Mixed Stands Research Articles

Climate Effects on Black Spruce and Trembling Aspen Productivity in Natural Origin Mixed Stands

Forest managers need site productivity estimates for tree species growing in mixed stands. Models developed in the past are generally for pure stands and don’t factor in the effects of climate change on site productivity. Therefore, site index (SI) models were developed for black spruce (Picea mariana Mill. B.S.P.) and trembling aspen (Populus tremuloides Michx.) trees grown in natural origin mixed stands. For this, 186 trees (93 black spruce and trembling aspen each) were sampled from 31 even-aged natural mixed stands (sites) (3 trees/species/site) across Ontario, Canada. Stand height growth models were developed by incorporating climate variables during growth for each species. Stem analysis data collected from sampled trees were used to develop these models. A mixed effects modelling approach was used to fit the models. The relationship between SIs of black spruce and trembling aspen grown in mixed stands was analyzed by calculating correlation coefficients and plotting black spruce SIs against those of trembling aspen. Climate effects on site productivity were evaluated by predicting stand heights for 4 geographic areas of Ontario for the period 2021 to 2080. Three emissions scenarios reflecting different amounts of heat at the end of the century (i.e., 2.6, 4.5, and 8.5 watts m−2) were used in the stand height growth models developed here for evaluation. Climate effects were more pronounced for trembling aspen than black spruce only in the far west. The relationship between SIs of black spruce and trembling aspen trees grown in natural origin mixed stands could not be described using a linear/nonlinear mathematical function. The models developed here can be used to estimate stand height and SI of black spruce and trembling aspen trees grown in natural origin mixed stands in a changing climate. In the absence of climate data, models fitted without climate variables can be used to estimate SI of both species.

Comparative analysis of throughfall observations in six different forest stands: Influence of seasons, rainfall‐ and stand characteristics

AbstractThroughfall, that is, the fraction of rainfall that passes through the forest canopy, is strongly influenced by rainfall and forest stand characteristics which are in turn both subject to seasonal dynamics. Disentangling the complex interplay of these controls is challenging, and only possible with long‐term monitoring and a large number of throughfall events measured in parallel at different forest stands. We therefore based our analysis on 346 rainfall events across six different forest stands at the long‐term terrestrial environmental observatory TERENO Northeast Germany. These forest stands included pure stands of beech, pine and young pine, and mixed stands of oak‐beech, pine‐beech and pine‐oak‐beech. Throughfall was overall relatively low, with 54–68% of incident rainfall in summer. Based on the large number of events it was possible to not only investigate mean or cumulative throughfall but also its statistical distribution. The distributions of throughfall fractions show distinct differences between the three types of forest stands (deciduous, mixed and pine). The distributions of the deciduous stands have a pronounced peak at low throughfall fractions and a secondary peak at high fractions in summer, as well as a pronounced peak at higher throughfall fractions in winter. Interestingly, the mixed stands behave like deciduous stands in summer and like pine stands in winter: their summer distributions are similar to the deciduous stands but the winter peak at high throughfall fractions is much less pronounced. The seasonal comparison further revealed that the wooden components and the leaves behaved differently in their throughfall response to incident rainfall, especially at higher rainfall intensities. These results are of interest for estimating forest water budgets and in the context of hydrological and land surface modelling where poor simulation of throughfall would adversely impact estimates of evaporative recycling and water availability for vegetation and runoff.

Low rate of aminopyralid nearly eliminates viable seed production in barb goatgrass (Aegilops triuncialis) in the greenhouse

AbstractInvasive annual grasses such as medusahead [Taeniatherum caput-medusae (L.) Nevski] and barb goatgrass (Aegilops triuncialis L.) are negatively impacting grasslands of the western United States. Over the last decade, research has shown that aminopyralid and other growth-regulator herbicides applied just before flowering greatly reduce viable seed production in several invasive annual grasses. Moreover, it has been shown with T. caput-medusae that using aminopyralid to reduce seed production in one year consistently reduces and sometimes nearly eliminates cover the following year. Our goal in this study was to extend this research to A. triuncialis, a weed for which limited herbicide and other management options exist. Based on previous research, we hypothesized aminopyralid applied several days before flowering at just 22% of the maximum registered rate (0.069 kg ae ha−1) would almost completely prevent production of viable A. triuncialis seeds in the greenhouse. In four experiments, aminopyralid reduced seed viability from between 65% and 95% to between 1% and 5%. Therefore, aminopyralid will likely control A. triuncialis in the field. Because aminopyralid is phytotoxic to many broadleaf species, it may be possible to use aminopyralid to simultaneously control mixed stands of invasive forbs, A. triuncialis, and T. caput-medusae. However, there are risks to applying aminopyralid where native and desirable nonnative forbs occur. Past research on T. caput-medusae suggests controlling A. triuncialis with aminopyralid will increase production of desirable annual forage grasses.

Persistent composition legacy and rapid structural change following successive fires in Sierra Nevada mixed conifer forests

Mixed conifer forests in the Sierra Nevada, California, USA, face threats from frequent high-severity reburns caused by fuel accumulation and increasingly dry, hot conditions associated with climate change. Stand replacing fire and establishment of expansive shrub patches may result in positive feedbacks causing landscapes to convert to persistent shrubland or grassland. Our objective was to examine changes in mixed conifer forest density and species composition after successive fires across a range of initial and reburn severities. We resampled 134 field plots 5–6 years after the Chips Fire reburned stands initially burned by the Storrie and Rich fires on the Lassen and Plumas National Forests. Generalized Linear Models and post-hoc margins analyses were used to examine the interaction effects of initial and reburn fire severities on changes in conifer tree and seedling densities, percent cover of shrubs, and changes in species composition evaluated using fire tolerance index. We found that successive fires with severities less than high-severity significantly reduced tree densities to values within or close to the natural range of variation for mixed conifer stands. Despite these changes in density, species composition did not shift toward increasing dominance of fire tolerant species; mature trees and seedlings of true firs and other fire intolerant species remained dominant after successive low and moderate severity fires. Seedling establishment pulses were associated with sampling years with abundant precipitation, and unburned, unchanged, and low-severity plots in the reburn sample had significant increases in seedling densities across the range of initial burn severities. Shrub cover increased significantly with only a few reburn severity interactions, but declined significantly with repeated high-severity fire. Although two low- to moderate-severity fires may reduce tree densities to within the natural range of variation, they may not shift species composition towards historical patterns. Selective thinning in areas that burned at low- to moderate-severity may be necessary to restore historical species composition in Sierra Nevada mixed conifer forests.

Allocation to tree bark in pine and oak species in fire affected mixed forests across the Northern Hemisphere

Pines (Pinus, with 120 species) and oaks (Quercus, with at least 400 species), the two principal forest forming genera of the Northern Hemisphere occur in fire affected landscapes over a large geographical area from 120°W to 150°E long, and from 10° to 60°N lat. We compiled studies of 116 such sites of which 75 sites had data of bark thickness. Taking a meta-analysis approach, here we have compared the absolute and relative bark thickness (bark thickness per unit stem diameter) of oak species sharing mixed stands to generalize adaptational significance of bark in relation to fire. For the meta-analysis we considered only natural forests with adequate evidences of fire history. We gave importance to relative bark thickness, which is less sensitive to tree size than absolute thickness while comparing species. At 100 cm girth the average absolute bark thickness was significantly higher for Diploxylon pines (3.65 cm) than for oaks (2.2 cm) and Haploxylon pines (1.65 cm). On an average, the relative bark thickness was higher for the fire adapted Diploxylon pines (6.3%) than for Quercus species, (4.4%). The resource allocation efficiency was higher in pine species than for oak species, emphasizing the importance of bark characters in their persistence and range expansion. The difference between species of two principal forest genera in relative bark thickness and hence success in fire affected landscapes across a wide geographical range strongly testifies its adaptational significance to fire.

Recolonization of epiphytic bryophytes after decades of air pollution in forest ecosystems in the Erzgebirge (Ore Mountains) shows the importance of deciduous trees for the diversity of this species group

In recent decades, great efforts have been made in Central Europe to convert homogeneous conifer stands into mixed stands. One major goal of this measure is to promote the biodiversity of forest ecosystems. Research on forest biodiversity is mostly limited to the spatial scale of the stand (alpha diversity), and only few studies focus on the landscape level (gamma diversity). In our study, we investigate the recolonization of epiphytic bryophytes after decades of air pollution on different host tree species. The study area is the Erzgebirge (Ore Mountains, eastern Germany), a low mountain range in which very high SO2 inputs from industrial emissions caused severe damage to the vegetation up to the end of the 20th century. We selected twelve plots each of the tree species Picea abies, Fagus sylvatica, Acer pseudoplatanus and Sorbus aucuparia and recorded the occurrence of all epiphytic bryophytes on trunk and branches at a height between approx. 0.5 and 2.0 m. We recorded a total of 84 species, finding a significantly higher species richness and number of species of conservation concern as well as a larger regional epiphytic species pool (RESP) on F. sylvatica, A. pseudoplatanus and S. aucuparia compared to P. abies. In contrast, there were only minor differences in epiphytic species diversity and composition between the studied deciduous tree species. The dominance of colonists in the current species composition shows that these epiphyte communities are still in the early stages of succession, supported by the observation that species with small range sizes are still very rare. Compared to other studies, the species pool of the examined tree species is relatively large. This is an indication of the much improved environmental conditions for epiphytes in the Erzgebirge. We also recorded Ulota drummondii in the stands, providing its first record in Germany since 1886. In general, we conclude that changing tree species composition from monospecific coniferous to broadleaved stands will lead to an increase in the epiphytic bryophyte diversity of forest ecosystems.

Network analysis reveals the regulatory effect of mixed stands on ecosystem structure and functions in the Loess Plateau, China

Afforestation, an important measure for ecological restoration, has been implemented all over the world, but fragile ecosystem structures and climate change endanger its ecological functions. One major obstacle to optimizing ecological function has been quantifying and characterizing a complex ecosystem structure. Here, the structure and functions of six types of land-use restoration were investigated in the hilly-gully region of the Loess Plateau, China. In total, 44 ecological factors from canopy, understory and soil were determined. We constructed the related network of reforestation ecosystems, quantified the structure of ecosystem through network topology, and explored the relationships between structure and functions. The results showed that changes in plantation type altered the network hubs, but some nodes, such as species height, breast-height diameter and understory biomass, were often keystone hubs. Mixed plantations enhanced the connectivity among different modules. In addition, we found that closeness of network connectivity was an important factor influencing ecological functions, while soil erodibility was the main limiting factor for reforestation ecosystem structure in this region. Moreover, mixed plantations tended to have more balanced topological metrics and ecological functions. Overall, this study suggests that mixed plantations or monoculture plantations should be designed according to the characteristics and ecological demands of the regional ecological environment. Although monoculture plantations may support local ecosystems, mixed plantations offer more resilience to a landscape because they were help to achieve a balance among the ecological functions.

Analysis of the association Galio rotundifolii-Abietetum albae Wraber (1955) 1959 on Manjača Mt (NW Bosnia and Herzegovina)

This research aimed to study phytocoenological characteristics of a fir-dominated community on silicate substrate at the locality of Sitnica on Manjača Mt, northwestern Bosnia and Herzegovina. This community originated from artificially forested mixed stands of fir and spruce planted in the habitat of the mountain Dinaric fir-beech forest, over a hundred years ago. With regular selective cuttings and natural regeneration, the structure shifted from even-aged to uneven-aged. In total, 18 phytocoenological relevés were made using the Braun-Blanquet method during the vegetation seasons of 2021 and 2022. Relevés were stored in Turboveg database. Ecological factors were calculated based on Ellenberg bioindicator values. Species composition was analyzed in terms of life form, geoelements and chorotypes. Our analysis indicates that collected relevés can be classified as the association Galio rotundifolii- Abietetum albae belonging to the alliance Fagion sylvaticae.

Mapping forest types over large areas with Landsat imagery partially affected by clouds and SLC gaps

The ecosystem services that forests provide depend on tree species composition. Therefore, it is important to map not only forest extent and its dynamics, but also composition. Open access to Landsat has resulted in considerable improvements in remote sensing methods for mapping tree species, but most approaches fail to perform when there is a shortage of clear observations. Our main goal was to map forest composition with Landsat imagery in various data availability conditions, and to investigate how the missing data, either due to clouds or scan line problems affect classification accuracy. We tested a data driven approach that is based on multi-temporal analysis of the tree species’ spectral characteristics making it applicable to regional-scale mapping even when the gap-free imagery is not available. Our study area consisted of one Landsat footprint (26/28) located in Northern Wisconsin, USA. We selected this area because of numerous tree species (23), heterogenic composition of forests where the majority of stands are mixed, and availability of high-quality reference data. We quantified how classification accuracy at the species level was affected by a) the amount of missing data due to cloud cover and Scanning Line Corrector (SLC) gaps, b) the number of acquisitions, and c) the seasonal availability of images. We applied a decision tree classifier, capable of handling missing data to both single- and a three-year Landsat-7 and Landsat-8 observations. We classified the dominant tree species in each pixel and grouped results to forest stands to match our reference data. Our results show four major findings. First, producer’s and user’s accuracies range from 46.2% to 96.2% and from 59.9% to 93.7%, respectively for the most abundant forest types in the study area (all types covering greater than 2% of the forest area). Second, all tree species were mapped with overall accuracy above 70% even in when we restricted our data set to images having gaps larger than 30% of the study area. Third, the classification accuracy improved with more acquisitions, especially when images were available for the fall, spring, and summer. Finally, producer’s accuracies for pure-stands were higher than those for mixed stands by 10 to 30 percentage points. We conclude that inclusion of Landsat imagery with missing data allows to map forest types with accuracies that previously could be achieved only for those rare years for which several gap-free images were available. The approach presented here is directly applicable to Landsat-like observations and derived products such as seasonal composites and temporal statistics that miss 30% or more of the data for any single date to develop forest composition maps that are important for both forest management and ecology.

Serra de São Mamede Natural Park, a macrofungal diversity hotspot in the Mediterranean region

The Serra de São Mamede Natural Park is a biodiversity hotspot in the broad region of Alentejo, Portugal, where the influence of the Atlantic Ocean allows for the continuity of a Eurosiberian-like forest in the heart of a Mediterranean region. The park is therefore unique among the few protected areas in Portugal. We attempt to describe the macrofungal diversity of the park for the first time. Our results reveal a rich and diverse assembly of macrofungal species (239 taxa), and in particular, mycorrhizal species (145 taxa). Furthermore, 26 taxa are newly recorded from Portugal, while 81 taxa are newly recorded from Alto Alentejo Province. Also, the majority of these newly reported taxa were recorded in mixed stands of Quercus pyrenaica Willd.—a European protected habitat of limited extent—whose importance is enhanced now the rich and diverse associated macrofungal community, as shown in our study.

Microclimatic Alteration after Logging Affects the Growth of the Endangered Lichen Lobaria pulmonaria.

Microclimatic conditions are important in determining lichen distribution at small scale, and may determine whether the species persist when the surrounding environmental conditions have drastically changed. This is the case with forest management, since a sudden variation of microclimatic conditions (increase of solar radiation, temperature, wind and a reduction of humidity) may occur after logging. In this study, the combined effect of forest logging and microclimatic conditions on the growth probabilities and growth rates of the model species Lobaria pulmonaria was assessed in mixed oak stands. To this purpose, 800 fragments of L. pulmonaria (<1 cm) were transplanted in logged and unlogged stands for two years. Young and adult fragments were positioned on Turkey oak boles according to distance from the ground (100 and 50 cm) and aspect (north and south). The results, evaluated by generalized linear mixed models on a yearly basis, highlighted differences in growth—particularly on isolated trees in the logged stand. South-exposed samples in the logged stand showed a low probability of growth, while samples transplanted north in the unlogged stand showed higher growth probabilities. However, the highest annual growth coefficients corresponded to south-exposed samples 50 cm from the ground in the unlogged stand. In general, higher growth rates were observed in young thallus fragments when compared with adult ones. Beyond confirming the importance of microclimate for lichen ecology, these results could be implemented in conservation actions to preserve L. pulmonaria populations in logged forests.

Response of Poplar Leaf Transcriptome to Changed Management and Environmental Conditions in Pure and Mixed with Black Locust Stands

Mixed cropping in short rotation coppice can be an alternative to monocultures. To design optimized mixtures, field trials are needed. Poplar, as an economically important and fast-growing species, and black locust, as a nitrogen-fixing species, are promising candidates for such studies. RNA sequencing (RNA-seq) was used to monitor effects of mixed and pure cultivations on the gene expression of poplar along with growth measurements during 2017 and 2018. Both biomass production and leaf transcriptomes revealed a strong competition pressure of black locust and the abiotic environment on poplar trees. Gene expression differed between the two study sites and pure and mixed stands. Shading effects from black locust caused the downregulation of photosynthesis and upregulation of shade avoidance genes in mixed stands in 2017. As a result of higher light availability after cutting black locust, plant organ development genes were upregulated in mixed stands in 2018. Drought conditions during the summer of 2018 and competition for water between the two species caused the upregulation of drought stress response genes in mixed stands and at the unfavorable growing site. Further investigations are required to discover the mechanisms of interspecific competition and to develop stand designs, which could increase the success and productivity of mixed plantations.

Litter decomposition and properties of soil under Dalbergia sissoo, Acacia mangium and Eucalyptus tereticornis

The quantity of litter fall on the forest floor is quite high and they have a significant contribution to the dynamics of forest ecosystem. The present investigation was undertaken for litter quantification and its decomposition as per litterfall type, canopy also characteristics of soil in sole and mixed stands of Acacia mangium, Eucalyptus tereticornis and Dalbergia sissoo in agroforestry system. Quantification of litterfall and nutrient analysis was carried out for three trees i.e., Acacia mangium, Eucalyptus tereticornis and Dalbergia sissoo in agroforestry system. In the research area, sissoo stand has higher litterfall than mangium and Eucalyptus, being maximum litterfall occur in the month of January. The mean values for litterfall were 4000, 2200 and 1800 kg ha-1 year-1 for sissoo, mangium and eukalyptus stands, respectively. Annual decay constant was minimum for eucalyptus (k=0.161) whereas in sissoo it was (k=0.276), indicating the variability in nitrogen content among the types of litter (Sissoo, 2.25% and for Eucalyptus its 1.72%,). In conclusion it is stated that N rich litter may speed up for decomposition process.

Species Mixing Proportion and Aridity Influence in the Height–Diameter Relationship for Different Species Mixtures in Mediterranean Forests

Estimating tree height is essential for modelling and managing both pure and mixed forest stands. Although height–diameter (H–D) relationships have been traditionally fitted for pure stands, attention must be paid when analyzing this relationship behavior in stands composed of more than one species. The present context of global change makes also necessary to analyze how this relationship is influenced by climate conditions. This study tends to cope these gaps, by fitting new H–D models for 13 different Mediterranean species in mixed forest stands under different mixing proportions along an aridity gradient in Spain. Using Spanish National Forest Inventory data, a total of 14 height–diameter equations were initially fitted in order to select the best base models for each pair species-mixture. Then, the best models were expanded including species proportion by area (mi) and the De Martonne Aridity Index (M). A general trend was found for coniferous species, with taller trees for the same diameter size in pure than in mixed stands, being this trend inverse for broadleaved species. Regarding aridity influence on H–D relationships, humid conditions seem to beneficiate tree height for almost all the analyzed species and species mixtures. These results may have a relevant importance for Mediterranean coppice stands, suggesting that introducing conifers in broadleaves forests could enhance height for coppice species. However, this practice only should be carried out in places with a low probability of drought. Models presented in our study can be used to predict height both in different pure and mixed forests at different spatio-temporal scales to take better sustainable management decisions under future climate change scenarios.

Evaluating nondestructive forage sampling techniques in alfalfa–bermudagrass mixtures in the southeastern United States

AbstractThe increased use of legume–grass mixtures in grazing systems has resulted in the need for more accurate forage estimation techniques for these diverse mixtures. In mixed stands, variations in species composition and canopy density make the estimation of herbage mass (HM) challenging. Three nondestructive sampling techniques [a rising plate meter (RPM), a pasture ruler, and digital image analysis] were compared with traditional botanical hand separation to determine their effectiveness in predicting HM in bermudagrass [Cynodon dactylon (L.) Pers.] and alfalfa (Medicago sativa L.) pastures when harvested to a 1‐ or 4‐inch stubble height. All models calibrated to forages harvested to 1 inch failed to meet the formal assumptions of the F‐test. The height and RPM were moderately successful at predicting HM when calibrated to samples harvested to 4 inches. However, the models were unable to predict HM above 4,000 lb acre−1 in their current form. Future research in alfalfa–bermudagrass mixtures should focus on isolating how HM changes within the canopy and increase the sample area used to collect the calibration data.

Models of Silviculture for Portuguese Species: Old and New Guidelines

Models of silviculture are used for the selection and scheduling of the silvicultural practices from installation to the end of the production cycle. Most of the published models of silviculture are for even aged stands. Those for mixed and uneven aged stands are scarce. The goal of this study was the development of models of silviculture for Portuguese species; with examples for Pinus pinea, Quercus suber Quercus rotundifolia, Pinus pinaster and Castanea sativa. Five stand structures were considered (pure even aged, mixed even aged, temporary mixed even aged, pure uneven aged and mixed uneven aged). For mixed stands were considered two species admixtures and for uneven aged 2, 3 and 4 cohorts. The local level models of silviculture developed in this study are conceptual frameworks where guidelines can be derived to define the model of silviculture for a stand, including target stand structure and production cycle, according to management goals, species and site. Overall, it was intended to stress the importance of defining models of silviculture that are flexible to accommodate a wide range of management options and that should be dynamic in space and time. These models cannot be used directly but have to be adapted to each stand.

Естественное возобновление в смешанных разновозрастных древостоях на урбанизированных территориях Москвы

The effectiveness of forests therapeutic impact is based on its species’ and age structure, silvicultural features, biological productivity, regenerative ability, forest management intensity and its methods. The processes of natural regeneration of a forest stand and its growth are the main factors of the forest’s ecosystem proper functioning and a disruption in these processes can lead to a transformation of the whole biocenosis, a change of a typological community. Technogenic pollution is a huge stress factor for trees, and its impact is especially evident in regions with a high concentration of industrial facilities, namely, in Moscow city. One of the most serious consequences of technogenic pollution is the deterioration of long-established forests, which subsequently may reduce its ability to adapt to ever-changing environmental conditions and its protective functions. The article discusses issues regarding the natural regeneration of forests on urbanized territories of Moscow on the example of the Forest experimental station of the Russian State Agrarian University - Moscow Timiryazev Agricultural Academy. The natural regeneration of tree species is one of the most relevant issues of forest and park management. The aim of this project is to estimate natural regeneration in mixed forest stands of urbanized areas, to provide recommendations on the organization of forest regeneration measures in urban environments. The article provides methods and results of field research and recommendations on reforestation measures under these conditions. The research of the cenobiotic connections and the undergrowth of different species with key elements of grass cover in its habitat, will allow a more positive dynamics in the use of natural resources, which will contribute to preservation and restoration of forests.

Fauna and flight activity of bats in natural forests in the southern Brdy Mts. and the first information on the occurrence of Hypsugo savii in this area (Chiroptera: Vespertilionidae)

The bat fauna was studied at six localities of protected natural forest fragments in the southern part of the Brdy Mts. (south-western Bohemia), in the years 2019–2020. Netting and acoustic detection on line transects were used in order to document the species composition and flight activity of bats at the localities under study. Altogether, 24 individuals of seven bat species were netted. In total, 643 minutes of the presence of flying bats were registered within 56.5 transect hours. With use of these methods, at least 16 bat species were recorded. Of them, Myotis myotis, M. mystacinus / M. brandtii, M. nattereri, Eptesicus nilssonii, Pipistrellus pipistrellus, Plecotus auritus, and Barbastella barbastellus represent the constant species group with respect to their occurrence at the localities. Pipistrellus pipistrellus was the most frequent species (54%), with the highest relative flight activity at all localities. The highest intensity of flight activity of the bat community was observed in habitats with rocks, boulder accumulation, and open stony debris (14.17 min+/h). The highest bat species diversity was registered in habitats with the prevalence of herb-rich mixed beech forest stands (15 species, diversity index H’=2.02; equitability E=0.75). A series of calls of Hypsugo savii was registered in the Na skalách Nature Reserve on 8 May 2020. It represents the first finding of this species in the region of the Brdy Mts.

Карта растительности памятника садово-паркового искусства «Осиновая роща» (Санкт-Петербург)

This article continues a series of publications devoted to vegetation mapping of existing and prospective specially protected natural areas of St. Petersburg. The “Osinovaya Roshcha” is a monument of garden art of the late XVIII–early XIX centuries. It is located on the northern border of St. Petersburg in a picturesque kame landscape, where sandy hills alternate with small bogged depressions and lakes. The landscape park of the Levashov-Vyazemsky estate was created in the forested area dominated by spruce, pine and birch. Since the 1780s oak, linden, ash, larch, fir, Siberian, Weymouth and other pines were planted there (Isachenko, 2004). A large-scale map of the actual vegetation of the “Osinovaya Roshcha” park and the adjacent territory was compiled for the first time. The natural forest, bog and meadow plant communities are characteristic features of the northern part of the area. The broad-leaved and coniferous trees, planted in the central part more than 200 years ago, have formed various plant communities, including mixed stands of local flora species and introduced trees. The southern part of the park is occupied mainly by broad-leaved introduced forest stands. Vegetation is divided into three sections in the map legend — natural, introduced, and formed by both native and introduced species. Each section represents vegetation types (or groups of types) (forest vegetation, mire vegetation, etc.); then forest communities are subdivided into classes of formations and formations, bog communities — according to the types of water-mineral nutrition. The mapped units are associations, subassociations and their variants, identified according the ecological-phytocoenotic classification. Territorial units — ecological series and combinations of plant communities — were also used in the map legend. Short-term secondary communities formed under various ecological (mainly anthropogenic) factors are subordinate to conventionally primary ones. They are indicated by indices at the legend numbers. Various types of shading were used on the map to distinguish natural and introduced vegetation. The vegetation map of the “Osinovaya Roshcha” represents a diversity of plant communities: they are forest (spruce, pine, birch) and bog (lowland, transitional, upland) communities typical of the region, as well as old-growth larch (Larix sibirica) and broad-leaved (oak, linden, elm, mixed composition) forests formed by introduced trees. Last ones are rare for the region. The plant community of Carex brizoides, found in the park, is of great interest among the communities of herbaceous plant introducers. This sedge is a rare species for St. Petersburg and the Leningrad region, which probably like the Poa chaixii was used for sodding the park soils.

Two-level optimization approach to tree-level forest planning

Laser scanning and individual-tree detection are used increasingly in forest inventories. As a consequence, methods that optimize forest management at the level of individual trees will be gradually developed and adopted. The current study proposed a hierarchical two-level optimization method for tree-level planning where the cutting years are optimized at the higher level. The lower-level optimization allocates the trees to the cutting events in an optimal way. The higher-level optimization employed differential evolution whereas the lower-level problem was solved with the simulated annealing metaheuristic. The method was demonstrated with a 30 ​m ​× ​30 ​m sample plot of planted Larix olgensis . The baseline case maximized the net present value as the only management objective. The solution suggested heavy thinning from above and a rotation length of 62 years. The baseline problem was enhanced to mixed stands where species diversity was used as another management objective. The method was also demonstrated in a problem that considered the complexity of stand structure, in addition to net present value. The objective variables that were used to measure complexity were the Shannon index (species diversity), Gini index (tree size diversity), and the index of Clark and Evans, which was used to describe the spatial distribution of trees. The article also presents a method to include natural advance regeneration in the optimization problem and optimize the parameters of simulated annealing simultaneously with the cutting years. The study showed that optimization approaches developed for forest-level planning can be adapted to problems where treatment prescriptions are required for individual trees.