Green Crown Research Articles

Habitat preferences of breeding Eurasian Sparrowhawks Accipiter nisus in Central Europe

ABSTRACT Capsule A description of habitats used for breeding by Eurasian Sparrowhawks, along with variables affecting their breeding habitat selection. Aims To describe the habitat preferences of breeding Eurasian Sparrowhawks, and to identify variables affecting their breeding habitat selection at different spatial scales, in a rural area of Central Europe (Czech Republic). Methods Eurasian Sparrowhawk nests were found and the habitat characteristics of breeding sites were measured at three spatial scales, and then compared with randomly selected locations. Results The nests were regularly distributed within the forests of the study area, avoiding small forest patches. The territories were somewhat associated with dense forest stands of a distinctive structure. All nests were built in coniferous trees, in the lower parts of their green crowns and close to the trunks. In the areas surrounding the nests, we found a greater abundance of some bird (prey) species and a higher diversity of birds, compared to the random areas. Conclusion The Eurasian Sparrowhawks preferred to breed in forests with a specific structure that provided sufficient concealment and access to their nests, and they located their breeding territories as far from each other as possible. The birds also seemed to prefer breeding in localities with a greater food supply. The variables affecting Eurasian Sparrowhawk breeding habitat selection may include intraspecific competition, size and structure of available forests, availability of coniferous trees for nest placement, and the composition of the food supply in the vicinity of their nests.

Effects of varieties and different micronutrients on growth and yield of broccoli (Brassica oleracea var. italica)

An experiment was conducted at the Horticulture Farm of Bangladesh Agricultural University, Mymensingh, during the period of November 2021 to February 2022. The experiment consisted of two factors, such as factor A: three varieties of broccoli i.e. V1: Early You, V2: Barbara, V3: Green Crown and factor B: four levels of micronutrients i.e. T0: control, T1: Boron @ 3 kg/ha, T2: Zinc @ 2 kg/ha, T3: Boron + Zinc @ (3+2) kg/ha. The two-factor experiment was laid out in Randomized Complete Block Design with three replications. Variety and micronutrients influenced significantly on most of the parameters under the study. In case of variety, the highest curd yield (13.35 t/ha) was found from V3 (Green Crown) and the lowest curd yield (11.12 t/ha) was found from V1 (Early You). V2 (Barbara) showed higher dry matter content of broccoli curd, which is 15.72%. On the other hand, V¬1 (Early You) showed lower dry matter content, which is 13.34%. For micronutrients, T3 (Boron +Zinc @3+2 kg/ha) performed the highest in respect of curd yield (19.37 t/ha) and the lowest (6.32 t/ha) was from T0 (control). T3 (Boron+Zinc @3+2kg/ha) showed higher dry matter content (13.01%), whereas T0 (control) showed the least (11.02%). For combined treatment, the highest curd yield (21.61t/ha) was obtained from V3T3 (Green Crown and Boron +Zinc @ 3+2 kg/ha micronutrient dose) and the lowest curd yield (5.23 t/ha) from V0T0 (Early You and control). V2T3 (Boron+ Zinc @3+2 kg/ha with Barbara variety) produced the highest dry matter content of curd, which is 17.34%. On the other hand, the lowest dry matter content of broccoli curd is provided by V1T0 (Early You variety with control) treatment combination which is 12.49%. Therefore, it can be concluded that V3 (Green Crown) along with Boron+Zinc @ 3+2 kg/ha and V2 (Barbara) along with Boron+Zinc @ 3+2 kg/ha were found to be the best in respect of yield and dry matter content of broccoli, respectively, compared to other treatments.

Estimating Tree Health Decline Caused by Ips typographus L. from UAS RGB Images Using a Deep One-Stage Object Detection Neural Network

Various biotic and abiotic stresses are causing decline in forest health globally. Presently, one of the major biotic stress agents in Europe is the European spruce bark beetle (Ips typographus L.) which is increasingly causing widespread tree mortality in northern latitudes as a consequence of the warming climate. Remote sensing using unoccupied aerial systems (UAS) together with evolving machine learning techniques provide a powerful tool for fast-response monitoring of forest health. The aim of this study was to investigate the performance of a deep one-stage object detection neural network in the detection of damage by I. typographus in Norway spruce trees using UAS RGB images. A Scaled-YOLOv4 (You Only Look Once) network was implemented and trained for tree health analysis. Datasets for model training were collected during 2013–2020 from three different areas, using four different RGB cameras, and under varying weather conditions. Different model training options were evaluated, including two different symptom rules, different partitions of the dataset, fine-tuning, and hyperparameter optimization. Our study showed that the network was able to detect and classify spruce trees that had visually separable crown symptoms, but it failed to separate spruce trees with stem symptoms and a green crown from healthy spruce trees. For the best model, the overall F-score was 89%, and the F-scores for the healthy, infested, and dead trees were 90%, 79%, and 98%, respectively. The method adapted well to the diverse dataset, and the processing results with different options were consistent. The results indicated that the proposed method could enable implementation of low-cost tools for management of I. typographus outbreaks.

Effects of Thinning Practice, High Pruning and Slash Management on Crop Tree and Stand Growth in Young Even-Aged Stands of Planted Silver Birch (Betula pendula Roth)

The objective was to quantify the influence of thinning, high pruning and slash management on crop tree and stand growth in young even-aged stands of planted silver birch (Betula pendula Roth). This study was based on two field experiments, aged six and eleven years at initiation and re-measured after six and eight years, respectively. Treatments included the unthinned control, moderate thinning mainly from below (removing 28–33% of standing volume), point thinning to favor 300 trees per ha and with no thinning elsewhere in the plot (removing 16–25%), and heavy thinning leaving 600 evenly distributed potential future crop trees per ha (removing 64–75%). Slash management (extraction or retention) was applied to heavily thinned plots. High pruning removing 30–70% of the green crown was carried out in some plots with point or heavy thinning on 300 or 600 trees per ha, respectively. Stand volume growth increased with increasing pre-treatment mean annual volume increment and decreased with increasing thinning intensity as compared to the unthinned control. LS-means estimates indicated a reduction for moderate thinning by 14%, for point thinning by 12% and for heavy thinning (combined with pruning) by 62%. However, in the youngest experiment, heavy thinning (without pruning) reduced growth by 54%. Combining these results with results from a similar experiment in Canada, the reduction in stand volume growth (RedIv%) depending on thinning removal (RemV%), both expressed as a percentage of the unthinned control, was quantified as RedIv% = −23.67 + 1.16·RemV% (calibration range: 30–83%). For heavy thinning (large quantities of slash), slash extraction resulted in no reduction in stand volume growth as compared to slash retention. The instantaneous numeric reduction in the average stem diameter of the 300 thickest trees per ha (D300) due to thinning was 3.5, 15–21% and 955–11% with moderate, point and heavy thinning, respectively. The subsequent average annual increase in D300 during the observation period was 8.5%, 25 and 18%, respectively. In the youngest experiment, pruning in unthinned plots led to a reduction in the annual increase of D300 by 14%, and heavy thinning in unpruned plots led to an increase by 30%. The growth of pre-selected potential future crop trees increased with increasing thinning intensity. In heavily thinned plots, pruning reduced growth increasingly with increasing pruning severity; LS-means estimates indicated 21% larger growth on stem diameter for unpruned trees and 3% for pruned trees. As an adverse side effect, heavily thinned plots with only 600 trees per ha were at increased risk of windthrow for some years after the thinning intervention. In the oldest experiment, 95–21% of the trees in these plots were damaged by wind.

Field Screening of Seven Cultivars of Cabbage Against Cabbage Butterfly (Pieris brassicae) and Cabbage Aphids (Brevicoryne brassicae) at Gkuleshor, Baitadi, Nepal

Field screening of seven cultivars of cabbage namely: Green Crown, Green Top, Green Coronet, Pioneer, Nepa Round, Copenhagen Market and Golden Acre were carried out against cabbage butterfly (Pieris brassicae) and cabbage aphid (Brevicoryne brassicae) at the research farm of entomology section, Gokuleshwor Agriculture and Animal Science College, Baitadi in RCBD design from October 2017 to February 2018. Five plants were tagged randomly after transplanting in field excluding border plants in each plot. Data were collected for the population dynamics of cabbage butterfly larvae and cabbage aphid on weekly basis. None of the seven cultivars were found resistant to cabbage butterfly and cabbage aphid, however their population density varied on tested cultivars. Cabbage butterfly population was recorded the highest on the cultivar Pioneer (22.88 larvae/plant) and the lowest on the cultivar Copenhagen Market (10.06 larvae/plant), and other cultivars were of intermediate types. Similarly, the population density of aphid ranged from 36.70 to 105.58 aphids/leaf. The highest population density of aphid was recorded on cultivar Green Crown (105.58 aphids/leaf) and the lowest on cultivar Copenhagen Market (39.82 aphids/leaf. From the results, Copenhagen Market proved to be the best against both cabbage butterfly and cabbage aphids.

Towards Tree Green Crown Volume: A Methodological Approach Using Terrestrial Laser Scanning

Crown volume is a tree attribute relevant in a number of contexts, including photosynthesis and matter production, storm resistance, shadowing of lower layers, habitat for various taxa. While commonly the total crown volume is being determined, for example by wrapping a convex hull around the crown, we present here a methodological approach towards assessing the tree green crown volume (TGCVol), the crown volume with a high density of foliage, which we derive by terrestrial laser scanning in a case study of solitary urban trees. Using the RGB information, we removed the hits on stem and branches within the tree crown and used the remaining leaf hits to determine TGCVol from k-means clustering and convex hulls for the resulting green 3D clusters. We derived a tree green crown volume index (TGCVI) relating the green crown volume to the total crown volume. This TGCVI is a measure of how much a crown is “filled with green” and scale-dependent (a function of specifications of the k-means clustering). Our study is a step towards a standardized assessment of tree green crown volume. We do also address a number of remaining methodological challenges.

Effects of early pruning on ring specific gravity in young loblolly pine trees

Juvenile wood is not well suited for use in many forest products. Understanding factors that affect the formation of juvenile and mature wood is important when managing commercially important conifer species. The purpose of this investigation was to determine the contribution of ring age, relative height in the stem, and crown position (within or not within the green crown) on ring specific gravity of loblolly pine trees pruned at young ages. A designed experiment consisting of five treatments, control; prune at age 3 yr, age 6 yr, or age 9 yr; and at ages 3,6, and 9 yr, was established at two locations in the Piedmont region of Virginia. Wood samples were acquired at three heights along the stem 15 yr after planting. Results showed that differences in ring specific gravity of the treated plots (Half of green crown removed at each scheduled pruning) were significantly higher than that of the control plots. All variables of ring age, relative height and ring position of within or not within the green crown, were statistically significant. The results suggest that cambial age, maturation, and proximity to green crown are important for controlling whole-ring specific gravity in loblolly pine trees.

Increasing production value in Scots pine plantation through mixing with lodgepole pine

ABSTRACTMixing tree species could be a silviculture model that allows early harvest of short-rotation trees, while longer-rotation crop trees remain in the stand. We examined the effects on growth and tree characteristics in a planted experiment with lodgepole pine (LP) and elite-bred Scots pine (SP) in mixed (50/50) and monospecific plots in three different spacings (at 28 years of age after planting). The future development under different thinning regimes, including net present value for one rotation, was analyzed using the Heureka simulation software. As expected, LP had higher survival and initially more rapid growth than SP, with highest stand productivity and biomass production in LP monoculture during a rotation period as a result. However, intimate mixtures of SP and LP at the two widest spacings could give greater production and economic benefits, compared to SP in monoculture. It seems that elite-bred SP will differ in competitiveness against LP, depending on spacing for growth and some quality traits (branch and bark thickness, height of green crown). The findings support developing management systems for combining sparsely planted, and expensive, elite-bred SP in mixture with other trees that maintains high stem volume production and secures certain properties of trees and stands.

MORPHOMETRY OF TRACHEIDS OF Pinus taeda L. FROM A PRUNING TEST IN NE ARGENTINA.

The northeast region of Argentina is characterized by fast-growing forest plantations, Pinus taeda among them. The objective of this study was to evaluate the influence of pruning and stand structure on the morphometric characteristics of tree tracheids. We evaluated 18 trees of 16 years old, from a silvicultural stand essay, with 1660 plants/ha as initial density, without thinning, three pruning treatments 0%, 50% and 70% removal of the green crown belong to the dominant, codominant and suppressed strata. Tree slices were taken at 1.3 m height, the conditioned samples were observed and measured with a microscope with digital camera. The data was analyzed using mixed linear models. Pruning did not have effect on the width and length of tracheids, but it affected to the cell wall thickness, which decreased with increasing pruning intensity. While the social position (stratum) had significant influences on the length of tracheids, given greater for individual in dominant stratum, followed by codominant and suppressed stratum. The cell wall width and thickness were not affected by the stratum. Regardless of the social position in the stand, the tracheid’s length showed an increasing pattern from pith to bark with the lower values near to the pith.

Effects on stem growth of Scots pine 33 years after thinning and/or fertilization in northern Sweden

ABSTRACTThinning and fertilization are two common and important stand treatments in forest management. In terms of area treated, thinning is the single most common form of stand treatment. The extent of forest fertilization on the other hand, has varied widely in recent decades and is currently not very common. Thinning is done primarily to promote stand properties while fertilization is done to increase growth before future final felling. After thinning stands of Scots pine, overall growth decreases, while growth of residual trees increases. An experiment was established outside Vindeln in northern Sweden where the long-term growth effects after thinning and/or fertilization were evaluated after 33 years. Experimental set-up was a randomized block design including 12 replications of four treatments. Treatments were control, fertilization, thinning, and thinning and fertilization combined. Thinning decreased overall and annual volume growth ha−1, and increased green crown size and diameter growth at breast height (1.3 m, DBH) for the individual trees. No positive growth responses to fertilization could be seen after 33 years. In summary, this study showed that thinning can have long term effects on the growth of a Scots pine stand in northern Sweden. Possible reasons for the lack of positive response following fertilization are discussed.

Calibrating Satellite-Based Indices of Burn Severity from UAV-Derived Metrics of a Burned Boreal Forest in NWT, Canada

Wildfires are a dominant disturbance to boreal forests, and in North America, they typically cause widespread tree mortality. Forest fire burn severity is often measured at a plot scale using the Composite Burn Index (CBI), which was originally developed as a means of assigning severity levels to the Normalized Burn Ratio (NBR) computed from Landsat satellite imagery. Our study investigated the potential to map biophysical indicators of burn severity (residual green vegetation and charred organic surface) at very high (3 cm) resolution, using color orthomosaics and vegetation height models derived from UAV-based photographic surveys and Structure from Motion methods. These indicators were scaled to 30 m resolution Landsat pixel footprints and compared to the post-burn NBR (post-NBR) and differenced NBR (dNBR) ratios computed from pre- and post-fire Landsat imagery. The post-NBR showed the strongest relationship to both the fraction of charred surface (exponential R2 = 0.79) and the fraction of green crown vegetation above 5 m (exponential R2 = 0.81), while the dNBR was more closely related to the total green vegetation fraction (exponential R2 = 0.69). Additionally, the UAV green fraction and Landsat indices could individually explain more than 50% of the variance in the overall CBI measured in 39 plots. These results provide a proof-of-concept for using low-cost UAV photogrammetric mapping to quantify key measures of boreal burn severity at landscape scales, which could be used to calibrate and assign a biophysical meaning to Landsat spectral indices for mapping severity at regional scales.

Assessment of crown woody biomass in Eucalyptus grandis and E. globulus plantations

Young trees were harvested to explore non-destructive methodologies to estimate live branch dry weights in young fast-growing Eucalyptus species under different spacing and fertilizer treatments. Branch growth can vary with silvicultural management such as spacing, fertilizing and thinning, and over relatively short periods in response to environmental conditions. Many published regressions based on standard measurements of height and diameter are site, age and treatment specific. The aim of this study was to improve our capacity to predict woody crown dry weight, based on stem measurements, and to minimize (or eliminate) treatment effects on the resulting model. In young trees, branches are temporary support structures for foliage and are often discarded as the base of the green crown rises. As temporary structures they represent an investment of biomass and nutrient elements, and are subject to selection pressures to maximize the return on investment by the tree. Trees were harvested from existing plantation experiments located in south-eastern Queensland for E. grandis W. Hill ex Maiden (ranging from 0.28 to 15.85 m in height, to 5 years old) and south-western Australia for E. globulus Labill. (0.10–34.4 m in height, to 10.2 years) in order to examine the impact of spacing, nitrogen and phosphorus fertilization on early growth. Relationships to estimate crown woody biomass from non-destructive measurements were developed, and these relationships tended to have different slopes and intercepts for trees with predominantly juvenile foliage and those with intermediate or adult foliage. Dry weight of whole-crown live branch wood (Wbranch) was related to heights and/or diameter at breast height (DBH), but the regressions parameters were different, depending on treatment. The relationships became more generic (i.e. less dependent on treatment effects) between Wbranch and stem sectional area at the height of the base of the green crown (SACB), consistent with the pipe model theory (R2 > 0.91 for the two species for trees with intermediate/adult leaves). However, Wbranch was more closely related again to the stem volume above the base of the green crown and treatment effects were not significant (VCon,gc, R2 > 0.93). Branches exit the stem below the green crown, and for E. grandis the best relationship was on stem volume above the lowest live branch (VCon,llb, R2 0.94). Limited sampling from four other species with similar or contrasting crown characteristics indicated that the relationship could be applied quite generally. Individual E. grandis branch woody dry weight was closely related to the conical volume of the main (first order) branch (Vcon,br, R2 0.98). The whole crown equivalent, branch woody dry weight plus stem dry weight above the lowest live branch, was also closely related to the stem volume within the woody crown (VCon,llb, R2 0.97–0.99). While the slope of this relationship was still significantly different between trees with juvenile and intermediate/adult foliage, it had a similar form, suggesting that trees with juvenile foliage allocated a different proportion of their woody biomass within the crown to branches than older trees.

Cumulative effect of needle cast on Scots pine saplings

Abstract Premature needle cast, affecting the needles on one-year old shoots, thus shrinks the size of green crown of Scots pines, and can cause reduction of increment or even death of trees, especially during first years of their growth. Aim of our study was to evaluate the lasting impact of pathological needle cast to young Scots pines and its implications for tree breeding. Assessment of needle cast damages in 5 grade scale and measurements of height were done repeatedly in Scots pine open pollinated progeny trial, consisting of 65 families, located in central part of Latvia. Proportion of saplings with different level of needle cast damage differed significantly between the years of impact: severely damaged were 51%, 30% and 17% of saplings in growing seasons 4, 5 and 6, respectively. Both the needle cast damage grade at current growing season, as well as height of the sapling before the needle cast infection (at the end of the third growing season) had a significant effect on its grade of needle cast damages in the next growing season. Cumulative level of needle cast damages at the age 4 to 6 years had significant negative effect on height of the saplings at the age of 12 years both at individual tree and family mean level, as well as on survival. Selection of best growing families in such trial would also lead to selection of genotypes least affected by the disease.

English

Tree pruning is a silvicultural operation that aims to improve wood quality, but care must be taken regarding the timing and height of the lift to ensure that tree growth is not negatively affected. The objective of this work was to evaluate the effects of different pruning heights on height and diameter growth of Eucalyptus grandis × Eucalyptus urophylla. The experiment was done in a one year old stand which was planted at 9 × 3 m spacing, managed under a silvopastoral regime, and located in Joao Pinheiro, Minas Gerais, Brazil. Pruning treatments removed branches carrying the lower green crown as follows: 0% (unpruned), 20, 40, and 60% of total tree height. Diameter at breast height (DBH at 1.3 m) and total height of all trees in the sample plots were measured prior to pruning and one year after pruning. Compared to the unpruned control, pruning significantly reduced mean DBH and total height in the 40 and 60% treatments but not in the 20% treatment. Thus, it was concluded that when pruning operation is done before canopy closure not more than 20% of lower green crow should be removed to avoid tree growth reduction. Key words: Silvopastoral regime, silvicultural intervention, forest management.

MODELOS PREDICTIVOS DE BIOMASA AÉREA DE<i> Eucalyptus grandis</i> PARA EL NORESTE DE ARGENTINA

http://dx.doi.org/10.5902/1980509819611Diferentes intereses industriales, energéticos y ambientales han motivado el análisis de las distintas posibilidades de aprovechamiento de la biomasa forestal, este tema está adquiriendo un creciente protagonismo, por lo que la cuantificación de la biomasa aérea de estos sistemas forestales constituye un primer paso fundamental e ineludible. El objetivo de este trabajo fue desarrollar modelos que permitan estimar la biomasa de los diferentes compartimentos aéreos de Eucalyptus grandis. Para ello se emplearon datos de 41 árboles provenientes de rodales de diferentes edades, entre 4 y 32 años, ubicados en la región NE de Argentina. Se tomaron 23 individuos ubicados en la Zona Norte y Alta de Misiones (zona 1) y 18 en el Sur de Misiones y NE de Corrientes (zona 2). Se determinó la biomasa de hojas, ramas menores a 5 cm, ramas mayores a 5 cm, total de ramas, fuste y biomasa total del árbol. Para el ajuste de modelos se tomaron diversas variables independientes, el diámetro a la altura de pecho (dap), la altura total del árbol (h), el producto (dap2*h) y la variable “dummy” (zona). Para el caso de la biomasa de ramas y de hojas, debido a que no se lograron resultados satisfactorios con el empleo de estas variables, se examinaron modelos que adicionaban índice de sitio, factor de espaciamiento, diámetro en la base de la copa verde (dbcv), altura hasta la base de la copa verde (hbcv), longitud de copa verde (lcv), el área transversal de albura en la base de copa verde (g Alb bcv) y diferentes combinaciones de estas variables. Los modelos fueron seleccionados en base al coeficiente de determinación y el error cuadrático medio. Para la biomasa de ramas menores a 5 cm, ramas mayores a 5 cm, total de ramas, fuste y total, los mejores modelos fueron los que incorporaron como variables regresoras, el diámetro a la altura de pecho, la altura total del árbol y la variable “dummy” (zona). Para la biomasa de hojas, las variables, edad, área basal y número de árboles por hectárea permitieron mejorar la estimación. Los coeficientes de determinación para los modelos de biomasa total y de fuste fueron de 0,99, para el total de ramas fue de 0,83, para ramas menores a 5 cm 0,69, para ramas mayores de 5 cm 0,53 y 0,65 para hojas. Se recomienda incrementar la base de datos a los efectos de intentar mejorar las predicciones de biomasa de hojas y ramas.

The influence of initial and post-thinning stand density on Douglas-fir branch diameter at two sites in New Zealand

Branches support the foliage needed for tree growth, but if the branch diameter is too large it may constitute a defect when the tree is assessed for timber quality and when the tree is processed into boards. Consequently branch diameter is an important consideration when developing a silvicultural regime. The objectives of this study were: (a) to develop site-specific models to predict branch diameter variation with position on the stem; and (b) to use the models to evaluate the influence of initial and post-thinning stand density on branch diameter in unpruned stands of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) at two sites in New Zealand. Branch diameters were measured using a photogrammetric technique, TreeD, on pre-selected sample trees from unpruned treatments in two silviculture experiments, one in the North Island and one in the South Island of New Zealand. The data were used to develop site-specific models to predict branch diameter along the stem. The models were then used to interpret response to a thinning at a stand age of approximately 10 years when the base of the green crown was still close to ground-level, and to make comparisons with a branch diameter limit of 40 mm. The models developed indicated that previously formed branches were influenced by the increased growing space created by thinning. At all three post-thinning stand densities (250, 500 and 750 stems ha−1), the diameter of some branches on the mean tree within a stand were likely to exceed 40 mm. In unthinned treatments, the model indicated that an initial stand density of at least 1333 stems ha−1 would be needed to keep branch diameters on the mean tree below 40 mm along the whole stem at age 29 years. This study indicates the importance of considering initial stand density, post-thinning stand density and timing of thinning when designing a silviculture regime that aims to control branch diameter.

Productivity and thinning effects in hybrid aspen root sucker stands

The Nordic countries have a vision to become carbon neutral by 2050. One way to approach this vision is to cultivate and harvest fast-growing tree species as bioenergy.In three study parts, this paper investigated how hybrid aspen performs in the second generation of root suckers. The three studies investigated; (1) initial growth, (2) growth effects following three early thinning strategies, and (3) individual tree development after the three early thinning strategies in study 2 and an intensive low thinning. In study 1, root suckers between 1- and 4-years-old were studied at four sites. Studies 2 and 3 followed growth dynamics for 12years at one site.After 2years, the four sites in study 1 had a mean stand density of 63,500 living root sucker stems ha−1 (ranged 46,800–72,900 stems ha−1) and the mean standing biomass (including living and dead stems) was 14.5Mg dry weight ha−1 (ranged 9.1–21.7Mg dry weight ha−1). Differences between sites were observed.Even though significant amounts of biomass had been harvested after 2years in two of the treatments in study 2, the density of living stems did no longer differ between the treatments at the end of the 12-year period. The stem diameter was largest for cross-corridor thinning, while the height development was not affected by thinning strategy. During the 12-year period, the obtainable biomass (included living, dead and harvested biomass) did not differ significantly among the thinning treatments and after 12years the mean annual increment was 9.8Mg dry weight ha−1yr−1 and had started to decrease.Results following the second thinning in study 3 showed that early biomass harvest had a large influence on the development of individual stems. Unthinned strategy resulted in smaller stem diameters and green crowns, while cross-corridor thinning showed the largest stem dimensions and green crowns. Green crowns became of similar size for the various thinning strategies, but the difference in stem diameter remained and the mean annual increment continued to diverge.This paper showed that the second generation of hybrid aspen can contribute significantly to the biomass supply, and that the strength of early thinning has a large effect on the continuing growth. The importance of early thinning, when striving for large fast-growing trees, is highlighted.

Different responses of stem and soil CO2 efflux to pruning in a Chinese fir (Cunninghamia lanceolata) plantation

Key message Pruning significantly reduced stem CO2 efflux, but had little effect on soil CO2 efflux and root respiration. Pruning did not alter temperature sensi- tivity of CO2 efflux from stem and soil. Abstract Pruning is one of the common silvicultural practices for Chinese fir (Cunninghamia lanceolata) plan- tations to produce knot-free wood. However, little is known about the effects of pruning on stem and soil CO2 efflux in Chinese fir plantations. In this study, we experimentally manipulated the canopy of Chinese fir by pruning the lower 50 % of the green crown length in a Chinese fir plantation. We monitored the effects of pruning on the stem and soil CO2 efflux, stem radial growth, xylem sap flow, and non- structural carbohydrate (NSC) concentrations. Our results showed that pruning resulted in the significant reduction of stem CO2 efflux, particularly during the growing season. Despite the removal of the lower 50 % of the green crown length, we did not observe a pronounced reduction in soil CO2 efflux and its components. Moreover, pruning had only little effect on sap flow. No significant difference was observed in the NSC concentrations between treatments in the stem cores and fine roots. We speculated that the dif- ferent responses of stem and soil CO2 efflux to pruning in the Chinese fir (sprouting species) plantation may have resulted from the different carbon allocations between aboveground and belowground tissues. However, further studies are required to confirm if our findings could be applied to other tree species or ecosystems.

Effects of site, silviculture and seedlot on wood density and estimated wood stiffness in radiata pine at mid-rotation

To understand the underlying control of patterns of important wood properties is fundamental to silvicultural control of wood quality and genetic selection. This study examines the influences of site, silviculture and seedlot on diameter growth, wood density and estimated wood stiffness in mid-rotation radiata pine (Pinus radiata D Don) stands across New Zealand. Selected treatment combinations were assessed across five sites in a 17-year-old experiment comparing silvicultural treatments and improved breeds of radiata pine. Diameter at breast height (DBH), and stress-wave velocity (an indicator of wood stiffness) and outerwood (outermost five growth rings) basic density at breast-height were assessed for ten trees from each plot in the experiment. There were large differences in DBH and wood properties between sites. Silviculture (stand density) had a stronger influence than seedlot on DBH and stress-wave velocity, while the converse applied to outerwood density. There was a positive relationship between stand density and both stress-wave velocity and outerwood density. Trees in the un-pruned 500 stems ha−1 treatment had larger DBH, lower outerwood density and lower stress-wave velocity than trees in the 400 stems ha−1 pruned treatment. This suggests that silvicultural manipulation (pruning) of green crown length is important for controlling both growth and wood properties. Results from this study support previous research which indicates that thinning, and to a lesser extent pruning, have a strong impact on DBH, stress-wave velocity and outerwood density. Increasing stand density is consistently associated with stiffer and denser outerwood.

Assessment of leaf mass and leaf area of tree crowns in young Eucalyptus grandis and E. globulus plantations from measurements made on the stems

Leaf area is a key driver of growth models and leaf weight is important for studying carbon and nutrient cycling in forestry. Both can change over relatively short intervals in young plantations in response to silvicultural treatments and climatic conditions. Relationships to estimate leaf dry weight and leaf area of young Eucalyptus grandis W. Hill ex Maiden and Eucalyptus globulus (Labill.) were developed from harvested trees ranging from 0.28 to 15.85 m and 0.12 to 34.4 m in height respectively. Trees were harvested from existing experiments in south-eastern Queensland and south-west Western Australia in order to assess the effects of spacing and application of nitrogen and phosphorus fertilizer on early plantation growth. A range of tree measurements were taken to determine the most efficient way to monitor the performance of young plantation eucalyptus. Leaf weight (Wleaf, kg) and leaf area (m2) were related to stem cross sectional area at the height of the base of the green crown (SACB), but the slope and intercept of the relationship differed for trees with predominantly juvenile foliage and those with predominantly intermediate or adult foliage. Specific leaf area (m2 kg−2) changed as the trees aged and leaf area was more closely related to the size of the support structure, represented by the stem volume within the green crown, approximated by the volume of a cone above the base of the green crown (VC,gc). Significantly, the relationships also applied to individual branches, that is, leaf weight was related to sectional area near the base of the branch (SAb) and leaf area to the volume of the main (first order) branch (VC,br). Most of the published work has been directed at trees of commercial size or to small trees in pot experiments, much less to small trees in the establishment phase of growth of interest to experimenters and managers looking at early intervention. This study provides a mechanism to directly assess canopies of intermediate size trees which are of interest for assessing treatment effects or early intervention for managers.