The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Hans Pretzsch - One of the best experts on this subject based on the ideXlab platform.

  • European beech stem diameter grows better in Mixed than in mono-specific Stands at the edge of its distribution in mountain forests
    European Journal of Forest Research, 2020
    Co-Authors: Hans Pretzsch, David I. Forrester, Kamil Bielak, Miren Río, Torben Hilmers, Enno Uhl, Michal Bosela, Laura Dobor, Thomas A. Nagel, Maciej Pach
    Abstract:

    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.

  • stand growth and structure of Mixed species and monospecific Stands of scots pine pinus sylvestris l and oak q robur l quercus petraea matt liebl analysed along a productivity gradient through europe
    European Journal of Forest Research, 2020
    Co-Authors: Hans Pretzsch, Felipe Bravo, Peter Biber, Kamil Bielak, Ch Ammer, M Steckel, Michael Heym, Martin Ehbrecht, C Ordonez
    Abstract:

    Past failures of monocultures, caused by wind-throw or insect damages, and ongoing climate change currently strongly stimulate research into Mixed-species Stands. So far, the focus has mainly been on combinations of species with obvious complementary functional traits. However, for any generalization, a broad overview of the mixing reactions of functionally different tree species in different mixing proportions, patterns and under different site conditions is needed, including assemblages of species with rather similar demands on resources such as light. Here, we studied the growth of Scots pine and oak in Mixed versus monospecific Stands on 36 triplets located along a productivity gradient across Europe, reaching from Sweden to Spain and from France to Georgia. The set-up represents a wide variation in precipitation (456–1250 mm year−1), mean annual temperature (6.7–11.5 °C) and drought index by de Martonne (21–63 mm °C−1). Stand inventories and increment cores of trees stemming from 40- to 132-year-old, fully stocked Stands on 0.04–0.94-ha-sized plots provided insight into how species mixing modifies stand growth and structure compared with neighbouring monospecific Stands. On average, the standing stem volume was 436 and 360 m3 ha−1 in the monocultures of Scots pine and oak, respectively, and 418 m3 ha−1 in the Mixed Stands. The corresponding periodical annual volume increment amounted to 10.5 and 9.1 m3 ha−1 year−1 in the monocultures and 10.5 m3 ha−1 year−1 in the Mixed Stands. Scots pine showed a 10% larger quadratic mean diameter (p < 0.05), a 7% larger dominant diameter (p < 0.01) and a 9% higher growth of basal area and volume in Mixed Stands compared with neighbouring monocultures. For Scots pine, the productivity advantages of growing in mixture increased with site index (p < 0.01) and water supply (p < 0.01), while for oak they decreased with site index (p < 0.01). In total, the superior productivity of Mixed Stands compared to monocultures increased with water supply (p < 0.10). Based on 7843 measured crowns, we found that in mixture both species, but especially oak, had significantly wider crowns (p < 0.001) than in monocultures. On average, we found relatively small effects of species mixing on stand growth and structure. Scots pine benefiting on rich, and oak on poor sites, allows for a mixture that is productive and most likely climate resistant all along a wide ecological gradient. We discuss the potential of this mixture in view of climate change.

  • tree ring wood density of scots pine and european beech lower in Mixed species Stands compared with monocultures
    Forest Ecology and Management, 2017
    Co-Authors: Laura Zeller, Peter Biber, Gerhard Schutze, Ch Ammer, Peter Annighofer, John D Marshall, M Del Rio Gaztelurrutia, Hans Pretzsch
    Abstract:

    Abstract Mixed species Stands are on the advance in Central Europe and many recently published studies have reported that they can overyield monocultures in terms of volume growth. However, as forest research has in the past been focused on monocultures, knowledge of how Mixed-species Stands and monocultures compare in terms of wood quality remains limited. Based on five triplets of fully stocked monocultures and Mixed Stands of Scots pine ( Pinus sylvestris L.) and European beech ( Fagus sylvatica L.), we analysed whether tree species mixing modifies wood quality and, more precisely, tree ring wood density. From a total of 322 trees we sampled increment cores for the analyses of tree ring width and tree ring wood density using a LIGNOSTATION™. We found that tree ring width of Scots pine was, on average, 14% wider in Mixed compared with pure Stands. Tree ring width of European beech did not differ between pure and Mixed Stands. Tree ring wood density was lower in Mixed Stands compared to pure Stands for both Scots pine (−12%) and European beech (−8%). Tree ring wood density and tree ring width were negatively correlated in the case of Scots pine and positively correlated for European beech. When considering tree size and Stand density index, it was found that only tree ring width and mean tree ring wood density of European beech were influenced by stand density. Tree size had a significant effect only on tree ring wood density of European beech. The overall result of larger tree rings of Scots pine in Mixed Stands and a lower tree ring wood density of both species in Mixed Stands compared to pure Stands was not influenced by stand density or tree size. Based on the measured values of tree ring wood density we conducted estimates of how Mixed Stands performed in terms of biomass. We found stem biomass to be 8% lower in Mixed Stands compared to pure Stands. Reasons for the revealed differences in tree ring wood density and consequences for, among others, overyielding, carbon storage, and wood quality are discussed.

  • stem growth is favored at expenses of root growth in Mixed Stands and humid conditions for douglas fir pseudotsuga menziesii and european beech fagus sylvatica
    Trees-structure and Function, 2017
    Co-Authors: Eric Andreas Thurm, Peter Biber, Hans Pretzsch
    Abstract:

    The study found an increased investment into stem growth (compared to root growth) if trees were surrounded by a complementary species. This response is consistent with known patterns about root–stem allometry under favorable conditions (humidity and stand density). The study investigated partitioning of resources between roots and stems in mono-species and Mixed-species Stands of Douglas-fir and European beech at four different sites. We combined tree ring analyses of stems and coarse roots to scrutinize root–stem allometry with a focus on how it is influenced by species mixture and humidity. The results show that allometry in Mixed Stands changed in favor of stem growth for both species. The greatest relative allocation into stem growth was observed for individual trees which were completely surrounded by trees of the other species. The data indicate that a decrease of stand density, which was used as a proxy for tree competition, has the same effect on allocation. To analyze the influence of humidity, we used a long- and short-term index. Based on these, we can show that allocation changes with general site conditions and annual humidity variations. We found that on both time scales, both species increase resource investment into stem growth if conditions are more humid. Under harsher conditions, allocation shifts into root growth. The findings contribute to understanding the overyielding in Mixed Stands. Mixing Douglas-fir and European beech leads to the same allocation patterns as an improvement of site conditions. We suggest that for both species, mixture is equivalent to growing on a better site.

  • improved productivity and modified tree morphology of Mixed versus pure Stands of european beech fagus sylvatica and douglas fir pseudotsuga menziesii with increasing precipitation and age
    Annals of Forest Science, 2016
    Co-Authors: Eric Andreas Thurm, Hans Pretzsch
    Abstract:

    The mixture of Douglas-fir and European beech produced more biomass compared to what would have been expected from a weighted average of pure Stands. Overyielding of the Mixed Stands improved with increasing stand age and under better site conditions. The mixture of Douglas-fir and European beech has the intrinsic potential to be one of the most productive forest types in Central Europe. The study investigated how the structure and productivity of Mixed Stands changed in comparison to pure ones. It analyzed whether there is overyielding in Mixed Stands and if it was modified due to stand development or along an ecological gradient. Throughout Germany, 18 research plot triplets with 1987 trees were established in seven different ecological regions from dry to moist site conditions at ages 30 to 120 years. To investigate the growth of the Stands, tree cores were collected from 1293 stems. The study revealed significant overyielding of biomass in Mixed Stands of 6 % or 0.81 Mg ha−1 year−1. It was found that: (i) Overyielding in Mixed Stands was driven by an increase in Douglas-fir growth. (ii) Both species modified their morphology in mixture. Compared to the species in pure Stands, Douglas-fir diameters in Mixed Stands were significantly larger, whereas European beech had a smaller diameter at breast height in the mixture. The effect increased with the age. (iii) The analyses revealed more pronounced overyielding in older Stands and on better sites. The findings show that overyielding of Douglas-fir and European beech in Mixed Stands results from a higher light interception by complementary space occupation.

Kamil Bielak - One of the best experts on this subject based on the ideXlab platform.

  • European beech stem diameter grows better in Mixed than in mono-specific Stands at the edge of its distribution in mountain forests
    European Journal of Forest Research, 2020
    Co-Authors: Hans Pretzsch, David I. Forrester, Kamil Bielak, Miren Río, Torben Hilmers, Enno Uhl, Michal Bosela, Laura Dobor, Thomas A. Nagel, Maciej Pach
    Abstract:

    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.

  • stand growth and structure of Mixed species and monospecific Stands of scots pine pinus sylvestris l and oak q robur l quercus petraea matt liebl analysed along a productivity gradient through europe
    European Journal of Forest Research, 2020
    Co-Authors: Hans Pretzsch, Felipe Bravo, Peter Biber, Kamil Bielak, Ch Ammer, M Steckel, Michael Heym, Martin Ehbrecht, C Ordonez
    Abstract:

    Past failures of monocultures, caused by wind-throw or insect damages, and ongoing climate change currently strongly stimulate research into Mixed-species Stands. So far, the focus has mainly been on combinations of species with obvious complementary functional traits. However, for any generalization, a broad overview of the mixing reactions of functionally different tree species in different mixing proportions, patterns and under different site conditions is needed, including assemblages of species with rather similar demands on resources such as light. Here, we studied the growth of Scots pine and oak in Mixed versus monospecific Stands on 36 triplets located along a productivity gradient across Europe, reaching from Sweden to Spain and from France to Georgia. The set-up represents a wide variation in precipitation (456–1250 mm year−1), mean annual temperature (6.7–11.5 °C) and drought index by de Martonne (21–63 mm °C−1). Stand inventories and increment cores of trees stemming from 40- to 132-year-old, fully stocked Stands on 0.04–0.94-ha-sized plots provided insight into how species mixing modifies stand growth and structure compared with neighbouring monospecific Stands. On average, the standing stem volume was 436 and 360 m3 ha−1 in the monocultures of Scots pine and oak, respectively, and 418 m3 ha−1 in the Mixed Stands. The corresponding periodical annual volume increment amounted to 10.5 and 9.1 m3 ha−1 year−1 in the monocultures and 10.5 m3 ha−1 year−1 in the Mixed Stands. Scots pine showed a 10% larger quadratic mean diameter (p < 0.05), a 7% larger dominant diameter (p < 0.01) and a 9% higher growth of basal area and volume in Mixed Stands compared with neighbouring monocultures. For Scots pine, the productivity advantages of growing in mixture increased with site index (p < 0.01) and water supply (p < 0.01), while for oak they decreased with site index (p < 0.01). In total, the superior productivity of Mixed Stands compared to monocultures increased with water supply (p < 0.10). Based on 7843 measured crowns, we found that in mixture both species, but especially oak, had significantly wider crowns (p < 0.001) than in monocultures. On average, we found relatively small effects of species mixing on stand growth and structure. Scots pine benefiting on rich, and oak on poor sites, allows for a mixture that is productive and most likely climate resistant all along a wide ecological gradient. We discuss the potential of this mixture in view of climate change.

  • mixing of scots pine pinus sylvestris l and european beech fagus sylvatica l enhances structural heterogeneity and the effect increases with water availability
    Forest Ecology and Management, 2016
    Co-Authors: Hans Pretzsch, Kamil Bielak, Gerhard Schutze, Ch Ammer, Peter Annighofer, M Del Rio, Admir Avdagic, Ignacio Barbeito, Gediminas Brazaitis, Lluis Coll
    Abstract:

    The mixing of tree species with complementary ecological traits may modify forest functioning regarding productivity, stability, or resilience against disturbances. This may be achieved by a higher heterogeneity in stand structure which is often addressed but rarely quantified. Here, we use 32 triplets of mature and fully stocked monocultures and Mixed Stands of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) located along a productivity and water availability gradient through Europe to examine how mixing modifies the stand structure in terms of stand density, horizontal tree distribution pattern, vertical stand structure, size distribution pattern, and variation in tree morphology. We further analyze how site conditions modify these aspects of stand structure. For this typical mixture of a light demanding and shade tolerant species we show that (i) mixing significantly increases many aspects of structural heterogeneity compared with monocultures, (ii) mixing effects such as an increase of stand density and diversification of vertical structure and tree morphology are caused by species identity (additive effects) but also by species interactions (multiplicative effects), and (iii) superior heterogeneity of Mixed Stands over monocultures can increase from dry to moist sites. We discuss the implications for analyzing the productivity, for modelling and for the management of Mixed species Stands.

  • Characterization of the structure, dynamics, and productivity of Mixed-species Stands: review and perspectives
    European Journal of Forest Research, 2016
    Co-Authors: Miren Río, Felipe Bravo, Andreas Brunner, Hans Pretzsch, Sonia Condes, Kamil Bielak, Iciar Alberdi, Mark J. Ducey, Teresa Fonseca, Nikolas Lüpke
    Abstract:

    The growth and yield of Mixed-species Stands has become an important topic of research since there are certain advantages of this type of forest as regards functions and services. However, the concepts and methods used to characterize Mixed Stands need to be understood, as well as harmonized and standardized. In this review we have compiled a set of measures, indices, and methods at stand level to characterize the structure, dynamics, and productivity of Mixed Stands, and we discuss the pros and cons of their application in growth and yield studies. Parameters for the characterization of Mixed stand structure such as stand density, species composition, horizontal (intermingling) and vertical tree distribution pattern, tree size distribution, and age composition are described, detailing the potential as well as the constraints of these parameters for understanding resource capture, use, and efficiency in Mixed Stands. Furthermore, a set of stand-level parameters was evaluated to characterize the dynamics of Mixed Stands, e.g. height growth and space partitioning, self- and alien-thinning, and growth partitioning among trees. The deviations and changes in the behaviour of the analysed parameters in comparison with pure stand conditions due to inter-specific interactions are of particular interest. As regards stand productivity, we reviewed site productivity indices, the growth–density relationship in Mixed Stands as well as methods to compare productivity in Mixed versus monospecific Stands. Finally, we discuss the main problems associated with the methodology such as up-scaling from tree to stand level as well as the relevance of standardized measures and methods for improving forest growth and yield research in Mixed Stands. The main challenges are also outlined, especially the need for qualitatively sound data.

  • Mixed Stands of scots pine pinus sylvestris l and norway spruce picea abies l karst can be more productive than monocultures evidence from over 100 years of observation of long term experiments
    Forest Systems, 2014
    Co-Authors: Kamil Bielak, M Dudzinska, Hans Pretzsch
    Abstract:

    Aim of study: The objective of this study was to analyse the effect of species mixing of Scots pine and Norway spruce on the productivity at the stand and species level. We also analysed to what extent the mixing effects is modified by drought stress. Area of study: The study was conducted in N-E Poland and based on three experiments located in Maskulinskie, Strzal/owo and Kwidzyn Forest Districts. Material and methods: We evaluated long-term Mixed-species experiments in Scots pine and Norway spruce which are under continuous survey since more than 100 years. Stand productivity was analysed based on the periodic annual increment and total yield of stem volume. Growth and yield were compared between Mixed and neighbouring pure Stands. As a substitute for the missing Norway spruce monocultures, we used appropriate yield table data. In order to characterize the effect of water supply on the mixing effects, we correlated the Martonne index of aridity with the ratio of Scots pine growth in Mixed versus pure Stands. Main results: We found that the Mixed Stands exceed the weighted mean of the pure Stands’ volume productivity on average by 41%. At the species level Scots pine benefits from the mixture by 34% and Norway spruce by 83%. Growth periods with harsh climate conditions reinforce overyielding, while periods with mild conditions reduce the benefit of mixing. The overyielding of Mixed Stands, especially when growing under unfavourable conditions, is explained by niche complementarity of both species and discussed in view of the stress-gradient-hypothesis. Research highlights: The revealed overyielding of Mixed compared with neighbouring pure Stands, particularly under harsh weather conditions, substantiates the preferences of Scots pine-Norway spruce mixtures regarding climate change.

Gerhard Schutze - One of the best experts on this subject based on the ideXlab platform.

  • tree ring wood density of scots pine and european beech lower in Mixed species Stands compared with monocultures
    Forest Ecology and Management, 2017
    Co-Authors: Laura Zeller, Peter Biber, Gerhard Schutze, Ch Ammer, Peter Annighofer, John D Marshall, M Del Rio Gaztelurrutia, Hans Pretzsch
    Abstract:

    Abstract Mixed species Stands are on the advance in Central Europe and many recently published studies have reported that they can overyield monocultures in terms of volume growth. However, as forest research has in the past been focused on monocultures, knowledge of how Mixed-species Stands and monocultures compare in terms of wood quality remains limited. Based on five triplets of fully stocked monocultures and Mixed Stands of Scots pine ( Pinus sylvestris L.) and European beech ( Fagus sylvatica L.), we analysed whether tree species mixing modifies wood quality and, more precisely, tree ring wood density. From a total of 322 trees we sampled increment cores for the analyses of tree ring width and tree ring wood density using a LIGNOSTATION™. We found that tree ring width of Scots pine was, on average, 14% wider in Mixed compared with pure Stands. Tree ring width of European beech did not differ between pure and Mixed Stands. Tree ring wood density was lower in Mixed Stands compared to pure Stands for both Scots pine (−12%) and European beech (−8%). Tree ring wood density and tree ring width were negatively correlated in the case of Scots pine and positively correlated for European beech. When considering tree size and Stand density index, it was found that only tree ring width and mean tree ring wood density of European beech were influenced by stand density. Tree size had a significant effect only on tree ring wood density of European beech. The overall result of larger tree rings of Scots pine in Mixed Stands and a lower tree ring wood density of both species in Mixed Stands compared to pure Stands was not influenced by stand density or tree size. Based on the measured values of tree ring wood density we conducted estimates of how Mixed Stands performed in terms of biomass. We found stem biomass to be 8% lower in Mixed Stands compared to pure Stands. Reasons for the revealed differences in tree ring wood density and consequences for, among others, overyielding, carbon storage, and wood quality are discussed.

  • mixing of scots pine pinus sylvestris l and european beech fagus sylvatica l enhances structural heterogeneity and the effect increases with water availability
    Forest Ecology and Management, 2016
    Co-Authors: Hans Pretzsch, Kamil Bielak, Gerhard Schutze, Ch Ammer, Peter Annighofer, M Del Rio, Admir Avdagic, Ignacio Barbeito, Gediminas Brazaitis, Lluis Coll
    Abstract:

    The mixing of tree species with complementary ecological traits may modify forest functioning regarding productivity, stability, or resilience against disturbances. This may be achieved by a higher heterogeneity in stand structure which is often addressed but rarely quantified. Here, we use 32 triplets of mature and fully stocked monocultures and Mixed Stands of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) located along a productivity and water availability gradient through Europe to examine how mixing modifies the stand structure in terms of stand density, horizontal tree distribution pattern, vertical stand structure, size distribution pattern, and variation in tree morphology. We further analyze how site conditions modify these aspects of stand structure. For this typical mixture of a light demanding and shade tolerant species we show that (i) mixing significantly increases many aspects of structural heterogeneity compared with monocultures, (ii) mixing effects such as an increase of stand density and diversification of vertical structure and tree morphology are caused by species identity (additive effects) but also by species interactions (multiplicative effects), and (iii) superior heterogeneity of Mixed Stands over monocultures can increase from dry to moist sites. We discuss the implications for analyzing the productivity, for modelling and for the management of Mixed species Stands.

  • temporal variation of competition and facilitation in Mixed species forests in central europe
    Plant Biology, 2014
    Co-Authors: M Del Rio, Gerhard Schutze, Hans Pretzsch
    Abstract:

    Facilitation, reduced competition or increased competition can arise in Mixed Stands and become essential to the performance of these Stands when compared to pure Stands. Facilitation and over-yielding are widely held to prevail on poor sites, whereas neutral interactions or competition, leading to under-yielding of Mixed versus pure Stands, can occur on fertile sites. While previous studies have focused on the spatial variation of mixing effects, we examine the temporal variation of facilitation and competition and its effect on growth. The study is based on tree ring measurement on cores from increment borings from 559 trees of Norway spruce (Picea abies [L.] Karst.), European beech (Fagus sylvatica [L.]) and sessile oak (Quercus petraea (Matt.) Liebl.) in southern Germany, half of which were in pure Stands and half in adjacent Mixed Stands. Mean basal area growth indices were calculated from tree ring measurements for pure and Mixed Stands for every species and site. The temporal variation, with positive correlations between species-specific growth indices during periods of low growth and neutral or negative correlations during periods of high growth, is more distinct in Mixed than in neighbouring pure Stands. We provide evidence that years with low growth trigger over-yielding of trees in Mixed as opposed to pure Stands, while years with high growth lead to under-yielding. We discuss the relevance of the results in terms of advancing our understanding and modelling of Mixed Stands, extension of the stress gradient hypothesis, and the performance of Mixed versus pure Stands in the face of climate change.

  • transgressive overyielding in Mixed compared with pure Stands of norway spruce and european beech in central europe evidence on stand level and explanation on individual tree level
    European Journal of Forest Research, 2009
    Co-Authors: Hans Pretzsch, Gerhard Schutze
    Abstract:

    The temperate, humid climate and nutrient-rich soils in the pre-alpine areas of southern Bavaria represent conditions where European beech and Norway spruce come out with rather equal above ground biomass production when cultivated in pure Stands. In order to reveal the effect of mixture we established 37 experimental plots in even-aged pure and Mixed Stands of Norway spruce and European beech covering an age span of 37–155 years. The site conditions ranged from warm, dry and base-rich to cool, wet and acidic sites. The ratio of above ground biomass growth of Norway spruce in relation to European beech decreases from 1.14:1 in the monocultures to 1.04:1 in the Mixed Stands. The mixing of spruce and beech results in a mutual stimulation of biomass production and acceleration of size growth. Together both species produce up to 59% more above ground biomass than the neighboring pure Stands. On average the overyielding amounts to 21% in the case of Norway spruce and 37% in the case of European beech. A total of 67% out of the plots indicate overyielding and 57% transgressive overyielding. In Mixed Stands both species’ tree sizes are significantly ahead of the corresponding pure Stands. Facilitation of spruce and competitive reduction of beech yields mutualism with respect to growth on tree and stand level. Consequences for analyzing and modeling interspecific competition and for silvicultural prescriptions are discussed. Ecological implications of the mixing effect on the occurrence and stability of natural and man-made Mixed Stands of spruce and beech are considered.

  • crown allometry and growing space efficiency of norway spruce picea abies l karst and european beech fagus sylvatica l in pure and Mixed Stands
    Plant Biology, 2005
    Co-Authors: Hans Pretzsch, Gerhard Schutze
    Abstract:

    : In pure and Mixed Stands of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) we have analyzed crown allometry and growing space efficiency at the tree level and have scaled this from tree level to stand level production. Allometry is quantified by the ratio A between the relative growth rates of laterally and vertically oriented tree dimensions. Efficiency parameters, EOC for efficiency in space occupation, EEX for efficiency in space exploitation, and EBI for efficiency in biomass investment, were evaluated, based on quantity and quality of growing space and were measured using crown size and competition index. The evaluation reveals why pure Stands of spruce are preferred by foresters, even though the natural vegetation would be dominated by beech. Spruce occupies its share of resources intensively by means of tightly packed pillar-like crowns, whereas beech seizes resources extensively by means of a multi-layered, veil-like canopy. With a given relative biomass increment, beech achieves a 57 % higher increment in crown projection area and a 127 % higher increment in height due to its particular capacity of lateral and vertical expansion. Beech trees are approximately 60 % more efficient in space occupation than spruce trees, however, on average, they are about 70 % less efficient in space exploitation. As a vertical fast growing tree, spruce is efficient in space exploitation under constant conditions, but far more susceptible to disturbances and less well equipped to overcome them when compared with beech. Beech is weaker in terms of space exploitation, while being superior in space occupation, where it encircles competitors and fills gaps after disturbances, which is a successful long-term strategy. A mixture of the two species reduces stand level production by 24 % in comparison to a pure spruce stand, however, when considering enhanced stabilization of the whole stand and risk distribution in the long term, the Mixed stand may exceed the production level of pure spruce Stands. EEX reflects a strong ontogenetic drift and competition effect that should be considered when scaling from tree to stand level production.

Hubert Sterba - One of the best experts on this subject based on the ideXlab platform.

  • effect of species proportion definition on the evaluation of growth in pure vs Mixed Stands
    Forest Systems, 2014
    Co-Authors: Hubert Sterba, Andreas Brunner, Miren Del Rio, Sonia Condes
    Abstract:

    Aim of study : The aim of this paper is to compare differences in growth per hectare of species in pure and Mixed Stands as they result from different definitions of species proportions. Area of Study : We used the data of the Spanish National Forest Inventory for Scots pine and beech mixtures in the province of Navarra and for Scots pine and Pyrenean oak mixtures in the Central mountain range and the North Iberic mountain range. Material and Methods : Growth models were parameterized with the species growth related to its proportion as dependent variable, and dominant height, quadratic mean diameter density, and species proportion as independent variables. As proportions we use once proportions by basal area or by stand density index and once these proportions considering the species specific maximum densities. Main Results : In the pine – beech mixtures, where the maximum densities do not differ very much between species, the mixing effects are very similar, independent of species proportion definitions. In the pine – oak mixture, where the maximum densities in terms of basal area are very different, the equations using the proportions calculated without reference to the maximum densities, result in a distinct overestimation of the mixing effects on growth. Research highlights : When comparing growth per hectare of a species in a Mixed stand with that of a pure stand, the species proportion must be described as a proportion by area considering the maximum density for the given species, wrong mixing effects could be introduced by inappropriate species proportion definitions. Keywords: Mixing effects; proportion by area; Stand Density Index; overyielding; Pinus sylvestris L.; Fagus sylvatica L.; Quercus pyrenaica Willd.

  • a comparison of different methods to estimate species proportions by area in Mixed Stands
    Forest Systems, 2014
    Co-Authors: Gerald Dirnberger, Hubert Sterba
    Abstract:

    Aim of the study: This paper presents the most appropriate ways to estimate the species proportions by area in Mixed Stands of Norway spruce ( Picea abies L. Karst.) and European beech ( Fagus sylvatica L.) by comparing stand level and individual tree level approaches. It also investigates whether different ways of describing species proportions by area can result in different judgments on the over- or under-yielding of species in mixtures. Area of the study: Three triplets of pure and Mixed Stands of Norway spruce and European beech in three locations in the northeast of Austria are investigated. The three locations differ considerably in slope, bedrock and soil type as well as in site index. Material and Methods: In all 9 plots the coordinates of all trees, their dbh, height, height to the crown base and five year increment were measured. The potentially available areas of individual trees are calculated by Voronoi- diagrams and potential densities are estimated from the comparable pure Stands, yield tables, and published equations for maximum basal area and Reineke’s maximum density line. Main results: The species proportions estimated by the individual tree approach with leaf area as growth characteristic gave the best fit with the stand approach with the most appropriate, regional maximum basal area equations. By using various definitions of species proportions, in the worst case the mixing effects on individual species can be seriously over- or underestimated while the mixing effects on the total increment is only negligibly affected. Research highlights Measures of species proportions by area are needed for comparing growth per hectare of a species in a Mixed stand with that of the same species in a pure stand Species proportions at the stand level are based on estimates of the species’ potential densities, either in terms of maximum basal area or of maximum stand density index Species proportions at the tree level are derived from the area potentially available (APA) to the individual trees, based on the coordinates of trees in the Stands, and on their growth characteristics, such as crown projection area or leaf area For the examples of Norway spruce - European beech Stands, the species proportions derived according to the individual tree approach using leaf area as growth characteristics fits best with the stand approach using the most appropriate maximum basal area equations Keywords: Picea abies ; Fagus sylvatica; mixture proportion; growth efficiency; mixing effect. Abbreviations used: APA – area potentially available.

  • mixing effect on volume growth of fagus sylvatica and pinus sylvestris is modulated by stand density
    Forest Ecology and Management, 2013
    Co-Authors: Sonia Condes, Miren Del Rio, Hubert Sterba
    Abstract:

    Abstract Despite the increasing relevance of Mixed Stands due to their potential benefits; little information is available with regard to the effect of mixtures on yield in forest systems. Hence, it is necessary to study inter-specific relationships, and the resulting yield in Mixed Stands, which may vary with stand development, site or stand density, etc. In Spain, the province of Navarra is considered one of the biodiversity reservoirs; however, Mixed forests occupy only a small area, probably as a consequence of management plans, in which there is an excessive focus on the productivity aspect, favoring the presence of pure Stands of the most marketable species. The aim of this paper is to study how growth efficiencies of beech ( Fagus sylvatica ) and pine ( Pinus sylvestris ) are modified by the admixture of the other species and to determine whether stand density modifies interspecific relationships and to what extent. Two models were fitted from Spanish National Forest Inventory data, for P. sylvestris and F. sylvatica respectively, which relate the growth efficiency of the species, i.e. the volume increment of the species divided by the species proportion by area, with dominant height, quadratic mean diameter, stocking degree, and the species proportions by area of each species. Growth efficiency of pine increased with the admixture of beech, decreasing this positive effect when stocking degree increased. However, the positive effect of pine admixture on beech growth was greater at higher stocking degrees. Growth efficiency of beech was also dependent on stand dominant height, resulting in a net negative mixing effect when stand dominant heights and stocking degrees were simultaneously low. There is a relatively large range of species proportions and stocking degrees which results in transgressive overyielding: higher volume increments in Mixed Stands than that of the most productive pure pine Stands. We concluded that stocking degree is a key factor in between-species interactions, being the effects of mixing not always greater at higher stand densities, but it depends on species composition.

  • Comparing volume growth in pure and Mixed Stands of Pinus sylvestris and Quercus pyrenaica
    Annals of Forest Science, 2009
    Co-Authors: Miren Del Río, Hubert Sterba
    Abstract:

    In Mediterranean forestry, it is important to improve knowledge about Mixed Stands dynamics, including their productivity. Previous studies have focused on the interactions between different species (competition, reduction of competition and facilitation) depending on site, species composition and structure. * At the centre of this research are the possible differences between pure and Mixed Stands of Pinus sylvestris and Quercus pyrenaica in terms of density-growth relationships and volume growth per species. * Using data from the second and third Spanish National Forest Inventory (606 plots), volume increment models for these species were fitted. Both species displayed a similar density-growth pattern for pure and Mixed Stands, with a maximum volume growth at maximum density. Volume increment per occupied area was also found to be greater in Mixed Stands as opposed to pure Stands, suggesting a species interaction with reduced levels of competition in the former. However, the total volume growth was generally lower in Mixed Stands since the growth rate of oak is much lower. * The results highlight the expedience of favouring P. sylvestris-Q. pyrenaica Mixed Stands with higher proportions of pine trees in order to gain the benefits of a more complex forest whilst retaining an acceptable level of wood production.

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  • stand growth and structure of Mixed species and monospecific Stands of scots pine pinus sylvestris l and oak q robur l quercus petraea matt liebl analysed along a productivity gradient through europe
    European Journal of Forest Research, 2020
    Co-Authors: Hans Pretzsch, Felipe Bravo, Peter Biber, Kamil Bielak, Ch Ammer, M Steckel, Michael Heym, Martin Ehbrecht, C Ordonez
    Abstract:

    Past failures of monocultures, caused by wind-throw or insect damages, and ongoing climate change currently strongly stimulate research into Mixed-species Stands. So far, the focus has mainly been on combinations of species with obvious complementary functional traits. However, for any generalization, a broad overview of the mixing reactions of functionally different tree species in different mixing proportions, patterns and under different site conditions is needed, including assemblages of species with rather similar demands on resources such as light. Here, we studied the growth of Scots pine and oak in Mixed versus monospecific Stands on 36 triplets located along a productivity gradient across Europe, reaching from Sweden to Spain and from France to Georgia. The set-up represents a wide variation in precipitation (456–1250 mm year−1), mean annual temperature (6.7–11.5 °C) and drought index by de Martonne (21–63 mm °C−1). Stand inventories and increment cores of trees stemming from 40- to 132-year-old, fully stocked Stands on 0.04–0.94-ha-sized plots provided insight into how species mixing modifies stand growth and structure compared with neighbouring monospecific Stands. On average, the standing stem volume was 436 and 360 m3 ha−1 in the monocultures of Scots pine and oak, respectively, and 418 m3 ha−1 in the Mixed Stands. The corresponding periodical annual volume increment amounted to 10.5 and 9.1 m3 ha−1 year−1 in the monocultures and 10.5 m3 ha−1 year−1 in the Mixed Stands. Scots pine showed a 10% larger quadratic mean diameter (p < 0.05), a 7% larger dominant diameter (p < 0.01) and a 9% higher growth of basal area and volume in Mixed Stands compared with neighbouring monocultures. For Scots pine, the productivity advantages of growing in mixture increased with site index (p < 0.01) and water supply (p < 0.01), while for oak they decreased with site index (p < 0.01). In total, the superior productivity of Mixed Stands compared to monocultures increased with water supply (p < 0.10). Based on 7843 measured crowns, we found that in mixture both species, but especially oak, had significantly wider crowns (p < 0.001) than in monocultures. On average, we found relatively small effects of species mixing on stand growth and structure. Scots pine benefiting on rich, and oak on poor sites, allows for a mixture that is productive and most likely climate resistant all along a wide ecological gradient. We discuss the potential of this mixture in view of climate change.

  • tree ring wood density of scots pine and european beech lower in Mixed species Stands compared with monocultures
    Forest Ecology and Management, 2017
    Co-Authors: Laura Zeller, Peter Biber, Gerhard Schutze, Ch Ammer, Peter Annighofer, John D Marshall, M Del Rio Gaztelurrutia, Hans Pretzsch
    Abstract:

    Abstract Mixed species Stands are on the advance in Central Europe and many recently published studies have reported that they can overyield monocultures in terms of volume growth. However, as forest research has in the past been focused on monocultures, knowledge of how Mixed-species Stands and monocultures compare in terms of wood quality remains limited. Based on five triplets of fully stocked monocultures and Mixed Stands of Scots pine ( Pinus sylvestris L.) and European beech ( Fagus sylvatica L.), we analysed whether tree species mixing modifies wood quality and, more precisely, tree ring wood density. From a total of 322 trees we sampled increment cores for the analyses of tree ring width and tree ring wood density using a LIGNOSTATION™. We found that tree ring width of Scots pine was, on average, 14% wider in Mixed compared with pure Stands. Tree ring width of European beech did not differ between pure and Mixed Stands. Tree ring wood density was lower in Mixed Stands compared to pure Stands for both Scots pine (−12%) and European beech (−8%). Tree ring wood density and tree ring width were negatively correlated in the case of Scots pine and positively correlated for European beech. When considering tree size and Stand density index, it was found that only tree ring width and mean tree ring wood density of European beech were influenced by stand density. Tree size had a significant effect only on tree ring wood density of European beech. The overall result of larger tree rings of Scots pine in Mixed Stands and a lower tree ring wood density of both species in Mixed Stands compared to pure Stands was not influenced by stand density or tree size. Based on the measured values of tree ring wood density we conducted estimates of how Mixed Stands performed in terms of biomass. We found stem biomass to be 8% lower in Mixed Stands compared to pure Stands. Reasons for the revealed differences in tree ring wood density and consequences for, among others, overyielding, carbon storage, and wood quality are discussed.

  • stem growth is favored at expenses of root growth in Mixed Stands and humid conditions for douglas fir pseudotsuga menziesii and european beech fagus sylvatica
    Trees-structure and Function, 2017
    Co-Authors: Eric Andreas Thurm, Peter Biber, Hans Pretzsch
    Abstract:

    The study found an increased investment into stem growth (compared to root growth) if trees were surrounded by a complementary species. This response is consistent with known patterns about root–stem allometry under favorable conditions (humidity and stand density). The study investigated partitioning of resources between roots and stems in mono-species and Mixed-species Stands of Douglas-fir and European beech at four different sites. We combined tree ring analyses of stems and coarse roots to scrutinize root–stem allometry with a focus on how it is influenced by species mixture and humidity. The results show that allometry in Mixed Stands changed in favor of stem growth for both species. The greatest relative allocation into stem growth was observed for individual trees which were completely surrounded by trees of the other species. The data indicate that a decrease of stand density, which was used as a proxy for tree competition, has the same effect on allocation. To analyze the influence of humidity, we used a long- and short-term index. Based on these, we can show that allocation changes with general site conditions and annual humidity variations. We found that on both time scales, both species increase resource investment into stem growth if conditions are more humid. Under harsher conditions, allocation shifts into root growth. The findings contribute to understanding the overyielding in Mixed Stands. Mixing Douglas-fir and European beech leads to the same allocation patterns as an improvement of site conditions. We suggest that for both species, mixture is equivalent to growing on a better site.

  • tree species mixing can increase maximum stand density
    Canadian Journal of Forest Research, 2016
    Co-Authors: Hans Pretzsch, Peter Biber
    Abstract:

    Mixed-species Stands are on the advance in Europe. They fulfil many functions better than monocultures. Recent papers show that Mixed Stands can have higher yields, but it remains open whether Mixed Stands simply grow faster along the same self-thinning lines as pure Stands or have higher maximum stand densities. We analyzed the effect of species mixing on maximum density based on triplets of pure and Mixed Stands at approximately maximum density. Most considered mixtures include Norway spruce (Picea abies (L.) H. Karst.). We show that (i) in Mixed Stands, maximum density is, on average, 16.5% higher than in neighbouring pure Stands, and (ii) species mixtures with Norway spruce exceed densities of pure Stands by 8.8%, on average. For individual species mixtures, we find a significant density effect of +29.1% for Norway spruce Mixed with European larch (Larix decidua Mill.) and +35.9% for Scots pine (Pinus sylvestris L.) in association with European beech (Fagus sylvatica L.). No significant links with sta...