Jet stream position explains regional anomalies in European beech forest productivity and tree growth.

The mechanistic pathways connecting ocean-atmosphere variability and terrestrial productivity are well-established theoretically, but remain challenging to quantify empirically. Such quantification will greatly improve the assessment and prediction of changes in terrestrial carbon sequestration in response to dynamically induced climatic extremes. The jet stream latitude (JSL) over the North Atlantic-European domain provides a synthetic and robust physical framework that integrates climate variability not accounted for by atmospheric circulation patterns alone. Surface climate impacts of north-south summer JSL displacements are not uniform across Europe, but rather create a northwestern-southeastern dipole in forest productivity and radial-growth anomalies. Summer JSL variability over the eastern North Atlantic-European domain (5-40E) exerts the strongest impact on European beech, inducing anomalies of up to 30% in modelled gross primary productivity and 50% in radial tree growth. The net effects of JSL movements on terrestrial carbon fluxes depend on forest density, carbon stocks, and productivity imbalances across biogeographic regions

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)

Raznolikost sestojnih struktur v dveh mešanih gorskih pragozdovih in bližnjih gospodarskih gozdovih v Bosni in Hercegovini

This study was conducted in Dinaric mixed mountain old-growth (OG) forests Janj and Lom and adjacent managed stands on the same site (Piceo-Abieti-Fagetum illyricum), which were managed with a selection (plenter) system for more than a century. The following attributes were examined: light climate, ground vegetation, regeneration, tree density, dbh distribution shapes, tree species composition, mean diameter, basal area (BA), growing stock (GS) and coarse woody debris (CWD). As expected, taller and larger trees, higher BA, higher share of senescent phase and more CWD were found in OG forests. Regeneration process in OG forests was characterized by lower levels and variability of light, lover ground vegetation coverage and vascular plant diversity, and the species composition was more dominated by beech. Beech seedling density indicated positive relation to beech BA, while all regeneration stages of fir showed negative relation with fir BA. Beech was significantly more represented in OG forests also in the middlestory. Dbh distributions in both managed and OG forests had shapes that indicate a demographic equilibrium, despite high values of GS. Most frequent species specific shapes indicated demographic stability or even progression of beech, and imbalance or regression of conifers. Despite significant shares of spruce and fir in the upperstory, their regeneration and small trees were given low chances to replace mature trees in OG forests in the near future. Similarly to the natural disturbance pattern in OG forests Janj and Lom, single tree selection in managed forests performed only slightly better regarding recruitment of spruce and maple into the stand middlestory. The long-term comparison of OG forest structure indicated decline of conifers (especially spruce). However, comparison of recent data in managed and OG forests indicated that silvicultural activities may hold back long-term conifer decline since managed forests exhibited greater compositional stability.Raziskava je bila izpeljana v Dinarskih jelovo-bukovih pragozdovih Janj in Lom (OG) ter gospodarskih gozdovih v bližini (MF) na primerljivih rastiščih (Piceo-Abieti-Fagetum illyricum), kjer že več kot stoletje prebiralno gospodarijo. Proučevale so se naslednje značilnosti gozdov: svetlobne in zeliščne razmere, pomlajevanje, drevesna sestava, gostota, temeljnica in debelinska struktura sestojev ter veliki drevesni ostanki. Kot je bilo pričakovati, so značilnosti OG: višja in večja drevesa, višje temeljnice, večji deleži terminalne faze in več drevesnih ostankov. Za ekologijo pomlajevanja v OG je bila značilna manjša količina in variabilnost svetlobe, manjša pokrovnost in raznovrstnost vaskularnih rastlin, v zmesi mladja pa je bolj prevladovala bukev kot v MF. Gostota manjšega bukovega mladja je bila v pozitivni povezavi s temeljnico bukve, medtem ko so vse razvojne faze jelovega mladja nakazovale negativno povezavo s temeljnico jelke. Bukev je tudi značilno prevladovala v srednji drevesni plasti pragozdov v primerjavi z MF. Porazdelitve prsnih premerov OG in MF so, kljub visokim lesnim zalogam, nakazovale demografsko ravnotežje. Najpogostejše vrstno specifične oblike porazdelitev so nakazovale demografsko stabilnost ali napredovanje bukve in demografsko neravnovesje ali nazadovanje iglavcev. Kljub znatnim deležem smreke in jelke v zgornji plasti, so njuni čakalci v spodnji plasti nakazovali slabe možnosti za nadomestitev odraslih dreves v OG. Podobno kot pri naravnem vzorcu motenj v OG Janj in Lom, prebiralno gospodarjenje ni bistveno izboljšalo deleža smreke in javorja v srednji plasti. Dolgoročna primerjava strukture OG je nakazala nazadovanje iglavcev (predvsem smreke). Vendar pa primerjalna analiza zadnjih podatkov v OG in MF nakazuje, da lahko gojenje gozdov prispeva k zadrževanju dolgoročnega nazadovanja iglavcev, kajti gospodarski gozdovi izkazujejo večjo stabilnost zmesi

Comparing the quantity and structure of deadwood in selection managed and old-growth forests in South-East Europe

The knowledge about the impact of selection silviculture on deadwood components is fairly scarce. This study compared two Dinaric old-growth forests (OGFs) with adjacent managed forests (MFs) in which the single-tree selection system has been applied for a century. The comparisons were made in terms of the current amounts of coarse woody debris (CWD), distribution of its decay stages, and diameter structure of different CWD types (snags, logs, stumps). The relationship between the volume of live and dead trees was also examined. In both OGFs and MFs, the most snags were found in the third decay stage, while the volume of logs and stumps increased from the first to fifth decay class. The study showed the clear advantage of OGFs over adjacent selection MFs in terms of CWD volume, whereas the basal area of live trees and growing stock were not always reliable indicators for distinguishing between MFs and OGFs. The diameter distribution of individual CWD types (snags, logs, stumps) also differed significantly between selection MFs and OGFs in all tested pairs. This fact, along with the significant differences in CWD volume, indicates that selection silviculture should be amended to incorporate practices that ensure more natural management of deadwood components

Relationships between structural indices and conventional stand attributes in an old-growth forest in Southeast Europe

Structural indices are often proposed as guiding measures for increasing structural heterogeneity. However, few studies have examined the association between such indices and conventional stand attributes. The primary objectives of this study were to evaluate changes in structural heterogeneity and tree species diversity at different plot sizes and to quantify the relationships between conventional stand attributes (mean tree diameter, absolute tree density, basal area, species proportion) and structural indices in a mixed old-growth forest in Southeast Europe. Paired tests were used to identify significant changes in structural heterogeneity with increased plot area, while the relationships between stand attributes and analyzed indices (Gini, diameter differentiation, species mingling, and Shannon’s index) were evaluated with Pearson’s correlations. The index values of Gini, diameter differentiation, and tree species mingling were rather stable with the increase of plot size, whereas tree species diversity increased significantly with the increase of plot area from 200 m$^2$ to 1500 m$^2$. The measures of tree species mingling and tree species diversity were strongly associated with each other, while their association with diameter variability was weak to moderately strong. Tree species mingling index was strongly associated with the changes in tree species proportions. However, conventional stand attributes were generally not strongly correlated with the examined indices. For restoring and maintaining old-growth characteristics, forest managers may use structural indices to increase small-scale structural heterogeneity, tree species mingling, and diversity, but only as an additional set of measures, not as surrogates for conventional stand attributes

Old-growth forests in the Dinaric Alps of Bosnia-Herzegovina and Montenegro: a continental hot-spot for research and biodiversity

International audienceIntroduction: According to various censuses, Europe has less than 1.5 million ha of old-growth forests (OGF). Most of them are in the boreal zone, while their presence in the temperate zone is residual and fragmented.In the framework of the EU biodiversity strategy, it has been adopted a broad definition of OGF which includes late-seral forests and forests with some management legacies. However, research purposes need to identify strictly defined OGFs characterized by structure, disturbance history, and processes typical and exclusive of the last stage of the forest dynamic. Methods: The present paper wants to contribute to this debate by presenting a research network of four mixed (Fagus-Abies-Picea) montane OGFs in the Dinaric Alps (Lom, BiH; Janj, BiH; Perućica, BiH; Biogradska Gora, MNE), summarizing 20 years of multidisciplinary research by focusing on the structural characteristics and the disturbance history of the whole network and their coherency with strict OGF indicators. These sites were selected in relatively structurally uniform study areas, where 142 permanent plots have been established since 2002. Results and discussion: The study sites have a high living (747–1,201 m3 ha−1) and coarse woody debris (CWD) biomass (304–410 m3 ha−1), resulting in the highest forest carbon sink at the continental level (398–484 Mg C ha−1). The presence of large and old trees is one of the critical characteristics of the old-growth stage: in Lom and Perućica, there are 19 trees and 14 ha−1 larger than 1 m at breast height, respectively, and 14 trees and 15 trees ha−1 older than 400 years. In the last three centuries, continuous small-scale disturbances have driven forest dynamics, developing stands characterized by gap-phase dynamics and quasi-equilibrium structure. The Dinaric OGF network presents robust indicators of old-growthness, similar structural characteristics, and dynamic processes across all four sites. Identifying this sub-set of OGF using strict criteria is critical for recognizing conservation priorities and for quantifying, along an old-growthness chronosequence, the current structural differences of managed or recently abandoned forests. Besides, only OGF selected with rigorous criteria can act as a reliable reference for ecological restoration and sustainable forest management as a benchmark for carbon sink and for quantifying the impact of climate change on forests

Impact of non- native tree species in Europe on soil properties and biodiversity: a review

In the context of global change, the integration of non-native tree (NNT) species into European forestry is increasingly being discussed. The ecological consequences of increasing use or spread of NNTs in European forests are highly uncertain, as the scientific evidence is either constraint to results from case studies with limited spatial extent, or concerns global assessments that lack focus on European NNTs. For either case, generalisations on European NNTs are challenging to draw. Here we compile data on the impacts of seven important NNTs (Acacia dealbata, Ailanthus altissima, Eucalyptus globulus, Prunus serotina, Pseudotsuga menziesii, Quercus rubra, Robinia pseudoacacia) on physical and chemical soil properties and diversity attributes in Europe, and summarise commonalities and differences. From a total of 103 publications considered, studies on diversity attributes were overall more frequent than studies on soil properties. The effects on soil properties varied greatly among tree species and depended on the respective soil property. Overall, increasing (45%) and decreasing (45%) impacts on soil occurred with similar frequency. In contrast, decreasing impacts on biodiversity were much more frequent (66%) than increasing ones (24%). Species phylogenetically distant from European tree species, such as Acacia dealbata, Eucalyptus globulus and Ailanthus altissima, showed the strongest decreasing impacts on biodiversity. Our results suggest that forest managers should be cautious in using NNTs, as a majority of NNT stands host fewer species when compared with native tree species or ecosystems, likely reflected in changes in biotic interactions and ecosystem functions. The high variability of impacts suggests that individual NNTs should be assessed separately, but NNTs that lack European relatives should be used with particular caution.ISSN:1619-003

Comparative Structural Dynamics of the Janj Mixed Old-Growth Mountain Forest in Bosnia and Herzegovina: Are Conifers in a Long-Term Decline?

Regression of conifers in European mixed old-growth mountain forests has been observed for a long period and studied from different aspects. Old-growth (OG) forests in Bosnia and Herzegovina (BiH) have not experienced heavy air pollution and chronic overbrowsing that have affected many other European OG forests, while climatic and anthropogenic disturbances have been well documented. We analysed stand structure in the Janj OG forest, compared it with inventories of Lom and Perucica OG forests (BiH) and with earlier inventories of the same reserves. At present, OG forest Janj is characterized by a high growing stock (1215 m3∙ha−1). This is due to good site quality, prevalence of conifers (84%) and dominant endogenous processes in recent decades. In all three OG forests, indicators of structural change exhibited progression of European beech over time. Historical evidence revealed the occurrence of warm summers and droughts followed by bark beetle outbreaks in the 1920s, 1940s and early 1950s, which in turn influenced a marked conifer decline. It seems likely that repeated canopy opening released waves of European beech regeneration. These stand structural changes have delayed the rejuvenation of conifers and can help explain the early observations of conifer decline

Jet stream position explains regional anomalies in European beech forest productivity and tree growth

The mechanistic pathways connecting ocean-atmosphere variability and terrestrial productivity are well-established theoretically, but remain challenging to quantify empirically. Such quantification will greatly improve the assessment and prediction of changes in terrestrial carbon sequestration in response to dynamically induced climatic extremes. The jet stream latitude (JSL) over the North Atlantic-European domain provides a synthetic and robust physical framework that integrates climate variability not accounted for by atmospheric circulation patterns alone. Surface climate impacts of north-south summer JSL displacements are not uniform across Europe, but rather create a northwestern-southeastern dipole in forest productivity and radial-growth anomalies. Summer JSL variability over the eastern North Atlantic-European domain (5-40E) exerts the strongest impact on European beech, inducing anomalies of up to 30% in modelled gross primary productivity and 50% in radial tree growth. The net effects of JSL movements on terrestrial carbon fluxes depend on forest density, carbon stocks, and productivity imbalances across biogeographic regions.Here the authors show that extremes in the summer jet stream position over Europe create a beech forest productivity dipole between northwestern and southeastern Europe and can result in regional anomalies in forest carbon uptake and growth