Uneven-aged Forests Research Articles

Honey-Bearing Potential of Tilia cordata Mill. Forests in the Southern Urals

This article examined the honey-bearing potential of Tilia cordata Mill. stands in the Southern Urals using forest management and taxation methods. The studies were conducted in pure and mixed even- and uneven-aged forests with T. cordata Mill. in different natural zones of the Southern Urals on the territory of the Bashkirs. These were forests of the South Ural forest-steppe region, the forest-steppe region of the European part of Russia, the area of coniferous-deciduous (mixed) forests of the European part of Russia. The research employed the method of laying temporary and permanent trial areas. T. cordata Mill. forests on the republic’s territory were divided into zones by forest districts. There is a discrepancy between the territorial localization of “nectar” (honey-bearing) linden and designated forest areas, that is, honey-bearing forest areas on the republic’s territory. It could be due to the lacking methodology for assigning linden to these categories. The increased rotation age of linden trees to 81–90 years for several decades, a ban on final cutting, reduced annual cut of soft-leaved forests by 15% enlarged the stocks of overmature forest to 48%. Depending on the age, the number of flowers on one T. cordata Mill. tree varies from 0 to 60.2 thousand pieces. The maximum amount of nectar is 69.04 kg/ha at 12-day linden flowering. The honey productivity of plants including T. cordata Mill., calculated concerning the linden age, its share in the forest composition, the average number of flowers on the tree, nectar per 1 ha of linden and the flowering period ranged from 252.8 to 662.8 kg/ha.

Spatial relationships of trees in middle taiga post-pyrogenic pine forest stands in the European North-East of Russia

Information on the structural organization of forest stands obtained on sample plots is the basis for long-term monitoring of post-fire pine forest structure and dynamics in the European North-East. These data can be used as a marker of native pine stands of the European taiga. Here, we studied vertical and horizontal structure in the post-pyrogenic pine forests of Vacciniosum, Vaccinioso-cladinosum and Myrtillosum site types in the boreal forest of the Komi Republic. The type of horizontal structure of uneven-aged forest stands changed with age from grouped to random one. Large trees were randomly distributed on the plot. We observed the weak aggregation of undergrowth trees (natural tree regeneration) in stands at distances of 2–6 m. Undergrowth individuals were characterized by group distribution at smaller distances than 1–2 m. Spatial relationships between large, small and codominant trees demonstrated random distribution in most cases. Undergrowth individuals did not show any competitive relations. However, we revealed a “taking off” effect between mature trees of pine and pine undergrowth. The direction of the displacement of tree crown centre projections relative to the bases of their trunks was ambiguous. The shift of the crown space towards the maximum solar radiation was detected in a thinned stand with old age and big size of trees. In other site types, no one-sided orientation of the tree crown development emerged.

Climate and ungulate browsing impair regeneration dynamics in spruce-fir-beech forests in the French Alps

Key messageDifferent components of water balance and temperature reduce density and height growth of saplings of Picea abies (L.) H. Karst (Norway spruce), Abies alba Mill. (silver fir) and Fagus sylvatica L. (European beech) in mixed uneven-aged forests in the French Alps and Jura mountains. Ungulate browsing is an additional pressure on fir and beech that could jeopardise the renewal of these species in the future.ContextThe uncertainty in tree recruitment rates raises questions about the factors affecting regeneration processes in forests. Factors such as climate, light, competition and ungulate browsing pressure may play an important role in determining regeneration, forest structures and thus future forest composition.AimsThe objective of this study was to quantify sapling densities and height increments of spruce, fir and beech and to identify dominant environmental variables influencing them in mixed uneven-aged forests in the French Alps and Jura mountains.MethodsSapling height increment and density were recorded in 152 plots, and non-linear mixed models were obtained to establish relations between them and environmental factors known to affect regeneration, namely altitude, slope, aspect, canopy openness, soil characteristics, temperature, precipitation and ungulate browsing.ResultsRegeneration density, varying from 0 to 7 saplings per m 2, decreased with sapling height and was also negatively affected for spruce by PET, but positively for fir by precipitation and for beech by mean annual soil water content. Height increment reached up to 50 cm annually, increasing with sapling height and canopy openness and decreasing under high maximum summer temperatures for spruce and beech. The statistical effect of different environmental variables varied slightly among species but trends were quite similar. Additionally, ungulate browsing was high, with fir being the most intensely browsed, followed closely by beech, while spruce was rarely browsed.ConclusionsAll these results suggest that more temperature warming and a decrease in water availability could negatively impact sapling growth and density in the three species, with possible reduction of forest renewal fluxes. The observed increase of ungulate populations leading to increased browsing could be particularly detrimental to fir saplings.

Machine Learning for the Estimation of Diameter Increment in Mixed and Uneven-Aged Forests

Estimating the diameter increment of forests is one of the most important relationships in forest management and planning. The aim of this study was to provide insight into the application of two machine learning methods, i.e., the multilayer perceptron artificial neural network (MLP) and adaptive neuro-fuzzy inference system (ANFIS), for developing diameter increment models for the Hyrcanian forests. For this purpose, the diameters at breast height (DBH) of seven tree species were recorded during two inventory periods. The trees were divided into four broad species groups, including beech (Fagus orientalis), chestnut-leaved oak (Quercus castaneifolia), hornbeam (Carpinus betulus), and other species. For each group, a separate model was developed. The k-fold strategy was used to evaluate these models. The Pearson correlation coefficient (r), coefficient of determination (R2), root mean square error (RMSE), Akaike information criterion (AIC), and Bayesian information criterion (BIC) were utilized to evaluate the models. RMSE and R2 of the MLP and ANFIS models were estimated for the four groups of beech ((1.61 and 0.23) and (1.57 and 0.26)), hornbeam ((1.42 and 0.13) and (1.49 and 0.10)), chestnut-leaved oak ((1.55 and 0.28) and (1.47 and 0.39)), and other species ((1.44 and 0.32) and (1.5 and 0.24)), respectively. Despite the low coefficient of determination, the correlation test in both techniques was significant at a 0.01 level for all four groups. In this study, we also determined optimal network parameters such as number of nodes of one or multiple hidden layers and the type of membership functions for modeling the diameter increment in the Hyrcanian forests. Comparison of the results of the two techniques showed that for the groups of beech and chestnut-leaved oak, the ANFIS technique performed better and that the modeling techniques have a deep relationship with the nature of the tree species.

Pith Eccentricity, Basal Area Increments and Disturbances Inferred from Tree-Ring Growth

Forest management constantly seeks tools that can optimize the production of goods and services. As natural archives, tree rings have proven to be effective in terms of refining the dynamics of growth on a temporal basis. This study evaluates the application of these tree rings in estimating the effect of pith eccentricity on forest growth, modeling the increase in basal area (BAI) and identifying disturbances in five coexisting species in northern Mexico. A Wilcoxon rank sum test showed significant differences, with higher radial growth in the north direction compared to the other directions. A mixed model analysis revealed two patterns of BAI growth, fast and slow growing. The former includes P. arizonica, P. engelmannii and P. leiophylla, whereas the latter comprises P. durangensis and P. lumholtzii. The fast-growing group shows a higher increment during the sapling stage. However, during subsequent stages, it presents growth rates similar to those of the slow-growing group. Finally, the percentage growth change (PGC) filter approach identified species disturbances with differential species responses, which temporarily cause uneven-aged forest. We conclude that tree rings can provide valuable information for forest management, and their temporal amplitude can be supported with information from permanent plots.

Silviculture of South American temperate native forests

Background: South America has the largest area of temperate forests in the Southern Hemisphere, which grow in diverse site conditions. The aim of this paper is to review the practices of silviculture applied and recommended for these temperate forests, and to discuss prospects to develop new silvicultural proposals to improve sustainability, adaptation and in-situ conservation of forest ecosystems. Methods: We reviewed the silviculture knowledge in four major forest types: 1) The Nothofagus-dominated forests of south-central Chile; 2) the Angiosperm-dominated evergreen forests; 3) the Nothofagus and Austrocedrus chilensis (D.Don) Pic. Serm. & Bizzarri forests in the Argentinean Northern Patagonia; and 4) the Cool temperate Nothofagus forests and Magellanic rainforests. Results: In Chile, both Nothofagus-dominated and Angiosperm-dominated evergreen forests are diverse in tree species, and mixed-species silviculture with commercially valuable species of variable shade tolerance is most promising. Some secondary forests can reach growth rates as high as 20 m3ha-1yr-1. After thinnings, stands with 35–60% of residual densities have shown the best responses in growth. Even-aged silvicultural methods have shown a rapid reorganization and development of new cohorts, although, where Chusquea species are conspicuous, regeneration establishment requires controlling competing vegetation. Preliminary results also show interesting prospects for single-tree selection cuts in uneven-aged forests. East of the Andes, in Argentina, mixed Nothofagus forests and pure and mixed Nothofagus and A. chilensis forests occur. The shelterwood method has been the most practised and successful in the mixed Nothofagus forests, with abundant regeneration, and good growth rates. For A. chilensis forests, an adaptive management approach is proposed, conditioned by the cypress disease attack (e.g., Phytophthora austrocedri). Conversion of pure A. chilensis to mixed A. chilensis–N. dombeyi forests could increase growth considerably. Finally, in the cool temperate Nothofagus forests and Magellanic rainforests, shared by Chile and Argentina, the regular shelterwood cuts have been the most common silvicultural method, with massive regeneration a decade after the regeneration felling. Since the two major Nothofagus species in these forests regenerate well in gaps, uneven-aged silviculture seems also promising. Conclusions: There is abundant knowledge about the silviculture of these forest types. However, there are opportunities for several silvicultural systems to better contribute to sustainable forest management, reverse forest degradation, and cope with climate change challenges, primarily through developing mixed and single-species productive and carbon-rich forests, with greater adaptive capacity.

Testing the Application of Process-Based Forest Growth Model Prebas to Uneven-Aged Forests in Finland

Testing the Application of Process-Based Forest Growth Model Prebas to Uneven-Aged Forests in Finland

ASSORTMENT DOWNGRADE CORRECTION FOR CLEAR CUT OF Pinus taeda L. WITH USE OF TRANSITION MATRIX

It is very important that the quantification of a forest's stock is determined efficiently and accurately, in such a way that more detailed information is desirable for the knowledge of the different multiproducts originated. However, the use of taper functions, a precise adjustment method for determining the assortments, does not foresee the appearance of defects in the stem that could disqualify the logs during the forest harvest. This study aimed to use the transition matrix method, a model traditionally used for predict the diametric structure of uneven-aged forests, to correct assortment estimates made by tapering functions, such as failures in tree processing, that provide a disqualification of the logs in the market values. Adapting the concept of the Markov Chain, for the correction of the assortment downgrade, the transition of the assortment classes can be obtained by dividing the actual volume obtained after the operation of the harvesting machine by the volume estimated by the tapering function. In this case, applying this alternative to the clear cut of a 16-year-old Pinus taeda plantation, it was possible to verify the existence of changes, mainly in assortment classes with a thin end diameter of 24 and 18 cm and presenting efficient correction in the estimates. In order to make realistic corrections to the assortment transition, probability matrices must be built for each compartment or forest site to be estimated. Divergences between processing machines or forestry operator’s qualifications can be decisive for the calibration of the model.

Growth and structural changes in Swiss uneven-aged forests over 100 years, and comparisons between 15 uneven-aged forest types of Europe, North America and Australia

Abstract Long-term changes in growth, physiology and stand structure, as well as differences due to species composition, were examined in six types of Swiss plenter forests: (1) Picea abies dominated, (2) mixtures of P. abies and Abies alba, (3) mixtures of P. abies, A. alba and Fagus sylvatica, (4) mixtures of Larix decidua, Pinus cembra/sylvatica and P. abies, (5) F. sylvatica dominated and (6) species diverse stands. Long-term changes were examined using 19 plots measured for an average of 94 years. These data were then combined with the literature plenter forest data to compare the growth and structure of 15 species compositions from Europe, North America and Australia. Over the past 100 years, common trends included increases in growth, maximum tree sizes, species diversity, and increasingly convex diameter distributions with fewer medium sized trees and more very large trees. Differences in growth between species compositions were generally consistent with their light-use efficiency, transpiration and water-use efficiency, which were calculated using a process-based model. Stand volume of each forest type was negatively correlated with the shade tolerance (but not crown architectures) of the species it contained, but no such correlations existed for stand basal area. This reflects the high structural variability of these forests (through time and between sites) as well as the high tree neighbourhood variability within plots, which appear to buffer the effects of stand density on regeneration and recruitment. This study shows that despite significant temporal and spatial variability in structure, the negative exponentially shaped diameter distributions were maintained in the long term by applying simple silvicultural principles rather than requiring a very specific stand structure, i.e. a certain stand density, or that all diameter classes strictly lie on the curve of a negative exponentially shaped diameter distribution. The values of stand structural characteristics reported in this study could be used as a guide for the conversion of relatively simply structured forests into plenter forests.

Sustainable regeneration in uneven-aged mixed deciduous forests managed by selection silviculture: the role of demographic structure

Abstract Selection silviculture aims to create and maintain uneven-aged forests with a diameter at breast height (DBH) structure that is balanced at small spatial scales such that the stem number in each DBH class is high enough to replace the harvested and outgrowing trees over time by ingrowth from the next lower class. In these forests, natural regeneration of shade-tolerant species is at an advantage over shade-intolerant species. This is particularly pronounced in continuous-cover stands dominated by European beech (Fagus sylvatica L.), which develops its crown laterally as a reaction to release events. The conditions necessary to sustain a mixture with less shade-tolerant species, e.g. sycamore (Acer pseudoplatanus L.), have been little studied. Therefore, we explored growth patterns and stand structures in mixed deciduous forests with light availability quantified using vegetation height models. Harvesting and growth patterns were derived from inventory data of beech-dominated selection forests in Thuringia, Germany and long-term forest monitoring plot data from four stands in Switzerland. Based on these data, models of stem number distributions confirmed that stand basal area in deciduous forests dominated by beech should not exceed 21–25 m2 ha−1 to maintain a sustainable structure. In these forests, a total of ~90–120 stems per ha are needed in the ingrowth DBH class (DBH 8–11.9 cm) to ensure demographic sustainability. At canopy light transmittance <10 per cent, total stem number required in the thicket stage (DBH < 8 cm) is 800–1700 ha−1. Under such shady conditions, only a small proportion of sycamore was observed (<25 per cent) in the thicket stage, as the species is likely to require canopy gaps >400 m2 (gap diameter > 22.5 m) to recruit successfully. Selection silviculture with shade-intolerant species therefore requires much lower stocking volume and larger canopy openings created by group selection cutting than what is routinely applied in practical forest management using single-tree selection principles.

Hierarchical log Gaussian Cox process for regeneration in uneven-aged forests

We propose a hierarchical log Gaussian Cox process (LGCP) for point patterns, where a set of points varvec{x} affects another set of points varvec{y} but not vice versa. We use the model to investigate the effect of large trees on the locations of seedlings. In the model, every point in varvec{x} has a parametric influence kernel or signal, which together form an influence field. Conditionally on the parameters, the influence field acts as a spatial covariate in the intensity of the model, and the intensity itself is a non-linear function of the parameters. Points outside the observation window may affect the influence field inside the window. We propose an edge correction to account for this missing data. The parameters of the model are estimated in a Bayesian framework using Markov chain Monte Carlo where a Laplace approximation is used for the Gaussian field of the LGCP model. The proposed model is used to analyze the effect of large trees on the success of regeneration in uneven-aged forest stands in Finland.

Current Status and Recent Stand Structure Dynamics in Mixed Silver Fir—European Beech Forests in Croatian Dinarides: Are There Differences between Managed and Unmanaged Forests?

The environmental, social and economic potential of Dinaric uneven-aged forests along with the complex stand dynamics influenced by different long-term management approaches and environmental factors require comprehensive forest monitoring. This study aimed to explore differences in the current status and recent past dynamics of stand structures between unmanaged and managed mixed fir-beech forests in the Croatian part of the Dinaric Alps using large-scale data from an established monitoring system. From the 74 permanent sample plots distributed within the forest type measured in 2008 and re-measured in 2019, we stratified four strata (types of management regimes): (1) forests out of regular management and tree harvest for at least 30 years, (2) managed state forests on carbonate bedrock, (3) managed state forests on non-carbonate bedrock and (4) managed private forests. In each sample plot, 34 structural attributes were computed to assess indicators of their current status and recent past dynamics of stands in the studied forests. An increasing Q shape diameter distribution with a high number of large and very large trees characterize unmanaged forests and managed forests on non-carbonate bedrock. In managed state forests and private forests, variable (rotated sigmoid) and constant (negative exponential) results were obtained, respectively. Principal component analysis (PCA) distinguished managed and unmanaged forests with decreasing harvest volume and recruitment, increasing basal area, number of very large trees, average diameter at breast height (DBH), crown defoliation of firs and basal area of died beech trees. The current structure, recent and expected stand dynamics in the unmanaged forests (accumulation of standing volume, increase of large diameter trees and large snags, large share of beech, large mean DBH) can be recognized as old-growth attributes. The differences between the studied forest types, potential of both unmanaged and state managed fir-beech forests and approaches to sustain multifunctional forest management in the Dinaric region were discussed.

Optimal Forest Management Using Stochastic Dynamic Programming Approach – A Case Study from the Hyrcanian Forests of Iran

ABSTRACT The aim of this study is to estimate the optimal forest harvest considering economic and environmental objectives in an uneven-aged forest in the north of Iran. Required data were collected such as stumpage price, harvesting variable costs, growth, volume, basal area, sequestrated carbon, carbon dioxide storage, and price. The required input models for optimization were estimated using the collected data. A stochastic dynamic programming technique was used for optimization. The results indicated that the harvesting volume was higher when only the economic objective was considered instead of considering economic and environmental objectives. The results also indicated that the harvesting volume would occur at a higher level of volume per hectare if we only consider the environmental objective. The results showed that the expected present value was higher when economic and environmental objectives were considered simultaneously. The results indicated when interest rate increased, the harvesting time and the expected present value decreased. The results showed that the expected present value increases with increasing the risk. The results of this study can be a guideline for optimal forest management.

Forest Structure and Composition under Contrasting Precipitation Regimes in the High Mountains, Western Nepal

The high mountains stretch over 20.4% of Nepal’s land surface with diverse climatic conditions and associated vegetation types. An understanding of tree species and forest structural pattern variations across different climatic regions is crucial for mountain ecology. This study strived to carry out a comparative evaluation of species diversity, main stand variables, and canopy cover of forests with contrasting precipitation conditions in the Annapurna range. Firstly, climate data provided by CHELSA version 1.2, were used to identify distinct precipitation regimes. Lamjung and Mustang were selected as two contrasting precipitation regions, and have average annual precipitation of 2965 mm and 723 mm, respectively. Stratified random sampling was used to study 16 plots, each measuring 500 m2 and near the tree line at an elevation range of 3000 to 4000 m across different precipitation conditions. In total, 870 trees were identified and measured. Five hemispherical photos using a fisheye lens were taken in each plot for recording and analyzing canopy cover. Margalef’s index was used to measure species richness, while two diversity indices: the Shannon–Wiener Index and Simpson Index were used for species diversity. Dominant tree species in both study regions were identified through the Important Value Index (IVI). The Wilcoxon rank-sum test was employed to determine the differences in forest structure and composition variables between the two precipitation regimes. In total, 13 species were recorded with broadleaved species predominating in the high precipitation region and coniferous species in the low precipitation region. Higher species richness and species diversity were recorded in the low precipitation region, whereas the main stand variables: basal area and stem density were found to be higher in the high precipitation region. Overall, an inverse J-shaped diameter distribution was found in both precipitation regions signifying uneven-aged forest. A higher proportion of leaning and buttressed trees were recorded in the high precipitation region. However, similar forest canopy cover conditions (>90%) were observed in both study regions. The findings of this research provide a comprehensive narrative of tree species and forest structure across distinct precipitation regimes, which can be crucial to administrators and local people for the sustainable management of resources in this complex region.

Dynamics and drivers of aboveground biomass accumulation during recovery from selective harvesting in an uneven-aged forest

Dynamics and drivers of aboveground biomass accumulation during recovery from selective harvesting in an uneven-aged forest

Effects of climate on the growth of Swiss uneven-aged forests: Combining >100 years of observations with the 3-PG model

Stand-level process-based models have rarely been applied to uneven-aged forests that contain many size classes and negative exponential shaped size distributions. However, the relative simplicity of such models, in terms of parameterisation, use and interpretation, could make them valuable tools for studying and managing such forests. In particular, the effects of climate change on the stand-level growth of forests with negative exponential shaped size distributions has received very little attention compared with even-aged forests. The first objective of this study was to validate 3-PG, a stand-level process-based model, for five types of uneven-aged forests in Switzerland; (1) Fagus sylvatica dominated, (2) Picea abies dominated, (3) mixtures of Picea abies and Abies alba, (4) mixtures of Picea abies, Abies alba and Fagus sylvatica, and (5) mixtures of Larix decidua, Pinus cembra and P. abies. The second objective was to use 3-PG to examine how climate change has influenced the growth of these forests since the 1930s.3-PG predictions of biomass, biomass partitioning in above- and belowground components, and light absorption were validated using inventory data from 23 plots, which had been monitored for an average of 81 years (15 to 112 years). For all species and size classes (2–3 per species), 3-PG produced accurate predictions of root biomass, stem biomass and outputs derived from it such as mean diameter, basal area and height, which were all highly correlated with the observed values (R2 > 0.86). The slope of predicted versus observed values was often not significantly different to 1 (averaged 1.13) and the bias averaged −1.2%.3-PG simulations to examine the effects of climate change without the confounding effects of stand structure and management, showed that the growth of the five forests types has, on average, increased by 17% since the 1930s. The growth was mainly influenced by temperature, while in the case of A. alba, growth was largely influenced by vapour pressure deficit. The accelerated growth rates imply that thinning intensities also need to increase to prevent high stand densities from inhibiting regeneration in these uneven-aged forests. This study shows that 3-PG can be used to predict the growth dynamics of uneven-aged mixed-species forests, and to our knowledge, this is the first time a stand-level process-based forest growth model has been used and validated for such forests.

High-frequency stable isotope signals in uneven-aged forests as proxy for physiological responses to climate in Central Europe.

Picea abies (L.) Karst. and Fagus sylvatica (L.) are important tree species in Europe, and the foreseen increase in temperature and vapour pressure deficit (VPD) could increase the vulnerability of these species. However, their physiological performance under climate change at temperate and productive sites is not yet fully understood, especially in uneven-aged stands. Therefore, we investigated tree-ring width and stable isotope chronologies (δ13C/δ18O) of these two species at 10 sites along a climate gradient in Central Europe. In these uneven-aged stands, we compared the year-to-year variability of dominant and suppressed trees for the last 80years in relation to the sites' spatial distribution and climate. δ18O and δ13C were generally consistent across sites and species, showing high sensitivity to summer VPD, whereas climate correlations with radial growth varied much more and depended on mean local climate. We found no significant differences between dominant and suppressed trees in the response of stable isotope ratios to climate variability, especially within the annual high-frequency signals. In addition, we observed a strikingly high coherence of the high-frequency δ18O variations across long distances with significant correlations above 1500km, whereas the spatial agreement of δ13C variations was weaker (~700km). We applied a dual-isotope approach that is based on known theoretical understanding of isotope fractionations to translate the observed changes into physiological components, mainly photosynthetic assimilation rate and stomatal conductance. When separating the chronologies in two time windows and investigating the shifts in isotopes ratios, a significant enrichment of either or both isotope ratios over the last decades can be observed. These results, translated by the dual-isotope approach, indicate a general climate-driven decrease in stomatal conductance. This improved understanding of the physiological mechanisms controlling the short-term variation of the isotopic signature will help to define the performance of these tree species under future climate.

Simulating conversion of even-aged Norway spruce into uneven-aged mixed forest: effects of different scenarios on production, economy and heterogeneity

Despite a general lack of knowledge on the effects of different strategies, conversion of even-aged stands to uneven-aged forest is ongoing across Europe. Conversion of Bavarian Norway spruce stands under the present climate scenario was simulated using the individual tree simulator SILVA. Three conversion strategies initiated at two different stand ages, 30 and 60 years, were simulated to develop uneven-aged mixed stands of Norway spruce, silver fir and European beech: gap creation, shelterwood and passive conversion. The three conversion strategies were furthermore combined with different harvesting rates. These conversion scenarios were compared with maintaining the even-aged Norway spruce management as reference. Scenarios were evaluated in terms of mean annual increment and structural development over a 150-year conversion period as well as the expectation value (EV) for eternal future rotations. Compared to the reference scenario, conversion scenarios reduced mean annual increment (6–43%) and also generally EV (−5–78%), except for some scenarios when stand age at conversion was 60 and applying a 3% discount rate. Conversion by shelterwood always reduced EV (both compared to the reference and other conversion scenarios) when initiated at age 30. With passive conversion, the effect on EV was dependent on the assumptions regarding regeneration costs. Gap conversion generally resulted in high EV and increased stand heterogeneity fastest among the different strategies. Other scenarios, especially passive conversion, were dependent on heavy thinning for developing heterogeneity faster (although still slower than with creation of gaps). Most conversion scenarios eventually resulted in similar structural heterogeneity, but the time it took to get to this stage varied greatly (50–120 years). Conversion by creation of smaller gaps in combination with a high rate of target diameter harvesting resulted in a favorable conversion in terms of economic returns and development of stand heterogeneity due to early income and differentiated regeneration.

Estimation of trees height and vertical structure using SAR interferometry in uneven-aged and mixed forests.

Estimation of forest height is an important parameter of stands structure that aids in the determination of forest biomass, successional stage dynamics, and the decision of the type of forest management. In addition, estimating the height of trees especially in uneven-aged, massive, and multi-storied forest stands always faces challenges in kind of inventory and accuracy of the assessment. In this research, the synthetic aperture radar (SAR) interferometry technique was used to estimate the height of trees for determining the vertical structure of forest. For this purpose, we focused on an area at the mixed and uneven-aged forest in Iran and evaluated the potential of Envisat ASAR data to characterize the tree height in the forest patches and the digital surface model (DSM) was produced via SAR interferometry. The height of trees and the vertical structure of the forest stands were estimated using produced DSM and Digital elevation Model (DEM). Furthermore, the accuracy of estimated parameters was evaluated with real ground data (11 × 1ha (100 × 100m) sample plots). The results indicated that the estimated height of trees was meanly 7.69m with a 22m STDV over the reality. Furthermore, the vertical structure in all the plots was three-storied that they are the same as ground truth, but the percentage of the share of trees in the under and middle story was different from the ground truth. In conclusion, the tree height and vertical structure of forest stands can be determined with acceptable accuracy via SAR interferometry and Envisat ASAR data.

Afforestation affects soil seed banks by altering soil properties and understory plants on the eastern Loess Plateau, China

To solve the serious soil erosion problem on the Loess Plateau, large-scale reforestation efforts have been carried out in the past few decades. However, previous studies on the species diversity of these reforestation plantations focused mainly on the aboveground vegetation while ignoring the value of soil seed banks for diversity conservation. An understanding of the determinants of the soil seed banks is particularly lacking. We investigated the compositional characteristics of understory plants and soil seed banks in rehabilitation areas with different vegetation types in the Caijiachuan watershed in Shanxi, China. The results indicated that the understory vegetation and soil seed banks differed significantly among the different vegetation types. The rehabilitation effect of plantations was significantly better than that of naturally restored abandoned farmland, while the selection of afforestation tree species was also crucial. In this respect, coniferous forests (Pinus tabulaeformis) were not as effective as broad-leaved forests (Robinia pseudoacacia) and mixed coniferous-broad-leaved forests in terms of vegetation recovery. In addition, there were significant differences between the composition of the seed bank and the actual vegetation, but the soil seed banks in the plantations may nonetheless contribute to the reconstruction of the aboveground vegetation; the R. pseudoacacia forest and mixed forest showed greater regeneration potential from the seed bank. Afforestation significantly affected the composition and structure of the understory plant and seed banks by altering the understory habitat. Correspondingly, we inferred that afforestation may restrict the development of understory plants and seed banks mainly by regulating soil moisture and canopy density. Therefore, in vegetation communities with high afforestation density or canopy density, measures such as thinning or pruning should be implemented to provide suitable habitat for understory plant growth and seed germination. In addition, most plantations in this area are composed of a single tree species, so we suggest that human interventions to promote the conversion of single-species plantations to diversified or uneven-aged forests should be performed.