured. A detailed description and delineation of forest stands was performed. Results showed that the forests stands play a crucial role in protection of infrastructural objects. For long-term protection efficiency, spatially-explicit regeneration patches are needed in uniform forest stands. In areas where silvicultural measures could not provide sufficient protection, technical measures are needed. Since these forests have not been managed for several decades, natural disturbances are frequent. Research findings suggest that assessment and management of these beech dominated protection forests is necessary, contrary to the current practice of non-management in protection forests in Slovenia

Comparison of natural and artificial regeneration after windthrows in 2008

Primerjali smo uspeh naravne in umetne obnove po treh vetrolomih v letu 2008. Na vsakem izmed raziskovalnih območij (Črnivec, Trnovski gozd, Bohor) smo leta 2012 zakoličili in analizirali ploskve z naravno in umetno obnovo ter jih ponovno premerili leta 2014. Znotraj ploskev smo zakoličili manjše vegetacijske ploskvice, na katerih smo popisali zeliščno plast in gostote mladja. Povprečna gostota samoniklega naravnega mladja šest let po ujmi je znašala 14.000 osebkov na hektar. Samoniklo mladje je bilo prostorsko neenakomerno porazdeljeno, kar nakazuje razlike med mikrorastišči. Ugotovili smo slabši uspeh obnove na južnih pobočjih, mestih, ki so bolj oddaljena od semenskih dreves in gozdnega roba, mikrorastiščih brez motenj oz. posebnosti in na večjih nadmorskih višinah. Na takih rastiščih je saditev smiselna in upravičena. Gostote naravnega samoniklega mladja so bile v pozitivni povezavi, preživetje naravnega dominantnega mladja in sadik pa v negativni s pokrovnostjo zeliščne plasti, prav tako je na preživetje negativno vplivalo objedanje. Višina osebka je bila najbolj značilen dejavnik za napovedovanje preživetja. Stopnja preživetja sadik in dominantnega mladja smreke je bila visoka, medtem ko sta sencozdržni bukev in jelka imeli višjo stopnjo mortalitete. Raziskava potrjuje velik potencial samoniklega naravnega mladja na območjih saditev, ki ga lahko z gojitvenimi deli zaviramo. Navedene so gozdnogojitvene usmeritve za ravnanje po vetrolomih.We studied regeneration dynamics in forests disturbed by three windthrows in 2008 to assess the success of natural regeneration vs planting. On each of the study sites (Črnivec, Trnovski gozd, Bohor) plots of dominant naturally regenerated saplings and plots with planted saplings were selected and measured in 2012 and 2014. Herbs and seedling establishment were studied in two subplots within each plot. Average seedling density six years after windthrow was 14,000 per ha. Seedlings were irregularly distributed, which suggests micro-site differences in regeneration dynamics. Results indicated lower seedling success on sites that were southerly exposed, farther from the forest edge and seed trees, on undisturbed micro-sites and at higher altitudes. On such sites planting was justified. While seedling density indicated a positive relation to herb coverage, sapling survival was negatively associated with it as well as with browsing. Sapling initial height was the strongest predictor of their survival. Spruce saplings had the lowest mortality, while shade-tolerant silver fir and beech experienced high mortality. The study revealed the high potential of naturally regenerated seedlings within young plantations, which can be reduced by silvicultural measures. Guidance for the improvement of silvicultural operations for post windthrow restoration is given

Challenges for uneven-aged silviculture in restoration of post-disturbance forests in Central Europe

Forest managers are often required to restore forest stands following natural disturbances, a situation that may become more common and more challenging under global change. In parts of Central Europe, particularly in mountain regions dominated by mixed temperate forests, the use of relatively low intensity, uneven-aged silviculture is a common management approach. Because this type of management is based on mimicking less intense disturbances, the restoration of more severe disturbance patches within forested landscapes has received little attention. The goal of this paper is to synthesize research on the restoration of forests damaged by disturbances in temperate forests of Slovenia and neighbouring regions of Central Europe, where uneven-aged silviculture is practiced. Research indicates that active management aimed at favouring mixed uneven-aged forest reduces the risk of disturbance and improves the resilience of stands. Salvage logging may have positive or negative effects on regeneration, much of which is due to the method applied and the quality of work. The most prominent factors that negatively affect restoration are: lack of advanced regeneration and decomposed woody debris, high altitude, steep slopes, dense ground vegetation, and overbrowsing. Planting or sowing should be applied in post-disturbance forests where many negative factors interact and where a high demand for sustainability of forest ecosystem services is present

Conversion of Pinus nigra plantations with natural regeneration in the Slovenian Karst

Since the mid-19th century, Pinus nigra plantations have played a key role in the restoration of degraded European landscapes. Nowadays, these plantations are aging and prone to natural disturbances, insect infestations, and diseases. For their successful gradual conversion, knowledge of optimal gap spatiotemporal dynamics is crucial. We studied herb and natural regeneration patterns along with site factors on 477 subplots within 44 plots distributed over four stand types: closed stand (14% diffuse light), open stand (21%), gap edge (23%), and gap (57%). Despite the abundant Quercus petraea, Q. cerris, and Q. pubescens mast year, no one-year seedlings were recorded, which is likely due to the summer drought. Short seedlings (h < 20 cm) of Quercus sp., Fraxinus ornus and Ostrya carpinifolia were more successful within closed stands. Short Quercus seedlings were positively associated with soil depth and negatively associated with soil nutrients, distance to seed trees, and Sesleria autumnalis coverage. Taller Quercus seedlings required more light than both of its strongest competitors and were positively related to humid soils and less rocky sites. Ungulate overbrowsing significantly impeded natural regeneration. The results indicate a satisfactory Quercus density for conversion and the importance of advanced regeneration, which should be gradually, but persistently, released by progressively widening gaps

Toward a beech-dominated alternative stable state in dinaric mixed montane forests

In the last century, a synchronous beech expansion has been observed for many mixed mountain forests in southeastern Europe. This change is associated with the interaction of various disturbances. We analyzed structural changes in the Pecka oldgrowth forest in Slovenia during the last century, using several inventories of the tree layer, regeneration, and site factors. Throughout the observation period, the density of silver fir in the regeneration layer and in the overstory steadily decreased. In 1893, silver fir accounted for about 60% of the growing stock, whereas in 2013 it accounted for less than 13%. This is likely because of silver fir’s decline in the canopy layer due to air pollution, successive windthrows, and overbrowsing. However, climate change may also have played an important role, as silver fir also declined in southeastern European old-growth forests where air pollution was less pronounced and ungulate densities were low. A gradual decline of silver fir in the overstory resulted in a decrease of overall tree density to 231 trees ha−1 , while growing stock remained relatively high at 712 m3 ha−1 . Median diffuse light at 1.3 m was 3.7% and regeneration density was 19,954 ha−1 . Beech was dominant (94%), followed by silver fir (4%), and sycamore maple (2%). No silver fir seedlings larger than 0.2 m were recorded. Silver fir, sycamore maple, and beech regeneration showed 87, 76, and 45% browsing damage, respectively. Regression models indicated some evidence of niche partitioning between silver fir and beech. However, many processes may be masked by the silver fir’s avoidance strategy. Given current red deer densities, climate change, and existing forest structure, the Pecka old-growth forest will likely reach an alternative stable state dominated by beech in a few decades. This calls for immediate reduction of ungulate populations. Despite the interaction of multiple disturbances, the Pecka old-growth forest has maintained a relatively high overall growing stock, a favorable microclimate, and succession pathway with shade-tolerant beech. This indicates the intrinsic resilience of natural forests. The mechanisms discussed here can be applied to the future governance of old-growth and managed montane mixed forests

Contemporary concepts for thinnings : connecting the principles of selective thinning, situational thinning, thinning of clusters and groups, and variable density thinning

V Evropi so razširjeni različni načini redčenj, ki so delno odgovor na različne cilje gospodarjenjadelno so posledica tradicije in različnih kulturnih okolij. S spremembami v okolju in zaostrovanjem družbeno-ekonomskih razmer ter splošnim nazadovanjem nege gozdov postajajo odločitve o najprimernejšim načinu in intenzivnosti redčenj vse pomembnejše. V prispevku primerjamo situacijsko redčenje, redčenje šopov in skupin, redčenje spremenljive gostote in pri nas ustaljeno izbiralno redčenje. Navajamo usmeritve, kako redčenja kombinirati ter kako izbrati primeren način in program redčenj. Na temelju sinteze dosedanjih raziskav izpostavljamo, da so za utemeljeno izboljšanje načinov redčenj pomembni poskusi v naravi.Various methods of thinning forest stands are common in Europe. These are partly a response to diverse management objectives, partly due to tradition and cultural context. With environmental changes, rapidly transforming socio-economic conditions, and a general decline in forest management, decisions about the optimal method and intensity of thinnings are becoming increasingly important. In this paper, we compare situational thinning, thinning of clusters and groups, thinning of variable density and selective thinning, traditional in Slovenia. We propose guidelines for combining various thinnings and choosing a suitable model and program of thinning. Based on the synthesis of previous research, we point out that field experiments are important for the evidence-based improvement of thinning methods