Forestry - recent issues

Pennsylvania sedge cover, forest management and Deer density influence tree regeneration dynamics in a northern hardwood forest

Powers, M. D., Nagel, L. M. — 2009-06-25

Pennsylvania sedge (Carex pensylvanica Lam.) is a native species that can form dense mats in the understory of northern hardwood forests. Resource managers suspect Pennsylvania sedge mats could limit tree regeneration, leading to changes in forest structure and composition. A number of other factors could alter the understory plant community, so any attempt to understand the effects of sedge populations should also account for these other processes. This study considered relationships between Pennsylvania sedge cover, management history, deer density and tree regeneration in a northern hardwood forest. All the factors considered had significant effects on saplings, but few significant relationships with tree seedlings. Stands managed using even-aged silvicultural systems had lower sapling densities for several species and species groups and lower species diversity than unharvested second-growth stands. High deer densities were associated with low levels of both sapling density and sapling species diversity. Pennsylvania sedge cover was negatively correlated with the density of secondary species and sapling species diversity in stands with moderate deer densities. Results from this study suggest a number of factors are influencing northern hardwood tree regeneration in these forests, and further research involving multifactor approaches is needed to clarify the mechanisms driving forest vegetation dynamics.

Carbon stock and stock changes across a Sitka spruce chronosequence on surface-water gley soils

2009-06-25

We assessed age-related alterations in carbon (C) stocks and sequestration rates of first rotation Sitka spruce (Picea sitchensis (Bong.) Carr) plantations on predominantly surface-water gley soils. Sites were selected to represent a typical Sitka spruce chronosequence following land use transition from grasslands dominated by surface-water gley soils. Based on inventory, eddy covariance, physiological and modelling assessments of net ecosystem productivity (NEP), we show that afforested stands are a C sink at 10 years, and possibly earlier, followed by an increase to a maximum of 9 t C ha^–1 year^–1 before the first thinning cycle. NEP subsequently declined from 9 t C ha^–1 year^–1, at closed canopy, to 2 t C ha^–1 year^–1 in older and thinned stands. Reductions in the C sequestration rate of older stands were coupled with a decrease in gross primary productivity, increases in maintenance/growth respiration and decomposition losses following harvest. We suggest that the high sequestration potential of these forests may be associated with the high net primary productivity of these plantations in Ireland, a high allocation of assimilates and litter into the belowground C pool and accumulation of C in mineral gley soils following afforestation.

Modelling the anchorage of shallow-rooted trees

Achim, A., Nicoll, B. C. — 2009-06-25

We present here a mechanistic model (the ‘Resistance’ model) that uses easily measurable or predictable input parameters describing tree, soil and root–soil plate characteristics to predict the anchorage strength of Sitka spruce (Picea sitchensis (Bong.) Carr.) trees. Results show that for a given soil group and rooting depth, the anchorage moment can be modelled as being proportional to the square of the root–soil plate spread. Models are also developed of root–soil plate spread in relation to soil group and tree characteristics and are applied with the Resistance model to provide predictions of anchorage based on the diameter at breast height. To examine the relative sensitivity of trees on different soil groups and with different rooting depths, the models are applied here to an example where the leeward ‘hinge’ radius is constrained to a maximum of 1 m. The results are discussed in relation to forest wind risk modelling and stand management.

Deep shade alters the acclimation response to moderate water stress in Quercus suber L.

Jimenez, M. D., Pardos, M., Puertolas, J., Kleczkowski, L. A., Pardos, J. A. — 2009-06-25

The interactive effects of shade and drought on different morphological and physiological traits were addressed on Quercus suber L. seedlings. In our experiment, limited light treatment (1 per cent) represented the main factor constraining cork oak seedlings growth. Maximal photochemical efficiency (F_v/F_m) with light ≥15 per cent exhibited a midday fall, but under deep shade (1 per cent), F_v/F_m remained constant (<0.8 values) throughout the day. The quantum efficiency of photosystem II (PSII) was lower under moderate drought only in deeply shaded plants. The drought also interacted with light through the increase of the soluble sugar content at 100 per cent light, but not under shade. Under deep shade, soluble sugar content tended to be even lower under moderate drought conditions. The chlorophyll content was not the highest under deep shade as could be expected, while the efficiency of PSII was the lowest under deep shade. We concluded that cork oak can acclimate to moderate shade (15 per cent light), but deep shade impairs some of the physiological responses to cope with low light conditions under moderate drought stress. Plants growing under deep shade were very sensitive to moderate water stress in terms of loss of carbon fixation capacity.

Vegetation response to midstorey mulching and prescribed burning for wildfire hazard reduction and longleaf pine (Pinus palustris Mill.) ecosystem restoration

Brockway, D. G., Outcalt, K. W., Estes, B. L., Rummer, R. B. — 2009-06-25

Dense midstorey vegetation, developed during fire exclusion, not only reduces understorey plant diversity and increases the risk of damaging wildfire but also impedes efforts to safely restore prescribed burning in longleaf pine (Pinus palustris Mill.) ecosystems. Our study examined the effects of midstorey reduction on stand structure and plant diversity in a forest treated by mulching alone and also when followed by prescribed fire during the winter, spring or summer. For trees ≥5 cm diameter at breast height (d.b.h.), mulching reduced stand density (1220–258 trees ha^–1) and basal area (24–17.7 m² ha^–1) and increased mean d.b.h. (12.8–29.2 cm), with the largest reductions in loblolly pine (Pinus taeda L.), sweetgum (Liquidambar styraciflua L.) and oaks (Quercus spp. L.). Removing hardwoods and smaller pines resulted in a decline in tree species richness (8.9–4.4). Despite a modest increase in evenness (0.72–0.79), tree species diversity (H' = 1.32–0.84) dynamics were largely driven by changes in richness. While the cover of tree seedlings initially declined from 32.4 to 16.9 per cent, rapid regrowth of hardwoods led to recovery by end of the second growing season. This, along with gains by shrubs, vines, grasses and forbs, resulted in a near doubling of understorey plant cover. Although tree seedling increases were not related to fire season, peak responses occurred for shrubs and vines after winter fire and spring fire, grasses following winter fire and forbs after summer fire. An increase in species richness (18.7–24.5) and decline in species evenness (0.86–0.70) produced only a small increase in understorey species diversity (H' = 2.31–2.45). The greater number of understorey species following treatment were less equitably distributed as a result of differential rates of plant growth. While mulching led to a short-term increase in woody and herbaceous understorey plants, prescribed fire is needed to curtail redevelopment of the woody midstorey and further increase grasses and forbs.

A volume change index for forest growth and sustainability

Van deusen, P. C., Roesch, F. A. — 2009-06-25

A volume change index is suggested that is derived from growth components that can be estimated from remeasured plots. The new index incorporates more information than the traditional growth over removals ratio. The new index directly indicates whether the standing volume will be increasing or decreasing if current conditions persist, whereas the ratio of growth over removals obscures the impact of mortality. The details of estimating the components of growth are discussed with regard to interpreting the new index. The effect of spatial scale on the index is explored and a variance estimator is suggested. The new index is estimated from US Department of Agriculture Forest Service annual inventory data for two example applications. The first application looks at spatial trends in the index. The second application applies the index to a mill working circle.

Development and long-term evaluation of harvesting patterns to reduce windthrow risk of understorey spruce in aspen-white spruce mixedwood stands in Alberta, Canada

Macisaac, D. A., Krygier, R. — 2009-06-25

The Hotchkiss River Mixedwood Timber Harvesting Study developed new approaches to harvesting systems for western Canada's boreal mixedwood forests. Conventional harvesting equipment was used to test 11 harvesting and silvicultural systems over a 530-ha site. These include one- and two-pass modified uniform shelterwoods, two- and three-pass strip shelterwoods, two-pass alternate strip shelterwoods and four-pass progressive strip shelterwoods. These were used to test varying levels of wind protection designed to protect and minimize wind damage to understorey (immature) white spruce residuals following harvest of the aspen overstorey. Ongoing monitoring of wind dynamics and associated windthrow patterns since 1992 have provided clear management practice guidelines for reducing windthrow of immature spruce and residual aspen following harvesting. There are thresholds related to spruce height and distance from aspen residuals, beyond which windthrow damage increases significantly. The influence of topography, timing of harvest and the spatial configurations of multiple harvests on windthrow dynamics have been clarified through this research. These results have provided valuable information to help forest planners to utilize harvesting and silvicultural systems that best reduce windthrow damage to understorey spruce, following harvest of overstorey aspen.

The effect of duration of vegetation management on broadleaved woodland creation by direct seeding

Willoughby, I., Jinks, R. L. — 2009-06-25

The need for vegetation management when practising direct seeding, and the potential for using the technique to establish a range of tree and shrub species used for new native woodland creation, was investigated on a good quality, fertile ex-agricultural site in lowland Britain. After 4 years, an average of nearly 20 000 stems ha^–1 of all species had established, amounting to 20 per cent of viable seed sown, with the trees from the fastest growing species being over 2.6 m in height on average, with the tallest trees reaching over 3.7 m. Weeding using selective herbicides improved survival by up to 50 per cent and growth rates by up to 80 per cent. Weeding for 1 year gave a significant benefit to overall survival, but weeding for a maximum of 3 years gave the most improvement to survival and growth of the remaining trees. Tree form was improved by increased stocking densities. Direct seeding proved to be a viable technique for creating a mixed woodland of ash (Fraxinus excelsior L.), cherry (Prunus avium L), field maple (Acer campestre L), oak (Quercus robur L.), hawthorn (Crataegus monogyna Jacq.), hazel (Corylus avellana L.), dogwood (Cornus sanguinea L.), blackthorn (Prunus spinosa L.), guelder rose (Viburnum opulus L.), spindle (Euonymus europaeus L.), wayfaring tree (Viburnum lantana L.), sweet chestnut (Castanea sativa Mill.) and sycamore (Acer pseudoplatanus L.). The work confirmed the importance of achieving good weed control immediately before sowing and for at least the first growing season thereafter, to reduce seedling mortality and increase the chances of achieving successful woodland creation by direct seeding.

Using focal species modelling to evaluate the impact of land use change on forest and other habitat networks in western oceanic landscapes

Humphrey, J., Ray, D., Brown, T., Stone, D., Watts, K., Anderson, R. — 2009-04-24

Habitat networks have an important role in combating the deleterious effects of habitat fragmentation on biodiversity. This paper demonstrates how focal species modelling can be used to help predict the effects of land use change on habitat networks in western oceanic landscapes. The modelling was applied to the Isle of Mull in Western Scotland using three focal species: Pseudocyphellaria norvegica (Gyeln.) P. James, a lichen of native broadleaved woodland; marsh fritillary (Eurodryas aurinia Rottemburg), a butterfly of damp grassland and song thrush (Turdus philomelos CL Brehm), an avian habitat generalist. Significant areas of planted conifer forest on Mull will be converted to open ground habitat and native woodland. These land use changes, together with modest expansion of native woodland, are predicted to have a positive impact on networks for the lichen and marsh fritillary without unduly compromising networks for habitat generalists. There may be scope therefore for a more ambitious strategy for developing native woodland and damp grassland networks, but further testing using focal species with more exacting ecological requirements is desirable. Focal species modelling has value in informing strategies for land use change and the development of habitat networks provided that care is taken to select species with relevant ecological requirements.

Long-term spatio-temporal dynamics and historical continuity of European aspen (Populus tremula L.) stands in the Koli National Park, eastern Finland

Vehmas, M., Kouki, J., Eerikainen, K. — 2009-04-24

Although the European aspen (Populus tremula L.) is regarded as a keystone species for the biodiversity of northern Europe, its mechanisms of regeneration and persistence under old-growth conditions without large-scale disturbances have remained obscure. The aim of this paper is to describe the long-term dynamics and regeneration of European aspen in the old-growth forests of the Koli National Park, eastern Finland, in order to gain a better understanding of the occurrence of this species under natural forest conditions. The park includes both natural forests and forests that were previously managed. The long-term occurrence of aspen populations was determined on the basis of inventory data available for the years 1910, 1936 and 2004. Aspen is shown to have occurred at least temporarily over 34 per cent of the total forest area (840 ha). In addition, 13 per cent of the forest area continuously supported stands that contained large aspen trees between 1910 and 2004. In areas where no management took place (6.4 per cent of the area), about one-third of all the aspen stands contained large trees and persisted throughout the period. The results show that aspen can maintain long-term occurrence in old-growth forests and that the species is not only transient or confined to young successional stages. Areas where aspen regeneration is possible, as deduced from its long-term occurrence should be regarded as highly valuable for biodiversity because they offer long-term habitats for several threatened species that are associated with aspen trees. Recent changes in ecological conditions, however, may affect this in the future. Most notably, the increased population of large mammalian browsers may make aspen regeneration more difficult and should be taken into account when restoration and management measures are planned.

A process-based model to evaluate site quality for Eucalyptus nitens in the Bio-Bio Region of Chile

Rodriguez, R., Real, P., Espinosa, M., Perry, D. A. — 2009-04-24

A simplified, physiologically based (3-PG) model was used to evaluate the effects of spatial variation in climate and soils on the potential productivity of Eucalyptus nitens Deane and Maiden (Maiden). The model was parameterized based on the physiology of E. nitens to predict potential productivity and leaf area index as influenced by environmental factors. Data obtained from conventional weather stations were utilized by the 3-PG model to predict productivity site classes. A final plantation suitability grid was mapped to show areas of the region with productivity classes predicted to be very high (>52 m³ ha^–1 year^–1), high (47.5–52 m³ ha^–1 year^–1), moderate (45–47.5 m³ ha^–1 year^–1), low (35–45 m³ ha^–1 year^–1) and very low (<35 m³ ha^–1 year^–1). The lowest potential productivity was attributable to soil water and nutrients limitations. A process-based forest growth model that can be widely extrapolated using geographic information system is particularly useful to screen areas as prospective plantation sites.

Using dendrochronology to obtain annual data for modelling stand development: a supplement to permanent sample plots

Metsaranta, J. M., Lieffers, V. J. — 2009-04-24

Permanent sample plots (PSPs), measured at 5- to 10-year intervals, are presently used to monitor stand development in boreal forests in Canada. These data cannot easily be used to study inter-annual variability in stand development processes nor can they monitor the effects of transient factors affecting stands annually because of their coarse temporal resolution. It also takes a considerable period of time to obtain time series of data for regions without PSPs. Long re-measurement intervals are necessary because instruments like diameter tapes, calipers and clinometers cannot discern annual growth in these slow-growing forests. Dendrochronological stand reconstruction techniques are a method that can be used to obtain annual data on forest growth and stand development. We show that these techniques can provide annual information on stand development patterns while periodic measurements of PSPs cannot, and that these data can be obtained in a short period of time, relative to waiting to obtain data from PSPs established today. Detailed, annual data will become more important in the future, as climate change will affect both forest growth and stand dynamics. Annual resolution data on these processes will be required to describe and account for these effects.

An improved micropropagation protocol for maritime pine (Pinus pinaster Ait.) isolated cotyledons

Alvarez, J. M., Majada, J., Ordas, R. J. — 2009-04-24

In this work an improved micropropagation protocol for Pinus pinaster Ait. using isolated cotyledons is presented. The variables studied during bud induction were embryo preculture, type and concentration of cytokinin and influence of illumination culture conditions. Shoot development and proliferation was obtained by transfer to hormone-free medium with activated charcoal. This protocol also describes a procedure for successful continuous multiplication using axillary shoots and brachyblasts formed during shoot development. Based on 86 per cent rooting success rate, at least 70 plantlets can be expected per seed after 16 weeks.

Seedling height and the impact of harvesting operations on advance regeneration of conifer species in upland Britain

Stokes, V., Kerr, G., Ireland, D. — 2009-04-24

Extensive damage to and mortality of understorey seedlings during overstorey thinning could prevent the use of natural regeneration as a method of restocking. Experiments carried out on three upland conifer sites in Britain assessed the short-term impact of thinning operations on survival and damage to advance regeneration seedlings of different heights. At two sites dominated by Sitka spruce, the number of small-sized (<50 cm) and medium-sized (50–200 cm) seedlings lost during harvesting was significantly higher than the number of large seedlings (>200 cm) which tended to be damaged rather than lost. At the Scots pine/Japanese larch site, damage and loss were not related to seedling size. Survival or damage was significantly related to the distance from the nearest extraction rack (striproad). At two of the sites, survival or damage was related to distance to the nearest felled tree stumps. The seedlings in 25–30 per cent of the area were lost due to clearing the extraction racks prior to harvesting. In the stand matrix, 40–80 per cent of the regeneration survived and was not severely damaged; the remaining regeneration was likely to be sufficient to restock at all three sites, although distributions were clumped. There were no marked differences between motor-manual and harvester felling.

Side shelter on lowland sites can benefit early growth of ash (Fraxinus excelsior L.) and sycamore (Acer pseudoplatanus L.)

Willoughby, I., Stokes, V., Kerr, G. — 2009-04-24

The influence of side shelter on the growth of newly planted ash (Fraxinus excelsior L.) and sycamore (Acer pseudoplatanus L.) was investigated at a lowland site in Britain. Although tatter flag analysis classified the site as ‘very sheltered’ in comparison to upland sites, after three years, both species benefited to some degree from the provision of shelter, with height increment being improved by up to two to four times. The most effective shelter was provided by a wall of straw bales. Plastic netting also reduced exposure, but required regular maintenance in winter months. Our work suggests that on equivalent sites in southern Britain, where mean daily tatter rates of more than 2.4 cm² day^–1 (equivalent to windiness scores of greater than 10.3) occur, without side shelter, severe suppression of height growth in ash and sycamore is likely, and that exposure to wind is likely to be a significant cause of this reduction in growth. Currently, using artificial shelter materials on a large scale on lowland sites solely to improve early tree growth is unlikely to be cost-effective in most cases. However, the provision of side shelter, particularly through use of nurse species, is likely to become an increasingly important silvicultural consideration in the future.

A Bayesian approach to classification accuracy inference

Magnussen, S. — 2009-04-24

Bayesian accuracy assessments draw inference about random (super-population) parameters characterizing the classification process and accuracy statistics derived from these parameters. A conventional frequentist approach seeks to estimate the same parameters, but view them as fixed finite population quantities. Both approaches are detailed and contrasted with a real land cover data example. Bayesian results are given for non-informative and informative priors. The latter is justified in past experience. Results from simple and stratified random samplings on overall and class-specific accuracies and kappa coefficients of agreement are detailed for samples representing the 10 per cent, the 50 per cent and the 90 per cent quantile in a Monte Carlo sampling distribution of overall accuracy. A Bayesian approach is recommended for applications with small sample sizes and for quality assurance monitoring where prior data can boost effective sample sizes.

Profiles of private forest owners and the importance of landscape-scale management in the timber trade process of Finnish wood procurement

Palander, T., Ovaskainen, H., Tikkanen, L. — 2009-04-24

In the decision-making process that determines timber sales between private forest owners and the Finnish forest industry, opinions frequently conflict about the extent to which the forest landscape should be managed. The objective of this study was to investigate whether it would be useful to develop a landscape visualization tool that would help forest owners understand the consequences of harvesting so they could make a more informed decision on whether to sell their timber. We evaluated responses to a survey sent to forest owners in two regions of Finland to provide insights into owner appreciation of the forest landscape. The 545 forest owners who responded also evaluated the value of computer visualizations and a set of computer-generated images of the landscape. Our analysis concentrated on whether visualizing the landscape would affect sales decisions and – since women are increasingly becoming forest owners – how gender affected perceptions of the landscape and decision making. Visualization proved to be a popular tool for all forest owners. However, male and female forest owners had different perspectives on the forest landscape. Factors that differed between men and women for the statements with the strongest weightings in the principal component analysis explained 26 per cent of the overall variation in perceptions. Women particularly wanted to be able to visualize the post-harvesting landscape and preferred different types of visualization than men. Values associated with forest landscapes and their visualization seem more important to women and may therefore affect their sales decisions more than those of men. Based on these results, it will be useful to design and implement a decision support tool that will help forest owners visualize the consequences of harvesting and help the Finnish forest industry provide a more environmentally friendly service that accounts for the owner's landscape-related goals.

Development of a stand density management diagram for radiata pine stands including assessment of stand stability

Castedo-Dorado, F., Crecente-Campo, F., Alvarez-Alvarez, P., Barrio-Anta, M. — 2009-02-03

A stand density management diagram (SDMD) was constructed for Pinus radiata D. Don plantations in Galicia (north-western Spain) on the basis of four equations that were fitted simultaneously to data collected from 223 permanent plots. The relative spacing index was used to characterize the growing stock. The diagram provides information about quadratic mean diameter, stand merchantable volume, stand above-ground biomass, stand stem biomass and stand carbon pools. In addition, an estimation of the average slenderness coefficient for the whole stand and for each quarter of the stand diameter distribution was included. This information can be used to assess the stability of the whole stand and different crown classes, respectively. The SDMD outlined here allows foresters to make quick and easy comparisons among different thinning schedules in which both timber production and the risk of damage from wind or snow are considered. Two alternative density management systems, one that includes thinning operations and another that only includes the density-related mortality provided by a mortality function, are outlined in the diagram.

Unequal deployment of clones to seed orchards by considering genetic gain, relatedness and gene diversity

Lindgren, D., Danusevicius, D., Rosvall, O. — 2009-02-03

Related clones in seed orchards lead to inbreeding depression and reduced genetic value of the seeds. This study aims to develop the methodology for deployment of related clones to seed orchards when the breeding value and the pedigree are available for each candidate. The following goals were considered: high genetic gain, high genetic gain adjusted for predicted inbreeding depression (net gain), high gene diversity, and high effective clone number. The selection strategies included truncation selection with or without relatedness restrictions, maximizing genetic gain (linear deployment) with or without restrictions on relatedness and maximizing net gain. The selection strategies were applied to Norway spruce seed orchard candidates evaluated in clonal tests. The material comprised full-sib and half-sib relationships. Comparisons were made both at the same gene diversity and at the effective clone number. Maximizing net gain by unequal ramet number deployment resulted in considerable higher net gain and a considerable reduction of related ramets in many comparisons. Linear deployment restricted against related clones compared at the same status number resulted in almost as high net gain. Reduction in gene diversity may be a more important reason to avoid relatives in seed orchards than the subsequent inbreeding for achieving a high net gain.

Root anchorage and stem strength of black spruce (Picea mariana) trees in regular and irregular stands

Bergeron, C., Ruel, J.-C., Elie, J.-G., Mitchell, S.J. — 2009-02-03

A tree winching experiment was conducted, simulating wind action and resulting damage, in order to assess mechanical resistance of black spruce (Picea mariana (Mill.) B.S.P.) trees in stands of regular and irregular structures. The critical bending moment (M_c) of winched trees was determined and the relationship between M_c and tree and stand characteristics was investigated through statistical analyses. Stem mass (SW), average spacing between trees (S) and height:diameter ratio (H/d.b.h.) were initially selected by a screening procedure to predict M_c. Potential differences between stand structures were tested in mixed models using different subsets of the data. Included fixed effects varied between the different models. SW was the most useful and significant variable in all models and H/d.b.h. was significant only when snapped trees were included in the analysis. When decayed samples were excluded, resistance to uprooting was higher in irregular stands. Decay seemed to play an important role in irregular stands and should be investigated further. Since no difference was observed in the relationship between stem mass and critical turning moment between distant sites, relationships should be applicable across wide regions. This study provides some of the basic relationships required to model windthrow risk in irregular stands. However, the effects of stand structure on wind load for individual trees will also need to be considered.

Frost hardening and dehardening in Abies procera and other conifers under differing temperature regimes and warm-spell treatments

Norgaard Nielsen, C. C., Rasmussen, H. N. — 2009-02-03

Frequent bud frost damage in cultivation of Abies procera Rehder and pending climate changes are the background for this study of cold hardiness under varying acclimation regime (in closed-top chambers) and experimental warm spells during the cold season. LT₅₀ values were established by freezing tests at different times of year. Damage and deaths were assessed on leader buds, subapical lateral buds, needles and cambium. Minor parallel experiments involved Abies nordmanniana, Picea abies and Picea sitchensis. Lower acclimation temperatures resulted in deeper frost hardiness during late autumn but less during spring, compared with ambient temperature controls. Elevated temperatures resulted in less deep frost resistance. Apical buds generally developed deeper frost hardiness than lateral buds but less deep than the cambium, varying with species, however. Frost damage in buds ranged from death over partially destroyed bud contents resulting in distorted shoots to buds seemingly remaining dormant. Responses to warm spells differed with duration, timing and species, ranging from dramatic decrease in frost hardiness with or without subsequent recovery to no reaction. Furthermore, the reactions did not show any clear relation to dormancy level. For A. procera, exposure to fluctuating temperatures appeared to be particularly problematic. This explains why this species develops best in coastal climates, and in sites sheltered from temperature extremes either by hedging, a winter snow cover, or topography. The Christmas tree production will suffer severely on sites with harsh temperatures due to losses of lateral and terminal buds, which destroy the crown symmetry. Clipping of greenery is less influenced by frost damages, although the development of normal branch whorls is often disturbed.

The dynamics of biomass production in relation to foliar and root traits in a grey alder (Alnus incana (L.) Moench) plantation on abandoned agricultural land

Uri, V., Lohmus, K., Kiviste, A., Aosaar, J. — 2009-02-03

The dynamics of the above-ground biomass production of a grey alder plantation on abandoned farmland was investigated during 11 years after establishment. In the 12-year-old stand, the total biomass of the above-ground part of the stand was 68.8 t dry matter (DM) ha^–1 and the current annual production (CAP) was 14.0 t DM ha^–1 year^–1. The predicted mean annual increment (MAI) reached is maximum at the age of 16 years, which indicates bulk maturity (the stand age when CAI = MAI) and appropriate rotation time for obtaining maximum biomass production. In the case of short-rotation forestry, initial stand density should not be higher than 6500–6000 trees per hectare. Below-ground biomass accounted for 18 and 16 per cent of total stand biomass at a stand age of 5 and 10 years, respectively. The biomass of the nodules was estimated at 155 ± 63 kg DM ha^–1 and the biomass of the fine roots was estimated at 870 ± 130 kg DM ha^–1 in the 10-year-old grey alder stand. Of the fine roots, 80 per cent and almost all nodules were located in the upper 0–20 cm soil layer in both the 5-year-old and the 10-year-old stand. The value of leaf area index increased with stand age, ranging between 1.38 and 5.43 m² m^–2 during the development of the stand. Specific leaf area varied in different years from 11.1 to 13.5 m² kg^–1.

Forest soil carbon cycle under elevated CO2 - a case of increased throughput?

2009-02-03

Forest soils account for a large part of the stable carbon pool held in terrestrial ecosystems. Future levels of atmospheric CO₂ are likely to increase C input into the soils through increased above- and below-ground production of forests. This increased input will result in greater sequestration of C only if the additional C enters stable pools. In this review, we compare current observations from four large-scale Free Air FACE Enrichment (FACE) experiments on forest ecosystems (EuroFACE, Aspen-FACE, Duke FACE and ORNL-FACE) and consider their predictive power for long-term C sequestration. At all sites, FACE increased fine root biomass, and in most cases higher fine root turnover resulted in higher C input into soil via root necromass. However, at all sites, soil CO₂ efflux also increased in excess of the increased root necromass inputs. A mass balance calculation suggests that a large part of the stimulation of soil CO₂ efflux may be due to increased root respiration. Given the duration of these experiments compared with the life cycle of a forest and the complexity of processes involved, it is not yet possible to predict whether elevated CO₂ will result in increased C storage in forest soil.

Analysing effects of thinning on stand volume growth in relation to site conditions: A case study for even-aged Sitka spruce (Picea sitchensis (Bong.) Carr.)

Skovsgaard, J.P. — 2009-02-03

This study challenges all-else-equal assumptions in the analysis of thinning effects and more specifically those regarding local variation in forest site productivity. It is demonstrated that considerable variation may occur in site productivity in apparently homogeneous forest stands, whether thinned or unthinned, and that this may not be reflected in height, but rather in basal area growth. To account for such variation, the suggestion is to include an unbiased pre-treatment measure of site productivity, such as total volume production prior to first thinning, as a covariate in the analysis. In a wider perspective, the study further challenges two general site productivity hypothesis, namely, the general assumption that stand volume growth correlates well with stand height (the site index hypothesis, i.e. that site productivity can be estimated based on stand height) and the assumption that, for a given species, total volume production at a given stand height is identical for all site classes (Eichhorn's rule). The thinning response pattern for even-aged Sitka spruce is quantified for different site types based on two thinning experiments in Denmark and six comparable experiments in Great Britain, Norway and Sweden. The effect of thinning from below on stand volume growth is strongly site dependent, but heavy thinning usually leads to a reduction in volume growth as compared with an unthinned stand growing under similar site conditions. For some sites, typically those with stable and ample water supply and a deeply developed root system, stand volume growth is maximized through light thinning. For some other sites, typically those with a high ground water table and a shallow root system, thinning reduces stand volume growth and considerably so with increasing thinning grade. There seems to be a gradient in the reduction, so that it is lessened with increasing rooting depth and with increasing stability of water supply. Due to site-dependent variation in the relation between height growth and stand volume growth as well as site-dependent variation in thinning response pattern, it is recommended to establish and maintain unthinned observation plots in managed stands to ensure reliable growth and yield prognoses. Such plots can serve as a reference for thinning practices as well as a standard for potential volume growth. This recommendation could also hold for other species and in other parts of the world.

Biomass carbon sinks in Japanese forests: 1966-2012

Sasaki, N., Kim, S. — 2009-02-03

The role of forests in absorbing atmospheric carbon has been recognized under the Kyoto Protocol, which allows signatory countries to use forests as a mitigation option. Although several studies have estimated carbon stock changes in Japanese forests, most only estimate changes up to 1995 or ignore carbon stock changes in natural forests. This study is the first attempt to estimate carbon stock changes in Japanese forests from 1966 to 2012, to coincide with the final year of the Kyoto Protocol's first commitment period. Forest area and growing stock data were analysed. Then, two models for predicting the change in forest area and growing stock were developed. Results showed that most natural forest loss resulted from conversion to plantation forest. The total above-ground and below-ground carbon stock in Japanese forests has been estimated to have increased from 1114.8 TgC in 1966 to 2076.0 TgC in 2012, representing an increase of 20.9 TgC year^-1 over the same period. During the first commitment period of the Kyoto Protocol (2008–2012), annual carbon sinks were estimated at 20.1 TgC, of which ~76.9 per cent were sequestered in plantation forests. Of the 20.1 TgC year^-1, eligible carbon sinks are estimated at 10.2 TgC or ~78.7 per cent of the maximum or capped amount as allowed under the Marrakesh Accord. Although further effort is needed so that the capped amount of 13 TgC year^-1 could be achieved, this study suggests that carbon sinks through forest management could be used to offset industrial carbon emissions.

Editor's Note

2009-02-03