Optimizing the Management of a Butt-rotted Picea abies Stand Infected by Heterobasidion annosum from the Previous Rotation

There are no instructions on the management of stands of Norway spruce [ Picea abies (L.) Karst.] in which butt rot caused by Heterobasidion annosum coll. (Fr.) Bref. was not discovered until the time of first thinning. A stochastic simulation model describing the spread of butt rot in a stand of Norway spruce was used with a new submodel describing the butt rot of young trees. Non-linear stochastic optimization was used to determine the most profitable management schedule of a young Norway spruce stand with butt rot. If the initial level of butt rot was 5% or 10%, or the stand was thinned in summer with stump treatment, one thinning with a rotation of 55 yrs was optimal. Two winter thinnings with a rotation of 61 yrs was optimal in an initially healthy stand. Optimizations indicated that silvicultural measures that decrease the transfer of H. annosum to next generation at clear-cuttings could be economically fulfilled.     

How to quantify forest management intensity in Central European forests

Existing approaches for the assessment of forest management intensity lack a widely accepted, purely quantitative measure for ranking a set of forest stands along a gradient of management intensity. We have developed a silvicultural management intensity indicator (SMI) which combines three main characteristics of a given stand: tree species, stand age and aboveground, living and dead wooden biomass. Data on these three factors are used as input to represent the risk of stand loss, which is a function of tree species and stand age, and stand density, which is a function of the silvicultural regime, stand age and tree species. Consequently, the indicator consists of a risk component (SMI_r) and a density component (SMI_d). We used SMI to rank traditional management of the main Central European tree species: Norway spruce (Picea abies [Karst.] L.), European beech (Fagus sylvatica L.), Scots pine (Pinus sylvestris L.), and oak (Quercus robur L. and Quercus petraea L.). By analysing SMI over their whole rotation period, we found the following ranking of management intensity: oak<beech<pine?spruce. Additionally, we quantified the SMI of actual research plots of the German Biodiversity exploratories, which represent unmanaged and managed forest stands including conifer forests cultivated outside their natural range. SMI not only successfully separate managed from unmanaged forests, but also reflected the variability of forest management and stand properties across the entire sample and within the different management groups. We suggest using SMI to quantify silvicultual management intensity of stands differing in species composition, age, silvicultural system (even-aged vs. uneven-aged), thinning grade and stages of stand conversion from one stand type into another. Using SMI may facilitate the assessment of the impact of forest management intensity on biodiversity in temperate forests.     

A silvicultural management tool for the Oriental beech (Fagus orientalis Lipsky) forests

Stand density management tools help forest managers and landowners to more effectively allocate growing space so that specific silvicultural objectives can be met. Due to the economic importance of Oriental beech (Fagus orientalis Lipsky) forests in Turkey, a stand density management tool was developed for this species to optimize regeneration success rate and tree growth. For the development of this tool, named stand density management diagram (SDMD), we utilized forest inventory data from the Kastamonu Regional Forest Directorate in Turkey. Previously published forest management approaches and models were employed during the development of the tool. The SDMD illustrates the relation among four forest indexes: the basal area per hectare, number of trees per hectare, forest stand volume per hectare, and quadratic mean diameter of the beech stands. The stand stocking percent (SSP) can be determined based upon any two of these four measurements. The results suggest that SSP is a better predictor of tree growth than BA in Oriental beech forests. The newly developed SDMD allows for a more effective use of the growing space to achieve specific silvicultural objectives including tree regeneration, timber production, thinning planning, and wildlife protection in Oriental beech forests.     

Carbon stocks and soil respiration rates during deforestation, grassland use and subsequent Norway spruce afforestation in the Southern Alps, Italy

Changes in carbon stocks during deforestation, reforestation and afforestation play an important role in the global carbon cycle. Cultivation of forest lands leads to substantial losses in both biomass and soil carbon, whereas forest regrowth is considered to be a significant carbon sink. We examined below- and aboveground carbon stocks along a chronosequence of Norway spruce (Picea abies (L.) Karst.) stands (0-62 years old) regenerating on abandoned meadows in the Southern Alps. A 130-year-old mixed coniferous Norway spruce-white fir (Abies alba Mill.) forest, managed by selection cutting, was used as an undisturbed control. Deforestation about 260 years ago led to carbon losses of 53 Mg C ha(-1) from the organic layer and 12 Mg C ha(-1) from the upper mineral horizons (Ah, E). During the next 200 years of grassland use, the new Ah horizon sequestered 29 Mg C ha(-1). After the abandonment of these meadows, carbon stocks in tree stems increased exponentially during natural forest succession, levelling off at about 190 Mg C ha(-1) in the 62-year-old Norway spruce and the 130-year-old Norway spruce-white fir stands. In contrast, carbon stocks in the organic soil layer increased linearly with stand age. During the first 62 years, carbon accumulated at a rate of 0.36 Mg C ha(-1) year(-1) in the organic soil layer. No clear trend with stand age was observed for the carbon stocks in the Ah horizon. Soil respiration rates were similar for all forest stands independently of organic layer thickness or carbon stocks, but the highest rates were observed in the cultivated meadow. Thus, increasing litter inputs by forest vegetation compared with the meadow, and constantly low decomposition rates of coniferous litter were probably responsible for continuous soil carbon sequestration during forest succession. Carbon accumulation in woody biomass seemed to slow down after 60 to 80 years, but continued in the organic soil layer. We conclude that, under present climatic conditions, forest soils act as more persistent carbon sinks than vegetation that will be harvested, releasing the carbon sequestered during tree growth.     

A density management diagram for Norway spruce in the temperate European montane region

Norway spruce is one of the most important conifer tree species in Europe, paramount for timber provision, habitat, recreation, and protection of mountain roads and settlements from natural hazards. Although natural Norway spruce forests exhibit diverse structures, even-aged stands can arise after disturbance or as the result of common silvicultural practice, including off-site afforestation. Many even-aged Norway spruce forests face issues such as senescence, insufficient regeneration, mechanical stability, sensitivity to biotic disturbances, and restoration. We propose the use of Density Management Diagrams (DMD), stand-scale graphical models designed to project growth and yield of even-aged forests, as a heuristic tool for assessing the structure and development of even-aged Norway spruce stands. DMDs are predicated on basic tree allometry and the assumption that self-thinning occurs predictably in forest stands. We designed a DMD for Norway spruce in temperate Europe based on wide-ranging forest inventory data. Quantitative relationships between tree- and stand-level variables that describe resistance to selected natural disturbances were superimposed on the DMD. These susceptibility zones were used to demonstrate assessment and possible management actions related to, for example, windfirmness and effectiveness of the protective function against rockfall or avalanches. The Norway spruce DMD provides forest managers and silviculturists a simple, easy-to-use, tool for evaluating stand dynamics and scheduling needed density management actions.     

3-level MCGP: an efficient algorithm for MCGP in solving multi-forest management problems

The efficiency gains when harvests are determined using the Faustmann approach instead of Maximum Sustained Yield (MSY), Forest Rent or some silvicultural rules were studies. The analysis was based on a variable-density stand growth model and computations over all admissible combinations of initial stand age and basal area for Finnish Norway spruce and Scots pine sites. Following MSY or Forest Rent led to a major reduction in the economic value of especially highly stocked stands. Finnish silvicultural recommendations (an example of silvicultural rules) encouraged production of higher than optimal quality timber. Applying Forest Rent, MSY or silvicultural recommendations led to respective reductions of 63%, 30% and 13% in the value of a typical conifer forest at a 4% rate of interest. The results also showed that an increase in the rate of interest may lengthen the ongoing rotation if the initial state falls outside the optimal path initiated at bare land.     

Heterobasidion annosum root rot in Picea abies: Modelling economic outcomes of stump treatment in Scandinavian coniferous forests

Abstract

The economic outcomes of stump treatment against spore infections of the root rot pathogen Heterobasiodion annosum s. l. were analysed based on simulations in four stands typical of Swedish forestry and forest management: (A) Norway spruce [Picea abies (L.) Karst.] stand on former agricultural soil (SI?=?32), (B) Norway spruce stand (SI?=?26) on forest land; (C) Mixed stand of Norway spruce and Scots pine (Pinus sylvestris L.) (SI?=?24) with only H. parviporum present, i.e. no infection of Scots pine and no possibility of interspecies spread of disease between hosts; and (D) same as C, but H. annosum s. str. (Fr.) Bref and H. parviporum Niemelä & Korhonen present, i.e. interspecies spread of disease possible. Models for disease development, growth and yield and cross-cutting were used in the simulations. The simulated decay frequency in Norway spruce trees ranged between 2 and 90%. Stump treatment at the previous final felling and in all thinning operations was profitable at interest rates 1 and 3% in stands A, B and D, but not in stand C. In stand C, no stump treatment at all or treatment in thinnings only gave the highest net future value. Implications for stump treatment in practical forestry are discussed.     

Optimizing the joint production of timber and bilberries

Berries and mushrooms are increasingly appreciated products of Finnish forests. Therefore, there is a need to integrate them in silvicultural planning. Bilberry (Vaccinium myrtillus L.) is an economically important wild berry that is widely collected for household consumption and sale in North Karelia, Finland. In this study, bilberry yield models developed recently were included in a stand growth simulator and the joint production of timber and bilberry was optimized by maximizing soil expectation value (SEV) with 3% discounting rate, assuming that 75% of the bilberry yield is harvested. The effect of bilberry production on the optimal stand management increased with increasing bilberry price. With high bilberry prices (4–8 € kg⁻¹) it was optimal to manage the mixed stand of Scots pine, Norway spruce and birch, and the pure stand of Norway spruce so as to promote bilberry production. In the Scots pine stand, where bilberry yields are higher, bilberry production affected optimal stand management already with a price of 2 € kg⁻¹. Compared to timber production, joint production led to longer rotation lengths, higher thinning intensities, more frequent thinnings, and higher share of Scots pine in the mixed stand. The contribution of bilberries to the total SEV increased with increasing bilberry price and discounting rate. In the mixed stand and pine stand the SEV of bilberry production, calculated with 3% discounting rate, exceeded the SEV of timber production when bilberry price was 4 € kg⁻¹.With 4% discounting rate this happened already with bilberry price of 2 € kg⁻¹. It was concluded that forest management which promotes bilberry yields is the most profitable in pine stands where the potential bilberry yields are high.     

Trade-offs between seedling growth,thinning and stand stability in Sitka spruce stands: a modelling analysis

The forest industry is increasingly adopting alternative silvicultural systems, involving regeneration beneath an existing forest canopy, rather than clear-felling and replanting. To apply these silvicultural systems in windy regions such as Britain and Ireland, it is essential that the interactions between thinning intensity, stand stability and seedling growth are properly understood. Here, we present a modelling analysis of the three key relationships between: (i) stand density and the proportion of incident radiation transmitted through a forest canopy as a stand is thinned; (ii) transmitted radiation and seedling growth, and (iii) stand density and stand stability. These relationships were examined using separate models of radiative transfer (MAESTRO), seedling growth, and stand stability/wind risk (ForestGALES). Output from the three models was synthesised to calculate whether a given stand thinned to a pre-defined stability limit would allow sufficient light to penetrate the canopy for seedling growth. A minimum transmittance of 20% was identified as a requirement for seedling growth, which corresponds to removing 45% of stand basal area. A thinning of this intensity left some stands susceptible to unacceptable wind damage, especially in old or previously thinned stands on soils where rooting is impeded. The results emphasised the fact that rooting conditions, thinning history and age of intervention are major constraints on the silvicultural options. In general, older stands are not suitable for conversion to continuous cover forestry (CCF) systems, and the transformation process should begin at pole stage, when heavy thinning does not leave the stand unstable. The analysis approach used here illustrates the potential for combining models to address complex forest management issues.     

德国北部挪威云杉林可持续经营中期计划的实例分析

可持续森林经营理论为中期林业计划和收获调整提供了丰富的模型选择,其不同的方法可应用于各种特定的场合和不同经营类型.本文简要回顾了传统的森林计划方法,一种称为"多林分发展"的概念可以用于任意的经营系统,这个概念把森林看作由一系列林分组成,在每一个林分中可以预先制定多种经营措施的选项,每种选项都可以通过木材或其它产品以及消耗的资源计算出一个目标值.这种简单的概念可以应用到大量的不同森林经营场合,它为森林经营者制定切实可行的森林措施和评价森林经营计划提供方法.在本研究中,以德国北部一片包括21个小班的挪威云杉林班的一个中期计划为例,说明"多林分发展"这一经营系统在实际生产中的应用.每个小班具有不同的初始状态,每个小班预设了若干经营选项,根据小班的初始状态、生长模型为各种选项计算各时期的木材产出.在林班的水平上,经营目标方程包括两个组成部分:净现值和均衡木材收获值.用模拟退火的方法来优化总体目标方程值.优化的总体解决方案在为每个小班选定合适的经营选项的同时,在全林的水平上获得最优的经济和均衡产出组合.     

Stand density and growth of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> (L.) Karst.) and European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.): evidence from long-term experimental plots

On the basis of nine Norway spruce (Picea abies (L.) Karst.) and ten European beech (Fagus sylvatica L.) thinning experiments in Germany, for which both residual and removed stock had been registered first during 1870, I scrutinize how moderate and heavy thinning from below (B-, C-grade) affects the production of merchantable volume compared with light thinning (A-grade). In relation to A-grade, cumulative merchantable volume (CV) of B- and C-grade amounts in average to 103–107% in juvenile and to 97–102% in mature Norway spruce stands. The corresponding findings for European beech are 101–106% and 94–102%. CV of individual stands varies between 89% and 130% for Norway spruce and 73% and 155% for European beech (CV of A-grade = 100%). These findings are substantiated by the relation between stand density (SDI) and periodic annual increment (PAI). On the B- and C-grade plots of spruce and beech, respectively, SDI was reduced down to 41–91% and 31–83% of the A-grade. When SDI is reduced in young stands, PAI follows a unimodal curve. Norway spruce’s PAI culminates in 109% if SDI is reduced to 59%; European beech’s PAI culminates in 123% when density is reduced to 50%. Whereas Norway spruce’s growth reacts most positively on thinning under poor site conditions and with increment reduction on favourable sites, European beech behaves oppositely. With stand development the culmination point of the unimodal relation moves towards maximum density, so that in older stands PAI follows the increasing pattern, which is the left portion of a unimodal curve. A model is presented which apparently unifies contradictory patterns of stand density–growth reactions by integrating relative stand density, average tree size and site fertility effects, and makes the findings operable for forest management.     

Impacts of initial stand density and thinning regimes on energy wood production and management-related CO<Subscript>2</Subscript> emissions in boreal ecosystems

An ecosystem model (Sima) was utilised to investigate the impact of forest management (by changing both the initial stand density and basal area thinning thresholds from current recommendations) on energy wood production (at energy wood thinning and final felling) and management-related carbon dioxide (CO₂) emissions for the energy wood production in Finnish boreal conditions (62°39′ N, 29°37′ E). The simultaneous effects of energy wood, timber and C stocks in the forest ecosystem (live and dead biomass) were also assessed. The analyses were carried out at stand level during a rotation period of 80 years for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) growing in different fertility sites. Generally, the results showed that decreased basal area thinning thresholds, compared with current thinning, reduced energy wood (logging residues) and timber production, as well as carbon stocks in the forest ecosystem. Conversely, increased thinning thresholds increased energy wood production (ca. 1–27%) at both energy wood thinning and final felling and reduced CO₂ emissions (ca. 2–6%) related to the production chain (e.g. management operations), depending on the thinning threshold levels, initial stand density, species and site. Increased thinning thresholds also enhanced timber production and carbon stocks in the forest ecosystem. Additionally, increased initial stand density enhanced energy wood production for energy wood thinning for both species, but this reduced energy wood production at final felling for Scots pine and Norway spruce. This study concluded that increases in both initial stand density and thinning thresholds, compared with the current level, could be useful in energy wood, timber and carbon stocks enhancement, as well as reducing management-related CO₂ emissions for energy wood production. Only 2.4–3.3% of input of the produced energy (energy wood) was required during the whole production chain, depending on the management regime, species and sites. However, a comprehensive substitution analysis of wood-based energy, in respect to environmental benefits, would also require the inclusion of CO₂ emissions related to ecosystem processes (e.g. decomposition).     

Assemblages of wood-inhabiting fungi related to silvicultural management intensity in beech forests in southern Germany

Current silvicultural treatments in beech forests are aimed at achieving thick logs without discoloured hardwood. Therefore intensive thinning is applied already in younger stands with the objective of large-sized trunks at an age of 100 years. However, this approach bears the risk that dead wood structures and broken trees are completely removed from the forest. The impact of three different silvicultural management intensity levels on wood-inhabiting fungi over decades was investigated in a large beech forest (>10,000 ha) in southern Germany in 69 sampling plots: A Intensive Thinning and Logging with high-value trees, B Conservation-Oriented Logging with integration of special structures such as dead wood and broken trees and C Strict Forest Reserves with no logging for 30 years. The analysis of community showed marked differences in the fungus species composition of the three treatments, independent of stand age. The relative frequencies of species between treatments were statistically different. Indicator species for naturalness were more abundant at sites with low silvicultural management intensity. Fomes fomentarius, the most common fungus in virgin forests and strict forest reserves, is almost missing in forests with high-management intensity. The species richness seemed to be lower where intensive thinning was applied (P = 0.051). Species characteristic for coarse woody debris were associated to low management intensity, whereas species with a significant preference for stumps became more frequent with increasing management intensity. A total amount of dead wood higher than 60 m³/ha was found to enable significantly higher numbers of species indicators of naturalness (P = 0.013). In conclusion, when applying intensive silvicultural treatment, the role of dead wood needs to be actively considered in order to maintain the natural biocoenosis of beech forests.     

Temporal variation and efficiency of leaf area index in young mountain Norway spruce stand

Temporal variation of leaf area index (LAI) in two young Norway spruce stands with different densities was monitored during eight consecutive growing seasons (1998–2005). We focused on: (1) LAI dynamics and above-ground mass production of both spruce stands and their comparison, (2) leaf area duration (LADU), crop production index (CPI) and leaf area efficiency (LAE) evaluation, and (3) thinning impact on the above-mentioned parameters. Also, we tried to deduce the most effective LAI value for the Norway spruce forest investigated. The LAI values of both spruce stands showed a typical seasonal course. To describe the LAI dynamics of the stand, we recommend taking LAI measurements within short time intervals at the time of budding and needle expansion growth (i.e., in early spring) and close to the LAI peak, when the twig growth has been completed. The reason was that after reaching the seasonal maximum, no significant differences between subsequently obtained values were found in the following 2 months. Therefore, we recommend this period for the estimation of seasonally representative LAI values, enabling the comparison of various spruce stands. The maximum hemi-surface LAI value reached 12.4. Based on our results, the most effective LAI values for maximum above-ground biomass production were within the range of 10–11. We found an LAI over these values to be less effective for additional production of above-ground biomass. In forest practice, thinning intensity is mostly described by percentage of stocking reduction. We want to show that not only thinning intensity, but also the type of thinning is important information. The type of thinning significantly affected the stand above-ground biomass increment, canopy openness, stand LAI and LAI efficiency. The stimulating effect of high-type thinning was observed; the LAE as well as the CPI increased. Low-type thinning had no such effects on LAE increments compared to the high-type thinning with similar intensity.

---

     

Spatially explicit assessment of carbon stocks of a managed forest area in eastern Germany

The Kyoto-protocol permits the accounting of changes in forest carbon stocks due to forestry. Therefore, forest owners are interested in a reproducible quantification of carbon stocks at the level of forest management units and the impact of management to these stocks or their changes. We calculated the carbon stocks in tree biomass and the organic layer including their uncertainties for several forest management units (Tharandt forest, Eastern Germany, 5,500 ha) spatially explicit at the scale of individual stands by using standard forest data sources. Additionally, soil carbon stocks along a catena were quantified. Finally, carbon stocks of spruce and beech dominated stands were compared and effects of thinning intensity and site conditions were assessed. We combined forest inventory and data of site conditions by using the spatial unions of the shapes (i.e., polygons) in the stand map and the site map. Area weighted means of carbon (C) stocks reached 10.0 kg/m2 in tree biomass, 3.0 kg/m2 in the organic layer and 7.3 kg/m2 in mineral soil. Spatially explicit error propagation yielded a precision of the relative error of carbon stocks at the total studied area of 1% for tree biomass, 45% for the organic layer, and 20% for mineral soil. Mature beech dominated stands at the Tharandt forest had higher tree biomass carbon stocks (13.4 kg/m2) and lower organic layer carbon stocks (1.8 kg/m2) compared to stands dominated by spruce (11.6, 3.0 kg/m2). The difference of tree biomass stocks was mainly due to differences in thinning intensity. The additional effect of site conditions on tree carbon stocks was very small. We conclude that the spatially explicit combination of stand scale inventory data with data on site conditions is suited to quantify carbon stocks in tree biomass and organic layer at operational scale.     

Regeneration decisions in forestry under climate change related uncertainties and risks: Effects of three different aspects of uncertainty

Future climate development and its effects on forest ecosystems are not easily predicted or described in terms of standard probability concepts. Nevertheless, forest managers continuously make long-term decisions that will be subject to climate change impacts. The manager's assessment of possible developments and impacts and the related uncertainty will affect the combined decision on timing of final harvest and the choice of species for regeneration. We analyse harvest of a Norway spruce stand with the option to regenerate with Norway spruce or oak. We use simulated variations in biophysical risks to generate a set of alternative outcomes, investigating effects on decision making of three aspects of uncertainty: (i) the perceived time horizon before there will be certainty on outcome, (ii) the spread of impacts across the set of alternative outcomes, and (iii) the subjective probability (belief) assigned to each outcome. Results show that the later a forest manager expects to obtain certainty about climate change or the more skewed their belief distribution, the more will decisions be based on ex ante assessments — suggesting that if forest managers believe that climate change uncertainty will prevail for a longer period of time, they may make sub-optimal decisions ex ante.     

Permanence of resilience and protection efficiency in mountain Norway spruce forest stands: A simulation study

An objective of mountain forest management is to increase the ability of forest stands to protect human activities against natural hazards such as rock-falls and snow avalanches in a sustainable way. The challenge is to find a compromise between efficient instantaneous protection, favoured by dense stands, and continuous renewal, minimizing time periods of low protection efficiency. We used a Norway spruce stand dynamics model to compare the respective advantages of individual tree and gap selection silviculture in this context. We simulated stand dynamics over 800 years with either individual tree or gap thinning every 20 years with several thinning intensities. At each time step, we evaluated stand resilience, protection efficiency against rock-falls, protection efficiency against avalanches, and structural complexity with four indicators based on stand structure. Every scenario produced short time periods with low stand resilience and protection efficiency. Such periods can be tolerated if they are sufficiently rare compared to the local disturbance regime. We characterized the permanence of resilience and protection of a forest stand as its ability to remain within boundary values of the different indicators, without going out of them during continuous time periods longer than fixed maximum durations. Permanence of resilience and permanence of protection decreased with thinning intensity. Efficient protection against rock-falls was obtained with gap thinning of intermediate intensity while protection against avalanches was obtained only for very low thinning intensities. For our ecological context, the best compromise between resilience and protection was obtained with three 10 m radius gaps per hectare every 20 years (9.5% of the area of a stand). This strategy led to uneven-aged stand structures with a high diversity of diameters classes. Our results suggest that small gap silviculture may be a good way to combine forest renewal and protection efficiency in mountain regions.     

Pre-commercial thinning,birch admixture and sprout management in planted Norway spruce stands in South Sweden

Early management of the regenerated seedlings shapes the future stand properties. To address these issues, pre-commercial thinning (PCT) and control treatments were applied to planted Norway spruce (Picea abies L. Karst) and naturally regenerated birch (Betula pendula Roth., Betula pubescens Ehrh.) stands in forest experiments in southern Sweden (lat. 56–57?N) containing 1.1–5.5?m tall saplings. The treatments were retention of 1000 or 2000?stems?ha^?1 of Norway spruce, with no birch or birch at 1000?stems?ha^?1. Treatments were replicated with and without annual removal of birch sprouts from stumps. The periodic annual increment (PAI) over five years was calculated for total stand volume and individual trees. The mean PAI of dominant trees was significantly higher both following all PCT treatments than controls, and following low rather than high-density PCT. Birch retention did not affect growth of the dominant trees but PAI was lower in plots with uncontrolled sprouting. The PAI of birch was significantly higher in low-density Norway spruce plots than in control plots and the high-density plots. The treatment response was significant even in stands with initial heights of only 1–2?m.     

Microsite patterns of conifer seedling establishment and growth in a mixed stand in the southern Alps

In many forests of the Alps, permanent forest cover and, therefore, its continuous renewal is the main silvicultural goal. Regenerating these forests must be based on a sound understanding of the ecology of the tree species in question. The regeneration of silver fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) Karst.) in the upper montane zone of the southern central Alps has so far received little attention. The aim of this study was, therefore, to characterize the ecological niche for the establishment and growth of silver fir and Norway spruce seedlings in this zone. The study was conducted as a case study on a plot of 1.5 ha in the upper montane zone of southern Switzerland, at an altitude of 1380 m. The basal area of the mixed Norway spruce–silver fir stand was 43.7 m² ha⁻¹. Seedlings were censused on 375 plots of 1.0 m² area. Seedling density was 1.30 ± 4.25 m⁻² (mean ± standard deviation) for Norway spruce and 0.87 ± 1.50 m⁻² for silver fir. Logistic regression models were used to test the effect of microsite characteristics on seedling occurrence, and general linear models for effects on seedling height growth and biomass increment. Most seedlings received less than 10% light (photosynthetic photon flux density) as compared to values in the open. Silver fir occurrence was positively related to microsites at the edge of canopy trees, but unrelated to ground cover type, light and micro-relief. Norway spruce occurrence was only, and positively, related to the presence of mosses. Height growth and biomass increment of seedlings of both species were only loosely correlated with microsite conditions. Seedlings without canopy cover grew faster than those under canopy cover, probably as a result of light and moisture limitations under the canopy of adult trees. Diffuse radiation was positively correlated with average annual biomass increment of silver fir, but not of Norway spruce seedlings. In general, the results suggest that silver fir seedlings have less specific microsite requirements than Norway spruce seedlings in terms of ground cover. They are also more shade tolerant, and therefore, grow faster than Norway spruce in low-light environments of the upper montane zone of the southern Alps. While the microsite concept can be helpful in designing silvicultural operations, it has limitations when only patch characteristics that are easy to assess are used, and others neglected. Finally, our study suggests that counting the number of green shoots is a promising method to quickly and non-destructively estimate the biomass of a great number of small seedlings.     

Distance-independent tree basal area growth models for Norway spruce,Douglas-fir and Japanese larch in Southern Belgium

This paper presents new harmonized distance-independent individual tree basal area growth models for Norway spruce, Douglas-fir and Japanese larch in pure even-aged stands in Southern Belgium. The selected model was originally developed for Norway spruce and Douglas-fir in neighboring France. New formulations are proposed for some of the model components in order to lower the number of fitted parameters and facilitate the fitting procedure. The resulting models integrate the most recent corresponding top-height growth models and use four simple and usually collected explanatory variables: stand age, top-height, total basal area and tree girth at breast height. The modified formulations maintain similar fitting performances and make it easier to interpret the influence of the explanatory variables on tree growth. Parameters estimates were fitted on thousands of growth measurements gathered from several monitoring plots, forest management inventories and silvicultural field experiments that represent the wide range of site conditions and of forest management scenarios applied to coniferous stands in Southern Belgium. Cross-validation of the models revealed no bias and highlighted their consistent behavior over the entire range of girth at breast height, age, top-height, site index and density represented in our dataset. Combining utility and robust performances, these models represent useful forest management tools, purposely ideal for forest simulation software development. Moreover, the flexibility and generic capabilities of the model formulation should make it easily adjustable for other species in even-aged stands.