Tzvetan Zlatanov

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• PhD
• Professor at Bulgarian Academy of Sciences

Dry and warm climate conditions in southern Europe represent clear limits for European beech (Fagus sylvatica) growth near the species southern distribution limit, but it is unclear how aridification and changes in seasonal precipitation regimes will affect these forests at the individual level. We explored climate-growth relationships and the seas...

Balancing increasing demand for wood products while also maintaining forest biodiversity is a paramount challenge. Europe’s Biodiversity and Forest Strategies for 2030 attempt to address this challenge. Together, they call for strict protection of 10% of land area, including all primary and old growth forests, increasing use of ecological forestry,...

Key message We found a significant increase in the latewood density of European beech, and a decrease in the latewood and mean wood density of silver fir and Norway spruce in European mountain forests over the period 1901–2016. In the past century, drought did not directly influence the wood density trend of the three studied species. However, for...

With ongoing global warming, increasing water deficits promote physiological stress on forest ecosystems with negative impacts on tree growth, vitality, and survival. How individual tree species will react to increased drought stress is therefore a key research question to address for carbon accounting and the development of climate change mitigati...

A major challenge for forestry and nature conservation is the adaptation of forests to climate change, as there are many different climate projections, uncertain about which one will prove accurate. We aimed to estimate current and future changes in the potential ranges of common and cultivated native and exotic tree species in Europe. We also aime...

Carbon accounting in the land sector requires a reference level from which to calculate past losses of carbon and potential for gains using a stock-based target. Carbon carrying capacity represented by the carbon stock in primary forests is an ecologically-based reference level that allows estimation of the mitigation potential derived from protect...

The future performance of the widely abundant European beech (Fagus sylvatica L.) across its ecological amplitude is uncertain. Although beech is considered drought-sensitive and thus negatively affected by drought events, scientific evidence indicating increasing drought vulnerability under climate change on a cross-regional scale remains elusive....

Mixed mountain forests consisting of Norway spruce (Picea abies (L.) Karst.), European beech (Fagus sylvatica L.), and silver fir (Abies alba Mill.) are among the most productive and stable forest ecosystems in Europe. Their southeasternmost geographical distribution range is located in the Western Rhodopes, where they have high economic, recreatio...

Един от районите с очаквани най-сериозни промени в горите като следстиве от климатичните промени е Югозападна България,където според климатичните модели е много вероятен бъдещ средиземноморскитип климат със значително повишаване на температурите. Това е сред основните причини територията на Югозападното Държавно предприятие (ЮЗДП) да бъде избрана з...

To enhance our understanding of forest carbon sequestration, climate change mitigation and drought impact on forest ecosystems, the availability of high-resolution annual forest growth maps based on tree-ring width (TRW) would provide a significant advancement to the field. Site-specific characteristics, which can be approximated by high-resolution...

Canopy accession strategies reveal much about tree life histories and forest stand dynamics. However, the protracted nature of ascending to the canopy makes direct observation challenging. We use a reconstructive approach based on an extensive tree ring database to study the variability of canopy accession patterns of dominant tree species (Abies a...

Tree regeneration is a key demographic process influencing long‐term forest dynamics. It is driven by climate, disturbances, biotic factors and their interactions. Thus, predictions of tree regeneration are challenging due to complex feedbacks along the wide climatic gradients covered by most tree species. The stress gradient hypothesis (SGH) provi...

Alien tree species are considered both a threat to nature conservation and a base for forest management. We compiled species occurrences from biodiversity databases, forest inventories, and literature data. We modeled the availability of potential niches using the MaxEnt method and bioclimatic variables for current conditions, 2041–2060, and 2061–2...

Process-based models and empirical modelling techniques are frequently used to (i) explore the sensitivity of tree growth to environmental variables, and (ii) predict the future growth of trees and forest stands under climate change scenarios. However, modelling approaches substantially influence predictions of the sensitivity of trees to environme...

Many studies show that mixed species stands can have higher gross growth, or so-called overyielding, compared with monocultures. However, much less is known about mortality in mixed stands. Knowledge is lacking, for example, of how much of the gross growth is retained in the standing stock and how much is lost due to mortality. Here, we addressed t...

Global change outcomes for forests will be strongly influenced by the demography of juvenile trees. We used data from an extensive network of forest inventory plots in Europe to quantify relationships between climate factors and growth rates in sapling trees for two ecologically dominant species, Norway spruce and European beech. We fitted nonlinea...

Tree regeneration is a key demographic process influencing long-term forest dynamics. It is driven by many biotic and abiotic factors. Thus, predictions of tree regeneration are challenging because of complex feedbacks along climatic gradients. The stress gradient hypothesis (SGH) and life-history strategies (LHS) provide a framework for assessing...

Increasing species diversity is considered a promising strategy to mitigate the negative impacts of global change on forests. However, the interactions between regional climate conditions and species-mixing effects on climate-growth relationships and drought resistance remain poorly documented. In this study, we investigated the patterns of species...

The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosyste...

Climate change impacts are an increasing threat to forests and current approaches to management. In 2020, Climate-smart Forestry (CSF) definition and set of indicators was published. This study further developed this work by testing the definition and indicators through a forest manager survey across fifteen member European countries. The survey co...

Riparian zones are the paragon of transitional ecosystems, providing critical habitat and ecosystem services that are especially threatened by global change. Following consultation with experts, 10 key challenges were identified to be addressed for riparian vegetation science and management improvement: (1) Create a distinct scientific community by...

Heterogeneity of structure can increase mechanical stability, stress resistance and resilience, biodiversity and many other functions and services of forest stands. That is why many silvicultural measures aim at enhancing structural diversity. However, the effectiveness and potential of structuring may depend on the site conditions. Here, we reveal...

1. Riparian zones are vital areas of interaction between land and rivers and are often degraded by several pressures such as urbanisation, intensive agriculture and river engineering works. 2. This policy brief provides five key policy messages and recommendations to be considered by policy-makers, scientists, managers, and stakeholders to enhance...

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 growth of past, present, and future forests was, is and will be affected by climate variability. This multifaceted relationship has been assessed in several regional studies, but spatially resolved, large-scale analyses are largely missing so far. Here we estimate recent changes in growth of 5800 beech trees ( Fagus sylvatica L.) from 324 sites...

Rear-edge populations of montane species are known to be vulnerable to environmental change, which could affect them by habitat reduction and isolation. Habitat requirements of two cold-adapted boreo-alpine owl species — Boreal Owl (Aegolius funereus) and Pygmy Owl (Glaucidium passerinum) — have been studied in refugial montane populations in the w...

Forest composed of Picea abies L., Abies alba Mill. and Fagus sylvatica L. cover a large area in the European mountain regions and have a high ecological and socio-economic importance as they supply many ecosystems services. Because of climate change, these forests are exposed to warming, and this effect increases with elevation, which may impact t...

Mountain forests in Europe have to face recently speeding-up phenomena related to climate change, reflected not only by the increases in the mean global temperature but also by frequent extreme events, that can cause a lot of various damages threatening forest stability. The crucial task of management is to adapt forests to environmental uncertaint...

Associations of pedunculate oak (Quercus robur L.) radial growth with satellite-based soil moisture (SM) during the intensive tree growth period over a 30-year time span (1980–2010) were analyzed. This study included tree-ring width (TRW) chronologies from 22 stands located in four southeastern (SE) European countries (Slovenia, Croatia, Serbia and...

Exploitation of natural forests forms expanding frontiers. Simultaneously, protected area frontiers aim at maintaining functional habitat networks. To assess net effects of these frontiers, we examined 16 case study areas on five continents. We (1) mapped protected area instruments, (2) assessed their effectiveness, (3) mapped policy implementation...

Forests in Europe are currently not endangered by soil erosion. However, this can change with climate change or with intensified forest management practices. Using a newly established network of plots in beech forests across Europe, the aims of this study were to (i) distinguish soil properties and erodibility indices in relation to bedrock, (ii) d...

Primary forests, defined here as forests where the signs of human impacts, if any, are strongly blurred due to decades without forest management, are scarce in Europe and continue to disappear. Despite these losses, we know little about where these forests occur. Here, we present a comprehensive geodatabase and map of Europe’s known primary forests...

Aims We examined differences in lifespan among the dominant tree species (spruce (Picea abies (L.) H. Karst.), fir (Abies alba Mill.), beech (Fagus sylvatica L.), and maple (Acer pseudoplatanus L.)) across primary mountain forests of Europe. We ask how disturbance history, lifetime growth patterns, and environmental factors influence lifespan. Loc...

Developing “climate smart forestry” (CSF) indicators in mountain forest regions requires collection and evaluation of local data and their attributes. Genetic resources are listed among the core indicators for forest biological diversity. This study is a report on the evaluation of the standing genetic diversity within and across 12 pure beech stan...

New technologies, such as satellites and sensors, provide a wealth of new information about all ecosystems. In dendrochronological studies, all drought-related factors are of great importance for a more comprehensive understanding of associations between radial growth and water loss. Soil moisture directly reflects the wetness of immediate root sur...

Fagus sylvatica L. is widely distributed across Europe thanks to its high adaptability in a wide variety of soils and climate. Microbial communities are essential for maintaining forest soil quality and are responsible for forest ecosystem functioning; the ability of soil microorganisms to respond to abiotic stressors (e.g., organic carbon losses,...

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 fore...

Spruce-fir-beech mixed forests cover a large area in European mountain regions, with high ecological and socioeconomic importance. As elevation-zone systems they are highly affected by climate change, which is modifying species growth patterns and productivity shifts among species. The extent to which associated tree species can access resources an...

Key message The diameter at breast height of the largest sprout per coppiced stool proved to be accurate for the total sprout biomass estimates at stand level. Abstract Traditional coppicing is one of the oldest silvicultural systems for biomass production. However, a quick and simple biomass estimate methodology across the entire growth period is...

Tree species-mixing has been suggested as one option to counteract the adverse effects of global change on tree mineral nutrition, yet the effect of mixing on nutrient availability remains poorly documented. We therefore analyzed the current foliar nutrient (N, P, K, Ca, Mg) quantities and ilr balances (isometric log transformed ratios between elem...

Primary forests are critical for forest biodiversity and provide key ecosystem services. In Europe, these forests are particularly scarce and it is unclear whether they are sufficiently protected. Here we aim to: (a) understand whether extant primary forests are representative of the range of naturally occurring forest types, (b) identify forest ty...

The results of the first comprehensive radar survey of the spring and autumn bird migration in Bulgaria in a key area of the migratory flyway Via Pontica are presented. The weather radar of Bulgarian Air Traffic Services Authority (BULATSA) located nearby the town of Aksakovo (Varna Region, NorthEastern Bulgaria) was used. The survey covered 1101 d...

Establishing mixed-species stands is frequently proposed as a strategy to adapt forests to the increasing risk of water scarcity, yet contrasted results have been reported regarding mixing effects on tree drought exposure. To investigate the drivers behind the spatial and temporal variation in water-related mixing effects, we analysed the δ¹³C vari...

In Europe, mixed mountain forests, primarily comprised of Norway spruce (Picea abies (L.) Karst.), silver fir (Abies alba Mill.), and European beech (Fagus sylvatica L.), cover about 10 × 10⁶ ha at elevations between ∼600 and 1600 m a.s.l. These forests provide invaluable ecosystem services. However, the growth of these forests and the competition...

There is concern in the scientific community and among forest managers about potential reductions in the provisioning of forest ecosystem services due to the loss of tree species diversity. Many studies have shown how species diversity influences forest functioning, especially productivity, but the influence of structural diversity, such as tree si...

Mixed mountain forests of European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst), and silver fir (Abies alba Mill.) cover a total area of more than 10 million hectares in Europe. Due to altitudinal zoning, these forests are particularly vulnerable to climate change. However, as little is known about the long-term development of...

Climate change may reduce forest growth and increase forest mortality, which is connected to high carbon costs through reductions in gross primary production and net ecosystem exchange. Yet, the spatiotemporal patterns of vulnerability to both short‐term extreme events and gradual environmental changes are quite uncertain across the species’ limits...

White-backed woodpecker (Dendrocopos leucotos) is an old-growth forest specialist and one of the rarest woodpeckers in Europe. The southern subspecies of the white-backed woodpecker (Dendrocopos leucotos lilfordi) is among the least studied. We assessed which environmental variables influence the landscape distribution of the southern white-backed...

Currently, about 70% of the forest land in Europe is covered by stands composed of two or more tree species. The similar situation can be found outside Europe too. While forest management of monocultures is well described, multispecies forests still need a better understanding to develop appropriate forest practice. Managing mixed forests can be mo...

In Europe, assessment of the ecological function of forests is increasingly important as evidenced by Natura 2000, which has seen the establishment of protected sites that are of ecological importance. The presence of canopy gaps has proved to be a useful indicator of the forest structure and biodiversity in these areas. Two methods – Object Based...

Aim Primary forests have high conservation value but are rare in Europe due to historic land use. Yet many primary forest patches remain unmapped, and it is unclear to what extent they are effectively protected. Our aim was to (1) compile the most comprehensive European‐scale map of currently known primary forests, (2) analyse the spatial determina...

Natural diversity of relief, climate variability, geographical as well as historical reasons contribute to the presence of old-growth forest patches in various forest types in Bulgaria. For reasons of biodiversity protection, scientific studies and forest certification several projects aimed at locating and collecting data for old-growth forests in...

When tree‐species mixtures are more productive than monocultures, higher light absorption is often suggested as a cause. However, few studies have quantified this effect and even fewer have examined which light‐related interactions are most important, such as the effects of species interactions on tree allometric relationships and crown architectur...

Research into mixed-forests has increased substantially in the last decades but the extent to which the new knowledge generated meets practitioners’ concerns and is adequately transmitted to them is unknown. Here we provide the current state of knowledge and future research directions with regards to 10 questions about mixed-forest functioning and...

Zusammenfassung Bergmischwälder aus Fichte (Picea abies (L.) Karst), Weißtanne (Abies alba Mill.) und Europäischer Rot-buche (Fagus sylvatica) bedecken in Europa eine Gesamtfläche von mehreren Millionen Hektar. Sie verbinden die Buchenwaldgesellschaften im Tiefland mit den fichtendominierten, alpinen Waldtypen. Aufgrund ihrer Höhenzonierung sind di...

The productivity and functioning of mixed-species forests often differs from that of monocultures. However, the magnitude and direction of these differences are difficult to predict because species interactions can be modified by many potentially interacting climatic and edaphic conditions, stand structure and previous management. Process-based for...

The White-backed Woodpecker (WBW, Dendrocopos leucotos lilfordi) inhabits mainly mature broadleaved and mixed forests in Bulgaria. In 2015–2017 we analysed the breeding habitat selection of the D.l.lilfordi, which has not been studied in the country yet. The study was conducted in “Strandzha” Nature Park (NP) (116 100 ha), South-eastern Bulgaria, w...

Key messageThis data set provides unique empirical data from triplets of Scots pine (Pinus sylvestrisL.) and European beech (Fagus sylvaticaL.) across Europe. Dendrometric variables are provided for 32 triplets, 96 plots, 7555 treesand 4695 core samples. These data contribute to our understanding of mixed stand dynamics.Dataset access athttp://dx.d...

Mountain forests provide a diverse range of ecosystem services (ES). In case of conflicting ES, trade-offs must be considered in forest resource planning. In this study, simulation-based scenario analysis and multi-criteria decision analysis is used to analyse expected utilities and value-based trade-offs in multi-objective forest management relate...

Biomass and leaf area equations are often required to assess or model forest productivity, carbon stocks and other ecosystem services. These factors are influenced by climate, age and stand structural attributes including stand density and tree species diversity or species composition. However, such covariates are rarely included in biomass and lea...

Overlaid to a general reduction of European beech and sessile oak tree growth over the recent decades in the Mediterranean Basin, tree-ring records from western Mediterranean populations display a stronger growth decrease than eastern populations. We investigate here to what extent the impact of sustained atmospheric circulation patterns in summert...

Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) dominate many of the European forest stands. Also, mixtures of European beech and Scots pine more or less occur over all European countries, but have been scarcely investigated. The area occupied by each species is of high relevance, especially for growth evaluation and compar...

There is increasing evidence that species diversity enhances the temporal stability (TS) of community productivity in different ecosystems, although its effect at the population and tree levels seems to be negative or neutral. Asynchrony in species responses to environmental conditions was found to be one of the main drivers of this stabilizing pro...

The vulnerability of forest ecosystem services to climate change is expected to depend on landscape characteristic and management history, but may also be influenced by the proximity to the southern range limit of constituent tree species. In the Western Rhodopes in South Bulgaria, Norway spruce is an important commercial species, but is approachin...

The digital edition is part of a joint project for a print and digital edition of the Red Data Book of the Republic of Bulgaria. It includes the full information from the print edition (vol 1 Plants and Fungi, vol 2 Animals, vol 3 Natural habitats), enriched with videos, extended photo gallery, higher-resolution drawings, distribution maps with rel...

European beech Fagus sylvatica L. represents one of the most commercially and ecologically important forest tree species in Europe. The study of climate-growth relationships may provide relevant information to assist projections of future species' distribution as well as forest management strategies. In this study, 9 European beech stands were sele...

Mixing of complementary tree species may increase stand productivity, mitigate the effects of drought and other risks, and pave the way to forest production systems which may be more resource-use efficient and stable in the face of climate change. However, systematic empirical studies on mixing effects are still missing for many commercially import...

Chestnut forests in the Belasitsa Mountain region of southwest Bulgaria were traditionally intensively managed as orchard-like stands for nut production. More recently, management intensity has been sharply reduced as a result of rural abandonment, which combined with the effects of chestnut blight has led to marked structural changes in these fore...