Management of silver fir (Abies alba Mill.) in Slovenia

V prispevku analiziramo strukturo in razvojne značilnosti sestojev z jelko, gospodarjenje in posek jelke po stirih rastiščnih skupinah (A-D) glede na gojitveno ekološke značilnosti jelke na podlagi podatkovnih zbirk Zavoda za gozdove Slovenije. V lesni zalogi jelke prevladuje srednje debelo (d=30-49 cm)in debelo drevje (d=50 cm in veè) (84,9 %). Najveè (45 %) debelih jelk je vdinarskih jelovjih in jelovih bukovjih (skupina B), razvojno najmlajsa je jelka v jelovjih s praprotmi in na drugih jelovih rastiščih na nekarbonatu (skupina C). Analiza debelinske strukture jelke in stevila dreves iz prve in druge izmere na stalnih vzorčnih ploskvah ter naraščanje povprečnega premera posekanih jelk v obdobju zadnjih 14 let nakazujejo staranje in regresijo jelke, ki sta izrazitejša v skupini B. Vraščanje jelke prek meritvenega praga je največje v skupini C (19,2/ha/10 let) in se statistično značilno razlikuje od drugih skupin. Najmanjšo vrast jelke ugotavljamo v skupini B (4,2/ha/10 let), jakost poseka jelke je tu najvišja (22,3 % LZ) z najvišjim povprečnim premerom posekanih jelk (42,5 cm) in 48 % sanitarne sečnje. Za aktivno ohranjanje jelke je pomembno predvsem zmanjšanje vpliva jelenjadi in skrbno ter diferencirano gojitveno ukrepanje z daljšimi parcialnimi pomladitvenimi dobami. Predlagamo tudi nekatere druge ukrepe.In the paper, we analysed the structure and developmental characteristics of forest stands with silver fir in Slovenia, the management and cut in four forest site strata, where silver fir occurs. We used databases from the Slovenia Forest Service. In growing stock (GS) of silver fir, large (dbh=30-49cm) and very large (d=50 cm and more) diameter trees account for 84.9 % at the national level. The highest share of very large diameter silver fir trees (45 %) is in Dinaric silver fir forests and silver fir-beech forests(B), the lowest in silver fir forests with fern and silver fir forests on non-carbonate ground (C). The dbh structure of GS, number of silver fir trees recorded from two subsequent measurements from permanent sampling plots,rising mean dbh of harvested silver fir trees all indicate general agingand regression of silver, which is typical of stratum B but not in all other strata. The ingrowth of silver fir in 10 years is highest in stratum C (19.2 trees/ha), the lowest in B (4.2 trees/ha). In the latter, cut intensity (22.3 % of GS), the mean dbh of harvested silver firs are highest, too. For active conservation of silver fir, reduction of the impact of large ungulates and differentiated silviculture with longer regeneration periods is of crucial importance. Some other measures are also suggested

European beech stem diameter grows better in mixed than in mono-specific stands at the edge of its distribution in mountain forests

Recent studies show that several tree species are spreading to higher latitudes and elevations due to climate change. European beech, presently dominating from the colline to the subalpine vegetation belt, is already present in upper montane subalpine forests and has a high potential to further advance to higher elevations in European mountain forests, where the temperature is predicted to further increase in the near future. Although essential for adaptive silviculture, it remains unknown whether the upward shift of beech could be assisted when it is mixed with Norway spruce or silver fir compared with mono-specific stands, as the species interactions under such conditions are hardly known. In this study, we posed the general hypotheses that the growth depending on age of European beech in mountain forests was similar in mono-specific and mixed-species stands and remained stable over time and space in the last two centuries. The scrutiny of these hypotheses was based on increment coring of 1240 dominant beech trees in 45 plots in mono-specific stands of beech and in 46 mixed mountain forests. We found that (i) on average, mean tree diameter increased linearly with age. The age trend was linear in both forest types, but the slope of the age–growth relationship was higher in mono-specific than in mixed mountain forests. (ii) Beech growth in mono-specific stands was stronger reduced with increasing elevation than that in mixed-species stands. (iii) Beech growth in mono-specific stands was on average higher than beech growth in mixed stands. However, at elevations > 1200 m, growth of beech in mixed stands was higher than that in mono-specific stands. Differences in the growth patterns among elevation zones are less pronounced now than in the past, in both mono-specific and mixed stands. As the higher and longer persisting growth rates extend the flexibility of suitable ages or size for tree harvest and removal, the longer-lasting growth may be of special relevance for multi-aged silviculture concepts. On top of their function for structure and habitat improvement, the remaining old trees may grow more in mass and value than assumed so far.The authors would like to acknowledge networking support by the COST (European Cooperation in Science and Technology) Action CLIMO (Climate-Smart Forestry in Mountain Regions—CA15226) financially supported by the EU Framework Programme for Research and Innovation HORIZON 2020. This publication is part of a project that has received funding from the European Union’s HORIZON 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No 778322. Thanks are also due to the European Union for funding the project ‘Mixed species forest management. Lowering risk, increasing resilience (REFORM)’ (# 2816ERA02S under the framework of Sumforest ERA-Net). Further, we would like to thank the Bayerische Staatsforsten (BaySF) for providing the observational plots and to the Bavarian State Ministry of Food, Agriculture, and Forestry for permanent support of the Project W 07 ‘Long-term experimental plots for forest growth and yield research’ (#7831-26625-2017). We also thank the Forest Research Institute, ERTI Sárvár, Hungary, for assistance and for providing observational plots. Furthermore, our work was partially supported by the SRDA via Project No. APVV-16-0325 and APVV-15-0265, the Ministry of Science and Higher Education of the Republic of Poland, the Project “EVA4.0” No. CZ.02.1.01/0.0/0.0/16_019/0000803 funded by OP RDE and the Project J4-1765 funded by the Slovenian Research Agency and also by the Bulgarian National Science Fund (BNSF) and the Project No. DCOST 01/3/19.10.2018

Forest stand dynamics of silver fir-european beech forests in Slovenia from the beginning of regular forest management until the present

Dinamika pretežno raznomernih jelovo-bukovih gozdnih sestojev v zadnjem stoletju in njeni poglavitni vplivni dejavniki so bili proučevani v treh prostorsko dislociranih raziskovalnih objektih (Jelovica, Trnovo in Leskova dolina). S pomočjo arhivskih podatkov iz gozdnih inventur in pripadajočih gozdnogospodarskih kart je bila izdelana GIS podatkovna zbirka, v kateri je bil odsek osnovna prostorska enota. Spremembe v zgradbi gozdnih sestojev so bile ovrednotene z izbranimi sestojnimi parametri: lesno zalogo, debelinsko strukturo, diverziteto debelinske strukture, drevesno sestavo in vrastjo dreves. V zadnjem stoletju so se proučevani sestojni parametri značilno spreminjali. Med objekti so bile odkrite značilne razlike v sestojni dinamiki,vendar tudi nekatere podobnosti. V proučevanem obdobju je lesna zaloga gozdnih sestojev v vseh raziskovalnih objektih stalno naraščala. Spremembe debelinske strukture so nakazale dva različna razvoja sestojev: povečevanje sestojne gostote in količine tanjšega drevja ( pomlajevanje sestojev ) na Jelovici in Trnovem in znižanje sestojne gostote ob hkratnem povečevanju količine debelega drevja ( staranje sestojev ) v Leskovi dolini. Med objekti so bile ugotovljene opazne razlike v diverziteti debelinske strukture, vrasti dreves in drevesni sestavi. Na Trnovem in v Leskovi dolini sta jelka in bukev v proučevanem obdobju izmenjaje prevladovali v lesni zalogi. Med glavnimi drevesnimi vrstami so bile največje spremembe obilja in debelinske strukture opažene pri jelki, vendar so se te spremembe med objekti razlikovale. V proučevanem obdobju so na različen razvoj jelovo-bukovih gozdovv treh analiziranih območjih najpomembneje vplivale razlike v pretekli rabi gozdov, režimih abiotskih in biotskih naravnih motenj in rastiščnih razmerah. Na podlagi presoje vplivov posameznih dejavnikov so bili podani predlogi za prihodnje gospodarjenje z jelovo-bukovimi gozdovi ter nakazane možnosti raziskav v prihodnosti

A century long dynamics of silver fir population in mixed silver fir-european beech forests

The long-term dynamics of silver fir in mixed silver fir-European beech forests in Slovenia was studied in three geographically dislocated study areas, i.e. Leskova dolina, Trnovo and Jelovica. In the study, archival data on forest stands for the past century were used to create the GIS database, which included data for the periods 1912-2004 for the Leskova dolina study area, 1897-2003 for the Trnovo study area, and 1899-2002 for the Jelovica study area. In the observed period, substantial changes in diameter structure of silver fir and its proportion in stand volume were recognized. In Leskova dolina and Trnovo, the silver fir population was ageing, while in Jelovica it rejuvenated. In Leskova dolina and Trnovo, the silver fir proportion in stand volume decreased in the observed period, indicating its reciprocal replacement with European beech. The analyses of regeneration and recruitment designated different future potential of silver fir in the study areas. The found dynamics of silver fir is underpinned by a complex array of influential factors, notably past forest use, the impact of large ungulates, and site conditions

The applicability of the SiWaWa stand model for simulating stand development of pure beech and spruce even-aged forest stands in Slovenia

Modeli razvoja gozdov napovedujejo razvoj dreves in gozdnih sestojev glede na drevesne, sestojne, rastiščne in gozdnogospodarske dejavnike. Zaradi kompleksne narave gozdnih ekosistemov in dolgih proizvodnih ciklov je modeliranje razvoja gozdov pomemben sestavni del upravljanja gozdov. Sestojni modeli so bili prepoznani kot primerni za podporo odločanju pri upravljanju z gozdovi. Primer takega modela je švicarski model SiWaWa, ki smo ga preizkusili v pričujoči raziskavi. Na štirih vzorcih po 50 stalnih vzorčnih ploskev v negospodarjenih in gospodarjenih čistih bukovih in čistih smrekovih enomernih sestojih smo izvedli simulacije razvoja gozdov za obdobje 10 let, nato pa smo primerjali dejanske vrednosti in modelske napovedi za sestojno temeljnico G, število dreves N in srednje temeljnični premer Dg. Napovedovanje razvoja čistih bukovih gozdov je bilo zadovoljivo točnov negospodarjenih sestojih je celotna napaka RMSE za sestojno temeljnico znašala 2,35 m2 /ha, v gospodarjenih sestojih pa 3,42 m2/ha ob upoštevanju le posekanih dreves in 4,35 m2/ha ob upoštevanju celotne mortalitete. Enako ne moremo trditi za napovedovanje razvoja čistih smrekovih sestojev. Pri slednjih so bile mere točnosti znatno slabše, saj so RMSE za napovedano sestojno temeljnico znašali 8,94 m2/ha za negospodarjene in 6,13 m2/ha ter 6,11 m2/ha za gospodarjene sestoje ob upoštevanju poseka oziroma celotne mortalitete. Model SiWaWa, ki je parametriziran za švicarske gozdove, se zdi uporaben za simuliranje razvoja čistih bukovih gozdov brez simuliranega ukrepanja (poseka) ali z njim. Zanesljive simulacije razvoja čistih smrekovih sestojev pa model zaenkrat še ne omogoča.Forest development models predict development of trees and forest stands according to tree, stand, site, and forest management factors. Due to complex nature of forest ecosystems and long production cycles, forest development modelling is an important feature of forest management. Stand models have been identified as suitable for decision support in forest management, an example of such a model is the Swiss model SiWaWa, which was tested in Slovenian forests in the present study. Forest development simulations for 10-y periods were performed on four samples of 50 permanent sample plots in unmanaged and managed pure beech and pure spruce stands. Afterwards, we compared the actual and modelled values of stand basal area G, number of trees N, and mean squared diameter Dg. Predicting the development of pure beech forests was fairly accurate, the root mean square error RMSE for G was 2,35 m2 /ha for unmanaged, and 3,42 m2 /ha and 4,35 m2 /ha for managed stands considering only harvesting or entire mortality, respectively. We cannot claim the same for the development of pure spruce stands. Measures of accuracy were significantly worse, the RMSE was 8,94 m2 /ha for unmanaged stands, and 6,13 m2 /ha and 6,11 m2 /ha for managed stands considering only harvesting or entire mortality, respectively. The SiWaWa model, parameterized for Swiss forests, seems to be applicable for simulating the development of pure beech forests without or with simulated fellings, but the model does not yet provide reliable simulations for pure spruce stand