Structure Of Forest Stands Research Articles

Multi-Agent Reinforcement Learning for Stand Structure Collaborative Optimization of Pinus yunnanensis Secondary Forests

This study aims to investigate the potential and advantages of multi-agent reinforcement learning (MARL) in forest management, offering innovative insights and methodologies for achieving sustainable management of forest ecosystems. Focusing on the Pinus yunnanensis secondary forests in Southwest China, we formulated the objective function and constraints based on both spatial and non-spatial structural indices of the forest stand structure (FSS). The value of the objective function (VOF) served as an indicator for assessing FSS. Leveraging the random selection method (RSM) to select harvested trees, we propose the replanting foreground index (RFI) to enhance replanting optimization. The decision-making processes involved in selection harvest optimization and replanting were modeled as actions within MARL. Through iterative trial-and-error and collaborative strategies, MARL optimized agent actions and collaboration to address the collaborative optimization problem of FSS. We conducted optimization experiments for selection felling and replanting across four circular sample plots, comparing MARL with traditional combinatorial optimization (TCO) and single-agent reinforcement learning (SARL). The findings illustrate the superior practical efficacy of MARL in collaborative optimization of FSS. Specifically, replanting optimization based on RFI outperformed the classical maximum Delaunay generator area method (MDGAM). Across different plots (P1, P2, P3, and P4), MARL consistently improved the maximum VOFs by 54.87%, 88.86%, 41.34%, and 22.55%, respectively, surpassing those of the TCO (38.81%, 70.04%, 41.23%, and 18.73%) and SARL (54.38%, 70.04%, 41.23%, and 18.73%) schemes. The RFI demonstrated superior performance in replanting optimization experiments, emphasizing the importance of considering neighboring trees’ influence on growth space and replanting potential. Following selective logging and replanting adjustments, the FSS of each sample site exhibited varying degrees of improvement. MARL consistently achieved maximum VOFs across different sites, underscoring its superior performance in collaborative optimization of logging and replanting within FSS. This study presents a novel approach to optimizing FSS, contributing to the sustainable management of Pinus yunnanensis secondary forests in southwestern China.

Needles carbon pool structure in pine stands growing on abandoned farmland in subtaiga/forest-steppe zone of Сentral Siberia

Studying green biomass carbon pool makes it possible to assess carbon sequestration potential of both forests stands and individual trees. Such a study is highly relevant considering the fact that pine stands are replacing abandoned farmlands in Central Siberia. The criterion used to differentiate pine forests was the stand density. Modelling the stands structure (in terms of number of trees and needles carbon pool) considering trees diameter, showed that the Gaussian function is the most adequate. The stands diameter structure differs from the needles carbon pool structure. Trees average for a specific stand sequester the most carbon by their needles. Thus, forest managers should focus on saving medium-sized pine trees. In recent year, there has been a gradually increasing global temperature, which influence both the growth rate and the structure of forest stands. As a result, an equation was obtained that consider the change in the average diameter, standard deviation and maximum temperature extremes.

Reinforcement Learning for Stand Structure Optimization of Pinus yunnanensis Secondary Forests in Southwest China

Aiming to enhance the efficiency and precision of multi-objective optimization in southwestern secondary growth of Pinus yunnanensis forests, this study integrated spatial and non-spatial structural indicators to establish objective functions and constraints for assessing forest structure. Felling decisions were made using the random selection method (RSM), Q-value method (QVM), and V-map method (VMM). Actions taken to optimize the forest stand structure (FSS) through tree selection were approached as decisions by a reinforcement learning (RL) agent. Leveraging RL’s trial-and-error strategy, we continually refined the agent’s decision-making process, applying it to multi-objective optimization. Simulated felling experiments conducted across circular sample plots (P1–P4) compared RL, Monte Carlo (MC), and particle swarm optimization (PSO) in FSS optimization. Notable enhancements in the values of the objective function (VOFs) were observed across all plots. RL-based strategies exhibited improvements, achieving VOF increases of 17.24%, 44.92%, 34.66%, and 17.10% for P1–P4, respectively, outperforming MC-based (10.73%, 41.54%, 30.39%, and 15.07%, respectively) and PSO-based (14.08%, 37.78%, 26.17%, and 16.23%, respectively) approaches. The hybrid M7 scheme, integrating RL with the RSM, consistently outperformed other schemes across all plots, yielding an average 26.81% increase in VOF compared to the average enhancement of all schemes (17.42%). This study significantly advances the efficacy and precision of multi-objective optimization strategies for Pinus yunnanensis secondary forests, emphasizing RL’s superior optimization performance, particularly when combined with the RSM, highlighting its potential for optimizing sustainable forest management strategies.

A novel model to evaluate spatial structure in thinned conifer-broadleaved mixed natural forests

In order to ensure the effective analysis and reconstruction of forests, it is key to ensure the quantitative description of their spatial structure. In this paper, a distance model for the optimal stand spatial structure based on weighted Voronoi diagrams is proposed. In particular, we provide a novel methodological model for the comprehensive evaluation of the spatial structure of forest stands in natural mixed conifer-broadleaved forests and the formulation of management decision plans. The applicability of the rank evaluation and the optimal solution distance model are compared and assessed for different standard sample plots of natural mixed conifer-broadleaved forests. The effect of crown width on the spatial structure unit of the trees is observed to be higher than that of the diameter at breast height. Moreover, the influence of crown length is greater than that of tree height. There are nine possible spatial structure units determined by the weighted Voronoi diagram for the number of neighboring trees in the central tree, with an average intersection of neighboring crowns reaching 80%. The rank rating of natural forest sample plots is correlated with the optimal solution distance model, and their results are generally consistent for natural forests. However, the rank rating is not able to provide a quantitative assessment. The optimal solution distance model is observed to be more comprehensive than traditional methods for the evaluation of the spatial structure of forest stands. It can effectively reflect the trends in realistic stand spatial structure factors close to or far from the ideal structure point, and accurately assesses the forest spatial structure. The proposed optimal solution distance model improves the integrated evaluation of the spatial structure of forest stands and provides solid theoretical and technical support for sustainable forest management.

Effect of Stand Conversion on Forest Stand Structure in Planted Scots Pine Forests

Effect of Stand Conversion on Forest Stand Structure in Planted Scots Pine Forests

A Comprehensive Index Model of Spatial Structure of Forest Stands Based on Weighted Triangular Network

A Comprehensive Index Model of Spatial Structure of Forest Stands Based on Weighted Triangular Network

Above-Ground Biomass Estimation of Plantation with Complex Forest Stand Structure Using Multiple Features from Airborne Laser Scanning Point Cloud Data

Accurate forest above-ground biomass (AGB) estimation is important for dynamic monitoring of forest resources and evaluation of forest carbon sequestration capacity. However, it is difficult to depict the forest’s vertical structure and its heterogeneity using optical remote sensing when estimating forest AGB, for the reason that electromagnetic waves cannot penetrate the canopy’s surface to obtain low vegetation information, especially in subtropical and tropical forests with complex layer structure and tree species composition. As an active remote sensing technology, an airborne laser scanner (ALS) can penetrate the canopy surface to obtain three-dimensional structure information related to AGB. This paper takes the Jiepai sub-forest farm and the Gaofeng state-owned forest farm in southern China as the experimental area and explores the optimal features from the ALS point cloud data and AGB inversion model in the subtropical forest with complex tree species composition and structure. Firstly, considering tree canopy structure, terrain features, point cloud structure and density features, 63 point cloud features were extracted. In view of the biomass distribution differences of different tree species, the random forest (RF) method was used to select the optimal features of each tree species. Secondly, four modeling methods were used to establish the AGB estimation models of each tree species and verify their accuracy. The results showed that the features related to tree height had a great impact on forest AGB. The top features of Cunninghamia Lanceolata (Chinese fir) and Eucalyptus are all related to height, Pinus (pine tree) is also related to terrain features and other broadleaved trees are also related to point cloud density features. The accuracy of the stepwise regression model is best with the AGB estimation accuracy of 0.19, 0.76, 0.71 and 0.40, respectively, for the Chinese fir, pine tree, eucalyptus and other broadleaved trees. In conclusion, the proposed linear regression AGB estimation model of each tree species combining different features derived from ALS point cloud data has high applicability, which can provide effective support for more accurate forest AGB and carbon stock inventory and monitoring.

Fire mitigates bark beetle outbreaks in serotinous forests

Bark beetle outbreaks and forest fires have imposed severe ecological damage and caused billions of dollars in lost resources in recent decades. The impact of such combined disturbances is projected to become more severe, especially as climate change takes its toll on forest ecosystems in the coming years. Here, we investigate the impact of multiple disturbances in a demographically heterogeneous tree population, using an age-structured difference equation model of bark beetle outbreaks and forest fires. We identify two dynamical regimes for beetle and fire dynamics. The model predicts that fire helps dampen beetle outbreaks not only by removing host trees but also by altering the demographic structure of forest stands. We show that a stand thinning protocol, which reduces the population size of the largest few juvenile classes by a small percentage, is able to significantly reduce beetle-induced tree mortality. Our research demonstrates one approach to capturing compound disturbances in a mathematical model.

Restoration strategies in boreal forests: Differing field and ground layer response to ecological restoration by burning and gap cutting

The boreal biome is one of the largest in the world and its forests have been widely exploited for centuries. Consequently, large areas have suffered ecological simplification and loss of biodiversity. Under the current circumstances passive conservation measures are no longer enough and active restoration techniques need to be developed and assessed to preserve and recover the loss of biodiversity. We evaluated short- and long-term effects of two restoration methods aimed at mimicking natural disturbances on species richness, Shannon Diversity and community composition of vascular plants in the field layer and bryophytes in the ground layer. The experiment consisted of 18 forest stands in northern Sweden; each assigned to a different treatment: prescribed burning, gap cutting and untreated stands left as controls. A before-after control-impact (BACI) study design was applied and data was collected on three occasions: once prior to restoration (2010) and twice post restoration; one year (2012) and eight years after (2019). We analysed the differences in species richness and Shannon Diversity with linear mixed effect models and community composition changes with multivariate methods. Fire treatment caused an initial decline in diversity for both field and ground layer, but in the long-term, field layer surpassed the species richness and Shannon Diversity values found prior to restoration. Ground layer bryophytes species richness and Shannon Diversity remained lower than pre-treatment. Prescribed burning should, therefore, be used with caution in core areas for bryophyte diversity. Community composition in burned stands differed significantly between each time point as well as when compared to other treatments, for both layers. By contrast, we found no significant differences in diversity measures or community composition after gap cutting. The absence of effects from gap cutting suggests that minor changes in canopy cover does not affect the vegetation structure of forest stands. The organism group-specific responses, and temporal variability to restoration, highlight the importance of including more than one organism group, different restoration methodologies, and long-term studies in order to properly assess restoration outcomes at landscape level.

A 249-yr chronosequence of forest plots from eight successive fires in the Eastern Canada boreal mixedwoods.

A combination of wildfires and defoliating insect outbreaks play an important role in the natural successional dynamics of North American boreal mixedwood forests, which, in the long term, change the post-disturbance composition and structure of forest stands. After stand-replacing disturbances (mainly wildfires), early successional hardwoods typically dominate the affected areas. Provided enough time following disturbances, the increasing recruitment of mid- to late-successional softwoods as well as the mortality of hardwoods gradually change forest composition from hardwoods to admixtures of hardwood-conifer species and conifer-dominated stands in mid and late successional stages, respectively. Such mixedwoods are abundant across the southern Canadian boreal forest. In boreal Canada, mixedwoods are the most structurally heterogeneous forest ecosystems, are highly productive, and form an important source of timber supply. Here we present the EASTERN BOREAL MIXEDWOODS CANADA data set, which documents the changes in composition and structure of stands originating from eight different wildfires representing a chronosequence of 249 yr since fire in eastern Canada. This data set has been used in several different projects to study and model the influence of natural (e.g., insect outbreaks) and anthropogenic disturbances (e.g., harvesting) on the dynamics of post-fire stands. The data set covers a high range of variability in stand composition and structure, explained by species establishment, dominance, and mixture. It thus constitutes a useful source of information to trace the dynamics of the main boreal tree species of eastern North America, from their establishment to their replacement at different spatial scales (e.g., from stand to landscape level). Please cite this data paper when the data are used in publications. We also request that researchers and teachers inform us of how they are using the data. We are open to collaborate in developing or co-authoring relevant research projects based on this data set.

Influence of Forest Stand Structure and Competing Understory Vegetation on Ash Regeneration—Potential Effects of Ash Dieback

Background and Objectives: The existence of common ash (Fraxinus excelsior) in Europe is severely endangered by ash dieback. To support its future sustainability, it is essential to improve the natural ash regeneration. The main aim of this study was to investigate the influence of light conditions, conceivably influenced by stand structure/ash dieback, on ash regeneration and the competition between ash seedlings and species growing in the understory. Materials and Methods: We selected 40 plots in a riparian forest located in Bavaria, Germany. Light-related variables (Leaf Area Index, gap fraction) were gathered with fish-eye photography, whereas other environmental factors were derived from vegetation surveys (Ellenberg indicator values). We assessed vegetation parameters such as species’ richness and coverage of the herb layer to account for competition with ash seedlings. Results: Our results indicate that ash regeneration is favoured under shady conditions. The majority of other abiotic factors were not statistically associated with the analysed ash metrics. In contrast, the coverage of grass was negatively related to LAI and positively to gap fraction. Higher herb and grass coverages were linked to a suppression of ash regeneration. A higher litter coverage was associated with a higher frequency of ash seedlings. Nonparametric partial correlation analyses demonstrated the influence of light and stressed that litter coverage is of particular importance. Conclusions: We conclude that gaps, inter alia induced by ash dieback, favour grass invasion. In turn, this invasion might suppress regeneration of ash. In this regard, rapid silvicultural management such as reforestation of gaps after dieback of mature trees is recommended. The influence of litter on interspecific competition during growth should be also considered. The pace of dieback might additionally influence the timing and quantity of litter accumulation; thus, further research should also focus on these interrelations.

Estimating Forest Structure from UAV-Mounted LiDAR Point Cloud Using Machine Learning

Monitoring the structure of forest stands is of high importance for forest managers to help them in maintaining ecosystem services. For that purpose, Unmanned Aerial Vehicles (UAVs) open new prospects, especially in combination with Light Detection and Ranging (LiDAR) technology. Indeed, the shorter distance from the Earth’s surface significantly increases the point density beneath the canopy, thus offering new possibilities for the extraction of the underlying semantics. For example, tree stems can now be captured with sufficient detail, which is a gateway to accurately locating trees and directly retrieving metrics—e.g., the Diameter at Breast Height (DBH). Current practices usually require numerous site-specific parameters, which may preclude their use when applied beyond their initial application context. To overcome this shortcoming, the machine learning Hierarchical Density-Based Spatial Clustering of Application of Noise (HDBSCAN) clustering algorithm was further improved and implemented to segment tree stems. Afterwards, Principal Component Analysis (PCA) was applied to extract tree stem orientation for subsequent DBH estimation. This workflow was then validated using LiDAR point clouds collected in a temperate deciduous closed-canopy forest stand during the leaf-on and leaf-off seasons, along with multiple scanning angle ranges. The results show that the proposed methodology can correctly detect up to 82% of tree stems (with a precision of 98%) during the leaf-off season and have a Maximum Scanning Angle Range (MSAR) of 75 degrees, without having to set up any site-specific parameters for the segmentation procedure. In the future, our method could then minimize the omission and commission errors when initially detecting trees, along with assisting further tree metrics retrieval. Finally, this research shows that, under the study conditions, the point density within an approximately 1.3-meter height above the ground remains low within closed-canopy forest stands even during the leaf-off season, thus restricting the accurate estimation of the DBH. As a result, autonomous UAVs that can both fly above and under the canopy provide a clear opportunity to achieve this purpose.

Оценка истощения лесов северного региона: методика, алгоритм и результаты апробации на примере Республики Коми

The traditional understanding of forests as an inexhaustible source of forest resources is undergoing significant changes in the transition period to green economy with the sustainable development of the social economic systems. Production plans of large timber plants, an increase in the production of timber products with a high added value demand significant reserves of high-quality wood with forest stands which can generate a high output of sawlogs and plywood raw materials in the CTL structure. Being one of the largest forest regions of Russia, the Komi Republic finds it more and more difficult to provide sawmills and woodworking industries with high-quality wood. Traditional approaches to assessing the natural capital of forests fail to show the structure of forests and the degradation degree of forest ecosystems. The purpose of this article is to develop a new assessment methodological approach to forest resources in the Komi Republic. This approach is based on changes in natural and cost structure of forest stands. The novelty of the study lies in the fact that the depletion of forest capital is measured on the basis of assessing the long-term and geographically differentiated decrease in the stock and deterioration of the CTL structure of forest resources. An allotment database of forest resources of the Komi Republic, as well as statistical data on prices for forest products is an information base of the research. The result of the research is a special modeling methodological tool applied to assess the forest depletion and aggregating a huge set of primary data. Topol-L app helps develop a new assessment algorithm; a digitized database of CTL tables is adjusted; approaches are justified, and a representative segment of benchmarking forests is compiled; natural and cost indicators are calculated for forest depletion in the Komi Republic forestry. Forest depletion is assessed, which revealed nearly a two time decrease in the forest potential of the Komi Republic primarily caused by an advance fall in the value of the fine wood – pine tree sawlogs and veneering wood. A proclaimed principle of the uninterrupted and, ultimately, inexhaustible exploitation of forest resources is proven to be totally ignored in current performance of the region’s forestry. A further decrease in quality and volume of the region’s forest resources is predicted for the nearest decades, and a new model of forest recovery is recommended to be transferred to. This can change the existing negative trend of region’s forest depletion and significantly improve the quality and an aggregate cost of the forest stocks. A further research is seen to be connected with the evaluation of the forest resource potential and its depletion, as well as modeling forest recovery at the level of forest raw materials of a region’s large paper and pulp enterprise. It is also important to analyze the possibility to use selective cuttings during timber harvesting, when the efficiency of forest ecosystems is maintained.

Forest Stand Structure of Abies nephrolepis Population in Mt. Hwangbyeong

Forest Stand Structure of Abies nephrolepis Population in Mt. Hwangbyeong

Особенности структуры коренных темнохвойных древостоев Вишерского заповедника

On the basis of the standard techniques the pedigree structure of forest stands and distribution of trees on diameter of climax darkconiferous stands of the Vishera national Nature Reserve located in the northeast of Perm District (Northern Urals) is studied and analysed. It is established that the wood layer of the explored climax darkconiferous forests of Northern Urals has multispecies structure. At domination of a spruce fir and the fir (up to 5 units) and, substantially a birch and, also participates, the cedar. In type of the wood Firspruce fernytallgrass as the as a part of a forest stand there is a rowan. Both lowproductive, and highly productive forest stands are formed. In a structure of forest stands of the darkconiferos woods of Vishera Nature Reserve the considerable variation of trees on diameter caused both by forest vegetation conditions of plantings, and influence of negative natural factors the periodic local fires and a windfall is revealed. Distribution of trees on diameter in forest stands, except for postwindfall, is well approximated by the equations of the 2nd order. Distribution of trees on diameter in postwindfall darkconiferous community is best of all described by the equation of the 4th order. The considerable righthand asymmetry of distribution of trees on diameter for all studied forest stands, and, in particular, the affected local fires or a windfall is noted. Such distribution of trees on diameter classes of a trunk reflects processes of natural renewal and development of forest stands, long on time. The revealed features of distribution of trees on pedigree structure and of diameter classes in the studied radical forest stands demonstrate that even in the conditions of influence of negative natural factors processes of natural renewal in general, provide maintenance of multispecies structure of radical plantings. However, impact of the periodic local fires negatively affects renewal of a cedar.

Горизонтальная структура древостоев и подроста северотаежных коренных ельников чернично-сфагновых в Приуралье

Горизонтальная структура древостоев и подроста северотаежных коренных ельников чернично-сфагновых в Приуралье

Еталон лісових насаджень на заповідних територіях Національного природного парку «Сколівські Бескиди»

Облік лісових масивів природоохоронних об’єктів є первинним етапом оцінення їх потенціалу. Об’єктом дослідження є лісові насадження заповідної зони Національного природного парку «Сколівські Бескиди». Метою дослідження передбачено відібрати еталон, тобто лісові насадження із максимальним біорізноманіттям та продуктивністю, складною вертикальною структурою. Методику вибіркової лісової інвентаризації вважають найбільш адекватною для отримання репрезентативних даних. Для таких об’єктів лісівничо-таксаційна характеристика доповнюється аналізом просторової структури насаджень та оцінкою біорізноманіття.
 На території Майданського лісництва виявлено еталон лісових насаджень. Еталон представлений триярусними деревостанами. Після розроблення моделей залежності середнього приросту деревостану від середнього віку, а також запасу деревостану від середнього діаметра дерев першого ярусу, усі об’єкти розділено на дві групи. До першої групи відібрано об’єкти, котрі за величиною запасу (приросту) потрапляють до верхньої частини довірчої зони моделі з одностороннім обмеженням 1-2 стандартні відхилення.
 Відібрано шість еталонів у віковому діапазоні 55-136 років. Яруси лісового насадження складаються із бука лісового, ялиці білої та ялини європейської. Один еталон характеризує деревостан з модрини європейської, явора, ялини та ялиці. Частка дерев в першому ярусі змінюється в межах 43-63%, у другому – 4-32%, у третьому – 24-31%.
 Високопродуктивні структурно складні еталони є типовими природними утвореннями, на котрі повинна орієнтуватися господарська діяльність підприємства.

Біометричні ознаки таксаційної будови за діаметром ялицевих деревостанів Закарпаття

Проаналізовано літературні джерела з проблематики дослідження таксаційної будови насаджень в Україні та за її межами. Розглянуто питання, пов'язані з дослідженням біометричних ознак будови ялицевих деревостанів Закарпаття за діаметром у різних вікових групах. На підставі аналізу матеріалів 119 кругових пробних площ на території Закарпатського обласного управління лісового та мисливського господарства наведено аналіз біометричних ознак (середнього значення, основного відхилення, коефіцієнтів варіації, точності досліду, асиметрії та ексцесу) рядів розподілу дерев ялиці білої за діаметром та розподілу дерев за природними ступенями товщини у зв'язку з віковою зміною середніх діаметрів. З'ясовано, що серед усіх функцій, які використано у цих дослідженнях, найточніше будову ялицевих деревостанів за діаметром моделює функція Вейбулла. Здійснено перевірку узгодженості фактичних і теоретичних чисельностей за критерієм згоди Пірсона. За допомогою функції Вейбулла визначено теоретичні чисельності за ступенями товщини. На основі трипараметричної функції Вейбулла опрацьовано математичну модель рядів розподілу дерев за діаметром та віковими групами. Встановлено, що для будови ялицевих деревостанів Закарпаття за ступенями товщини характерне значне варіювання їхніх біометричних показників. Внаслідок виконаних досліджень побудовано узагальнені ряди розподілу дерев за діаметром, що є основою для подальшого розроблення нормативів товарної структури деревостанів.

Ecological characteristic and health of mangrove forest at Tanakeke Island South Sulawesi

Mangrove forest at Tanakeke Island has important roles both for ecology and economy. High pressure on mangrove caused mangrove degradation in the island. Knowledge of ecological conditions and health of mangrove forest are essential for mangrove ecosystem management at the island. The study aims to determine ecological characteristics and health status of mangrove forest at Tanakeke Island, Takalar District, South Sulawesi. This study employed quantitative methods using field survey with observations using plots of 10 m x 10 m. Observation plots were located evenly all over the island. Results showed mangrove forests at Tanakeke Island consist of 11 species belong to 8 families. Shannon-Wiener diversity index reached 2.01, 1.88, and 1.18 for tree, sapling, and seedling, respectively. Importance Value Index reached 115.31, 172.11, and 108.89 for tree, sapling, and seedling, respectively, and dominated by Rhizophora stylosa at all growth levels. Structure of mangrove forest stands resembles the letter "J" inverted, which means the structure of forest stands were quite normal as a result of the good process of plant regeneration. The density reached 706 ind/ha, 4,824 ind/ha, and 23,382 ind/ha for tree, sapling, and seedling, respectively. In general, mangrove forest health levels at Tanakeke Island were categorized in low to moderate levels.

森林からの蒸発散と林齢・葉量・林分構造との関係

森林からの蒸発散と林齢・葉量・林分構造との関係