Maciej Pach

Characterization of the structure, dynamics, and productivity of mixed-species stands: review and perspectives

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.

Tree diameter structural diversity in Central European forests with Abies alba and Fagus sylvatica: managed versus unmanaged forest stands

Abstract The biodiversity of forest stands should be analysed from the point of view of not only compositional elements but also structural diversity. The main objective of this study was to compare tree diameter structural diversity of the mixed managed and unmanaged stands with Abies alba and Fagus sylvatica. There were 62 study plots established in the Carpathians (Southern Poland) and in the Świętokrzyskie Mountains (Central Poland) in managed and unmanaged stands. The comparison of the studied stands involved the identification and modelling of size structures, the use of the Gini coefficient and the relative distribution method (including entropy and polarisation). Six structural types were distinguished: three unimodals of a different width of diameter at breast height (DBH) range (mainly for the managed stands), reverse-J, rotated-sigmoid and bimodal (for unmanaged stands). Modelling of the distinguished structural types by means of theoretical distributions has shown that the best results of approximation for unimodal skewed and reverse-J DBH distributions were obtained with the single Weibull and gamma distribution, while in the case of rotated-sigmoid and bimodal DBH distributions the best results were obtained with mixture models. The comparisons have shown that tree diameter structural diversity was more complex in unmanaged forests compared to managed stands. For managed stands the Gini coefficient assumed values from 0.31 to 0.48, while in the case of the unmanaged forests, from 0.33 to 0.73. One should aim to increase tree diameter structural diversity in managed forests, adopting the close-to-nature silviculture concept which consists of imitating natural processes.

Species proportions by area in mixtures of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.)

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 comparison of different species in mixed and monospecific stands. Thus, we studied different methods to describe species proportions and their definition as proportion by area. 25 triplets consisting of mixed and monospecific stands were established across Europe ranging from Lithuania to Spain in northern to southern direction and from Bulgaria to Belgium in eastern to western direction. On stand level, the conclusive method for estimating the species proportion as a fraction of the stand area relates the observed density (tree number or basal area) to its potential. This stand-level estimation makes use of the potential from comparable neighboring monospecific stands or from maximum density lines derived from other data, e.g. forest inventories or permanent observations plots. At tree level, the fraction of the stand area occupied by a species can be derived from the proportions of their crown projection area or of their leaf area. The estimates of the potentials obtained from neighboring monospecific stands, especially in older stands, were poorer than those from the maximum density line depending on the Martonne aridity index. Therefore, the stand-level method in combination with the Martonne aridity index for potential densities can be highly recommended. The species’ proportions estimated with this method are best approximated by the proportions of the species’ leaf areas. In forest practice, the most commonly applied method is an ocular estimation of the proportions by crown projection area. Even though the proportions of pine were calculated here by measuring crown projection areas in the field, we found this method to underestimate the proportion by 25% compared to the stand-level approach.

EuMIXFOR empirical forest mensuration and ring width data from pure and mixed stands of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) through Europe

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.doi.org/10.5061/dryad.8v04m. Associated metadata available athttps://metadata-afs.nancy.inra.fr/geonetwork/apps/georchestra/?uuid=b3e098ca-e681-4910-9099-0e25d3b4cd52&hl=eng.

A comparison of lower montane natural forest (Abies, Fagus, Picea) in Oszast Reserve and spruce monocultures in the Żywiecki Beskid and Śląski Beskid

Abstract The aim of this research was to find out what changes occurred between 1999-2009 in Oszast reserve in the volume, species composition and diameter at breast height (dbh) distribution of the forest stand, and the number and height of regeneration. The objective was to determine what would be condition of these managed lower montane multispecies forest stands (Swiss irregular shelterwood method or selection cuttings) and what role spruce would play in them if they have not been replaced by spruce monocultures. The research was conducted on three permanent circular sample plots (s.p.), each had size of 1/3 ha. Over 10 years, standing volume of the forest stand increased on s.p. 1 (from around 562 m3/ha to 649 m3/ha) and s.p. 3. (from 653 m3/ha to 660 m3/ha), while decreased on s.p. 2. (from 421 m3/ha to 378 m3/ha). The species composition, defined on the basis of volume share (averaged for the three s.p. jointly), did not undergo consistent changes. However, the relative dominance of beech over spruce was determined based on tree numbers. The average spruce mortality (averaged from three s.p.) did not exceed 10% and was slightly higher than that of beech (6%), and lower than fir mortality (15%). Nevertheless, spruce did not show any symptoms of dieback. The reasons behind its mortality were fallen trees and windbreaks. In regeneration, on the whole, beech or sycamore predominated, and the proportion of spruce and fir was small. In the future spruce and fir may even decrease further by competitive ability of dynamically regenerating beech. Abandonment of forest management to promote greater diversity of species, may favour the formation of beech monocultures, or forest stands dominated by beech, everywhere that beech is already present or will be introduced. The maintenance of stable, multispecies forest stands, with co-dominant fir, beech and spruce of native origin, requires natural or artificial regeneration of spruce and fir, manipulated to restore fir up to about 30%, and reduce spruce down to about 40%. This would be possible through the use of the Swiss irregular shelterwood method and selection system, and by continuous tending of regeneration

Crookedness of pedunculate oak (Quercus robur L.) growing under a canopy of Scots pine (Pinus sylvestris L.)

Natural regeneration of pedunculate oak growing under a canopy of Scots may be used for conversion into a mixed or predominantly broadleaved forest. From an economic perspective it is desirable that the oaks have straight stems. In this paper we present a case study for analysing oak stem curvature and its causes. The study was conducted in a mature pine stand with understorey oaks of age ca. 60 years in Poland. The oaks were classified into two main groups as either straight or crooked. The following variables were measured or assessed for the oaks: (1) stem curvature (crookedness), total tree height, diameter at breast height (DBH) and some tree crown characteristics, (2) the growth of DBH and height in each year of the life of each tree and (3) the competitive pressure of surrounding trees. Durable stem curvatures were formed at the culmination of the height increment. The first 20 years of the life of the oak were crucial in terms of stem quality. The annual height increment was larger in the years when the curvature was formed than in adjacent years. The factors that caused crooked stems were the same for straight and crooked oaks, but the magnitude of the response was different. When planning the conversion of Scots pine into oak, full overhead light should be provided as early as possible, but not later than 20 years since the establishment of the regeneration.

What Characteristics of Soil Fertility Can Improve in Mixed Stands of Scots Pine and European Beech Compared with Monospecific Stands

ABSTRACT According to the current trends in forest management, endeavors are made to adjust the species composition to the site conditions and to increase the biodiversity. Changes in the species composition of forest stands lead to modifications of soil properties and nutrients cycle. The objective of the study was to evaluate the effect of monocultures (beech and pine) and mixed-species stands (pine-beech) on soil properties, particularly accumulation of soil organic carbon. We aim to demonstrate how different vegetation types influence soil properties in surface horizons of soil. The study sites are located in Germany and Poland under different tree stands Pinus sylvestris L., Fagus sylvatica L., and mixed-species stand. Contents of organic carbon and nitrogen, pH, and soil texture were analyzed. The studies conducted confirmed the positive effect of beech and mixed-species stands on acidification of surface soil horizons. We ordered the stands tested according to acidification effect on soils: pine stand > mixed stand > beech stand, which is consistent with previous studies. The most beneficial impact on the accumulation of organic carbon was observed in mixed-species stands in which beech and pine were found. Lower carbon-to-nitrogen (C/N) ratios confirm the high rate of organic matter decomposition and lower C/N ratio was reported in soil under beech stand in comparison to pine stands.

Acer Pseudoplatanus L., Tilia Cordata Mill. and Pinus Sylvestris L. as Valuable Tree Species in the Carpathian Forests

Sycamore maple, little-leaf linden, and Scots pine occurring in unique mixed stands, such as beech and sycamore maple in the Bieszczady Mountains, linden forest in the Obrozyska Reserve (the Beskid Sądecki Mountains), and scattered Carpathian pine forests, were the subject of this study. It was found that sycamore maple can be a highly productive admixture and a co-dominant or even dominant species in beech forests as a protective species of the upper timberline at altitudes between 930 and 1,160 m. Little-leaf linden in stands where site conditions meet its requirements, especially in the lower part of the lower mountain zone at altitudes up to 600–700 m, is a suitable admixture or even co-dominant species that increases productivity. In the Polish Carpathian forests three pine population groups were distinguished on the basis of morphological (cone) traits—lowland, foothill, and mountain group—which also varied according to timber quality, stem, and crown traits, as well as copper (Cu), iron (Fe), and potassium (K) content in needles. Pine is a very good nursing tree species that enables other tree species, especially fir, to occur among pine trees or underneath their canopies.

Comparison of various cutting systems affecting those morphological features that determine stability in the Pilsko high mountain spruce forest

Charakterystyka wybranych cech morfologicznych świerków wpływających na ich stabilność, ukształtowanych w wyniku stosowania różnych rębni w borze górnoreglowym na Pilsku Comparison of various cutting systems affecting those morphological features that determine stability in the Pilsko high mountain spruce forest The morphology of trees was studied in four sample plots located within the Pilsko high mountain spruce forest. Between the years 1950-1970 a single-tree selection system (Einzelplenterung) was used in the stands Pilsko 1 and 2, whereas in a third stand, Pilsko 3, selection was by group cutting (Gruppenplenterung). The tree-stand Pilsko 4 was generated by artificial restocking of a clear-cut area. The live crown ratio, coefficient of slenderness (h/d) and vitality of these four stands was compared. Group cutting (Pilsko 3), resembling a mountain selection system, produced the highest live crown ratio, lowest coefficient of slenderness (h/d) and highest vitality index of the four tree-stands examined. The spruces grown in the diversified tree-stands where a single-cutting system was used had features indicative of lower stability. In the artificial one-storey and even-aged stands, the two features that determine tree stability (namely, live crown ratio and coefficient of slenderness) had the worst values compared the remaining three stands. Consequently, to improve the stability of high mountain spruce forests in the Beskidy Mountains, under active environmental protection, we recommend the creation of groups within the forest, thus producing an irregular shelterwood system of group cuttings within a belt of closed forest, or a mountain selection system within a loose spruce forest.