Lateral Picea shadow effects on Populus tremuloides understory vegetation in central Yukon, Canada

Laterally cast Picea albertiana ssp. albertiana (western white spruce) shadows were analyzed to determine their effect on understory plant abundance in two high-latitude (62.7°N) boreal Populus tremuloides (trembling aspen) forest stands. Each stand had a uniform and continuous overstory, and occurred on level to gently sloping terrain with a submesic moisture regime. Picea >1 m tall had <20% cover in each stand, with few trees equalling or exceeding the height of the P. tremuloides canopy. Understory vegetation composition was sampled in 30-m × 30-m plots that were subdivided into 1.5-m × 1.5-m cells (200 sampled per plot). Picea shadow locations and their areal extent were determined on an hourly basis (7:00-19:00 h Pacific Standard Time on the summer solstice) for individual plot cells using silhouette diagrams constructed from tree height and canopy-related data (n = 140 trees). Shadow data were analyzed using the lower- (Q_L, minimum to first-quartile values) and upper-most (Q_U, third-quartile values to maximum) portions of each species’ abundance distribution. Kruskal-Wallis tests (P < 0.001) indicated that greater Arctostaphylos uva-ursi (bearberry) abundance occurred where shadow cover was the least (daytime average ∼24%); whereas Geocaulon lividum (toadflax), Hylocomium splendens (stairstep moss), and Shepherdia canadensis (buffaloberry) incurred the most shadows (>34% cover) and had the shortest periods of continuous (<6 h) sunlight exposure with <30% Picea shadow cover. Hylocomium and Shepherdia also occurred nearer Picea than Arctostaphylos. Rosa acicularis (wild rose), Linnaea borealis (twinflower), Vaccinium vitis-idaea (bog cranberry), Chamerion angustifolium (fireweed), and Calamagrostis purpurascens (purple reedgrass) incurred intermediate amounts of shadow. Differences in hourly shadow abundance values (Q_U minus Q_L plot cells) were greatest for Arctostaphylos (−14.7%) and Rosa (−10.8%), but H. splendens (+3.8%) and Geocaulon had the least (+1.7%). Greater Hylocomium and Shepherdia abundance occurred in plot cells with more shadow indicating a tolerance for shade, which was contrary to the other species. These differences may represent examples of niche partitioning based on relative light availability. Individual understory species based on percent cover and species richness were more strongly correlated with Picea shadow cover than canopy cover. As a direct representation of impeded light transmittance, assessment of lateral tree shadows may represent a viable approach for investigating within stand compositional variation and temporal change among forest understory species, when a distinct physiognomic difference occurs between seral and climax overstory species.     

Populus tremuloides Michx. postfire stand dynamics in the northern boreal-cordilleran ecoclimatic region of central Yukon Territory, Canada

Postfire vegetation development among 8–185-year-old stand was assessed based on 100 relevés from the northern boreal-cordilleran ecoclimatic region (61–63°N) in the central Yukon Territory, Canada. Vegetation sampling included only stands thought to have originated from postfire Populus tremuloides Michx. regeneration that occurred on well drained and low gradient sites. Seven vegetation types were recognized based on cluster analysis and Kruskal–Wallis testing. Relevé ordination using Detrended Correspondence Analysis (70% explained variance) indicated six of the vegetation types represented a secondary successional chronosequence, based on their juxtaposition and a strong correlation of the primary axis with stand age (r = 0.89, P < 0.001). No correlation (P > 0.05) occurred between stand location and age. The youngest vegetation (8–11 years) had a moderate cover of P. tremuloides and Salix spp. up to 5 m tall, with a ground cover of Ceratodon purpureus (Hedw.) Brid. and Bryum caespiticium Hedw. This vegetation was expected to result in P. tremuloides, mixed P. tremuloides and Picea glauca (Moench) Voss, and P. glauca/Hylocomium splendens forest stands with increasing age, respectively. P. tremuloides//Calamagrostis purpurascens—Arctostaphylos uva-ursi stands formed the mid-seral vegetation. Along the chronosequence, total tree, P. tremuloides, shrub, and herb cover peaked 50–70 years after stand initiation; P. glauca cover, total and nonvascular species richness, and dominance concentration gradually increased (P < 0.001); vascular plant richness decreased; bryophytes had a U-shaped abundance pattern; and total plant cover was constant through time (125%). Richness totalled 113 species with averages of 13–18 per relevé. Coarse woody debris was most abundant (maxima 100–223 m³/ha) during the first 20 years of stand development then declined to <50 m³/ha. Successionally, a stem exclusion stage occurred (years 8–18), but with a delayed peak of 2–4 years and reduced densities (1.47 stems/m²) relative to southern boreal stands. No understory suppression, and therefore, no reinitiation stage occurred. Following stem exclusion, an accelerated canopy transition stage occurred relative to southern boreal forests due to early establishment rather than better height-growth rate of P. glauca relative to P. tremuloides. P. glauca tended to equal the cover of P. tremuloides 95–100 years after stand initiation. The oldest vegetation type in the chronosequence more closely resembled old-growth than a gap dynamic stage of development, possibly because of its youthful average age of 125 years. A modification was proposed for the canopy transition stage (Chen–Popadiouk stand development model) to account for the “forced” replacement of P. tremuloides by P. glauca. Differences in stand development were attributed to the cold northern climate.     

Climate and site characteristics affect juvenile trembling aspen development in conifer plantations across southern British Columbia

In southern British Columbia, juvenile trembling aspen is managed primarily as a competitor with conifers rather than for its ecological and economic value. As a result, brushing treatments have been applied on a widespread basis and this practice is likely to continue in the near future. Given the potential for climate change to affect our valuation of aspen, we require a better understanding of factors that affect its development, its competitive ability with conifers and its responses to brushing. We used data from 11 aspen management experiments to examine the influence of climate and site factors on aspen height, cover, and density in 17–24 year-old control stands and 9–16 years after manual cutting or girdling. Models explained 64% and 89% of the variation in aspen height in control and manually brushed stands, respectively, but were poor for girdling. Increasing length of the frost-free period was associated with increasing aspen height in control stands, whereas drier summer conditions on cool aspects favoured height growth of aspen suckers following manual cutting. We also examined the influence of climate and site factors on three simple competition indices that describe the height and density of aspen relative to conifer height, and then tested how well these indices predicted conifer growth. The density of aspen taller than conifers accounted for 39% of the variation in lodgepole pine diameter and the ratio of aspen/conifer height accounted for 33% of the variation in Douglas-fir height, suggesting that aspen competition was only moderately important to conifer growth. Our findings imply that aspen may become more productive with warmer summers provided it is not limited by summer moisture availability and that mixed stand management is a viable option in southern interior stands.     

An empirical model of crown shyness for lodgepole pine (Pinus contorta var. latifolia [Engl.] Critch.) in British Columbia

Crown shyness or canopy disengagement, the phenomenon wherein gaps around trees develop from swaying, whipping and shading, has been identified in the literature since the 1920s. Recent results by researchers at the University of Alberta have clearly described many of the processes involved for lodgepole pine [e.g. Rudnicki, M., Silins, U., Lieffers, V.J., Josi, G., 2001. Measure of simultaneous tree sways and estimation of crown interactions among a group of trees. Trees 15, 83–90; Rudnicki, M., Lieffers, V.J., Silins, U., 2003. Stand structure governs the crown collisions of lodgepole pine, Canadian Journal of Forestry Research 33, 1238–1244; Rudnicki, M., Silins, U., Lieffers, V.J., 2004. Crown cover is correlated with relative density, tree slenderness, and tree height in lodgepole pine. Forest Science 50, 356–363; Fish, H., Lieffers, V.J., Silins, U., Hall, R.J., 2006. Crown shyness in lodgepole pine stands of varying stand height, density, and site index in the upper foothills of Alberta. Canadian Journal of Forestry Research 9, 2104–2111]. However, explicit models of crown shyness are sparse in the literature. This paper describes the development of empirical models of crown shyness in lodgepole pine for British Columbia (BC). We measured crown area and neighbour locations on 60 trees growing in 13 stands in central BC. We estimated potential crown area (A_V) using stem maps and Voronoi polygons constrained by estimates of maximum crown width, and then related observed crown area (A_C) to A_V and additional individual tree variables. One of the nine prediction equations was coded into a spatially explicit tree growth model modified to evaluate the effects of crown shyness at the stand level. Crown shyness models validated well against two independent sources and when linked with a light model tRAYci [Brunner, A., 1998. A light model for spatially explicit forest stand models. Forest Ecology and Management 107, 19–46], increased the below-canopy light by 0.07–0.11.     

Successional development of silviculturally treated and untreated high-latitude Populus tremuloides clearcuts in northern Alberta,Canada

Seventy 1–28-year-old clearcuts were sampled to characterize post-harvest vegetation development and to determine the effect of mechanical site treatment and Picea glauca (Moench) Voss (white spruce) crop-seedling planting on regenerating boreal forest stands in the John D’Or—Wood Buffalo National Park area of northern Alberta in western Canada (58°35′N, 114°37′W). Natural Populus tremuloides/Rosa–Viburnum stands of wildfire origin (n = 25), widespread occurrence, and 52–91-year-old were sampled as a benchmark for comparison. Clearcut Populus-Picea and Picea stands reverted to early successional Populus tremuloides Michx. (trembling aspen)—dominated vegetation, with maximum sucker densities (mean 18 716, S.D. 13 239) within 4 years after stand initiation. Stem exclusion occurred most intensively 5–20 years after initiation, but was expected to continue until stands were >40–50-year-old. In untreated clearcuts, tree and understory shrub cover peaked near natural stand levels 18–20 years after harvesting, and graminoid cover remained constant (∼3%) but elevated compared to natural levels (<1%); whereas forb cover decreased linearly to natural stand levels by Year 28. The early composition of clearcuts was primarily composed of species that were common to the natural stands and also vegetatively reproduced. Mechanical site treatment and crop-seedling planting delayed attainment of maximum tree cover by 7 years, with total cover similar to natural stands. Site treatment reduced total shrub cover and prolonged the occurrence of elevated forb and graminoid cover values, probably in response to disruption of the pre-treatment ground vegetation. Calamagrostis canadensis L., a common crop-seedling competitor, was typically of minor importance on the sampled clearcuts compared to levels associated with more southerly boreal clearcuts. Detrended correspondence analysis ordinations based on species cover suggested untreated and treated clearcuts >13–16-year-old approximated the composition of natural stands. The data also suggested that silvicultural planting of P. glauca will accelerate stand development toward late-successional conifer-dominated vegetation relative to unplanted and natural stands.     

A crown profile model for Pinus radiata D. Don in northwestern Spain

A crown profile model was developed for radiata pine (Pinus radiata D. Don) in Galicia (northwestern Spain). Data from 443 trees located in 56 permanent plots, established by the Unidade de Xestión Forestal Sostible (UXFS) of the University of Santiago de Compostela in plantations of this species in the region, were used. The crowns of the trees were measured by a visual method based on similar triangles. Both simple geometric shapes and mathematical equations were used to describe the crown profiles. As crown profile models usually require variables that are expensive to measure, equations to estimate the maximum crown radius and the height to the maximum crown radius were also developed, using other easily measured tree and stand variables. Several models were fitted using a system of equations approach and accounting for an autocorrelated, heteroscedastic error structure. The selected crown profile model consists of a system of two allometric equations for the crown below (primarily shade needles) and above (primarily sun needles) maximum crown radius. The model explained 88% of the variability in crown radius with a mean error of 0.24 m.     

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.     

The interaction between competition in interior Douglas-fir plantations and disease caused by Armillaria ostoyae in British Columbia

Interior Douglas-fir trees in plantations were assessed for size differences related to the level of diseased neighbours infected with Armillaria ostoyae. The four Douglas-fir stands studied ranged from 25- to 34-year-old, and represented the oldest accessible planted stands in the Interior Cedar Hemlock (ICH) ecosystem in British Columbia. Twenty-three to 25, 10-m radius plots were established in each stand. The spatial coordinates, total height, and diameter at breast height of all live and dead trees in the plots were recorded. Subject trees whose competitors were contained in the 10-m radius plots were also identified. Trees were pulled out of the soil using a mechanical excavator and the root systems were surveyed for evidence of infection by A. ostoyae. Stem disks were taken from each tree at 1.3 m above the ground for a determination of basal area. Increasing proportion of diseased trees in the plots resulted in less total plot basal area, but did not affect the mean basal area or height. Individual subject tree basal area was negatively related to the level of disease in surrounding competitors, opposite to expectations; however, diseased subject trees had reduced height and basal area compared to disease-free subject trees. Increasing competition reduced both the height and basal area of the trees, while regular distribution of all trees increased both total and mean plot basal area but not height. Disease incidence at the plot level and in individual subject trees was mainly affected by the neighbourhood conditions in which it grew, and was also related to disease intensity in the tree root systems. Although disease may alter resource partitioning among trees, the utilization of these resources is mostly limited by the increasing disease incidence as the stands age, the higher probability of larger trees being diseased with time, the occurrence of dead trees in clumps, and the high probability that dead trees will eventually infect live neighbours. The widespread belowground incidence of A. ostoyae in the ICH, its rapid colonization of stumps, and its wide host range can reduce site potential in managed stands.     

Influence of woody and herbaceous vegetation control on leaf gas exchange,water status,and nutrient relations of eastern white pine (Pinus strobus L.) seedlings planted in a central Ontario clearcut

The influence of herbaceous and woody vegetation control, either singly or in combination, on leaf gas exchange, water status, and nutrient relations of planted eastern white pine (Pinus strobus L.) seedlings was examined in a central Ontario clearcut over four consecutive growing seasons (GSs). Net carbon assimilation (A_n), leaf conductance to water vapour (G_wv), water use efficiency (WUE), and midday leaf water potential (ψ_m) were measured periodically during the second to fourth GSs of vegetation control treatments, while leaf nutrient relations were examined in GS five. Leaf A_n and G_wv were reduced (p ≤ 0.05) in the presence of herbaceous vegetation in GS two, by both herbaceous and woody vegetation in GS three, and only by woody vegetation (largely trembling aspen (Populus tremuloides Michx.)) in GS four. Leaf WUE was increased (p ≤ 0.05) in all three GSs in which herbaceous vegetation control was applied and where woody vegetation provided partial shading of planted white pine. Leaf water status was comparatively less responsive to vegetation control treatments, but leaf ψ_m was increased (p ≤ 0.05) in the presence of woody vegetation in GSs two and four, likely due to shading and reduced atmospheric evaporative demand of the white pine seedling environment. Within a given GS, the effects of vegetation control on A_n, G_wv, and ψ_m were strongly linked to treatment-induced changes in total vegetative cover, and light and soil moisture availability. Seedling height, diameter, and volume growth rates were positively correlated with A_n and WUE in GSs two and three, but less so in GS four. Vector analysis suggested that herbaceous competition induced foliar N, P, and K deficiencies in five-year-old white pine seedlings while competition from aspen resulted in foliar Ca deficiency.     

Impacts of thinning on structure,growth and risk of crown fire in a Pinus sylvestris L. plantation in northern Spain

We studied the combined effects of thinning on stand structure, growth, and fire risk for a Scots pine thinning trial in northern Spain 4 years following treatment. The thinning treatments were: no thinning, heavy thinning (32–46% of basal area removed) and very heavy thinning (51–57% of basal area removed). Thinning was achieved via a combination of systematic and selective methods by removing every seventh row of trees and then by cutting suppressed and subdominant trees in the remaining rows (i.e., thinning from below). Four years after thinning, mean values and probability density distributions of stand structural indices showed that the heavier the thinning, the stronger the tendency towards random tree spatial positions. Height and diameter differentiation were initially low for these plantations and decreased after the 4-year period in both control and thinned plots. Mark variograms indicated low spatial autocorrelation in tree diameters at short distances. Diameter increment was significantly correlated with the inter-tree competition indices, and also with the mean directional stand structural index. Two mixed models were proposed for estimating diameter increment using a spatial index based on basal area of larger trees (BALMOD) in one model versus spatial competition index by Bella in the other model. As well, a model to estimate canopy bulk density (CBD) was developed, as this variable is important for fire risk assessment. Both heavy and very heavy thinning resulted in a decrease of crown fire risk over no thinning, because of the reduction in CBD. However, thinning had no effect on the height to crown base and thus on the flame length for torching. Overall, although thinning did not increase size differentiation between trees in the short term, the increase in diameter increment following thinning and the reduction of crown fire risks support the use of thinning. Also, thinning is a necessary first step towards converting Scots pine plantations to more natural mixed broadleaved woodlands. In particular, the very heavy thinning treatment could be considered a first step towards conversion of overstocked stands.     

中国沙棘树冠上中下部枝条的水碳代谢与生长结实性状研究

目的 为了解沙棘树冠不同位置枝条的水碳代谢与生长结实的关系,也为制定针对沙棘树形培养的栽培技术措施提供一定的理论依据。 方法 本研究选取中国沙棘树冠上部、中部、下部的2年生枝条为研究对象,比较其水分状况、光合作用、非结构性碳水化合物（NSC）含量、枝叶生长、结实性状和果实营养成分。 结果 树冠不同部位枝条凌晨水势差异不显著,下部枝条正午水势显著高于上部和中部枝条;中部枝条凌晨导水损失率（PLC）显著低于上部和下部枝条,下部枝条正午PLC显著高于上部和中部枝条;上部枝条的茎、叶面积比导水率显著高于中部和下部枝条;净光合速率按从大到小的顺序为上部枝条>中部枝条>下部枝条;中部枝条枝条木质部NSC含量显著高于上部枝条,但二者与下部枝条差异都不显著,各位置间枝条韧皮部NSC含量无显著性差异,上部和中部枝条的叶片NSC含量显著性高于下部枝条;下部枝条的花芽纵横径、纯花芽比例、发芽率、新梢数量、新梢基径、叶面积、比叶质量均显著低于上部和中部枝条,下部枝条的果实纵横径、坐果率、可溶性固形物含量也低于上部和中部枝条,上部枝条的枝长、基径显著高于中部枝条,中部枝条的百果质量和果实纵横径显著高于上部枝条,不同部位枝条总黄酮、维生素C和可滴定酸含量差异不显著。 结论 下部枝条受遮光的影响较大,明显限制光合产物摄取和生长,并较大程度的影响了其结实性状,上部枝条在生长上占有优势,中部枝条在结实性状上占有优势。因此,中国沙棘的树形培养应充分考虑其光照条件,及时清除下部低光照区域枝条;同时注意营养生长和生殖生长的平衡,充分利用树冠上部和中部枝条结实是提高沙棘产量和品质的重要措施。     

Spatial distribution,architecture, and development of the root system of Pinus banksiana Lamb. in natural and planted stands

In the province of Québec, Canada, the majority of planted jack pine (Pinus banksiana Lamb.) seedlings are produced in rigid wall containers. More than 95% of them exhibit deformations of the root system which may induce stem instability. Studies of the root architecture of planted jack pine have been limited to a 30 cm radius from the stem, as barely any studies have been devoted to naturally regenerated stands. Moreover, only a few researches have focused on temporal evolution of root systems. The aim of the present study was to characterize the architectural, spatial, and temporal development of jack pine roots in natural and planted stands. Study sites were located in the continuous boreal forest of Quebec. The plantation was done in 1987, so that the trees were 15 years old at the time of sampling. Trees from natural stand had regenerated after a fire in 1983 and were 13–16 years old. The root systems of 14 jack pine trees per site were manually excavated up to a <5 mm diameter, without regard to their distance from the stem. The number, length, diameter, and the spatial and temporal development of roots were analyzed according to three scales of root architecture: the root system, axes, and segments. Overall, the numbers and lengths of roots were higher with planted pines. However, naturally regenerated trees displayed a better distribution of their roots around the stem and at depth, combined with more rapid length growth during the first years. In natural stands, all the trees had a taproot and 30% of the main roots originated at a depth of more than 20 cm, and they are regularly distributed around the stems. Planted trees did not present a taproot and 97% of the main roots originated in the first 20 cm beneath the soil surface. Moreover, 50% of root length was located in one-third of the area surrounding the stems, an area that corresponded to the furrow. Finally, the annual development of lateral roots in planted stand displayed a 5-year delay when compared with natural stand, which also affected maximum growth length and development of the branching pattern. Root distribution and temporal development are known to play a major role in the stability of aerial parts. Seedling production methods, container type, site preparation and planting techniques need to be examined in greater detail in order to assess their effect throughout the development of the root system. It is necessary to compare different sylvicultural practices and with natural/planted stands to gain a clearer understanding of this problem.     

Change in historic fire disturbance in a Garry oak (Quercus garryana) meadow and Douglas-fir (Pseudotsuga menziesii) mosaic,University of Victoria,British Columbia,Canada: A possible link with First Nations and Europeans

We investigated late Holocene vegetation and fire changes on southeast Vancouver Island, British Columbia, through high-resolution analysis of pollen, spores and charcoal contained within a forest soil. Located in the Mystic Vale Endowment lands, University of Victoria campus, the site occurs adjacent to Garry oak (Quercus garryana) meadows within a Douglas-fir (Pseudotsuga menziesii) forest regionally influenced by First Nations burning. The age of the sequence is estimated from the occurrence of non-native plantain (Plantago spp.) pollen, between the early 19th century and the present. Prior to the 1850s, the Mystic Vale supported a Douglas-fir forest with a sword fern (Polystichum munitum) understory. Low-intensity fires may have burned either at or near the site, but did not destroy the stand. From the time of European settlement (ca. 1850s to 1872) to the early 20th century, Douglas-fir forests with a sword fern understory persisted but with more openings than in the past. Adjacent forests were cleared leading to successional stands of red alder (Alnus rubra). The site may have supported more grasses near or after 1872 because of adjacent cultivation and the introduction of livestock. Local establishment of Garry oaks at the margin of a field adjacent to the deposition site may have occurred at this time. The strong charcoal signal may be attributable to clearing and local fires of European settlers. Exotic weedy species such as plantain arrived during this time. From about the mid 20th century to the present a closed canopy Douglas-fir forest returned. Pre-European charcoal concentrations were significantly greater than modern-day charcoal concentrations. Peak charcoal concentrations coincided with the onset of European settlement in the area, a period in which land-clearing is thought to have been aided by the use of fire. This study suggests that the observed changes in charcoal concentrations in pre- and post-European contact time may be linked with a switch from aboriginal to European ignition sources. The study provides a historical impetus to consider partially restoring parts of southeast Vancouver Island by re-introducing fire via the application of controlled burns.     

Testing site index–site-factor relationships for predicting Pinus contorta and Picea engelmannii×P. glauca productivity in central British Columbia, Canada

Measures of forest productivity for various site conditions are necessary for forest management planning, where timber production is the objective. This study was undertaken to test whether autecological productivity relationships developed for lodgepole pine (Pinus contorta) and interior spruce (Picea engelmannii×P. glauca) using the biogeoclimatic ecosystem classification system of British Columbia are useful as practical field-based procedures to predict site index. Independent data sets consisting of 111 plots for pine and 114 plots for spruce were collected for use in testing the bias and precision of the models. A regression on residuals (predicted minus test values) indicated that the lodgepole pine model was unbiased in estimating site index (p=0.08). However, there was a lack of precision, with a square root of the mean squared prediction error (root-MSPR) of 2.8 m. Only 56% of the test plots had differences from the predicted values of 2.0 m or less. Residual analysis showed that the interior spruce model was biased in estimating site index (p<0.01), generally predicting greater site index than the test values. The model also lacked precision, with a root-MSPR of 3.2 m. Only 44% of the test plots had differences from the predicted values of 2.0 m or less. Forest managers requiring a site-index prediction tool need to decide whether the degree of accuracy precision provided by these models is acceptable.     

Influence of initial planting spacing and genotype on microfibril angle,wood density,fibre properties and modulus of elasticity in Pinus radiata D. Don corewood

Pinus radiata D. Don trees from six clones, grown at initial spacings of 2500 stems ha⁻¹ and 833 stems ha⁻¹ were destructively harvested. For these trees wood properties were measured on radial slices sampled at a height of 1.4 m above the ground. Relative to wide spacing, close initial stand spacing significantly reduced microfibril angle (MFA) and ring width and significantly increased dynamic modulus of elasticity (MOE), fibre length, latewood percentage and cell wall thickness. Density and fibre width were not significantly different between spacing treatments. Examination of the influence of genetic population on wood properties indicated that genotype significantly influenced MFA, MOE and ring width. The key wood properties MFA, MOE and fibre length were regressed against tree diameter, height and stem slenderness. All three wood properties were most strongly correlated with stem slenderness. Multiple regression models developed for MFA, MOE and ring width accounted for respectively 62%, 81% and 58% of the variation in these variables. The following changes occurred in sampled properties with increasing ring number: MFA and ring width declined markedly; MOE and fibre length increased markedly; latewood percentage and cell wall thickness increased slightly; and density and fibre width did not show any radial trend.