Determining the Optimal Density of Phoebe bournei Plantations Based on Dynamic Programming under Close-to-Nature Management Measures

Close-to-nature management (CTNM) is the most promising option for plantation silviculture and has received widespread attention in recent years. Stand density is a key variable in CTNM, as it directly influences growth and yield. Research for the optimal density that maximizes the total harvest has been ongoing. In this paper, a dynamic programming model was applied to the CTNM of Phoebe bournei plantations for the first time to solve the problem of stand density and target tree density control. This paper took Phoebe bournei plantations in Jindong Forest Farm of Hunan Province as the research object. Based on the data of seven consecutive years from 2015 to 2021, Richard’s growth equation was used to fit the height growth equation and basal area growth equation of Phoebe bournei. Stand growth was divided into five development stages according to the forest growth process and characteristics. Stand density and basal area were selected as two-dimensional state variables, and the maximum total harvest in the entire stand growth process was used as the objective function to establish a dynamic programming model. The optimal stand density and target tree density at each growth stage of the stand under three different site conditions were determined. According to the results obtained, the objective forest shape was designed for the stand under three types of site conditions, which can provide a theoretical basis for the CTNM of Phoebe bournei plantations to make the stand achieve the maximum harvest.

Changes of Tree and Stand Growth: Review and Implications

In this chapter, we review the current long-term growth trends and short-term growth reaction to single or repeated stress events on tree and stand level in Europe. Based on growth trend analyses, the chapter reveals the strong human footprint on forest ecosystems.First, we use long-term experiments and increment cores to show change in growth trends within the last centuries. Growth reactions are caused by deposition and climate change rather than by silvicultural measures. Second, we look closer on regional-specific deviations from the general trend. Climate change, drought events, acid rain and O3 are causing regional-specific growth reaction patterns. Third, we assess stress events and the resilience and resistance of monospecific and mixed stands against biotic and abiotic stress in view of the ongoing growth trends.The revealed tree and stand growth behaviours are highly relevant, as any changes of forest growth and structure have strong impacts on the provision of goods and ecosystem services. The results underline the importance of biomonitoring and suggest counteracting measures by forest planning, adaptation of silvicultural guidelines for existing forest and innovative design of future forests stands.

Managing Fuels, Tree, and Stand Growth Using Prescribed Fire and Alternatives in Young Mixed Conifer Stands

Background In the wake of increasingly frequent and severe wildfires in California, artificial regeneration and density management facilitate prompt reforestation and the rapid growth of large, fire-resistant trees. Young plantations are particularly prone to high-severity wildfire effects, suggesting the implementation of fuel reduction treatments in the early stages of stand development. The extent to which density management (i.e., thinning) and fuels management (i.e., prescribed fire) can work together is uncertain given their potentially conflicting effects on tree and stand level growth. We investigated how four different treatments – mastication, mastication plus herbicide, two prescribed burns, and mastication plus two burns – affected individual and stand-level growth versus fuel loads in mixed-conifer plantations during young stand development in the north-central Sierra Nevada, California, USA. Results The mastication plus herbicide treatment maximized individual tree growth, especially for white fir and incense-cedar, but fuel loads doubled after five years without the use of fire. The mastication only treatment resulted in a 151% increase in fuel loads over the same period, and individual tree growth was comparable to the burn only and mastication plus burn treatments. The burn only treatment greatly decreased fuel loads but also resulted in low relative stand growth. The mastication plus burn treatment prevented fuel accumulation and generally did not slow down individual tree growth. In addition, stand growth occurred at a rate similar to that of the mastication plus herbicide treatment. Conclusions Mastication followed by repeated prescribed burning could be a viable management strategy to reduce wildfire hazard without sacrificing growth in young mixed-conifer stands that are entering a vulnerable stage of fire risk. Mastication in combination with herbicide may grow trees to a large, fire-resistant size more quickly, but does not address fuel buildup. The use of fire alone can effectively reduce fuels while not substantially impacting individual tree growth, but stand growth may decline relative to mastication and herbicide.

Reinforcement Learning in Optimizing Forest Management

We solve a stochastic high-dimensional optimal harvesting problem by reinforcement learning algorithms developed for agents who learn an optimal policy in a sequential decision process through repeated experience. This approach produces optimal solutions without discretization of state and control variables. Our stand-level model includes mixed species, tree size structure, optimal harvest timing, choice between rotation and continuous cover forestry, stochasticity in stand growth, and stochasticity in the occurrence of natural disasters. The optimal solution or policy maps the system state to the set of actions, i.e. clear-cut/thinning/no harvest decisions and the intensity of thinning over tree species and size classes. The algorithm repeats the solutions for deterministic problems computed earlier with time-consuming methods. Optimal policy describes harvesting choices from any initial state and reveals how the initial thinning vs. clear-cut choice depends on the economic and ecological factors. Stochasticity in stand growth increases the diversity of species composition. Despite the high variability in natural regeneration, the optimal policy closely satisfies the certainty equivalence principle. The effect of natural disasters is similar to an increase in the interest rate, but in contrast to earlier results, this tends to change the management regime from rotation forestry to continuous cover management.

Drainage and Stand Growth Response in Peatland Forests—Description, Testing, and Application of Mechanistic Peatland Simulator SUSI

Drainage is an essential prerequisite in peatland forest management, which generally, but not always, increases stand growth. Growth response depends on weather conditions, stand and site characteristics, management and biogeochemical processes. We constructed a SUSI-simulator (SUoSImulaattori, in Finnish), which describes hydrology, stand growth and nutrient availability under different management, site types and weather conditions. In the model development and sensitivity analysis, we used water table (WT) and stand growth data from 11 Scots pine stands. The simulator was validated against a larger dataset collected from boreal drained peatlands in Finland. In validation, SUSI was shown to predict WT and stand growth well. Stand growth was mainly limited by inadequate potassium supply, and in Sphagnum peats by low oxygen availability. Model application was demonstrated for ditch network maintenance (DNM) by comparing stand growth with shallow (−0.3 m) and deep ditches (−0.9 m): The growth responses varied between 0.5 and 3.5 m3 ha−1 in five years, which is comparable to experimental results. SUSI can promote sustainable peatland management and help in avoiding unnecessary drainage operations and associated environmental effects, such as increased carbon emissions, peat subsidence, and nutrient leaching. The source code is publicly available, and the modular structure allows model extension to cost–benefit analyses and nutrient export to water courses.

Effects of Thinning Practice, High Pruning and Slash Management on Crop Tree and Stand Growth in Young Even-Aged Stands of Planted Silver Birch (Betula pendula Roth)

The objective was to quantify the influence of thinning, high pruning and slash management on crop tree and stand growth in young even-aged stands of planted silver birch (Betula pendula Roth). This study was based on two field experiments, aged six and eleven years at initiation and re-measured after six and eight years, respectively. Treatments included the unthinned control, moderate thinning mainly from below (removing 28–33% of standing volume), point thinning to favor 300 trees per ha and with no thinning elsewhere in the plot (removing 16–25%), and heavy thinning leaving 600 evenly distributed potential future crop trees per ha (removing 64–75%). Slash management (extraction or retention) was applied to heavily thinned plots. High pruning removing 30–70% of the green crown was carried out in some plots with point or heavy thinning on 300 or 600 trees per ha, respectively. Stand volume growth increased with increasing pre-treatment mean annual volume increment and decreased with increasing thinning intensity as compared to the unthinned control. LS-means estimates indicated a reduction for moderate thinning by 14%, for point thinning by 12% and for heavy thinning (combined with pruning) by 62%. However, in the youngest experiment, heavy thinning (without pruning) reduced growth by 54%. Combining these results with results from a similar experiment in Canada, the reduction in stand volume growth (RedIv%) depending on thinning removal (RemV%), both expressed as a percentage of the unthinned control, was quantified as RedIv% = −23.67 + 1.16·RemV% (calibration range: 30–83%). For heavy thinning (large quantities of slash), slash extraction resulted in no reduction in stand volume growth as compared to slash retention. The instantaneous numeric reduction in the average stem diameter of the 300 thickest trees per ha (D300) due to thinning was 3.5, 15–21% and 955–11% with moderate, point and heavy thinning, respectively. The subsequent average annual increase in D300 during the observation period was 8.5%, 25 and 18%, respectively. In the youngest experiment, pruning in unthinned plots led to a reduction in the annual increase of D300 by 14%, and heavy thinning in unpruned plots led to an increase by 30%. The growth of pre-selected potential future crop trees increased with increasing thinning intensity. In heavily thinned plots, pruning reduced growth increasingly with increasing pruning severity; LS-means estimates indicated 21% larger growth on stem diameter for unpruned trees and 3% for pruned trees. As an adverse side effect, heavily thinned plots with only 600 trees per ha were at increased risk of windthrow for some years after the thinning intervention. In the oldest experiment, 95–21% of the trees in these plots were damaged by wind.

Semi-natural regeneration and conservation in agroforestry system models on small-scale farmers

Suryanto P, Sadono R, Yohanifa A, Widyawan MH, Alam T. 2021. Semi-natural regeneration and conservation in agroforestry system models on small-scale farmers. Biodiversitas 22: 858-865. The regeneration capacity can provide an overview of the abundance of species so that it can be used to determine the potential and opportunities for the sustainability of agroforestry systems. The purpose of this study was to determine the capacity of semi-natural regeneration in agroforestry system models for small-scale farmers. The study was carried out in Banaran Sub-district, Playen District, Gunungkidul Regency, Special Province of Yogyakarta, Indonesia. The observation was conducted on plant diversity, floristic composition, and agroforestry contribution. The results showed that the mixed cropping (MC) model had a higher total of individuals and diversity compared to the trees along with border (TAB) model in the sapling and seedling level. The MC model was relatively shorter to the waiting time of harvesting compared to the TAB model. The MC models weakness was the relatively high competition and the lack of opportunities to growing annual crops. The TAB model had an advantage in developing annual crops in an agroforestry system, while longer in waiting time for harvesting perennial crops. This study recommends annual pruning in the MC model for optimal stand growth, while in the TAB model, it is the enrichment planting in sapling and seedling levels.

FLORISTIC DIVERSITY AND STRUCTURAL CHARACTERIZATION OF THE FOREST OF CHETTABA (ALGERIA)

"The structure of various stands, defined as the diversity of trees in the stands, can be an indication of overall biodiversity and habitat suitability, be useful in predicting stand growth and provide stand details for forest inventories. In an effort to find sustainable resource management strategies, a study was conducted on the structural and ecological characteristics of stands in Chettaba forest (Algeria). In this study, six diversity indices were used to characterize the horizontal and spatial distribution of individuals in multi-species stands, using four plots, located in the Chettaba forest (East-North Algeria). The results obtained allowed us to note that P2 and P3 present similar average densities (600 feet/ha), the plots P1 and P4 present low average densities (250 feet/ha and 350 feet/ha). The average DBH values vary from 25.65 cm for the P2 stand to 30.61 cm for the P1 stand. The average basal area varied between 33.73 m²/ha (P3) and 18.92 m²/ha (P1). The Shannon and Weaver index reached its maximum in plot 4 with 8 species. The study allowed us to evaluate the floristic diversity of the forest. Moreover, it indicated the need for its integral protection for its dynamics towards a dense forest vegetation."

Forecast of Growth and Development of Modal Fir Stands in the Lower Angara Region

The paper presents an assessment of the growth dynamics of the modal fir plantations in the Lower Angara region. At present, a vast area of fir forests in the Lower Angara region is characterised by a significant decrease in sustainability due to periodic forest fires, insect pests outbreaks and diseases, which lead to their natural degradation and death. However, the intensity of coniferous stand growth in certain forest site characteristics persists in the long term. Therefore, creating regression models of forest growth and development involving the identification of site conditions is very important both from a practical point of view and for environmental monitoring. The materials of the mass inventory of 3491 stands served as the initial data for studying the processes of fir plantations natural growth. The Hoerl Model function is suitable for the best approximation of stand growth since it is characterised by high levelling factor (from 0.970 to 0.987) and a small standard error (not exceeding 7%). As a result of the research, there have been constructed sketches of the growth rate tables for the modal Siberian fir stands of the third bonitet class of the forb and mossy groups of forest types.