Live Branches Research Articles

Growth and form of Quercus robur and Fraxinus excelsior respond distinctly different to initial growing space: results from 24-year-old Nelder experiments

Initial growing space is of critical importance to growth and quality development of individual trees. We investigated how mortality, growth (diameter at breast height, total height), natural pruning (height to first dead and first live branch and branchiness) and stem and crown form of 24-year-old pedunculate oak (Quercus robur [L.]) and European ash (Fraxinus excelsior [L.]) were affected by initial spacing. Data were recorded from two replicate single-species Nelder wheels located in southern Germany with eight initial stocking regimes varying from 1,020 to 30,780 seedlings·ha−1. Mortality substantially decreased with increasing initial growing space but significantly differed among the two species, averaging 59% and 15% for oak and ash plots, respectively. In contrast to oak, the low self-thinning rate found in the ash plots over the investigated study period resulted in a high number of smaller intermediate or suppressed trees, eventually retarding individual tree as well as overall stand development. As a result, oak gained greater stem dimensions throughout all initial spacing regimes and the average height of ash significantly increased with initial growing space. The survival of lower crown class ashes also appeared to accelerate self-pruning dynamics. In comparison to oak, we observed less dead and live primary branches as well as a smaller number of epicormic shoots along the first 6 m of the lower stem of dominant and co-dominant ashes in all spacing regimes. Whereas stem form of both species was hardly affected by initial growing space, the percentage of brushy crowns significantly increased with initial spacing in oak and ash. Our findings suggest that initial stockings of ca. 12,000 seedlings per hectare in oak and 2,500 seedlings per hectare in ash will guarantee a sufficient number of at least 300 potential crop trees per hectare in pure oak and ash plantations at the end of the self-thinning phase, respectively. If the problem of epicormic shoots and inadequate self-pruning can be controlled with trainer species, the initial stocking may be reduced significantly in oak.

Spacing affects stem form, early growth and branching in young whitewood (Endospermum medullosum) plantations in Vanuatu

SUMMARY This paper investigates the early growth response, branching and stem quality of Endospermum medullosum (whitewood) at different spacings. Whitewood plantings were established at stockings of 400–833 trees per hectare and early growth, tree stem quality and branching were quantified up to age 3 years. Growth, number of live branches and branch size were negatively correlated with stocking. The stocking of trees of acceptable quality had high spatial variation. Initial spacing in whitewood plantations can be used to manipulate branch size, crown rise and stem size; all of which are important for development of pruning and thinning regimes to produce high quality logs. If unimproved whitewood stock is used, to ensure that there are 300 stems per hectare of acceptable quality to produce sawlogs, more than 600 trees per hectare should be established at planting.

Crown structure and vertical foliage distribution in 4-year-old plantation-grown Eucalyptus pilularis and Eucalyptus cloeziana

Tree growth and form are both influenced by crown architecture and how it effects leaf distribution and light interception. This study examined the vertical distribution of foliage in 4-year-old plantation-grown Eucalyptus pilularis Sm. and E. cloeziana F. Muell. trees. Leaf area (LA) distribution was determined at two different sites using allometric approaches to determine LA in crown sections and for whole trees. Leaf area was distributed more towards the upper crowns when canopies had been closed for longer. Leaf area was also skewed more towards the upper crowns for Eucalyptus pilularis than E. cloeziana. These species differences were consistent with differences in vertical light availability gradients as determined by point quantum sensors. Leaf area of individual branches was highly correlated with branch cross-sectional area (CSA) and whole-tree LA was closely related to stem CSA. Branch-level allometric relationships were influenced by site and crown position. However, the general allometric equations between stem size and whole-tree leaf area could be applied across sites. Results from this study suggest that pruning of live branches in these species should follow species-specific guides for the timing and height of pruning to optimise the effects on stem growth and form.

Basic ecology of the Oaxacan Spiny-tailed Iguana <i>Ctenosaura oaxacana</i> (Squamata: Iguanidae), in Oaxaca, Mexico

The Oaxacan Spiny-tailed Iguana Ctenosaura oaxacana is a restricted species to the Isthmus of Tehuantepec in Southern Oaxaca, Mexico. This reptile is one of the less known iguanid species. We census-tracked a population in the South ofNiltepec, Oaxaca, Mexico from May 2010 to April 2011. Throughout one year, a total of 10 line transects were situated and recorded in the study area to determine relative abundance and density, and habitat type use (dry forest, Nanchal, grassland, riparian vegetation, and mangrove) by the species. This study reports a new C. oaxacana population on the Southeastern limit of species range. Although this species has a very restricted distribution and is in danger of extinction, C. oaxacana has a high population density when compared to other Ctenosaura species. A total of 108 individuals were recorded throughout the study. Dry forest (33.75ind/ha) and Nanchal (18.75ind/ha) were the habitats with higher densities. Comparisons between habitat types showed no significant differences between dry forest and Nanchal (W=15, p=0.0808). Results between seasons were similar. The Oaxacan Spiny tailed Iguana preferred first the dry forest, and then Nanchal, while avoided grassland, riparian vegetation, and mangroves. There was no difference in habitat use between males and females. Mean perch heights were 1.23 +/- 0.32 (n=30) in Nanchal, 2.11 +/- 0.30 (n=9) in grassland, 1.90 +/- 0.56 (n=54) in dry forest, 1.91 +/- 0.28 (n=9) in mangrove and 2.30 +/- 0.37 (n=6) in riparian vegetation. Species observed as refuge and perch were B. crassifolia (Nanchal); C. alata (grassland); Tabebuia sp., Genipa americana, G. sepium, Acacia sp., Ficus sp. and Haematoxylon sp. (dry forest); G. sepium, Acacia sp. and Guazuma ulmifolia (riparian vegetation); and C. erecta (mangrove). Live trees hollows and branches were used by species. Main threats to the species are excessive hunting and habitat loss. Furthermore, grassland fires are still common in the study area during the dry season, which can result in habitat loss and territorial displacement of individuals.

Can wood properties be predicted from the morphological traits of a tree? A canonical correlation study of plantation-grown white spruce

There is a growing interest in predicting wood quality from tree morphology traits, which can be measured using remote sensing techniques such as LiDAR, to enhance forest inventory for operational planning. In this study, we investigated the correlation structure between these two categories of traits in white spruce (Picea glauca (Moench) Voss) using canonical and multiple regression analyses with the objective of identifying key morphology variables that are predictive of wood quality. For 495 trees from a 30-year-old plantation, we obtained measurements of tree height and dimensions of the living crown, as well as the number and diameter of live branches at selected whorls. Wood traits were assessed from wood cores with SilviScan technology. Morphological traits explained almost 29% of the overall variation observed in wood traits. However, the magnitude of the correlations and the ability of crown morphological traits to predict wood traits differed widely among the latter. Average ring width and radial cell diameter, both related to increment, were well correlated with tree morphology, whereas traits related to subcellular structure, for instance, microfibril angle, were poorly correlated. These results could guide the choice of wood traits to improve inventory techniques aiming to optimize the forest product value chain.

Modelling number, vertical distribution, and size of live branches on coniferous tree species in British Columbia

A compound, nonhomogeneous Poisson process was used to model the number, vertical distribution, and size of branches on four coniferous tree species: 134 western hemlock ( Tsuga heterophylla (Raf.) Sarg.) on six sites, 45 amabilis fir ( Abies amabilis Douglas ex J. Forbes) (three sites), 60 lodgepole pine ( Pinus contorta var. latifolia Engelm. ex S. Watson) (six sites), and 60 white spruce ( Picea glauca (Moench) Voss) trees (five sites) and two varieties: 66 coastal Douglas-fir ( Pseudotsuga menziesii var. menziesii (Mirb.) Franco) (five sites) and 50 interior Douglas-fir ( Pseudotsuga menziesii var. glauca (Mayr) Franco) (four sites). Branches of these species are typically more or less clustered and have a characteristic, nonuniform vertical distribution along annual shoots. Total number and relative positions of clusters varied with shoot age. Clustering patterns in three of four species and two varieties appeared to scale proportionally with shoot length. However, in lodgepole pine, which has fewer clusters per metre and more branches per cluster, the vertical distribution of clusters along shoots ≤5 years old was consistent with a gamma-Poisson model but converged to a nonhomogeneous Poisson process model in shoots >5 years old. Separate mixed-effect regression models were developed for each species relating length and diameter of live branches to tree (crown), shoot, and branch (cluster) predictor variables.

Estimating Above Ground Biomass of Pinus caribaea stand in lower Hantana

Over 18, 000 ha of degraded wet lowland areas in Sri Lanka have been converted to Pinus caribaea plantations through an afforestation program. These plantations are poorly managed and subject to frequent fires, set by local people who do not see much value in them for their subsistence. Consequently, these plantations remain under-productive and under-utilized, particularly due to the paucity of plant and economic diversity for rural development. In response to this a Pinus enrichment trial has been launched to restore plant and economic diversity in these biodiversity poor monoculture plantations. In this field trial, in Hantana on land belonging to the University of Peradeniya, selected rows of Pines were removed. We used this opportunity to estimate the above ground biomass of P. caribaea.Total tree height, stem diameter at the two ends of the stem, middle and immediately below the lowest live branch were recorded at the time of logging. From each tree, fresh samples of stem discs at the root collar, middle and the end were collected, sealed in polythene bags and dry weights were measured at 700 C. Fresh weight of the branches, needles and cones were determined. Sub samples of these were taken for determination of fresh weight: dry weight ratios.In our study we predicted the tree form. Pine tree trunks are cylindrical at the lower part and conical at the upper part. Empirical formulae were derived separately to estimate biomass for the cylindrical part and the conical part of the tree. These formulae are site specific to theP. caribaea plantations in Hantana. Using the formulae, the above ground biomass of a 25-yr-old P. caribaea stand was calculated as 194 tha-1. Of the live standing crop the stem represented 60%, the branches 17%, the leaves 13%, the cones 3% and dead branches 7%. This Pine stand had 695 Pine trees ha-1, a mean dbh of 20.1 cm, a mean height of 20.7 m and mean basal area of 23.6 m2 ha-1. The estimated values showed that the P. caribaea plantation studied is good source for carbon sequestration.

Early responses to thinning treatments designed to accelerate late successional forest structure in young coniferous stands of western Oregon, USA

The loss of critical habitat provided by late successional forests has prompted the search for management options that can accelerate the development of late successional forest structure in young stands. We examined operational-scale commercial thinning treatments at seven sites to evaluate if thinning could accelerate development of late successional forest structures in 40–60 year old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests. Thinning treatments included an untreated control, high density, moderate density, and variable density retention. All thinning treatments had leave islands, and moderate density and variable density included harvest-created gaps. Thinned units, especially moderate density and variable density, had greater spatial variability in tree density, supported lower live branches, had greater tree regeneration and growth, and had slightly lower mortality relative to the control. Canopy gaps extended the range of stand densities and increased growth of trees immediately along gap edges. However, thinning had little effect on growth of the largest Douglas-fir trees and did little to provide large snags or coarse woody debris. These results suggest that thinning treatments can accelerate some aspects, e.g., spatial variability, of late successional forest structures. Other attributes, such as large trees and snags, may prove less responsive to thinning treatments, at least in the short term. Including tree retention levels lower than typical management applications and formation of canopy gaps provide the wide range of conditions that appears beneficial for developing late successional forest structure.

地上竞争对林下红松生物量分配的影响

Competition is an important factor in biology and plant鄄plant interactions has inspired an increasing concern in recent years. In plant communities, competition is defined as the interaction between individuals, brought about by limited resources. Aboveground competition is usually size鄄asymmetric: the bigger individuals have a disproportionate advantage in competing for light than the smaller ones. This study deals with biomass allocation patterns and aboveground competition influences on biomass partitioning and allometric equations of understory Korean pine (Pinus koraiensis). The results will contribute to understanding the mechanisms of aboveground competition and provide a theoretical guide for effective utilization and protection of Korean pine. The results show that: (1) When dividing live crown into three equal layers ( top, middle and bottom), live branch biomass increased from the top to the bottom layer, while needle biomass was highest in the middle and bottom layers of the crown. However, there was no significant difference between the needle biomass located at the middle and bottom layers (P>0. 05). The relative proportion of coarse root ( >5 mm) biomass increased while that of small fine root (<2 mm) and coarse fine root (2—5 mm) biomass both decreased with increasing

Exportação e reposição nutricional no primeiro desbaste de um povoamento de &lt;i&gt;Pinus taeda&lt;/i&gt; L. em área de segunda rotação

O trabalho tem por objetivo quantificar a biomassa, exportação e reposição dos nutrientes em árvores do primeiro desbaste de um povoamento de Pinus taeda, em Cambará do Sul, RS. Para isso, foi realizado um inventário em três parcelas (60 m x 60 m), sendo abatidas 3 árvores por parcela. Foram mensuradas acículas vivas e mortas, galhos vivos e mortos, casca, madeira comercial e madeira do ponteiro com casca. A biomassa totalizou 44,5 Mg ha-1, com 62,8% de madeira, 10,3% de galhos vivos, 8,9% de casca, 10,1% de acículas vivas, 6,1% de galho morto, 3,5% de ponteira com casca e 0,5% de acícula morta. A quantidade total de nutrientes na biomassa, em kg ha-1, foi de: 100,5 de N; 51,1 de Ca; 46,8 de K; 18,2 de S; 14,3 de Mg; 11,7 de P; 0,599 de Mn; 0,158 de Fe; 0,435 de Zn; 0,181 de B e 0,177 de Cu. A quantidade de adubos a serem repostos dependerá do tipo da exploração. Se ocorrer remoção total da biomassa, a quantidade de adubos a ser reposto será de 391 kg ha-1, e se considerar apenas a retirada da madeira esta reposição será aproximadamente 60% inferior, 169 kg ha-1.

Biology ofScolytus subscaber(Coleoptera: Curculionidae: Scolytinae) in Grand Fir in Idaho

AbstractWe studied the biology of Scolytus subscaber LeConte (Coleoptera: Curculionidae: Scolytinae) in grand fir, Abies grandis (Douglas) Lindley, in northern Idaho. Presented are new Idaho distribution records, description of the mature larva and adult, biological features, characteristics of infestation and galleries, and natural control factors. The beetle has one generation per year, taking flight in July to infest live branches in the crowns of mature trees. The uniquely shaped egg gallery deeply scores the wood; its two arms curve inward like the Greek letter ε. Eggs are laid along the outer edge of the gallery; hatched larvae mine hidden in the phloem for a short distance after which they mine next to the sapwood where they overwinter. A cerambycid, Tetropium abietis Fall, occurred often in the larger diameter portion of branches infested with S. subscaber. A scolytid, Scolytus abietis Blackman, also infested branches but not those containing S. subscaber. Mortality factors included a braconid parasitoid, Ecphylus arcuatus Muesebeck, on larvae and the flooding of egg galleries with resin evidently caused by defensive response of the host tree to a staining fungus, Spicaria anomala (Corda) Harz., carried by the beetle. In addition, we point out errors and lack of documentation concerning the identity, biology, and behavior of S. subscaber in secondary published sources.

Predicting maximum branch diameter from crown dimensions, stand characteristics and tree species

Forest resource inventories must include wood quality information to support the optimum use of wood fibre. The objective of this study was to develop models relating maximum live branch diameter (MBD), which affects lumber value, to tree and stand characteristics that can be measured through current and emerging remote sensing technologies. Using non-linear mixed effects models for six Canadian conifer species, as well as for three broad-leaved species, MBD was related to crown radius, tree height, crown length, stand basal area, and basal area of trees larger than the subject tree. Models that included only individual tree characteristics (crown radius, tree height, and crown length) did not perform as well as models that additionally included stand characteristics (stand basal area and basal area of larger trees). Models that took into account tree species performed better than models that did not; in particular, broadleaved species had much thicker branches than conifers. The best model did not show bias with respect to independent variables and had root mean square error of 0.32 cm. For the best model, prediction error was not related to silvicultural treatment. These model characteristics strongly support the potential to successfully predict MBD from remotely sensed data.

Biomassa e nutrientes removidos no primeiro desbaste de um povoamento de Pinus taeda L. em Cambará do Sul, RS

Objetivou-se, neste estudo, avaliar a biomassa e a remoção de nutrientes durante o primeiro desbaste de um povoamento de Pinus taeda, com nove anos de idade, em Cambará do Sul-RS. Realizou-se um inventário dendrométrico dos indivíduos que seriam retirados do povoamento no primeiro desbaste. Os indivíduos foram distribuídos em quatro classes diamétricas. Foram abatidos três indivíduos de cada classe e separados acículas, galhos vivos, galhos mortos, casca da madeira comercial, madeira comercial, casca da madeira do ponteiro e madeira do ponteiro. Esses componentes foram amostrados e analisados quanto aos teores de macro e micronutrientes. A biomassa resultante do primeiro desbaste foi de 35,7 Mg ha-1, com a seguinte magnitude de distribuição: madeira comercial &gt; galhos vivos &gt; casca contida na madeira comercial &gt; acículas &gt; madeira do ponteiro &gt; galhos mortos &gt; casca do ponteiro. As acículas apresentaram os maiores teores de macronutrientes e, juntamente com a casca do ponteiro, apresentaram também os maiores de micronutrientes. A colheita da casca e de madeira comercial resultou na seguinte remoção de macronutrientes, em kg ha-1: 46,2 de N; 25,1 de Ca; 15,2 de K; 10,0 de S; 6,7 de Mg e 5,4 de P; e de micronutrientes, em g ha-1: 2.641 de Mn; 1026 de Fe; 240 de Zn; 234 de B e 66 de Cu.

Characteristics of a Red Pine Plantation Occupied by Kirtland's Warblers in Wisconsin

Abstract We studied a newly established population of Kirtland's Warbler (Dendroica kirtlandii) in Adams County, Wisconsin, nesting in a red pine (Pinus resinosa) plantation. We found eight males and five females in Adams County in 2008 and 10 males and 10 females in 2009. Five of seven (71%) males color-banded in 2008 returned in 2009, and at least eight successful nests produced an estimated 33 young over the 2 years. Red pine comprised 66.9% of trees on the main site, 20.6% were northern pin oak/black oak (Quercus ellipsoidalis/Q. velutina), and 12.5% were jack pine (Pinus banksiana). Total tree density at the main site was 1,876 trees/ha, lower than generally reported in Michigan. Percent canopy cover and ground cover types were similar to Michigan sites. Lowest live branch height of jack pine was similar to Michigan sites, but lowest live branches of red pine at our site were closer to the forest floor. Significant red pine die-off at our site combined with substantial natural jack pine recruitment c...

Chloride content and biomass partitioning in Eucalyptus hybrids grown on saline sites

Eucalyptus camaldulensis × globulus and E.camaldulensis × grandis hybrids have been developed to combine the salt–waterlogging tolerance and high-quality wood fibre of their respective parents. The aim is to develop trees that will grow in relatively dry and/or saline environments and provide commercial wood products. Previous studies indicate that the hybrids exhibit faster growth than either of their pure species parents, and that there are significant differences in growth rates between them. We undertook a comparative study of the partitioning of above-ground biomass (AGB) to examine biomass and chloride (Cl) allocation of trees growing on two saline-irrigated sites in south-eastern Australia. Eucalyptus camaldulensis × globulus had a higher proportion of AGB in leaves (20–29% cf. 15–16%), and lower proportion in live branches (3–10% cf. 6–14%) than E.camaldulensis × grandis. The concentration of Cl was highest in the stembark (4.2–9.6 g kg−1) and lowest in the stemwood (0.6–2.0 g kg−1), suggesting that trees can export Cl through bark shedding. Total Cl content was strongly related to volume under bark (R2 = 0.99), and differences in partitioning of Cl into tree components differed between the hybrids in the same way as AGB. Preferential partitioning of Cl to live branches rather than foliage in E. camaldulensis × grandis suggests that this hybrid may be compartmentalising Cl to reduce the risk of Cl toxicity in the leaves.

Factors controlling deadwood availability and branch decay in two Prosopis woodlands in the Central Monte, Argentina

Deadwood is an important resource commonly used by inhabitants in arid lands. However, the low wood productivity and the presence of multi-stemmed trees restrict the use. Prosopis flexuosa woodlands are protected and inhabited by pastoralists who have land rights to use natural resources. As in other forests in the world, dead branches are the most commonly used. The factors causing the death of branches these trees are unknown. As P. flexuosa is a highly heliophilous species, branch mortality may depend on the growth habit and orientation of dry branches under the tree crown. With the participation of inhabitants, we assessed the present availability of deadwood in two Prosopis woodlands of different structure (semi-closed and open woodland), and evaluated the formation of deadwood in terms of shape and cardinal location of dry branches under the crown. We developed and compared regression models to estimate the amount of deadwood for erect, semi-erect and decumbent trees, and for the north and south areas under the crown ( n = 120 trees). In addition, to determine the period of growth decline and the factors determining branch mortality, we compared annual radial increment between live and dead branches ( n = 30 trees; 10 for each tree shape). The total amount of deadwood in adult Prosopis trees is higher in the semi-closed than in the open woodland (8.6 and 4.4 Tn ha −1, respectively). Only tree size determined the amount of deadwood present in each Prosopis tree, since we found no evidence related to the shape of the tree or the position of dry branches in the canopy. Branch decay was a large process of 18–20 years, and branch death appears to be the result of the action of climatic factors (dry period). The results suggest that the use of deadwood by the desert inhabitants is a tool that can potentially be used; however, the use of this resource taking into account the generation rates of deadwood has not been developed in arid lands. These practices at appropriate sites can contribute to a sustainable management of these woodlands, including the removal of deadwood in a model of local management on a site where potential productivity is relatively low.

Aboveground biomass of substitute tree species stand with respect to thinning - European larch (Larix decidua Mill.)

This study is focused on substitute European larch stands in the Kru&amp;scaron;n&amp;eacute; hory Mts. (northern part of the Czech Republic). Research was conducted within larch thinning experiment Kalek (780 m a.s.l. in the category Piceeto-Fagetum oligo-mesotrophicum &amp;ndash; Calamagrostis villosa). Results showed that the aboveground biomass of the investigated substitute unthinned larch stand represented approximately 102 thousand kg of dry matter per ha at the age of 20 years. Stemwood (ca 59%) is the most important part of the aboveground biomass. Needles, live and dead branches accounted approximately for 6%, 17% and 11%, respectively, and stem bark only for 7%. At the age of&lt;br /&gt;20 years, the investigated substitute unthinned larch stand accumulated: nitrogen &amp;ndash; 307 kg, phosphorus &amp;ndash; 21 kg, potassium &amp;ndash; 136 kg, calcium &amp;ndash; 122 kg, magnesium &amp;ndash; 53 kg per hectare. Thinning with consequent removal of aboveground biomass may result in nutrient losses. Especially, the removal of whole tree biomass by thinning for chipping in areas previously degraded by acid deposition may result in calcium and magnesium deficiency because of their low content in forest soil. On the other hand, thinning supported faster growth of trees left after thinning and consequently faster biomass and nutrient accumulation. Our results supported the recommendation that the use of biomass from thinning for chipping should be limited to stemwood only and the remaining aboveground biomass (mainly needles and branches) should be left in the forest ecosystem for decomposition in conditions of the historically disturbed area of the Kru&amp;scaron;n&amp;eacute; hory Mts.

Biomass structure and allometry of Abies nephrolepis (Maxim) in Northeast China

Above- and below-ground tree biomass structure and allometric relationships of Abies nephrolepis (Maxim) were assessed in an old secondary forest dominated by A. nephrolepis, Pinus koraiensis, Quercus mongolica, Tilia amurensis, Fraxinus mandshurica and Acer mono in northeast China. Based on the breast-height diameter (D), a total of 21 sample trees were divided into three tree size classes: the small trees (1 cm ≤ D &lt; 10 cm), the medium trees (10 cm ≤ D &lt; 20 cm) and the big trees (D ≥ 20 cm). The greatest amount of live branch biomass was located in the middle and bottom layers of the crown, while the largest foliage biomass was found in the middle layer in each tree size category. The relative contribution of canopy biomass components (live branches and foliage) decreased with increasing tree size, while that of coarse root biomass remained almost constant. The relationship between above- and belowground biomass was linear. D and tree height (H) decreased with increasing competition intensity. The small trees had lower average crown ratio and higher average height-to-diameter ratio than those of the medium and big trees. The big trees had higher average stem to foliage mass ratio than those of the small and medium trees. Crown ratio, height-to-diameter ratio and stem to foliage mass ratio were not correlated with competition intensity in the same tree size class. Root to shoot mass ratio was almost constant among tree sizes. Allometric equations based on D gave higher correlations compared to those with other stem diameters: at tree base, at 30-cm height and at crown base.

Inhibition response of Pinus densiflora clones to Bursaphelenchus xylophilus systemic dispersal and their resistance to pine wilt disease

AbstractTo determine the relationship between resistance to pine wilt disease and the inhibition of nematode systemic dispersal in Pinus densiflora, a suspension of 200 Bursaphelenchus xylophilus was placed on the upper cut end of 5-cm-long, living or boiled branch sections of 17 clones of pine that had different resistance levels. Significantly more nematodes passed through boiled sections than living sections during 24 h. Living branches of the resistant P. densiflora clone group significantly suppressed the dispersal of B. xylophilus compared with those of the susceptible group, suggesting that the inhibition of nematode systemic dispersal was involved in the resistance mechanism of selected disease-resistant pine clones. However, there was no significant correlation between the resistance class and the mean number of nematodes passing through live branch sections within the resistant clone group. The reason for the lack of correlation is discussed in relation with the resistance mechanism.

Stand development following precommercial thinning and fertilization treatments in a western redcedar (Thuja plicata) dominated forest

Western redcedar (Thuja plicata Donn ex D. Don.) is an important North American tree species, but little information is available on its long-term responses to silvicultural treatments. Stand responses (mortality, ingrowth, basal area and volume growth, and distributions of trees by diameter and height classes) were followed for 25 years after thinning and fertilization treatments (alone and in combination) were applied to a naturally regenerated, low site quality western redcedar stand on the Olympic Peninsula in western Washington, USA. Mortality was low overall, but the densest stands experienced competition-related mortality. Thinning resulted in additional stem recruitment; after 25 years, the number of ingrowth trees exceeded the number of trees in the cohort left after thinning. Fertilization (with nitrogen and phosphorus) flattened size distributions and skewed them to larger size classes. Thinning plus fertilization resulted in the largest individual trees and the most large trees, but also many trees in a wide range of diameter classes. The recruitment of a second cohort did not result in a two-storied stand. Fertilization without thinning resulted in the greatest stand basal area and volume, as well as trees with fewer live lower branches.