Recovery rate and quality of rotary peeled veneer from 30-year-old Pinus taeda L. logs

??Context

In the construction sector, wood is facing competition with other materials such as concrete, steel or plastics. Therefore, there is a need for more efficiency in the forest–wood chain by improving silvicutural management and wood processing technologies.

??Aims

The objective of the study is to analyse the influence of log diameter and quality to recovery rate, veneer quality and economic benefit.

??Methods

The trees used in the study came from a 30-year-old Pinus taeda L. thinning trial in Southern Brazil. In total, 57 logs (20.7 to 67.0 cm) were peeled following the standard industrial processing methods of the plywood mill.

??Results

Average recovery rate was 54 % ranging from 35 to 72.6 %, with a linear trend (R ²?=?0.48) of increasing recovery with an increment on the log small-end diameter. Results show that the gap between theoretically possible and real recovery was lower in the logs with bigger diameters, indicating their higher efficiency in industrial processing. Moreover, the economic analysis detected that the current prices for log assortments reflect only the industrial potential of low-quality pruned logs. An optimised pruning strategy would result in higher industrial efficiency, which would allow higher log prices.

??Conclusion

The results indicate that the recovery rate of bigger logs is higher in terms of volume of peeled veneer. The quality and therefore the value obtained from each log were negatively influenced by inadequate pruning strategies. Management of pines for higher value utilisation requires optimized thinning and pruning strategies in order to meet high growth rates and proportionally bigger dimensions of clear wood.     

Optimal management of larch (<Emphasis Type="Italic">Larix olgensis</Emphasis> A. Henry) plantations in Northeast China when timber production and carbon stock are considered

? Key message

The optimal management of larch (Larix olgensis) plantations in Northeast China consisted of 2 or 3 thinnings and a rotation length of 55–61 years when economic profitability, wood production, and carbon sequestration were simultaneously maximized. Wood production ranged from 5.4 to 11.7 m³ ha^?1 a^?1, depending on site quality.

? Context

L. olgensis is an important tree species in the northeast forest region of China, playing a significant role in the establishment of fast-growing and high-yielding plantation forests in China. However, the management of these plantations has not been optimized in previous studies.

? Aims

The objective of the study was to find the optimal combinations of thinning times, thinning types, and rotation length for L. olgensis stands when both timber production and carbon stock are considered.

? Methods

First, a growth and yield model was developed to simulate the dynamics of larch plantations. Then, the models were linked with the Hooke and Jeeves optimization algorithm to optimize forest management for two commonly used planting densities and three site qualities.

? Results

Two thinnings were found to be suitable for larch plantations when the stand density at 10 years was 2125 trees/ha (corresponding to a planting density of 2500 trees/ha) whereas three thinnings were recommended when the density at 10 years was 2800 trees/ha (planting density of 3300 trees/ha). When the stand density was 2800 trees/ha, the optimal rotation length was 61, 58, and 55 years for site indices (SI) 12, 16, and 20 m (dominant height at 30 years), respectively. The mean annual wood production was 5.4 m³ ha^?1 for SI 12, 8.2 m³ ha^?1 for SI 16, and 11.7 m³ ha^?1 for SI 20. The results were nearly the same for the lower initial stand density. The better the site quality of the stand, the earlier the thinnings were conducted.

? Conclusion

In multifunctional forestry, optimal rotation lengths of larch plantations were 10–20 years longer than advised in the current silvicultural recommendations for Northeast China.

     

Thinning has a positive effect on growth dynamics and growth–climate relationships in Aleppo pine (Pinus halepensis) trees of different crown classes

? Context

Modification of stand density by thinning may buffer the response of tree growth and vigor to changes in climate by enhancing soil water availability.

? Aims

We tested the impact of thinning intensity on cambial growth of Aleppo pine (Pinus halepensis L.) under semi-arid, Mediterranean conditions.

? Methods

A multiple thinning experiment was established on an Aleppo pine plantation in Spain. We analysed the stem growth dynamics of two different crown classes under four different thinning intensities (15 %, 30 %, and 45 % removal of the basal area) for 2 years, based on biweekly band dendrometer recordings. Local relative extractable soil water was derived from the use of a water balance model Biljou© (available at https://appgeodb.nancy.inra.fr/biljou/) and used as an explanatory variable.

? Results

Radial growth was mainly controlled by soil water availability during the growing season, and differed by crown class. The growth rates of dominant trees were significantly higher than the growth rates of suppressed trees. Removal of 30 % and 45 % of the initial basal area produced a growth release in both dominant and suppressed trees that did not occur under less intense thinning treatments.

? Conclusions

Soil water availability was the main driver of radial growth during the growing season. Forest management confirmed its value for ameliorating the effects of water limitations on individual tree growth. These results may help managers understand how altering stand density will differentially affect diameter growth responses of Aleppo pine to short-term climatic fluctuations, promoting forests that are resilient to future climatic conditions.     

Intra- and interspecific competition differently influence growth and stem quality of young oaks (Quercus robur L. and Quercus petraea (Mattuschka) Liebl.)

Context

Cluster planting has become a conventional establishment method for oaks in Central Europe, where the spacing of seedlings within clusters varies between ‘nests’ (0.2?×?0.2 m) and ‘groups’ (1?×?1 m). Although the space between clusters is expected to fill with voluntary regeneration, its competitive effect on oak growth and quality had not been studied yet.

Aims

The aim of the study was to analyse the effects of inter- and intraspecific interactions on growth and quality of oaks grown in cluster plantings by quantifying the influence of neighbouring trees. In addition, we analysed whether the spatial position of oaks within groups (inner section or periphery) influenced their quality development.

Methods

Using Hegyi’s competition index, the influence of competition from intra- and interspecific trees from early, mid- and late-successional species, on diameter, height, slenderness and quality (length of branch-free bole) of 10- to 26-year-old oaks grown in cluster planting stands was quantified at seven sites in Baden-Württemberg and Hessen, Germany.

Results

In general, mid- and late-successional trees exerted a stronger competitive influence on growth of target oaks in clusters than the conspecific oaks and pioneer tree species. Oak quality development benefited from intraspecific competition, but self-pruning was not further promoted through additional interspecific competition. Within groups, inner oaks had a higher probability of developing into potential future crop trees than outer oaks.

Conclusion

Our study showed that intra- and interspecific competition had different effects on target oak trees and that these effect differed between nest and group plantings. The development of naturally regenerated and planted trainer trees in group plantings should be monitored carefully and if necessary be controlled through thinning or pollarding.     

Cause–effect relationship among morphological adaptations,growth, and gas exchange response of pedunculate oak seedlings to waterlogging

Context

In response to waterlogging, pedunculate oak is known to develop adventitious roots and hypertrophied lenticels. However, to date, a link between these adaptations and the ability to maintain net CO₂ assimilation rates and growth has not been demonstrated.

Aims

The aim of this study was to explore the cause–effect relationship between the ability to form morphological adaptations (hypertrophied lenticels and adventitious roots) and the capacity to maintain high assimilation rate and growth.

Methods

The occurrence of morphological adaptations and the parameters of photosynthesis were monitored over 20 days of waterlogging in 5-week-old pedunculate oak seedlings presenting similar morphological development.

Results

Based on the development or not of morphological adaptations, the following three categories of responses were identified: development of hypertrophied lenticels and adventitious roots, development of hypertrophied lenticels alone, and the lack of development of adaptive structures. These categories, ranked in the order given, corresponded to decreasing levels of initial net CO₂ assimilation rate growth and photosynthesis parameters observed during waterlogging.

Conclusion

We observed a two-way cause–effect relationship between the capacity to form adaptive structures and the assimilation rate. Indeed, the initial assimilation rate determined the occurrence of hypertrophied lenticels and growth during stress, and then the development of morphological adaptations enhanced the ability to maintain assimilation levels during the stress.     

Tree species exhibit complex patterns of distribution in bottomland hardwood forests

?Context

Understanding tree interactions requires an insight into their spatial distribution.

?Aims

We looked for presence and extent of tree intraspecific spatial point pattern (random, aggregated, or overdispersed) and interspecific spatial point pattern (independent, aggregated, or segregated).

?Methods

We established twelve 0.64-ha plots in natural bottomland hardwood stands in the southeastern USA.

?Results

Spatial point pattern analyses (Ripley’s K, L, and L ₁₂) indicated that, when species were combined, trees were frequently aggregated and less commonly overdispersed. Plots with larger trees were more likely to exhibit overdispersion, confirming a shift to this pattern as trees grow. The intraspecific pattern of cherrybark oak and water oak was either aggregated or random. Sweetgum was aggregated on all plots and always at smaller distances (less than 5 m) than the two oak species. Intraspecific overdispersion was very rare. Interspecific segregation among the two oak species was more commonly observed (six plots) than aggregation (one plot). Cherrybark oak and sweetgum were segregated at some scale on seven of the 12 plots and aggregated on only two plots.

?Conclusion

The results from the analyses suggest that strong interspecific competition may result in segregation of trees from different species, while weaker intraspecific competition may lead to aggregations of conspecifics.     

Effects of pre-commercial thinning on growth and reproduction in post-fire regeneration of Pinus halepensis Mill

Context

Excessive recruitment in post-fire regeneration of Pinus halepensis can require pre-commercial thinning. The 1994 Moratalla fire (Spain) and the thinning applied there since 2004 provided good conditions for testing pre-commercial thinning effectiveness.

Aims

To analyse pre-commercial thinning effects on tree size, reproductive potential, stem biomass and annual growth in 15-year-old saplings.

Methods

Twenty nine circular plots (5 m radius) were established based on (1) years since thinning and (2) aspect. Non-thinned plots were included as controls. Sapling variables were measured and pine cones were counted and classified according to maturity. Three saplings per plot were felled, five sample disks were extracted from each and tree rings were analysed with Windendro® software.

Results

Sapling size, annual growth and stem biomass were higher in thinned plots than in control plots 2–4 years after thinning. Annual growth declined five years after thinning. Cone counts were higher 2–5 years after thinning, depending on the cone type. Aspect influenced some variables.

Conclusion

Thinning accelerated stand maturity but positive effects were indiscernible until 2–5 years later. Serotinous cones, which are fundamental to regeneration after fire, increased in number after 5 years. The effects of aspect were inconclusive due to interactions with years since thinning.     

Understory structure and function following release from cattle grazing and overstory thinning in Mediterranean conifer plantations

Key message

Cattle grazing and overstory cover restrict understory growth and interact in shaping the understory community structure in Mediterranean conifer plantations.

Context

Understanding how silvicultural manipulations drive understory structure and function in Mediterranean pine plantations is essential for their multifunctional management.

Aims

This paper aims to study the interactive effects of cattle grazing and overstory thinning on understory structure and function.

Methods

Ten plots (0.25 ha) were selected in East Mediterranean mature Pinus brutia plantation (rainfall = 600 mm year^?1) representing thinned (≈100 trees ha^?1, leaf area index (LAI) ≈ 1.6) and non-thinned (≈230 trees ha^?1, LAI ≈ 3.5) areas. Two subplots (100 m²) within each plot were fenced in 2000 and 2006 while a third one remained grazed. Understory growth and species composition were measured in 2010.

Results

Thinning and grazing exclusion both positively influenced woody growth with their combined effect during 10 years leading to 20-fold increase in vegetation volume. An increase (15-fold) in herbaceous biomass was recorded 4 years after grazing exclusion but disappeared 10 years after exclusion due to increased woody cover. Species richness was not influenced by grazing but was positively affected by thinning. Understory composition was affected by grazing × thinning interaction with herbaceous ephemerals and short woody species being more frequent in grazed, thinned areas while larger woody species were more associated with ungrazed, non-thinned areas.

Conclusion

Grazing impacts on forest understories depend on overstory cover. We propose variable grazing-thinning combinations to meet multiple management objectives.

     

Variation in log quality and prediction of sawing yield in oak wood (Quercus robur)

Context

The commercial feasibility of sawmilling depends on the expected volume and value of sawn planks. Models that predict the volume of sawn timber of a particular quality and produced from logs of known characteristics are therefore very useful.

Aims

The objectives were to study variation in sawing yield and to obtain models that predict lumber volume and grade recovery on the basis of easy-to-measure predictor variables of saw logs.

Methods

Forty-six oak trees growing in Galicia (NW Spain) were felled and cut into logs. The logs were visually graded and sawn mainly into quartersawn planks, which were dried, planed and visually graded for structural purposes.

Results

The total volumetric sawing yield was 47.6 %. The sawing yield for planks of structural dimensions (cross-section, 70?×?120 or 70?×?170 mm) was 43.4 %, but decreased to 8.4 % for structural sized and quality grade beams because of wane and biotic damage in many pieces. Log grade did not significantly affect sawing yield in the sample analysed, despite the wide range of diameter over bark at the smallest end in the sampled logs (22–77 cm). The sawing pattern affected total sawing yield (F?=?4.913; p value?=?0.001) and the sawing yield for structural planks (F?=?6.142; p value?=?0.0002); radial sawing with one cut and live sawing of half logs provided the highest yields. Three models were proposed for estimating sawn volume in timber products, with the small-end log diameter over bark as the predictor variable and R _adj ² between 0.31 and 0.78 (p value?<?0.01).

Conclusion

For the purpose of producing oak timber destined for structural use, the presence of bark and sapwood in planks must be reduced in the sawing process; this would decrease the total lumber recovery but increase the timber value yield. Air drying must be accelerated to reduce biotic damage in sawn planks. Geometric mean diameter over bark at the smallest end (d) outperforms other measures as a predictor variable for total or structural sawn timber volume.     

Oak powdery mildew changes growth patterns in its host tree: host tolerance response and potential manipulation of host physiology by the parasite

Context

Parasites can induce strong effects on their host’s growth, not only as a result of host resource exploitation (growth loss) but also with a potential adaptive value for host (tolerance response) and themselves (increased transmission).

Aims

We assessed these three types of phenotypic changes in oak seedlings infected by powdery mildew.

Methods

A manipulative field experiment with three levels of parasite inoculum was designed in order to tease apart infection from genetic effects on oak growth. Seedlings were monitored during 3 years for height growth, phenology and infection.

Results

Powdery mildew infection induced both significant growth loss and qualitative changes in plant architecture. The most striking and unexpected change was increased growth polycyclism in infected seedlings. This benefitted both the host as a form of compensation for infection-caused height loss, and the pathogen, by increasing sporulation.

Conclusion

The study highlights the effect of parasites in the expression of plant phenotypic traits, such as phenology and ultimately tree architecture. Both host tolerance and parasitic manipulation may be involved in the observed changes in growth patterns. These results suggest a complex interplay between development and defence in trees and emphasize the need to better assess tolerance mechanisms when considering the defence strategies of trees against pathogens.     

Optimal seed water content and storage temperature for preservation of Populus nigra L. germplasm

Context

Black poplar (Populus nigra L.) is an alluvial forest tree species whose genetic pool is decreasing in Europe. Poplar trees produce short-lived seeds that do not store well.

Aim

The feasibility of seed storage in conventional and cryogenic conditions after their desiccation from water content (WC) of 0.15 to 0.07 g H₂O g^?1 dry mass (g g^?1) was investigated.

Methods

Seed germinability was evaluated (seeds with a radicle and green cotyledons were counted) after storage of seeds for a period of 3 to 24 months at different temperatures: 20°, 10°, 3°, ?3°, ?10°, ?20° or ?196°C.

Results

Seeds desiccated to a 0.07 g g^?1 WC can be stored successfully at ?10 °C and ?20 °C for at least 2 years. A significant decrease in germination was observed only after 12 months of seed storage (WC 0.15 g g^?1) at temperatures above 0 °C. We demonstrated that both fresh (0.15 g g^?1 WC) and desiccated (0.07 g g^?1 WC) seeds can be preserved at ?196 °C for at least 2 years.

Conclusions

Seed storage temperature and time of storage were statistically significant factors affecting seed storability. The presented data provide a foundation for the successful gene banking of P. nigra seeds.     

Coastal and interior Douglas-fir provenances differ in growth performance and response to drought episodes at adult age

Context

Since the 2003 drought and heat wave, Douglas-fir dieback has been reported in France in trees older than 30 years. Consequently, it is questioned whether selected Douglas-fir provenances are suited to the frequent and severe drought events which are forecast due to climate change.

Aims

Our objective was to contribute to the screening of variability in productivity and growth response to soil-water deficit of mature trees from provenances not currently used for plantation in France.

Methods

We sampled 22 provenances, including coastal and interior Douglas-fir, covering a wide part of its natural distribution, from Oregon to California for coastal provenances and from British Columbia to New Mexico for interior provenances. These provenances were planted at the mid 1970s in two provenance trials located in the south-west area of France. Variability of productivity, of wood density, and of radial growth in response to drought episodes among provenances was quantified and related to soil-water deficit computed by daily water balance calculations.

Results

Whatever the provenance, annual radial growth is highly dependent on local soil-water deficit (Felines R ² = 0.57, Le Treps R² = 0.49). Radial growth and wood properties exhibit large differences between provenances at 30 years old. Variability between provenances for all wood characteristics studied is mainly structured geographically. Coastal provenances perform best for productivity at 30 years old (619 cm²?±?59), and exhibit a small growth reduction in 2004, the second successive year of drought (?10.7 %?±?3.8). Surprisingly, the southern interior provenances from the driest environments in the natural range show a large growth reduction in 2004 (?30.5 %?±?5.2).

Conclusions

The provenances tested exhibited significant differences in growth performance and growth reduction induced by the soil-water deficit. The approach coupling retrospective analysis of radial growth on mature trees and water balance modelling is relevant for evaluating provenance adaptation to more frequent or severe drought episodes.     

Adventitious sprouting of Pinus leiophylla in response to salt stress

Context

Although adventitious shoots are produced in many tree species in response to injury, little is known about the effects of salinity on sprouting.

Aims

The main objective was to examine the sprouting capacity of Pinus leiophylla seedlings in relation to injury and physiological changes induced by NaCl.

Methods

Seedlings were grown in controlled-environment growth rooms and treated with 0, 100, 150, and 200 mM NaCl. Numbers of adventitious shoots were recorded and growth and physiological parameters measured after 64 days of treatments and following a 30-day recovery period.

Results

NaCl treatments triggered sprouting of adventitious shoots, mainly in the lower parts of the stems. However, fewer sprouts were induced by 200 mM NaCl compared with the lower concentration treatments. These changes were accompanied by needle necrosis, decreased chlorophyll concentrations, seedling dry mass, and stem diameter. Stomatal conductance, net photosynthesis, and root hydraulic conductance decreased with increasing NaCl concentrations and did not return to the control levels after 30 days of stress relief.

Conclusions

Pinus leiophylla has the regeneration potential when exposed to salinity. However, very high salt concentrations induce severe physiological impairments and, consequently, a decrease of this regeneration potential.     

Patterns of mass,carbon and nitrogen in coarse woody debris in five natural forests in southern China

? Context

Coarse woody debris (CWD, ≥10 cm in diameter) is an important structural and functional component of forests. There are few studies that have estimated the mass and carbon (C) and nitrogen (N) stocks of CWD in subtropical forests. Evergreen broad-leaved forests are distributed widely in subtropical zones in China.

? Aims

This study aimed to evaluate the pools of mass, C and N in CWD in five natural forests of Altingia gracilipes Hemsl., Tsoongiodendron odorum Chun, Castanopsis carlesii (Hemsl.) Hayata, Cinnamomum chekiangense Nakai and Castanopsis fabri Hance in southern China.

? Methods

The mass of CWD was determined using the fixed-area plot method. All types of CWD (logs, snags, stumps and large branches) within the plot were measured. The species, length, diameter and decay class of each piece of CWD were recorded. The C and N pools of CWD were calculated by multiplying the concentrations of C and N by the estimated mass in each forest and decay category.

? Results

Total mass of CWD varied from 16.75 Mg ha^?1 in the C. fabri forest to 40.60 Mg ha^?1 in the A. gracilipes forest; of this CWD, the log contribution ranged from 54.75 to 94.86 %. The largest CWD (≥60 cm diameter) was found only in the A. gracilipes forest. CWD in the 40–60 cm size class represented above 65 % of total mass, while most of CWD accumulations in the C. carlesii, C. chekiangense and C. fabri forests were composed of pieces with diameter less than 40 cm. The A. gracilipes, T. odorum, C. carlesii and C. chekiangense forests contained the full decay classes (from 1 to 5 classes) of CWD. In the C. fabri forest, the CWD in decay classes 2–3 accounted for about 90 % of the total CWD mass. Increasing N concentrations and decreasing densities, C concentrations, and C:N ratios were found with stage of decay. Linear regression showed a strong correlation between the density and C:N ratio (R ²?=?0.821). CWD C-stock ranged from 7.62 to 17.74 Mg ha^?1, while the N stock varied from 85.05 to 204.49 kg ha^?1. The highest overall pools of C and N in CWD were noted in the A. gracilipes forest.

? Conclusion

Differences among five forests can be attributed mainly to characteristics of the tree species. It is very important to preserve the current natural evergreen broad-leaved forest and maintain the structural and functional integrity of CWD.     

Multi-coefficient goal programming in thinning schedules to increase carbon sequestration and improve forest structure

Context

Current decision analysis techniques are ineffective for planning thinning operation to improve the forest structure.

Aims

The purpose of this study is to use multi-coefficient goal programming (GP) to plan a thinning schedule that allows more carbon sequestration and diverse forest structure.

Methods

A multi-coefficient GP is applied to plan a thinning schedule for a 2,633-ha plantation forest.

Results

This technique efficiently fine-tunes the thinning schedule to obtain 420,500 tons of carbon sequestration which was a little higher than the result by a multi-segment goal programming (MSGP). Moreover, a fixed-ratio multi-coefficient GP is applied to efficiently generate mosaic of thinned areas with various thinning intensities. Although the captured carbon by a fixed-ratio multi-coefficient GP is lower, the thinned areas can provide various habitats for forest life with multiform contrasting edges.

Conclusion

The use of a multi-coefficient GP allows practicable planning of better thinning alternatives to increase carbon sequestration and forest structure.     

Impact of management on nutrients,carbon, and energy in aboveground biomass components of mid-rotation loblolly pine (Pinus taeda L.) plantations

Context

To sustainably manage loblolly pine plantations for bioenergy and carbon sequestration, accurate information is required on the relationships between management regimes and energy, carbon, and nutrient export.

Aims

The effects of cultural intensity and planting density were investigated with respect to energy, carbon, and essential nutrients in aboveground biomass of mid-rotation loblolly pine plantations, and the effects of harvesting scenarios on export of nutrients were tested.

Methods

Destructive biomass sampling of a 12 years-old loblolly pine culture/density experiment, and analysis of variance were used to assess the effects of cultural intensity (operational vs. intensive) and six planting densities ranging from 741 to 4,448 trees ha^?1. Two harvesting scenarios (stem-only vs. whole-tree harvesting) were assessed in terms of energy, carbon, and nutrient export.

Results

The concentrations of energy, carbon, and nutrients varied significantly among stem wood, bark, branch, and foliage components. Cultural intensity and planting density did not significantly affect these concentrations. Differences in energy, carbon and nutrient contents among treatments were mainly mediated by changes in total biomass. Nutrient contents were affected by either cultural intensity or planting density, or both. Stem-only harvesting removed 71–79 % of aboveground energy and carbon, 29–45 % of N, 28–44 % of P, 44–57 % of K, 51–65 % of Ca, and 50–61 % of Mg.

Conclusions

Stem-only harvesting would be preferred to whole-tree harvesting, from a site nutrient conservation perspective.     

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.     

European oak powdery mildew: impact on trees,effects of environmental factors,and potential effects of climate change

? Context

Powdery mildew is one of the most common diseases of oaks in Europe. After alarming reports in the beginning of the twentieth century following the presumed introduction of the invasive fungus, the disease has become familiar to foresters. However, its impact may vary greatly according to intrinsic and extrinsic factors.

? Aims

We aimed at providing updated and synthesised information on the impact of powdery mildew on oak and on the effects of environment on disease.

? Methods

A comprehensive literature review was performed, including old reports of the early epidemics to more recent data.

? Results

Tree growth patterns are of critical importance to explain the severity of the disease and the differences between juvenile and mature trees. A critical element, especially for infection of mature trees, is the availability of spores during the production of the first leaf flush. High disease impact is often related to modified growth patterns, either by environmental factors (insects or frost) or silvicultural practices (e.g., coppicing).

? Conclusion

Powdery mildew can have important impacts in natural oak regenerations and a significant role in decline of mature trees. Climate change might influence the disease severity mainly by altering the host pathogen phenological synchrony. Process-based models are required for reliable predictions.     

Variations of wood basic density with tree age and social classes in the axial direction within Pinus massoniana stems in Southern China

Context

Reliable estimates of wood density (WD) within individual trees could maximize the value of Pinus massoniana for specific end-use.

Aim

We examined and quantified the axial patterns of WD in trees with different social status in the stands.

Methods

Wood disks were sampled at the bottom, breast height, and middle of each 1-m sections from 108 stems, harvesting from three social classes in subtropical forests. A mixed-effects model was designed to quantify axial variation.

Results

The WD at different height was significantly different from the whole-stem WD (WWD) except the relative height of 0.1. An overall decrease of 133.8 kg m^?3 in WD was found from stem base to top. WD was significantly influenced by relative heights, tree age, and social class. WD of each relative height in mature trees was significantly higher than that of younger trees. Tree social class can affect WD development in the axial direction at age classes 2 and 3. Combining the fixed plus random effects, the final model explained 91 % of the observed variation in WD.

Conclusion

The WD development patterns in the axial direction vary considerably among tree age, diameter at breast height, and social class. To distinguish and supply timber for specific end-uses, we should use the axial variation in disk WD (DWD) instead of WWD directly. The accurate predictions of WD provided by the model could be used to optimally classify logs into different product classes and maximize economic benefits. We can use DWD at the relative height of 0.1 instead of WWD of a single tree.