Forestry - recent issues

Forest ecosystem carbon accumulation during a secondary succession in the Eastern Prealps of Italy

Alberti, G., Peressotti, A., Piussi, P., Zerbi, G. — 2008-03-26

Forest site productivity: a review of the evolution of dendrometric concepts for even-aged stands

Skovsgaard, J. P., Vanclay, J. K. — 2008-03-26

Forest site productivity is the production that can be realized at a certain site with a given genotype and a specified management regime. Site productivity depends both on natural factors inherent to the site and on management-related factors. This review of the evolution of site assessment highlights three tenets of forest site productivity: the height–age site index, Eichhorn's rule and the thinning response hypothesis. These tenets rely on the hypotheses that height growth correlates well with stand volume growth, that total volume production of a given tree species at a given stand height should be identical for all site classes and that stand volume growth is independent of thinning practice for a wide range of thinning grades. The maturation of long-term field experiments has provided for the revision of these hypotheses, and contributed to an understanding of situations where they do not hold. This led to the introduction of the concept of yield level, the stand volume growth per unit of height growth. The use of the yield level theory for estimating site productivity has facilitated the development of a three-dimensional model of the relationship between stem number, quadratic mean diameter and stand basal area. Given this model, a stand density index based on the combination of stem number and quadratic mean diameter provides an indication of the yield level, which may be used to adjust height-age–based estimates of site productivity.

Possibilities for harmonizing national forest inventory data for use in forest biodiversity assessments

Winter, S., Chirici, G., McRoberts, R. E., Hauk, E., Tomppo, E. — 2008-03-26

Representatives of the national forest inventories (NFIs) of 27 European countries and the USA evaluated possibilities for a common approach to forest biodiversity reporting. The project was conducted under the auspices of COST (European Cooperation in the field of Scientific and Technical Research) Action E43, ‘Harmonisation of National Forest Inventories in Europe: Techniques for Common Reporting’. Based on the analysis of responses to an initial questionnaire regarding the most ecologically important and technically feasible variables for monitoring forest biodiversity using NFI data, 16 key variables were selected. Responses to a second questionnaire consisting of six questions regarding assessment of the 16 key variables revealed that the NFIs of most responding countries already assess a large proportion of these variables. Each of the 16 variables is assessed in at least eight NFIs. However, the responses regarding assessment methods and necessary field crew expertise varied considerably. As a first example, although tree diameters at breast height (d.b.h.) are assessed by every country, there is a wide range of minimum d.b.h. thresholds from 0 mm in Finland to 12 cm in Cyprus and Switzerland. As a second example, eight countries estimated that almost all inventory variables require highly skilled forest staff with specialized training, but most countries agree that a middle level of expertise is sufficient. Despite differences in current NFI methods, overall, the results of the study indicate positive possibilities for achieving a moderate level of European-wide harmonization.

Structure, reproduction and flood-induced dynamics of riparian Tugai forests at the Tarim River in Xinjiang, NW China

Thevs, N., Zerbe, S., Schnittler, M., Abdusalih, N., Succow, M. — 2008-03-26

Tugai forests are the riparian forests along the rivers in the continental desert regions of Central Asia, i.e. the Tarim River, Amu Darya and Syr Darya. They mainly consist of Populus euphratica Oliv., Populus pruinosa Schrenk. and Elaeagnus oxycarpa Schltdl. As a consequence of land opening campaigns, large areas of Tugai forests were destroyed after the 1950s. Due to excessive use of water for irrigation, the remaining Tugai forests are under severe threat. Near natural Tugai forests still exist along the Tarim middle reaches in the Tarim Huyanglin Nature Reserve, Xinjiang, NW China. There is a gap in understanding, how the seedlings of P. euphratica establish as trees which continuously connect to the groundwater. Therefore, the set of conditions which must be met for germination and successful establishment, i.e. formation of Tugai forests, was investigated along a representative transect still under natural conditions. P. euphratica seedlings germinate in belts during the retreat of the summer flood on freshly deposited sites bare of other vegetation. Such germination sites are formed by river dynamics. While germination takes place regularly in the study area, successful establishment is restricted to few germination events. Seedlings face dropping groundwater levels during spring and early summer of the second year after germination. Therefore, for successful establishment, it is essential that the flood of the second year starts in time and is high enough, in order to replenish the groundwater. Furthermore, clayey soil layers in the subsoil may play a role for successful establishment, too, as they store water better than sandy soil layers.

Effects of climate and management history on the distribution and growth of sycamore (Acer pseudoplatanus L.) in a southern British woodland in comparison to native competitors

Morecroft, M. D., Stokes, V. J., Taylor, M. E., Morison, J. I.L. — 2008-03-26

Sycamore (Acer pseudoplatanus L.) is an invasive, non-native species in Great Britain and its management in conservation areas is controversial. Climate change adds further uncertainty to decision making. We investigated the role of management history in determining present-day abundance and the effects of climatic variability on growth, photosynthesis and phenology at Wytham Woods, a UK Environmental Change Network (ECN) monitoring site. Relatively few sycamore trees were found in undisturbed ancient, semi-natural woodland and recent plantations, despite being common in other areas of the site. Sycamore grew more slowly than ash (Fraxinus excelsior L.), its principal competitor, but at a similar rate to pedunculate oak (Quercus robur L.) in the period 1993–2005. There were fewer sycamore than ash seedlings, regardless of which species dominated the canopy. Growth of sycamore was slower in dry periods than wet ones and lower photosynthetic rates were measured in canopy leaves under dry compared with wet soil conditions. This study therefore suggests that sycamore does not present a serious threat to undisturbed ancient woodland on the site and that it may eventually decline in areas of the site where it competes with ash, in the absence of disturbance. It may also decline under climate change if summer droughts become more frequent.

Reporting the results of forest monitoring--an evaluation of the European forest monitoring programme

Moffat, A. J., Davies, S., Finer, L. — 2008-03-26

An evaluation of the pan-European forest monitoring programme set up in the 1980s to examine the effects of atmospheric pollution on forest condition is presented. This is based on a questionnaire survey of national stakeholders and an examination of the quality of scientific information contained in the programme reports. The relevance of the results to different types of stakeholder is discussed. Annual reports from the programme have focussed on scientific understanding, but have only partially satisfied policy needs. Basic principles for an effective communication strategy to improve the content, accessibility and usability of the monitoring results are put forward. Future monitoring requires a proper analysis of policy-relevant indicators and more effort to get appropriate information to policy makers when they need it. Modelling and decision support tools should be seen as vital parts of knowledge transfer.

Artificial hybridization between Robinia pseudoacacia L. and R. pseudoacacia var. monophylla Carr.

Dini-Papanastasi, O., Aravanopoulos, F. A. — 2008-03-26

Results regarding artificial cross- and self-pollination between Robinia pseudoacacia L. and R. pseudoacacia var. monophylla Carr. are reported. Parental clones involved in a diallel mating scheme were selected according to leaf type phenotype and included (1) single-leaf type, (2) 25-leaf type, (3) three-leaf type and (4) common Robinia. Artificial pollination proved to be a difficult and delicate procedure. A total of 33 pollinations were made that resulted in the formation of 84 pods, of which 24 developed fully and produced 65 seeds. Fifteen seeds were germinated, resulting in the production of two putative fertile hybrids. The success of hybridization was assessed by genetic markers, while parental clones and hybrid progeny were assigned multilocus genotypes. The mode of inheritance of the leaf type trait was studied in open-pollinated families where the monophylla type was the maternal parent. The study indicated that leaf type in the monophylla variety may be associated with major gene effects.

Effect of pruning severity and timing of treatment on epicormic sprout development in giant sequoia

O'Hara, K. L., York, R. A., Heald, R. C. — 2008-03-26

Giant sequoia (Sequoiadendron giganteum (Lindl.) Buchh.) trees were pruned monthly over a 12-month period to assess the effects of timing of pruning operations on epicormic sprout development. Trees were pruned to three pruning heights in each month. Periodic counts of total sprouts and measurement of the length of the longest sprout were used to assess sprout development following pruning. Sprouting was initially delayed following pruning during growing season months as compared with non-growing season months. Six years after study initiation, greater numbers of sprouts and larger maximum branch lengths were found from pruning outside the May through September growing season. These differences were most pronounced in the first years following treatment but differences diminished markedly after 6 years. However, a logistic model to predict the probability of sprouting indicates that pruning severity was a much more significant explanatory variable than season of pruning. Seasonal differences in epicormic sprout development may be temporary and are of less importance in affecting sprout development than pruning severity. Epicormic sprouts also occurred with greater frequency on the south or exposed side of pruned tree boles.

Thirty years of gap dynamics in a central european beech forest reserve

Kenderes, K., Mihok, B., Standovar, T. — 2008-03-26

Investigation of gap characteristics and tree regeneration patterns is central for our understanding of forest dynamics. By integrating aerial photograph analyses and ground surveys, we provide a study of long-term canopy gap dynamics and tree regeneration patterns in a Hungarian beech forest reserve. We found (1) that in spite of the overall increase of gap area during the investigated 30-years (from 2.5 to 7.7 per cent), total gap area and average gap size (40–93 m²) were remarkably similar to those found in other temperate and tropical forests, (2) if the fate of individual gaps was followed, two to three times more intensive canopy dynamics (gap creation, closure and expansion) could be recognized than simple change of gap area indicated, and (3) average seedling density was considered to be sufficient for natural regeneration. However, it was apparent that recent increased deer browsing had prevented establishment of younger trees of 1–2 m in height, as taller saplings were recorded only in old gaps. Our results not only provide useful information on forest dynamics but can also contribute to understanding the potential roles that small forest reserves can play in providing essential reference data for nature-based forest management of this forest type.

Formal and informal institutions and their hierarchy in the regulation of the forest lease in Russia

Torniainen, T. J., Saastamoinen, O. J. — 2008-02-01

The aim of this study is to identify and analyse the institutional arrangements that regulate the forest lease and related markets of industrial timber in Russia. A theoretical framework is derived from institutional economics. Institutions, their hierarchy and cohesion are surveyed at constitutional, collective-choice and operational levels. The organization of the long-term forest lease and its contribution to the sustainable forest management and development of forest industries are described and regional differences in the organization of forestry are tested. In addition, the expected impacts of the new federal Forest Code are analysed.

Breeding birds in hemiboreal clear-cuts: tree-retention effects in relation to site type

Rosenvald, R., Lohmus, A. — 2008-02-01

The variability of natural disturbance regimes implies that retention cutting, aimed at emulating natural disturbances to support biodiversity, should be forest-type specific. We explored in four site types (ranging from dry nutrient-poor to wet nutrient-rich) in Estonia how the retention of live and dead trees affects post-cut abundance and species richness of birds. The whole bird communities and harvest-sensitive species groups responded differently: while the total abundance and relative species richness of birds increased along with the abundance of dead trees, the species of national conservation concern occurred more frequently at higher densities of live trees. Hence, although the species of conservation concern and hole-nesters preferred the cuts having the generally densest and most species-rich avian communities, this co-variation was obviously insufficient for using the total community characteristics (particularly density) as indicators of forestry impacts on bird biodiversity. In contrast to expectations, tree retention always influenced birds independently of forest type. This may be related to the particular study system (notably low retention levels) but future studies should nevertheless explicitly address to what extent forest species are adapted to natural disturbances, and in which cases that knowledge can be used for forestry planning.

Ectomycorrhiza formation and growth of Picea abies seedlings inoculated with alginate-bead fungal inoculum in peat and bark compost substrates

Repac, I. — 2008-02-01

Sphagnum peat (peat), spruce bark compost (compost), peat + perlite (1 : 1, v : v) and compost + perlite (1 : 1, v : v) substrates were inoculated with vegetative alginate-bead inoculum of Hebeloma crustuliniforme, Hygrophorus agathosmus or Paxillus involutus or left uninoculated prior to the addition of Norway spruce seed. Growth and percentage of mycorrhization of bareroot seedlings cultivated in a greenhouse were evaluated after the first growing season. Seedlings grown in peat-based substrates had significantly larger aboveground and total dry weight, but significantly lower mycorrhization percentage than those grown in compost-based substrates. There were no significant differences between fungal treatments (including control) for both the percentage of mycorrhization and growth of seedlings. The artificially introduced fungi were not efficient in mycorrhizal formation – naturally occurring fungi were common in all treatments. However, a significant interaction between substrate and fungus treatments in root dry weight was detected. Hebeloma-inoculated seedlings grown in peat showed the highest value of root dry weight. This fact indicates other possible effects of the fungi on root growth independent of mycorrhization. Growth parameters were negatively correlated with the extent of mycorrhization, indicating allocation of host photosynthates to the fungi. To the best of our knowledge, operational inoculation of Norway spruce seedlings with the test fungi has not been reported previously.

The potential of 44 native and non-native tree species for woodland creation on a range of contrasting sites in lowland Britain

Willoughby, I., Stokes, V., Poole, J., White, J. E. J., Hodge, S. J. — 2008-02-01

A series of species trials were set up to investigate the establishment and early growth (up to 14 years old) of 44 native and non-native tree species on a variety of different site types in lowland Britain. On good quality lowland afforestation sites, Platanus x hispanica (London plane) established and grew more successfully than the native trees tested, and may be an example of a species that could theoretically be established in anticipation of future climate change. Experiments on a variety of community woodland sites indicated that a range of exotic species, such as X Cupressocyparis leylandii (Leyland cypress), may have the potential for establishing a woodland cover on poorly restored land where few other trees would grow. However, on less challenging, better restored sites, a wide range of native species also grew successfully. Further long-term and larger scale trials on a wider variety of sites are required to confirm the potential of the species tested for British conditions. The results from these experiments also showed that relative growth rates of different species can vary through time, highlighting the danger in making premature judgements about species suitability based solely on very early tree growth.

Effects of weather conditions on mast year frequency in beech (Fagus sylvatica L.) in Sweden

Overgaard, R., Gemmel, P., Karlsson, M. — 2008-02-01

During the last two decades, an increase of the frequency of naturally regenerated beech seedlings has been reported. This may be due to an increased masting. In this investigation in southern Sweden, mast year frequency, mast crop size and the relationships between mast year and climatic variables were studied. Our analysis shows that while the average mast year interval was 4–6 years from the end of the seventeenth century up to the 1960s, the mean interval has decreased to 2.5 years during the most recent 30 years, and there have been two consecutive mast years on two occasions during this later period. Mast years have often followed years in which the temperature in July and September was higher than the 30-year mean. However, there were significant variations in the amounts of beechnuts produced between different mast years, and beechnut production increased with increasing site index. Climatic changes, especially increases in temperature, may have been responsible for the higher frequency of mast years, but increased atmospheric nitrogen deposition may also have been a contributory factor.

Spatial structure of semi-natural and plantation stands of Scots pine (Pinus sylvestris L.) in northern Scotland

Mason, W. L., Connolly, T., Pommerening, A., Edwards, C. — 2008-02-01

The success of current initiatives to maintain and enhance the area of and the special habitats provided by the remnant semi-natural pinewoods of northern Scotland will depend upon foresters' ability to foster more natural structures in even-aged plantations through stand manipulation. However, there is little information on the structures and spatial patterns that can be found in Scottish pinewoods; such knowledge could be used to design appropriate silvicultural regimes. A study was carried out to compare spatial structure in three 0.8–1.0 ha plots in the Cairngorms National Park; one plot was a 78-year-old plantation stand, the other two were semi-natural stands with trees up to 300 years old. Basic mensurational data showed that the semi-natural stands were characterized by a wider range of tree sizes and more large (>50 cm d.b.h.) trees. Spatial structure was evaluated with a range of different indices: the aggregation index of Clark–Evans (CE), the uniform angle and diameter differentiation indices, Ripley's L function of tree spatial distribution, pair and mark correlation functions and experimental variograms of tree diameter. The CE revealed a regular distribution in the plantation with the semi-natural stands having a random pattern. Further analysis of the latter stands indicated that, in each case, the older trees in the stand were regularly distributed while the younger ones were clustered. There was little difference in uniform angle values between the stands while the diameter differentiation distributions suggested greater variety in diameter within the semi-natural stands than in the plantation. The Ripley's L function showed that trees in the plantation were regularly distributed at close distances but clustered over wider distances. There were differences in pattern between the semi-natural stands; in one, trees were clustered because the positions of the younger trees were influenced by past regeneration trials, whereas in the other stand a random pattern was observed. Similarly, the variogram indicated widespread homogeneity in diameter within the plantation, while the semi-natural stands showed high variation at close spacing because of competition followed by spatial autocorrelation up to ~20 m distance. Thereafter, one of these stands had a very different pattern because of a more intensive regeneration history. All the indices, apart from uniform angle, were able to discriminate between the plantation and the two semi-natural stands, but only the more detailed spatial indices were capable of identifying differences within the latter. The implications of these results for management strategies in plantations are discussed.

Growth response of young lodgepole pine to thinning and repeated fertilization treatments: 10-year results

2008-02-01

This study was designed to test the hypothesis that large-scale pre-commercial thinning (PCT) to various stand densities, at ages 12–14 years, combined with repeated fertilization, would, over a 10-year treatment period, enhance productivity of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) crop trees. Study areas were located near Summerland, Kelowna and Williams Lake in south-central British Columbia, Canada. Each study area had nine treatments: four pairs of stands thinned to densities of ~250 (very low), ~500 (low), ~1000 (medium) and ~2000 (high) stems ha^–1, with one stand of each pair fertilized five times at 2-year intervals, and an unthinned stand. The very low, low- and medium-density stands were also pruned to a 3-m lift 5 years after thinning. At the tree level, fertilization treatments significantly increased diameter at breast height (DBH), basal area (BA) and volume growth and heavy PCT significantly increased DBH and BA growth. Pruning may mitigate some of the negative stem form and wood quality attributes associated with fast-growing trees without adversely affecting stem growth. At the stand level, PCT to very low and low densities significantly decreased the volume growth compared with high-density stands. The potential beneficial impacts that PCT and repeated fertilization treatments have for mitigating timber supply shortfalls, as well as potentially minimizing crop tree losses due to mountain pine beetle (Dendroctonus ponderosae Hopk.), are also discussed.

Corrigendum

2008-02-01

Individual seedling mortality as a function of size, growth and competition in naturally regenerated beech seedlings

Collet, C., Le Moguedec, G. — 2007-09-27

Young forest stands that are naturally regenerated are characterized by a large number of seedlings and high mortality rates. Good prediction of seedling mortality is therefore necessary to model the dynamics of young stands. We used data obtained in a natural beech (Fagus sylvatica L.) regeneration in north-eastern France, to fit logistic models to predict seedling mortality and to analyse how seedling size, seedling growth and local competition relate to seedling mortality. Good relationships were obtained with recent seedling diameter growth, and with a combination of local competition and initial seedling size. However, the relationships between the probability of mortality and recent growth appeared to be unstable and to vary substantially with local competition and among measurement years, precluding the use of these relationships in regeneration models.

Growth and mortality in underplanted tree seedlings in response to variations in canopy closure of Norway spruce stands

Lof, M., Karlsson, M., Sonesson, K., Welander, T. N., Collet, C. — 2007-09-27

Six broadleaved tree species and Picea abies (L.) Karst. were planted under spruce plantations of varying densities, in Sweden. Treatments included control (994 stems ha^–1), dense (538 stems ha^–1), sparse (294 stems ha^–1) and gap (0 stems ha^–1) overstory treatments. There was an increase in height and diameter growth from control to sparse overstory treatment of all underplanted tree species except for ash (Fraxinus excelsior L.) and Norway maple (Acer platanoides L.). Site conditions may have hampered the growth of these species, as well as wild cherry (Prunus avium L.). Both oak (Quercus robur L.) and spruce had greater growth in the gap treatment, relative to the other treatments. Insecticide application did not influence seedling growth or survival. The performance of beech (Fagus sylvatica L.), lime (Tilia cordata Mill.), spruce and oak was consistent with shade tolerance ranking. Beech and lime had a very high survival rate, even under the densest canopy. The growth and mortality of ash, maple and wild cherry differed significantly from what was expected. This experiment demonstrated significant variation in interspecific growth and mortality between seven planted tree species in relation to canopy density. Correct site and species selection is crucial when underplanting in shelterwood systems.

Which grow better under the canopy of Norway spruce planted or sown seedlings of European beech?

Ammer, C., Mosandl, R. — 2007-09-27

Direct seeding and planting of European beech (Fagus sylvatica L.) are two common techniques for the conversion of pure Norway spruce (Picea abies [L.] Karst.) stands into mixed stands. This study tested whether the growth of sown beech seedlings differs from that of planted seedlings of two stock types. Therefore at two experimental sites repeated measurements were made of height, stem and first order branch diameter on sown and planted seedlings over a period of nine years. The results showed that the growth responses of planted and sown seedlings to the environmental conditions below the canopy of overstorey Norway spruce were rather similar. No differences between planted and sown seedlings were found in their diameter and their estimated aboveground dry weight. For all three batches the ratio between the estimated branch dry weight and the estimated main stem dry weight (branch-shoot-ratio (BSR)) was increased with age. Due to intraspecific competition BSR was lowest for the sown seedlings irrespective of their age. Differences in growth dynamics between planted and sown seedlings were found. For example, differences in the height or the estimated aboveground woody dry weight between sown and planted seedlings at a given age were not constant. Height, diameter and estimated dry mass of the seedlings in relation to age could be modelled precisely by a second-order polynomial function in the hitherto studied period.

Effects of shade on growth and mortality of maple (Acer pseudoplatanus), ash (Fraxinus excelsior) and beech (Fagus sylvatica) saplings

Petritan, A. M., Von Lupke, B., Petritan, I. C. — 2007-09-27

We compared shade tolerance of maple, ash and beech in the sapling stage from two sites with rich soils differing in water supply, growing in dense thickets underneath a beech shelterwood of varying canopy densities. Shade tolerance was described by two components: mortality in shade and height growth in high light. At low light, beech showed the least mortality, maple the highest and ash in between on both sites. The decline with increasing light was steepest in beech and more gradual with ash and maple. At ~15 per cent above canopy light, all three species approached zero mortality. Beech as the most shade-tolerant species had the highest survival rate under low light and the least length growth rate under high light (>17 per cent). Ash had a lower survival rate at low light than beech and a highest growth rate at high light. Maple showed a bit weaker trade-off with the lowest survival rate but a growth rate inferior to ash. On the better water-supplied site, height growth was significantly superior in all three species only under high light. On the basis of these results, silvicultural conclusions are drawn with respect to appropriate light levels and cutting types.

The north-eastern distribution range of European beech a review

Bolte, A., Czajkowski, T., Kompa, T. — 2007-09-27

Today, European beech (Fagus sylvatica L.) seems to be a markedly successful tree species in the north-east of its distribution range. The distribution area may be larger than originally assumed; past forest management is probably the main cause of the contraction in the postglacial European beech range. Numerous attempts consistently have failed to locate a distinct distribution edge for European beech. Therefore, we define northern and eastern Poland and the southern regions of the Baltic States as margins of European beech distribution. Ecophysiological approaches have identified the drought constraints for European beech in terms of (1) the critical limit for xylem cavitation and loss of hydraulic conductivity, reached at a shoot water potential of –1.9 MPa, and (2) a reduction in gross primary production and total ecosystem respiration when relative extractable soil water reaches 40 and 20 per cent, respectively. However, it is difficult to correlate European beech distribution margins with single macro-climatic factors. Moreover, the adaptation of European beech populations and provenances to drought and frost varies. The phenotypic plasticity and evolutionary adaptability of European beech appear to be underestimated. These characteristics may counteract a further contraction of the European beech range arising from climate change in the future.

Gap regeneration patterns in relationship to light heterogeneity in two old-growth beech fir forest reserves in South East Europe

Dusan, R., Stjepan, M., Igor, A., Jurij, D. — 2007-09-27

Gap regeneration in two old-growth forest reserves in Slovenia (Rajhenavski Rog) and Croatia (Corkova Uvala) was analysed in relation to within gap light heterogeneity. Both reserves were located in the Dinaric mountain range in south-central Europe and were dominated by beech (Fagus sylvatica L.) – silver fir (Abies alba Mill.) forest communities with similar growing conditions. In total, the two largest gaps (700–2000 m²) in each reserve were included in the study (n = 4), plus a further four gaps in Rajhenavski Rog and three in Corkova Uvala (200–500 m²). All the gaps were ~10 years old and originated from one or two successive events, mostly due to a combination of fungi attack and windthrow. Consequently, all gaps had complex geometry and were covered by a well-developed regeneration layer. Each gap was mapped, followed by establishment of a N–S oriented 5 x 5 m grid within and around the area of the canopy opening. At the grid intersections 773, 1.5 x 1.5 m plots were established. On each plot, the coverage of tree regeneration and ground vegetation, seedling density in different height classes and browsing damage were recorded. In addition, the total stretched length and last growing season increment of the leading stem was measured on selected seedlings in each plot. Relative diffuse and direct radiation were estimated using digital hemispherical photographs. All plots were classified into four microsites according to direct and diffuse radiation levels, and microsites were tested for differences in regeneration height and density. While there was more woody regeneration and an almost fivefold higher (6.2 vs 1.3 m^–2) average total regeneration density in Rajhenavski Rog, mainly due to a high (5.5 vs 0.6 m^–2) density of beech, there was more ground vegetation and a higher density of silver fir seedlings in Corkova Uvala. The within-gap regeneration patterns proved to be similar in both forest reserves and showed that 1-year-old seedlings of beech and silver fir and small beech seedlings preferably recruit on microsites under closed canopy or close to gap edges with lower levels of direct and diffuse radiation. There was no significant difference in density of large-beech seedlings among the microsites, yet height and height increment were higher on microsites receiving the highest levels of direct and diffuse radiation. Within-gap heterogeneity in light conditions appears to significantly influence general patterns of beech and silver fir regeneration, while the differences in total average density, regeneration and ground vegetation abundance and spatial distribution cannot solely be explained by light. Since climate, parent material, soil, exposition, relief and stand conditions were very similar between both reserves, it appears that these differences are a result of different densities of large herbivores, which are reported to be much higher in Rajhenavski Rog. This was also confirmed in our research, as much more browsing damage was found in Rajhenavski Rog compared with Corkova Uvala. Implications for silvicultural practice are outlined.

Constrained map-based inventory estimation

Van Deusen, P. C., Roesch, F. A. — 2007-09-27

A region can conceptually be tessellated into polygons at different scales or resolutions. Likewise, samples can be taken from the region to determine the value of a polygon variable for each scale. Sampled polygons can be used to estimate values for other polygons at the same scale. However, estimates should be compatible across the different scales. Estimates are often required for zones within a region, where a region might be a state and counties could be the zones. A method is developed for estimating high-resolution (pixel) values that are constrained to be compatible with results for lower resolution values. The high-resolution values are constrained to sum to totals for zones within a region, where the totals are being simultaneously estimated from measurements taken at a different scale. If the zone estimates are unbiased, then the pixel-based estimates for the zone will be less biased. Sums of pixels in arbitrary polygons are thereby constrained to approach unbiased estimates. Approximate variance estimators are developed for the summed pixel estimates. Two example applications are provided. The first example is based on simulated data and verifies that the proposed variance estimators give reasonable results. The second example estimates the volume in a circle around a possible mill site in North Carolina. This example uses publicly available US Forest Service inventory data and simulated inventory data that the mill would provide.

Estimates of decay rates of components of coarse woody debris in thinned Sitka spruce forests

Tobin, B., Black, K., McGurdy, L., Nieuwenhuis, M. — 2007-09-27

The requirement for reporting of changes in forest carbon (C) stocks under the United Nations Framework Convention on Climate Change and to the Kyoto Protocol has underlined a need for information on the deadwood pool. As the coarse woody debris (CWD) component of the deadwood pool falls outside the remit of most C-stock change models used in reporting processes, this study set out to develop a methodology to evaluate the C-content of CWD stocks in the main Irish forest type (Sitka spruce plantations). In order to calculate CWD stocks without information on thinning/harvesting dates, the development of a system of classifying CWD into five decay classes (DCs) is presented. DCs were based mainly on visual characteristics linked to the degree of decomposition. Samples were taken from thinned first rotation plantations to establish the basic density loss associated with each DC. Stocks, including logs, stumps and roots, ranged from 5.1 to 13.1 t C ha^–¹ in forests aged 30 and 33 years, respectively. Decay rates for both stump and log material were 0.0592 and 0.0466 g cm^–³ a^–¹, respectively.

The threat of the ambrosia beetle Megaplatypus mutatus (Chapuis) (=Platypus mutatus Chapuis) to world poplar resources

Alfaro, R. I., Humble, L. M., Gonzalez, P., Villaverde, R., Allegro, G. — 2007-09-27

We describe the life cycle of Megaplatypus mutatus (Chapuis) (=Platypus mutatus) and the damage it causes to poplar resources in Argentina. This insect, native to the subtropical and tropical areas of South America, has extended its range into temperate regions, reaching as far south as Neuquén in Argentinean Patagonia. The damage is caused by the adult insects, which bore large gallery systems into living poplars (Populus spp.), willows (Salix spp.) and many other broadleaf species, including important fruit trees species such as apples (Malus spp.), walnuts (Juglans spp.) and avocados (Persea spp.). The galleries degrade the lumber and weaken the tree stems, which often then break during windstorms. A recent introduction of M. mutatus to Italy demonstrates that this insect can be transported long distances between countries, and therefore presents a threat worldwide—particularly to poplar cultivation. We review the taxonomic nomenclature for this pest, provide a summary of the life cycle, hosts and damage and summarize actions taken to reduce the risk of introduction of M. mutatus to Canada.

The effect of roots and litter of Calamagrostis canadensis on root sucker regeneration of Populus tremuloides

Landhausser, S. M., Mulak, T. L., Lieffers, V. J. — 2007-09-27

Marsh reed grass (Calamagrostis canadensis (Michx.) Beauv.) is a common, highly competitive grass native to the boreal mixedwood forest. This grass increases in abundance after clear-cut logging but little is known about its effects on trembling aspen (Populus tremuloides Michx.) sucker regeneration. The effects of Calamagrostis sod and its litter on aspen regeneration were studied in two separate greenhouse studies. Calamagrostis sod did not affect the initiation of suckers, but resulted in 30 per cent fewer suckers emerging above the soil that were smaller and had 40 per cent less leaf area. Calamagrostis litter had little effect on the initiation and number of emerged suckers; however, it delayed emergence by 10 days. The physical barrier by roots and litter of Calamagrostis reduced or delayed the expansion of suckers and therefore prolonged their dependence on root reserves. By the time the suckers reached the surface, they had to compete for light with Calamagrostis shoots that had emerged a week earlier. This, coupled with low soil temperatures associated with Calamagrostis in other experiments, will significantly reduce the number and growth of suckers. Any reduction and delay in sucker emergence will decrease aspen regeneration and productivity since the growing season in the boreal forest region is short.