Intra-specific differences in allometric equations for aboveground biomass of eastern Mediterranean Pinus brutia

? Context

Biomass prediction is important when dealing for instance with carbon sequestration, wildfire modeling, or bioenergy supply. Although allometric models based on destructive sampling provide accurate estimates, alternative species-specific equations often yield considerably different biomass predictions. An important source of intra-specific variability remains unexplained.

? Aims

The aims of the study were to inspect and assess intra-specific differences in aboveground biomass of Pinus brutia Ten. and to fill the gap in knowledge on biomass prediction for this species.

? Methods

Two hundred one trees between 2.3 and 55.8 cm in diameter at breast height were sampled throughout the eastern- and southernmost natural distribution area of P. brutia, in Middle East, where it forms different stand structures. Allometric equations were fitted separately for two countries. The differences in biomass prediction at tree, stand, and forest level were analyzed. The effect of stand structure and past forest management was discussed.

? Results

Between-country differences in total aboveground biomass were not large. However, differences in biomass stock were large when tree components were analyzed separately. Trees had higher stem biomass and lower crown biomass in dense even-aged stands than in more uneven-aged and sparse stands.

? Conclusion

Biomass and carbon predictions could be improved by taking into account stand structure in biomass models.     

Snow gliding on a south-facing slope covered with larch trees

? Context

Snow gliding is a downhill motion of snow on the ground; observations have shown gliding to be possible not only on open slopes but also in forest stands. Larch stands, with their low canopy density and open forest structure with clearings and gaps, are particularly prone to high glide rates. Snow gliding may have negative effects on juvenescent trees which can be damaged by extraction from the ground.

? Aim

The goal of this study was to determine whether snow gliding depends on forest cover (canopy) and size of clearings.

? Methods

Snow gliding was measured during eight winter periods at six measuring positions (ranging from ‘dense forest’ to ‘open slope’) in and beside a larch stand in the Stubai Valley, Tyrol, Austria.

? Results

The results showed that gliding is strongly influenced by forest cover. Snow gliding increases with decreasing canopy density. The difference between the six measuring positions was highly significant (p?<?0.005).

? Conclusion

The identified glide cracks on at least two measuring positions, indicating extreme glide rates and, therefore, strong negative effects on juvenescent trees. To prevent glide rates of a magnitude such as this requires a mature forest with at least 300 stems/ha.     

A tree distance-dependent growth and yield model for naturally regenerated pure uneven-aged maritime pine stands in central inland of Portugal

? Context

Maritime pine (Pinus pinaster Aiton) is one of the most important Portuguese species, growing in pure stands ranging from even-aged to multi-aged structures. Current growth and yield models were developed only for even-aged, managed stands and/or for very specific regions of Portugal.

? Aims

This paper focuses on the validation of the existing size-class model PBRAVO, adapted to even-aged stands, and on the subsequent development of a single tree distance-dependent growth and yield model (PBIRROL), both in distance-independent and distance-dependent versions, for uneven-aged stands.

? Methods

The new model is composed of four modules, each with a set of sub-models for: tree variable prediction, tree volume prediction, future tree list prediction and growth projection.

? Results

The evaluation of the PBRAVO and PBIRROL models showed that the new model gives more accurate predictions. Moreover, medium-term simulations provided consistent and logical predictions.

? Conclusion

It was verified that individual tree models are more suited to simulate poorly managed uneven-aged stands than diameter distribution models. No clear superiority of distance-dependent models was found over models using just distance-independent measures of inter-tree competition.     

Managing coppice forests for rockfall protection: lessons from modeling

? Context

One eighth of Europe’s forests are still managed as coppice. In some European countries, more than half of the forest exhibits coppice structures from the past or present coppice management. Many of these forests grow in the broadleaf zone of mountainous regions, often on steep slopes. Here, they play an important role in rockfall protection. However, it remains unclear how coppice forests should be structured for optimal rockfall protection or how the protection effect changes during the aging of the coppice.

? Aim

A few studies have applied rock trajectory analyses, but so far, no process-based model has been used to quantify the protective effect of differently structured coppice forests. The present study compared 40 coppice patches from two chronosequences in South Tyrol, North Italy, regarding their protective effect against rocks of two sizes using the rockfall simulation model Rockyfor3D.

? Results

The results indicate that coppice stands older than 30 years better protect against rockfall than medium-aged and young stands, although the old ones have lower stem densities. Surprisingly, a random stem distribution had a better protective effect than the clumped stem distribution typical for coppice stands.

? Conclusion

Implications for future management are discussed in detail, including the relevance of standards in coppice forests.     

Effect of nutrient removal on radial growth of Pinus sylvestris and Quercus petraea in Southern Germany

? Context

The rising demand of energy wood for heating purposes in Germany leads to concerns regarding the overexploitation of forests. A major aspect is the impact of whole-tree harvesting on long-term productivity of forest soils.

? Aims

This study aimed to analyze the effects of nutrient removal on productivity using the historically prevalent practice of litter raking. Since there is a lack of controlled whole-tree harvesting experiments in Germany, we used litter raking as a surrogate management practice entailing the removal of nutrients from forest stands.

? Methods

We used three sites with documented litter raking to analyze the effects of nutrient removal on productivity using dendroecological methods: two recent litter removal experiments in two Scots pine stands (Siegenburg and Burglengenfeld) and one oak stand (Eichhall) with documented historic litter raking. Basal area increment (BAI) and tree-ring characteristics were compared between periods with litter raking and the preceding periods for both treatment and control plots.

? Results

For the two Scots pine sites with a relatively short litter raking period, no effects of litter raking on BAI could be ascribed to nutrient removal. On the oak site with a longer history of litter utilization, the loss in BAI due to litter raking amounts to 22 % during the period with active raking and to still 17 % in the recovery period.

? Conclusions

These results contribute to the still very limited understanding about the impact of whole-tree harvesting on forest productivity in Germany by laying down an upper limit of possible effects due to nutrient removal, as nutrient loss by litter raking tends to be higher than nutrient loss by whole-tree harvesting.     

Projections of regional changes in forest net primary productivity for different tree species in Europe driven by climate change and carbon dioxide

? Context

Projecting changes in forest productivity in Europe is crucial for adapting forest management to changing environmental conditions.

? Aims

The objective of this paper is to project forest productivity changes under different climate change scenarios at a large number of sites in Europe with a stand-scale process-based model.

? Methods

We applied the process-based forest growth model 4C at 132 typical forest sites of important European tree species in ten environmental zones using climate change scenarios from three different climate models and two different assumptions about CO₂ effects on productivity.

? Results

This paper shows that future forest productivity will be affected by climate change and that these effects depend strongly on the climate scenario used and the persistence of CO₂ effects. We find that productivity increases in Northern Europe, increases or decreases in Central Europe, and decreases in Southern Europe. This geographical pattern is mirrored by the responses of the individual tree species. The productivity of Scots pine and Norway spruce, mostly located in central and northern Europe, increases while the productivity of Common beech and oak in southern regions decreases. It is important to note that we consider the physiological response to climate change excluding disturbances or management.

? Conclusions

Different climate change scenarios and assumptions about the persistence of CO₂ effects lead to uncertain projections of future forest productivity. These uncertainties need to be integrated into forest management planning and adaptation of forest management to climate change using adaptive management frameworks.     

When tree rings behave like foam: moderate historical decrease in the mean ring density of common beech paralleling a strong historical growth increase

? Context

While historical increases in forest growth have been largely documented, investigations on historical wood density changes remain anecdotic. They suggest possible density decreases in softwoods and ring-porous hardwoods, but are lacking for diffuse-porous hardwoods.

? Aims

To evaluate the historical change in mean ring density of common beech, in a regional context where a ring-porous hardwood and a softwood have been studied, and assess the additional effect of past historical increases in radial growth (+50 % over 100 years), resulting from the existence of a positive ring size–density relationship in broadleaved species.

? Methods

Seventy-four trees in 28 stands were sampled in Northeastern France to accurately separate developmental stage and historical signals in ring attributes. First, the historical change in mean ring density at 1.30 m (X-ray microdensitometry) was estimated statistically, at constant developmental stage and ring width. The effect of past growth increases was then added to assess the net historical change in wood density.

? Results

A progressive centennial decrease in mean ring density of ?55 kg?m^?3 (?7.5 %) was identified (?10 % following the most recent decline). The centennial growth increase induced a maximum +25 kg?m^?3 increase in mean ring density, whose net variation thus remained negative (?30 kg?m^?3).

? Conclusions

This finding of a moderate but significant decrease in wood density that exceeds the effect of the positive growth change extends earlier reports obtained on other wood patterns in a same regional context and elsewhere. Despite their origin not being understood, such decreases hence form an issue for forest carbon accounting.     

Soil enzyme activities as potential indicators of soluble organic nitrogen pools in forest ecosystems of Northeast China

Context

Soluble organic nitrogen is considered to reflect the effect of forest types on soil nitrogen status. As a major process affecting the soil-soluble organic nitrogen pool, degradation of insoluble organic nitrogen in the production of soluble organic nitrogen is mediated by a suite of soil enzymes.

Aims

This study aims to examine soil-soluble organic nitrogen pools and their relationships with the activities of soil enzymes in natural secondary forest stands and adjacent larch plantation stands.

Methods

Four pairs of larch plantation stands and secondary forest stands were randomly selected from a mountainous area, and the top 15?cm of the mineral soils were sampled from each field.

Results

The soil-soluble organic nitrogen concentrations were up to 2-fold greater in the secondary forest stands than in the larch plantation stands, whereas the ratio of soluble organic nitrogen/total nitrogen was comparable between the two forest types. The concentrations of soluble organic nitrogen were positively correlated with approximately 2-fold differences in urease and protease activities, a 1.2-fold difference in N-acetyl-??-glucosaminidase and a 1.7-fold difference in l-asparaginase between the two forest types.

Conclusions

Our results suggest that relationships between soil-soluble organic nitrogen and enzyme activities are independent on sampling time, and that the soil enzyme activities can be used as potential indicators of soil soluble organic nitrogen pools in the temperate forest ecosystem.     

Summer drought and canopy opening increase the strength of the oak seedlings–shrub spatial association

? Context

The knowledge of how shrub–seedling interactions vary with summer drought, canopy opening, and tree species is crucial for adapting forest management to climate change.

? Aims

The aim of this study was to assess variation in shrub–oak recruitment associations along a south–north drought climate gradient and between two levels of canopy cover in coastal dune forest communities in a climate change-adapted forest management perspective.

? Material and methods

Mapped data of associational patterns of seedlings of three oak species with interspecific pooled shrubs were analyzed using a bivariate pair correlation function in 10 (0.315 ha) regeneration plots located in forest and recent gap sites along the climate gradient. An index of association strength was calculated in each plot and plotted against a summer moisture index.

? Results

The association strength increased with increasing summer drought from wet south to dry north and from closed forests to gaps.

? Conclusion

Consistent with facilitation theory, our results suggest that climate change may shift associational patterns in coastal dune forest communities towards more positive associations, in particular in canopy gaps. In a perspective of climate change, foresters may need to conserve understory shrubs in gaps in order to promote oak species regeneration.     

Modeling recent bark stripping by red deer (Cervus elaphus) in South Belgium coniferous stands

? Context

Over the past few decades, the impact of large herbivorous ungulates on forest vegetation has been clearly highlighted. Among those impacts, bark stripping of coniferous trees is one of the most damaging. Bark stripping leads to rot development, inducing serious loss of timber value.

? Aims

The present study aimed firstly at evidencing the factors explaining the variations observed in fresh bark peeling rate for spruce and Douglas-fir in southern Belgium and secondly at identifying the key factors to consider when setting up a deer management plan.

? Method

Fresh bark peeling rate was recorded with a systematic sampling survey from 2004 to 2007. The covered territory was then divided into 63 distinct hunting zones of area ranging from 1,000 to 25,000 ha. About 5,000 plots were monitored annually. Each zone was characterized with a large number of explanatory variables. The explanatory variables were integrated firstly into fixed linear models using a stepwise procedure, and then into a mixed model.

? Results

The significant variables included in the model (R ²?=?44 %) are (by decreasing order of importance) red deer densities, proportion of coniferous stands and agricultural areas, snow cover, distance to urban habitats, and species diversity in the understory.

? Conclusion

The models revealed the impacts of several factors on bark peeling: deer density, deer-carrying capacity of the territory, landscape structure, and severity of winter conditions. The adjusted model allowed subtracting the impact of winter conditions in order to produce a relevant indicator for hunting management. In addition, the model was used to assess the sensitivity of a forested area to bark peeling based on its environmental characteristics.     

A comprehensive framework of forest stand property–density relationships: perspectives for plant population ecology and forest management

? Context

There are many stand property–density relationships in ecology which represent emergent properties of plant populations. Examples include self-thinning, competition–density effect, constant final yield, and age-related decline in stand growth. We suggest that these relationships are different aspects of a general framework of stand property–density relationships.

? Aims

We aim to illustrate the generalities and ecological implications of stand property–density relationships, and organize them in a comprehensive framework.

? Methods

We illustrate relationships between stand property and density (1) at one point in time, (2) over time, and (3) independent of time. We review the consequences of considering different variables to characterize stand property (mean tree size, mean tree growth, stand growth, stand yield, stand leaf area).

? Results

We provide a framework that integrates the broad categories of stand property–density relationships and individual expressions of these relationships. For example, we conclude that constant final yield is a special case of the growth–growing stock relationship for life forms were yield is a reasonable approximation of growth (non-woody plants).

? Conclusion

There is support in the literature for leaf area being broadly integrative with respect to various expressions of stand property–density relationships. We show how this is and suggest implications for plant population ecology and forest management.     

Is the private forest sector adapting to climate change? A study of forest managers in north Wales

? Context

Two-thirds of Britain’s forest area is privately owned. Thus, understanding private forest owners and managers, and their attitudes to uncertainty and change, is essential for the success of climate change adaptation policies.

? Aim

The aims of this study are to (1) assess how beliefs in climate change in the private sector have influenced forest management practices; (2) identify constraints related to changes in species choice and silvicultural systems; (3) analyse the implications for implementing climate change policy in forestry.

? Method

Semi-structured interviews with key informants who provide advice to, or manage woodlands in, the private forest sector in north Wales.

? Results

Woodland managers and some advisers are not generally convinced of a need to adapt. They feel the future is uncertain, more usually in relation to tree disease than to climate change itself. Species choice is the principle focus of adaptation activities and reveals a deep divide in opinion. Commercial advisors look to new exotics but are inhibited by absence of markets, while small-scale owners rely more on native genetic diversity.

? Conclusions

Findings that are likely to apply widely include: the influential role of forest agents in forest management decisions including species choice; lack of confidence in climate change predictions, and in markets; more immediate concerns about tree pests and diseases; demand for leadership from the public sector, and for engagement amongst the private sector. Further research is needed across a wider area to test the variability in relationship between attitudes and behaviours, and local conditions including climate change predictions.     

Effect of selective logging on stand structure and tree species diversity in a subtropical evergreen broad-leaved forest

?Context

Selective logging followed by natural regeneration is rarely employed for restocking subtropical evergreen broad-leaved forests in East Asia compared with the use of clear-cutting.

?Aims

To clarify the succession of these forests, the effects of selective logging on stand structure, species diversity, and community similarity were studied in a mature and regenerating forest in Okinawa, Japan.

?Methods

Four study plots were established, and trees ≥1.2 m height were identified by species name, tree height, and diameter at breast height.

?Results

The results showed that the species composition of regenerating forest was similar to mature forest; however, the former had a greater species density and Shannon–Wiener index than the latter. Castanopsis sieboldii and Distylium racemosum, the predominant trees in the mature forest, continued to dominate the regenerating forest, with a broad layer distribution. High Sørensen and Jaccard community similarity indices for mature and regenerating forest indicated that the regeneration occurred in a progressive succession.

?Conclusion

The similar species composition and stand structure for both mature and regenerating forest, and the higher species diversity for the latter, provided no evidence of forest degeneration and suggested that the regenerating forest may develop into a stand similar to preselective logging forest.     

Soil compaction due to heavy forest traffic: measurements and simulations using an analytical soil compaction model

? Context

Models for predictions of soil compaction following forest traffic represent important decision tools for forest managers in order to choose the best management practices for preserving soil physical quality. In agricultural soil compaction research, analytical models are widely used for this purpose.

? Aims

Our objective was to assess the ability of an analytical model to predict forest soil compaction under forwarder traffic.

? Methods

We used the results from two experimental sites set up in north-eastern France in 2007 and 2008 to compare simulations using the SoilFlex model with observed bulk density following forwarder traffic.

? Results

The best model-based predictions were found when considering the mean initial soil conditions and an increased rebound parameter in the upper soil layers (0–10 cm) in comparison to the deeper layers (10–50 cm). The need to increase the rebound parameter in the soil surface layer to improve model accuracy was attributed to a large soil organic matter content in the uppermost layers of forest soils. For the site where initial soil mechanical parameters were measured as a function of soil bulk density and water content, the model performance was good, with a root mean square error (RMSE) of 0.06. The model performed poorer (RMSE of 0.11), especially for the surface soil layer, for the second site that was wetter at the time of traffic and where soil mechanical properties were not measured but estimated by means of pedo-transfer functions.

? Conclusions

SoilFlex was found to yield satisfactory predictions and could help forest managers estimate the risk of compaction and to select the most appropriate machinery for given soil conditions in order to preserve the soil from physical degradation during traffic in forest ecosystems. However, our results emphasise the need for research on soil mechanical properties of forest soils, in particular on the role of soil organic matter and roots on soil compressive properties.     

Clustering forest harvest stands on spatial networks for optimised harvest scheduling

Context

Clustering forest harvest stands reduces the movements of the harvesters, forwarders and staff. Moreover, it simplifies the subsequent log transport, when compared with dispersed stands.

Aims

Harvesting activities are generally based on silvicultural motivated planning data. The development of an analytical method to cluster harvest stands with respect to the spatial network of roads should improve the harvesting effort.

Material and method

The clustering of harvest stands was developed for Aracruz (Brazil) in 2004, where it is used there successfully since. The hierarchical method ??single linkage cluster analysis?? is applied. As a distance function, the Euclidian distance was substituted by the shortest path on the spatial network.

Result

The clustering method is based on the minimum spanning tree, which is the spatial equivalent to the dendrogram of an ordinary cluster analysis. Applying the Delaunay triangulation to fill the distance matrix reduces the distance calculation time from O(n ²) to O(n). The method is illustrated by a planning district of the Aracruz enterprise.

Conclusion

Harvesting units are properly clustered spatially by the discussed method. Topographic obstacles are automatically avoided and the need to relocate machinery is reduced as well as the total driving distance.     

Increasing the use of expert opinion in forest characterisation approaches based on LiDAR data

Context

Forest structure characterisation approaches using LiDAR data and object-based image analysis remain scarce to forestry agencies as these automated procedures usually require the use of expensive software and highly skilled analysts. The integration of forest expert opinion into semi-automated approaches would simplify the access of forest managers to new technologies and would allow the incorporation of personal experience and the introduction of specific forest management criteria.

Aim

The aim of this study is to explore new alternatives to a previously published automated approach based on LiDAR data and object-based image analysis.

Methods

We compare four approaches, ranging from null to high incorporation of expert opinion and from fully automated to fully manual. These four approaches consist of three stages: (1) forest stand identification from LiDAR models, (2) forest stand classification into forest structure classes (manual and based on cluster analysis), and (3) validation.

Results

Quantitative attributes for validation (i.e. hypsographs and percentiles) provided slightly lower degree of separability for forest structure classes, in the mixed procedures with increasing incorporation of expert opinion than for the fully automated approach.

Conclusions

The new mixed approaches proposed are comparable to the automated procedures for the characterisation of forest structure in heterogeneous pine forest stands. They also offer additional advantages: (1) they make it possible to give a specific management focus and (2) they provide accessibility by the forest managers to the source of LiDAR information.     

Can random components explain differences in the height–diameter relationship in mixed uneven-aged stands?

? Context

Tree height prediction is an important issue in forest management since tree heights are usually measured only in a sample of trees. Although numerous model approaches have been used for this purpose, no agreement on which one is more appropriate has been achieved.

? Aims

To analyse the random effects of basic and generalised height–diameter (h–d) models fitted to multi-species uneven-aged forest stands, and to establish their ability to explain differences between ecoregions, plots and species.

? Methods

Height and diameter measurements for 29,084 trees from 187 sample plots located in the state of Durango (Mexico) were used. Basic and generalised h–d models were fitted in a mixed-models framework. The variability between ecoregions, plots and species was considered in the random effects definition. Model calibration for different height sampling designs and sampling sizes was also analysed.

? Results

Random components performed well in explaining the differences in the h–d relationship between the different plots and species; however, no significant variance for the random effects was found for the different ecoregions. A calibrated basic h–d model produced similar results to a fixed-effects generalised h–d model when a sufficiently large number of trees was used in the calibration process.

? Conclusion

From a practical point of view, if no calibration is carried out, different models should be used for the different species, so that at least the variation among species is captured.     

Impacts of the Kyoto Protocol on boreal forest climate change mitigation

? Context

The Kyoto Protocol allows the use of domestic forest carbon sequestration to offset emissions to a limited degree, while bioenergy as an unlimited emission reduction option receives substantial financial support in many countries.

? Aim

The primary objective of this study was to analyze (1) whether these limits on forest carbon sequestration would be binding, thereby leading to inefficient mitigation, and (2) the total potential effect of the protocol on the greenhouse gas (GHG) fluxes in the forest sector.

? Methods

A partial equilibrium model of the Norwegian forest sector was used to quantify the GHG fluxes in a base scenario with no climate policy, a Kyoto Protocol policy (KP policy), and a policy with no cap on forest carbon sequestration (FC policy), assuming that the policies apply the rest of the century.

? Results

Carbon offsets are higher under the KP policy than in the base scenario and likewise higher than under the FC policy in the short run, but the KP policy fails to utilize the forest carbon sequestration potential in the long run as it provides considerably less incentives to invest in forestry than the FC policy.

? Conclusion

The KP increases the Norwegian forest sector’s climate change mitigation compared to no climate policy but less in the long run than a carbon policy with no cap on forest carbon credits.     

Effects of pruning and stand density on the productionof new epicormic shoots in young stands of pedunculate oak (Quercus robur L.)

Context

Avoidance or control of epicormic shoots is among the major silvicultural challenges for the production of high-quality oak timber. In northern Europe, contemporary oak silviculture aims to produce valuable timber on a relatively short rotation, applying early, heavy thinning combined with artificial pruning.

Aims

The aim of this study was to analyse the effects of pruning and stand density on the production of new epicormic shoots on young trees of pedunculate oak (Quercus robur L.).

Methods

The study was based on two field experiments in even-aged stands of pedunculate oak subjected to different thinning practices and early selection of potential future crop trees. From ages 13 to 15 years, stem density was reduced to 300 trees ha^?1, 1,000 ha^?1 or stands remained unthinned. Pruning was conducted on selected trees at ages 22–24 years. At that age, the stem density in unthinned control plots ranged from 2,500 to 3,100 ha^?1. All treatments were replicated twice within each experiment.

Results

Pruning led to an overall increase in the total production of new epicormic shoots. More epicormic shoots were produced in the lower part of the stem (0–3 m in height) than in the upper part (3–6 m). The number of new epicormic shoots increased with increasing stand density.

Conclusion

Early, heavy thinning combined with high pruning at regular intervals may help shorten the rotation length for pedunculate oak without further reduction in wood quality than that which is caused by wider annual growth rings.     

Variation in biomass expansion factors for China’s forests in relation to forest type, climate, and stand development

? Context

Biomass expansion factors (BEFs, defined as the ratios of tree component biomass (branch, leaf, aboveground section, root, and whole) to stem biomass) are important parameters for quantifying forest biomass and carbon stock. However, little information is available about possible causes of the variability in BEFs at large scales.

? Aims

We examined whether and how BEFs vary with forest types, climate (mean annual temperature, MAT; mean annual precipitation, MAP), and stand development (stand age and size) at the national scale for China.

? Method

Using our compiled biomass dataset, we calculated values for BEFs and explored their relationships to forest types, climate, and stand development.

? Results

BEFs varied greatly across forest types and functional groups. They were significantly related to climate and stand development (especially tree height). However, the relationships between BEFs and MAT and MAP were generally different in deciduous forests and evergreen forests, and BEF–climate relationships were weaker in deciduous forests than in evergreen forests and pine forests.

? Conclusion

To reduce uncertainties induced by BEFs in estimates of forest biomass and carbon stock, values for BEFs should be applied for a specified forest, and BEF functions with influencing factors (e.g., tree height and climate) should be developed as predictor variables for the specified forest.