Search Results (6)

Increased tree species diversity can promote forest production by reducing intra-specific competition and promoting an efficient unitization of resources. However, questions remain on whether and how mixed stands affect the dynamics of intra–annual xylem formation in trees, especially in subtropical forests. In this study, we randomly selected 18 trees from a monoculture of 63-year-old Masson pine (Pinus massoniana) growing in pure stands and mixed them with 39-year-old Castanopsis hystrix in Pinxiang, southern China. A total of 828 microcores were collected biweekly throughout the growing season from 2022 to 2023 to monitor the intra-annual xylem formation. Cell production started in early March and ended in late December and lasted about 281 to 284 days. Xylem phenology was similar between mixed and pure stands. During both seasons, the Masson pine in mixed stands showed higher xylem production and growth rates than those in pure stands. The Masson pine in mixed stands produced 45–51 cells in 2022 (growth rate of 0.22 cells day⁻¹) and 35–41 cells in 2023 (0.17 cells day⁻¹). Growth rate, and not growth seasons, determined the superior xylem growth in the mixed stands. Our study shows that after 39 years of management, Masson pine and C. hystrix unevenly aged mixed stands have a significant positive mixing effect on Masson pine xylem cell production, which demonstrates that monitoring intra-annual xylem growth dynamics can be an important tool to evaluate the effect of species composition and reveal the mechanisms to promote tree growth behind the mixing effect. Full article

There is increasing interest in optimizing stand structure through forest management. The forest structure influences growth and maintains the structure, promoting sustainability. Structure-based forest management (SBFM), which is based on the spatial relationships between a reference tree and its four nearest neighbors, considers the best spatial structure for the stand and promotes the development towards a healthy and stable state by selectively thinning specific trees. This management method is a scientific approach for sustainable forest management, and appropriate harvesting is the core principle of uneven-aged forest management. However, the application of this approach in the management of uneven-aged mixed stands is a challenge because their dynamics are more difficult to elucidate than those of planted or pure stands. This study presented a stand spatial structure optimization model with a transition matrix growth model for selecting suitable timber harvest during uneven-aged mixed-forest management optimization. The model was developed using three neighborhood-based structural indices (species mingling, diametric differentiation, and horizontal spatial pattern) and diameter diversity indices. The approach was applied to four broadleaf stands in the Maoershan Forest Farm of the Heilongjiang Province. The results demonstrate that optimizing the stand spatial structure with a transition matrix growth model improved the objective function values (F-index) by 23.8%, 12.8%, 14.6%, and 28.3%, and the optimal removal of trees from the stands ranged from 24.3% to 25.5%. The stand structure in the next cycle (after 5 years) was closer to the uneven-mixed state. The main conclusion of this study is that optimizing the stand spatial structure with a transition matrix growth model can improve the speed and accuracy of tree selection for harvesting in unevenly mixed forests, thus helping regulate stable and diverse forest growth. Full article

The rapid development of non-parametric machine learning methods, such as random forest (RF), extreme gradient boosting (XGBoost), and the light gradient boosting machine (LightGBM), provide new methods to predict the site index (SI). However, few studies used these methods for SI modeling of Masson pine, and there is a lack of comparison of model performances. The purpose of this study was to compare the performance of different modeling approaches and the variability between models with different variables. We used 84 samples from the Guangxi Tropical Forestry Experimental Centre. Five-fold cross-validation was used and linear regression models were established to assess the relationship between the dominant height of the stand and different types of variables. The optimal model was used to predict the SI. The results show that the LightGBM model had the highest accuracy. The root mean square error (RMSE) was 3.4055 m, the relative RMSE (RMSE%) was 20.95, the mean absolute error (MAE) was 2.4189 m, and the coefficient of determination (R²) was 0.5685. The model with climatic and soil chemical variables had an RMSE of 2.7507 m, an RMSE% of 17.18, an MAE of 2.0630 m, and an R² of 0.6720. The soil physicochemical properties were the most important factors affecting the SI, whereas the ability of the climatic factors to explain the variability in the SI in a given range was relatively low. The results indicate that the LightGBM is an excellent SI estimation method. It has higher efficiency and prediction accuracy than the other methods, and it considers the key factors determining site productivity. Adding climate and soil chemical variables to the model improves the prediction accuracy of the SI and the ability to evaluate site productivity. The proposed Masson pine SI model explains 67.2% of the SI variability. The model is suitable for the scientific management of unevenly aged Masson pine plantations. Full article

(1) Background: This paper deals with unevenly aged, whole-stand models from mixed-effect parameters diffusion processes and Voronoi diagram points of view and concentrates on the mixed-species stands in Lithuania. We focus on the Voronoi diagram of potentially available areas to tree positions as the measure of the competition effect of individual trees and the tree diameter at breast height to relate their evolution through time. (2) Methods: We consider a bivariate hybrid mixed-effect parameters stochastic differential equation for the parameterization of the diameter and available polygon area at age to ensure a proper description of the link between them during the age (time) span of a forest stand. In this study, the Voronoi diagram was used as a mathematical tool for the quantitative characterization of inter-tree competition. (3) Results: The newly derived model considers bivariate correlated observations, tree diameter, and polygon area arising from a particular stand and enables defining equations for calculating diameter, polygon-area, and stand-density predictions and forecasts. (4) Conclusions: From a statistical point of view, the newly developed models produced acceptable statistical measures of predictions and forecasts. All the results were implemented in the Maple computer algebra system. Full article

In forests, tree mortality is strongly determined by complex interactions between multiple biotic and abiotic factors, and the analysis of tree mortality is widely implemented in forest management. However, age-based tree mortality remains poorly evaluated quantitatively at the stand scale for unevenly aged forests. The objective of this study was to predict the age distributions of living and dead trees based on survival analyses. We used a combination of tree-ring and census data from the two preserved permanent plots in the University of Tokyo Hokkaido Forest in pan-mixed and sub-boreal natural forests, Hokkaido, northern Japan, to derive site-specific survival models. All the living trees (diameter at breast height, ≥5 cm in 2009) were targeted to identify the tree ages using a RESISTOGRAPH, a semi-nondestructive device. Periodical tree age data with a 10-year age class were used during the observation periods of 2009–2019, and all the changes (i.e., death and new ingrowth) during the periods were recorded. We determined the time stabilities of the survival functions between periods in advance. The results show that the parametric survival analysis with the Weibull distribution successfully yielded the mortality rate, mortality probability, and survival probability in each plot. Finally, we predicted the future age class distributions of living and dead trees of each plot based on the survival analysis results and discussed their management implications. We recommend that the estimated mean lifetimes facilitate making decisions on the selection of harvesting trees in uneven forest management based on selective cutting. Full article

In the northern Appalachian region of North America, mortality of mature American beech (Fagus grandifolia Ehrh.) via the introduced beech bark disease (BBD) can result in dense thickets of beech saplings that inhibit the regeneration of other species. It is unknown if similar structures characterize more recently infested managed forests in the Great Lakes region. If these dense beech sapling layers do exist, management would be aided by knowing which site/regional factors they are associated with and by identifying particular sapling structures that may threaten the sustainability of these forests under current management paradigms. To examine these patterns, we used a natural experiment with sample plots in 69 unevenly aged, selection silviculture-managed, maple (Acer spp.)-dominated northern hardwood stands. Our stands were dispersed across northern Michigan, USA and had undergone BBD-motivated partial harvests favoring beech removal (mean = 5.5 years before measurement). In each stand, we quantified tree regeneration structure in relation to winter deer use (fecal pellet count density), site quality (habitat type), geographic region (Eastern Upper Peninsula and Northern Lower Peninsula), and multiple measures of overstory stand density. We also examined the density effects of taller regeneration strata on subordinate strata. Across sites, the small sapling recruit class (i.e., >137 cm tall and <5 cm diameter at 137 cm tall) was dominated by beech and was often dense (44% of subplots > 2000 stems ha⁻¹ and 16% of subplots > 5000 ha⁻¹) but never exceeded the > 10,000 stems ha⁻¹ reported in the northern Appalachian region. Beech sapling density was higher in the Northern Lower Peninsula, on lower quality sites, at lower postharvest overstory densities, and on sites with higher densities of preharvest overstory beech. In contrast to the beech-dominated small sapling recruit class, seedlings (i.e., <25 cm tall) were generally more species diverse than sapling strata and were dominated by maple species. Although generally dense, seedling density was negatively related to small sapling recruit density, suggesting that saplings may suppress the seedling stratum. The general pattern for the small sapling recruit layer of browsing-insensitive beech (and ironwood, Ostrya virginiana Mill. K. Koch) dominance and low representation of browsing-sensitive species (e.g., Acer spp.) circumstantially supports the notion that regeneration structure is heavily influenced by deer. However, current deer use was generally low in our stands, and relationships with tree regeneration structure were weak. Instead, regeneration structure is likely shaped by a combination of factors operating at long time scales (i.e., legacies of deer browsing pressure, selection silviculture (given beech and ironwood are shade tolerant), overstory composition, and site quality) and by those effects that are more proximal, such as postharvest overstory density. Minimum stocking criteria for species considered desirable for management (e.g., sugar maple and Acer saccharum Marshall) suggest many stands are inadequately stocked in the sapling recruit classes. Although future regeneration dynamics are unclear, current patterns suggest that many stands with high beech/ironwood small sapling recruit densities may require management intervention to overcome insufficient recruitment of species targeted for management. Full article