Wide Range Of Tree Sizes Research Articles

The effect of tree and harvester size on productivity and harvester investment decisions

ABSTRACT Long-term machine-derived data sets comprising 140,000 trees were collected from four harvesters of equal age and similar working conditions, into two machine size classes, viz. two Ponsse Bears and two smaller Ponsse Beavers. Productivity functions for each size class were modelled using a nonlinear mixed effects approach. Based on these functions, unit costs and their sensitivity to utilization rates and cost of capital were assessed. Results showed that despite considerably higher capital costs (32%) on the Bear, a 50% higher mean productivity resulted in a unit cost only 17% higher than the Beaver in a disadvantageous scenario (high interest rates and low utilisation), and a 6% lower unit cost than the Beaver in an advantageous scenario (low interest and high utilisation), within the range of tree sizes observed. Between these extremes, only marginal differences in unit costs were observed. This demonstrates that the difference in ownership and operating costs between larger and smaller harvesters is largely negated by the difference in productivity rates. These results can provide useful insight into timber harvester investment decisions. Harvesters from two adjacent size classes can be used interchangeably at the same unit cost within a wide range of tree sizes despite productivity differences. It should be noted that increased repair costs and an eventual reduction in expected economic lifetime on a smaller harvester, or the negative effects of using a larger harvester in smaller trees, e.g. thinning operations, were not taken into account in this work.

Mapping tillage direction and contour farming by object-based analysis of UAV images

Tillage is a primary agricultural task that causes progressive soil movement and, consequently, severe erosion in sloping farmland, with a high impact on crop productivity, soil quality and landscape features. Governments and public administrations acknowledge the need to control tillage operations for a better soil conservation in vulnerable areas, recommending the practice of contour farming. Despite this importance, there is currently no mechanism for the effective and large-scale monitoring of tillage patterns at the field or regional scale. Accordingly, this research combined aerial images taken with unmanned aerial vehicles and object-based image analysis (OBIA) to develop an innovative OBIA4tillage procedure with three main objectives: (i) analysing plowed agricultural fields, identifying and mapping the tillage marks, and automatically computing the main direction of the tillage furrows, (ii) validating the procedure quality in different scenarios by evaluating the accuracy of the results as affected by the sensor used (visible-light vs. multispectral), background soil hue, and ground vegetation density; and (iii) mapping contour farming and non-contour farming areas as indicators of potential low and high soil erosion risk, respectively. Twenty olive parcels from two different locations with a wide range of tree sizes, soil hue, parcel shapes and land slopes were selected as model systems to develop and validate the procedure. The OBIA4tillage procedure produced tillage maps with very high accuracy for both RGB and multispectral images (R2 of 0.99 and 0.93, respectively), as obtained from the linear equation between estimated and ground-truth values. The results were similar in clear and dark soils (R2 of 0.96 in both cases), although there were notable differences between areas of dense ground vegetation or bare soil (R2 of 0.99 in both cases) and areas of medium vegetation cover (R2 of 0.81). The application of contour farming in the study region was moderate at location 1 (42.35% of the study area) but more widespread at location 2 (72.60% of the study area), which revealed the uneven involvement of the local farmers in the challenge of controlling soil erosion risks. The valuable information in the OBIA4tillage outputs can also be used to study tillage events at various spatial and temporal scales, feed soil erosion models and promote good agricultural and environmental conditions measures implemented at the parcel scale.

Epiphytes in wooded pastures: Isolation matters for lichen but not for bryophyte species richness.

Sylvo-pastoral systems are species-rich man-made landscapes that are currently often severely threatened by abandonment or management intensification. At low tree densities, single trees in these systems represent habitat islands for epiphytic cryptogams. Here, we focused on sycamore maple (Acer pseudoplatanus) wooded pastures in the northern European Alps. We assessed per tree species richness of bryophytes and lichens on 90 sycamore maple trees distributed across six study sites. We analysed the effects of a range of explanatory variables (tree characteristics, environmental variables and isolation measures) on the richness of epiphytic bryophytes and lichens and various functional subgroups (based on diaspore size, habitat preference and red list status). Furthermore, we estimated the effect of these variables on the occurrence of two specific bryophyte species (Tayloria rudolphiana, Orthotrichum rogeri) and one lichen species (Lobaria pulmonaria) of major conservation concern. Bryophytes and lichens, as well as their subgroups, were differently and sometimes contrastingly affected by the variables considered: tree diameter at breast height had no significant effect on bryophytes but negatively affected many lichen groups; tree phenological age positively affected red-listed lichens but not red-listed bryophytes; increasing isolation from neighbouring trees negatively affected lichens but not bryophytes. However, the high-priority bryophyte species T. rudolphiana was also negatively affected by increased isolation at small spatial scales. Orthotrichum rogeri was more frequent on young trees and L. pulmonaria was more frequent on trees with thin stems and large crowns. The results indicate that local dispersal is important for lichens, whereas long distance dispersal seems to be more important for colonisation by bryophytes. Furthermore, our study highlights that different conservation measures need to be taken depending on the taxonomic and functional species group or the individual species that is addressed. In practice, for the conservation of a high overall richness in sylvo-pastoral systems, it is crucial to sustain not only old and large trees but rather a wide range of tree sizes and ages.

Fire scar growth and closure rates in white oak (Quercus alba) and the implications for prescribed burning

In burned forestlands, fire scar wounds commonly occur on tree stems as a result of cambial heating. In hardwood forests in particular, wounding can lead to stem decay with the extent of decay being related to scar size and exposure time. Therefore, wound closure rates are important to understand in the context of fire management such that allowing sufficient time for wound closure to occur between fires would enhance wood quality. Conversely, in the context of wildlife management, understanding wound closure rates would improve fire prescriptions needed for creating basal tree cavities as keeping wounds open prior to wound closure could enhance cavity development. The objectives of this study were to quantify growth and wound closure rates of white oaks (Quercus alba), one of the most valuable tree species in the central U.S. to both commercial forestry and wildlife. From historically burned, mature, oak-hickory forest site in Missouri, we sampled a wide range of tree sizes, fire scar sizes, and fire scar ages to determine the environmental and tree factors related to closure rates. Dendrochronological techniques were paired with new approaches of digitizing tree rings to capture malformed woundwood areas. The time required for wound closure ranged from 1 to 24years and was significantly correlated to scar size. Surprisingly, post-fire growth trends were positive following scarring. Growth was positively related to scar and tree size. With this information, we expect that the process of basal wound closure and tree growth can be considered in a quantitative framework and used to guide fire management for wood quality or wildlife tree cavities.

Comprehensive dataset of mangrove tree weights in Southeast Asia

AbstractWe assembled a dataset tabulating the weights of Thai and Indonesian mangrove trees that we measured between 1982 and 2001. We selected four Thai study sites in Phang Nga, Ranong, Satun, and Trat Provinces and one site in eastern Indonesia on Halmahera Island in Maluku Province. The stands in Ranong Province and on Halmahera Island were in primary forests with data collected in the 1980s and the remaining stands were in secondary forests with data collected later. We collected 124 tree samples from ten species (Avicennia alba, Bruguiera cylindrica, B. gymnorrhiza, Ceriops tagal, Rhizophora apiculata, R. mucronata, Sonneratia alba, S. caseolaris, Xylocarpus granatum, and X. moluccensis) and measured the root weights of 32 individuals of nine species (A. alba, B. cylindrica, B. gymnorrhiza, C. tagal, R. apiculata, R. mucronata, S. alba, S. caseolaris, and X. granatum). All sampled trees were subjected to a standardized protocol to obtain aboveground weights. The trunks were divided into horizontal segments from which the leaves and branches were collected separately. Roots were collected by winching them out of the ground, by trench digging, or by complete excavation. Thus, we were able to compile the weights of the trunk, branches, leaves, and roots of each tree sampled. Aerial roots were included in root weight measurements, although they were collected above ground. We compiled separate lists of trunk diameters, trunk heights, heights of the lowest living branches, and the heights of aerial roots on the trunks of trees in different size categories. Our dataset includes a wide range of tree sizes (maximum trunk diameter 48.9 cm), geographical locations (1°10′N–12°24′N, 98°32′E–123°49′E) and organ weights (trunks, branches, leaves, and roots), and therefore should prove useful in future biomass studies of mangrove forests.

Scaling-up from tree to stand transpiration for a warm-temperate multi-specific broadleaved forest with a wide variation in stem diameter

Previous studies have demonstrated a clear relationship between diameter at breast height (DBH) and tree transpiration (QT) in multi-specific broadleaved forests. However, these studies were conducted with a limited range of tree sizes and species, and thus many multi-specific broadleaved forests fall outside these conditions. Therefore, this study examined the relationship between DBH and QT in a warm-temperate multi-specific broadleaved forest (n = 12 species) with a wide range of tree sizes (5.0–70.0 cm DBH) using the Granier-type heat dissipation method. The results showed that, although sap flow density varied between individual trees and species, there was a significant relationship between log QT and log DBH (r2 = 0.66, P < 0.001) because of the strong dependence of sapwood area on DBH. This study confirmed the applicability of the relationship for the stand transpiration (EC) estimates even in a multi-specific broadleaved forest with a wide variation in DBH. Our results also revealed that selecting the sample trees in descending order of DBH effectively reduced potential errors in EC estimates for a specific sample size, as larger trees contribute more to EC. This information should be useful for future studies investigating the transpiration of multi-specific broadleaved forests, reducing errors during the scaling-up procedure.

Linking functional traits and demographic rates in a subtropical tree community: the importance of size dependency

Summary An important goal in plant community ecology is to understand how species traits determine demographic performance. Several functional traits have been shown to correlate with growth and mortality rates in trees, but less is known about how the relationships between functional traits and demographic rates change with tree size. We examined the associations of functional traits with growth and mortality across 43 tree species in the Fushan 25‐ha subtropical rain forest plot in northern Taiwan. We estimated the 95th percentile maximum stem diameter, wood density and six leaf functional traits (leaf area, specific leaf area, thickness, succulence, and mass‐based nitrogen and phosphorus contents) obtained from leaves on juvenile and adult individuals of each species. To quantify size‐dependent changes in growth and mortality, relative growth rate (RGR) and mortality were estimated as a function of stem diameter using hierarchical Bayesian models. These rate estimates were then correlated with functional traits at a range of stem diameter classes. Relationships between functional traits and demographic rates varied with tree size. Maximum size was positively correlated with RGR across a wide range of tree sizes. Wood density was negatively correlated with RGR and mortality for small‐sized trees. Leaf traits such as leaf area and specific leaf area at juvenile and adult stages were associated more strongly with demographic rates for corresponding sizes than from other sizes. Synthesis. The observed size‐dependent changes in the trait–demography relationships are possibly due to the effects of developmental and environmental changes with increasing tree size. The underlying effects of functional traits on demographic performance vary with tree size, and this should influence dynamics in a tree community.

Linking size‐dependent growth and mortality with architectural traits across 145 co‐occurring tropical tree species

Tree architecture, growth, and mortality change with increasing tree size and associated light conditions. To date, few studies have quantified how size-dependent changes in growth and mortality rates co-vary with architectural traits, and how such size-dependent changes differ across species and possible light capture strategies. We applied a hierarchical Bayesian model to quantify size-dependent changes in demographic rates and correlated demographic rates and architectural traits for 145 co-occurring Malaysian rain-forest tree species covering a wide range of tree sizes. Demographic rates were estimated using relative growth rate in stem diameter (RGR) and mortality rate as a function of stem diameter. Architectural traits examined were adult stature measured as the 95-percentile of the maximum stem diameter (upper diameter), wood density, and three tree architectural variables: tree height, foliage height, and crown width. Correlations between demographic rates and architectural traits were examined for stem diameters ranging from 1 to 47 cm. As a result, RGR and mortality varied significantly with increasing stem diameter across species. At smaller stem diameters, RGR was higher for tall trees with wide crowns, large upper diameter, and low wood density. Increased mortality was associated with low wood density at small diameters, and associated with small upper diameter and wide crowns over a wide range of stem diameters. Positive correlations between RGR and mortality were found over the whole range of stem diameters, but they were significant only at small stem diameters. Associations between architectural traits and demographic rates were strongest at small stem diameters. In the dark understory of tropical rain forests, the limiting amount of light is likely to make the interspecific difference in the effects of functional traits on demography more clear. Demographic performance is therefore tightly linked with architectural traits such as adult stature, wood density, and capacity for horizontal crown expansion. The enhancement of a demographic trade-off due to interspecific variation in functional traits in the understory helps to explain species coexistence in diverse rain forests.

On the growth of locally interacting plants: differential equations for the dynamics of spatial moments

Ecologists are faced with the challenge of how to scale up from the activities of individual plants and animals to the macroscopic dynamics of populations and communities. It is especially difficult to do this in communities of plants where the fate of individuals depends on their immediate neighbors rather than an average over a larger region. This has meant that algorithmic, agent-based models are typically used to understand their dynamics, although certain macroscopic models have been developed for neighbor-dependent, birth death processes. Here we present a macroscopic model that, for the first time, incorporates explicit, gradual, neighbor-dependent plant growth, as a third fundamental process of plant communities. The model is derived from a stochastic, agent-based model, and describes the dynamics of the first and second spatial moments of a multispecies, spatially structured plant community with neighbor-dependent growth, births, and deaths. A simple example shows that strong neighborhood space-filling during tree growth in an even-aged stand of Scots pine is well captured by the spatial-moment model. The space-filling has a spatial signature consistent with that observed in several field studies of forests. Small neighborhoods of interaction, nonuniform spacing of trees, and asymmetric competition all contribute to the buildup of a wide range of tree sizes with some large dominant individuals and many smaller ones.

Biomass, basic density and biomass expansion factor functions for European beech (Fagus sylvatica L.) in Denmark

The objective of this study was to analyse the within-tree allocation of biomass and to develop biomass functions for above- and below-ground components of European beech in Denmark. Separate functions were developed for stem, branches, below-ground stump and root system, total above-ground biomass and total tree biomass. For each of these components or aggregate components, models were also developed for the average basic density of wood and bark. To enhance the versatility of the models, a function for estimating the biomass expansion factor (BEF) was also developed. The functions were based on 66 trees measured for total biomass. Model performance was evaluated based on 74 trees measured only for above-ground biomass. The trees were sampled in 18 different forest stands covering a wide range of tree sizes and stand treatments. Models were estimated using a linear mixed-effects procedure to account for within-stand correlations. The functions for biomass and BEFs included only diameter at breast height and total tree height for individual trees as predictor variables. Inclusion of additional variables reflecting site quality or stand density did not improve model performance. The functions for basic density included individual tree diameter, tree height and quadratic mean diameter as predictor variables, indicating an effect of stand density on the basic density of wood and bark.

Competition, species interaction and ageing control tree mortality in boreal forests

Summary1. Tree mortality has important influences on forest structure and composition, but the mechanisms that cause tree mortality are not well understood. Asymmetric competition is known to be a dominant cause of plant mortality, but this idea has not received much attention in studies of long‐lived trees.2. We hypothesised that while tree mortality is dependent on size relative to neighbours as a result of asymmetric competition, tree mortality of shade‐tolerant species varies little with size because of their physiological and morphological adaptations to shaded environments. Furthermore, we hypothesised that tree mortality is higher in more crowded stands because of higher average resource competition, in conspecific stands because of potential negative intra‐specific interactions, and in older stands because of the physiological limitations and susceptibility to minor disturbances of large trees.3. Using data from repeatedly measured permanent sampling plots that covered a wide range of tree sizes, stand developmental stages and stand compositions in boreal forests, we simultaneously tested, by boosted regression tree models, the effects of an individual’s relative size, stand crowding, species interaction and ageing on mortality of Pinus banksiana, Populus tremuloides, Betula papyrifera and Picea mariana.4. Mortality increased strongly with decreasing relative size for all study species, and the size‐dependent mortality was stronger for shade‐intolerant than for shade‐tolerant species. With increasing stand basal area, mortality increased for Pinus banksiana, Populus tremuloides and Picea mariana but decreased for Betula papyrifera. Mortality was higher in stands with more conspecific neighbours for Populus tremuloides, Betula papyrifera and Picea mariana, but was slightly lower for Pinus banksiana. Mortality also increased with stand age for all species. Furthermore, the size‐dependent mortality was generally stronger in more crowded stands.5. Synthesis. Our findings show that tree mortality over a wide range of tree sizes, stand developmental stages and stand compositions in non‐equilibrium boreal forests was strongly controlled by competition, but species interactions and ageing were also important mechanisms. Furthermore, the relative importance of these mechanisms to tree mortality differed with the shade tolerance of species.

Increasing wood production through old age in tall trees

How long forest trees can sustain wood production with increasing age remains an open question, primarily because whole-crown structure and growth cannot be readily measured from the ground or on felled trees. We climbed and directly measured crown structures and growth rates of 43 un-suppressed individuals (site trees) of the two tallest species – Eucalyptus regnans and Sequoia sempervirens – representing a wide range of tree sizes and ages. In both species, ground-level measurements of annual growth, including height, ring width, and basal area increment, exhibited the oft-reported trend of decreasing growth (or no change in growth) with age, yet wood production of the entire main trunk and whole crown both increased with size and age up to and including the largest and oldest trees we measured. The balance between structural metrics of whole-crown respiratory demands (cambium area, inner bark volume, sapwood volume, and heartwood deposition area) and photosynthetic capacity (leaf area and green bark area) was statistically independent of size but not age. After accounting for the effect of size, trees with lower potential respiratory demands grew more than trees with higher potential respiratory demands per unit photosynthetic area. The strongest determinant of tree energy balance was the ratio of aboveground cambium area to leaf area. Among the site trees we examined, over 85% of the variation in annual wood production was explained by variation in size, and the proportion of total aboveground wood production in appendages (branches, limbs, and reiterated trunks) increased linearly with size. With increasing age in both species, the proportion of annual wood production converted to heartwood increased in main trunks and appendages. The oldest tree we measured produced more heartwood in its main trunk over 651 years (351 m

Decoupling structural and environmental determinants of sap velocity: Part I. Methodological development

This paper presents a novel theoretical framework for the study of individual tree sap flow that incorporates both spatial and temporal variability in sap velocities. In this formulation, the instantaneous sap velocity at any point in the radial profile of xylem tissue is defined as the product of a time-invariant sap velocity distribution and a time-varying term which is defined as a stem conductance. We hypothesize that the characteristic distribution of sap velocity is relatively uniform both within individual trees and between trees of the same species if location in the xylem tissue is expressed in normalized units relative to the total xylem depth (i.e. tree size). Experimental evidence confirms our hypothesis in the case of a population of sugar maples in a mixed deciduous forest and dwarf apple trees in an orchard, despite the fact that observations were drawn from a wide range of tree sizes and under varying soil moisture levels and atmospheric conditions that determines water demand. Furthermore, profiles of sap velocity and resulting integrals of total sap flow exhibit significant reduction in bias (by 30–40%) in comparison to prior methods used to extrapolate point observations of sap velocity. The method we describe exhibits the greatest improvement when only a small fraction of the total sapwood is measured, which is the typical scenario for most applications. While these results require further confirmation in order to be generalized, they nevertheless offer the basis to improve both the specific sampling strategies used to estimate whole-tree transpiration using sap velocity probes as well as methods employed to upscale water use of individual trees to larger scales for evaluation of landscape water balance.

Trends in forestry modelling.

Abstract Different types of models have been developed and applied to address various problems and issues in forestry. This paper reviews modelling trends in four areas, namely, forest management planning and decision-making, forest dynamics and growth projection, forest landscape and spatial models and participatory forest management models. The first type includes decision models generally structured as optimization models applied to forest planning. These models evolved from single objective to multiple objectives with spatial dimensions, including visualization. The second type includes forest dynamics models designed to examine the growth response of trees using process-based empirical or conceptual models. Demands for 'close to nature' forest management created new challenges for modellers to provide models with expanded capabilities to deal with tree growth, succession, and competition in stands with many species and wide range of tree sizes. The third type takes advantage of increased computational and graphic capabilities to model landscapes and display them as 'virtual' realities. These models combine spatial models such as geographical information systems (GIS), visualization tools and analytical models to form an integrated decision support system. The fourth type includes participatory models designed to accommodate multiple stakeholders in addressing collaborative forest management. These models are particularly adaptable to community-based forest management. Finally, the uses of models as 'learning' tools and as 'problem structuring' tools are also described.

Does tree size influence timing of flowering in Cerberiopsis candelabra (Apocynaceae), a long-lived monocarpic rain-forest tree?

Cerberiopsis candelabra is a long-lived monocarpic rain-forest tree endemic to New Caledonia that shows mass flowering across a substantial proportion of a population, and across a substantial number of populations. We investigated the relationship between tree size and flowering (and subsequent dying) across 18 populations from the flowering event of 2003 in order to understand the role of possible size thresholds for flowering in the life history and regeneration ecology of this monocarpic species. There was a strong positive correlation between trunk diameter and the incidence of flowering when population data were combined. However, the relationship between size and flowering was complex in that flowering occurred across a wide range of tree sizes, with almost complete overlap in size between flowering (5–79 cm dbh) and non-flowering trees (5–64 cm dbh), and with large trees in both the flowering and non-flowering state in the same population. In about half the populations studied there was no significant difference in mean trunk diameter of flowering and non-flowering trees. Nonetheless, we suggest that tree size may play a fundamental role in the life history and regeneration ecology of this species. The seedlings appear to be relatively shade-intolerant and dependent on large canopy gaps for recruitment. A significant effect of mass flowering and subsequent death of multiple large trees is the potential to form large canopy gaps and enhance seedling survival, as the gap is temporally linked with seed germination. However, it is unclear why there is such a large size range of flowering trees, i.e. whether this is just a consequence of the proximate cue, or whether the optimal size for flowering does indeed vary among individuals.

A comparison of heat pulse and deuterium tracing techniques for estimating sap flow in Eucalyptus grandis trees.

Sap flow rates were measured simultaneously by the heat pulse and deuterium tracing techniques in nine Eucalyptus grandis W. Hill ex Maiden. trees at two sites (1) to compare results from the two techniques and (2) to assess the impact of the assumptions underlying the deuterium tracing method on the calculation of sap flow for a range of tree sizes. The trees ranged in height from 4 to 14 m with leaf areas of 5 to 35 m(2). In all trees, sap flow estimated by the deuterium tracing technique was higher than sap flow estimated by the heat pulse method, with differences of 11 to 43% in eight of the trees and 113% in one tree. The largest difference was attributed to errors in the heat pulse method, as indicated by aberrant relationships between sap flow measured by the heat pulse method and tree size characteristics (i.e., diameter, sap wood area, leaf area) for that tree compared with the other experimental trees. Drilling holes in the trees to allow injection of deuterium had no significant effect on sap flow, even when 32 holes were drilled. Sap flow measured by the heat pulse method was only lower after drilling than before drilling in three trees, and the difference only persisted for about 1 h. Deuterium concentrations of water collected from the tree canopies had not returned to background values 17 days after injection. Twenty-one days after injection, sapwood and heartwood samples taken from trunks near the injection sites contained considerable concentrations of deuterium, indicating that some of the deuterium injected into the trees was still present. An experiment performed on two trees showed that deuterium was stored in the heartwood and sapwood throughout the trees, and its distribution within the trees four days after injection was similar whether it was injected into only the sapwood (where it should mix with sap and be transported from the tree most readily) or into both the sapwood and heartwood, indicating that there was considerable movement of deuterium between the heartwood and sapwood. Deuterium storage was accounted for by an approximate means in the sap flow calculations, and may have resulted in an error of about 10% in sap flow estimated by this method. We conclude that the heat pulse and deuterium tracing techniques can be used simultaneously to increase the number of sap flow measurements obtained from a forest, thereby increasing the precision of forest water use estimates. Their combination would be most effective in stands with a wide range of tree sizes and sap flow rates, where the relative differences in sap flux estimates between the methods is small compared with differences in sap flow between trees.

Comparative ecology of 11 sympatric species of Macaranga in Borneo: tree distribution in relation to horizontal and vertical resource heterogeneity

1 Horizontal and vertical heterogeneity of resource availability, coupled with the specialized use of resources by tree species, results in complex patterns of tree species distributions in tropical rain forests. We studied the horizontal and vertical distributions of 4014 individuals in 11 species of early successional Macaranga (Euphorbiaceae) in tropical rain forest in Sarawak, Malaysia. 2 The horizontal distribution of individual trees was assessed with respect to crown light levels, establishment microsites, and broader scale variation in soil textural properties. Vertical distribution was assessed using an allometric approach to estimate maximum tree height (Hmax) and the slope of the sapling height–diameter relationship. 3 Average light levels intercepted and the proportion of individuals in each of five crown illumination classes varied significantly among the 11 species. Species ranged from extremely high‐light demanding, to quite shade tolerant. Average light levels intercepted by trees generally increased through ontogeny, but the ranking of species did not change significantly. 4 Fewer individuals of the more shade‐tolerant species established on disturbed microsites, irrespective of light levels. Among the more high‐light demanding species, the proportion of trees on different types of disturbed sites varied. 5 Trees of seven species were significantly more common on clay‐rich soils, two preferred sand‐rich soils, and two were not strongly affected by soil texture. 6 Hmax ranged from 5.5 to 31.3 m and was negatively correlated with shade tolerance among species, although among the more high‐light demanding species there was a wide range of tree sizes. Among species, Hmax was negatively correlated with both the slope and y‐intercept of the sapling height–diameter relationship, indicating that small‐statured species (also more shade tolerant) had more slender saplings than larger statured species. 7 Heterogeneity of resource availability leads to differences in horizontal and vertical tree distribution, which are important for the coexistence of 11 Macaranga species.

Cross-validation of Non-linear Growth Functions for Modelling Tree Height–Diameter Relationships

Six non-linear growth functions were fitted to tree height–diameter data of ten conifer species collected in the inland Northwest of the United States. The data sets represented a wide range of tree sizes, especially large-sized trees. According to the model statistics, the six growth functions fitted the data equally well, but resulted in different asymptote estimates. The model prediction performance was evaluated using Monte Carlo cross-validation or data splitting for 25-cm diameter classes. All six growth functions yielded similar mean prediction errors for small- and middle-sized trees. For large-sized trees [e.g. DBH (diameter at breast height)>100 cm], however, five of the six growth functions (except the Gompertz function) overestimated tree heights for western white pine, western larch, Douglas-fir, subalpine fir, and ponderosa pine, but underestimated tree heights for western hemlock and Engelmann spruce. Among these five functions, the Korf/Lundqvist and Exponential functions produced larger overestimations. The Schnute, Weibull, and Richards functions were superior in prediction performance to others. The Gompertz function seemed always to underestimate tree heights for large-sized trees.

Modifying Apple Tree Canopies for Improved Production Efficiency

Canopy development in perennial crops has a seasonal and a lifetime developmental pattern. The sum of development over individual seasons results in the final canopy dimensions and form. In apple, there is a natural progression from a single-shoot tree toward the tall (10 m), umbrella-shaped tree (Fig. 1). There are many disadvantages to this large umbrella-shaped tree: 1) it is difficult to spray, prune, and hand-harvest; 2) it has poor distribution of light throughout the canopy; and 3) it has a low early life light interception, leaf area index, and fraction of land covered by canopy, leading to delayed cropping. These disadvantages have resulted in widespread efforts to reduce tree size, increase tree density, accelerate canopy and yield development, and improve canopy form to overcome the limitations of the large tree. In apple, there are several practical approaches to tree size control and canopy modification, including the use of rootstocks, scions, pruning, and tree training. Rootstocks are available that will give a wide range of tree sizes ranging from the 10-m tree described above to fully dwarf trees <2 m high. There is also available a range in scion types, ranging from the nonbranching, columnar types to the spreading, nonspur types. In addition, apples respond well to canopy modification by pruning and training. These four variables make possible a myriad of tree forms, planting arrangements, and tree heights, widths, and geometric forms (spheric, rectangular, conic V, T, and A forms). The practical value of canopy modifications depends on their effect on orchard production efficiency.

Nest Site Selection in Eastern and Western Kingbirds: A Multivariate Approach

-Nest site selection by Eastern and Western kingbirds (Tyrannus tyrannus and T. verticalis) was studied at Delta Marsh, Manitoba, and results were analyzed using multivariate techniques. Principal component analysis of overstory vegetation characteristics for randomly selected plots defined the habitat space of the study area in terms of the major components of variation in the vegetation. Discriminant function analysis of the random plots identified the major trend in the vegetation (corresponding roughly to a north-south topographical gradient), and characterized the differences between northand south-zone habitat types. Principal component analysis of the vegetation characteristics of kingbird nest sites determined the relative position of each species in the habitat space. Virtually all of the Western Kingbird sites and most of the Eastern Kingbird sites appeared to be situated in that portion of the habitat space considered to represent north-zone habitat. Projection of the nest site data onto the random plot discriminant axis indicated that Eastern Kingbird nest sites were more evenly distributed than those of Western Kingbirds along the major trend of variation in the forest vegetation. Discriminant function analysis of the nest sites identified the variables most important in characterizing the difference between the nest sites of the two species. Western Kingbird sites were characterized by fewer but larger trees than Eastern Kingbird sites. Western Kingbird nest trees were larger and taller, and Western Kingbird nests were placed higher than those of Eastern Kingbirds. Eastern Kingbirds behaved as habitat generalists, selecting nest sites from both available habitat types, and selecting nest trees from a wide range of tree sizes. Western Kingbirds behaved as specialists, selecting sites in only the north-zone habitat type, and nest trees from the larger sizes. The Eastern Kingbird (Tyrannus tyrannus) and the Western Kingbird (T. verticalis) are sympatric over much of western North America (Fig. 1). The area of sympatry constitutes 35% of the breeding range of the Eastern Kingbird, and 60% of that of the Western Kingbird. Within their common range, where one species is abundant the other is usually much less so, and there is also regional variation as to which species exploits the wider range of habitats (Hiatt 1942, Hamilton 1962, Smith 1966, Tatschl 1973). Over much of its range the Eastern Kingbird nests along the edges of woodlots, in orchards, near marshes, and frequently in riparian communities (Bent 1942, Smith 1966). In the parts of its range where woods are scarce, the Eastern Kingbird inhabits open country, often nesting in low shrubs. The Western Kingbird is typical of dry grassland areas, but over much of its range its distribution appears to depend on the presence of at least a few trees for nesting. It is, therefore, a common inhabitant of prairie riparian woodlands, where it often reaches high nesting densities (e.g., see Carothers et al. 1974). This preference for trees or other tall structures (e.g., utility poles) for nesting suggests that the recent expansion of the breeding range of the West rn Kingbird (since 1900) may have been influenced by the planting of trees and erection of man-made structures which accompanied settlement of the plains at the turn of the century (see Nice 1924). The association of these species in Manitoba is the result of this recent breeding range expansion of the Western Kingbird (Taverner 1927). Analysis of census data from the Breeding Bird Survey (Robbins and Van Velzen 1967) for the period 19701975 revealed that the Eastern Kingbird was four times as abundant as the Western Kingbird in Manitoba. Both species breed in high densities on the forested dune ridge