European Mixed Forests

We aim at (i) developing a reference definition of mixed forests in order to harmonize comparative research in mixed forests and (ii) briefly review the research perspectives in mixed forests. Area of study: The definition is developed in Europe but can be tested worldwide. Material and methods: Review of existent definitions of mixed forests based and literature review encompassing dynamics, management and economic valuation of mixed forests. Main results: A mixed forest is defined as a forest unit, excluding linear formations, where at least two tree species coexist at any developmental stage, sharing common resources (light, water, and/or soil nutrients). The presence of each of the component species is normally quantified as a proportion of the number of stems or of basal area, although volume, biomass or canopy cover as well as proportions by occupied stand area may be used for specific objectives. A variety of structures and patterns of mixtures can occur, and the interactions between the component species and their relative proportions may change over time. The research perspectives identified are (i) species interactions and responses to hazards, (ii) the concept of maximum density in mixed forests, (iii) conversion of monocultures to mixed-species forest and (iv) economic valuation of ecosystem services provided by mixed forests. Research highlights: The definition is considered a high-level one which encompasses previous attempts to define mixed forests. Current fields of research indicate that gradient studies, experimental design approaches, and model simulations are key topics providing new research opportunities

Crown volume in forest stands of pedunculate oak and common hornbeam

Background and Purpose: The structure of the crown volume in a forest stand is one of the main factors that drive the growth and development of trees. It changes dynamically with the age of the forest stand and according to the management activities and natural disturbances that remove trees from the stand. The aim of this article is to analyse crown volume structure in relation to the stand age and diameter at breast height (DBH) of pedunculate oak and common hornbeam trees in one of the most important forest types in Croatia. Materials and Methods: Data for the research were collected from a set of 47 permanent sample plots established as a chronosequence over the distribution range of pedunculate oak and common hornbeam forests in Croatia. The combined area of all the plots amounted to 33.45 ha. Trees were measured for DBH, total height and height to crown base, and a detailed map of crown projection areas was made for each plot. In total, the crowns of 1,609 pedunculate oak trees and 1,979 common hornbeam trees were measured. Crown volumeswere calculated for each tree, the trees were pooled into age classes of 20 years, and analyses were carried out per tree species, per age class. A nonlinear regression with an exponential function of crown volume was performed to establish the relationship between the crown volume and DBH in each age class. Results and Discussion: Up to a stand age of 40 years, crowns of pedunculate oak dominate in the canopy layer (66%), after which crowns of common hornbeam trees assume dominance. Coefficients of determination for the regression lines for pedunculate oak crowns are higher than the coefficients for common hornbeam. In all age classes, they are higher than 0.50, except for the first age class for common hornbeam and the seventh age class for pedunculate oak. The shape of the regression lines of pedunculate oak crown volume shift more to the right side of the diameter range as the stand matures, while those of common hornbeam are more static and form a bundle of lines. Conclusions: Results indicate that the relationship between the crown volume of pedunculate oak and common hornbeam trees and DBH can be described by a nonlinear regression model with an exponential function. Further research is needed to assess the possibilities of integrating the obtained regression models into simulators of forest growth and development

Crown volume in forest stands of pedunculate oak and common hornbeam

Background and Purpose: The structure of the crown volume in a forest stand is one of the main factors that drive the growth and development of trees. It changes dynamically with the age of the forest stand and according to the management activities and natural disturbances that remove trees from the stand. The aim of this article is to analyse crown volume structure in relation to the stand age and diameter at breast height (DBH) of pedunculate oak and common hornbeam trees in one of the most important forest types in Croatia. Materials and Methods: Data for the research were collected from a set of 47 permanent sample plots established as a chronosequence over the distribution range of pedunculate oak and common hornbeam forests in Croatia. The combined area of all the plots amounted to 33.45 ha. Trees were measured for DBH, total height and height to crown base, and a detailed map of crown projection areas was made for each plot. In total, the crowns of 1,609 pedunculate oak trees and 1,979 common hornbeam trees were measured. Crown volumeswere calculated for each tree, the trees were pooled into age classes of 20 years, and analyses were carried out per tree species, per age class. A nonlinear regression with an exponential function of crown volume was performed to establish the relationship between the crown volume and DBH in each age class. Results and Discussion: Up to a stand age of 40 years, crowns of pedunculate oak dominate in the canopy layer (66%), after which crowns of common hornbeam trees assume dominance. Coefficients of determination for the regression lines for pedunculate oak crowns are higher than the coefficients for common hornbeam. In all age classes, they are higher than 0.50, except for the first age class for common hornbeam and the seventh age class for pedunculate oak. The shape of the regression lines of pedunculate oak crown volume shift more to the right side of the diameter range as the stand matures, while those of common hornbeam are more static and form a bundle of lines. Conclusions: Results indicate that the relationship between the crown volume of pedunculate oak and common hornbeam trees and DBH can be described by a nonlinear regression model with an exponential function. Further research is needed to assess the possibilities of integrating the obtained regression models into simulators of forest growth and development

SCOTS PINE (PINUS SYLVESTRIS L.) RESPONSE TO CLIMATE CHANGES AND THINNING ACTIVITIES: A TREE-RING STUDY FROM SOUTH-EAST RILA MOUNTAIN, BULGARIA

Abstract As a result of the study, the Scots pine (Pinus sylvestris L.) local chronology in 'Vasil Serafimov' Ecological Station (Southeast Rila Mountains, Bulgaria) was extended with 21 years, till 2008. A significant relationship (α < 0.01) was ascertained between tree-growth indices (ITR) of the Scots pine and precipitation indices (IP), temperature indices (IT) and presence of Norway spruce (Picea abies (L.) Karst) understorey (SU). Initially, pine decreased its radial growth rate as a consequence of the drought started in 1993. Removal of Spruce understorey in the middle of the dry period (1995), however, positively influenced Scots pine radial growth since 1997. The cooler and wetter years from 2001 to the end of the studied period resulted in increased growth rate for the pine

Local characteristics of the standing genetic diversity of European beech with high within-region differentiation at the eastern part of the range

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 stands (Fagus sylvatica L.) established within the CLIMO (CLImate Smart Forestry in MOuntain Regions) project, using nuclear microsatellite markers. The sampling sites were set along the species' distribution range, including the Balkan region and extending towards the Iberian Peninsula. Cores or leaves from 20 to 23 old, mature trees per plot were sampled for DNA analysis. Genetic diversity indices were high across the range (H-E = 0.74-0.81) with the highest in the Bosnian Mountains. Genetic divergence increased significantly with the geographical distance (Mantel test: r = 0.81, p < 0.001). Most of the stands exhibited an excess of heterozygotes, with the highest value at the Hungarian site (H-O/H-E = 1.177), where beech persists close to the eastern xeric limit of the species' distribution. STRUCTURE revealed within-region differentiation in the Balkan Peninsula, where the Bulgarian stand was the most outstanding. The genetic parameters of each stand could be assessed as a resource for CSF indicators interpreted especially at the local level.The authors acknowledge the 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. Michal Bosela was additionally supported by the Slovak Research and Development Agency (project Nos. APVV-15-0265 and APVV-19-0183)

Mortality reduces overyielding in mixed Scots pine and European beech stands along a precipitation gradient in Europe

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 mor-tality. Here, we addressed this knowledge gap of mixed stand dynamics by evaluating 23 middle-aged, unthinned triplets of monospecific and mixed plots of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) repeatedly surveyed over 6-8 years throughout Europe. For explanation of technical terms in this abstract see Box 1.First, mixed stands produced more gross growth (+10%) but less net growth (-28%) compared with the weighted mean growth of monospecific stands. In monospecific stands, 73% of the gross growth was accumu-lated in the standing stock, whereas only 48% was accumulated in mixed stands. The gross overyielding of pine (2%) was lower than that of beech (18%). However, the net overyielding of beech was still 10%, whereas low growth and dropout of pine caused a substantial reduction from gross to net growth.Second, the mortality rates, the self-and alien-thinning strength, and the stem volume dropout were higher in mixed stands than monospecific stands. The main reason was the lower survival of pine, whereas beech persisted more similarly in mixed compared with monospecific stands.Third, we found a 10% higher stand density in mixed stands compared with monospecific stands at the first survey. This superiority decreased to 5% in the second survey.Fourth, the mixing proportion of Scots pine decreased from 46% to 44% between the first and second survey. The more than doubling of the segregation index (S) calculated by Pielou index (S increased from 0.2 to 0.5), indicated a strong tendency towards demixing due to pine.Fifth, we showed that with increasing water supply the dropout fraction of the gross growth in the mixture slightly decreased for pine, strongly increased for beech, and also increased for the stand as a whole. We discuss how the reduction of inter-specific competition by thinning may enable a continuous benefit of diversity and overyielding of mixed compared with monospecific stands of Scots pine and European beech

Storm event impact on organic matter flux, composition and reactivity in Taskinas Creek, VA

Carbon export from the land to the ocean are an important part of the global carbon cycle, linking terrestrial watersheds and the global carbon cycle. Burial of terrestrial organic carbon represents a long term sink for atmospheric CO2. Approximately 0.4 Pg Cy-1 is delivered to the global ocean from rivers, equally divided between POC and DOC. However, the amount of carbon entering the ocean is a small portion of the total amount entering rivers from the terrestrial environment, suggesting a large amount of processing in inland waters and estuaries. Most monitoring efforts have focused the processing of organic matter on baseflow conditions. However, recent studies have shown that POC and DOC exported during storm events, a small time period during a hydrologic year, can account for the majority of the annual carbon exported from small watersheds. This dissertation identifies the impact different magnitudes of storm events have on the source, composition and reactivity of organic carbon released to downstream waters from the terrestrial environment at Taskinas Creek, Virginia. The proximity of the Creek to the York River estuary, the changes in water table at the site, along with the small size of the watershed allowing opportunity to examine the connectivity between the watershed processes and delivery of organic matter made the site ideal for identifying how hydrology and environment alter POM and DOM export and reactivity. The sources, composition and flux of DOM and POM were measured during four storm events of different magnitudes to determine how events impacted the sources and fluxes of organic matter and the % reactive DOC exported. Events of different magnitudes with varying sources of DOC and POC had similar % reactive DOC that was not predicted using excitation emission spectroscopy. The events resulted in DOC fluxes 1.5-490 fold higher than baseflow. POC fluxes for storm were 6.7-55 times higher than DOC fluxes. Although the % reactive DOC did not increase during storm event conditions, coupled with the overall flux, storm events represent a considerable pulse of % reactive DOC to downstream waters, well above baseflow levels. When considered with increases in storm intensity due to climate change, storm event fluxes of reactive OM may have broad impacts on estuaries and the global carbon cycle through changes in carbon storage

European Mixed Forests: definition and research perspectives

peer-reviewedAim of study: We aim at (i) developing a reference definition of mixed forests in order to harmonize comparative research in mixed forests and (ii) briefly review the research perspectives in mixed forests. Area of study: The definition is developed in Europe but can be tested worldwide. Material and methods: Review of existent definitions of mixed forests based and literature review encompassing dynamics, management and economic valuation of mixed forests. Main results: A mixed forest is defined as a forest unit, excluding linear formations, where at least two tree species coexist at any developmental stage, sharing common resources (light, water, and/or soil nutrients). The presence of each of the component species is normally quantified as a proportion of the number of stems or of basal area, although volume, biomass or canopy cover as well as proportions by occupied stand area may be used for specific objectives. A variety of structures and patterns of mixtures can occur, and the interactions between the component species and their relative proportions may change over time. The research perspectives identified are (i) species interactions and responses to hazards, (ii) the concept of maximum density in mixed forests, (iii) conversion of monocultures to mixed-species forest and (iv) economic valuation of ecosystem services provided by mixed forests. Research highlights: The definition is considered a high-level one which encompasses previous attempts to define mixed forests. Current fields of research indicate that gradient studies, experimental design approaches, and model simulations are key topics providing new research opportunities.The networking in this study has been supported by COST Action FP1206 EuMIXFOR