Even-aged Forest Research Articles

Identifying suitable areas for plenter forest management

Plenter forests, also known as uneven-aged or continuous cover forests enhance forest resilience and resistance against disturbances compared to even-aged forests. They are considered as an adaptation option to mitigate climate change effects. In this study, we present a conceptual approach to determine the potentially suitable area for plenter forest management within central European mixed species forests and apply our approach to the case study area in Styria, the south-eastern Province of Austria. The concept is based on ecological and technical-economic constraints and considers expected future climate conditions and its impact on plenter forest management. For each 1 ha forest pixel, we assess the ecological conditions for plenter forest management according to the autecological growth conditions of silver fir, and at least one additional shade tolerant tree species. The technical-economic constraints are defined by slope (≤ 30%) and distance to the next forest road (≤ 100 m) to ensure cost-efficient harvesting. The results show that under current climate conditions 28.4% or 308,349 ha of the forests in Styria are potentially suitable for plenter forest management. For the years 2071 to 2100 and under the climate change scenario RCP 4.5, the potential area decreases to 286,098 ha (26.3% of the total forest area) and for the scenario RCP 8.5 to 208,421 ha (19.1% of the total forest area). The main reason for these changes is the unfavourable growing conditions for silver fir in the lowlands, while in the higher elevations silver fir is likely to expand. Our results may serve forest managers to identify areas suitable for plenter forests and assist in the transformation of even-aged pure forests to uneven-aged forests to increase resistance, resilience, and biodiversity under climate change.

Simulating the Net Primary Production of Even-Aged Forests by the Use of Remote Sensing and Ecosystem Modelling Techniques

Simulating the Net Primary Production of Even-Aged Forests by the Use of Remote Sensing and Ecosystem Modelling Techniques

Amount of carbon fixed, transit time and fate of harvested wood products define the climate change mitigation potential of boreal forest management—A model analysis

Boreal forests are often managed to maximize wood production, but other goals, among which climate change mitigation, are increasingly important. Hence, it is necessary to examine synergies and trade-offs between forest production and its potential for carbon sequestration and climate change mitigation in forest stands. To this aim, we develop a novel mass-balanced process-based compartmental model that allows following the carbon path from its photosynthetic fixation until its return to the atmosphere by autotrophic or heterotrophic respiration, or by being burnt as wood product. Following carbon in the system allows to account for how long forest ecosystems and wood products retain carbon away from the atmosphere (i.e., the carbon transit time). As example, we apply the model to four management scenarios, i.e., mixed-aged pine, even-aged pine, even-aged spruce, and even-aged mixed forest, and contrast metrics of performance relative to wood production, carbon sequestration, and climate change mitigation potential. While at the end of an 80 yr rotation the even-aged forests held up to 31% more carbon than the mixed-aged forest, the mixed-aged forest was superior during almost the entire rotation when factoring in the carbon retention time away from the atmosphere, i.e., in terms of climate change mitigation potential. Importantly, scenarios that maximize production or amount of carbon stored in the ecosystems are not necessarily the most beneficial for carbon retention away from the atmosphere. These results underline the importance of considering carbon transit time when evaluating forest management options for potential climate change mitigation.

Responses of Enzymatic and Microbiological Soil Properties to the Site Index and Age Gradients in Spanish Black Pine (Pinus nigra Arn ssp. salzmannii) Mediterranean Forests

This research analyzes how enzymatic and microbiological soil properties relate to site index (SI) and forest maturity (stand age) in Pinus nigra (P. nigra) even-aged forests. The soil parameters selected for multivariate analysis were four enzymatic activities (β-glucosidase, urease, dehydrogenase, and alkaline phosphatase), two microbiological properties (microbial biomass C and basal respiration), and five physicochemical parameters (TOC, N, P, pH, and soil water content). We used LiDAR, the digital elevation model, and the terrain model to obtain a result for the dominant height in each plot. The soil parameters were analyzed in the function of five site index classes (8, 11, 14, 17, and 20) and six age classes (50, 70, 90, 110, 170, and 210 years). Our findings emphasize that the dehydrogenase enzyme exhibited variations in response to both the site index and stand age. The activity of dehydrogenase positively correlated with sites characterized by a higher nutrient demand, particularly on young and poor-quality sites (lower SI), indicating activation. Therefore, dehydrogenase could serve as an index to elucidate both site quality and stand development in P. nigra stands, making it a potential indicator of forest ecosystem development.

Modelling individual tree maximum basal area growth rates of five tall eucalypt species growing in even-aged forests

Inventory plot data were available providing over 87,000 individual tree basal area growth rates from even-aged native forests of three ash eucalypts (Eucalyptus regnans, E. obliqua, and E. delegatensis), from temperate regions, and two other species from more sub-tropical climes (E. grandis and E. pilularis). Models were developed relating maximum observed growth rates for these species in relation to tree size when, presumably, trees were under ideal environmental conditions and without competition from neighbours for site growth resources. These maximum growth rates increased with increasing tree size to a maximum of their own and then declined as tree size (hence age) increased further. The tree sizes, at which these maximum growth rates reached their maxima, were much greater for the ash eucalypts than for the other two species. It is hypothesised that the ash eucalypts may have evolved physiological characteristics that make them more efficient in compensating for the well-known physiological constraints imposed on growth rates as trees grow to great heights and ages.

Terrestrial vs. UAV-Based Remote Measurements in Log Volume Estimation

This study compared oak butt-log volume estimations gained through terrestrial measurements in the forest stand with a remote approach using an unmanned aerial system (UAS) and photogrammetric post-processing. Terrestrial measurements were conducted in the lowland part of Croatia after a completed motor–manual final felling of a 140-year-old even-aged oak stand. Butt-logs’ volumes were estimated with four methods: the sectioning method and Huber’s, Smailan’s and Riecke–Newton’s methods. Measuring diameters and lengths and estimating volumes remotely were based on orthophotos using four different software: ArcGIS, QGIS, AutoCAD and Pix4D. Riecke–Newton’s method for volume estimation had the smallest relative bias of +1.74%, while for Huber’s method it was −8.07% and with Smailan’s method it was +21.23%. Log volume estimations gained remotely via ArcGIS and QGIS were, in the case of Huber’s method, at +3.63% relative bias, and in the case of Riecke–Newton’s method at +1.39% relative bias. Volume estimation using the sectioning method resulted in a total of 51.334 m3 for the whole sample, while the sectioning method performed with the help of AutoCAD resulted in 55.151 m3, i.e., +7.43% relative bias. Volume estimation of thirty oak butt-logs given by Pix4D software (version 4.8.4) resulted in +9.34% relative bias (56.134 m3). Comparing terrestrial measurements and the volume estimations based on them to those gained remotely showed a very high correlation in all cases. This study showed that using a UAS for log volume estimation surveys has the potential for broader use, especially after final felling in even-aged forests where the remaining trees in the stand would not block photogrammetric analysis.

Adapting the tree growth model MOSES to manage uneven-aged mixed species forests in Bosnia & Herzegovina

In Bosnia & Herzegovina, uneven-aged Plenter forest is the dominating forest management system and applied to 90% of the high forest area. This differs from most other European countries, where even-aged forest management is dominating. However, the interest in Plenter forest management is increasing, as mixed diverse forest stands are considered to be more resilient versus even-aged forests. In this study, we analyze uneven-aged forest management in Bosnia & Herzegovina and demonstrate the application of the tree growth model MOSES (Modeling Stand rESponse) for Plenter forest management in the region. After validating the model using independent data, we perform simulation scenarios to demonstrate the applicability of the model to the local conditions. Our results suggest that the model exhibits no bias or inconsistencies in the resulting predictions. The simulation runs show how the model can be used for scenario analysis within Plenter forests and that continuous management is needed to maintain the diversity of Plenter forest ecosystems.

Shape still matters: rockfall interactions with trees and deadwood in a mountain forest uncover a new facet of rock shape dependency

Abstract. Mountain forests have a substantial protective function in preventing natural hazards, in part due to the presence of dead wood on the forest floor. Rates of deadwood accumulation have increased within the Alps and are predicted to rise further, due to natural disturbances. In particular, higher windthrow event frequencies are expected, primarily due to large-scale even-aged forest stands in many alpine regions combined with climate change. We quantified the rockfall protection effect of mountain forests with and without deadwood, in unprecedented detail, in experiments using two rock shapes with important hazard potential and masses of 200–3200 kg. Based on a multi-camera setup, pre- and post-experimentally retrieved high-resolution lidar data, and rock data measured in situ, we precisely reconstructed 63 trajectories. The principal parameters of interest describing the rockfall kinematics were retrieved for each trajectory. A total of 164 tree impacts and 55 deadwood impacts were observed, and the currently applied energy absorption curves – partially only derived theoretically – could consequently be corroborated or even expanded to a greater absorption performance of certain species than hitherto assumed. Standing trees, in general, and deadwood, in particular, were found to strongly impede the notorious lateral spreading of platy rocks. Platy rocks featured a shorter mean runout distance than their compact counterparts of similar weight, even in the absence of deadwood. These results indicate that the higher hazard potential of platy rocks compared with more compact rocks, previously postulated for open-field terrain, applies less to forested areas. Last, reproducing the experimental setting showcases how complex forest states can be treated within rockfall simulations. Overall, the results of this study highlight the importance of incorporating horizontal forest structures accurately in simulations in order to obtain realistic deposition patterns.

Assessing Site Productivity via Remote Sensing—Age-Independent Site Index Estimation in Even-Aged Forests

Forest productivity is a key driver of forest growth and yield and a critical information need for forest management and planning. Traditionally, this information has come from field plots, but these are expensive to measure and have limited coverage. Remote sensing, on the other hand, can provide forest inventory attributes on landscape scales and with a relatively low cost. A common predictor of forest productivity is site index (SI), traditionally estimated from age and height. In plantations, age can often be treated as a known quantity, but in natural-origin forests (of which Canada has vast swaths), age is often unknown and must be estimated, requiring expensive field work and resulting in a high level of error which, in turn, introduces error into SI estimates. The objective of this study is to generate estimates of SI from two successive LiDAR captures. The 99th percentiles (p99) of LiDAR returns from two successive captures 13 years apart were used along with species-specific SI curves to estimate SI. The results were compared to field-based estimates of SI for two major boreal species, jack pine and black spruce in managed and unmanaged conditions. Overall, the difference between the LiDAR-based SI and the field estimate was 2% with a relative mean squared error of 18%. For the few situations in which the height change was small or negative (less than 0.5%/year), SI was estimated from the average p99 and an assumed age of 100. The advantage of this method is that it does not require field sampling or estimates of age. Using two successive LiDAR captures, wall to wall estimates of SI can be generated at the grid cell level (e.g., 20 × 20 m), a level of detail generally not found in inventories. Overall, our results demonstrate the excellent potential for estimating SI from LiDAR alone, without age, to provide detailed productivity information for forest management and inventory that has been lacking in most large-scale inventories until now.

Continuous cover forestry: Which sampling method should be used to ensure sustainable management?

The transformation of even-aged forests into continuous cover forests to improve resilience and to promote biodiversity in Central Europe necessitates a re-evaluation of forest sampling designs. This study examines the precision and accuracy of two widely used terrestrial sampling methods, namely Angle Count Sampling and Fixed Area Plot Sampling. By simulating multiple samples in typical well-established Plenter forests in Switzerland, we analyse the error components and variabilities of the different methods for three key stand parameters: stem number per hectare, basal area per hectare and annual basal area increment per hectare. Our results suggest that, depending on the parameter of interest, the standard deviation, and the acceptable margin of error, the number of needed sample plots exhibits a large variation. Since the key stand parameters for ensuring sustainability in Plenter forests are the stem number by diameter at breast height class and the basal area increment, our results suggest that a Fixed Area Plot with 300 m² circles is the best compromise between cost efficiency and precision for the sampled Plenter forest data. Alternatively, a Fixed Area Plot of 500 m² or a combined Angle Count Sampling method with a basal area factor of 4 m²/ha and a 200 m² Fixed Area Plot may be considered.

Canopy responses of Swedish primary and secondary forests to the 2018 drought

Boreal forest ecosystems are predicted to experience more frequent summer droughts due to climate change, posing a threat to future forest health and carbon sequestration. Forestry is a regionally dominant land use where the managed secondary forests are typically even-aged forests with low structural and tree species diversity. It is not well known if managed secondary forests and unmanaged primary forests respond to drought differently in part because the location of primary, unmanaged, forests has remained largely unknown. Here we employed a unique map detailing over 300 primary forests in Sweden. We studied impacts of the 2018 nationwide drought by extracting and analyzing a high-resolution remote sensing vegetation index over the primary forests and over buffer zones around the primary forests representing secondary forests. We controlled for topographical variations linked to soil moisture, which was a strong determinant of drought responses, and analyzed Landsat-derived EVI2 anomalies during the drought year from a multiyear non-drought baseline. We found that primary forests were less affected by the drought compared to secondary forests. Our results indicate that forestry may exacerbate the impact of drought in a future climate with more frequent and extreme hydroclimatic events.

Cutting height as a competition control factor in teak (Tectona grandis L.f) plantations in southern Benin

The effect of stump sprouts on the growth of trees in the main plantation under system of even-aged forest was investigated in this study. In this context, eight plantations taking into account the age, the number of thinning and the type of soil were selected. In order to assess the practices related to cutting height, a survey was carried out in each plantation. In each plantation, at least, two square plots measuring 50 × 50 m (one containing trees with less stump sprouts and the other containing trees with stump sprouts) were installed. The density of stump sprouts and filler trees had a detrimental effect on the growth of trees in the main plantation. Competition for resources was the main cause. The density of stumps and those of filler trees within a radius of 5 m around each future tree were estimated at 3 stumps and 3 filler trees respectively. The distance between the future trees and the stump sprouts or the filler trees was estimated at around 3 m. The search for an appropriate cutting level, spacing of trees and compliance with recommendations related to silvicultural practices are among other solutions to limit this competition.

Quantifying the impact of management on the three-dimensional structure of boreal forests

Forest management practices modify the composition and three-dimensional structure of boreal forests. Such changes affect light regimes, microclimate and habitat availability in forests, thus contributing to the regulation of ecosystem functioning and biodiversity. Compared to traditional even-aged forestry, prevalent in Fennoscandia since the mid-20th century, uneven-aged forestry has emerged as an alternative approach that may lead to more diverse and resilient forests, as well as a more sustainable provision of ecosystem services. However, the biophysical impacts of uneven-aged strategies have not yet been robustly quantified. Here, we present a detailed assessment of the structural characteristics of even-aged and uneven-aged boreal forest stands in southern Finland, aiming to clarify how these different management approaches regulate three-dimensional forest structure. Using terrestrial laser scanning, we derived and compared several structural traits closely linked to forest functioning. We found that, although different management types result in similar patterns in total plant material, they differ significantly on how plant material is allocated within vertical strata. Moreover, we demonstrated that commonly used structural diversity metrics cannot not capture the morphological intricacies arising from the three-dimensional dispersion of plant material inside the forest stand. Our results highlight the dynamic nature of even-aged forests, where the structural characteristics change with the rotation, whereas uneven-aged forest structures are more stable over time. Precise quantification of forest structure will help to understand which attributes impact the environmental functions and conditions that modify ecosystem services, and how these are altered with forest management.

Predicting stem taper using artificial neural network and regression models for Scots pine (Pinus sylvestris L.) in northwestern Türkiye

ABSTRACT Stem taper models are helpful tools for predicting diameter of a tree at any height or volume of any stem section. In this study, traditional and artificial neural network (ANN) approaches were used to predict stem tapers of Scots pine individuals. The data used in this study correspond to destructively sampled trees in even-aged forest stands located in the three important locations where Scots pine grows naturally in northwestern Türkiye. In total, three regression type stem taper models from different categories and an ANN model were developed and evaluated both statistically and graphically. The best results were obtained by Kozak’s taper model accounting for the 99% of the total variance in stem diameter predictions.

Variable self-thinning explains hydrological responses to stand replacement in even-aged forests

That streamflow from even-aged forests is a function of forest age (the Kuczera curve) is an accepted paradigm in Australian forest hydrology and less commonly in the Northern Hemisphere. However, none of a dozen stand replacement experiments in Australian obligate seeder forests have faithfully reproduced the Kuczera curve. Here we test an alternative model based on the self-thinning line, showing that both the Kuczera curve and results of subsequent stand replacement experiments can be explained by observed changes in self-thinning after disturbance.Self-thinning in even-aged forests is dictated by the rate of reduction in stocking density as mean tree size increases. Comparison of stand basal area and stocking densities in stands of Eucalyptus regnans F. Muell, regenerated after wildfires in 1851 and 1939, suggested significant differences in self-thinning lines between age cohorts. In three large catchments, a simple forest growth and water use model only reproduced observed substantial long-term reductions in streamflow after stand replacement (mean reduction from 1940 to 1982 of 233 mm year−1) when observed cohort-specific changes in the intercept of the self-thinning line (STL) were incorporated (modelled mean reduction 235 mm year−1). Use of a single STL intercept in both pre- and post-disturbance simulations did not produce the observed streamflow responses (modelled mean reduction 37 mm year−1). Averaged over six E. regnans experimental catchments in which the dominant forest was either partly or completely removed and replaced with the same species, the observed decadal maximum streamflow reduction was only 7 mm year−1, compared to 22 mm year−1 using the model with observed STL intercepts but 200 mm year−1 using the Kuczera curve. Consequently, hydrological responses to disturbance are less predictable than previously assumed, as the reasons for changes in self-thinning behaviour are not yet understood. We speculate that in this case it is related to variability in seed supply and competition with shorter-lived understorey species in the early stages of regeneration.

Effect of forwarder multipassing on forest soil parameters changes

In the lowland part of Croatia, heavy machinery such as forwarders is mainly used for the purpose of extracting wood from even-aged forest stands. According to the forest management plan, forwarders are used intensively in the winter period when the soil is mostly saturated with water and when their activity can cause significant damage to the soil. The aim of this study was to determine changes in soil characteristics as a consequence of the repeated passage of a loaded 8-wheel forwarder on silty clay loam type of soil. The research was conducted in an area where the forwarder usually works and in a way that did not significantly disrupt his normal workflow. The results indicate that during the study period the soil had a good bearing capacity and that the observed changes in soil characteristics (bulk density, total soil porosity, soil moisture, particle density, soil water retention capacity etc.) occurred as a result of breaking structural soil aggregates after soil compaction by multiple passes. Characteristic points (T) of equalized penetration curves indicate the compaction of the soil surface layer. Cone penetration index (CI) values did not show a proportional increase as the number of forwarder passes increased, although significant differences in their values with respect to the number of passes were found. Shear strength (τ) did not significantly increase with increasing the number of passes, but a statistically significant difference in the measured values was detected at the soil surface, which was not observed at a depth of 15 cm. Exceeding the rut depth limit of 10 cm occurred only after the 20th pass. Our results indicate that the soil at the harvesting site had a good bearing capacity during the study period.

Testing the application of process-based forest growth model PREBAS to uneven-aged forests in Finland

The challenges of applying process-based models to uneven-aged forests are the difficulties in simulating the interactions between trees and resource allocation between size classes. In this study, we focused on a process-based forest growth model PREBAS which is a mean tree model with Reineke self-thinning mortality and was originally developed for even-aged forests. The primary aim was to test the application of PREBAS model to uneven-aged forests by introducing different diameter at breast height (DBH) size classes to better represent the forest structure. Additionally, we introduced a new mortality model MORnew to PREBAS which is developed for uneven-aged stands and compared with the current PREBAS version in which a modification Reineke rule is used. The tests were conducted in 26 old Norway spruce dominated stands in southern and central Finland with three consecutive measurements (on average a 25-year study period). To evaluate the model performance, we compared the estimations of stand averaged diameter at breast height (D), stand averaged tree height (H), stand averaged crown base height (Hc), stand basal area (B) and density (N) with measurements. Moreover, biomass estimations of each tree component (foliage, branch and stem) were compared to estimations from empirical models. Results showed that introducing size distributions can represent better stand structure and improve the model predictions compared with data. Moreover, the new mortality model MORnew showed promise with qualitatively more realistic results especially among the largest tree size classes. However, model bias still existed in the simulation although the predictions were improved. It revealed that further calibration of the PREBAS model with size classes should be done to better extend the model applicability to uneven-aged forests.

Influence of environmental variables on leaf area index in loblolly pine plantations

The productivity of even-aged forest stands varies from one year to the next as a function of canopy size and its interaction with the effective radiation used for photosynthesis. To characterize this relation, ecologists use leaf area index (LAI), a metric that serves as an indicator of the photosynthetic capacity on a given site. In this research, we proposed a model describing leaf area index dynamics in loblolly pine plantations growing in the southeastern United States. The model implements a delayed differential equation using periodic coefficients that enforce the seasonality in resource availability. The equation was further expanded to accommodate climatic variables to evaluate their contribution in reducing the observed variability. The proposed model uses environmental modifiers to account for the changes in resource availability and to adjust the carrying capacity in forest stands. From a range of tested variables, we found monthly maximum temperature and monthly excess water to be the most influential on leaf area index dynamics. With the addition of environmental modifiers and a local carrying capacity parameter, root mean square error was reduced to 0.3802 units LAI (m2/m2) from a base model RMSE of 0.4427 units LAI (m2/m2). The results indicate that the delay component has a small 41-day effect in the model, which is contrary to our initial hypothesis that stored within-tree carbohydrates can be used for further seasons to build foliage.

Stand-level growth models for long-term projections of the main species groups in Norway

ABSTRACT Stand-level growth and yield models are important tools that support forest managers and policymakers. We used recent data from the Norwegian National Forest Inventory to develop stand-level models, with components for dominant height, survival (number of survived trees), ingrowth (number of recruited trees), basal area, and total volume, that can predict long-term stand dynamics (i.e. 150 years) for the main species in Norway, namely Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and birch (Betula pubescens Ehrh. and Betula pendula Roth). The data used represent the structurally heterogeneous forests found throughout Norway with a wide range of ages, tree size mixtures, and management intensities. This represents an important alternative to the use of dedicated and closely monitored long-term experiments established in single species even-aged forests for the purpose of building these stand-level models. Model examination by means of various fit statistics indicated that the models were unbiased, performed well within the data range and extrapolated to biologically plausible patterns. The proposed models have great potential to form the foundation for more sophisticated models, in which the influence of other factors such as natural disturbances, stand structure including species mixtures, and management practices can be included.

Особенности строения сосновых древостоев на острове Большом Соловецком

The studies were carried out on Bolshoy Solovetsky Island in the White Sea. The research purpose is to identify the features of pine forests in the most frequent growing conditions on the island. For this purpose, 34 sampling areas were laid out in the prevailing types (cowberry, blueberry, and sphagnum) of pine forests. In each sampling area reference trees were selected and measured, and core samples were taken from 64 trees for age determination. The paper shows that the stands are characterised by low quality class and therefore low timber stocks. The quality class in cowberry and sphagnum pine forests is Va; and in blueberry pine forests it is V. Timber stock in cowberry, blueberry and sphagnum pine forests is 92, 90 and 53 m3/ha, respectively, with a fairly close average age of 109–114 yrs. The average diameters in the stands are relatively high, while the average heights, on the other hand, are low. The diameter in cowberry and blueberry pine forests is 21 and 22 cm, respectively, and the height is 12 and 14 m, respectively. Forest stands are mostly unevenaged. An even-aged pine forest was found in only one sampling area, which is 3 % of the total amount; 21 % of stands are relatively uneven-aged, and all the rest are uneven-aged. Absolute age difference and cyclical age difference are the most typical. There is a significant share of relatively uneven-aged pine stands in blueberry and sphagnum forests. Trees in all forest types have a very low relative height. On average, it is equal to 63 cm/cm for cowberry pine forests, 61 cm/cm for blueberry pine forests, and 55 cm/cm for sphagnum pine forests, i.e. for every centimeter of diameter, trees grow in height by 55–63 cm depending on the forest type, and 36–45 % lower than the relative height in mainland pine forests. This indicates that the trees on Bolshoy Solovetsky Island are highly tapering. A negative correlation between relative height and age has been found. For citation: Sobolev A.N., Feklistov P.A. Features of the Structure of Pine Stands on Bolshoy Solovetsky Island. Lesnoy Zhurnal [Russian Forestry Journal], 2022, no. 1, pp. 77–87. DOI: 10.37482/0536-1036-2022-1-77-87