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

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

基于土壤水分承载力的林分密度计算与调控——以六盘山华北落叶松人工林为例

立地水分条件决定的植被承载力是干旱缺水地区森林合理经营的重要依据。考虑到干旱缺水地区的森林蒸散耗水在水分输出中占据绝对主导地位,其大小直接与叶面积指数(LAI)相关,将林冠LAI在生长季一段时间内的最大值(LAImax)作为植被承载力(LAIc)的量化指标,利用冠层分析仪(LAI-2000),在六盘山香水河小流域和叠叠沟小流域的44个华北落叶松人工林样地,实测了冠层LAI的季节动态变化,研究了生长季内LAImax与林分断面积、郁闭度、平均树高、密度等常用林分结构指标的关系。结果表明:LAImax与林分不同结构指标均呈幂函数关系,其决定系数(R2)依次为0.84、0.82、0.56、0.47,说明能同时反映林分密度和树体大小的林分断面积与林冠LAI相关最紧密。将LAImax与林分断面积的幂函数关系嵌入了林分平均胸径与林分密度和林龄关系的模型,用以描述LAImax与林龄和密度的关系,并利用样地实测数据拟合了模型参数。拟合建立的模型对所有样地的LAImax的计算值与实测值的相对误差平均为8.6%(0%20.4%),能较好地描述LAI与林龄和密度的关系。利用此模型,进一步导出了能依据给定的LAIc,简捷计算出不同林龄时的可承载林分密度的模型,从而为基于立地水分植被承载力的林分密度管理和森林多功能经营等提供技术支持。     

Influence of individual reserve trees on nearby reproduction in two-aged Appalachian hardwood stands

In the 1970s, public opposition to clearcut harvesting in hardwood forests of the eastern United States led forest managers and scientists to consider alternative practices that retain a low-density overstory forest cover. From 1979 to 1984, a form of clearcut-with-reserves harvesting was applied in 80-year-old Appalachian mixed-hardwoods to create four experimental stands with two-aged structures. The residual stand basal area averaged 5.3 m²/ha, comprising an average of 36 reserve trees/ha. The reserve trees were evenly distributed throughout the stand, initially with considerable space between their crowns, thus providing the sunlight and seedbed conditions needed to recruit desirable shade-intolerant reproduction after harvest. This study examined the response of the 100-year-old reserve trees and the development of the 20-year-old natural reproduction located in their immediate vicinity.Diameter at breast height (Dbh), height, and relative position were recorded for all reproduction ≥2.5 cm within transects adjacent to northern red oak (Quercus rubra L.) and yellow-poplar (Liriodendron tulipifera L.) reserve trees. Each transect was divided into five zones, which represented positions relative to the reserve tree crown edge, and basal area was computed for each of three shade tolerance classes within each zone. A repeated measures ANOVA was used to compare basal area of reproduction by tolerance classes and zone. In general, basal area of reproduction, particularly that of shade-intolerant species, increased with distance from the reserve tree. Regression analyses also indicated that dbh and height of reproduction was positively related to distance from the reserve trees. Although height growth of reserve trees was similar for both species, northern red oak exhibited significantly greater dbh and crown radial growth than yellow-poplar.The results indicated that reserve trees influence the growth rate and species composition of reproduction in their immediate vicinity. Basal area of reproduction increased from 10.1 to 17.7 m²/ha with increasing distance from the reserve trees. Basal area of intolerant species more than doubled along the same gradient. Basal area of reproduction in the two-age stands was 30–40% less than that observed in even-aged stands on similar growing sites, but the reduction was offset by growth of the reserve trees. The surface area covered by the reserve tree crowns increased approximately 88% for northern red oak and 44% for yellow-poplar. Since the sphere of influence of reserve trees increases over time, forest managers must consider their long-term impact on reproduction when prescribing clearcut-with-reserves harvests and other practices that involve retaining trees for many years.     

Applicability of non-destructive substitutes for leaf area in different stands of Norway spruce (Picea abies L. Karst.) focusing on traditional forest crown measures

Since individual tree leaf area is an important measure for productivity as well as for site occupancy, it is of high interest in many studies about forest growth. The exact determination of leaf area is nearly impossible. Thus, a common way to get information about leaf area is to use substitutes. These substitutes are often variables which are collected in a destructive way which is not feasible for long term studies. Therefore, this study aimed at testing the applicability of using substitutes for leaf area which could be collected in a non-destructive way, namely crown surface area and crown projection area. In 8 stands of Norway spruce (Picea abies L. Karst.), divided into three age classes and two thinning treatments, a total of 156 trees were felled in order to test the relationship between leaf area and crown surface area and crown projection area, respectively. Individual tree leaf area of the felled sample trees was estimated by 3P-branch sampling with an accuracy of ±10%. Crown projection area and crown surface area were compared with other, more commonly used, but destructive predictors of leaf area, namely sapwood area at different heights on the bole. Our investigations confirmed findings of several studies that sapwood area is the most precise measure for leaf area because of the high correlation between sapwood area and the leaf area. But behind sapwood area at crown base and sapwood area at three tenth of the tree height the predictive ability of crown surface area was ranked third and even better than that of sapwood area at breast height (R² = 0.656 compared with 0.600). Within the stands leaf area is proportional to crown surface area. Using the pooled data of all stands a mixed model approach showed that additionally to crown surface area dominant height and diameter at breast height (dbh) improved the leaf area estimates. Thus, taking dominant height and dbh into account, crown surface area can be recommended for estimating the leaf area of individual trees. The resulting model was in line with many other findings on the leaf area and leaf mass relationships with crown size. From the additional influence of dominant height and dbh in the leaf area model we conclude that the used crown model could be improved by estimating the position of the maximum crown width and the crown width at the base of the crown depending on these two variables.     

Within-stand and seasonal variations of specific leaf area in a clonal Eucalyptus plantation in the Republic of Congo

Specific leaf area (SLA; m²_leaf kg^?1_leaf) is a key ecophysiological parameter influencing leaf physiology, photosynthesis, and whole plant carbon gain. Both individual tree-based models and other forest process-based models are generally highly sensitive to this parameter, but information on its temporal or within-stand variability is still scarce. In a 2–4-year-old Eucalyptus plantation in Congo, prone to seasonal drought, the within-stand and seasonal variability in SLA were investigated by means of destructive sampling carried out at 2-month intervals, over a 2-year period. Within-crown vertical gradients of SLA were small. Highly significant relationships were found between tree-average SLA (SLA_t) and tree size (tree height, H_t, or diameter at breast height, DBH): SLA_t ranged from about 9 m² kg^?1 for dominant trees to about 14–15 m² kg^?1 for the smallest trees. The decrease in SLA_t with increasing tree size was accurately predicted from DBH using power functions. Stand-average SLA varied by about 20% during the year, with lowest values at the end of the 5-month dry season, and highest values about 2–3 months after the onset of the wet season. Variability in leaf water status according to tree size and season is discussed as a possible determinant of both the within-stand and seasonal variations in SLA.     

Millet production under pruned tree crowns in a parkland system in Burkina Faso

As a tree management tool, three treatments of crown pruning (total-pruning, half-pruning and no-pruning) were applied to Vitellaria paradoxa (karité) and Parkia biglobosa (néré) in agroforestry parkland systems in Burkina Faso. The area under each tree was divided into four concentric tree influence zones (Zones A: up to 2 m from the tree trunk, B: up to half of the radius of the tree crown, C: up to the edge of the tree crown and D: up to 2 m away from the edge of the tree crown). Millet production under these zones and outside was assessed during two cropping seasons over the study period of three years and the results showed that tree crown pruning had significant effect on millet production and the highest millet grain yield and total dry matter were produced under total-pruned trees (507 ± 49 and 2033 ± 236 kg ha⁻¹ year⁻¹, respectively). Light transmission, transpiration and soil nutrient status under the trees were also analysed in relation to millet production. The results of the analysis showed that total-pruned trees gave the highest millet production due to the reduction by crown pruning of the effects of large tree crowns on PAR transmission below crowns and rates of transpiration by trees. Soil was more fertile closer to the tree trunks than outside tree crowns. This may also be one of the reasons why millet overall performed better under Zone B than outside tree crowns. The higher production of millet under Zone B than under Zone A, the zone closer to the tree trunk, may be due to lower light intensity and more intense competition for water between trees and crops under Zone A. It was concluded that at least in the short term millet production could be improved by crown pruning of both karité and néré, but long term effects may depend on the ability of the trees to maintain the amelioration of soil fertility and on how quickly the trees recover from pruning. This revised version was published online in June 2006 with corrections to the Cover Date.     

Crown structure and leaf area index development in thinned and unthinned Eucalyptus nitens plantations

The crown structure of Eucalyptus nitens (Deane & Maiden) Maiden 6 years after thinning, and the development of stand leaf area index both immediately and 6 years after thinning, were investigated. Thinning did not alter branch angle, branching density or the relationship between branch size and branch leaf area. However, larger branches were found in the lower crown of thinned trees and the increase in leaf area as a result of thinning occurred on the northern aspect of the crown. The vertical distribution of leaf area in unthinned trees was skewed toward the top of the crown and correlated with live crown ratio. The vertical distribution of leaf area in thinned trees tended to be less skewed and was unrelated to tree size or dominance. Leaf area index, as estimated from light interception measurements, increased at a constant rate soon after thinning regardless of residual stocking. In the longer term, residual stocking had a strong influence on leaf area increase per tree and was correlated with changes in crown length.     

Model computations on the critical combination of snow loading and windspeed for snow damage of scots pine,Norway spruce and Birch sp. at stand edge

Model computations were made on the critical combination of snow loading and windspeed for snow damage of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karst.) and birch sp. (Betula sp.) at the newly formed stand edge with varying tree height and stem taper using the model developed by H. Peltola, S. Kellomäki and H. Väisänen (1996, HWIND: A Mechanistic Model for Wind and Snow Damage of Scotts Pine, Norway Spruce and Birch sp.) for the mechanism of wind and snow damage. In the computations, the total turning moment arising from the wind and snow load and from the bending of stem and crown was calculated along with the breaking stress of the stem and root anchorage. Windspeed variation within the crown and the vertical distribution of snow, stem and crown weight were also taken into account.According to computations, the critical combination of snow and wind loading for stem breakage and uprooting of trees was caused mainly by accumulation of snow on tree crowns, rather than by wind, which did, however, increase the risk of damage. The risk of damage increased along with stem taper decrease or tree height increase for all tree species studied. However, Scots pine and Norway spruce were found much more susceptible to snow damage than birch, which (being leafless) had much less crown area for snow attachment and wind loading.The trees most likely to suffer stem breakage were slightly tapering Scots pines and Norway spruces with tapers of 1:120 for varying tree heights of 12–20 m under short-term snow loading of 60 kg m⁻², i.e. they would have suffered stem breakage under windspeeds of less than 9 m s⁻¹ above the tree canopy top. Respectively, even Scots pine and Norway spruce with tapers of 1:100 were at risk of stem breakage through sustained snow loading of 60 kg m⁻². In addition, even snow loads of 20–40 kg m⁻² were found big enough to cause stem breakage of these trees with stem tapers of 1:120 during sustained snow loading. Correspondingly, similar pines and spruces with stem tapers of 1:120 were found to even more liable to be uprooted during conditions of unfrozen soil than of having their stem broken by short-term snow loading of 20–60 kg m⁻², i.e. less windspeed was needed to cause uprooting. However, pines and spruces with tapers of 1:80 were not at risk for stem breakage and uprooting. This was because snow would have more probably been dislodged from the tree crowns by windspeeds greater than 9 ms⁻¹ which are needed to worsen the damage. Nor would very slender birch without leaves have suffered stem breakage or uprooting under any circumstances with windspeeds of less than 9 ms⁻¹.     

Dendrometric analysis of olive trees for wood biomass quantification in Mediterranean orchards

This work focuses on the development of dendrometric algorithms to calculate the volume and total biomass contained in olive trees. This laid the foundation for the use of this methodology as a tool to manage resources from orchards, establishing adequate prediction models for assessing other parameters such as income from raw materials from the cultivation, fruit production, CO₂ sinks, and waste materials (residual wood) used for energy or industry. Dendrometry has traditionally been applied to forest trees. However, little research has been conducted on fruit trees because of their heterogeneous structure. This issue was the first step of this research. For this, the form factors were calculated. This relates to the actual volume of the branch with a model volume, calculated as a revolution solid from the base diameter and length. The shape more approximated to 1 was the cylinder model with a mean value of 0.76 and standard deviation (SD) of 0.23. On the other hand, volume equations were obtained for the branches. The distribution of biomass in the tree was analyzed. It is estimated that 40 % of biomass is located in the stem and 60 % in the crown, and most of the crown biomass is concentrated in the first branches (60 %). Afterwards, occupation factors were calculated to relate the wood volume in the crown to its apparent volume, the mean being 0.005 dm³/m³ and SD 0.0025 dm³/m³. Also, equations for predicting the whole wood in the crown were obtained. In this regard, the best results were obtained when the crown diameter was used (R ² = 0.74). These results could be correlated with the production and quality of the fruit, amount of residual biomass coming from pruning, and LIDAR data, which may indicate a simple, quick, and accurate method for predicting biomass.     

Coordination of crown structure, leaf plasticity and carbon gain within the crowns of three winter-deciduous mature trees

We examined the vertical profiles of leaf characteristics within the crowns of two late-successional (Fagus crenata Blume and Fagus japonica Maxim.) and one early-successional tree species (Betula grossa Sieb. et Zucc.) in a Japanese forest. We also assessed the contributions of the leaves in each crown layer to whole-crown instantaneous carbon gain at midday. Carbon gain was estimated from the relationship between electron transport and photosynthetic rates. We hypothesized that more irradiance can penetrate into the middle of the crown if the upper crown layers have steep leaf inclination angles. We found that such a crown has a high whole-crown carbon gain, even if leaf traits do not change greatly with decreasing crown height. Leaf area indices (LAIs) of the two Fagus trees (5.26-5.52) were higher than the LAI of the B. grossa tree (4.50) and the leaves of the F. crenata tree were more concentrated in the top crown layers than were leaves of the other trees. Whole-crown carbon gain per unit ground area (micromol m(-2) ground s(-1)) at midday on fine days in summer was 16.3 for F. crenata, 11.0 for F. japonica, and 20.4 for B. grossa. In all study trees, leaf dry mass (LMA) and leaf nitrogen content (N) per unit area decreased with decreasing height in the crown, but leaf N per unit mass increased. Variations (plasticity) between the uppermost and lowermost crown layers in LMA, leaf N, the ratio of chlorophyll to N and the ratio of chlorophyll a to b were smaller for F. japonica and B. grossa than for F. crenata. The light extinction coefficients in the crowns were lower for the F. japonica and B. grossa trees than for the F. crenata tree. The leaf carbon isotope ratio (delta(13)C) was higher for F. japonica and B. grossa than for F. crenata, especially in the mid-crown. These results suggest that, in crowns with low leaf plasticity but steep leaf inclination angles, such as those of F. japonica and B. grossa trees, irradiance can penetrate into the middle of the crowns, thereby enhancing whole-crown carbon gain.     

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 m³) than contained in any tree we measured <1500 years old. The two tallest tree species achieve similar stature despite divergent growth dynamics and ecologies. At one extreme, E. regnans attains great size quickly but dies relatively young because trees are susceptible to fire and fungi. At the other extreme, S. sempervirens attains great size more slowly but has a long lifespan because trees resist fire and prioritize investment in decay-resistant heartwood. Increasing wood production as trees age is a mechanism underlying the maintenance of biomass accumulation during forest development and the carbon-sink capacity of old-growth forests.     

Crown architecture of stand-grown sugar maple (Acer saccharum Marsh.) in the Adirondack Mountains

Leaf and crown morphology of shade-tolerant sugar maple (Acer saccharum Marsh.) were examined to test the hypotheses (1) that leaf area exhibits significant plasticity both within and between crown classes and individual tree crowns and (2) that leaf area is accurately predicted from estimates of crown volume. A total of 18 trees, ranging from 3.3 to 43.4 cm dbh, were felled and dissected into upper, middle, lower, and below-crown layers, for measurements of leaf, bark, and xylem dimensions. For dominant trees only, bark thickness and xylem radii were higher within the crown than below the crown. Cumulative leaf area index increased with decreasing stratum height at similar rates in all trees, except for two trees that were located in the understory. Area leaf weight declined with decreasing stratum height within the crown of all except four overstory trees. These four trees showed an increase with decreasing stratum height, i.e., leaves were heavier per unit area in the lower crown stratum and below the crown than they were at mid-crown. Within-tree leaf area density was usually higher in the upper crown of overstory trees and in the lower crown of understory trees. Total crown volume was the best predictor of whole-tree leaf area, but it was only slightly better than dbh.     

Examining age- and altitude-related variation in tree architecture and needle efficiency in Norway spruce using trend surface analysis

The aim of this study was to examine the variation in tree architecture and needle efficiency in stemwood production in Norway spruce in relation to tree age and altitude of growing site. The data, which were obtained from the literature, described individual Norway spruce (Picea abies (L.) Karst.) trees from even-aged stands in Switzerland. Second-order trend surface models, with tree age and altitude as independent variables, were used in the analysis. The fitted models for stem, branch and needle dry masses explained 95%, 75% and 64% of the variation, respectively. The model for the estimated mean branch density in the crown (kg m⁻³) explained 64% of the variation and the model for mean needle density in the crown (kg m⁻³) only 28% of the variation. Crown structural characteristics, which showed age- and altitude-related variations, included live crown ratio (59% of variation explained), number of living whorls (43% of variation explained), mean weight of single needle (40% of variation explained) and specific needle area (27% of variation explained). Tree age had a strong effect on needle efficiency in stemwood production, so that needle efficiency increased up to the age of 50–70 years, depending on altitude.     

Feeding in the Crowns of Scots Pine Trees by the Pine Weevil Hylobius abietis

Hylobius abietis (L.) (Coleoptera:Curculionidae) is the major insect pest of forest regeneration in Europe, where adult weevils kill conifer seedlings by feeding on the bark. This study demonstrates that pine weevils also feed extensively in the crowns of mature coniferous trees. Crown feeding primarily took place during a limited period immediately after the migration to new breeding sites (roots of freshly cut coniferous trees). The weevils reached the crowns mainly by flight and tended to concentrate on trees in freshly cut-over areas. The proportion of sexually mature females successively increased during the crown-feeding period, indicating that they require a certain period of maturation feeding. The pine weevils fed on twigs of 3-20 mm thickness, and they consumed about 0.2-0.3% (200 cm²) of the total bark surface in the crowns of mature Scots pine trees. Calculations suggested that the amount of food consumed in the trees surrounding a fresh clear-cutting should have met the nutrient requirements of the weevil population in the area during the maturation feeding period. In the crowns of shelterwood trees, about 50 cm² of the bark was consumed per tree (0.63 m² ha-1). This level of consumption is not believed to be high enough to relieve the feeding pressure on seedlings and thereby explain the low level of damage usually found under shelterwoods.     

Leaf traits in relation to crown development, light interception and growth of elite families of loblolly and slash pine

Crown architecture and size influence leaf area distribution within tree crowns and have large effects on the light environment in forest canopies. The use of selected genotypes in combination with silvicultural treatments that optimize site conditions in forest plantations provide both a challenge and an opportunity to study the biological and environmental determinants of forest growth. We investigated tree growth, crown development and leaf traits of two elite families of loblolly pine (Pinus taeda L.) and one family of slash pine (P. elliottii Mill.) at canopy closure. Two contrasting silvicultural treatments -- repeated fertilization and control of competing vegetation (MI treatment), and a single fertilization and control of competing vegetation treatment (C treatment) -- were applied at two experimental sites in the West Gulf Coastal Plain in Texas and Louisiana. At a common tree size (diameter at breast height), loblolly pine trees had longer and wider crowns, and at the plot-level, intercepted a greater fraction of photosynthetic photon flux than slash pine trees. Leaf-level, light-saturated assimilation rates (A(max)) and both mass- and area-based leaf nitrogen (N) decreased, and specific leaf area (SLA) increased with increasing canopy depth. Leaf-trait gradients were steeper in crowns of loblolly pine trees than of slash pine trees for SLA and leaf N, but not for A(max). There were no species differences in A(max), except in mass-based photosynthesis in upper crowns, but the effect of silvicultural treatment on A(max) differed between sites. Across all crown positions, A(max) was correlated with leaf N, but the relationship differed between sites and treatments. Observed patterns of variation in leaf properties within crowns reflected acclimation to developing light gradients in stands with closing canopies. Tree growth was not directly related to A(max), but there was a strong correlation between tree growth and plot-level light interception in both species. Growth efficiency was unaffected by silvicultural treatment. Thus, when coupled with leaf area and light interception at the crown and canopy levels, A(max) provides insight into family and silvicultural effects on tree growth.     

Competition and tree crowns: A neighborhood analysis of three boreal tree species

Competition for canopy space is a fundamental structuring feature of forest ecosystems and remains an enduring focus of research attention. We used a spatial neighborhood approach to quantify the influence of local competition on the size of individual tree crowns in north-central British Columbia, where forests are dominated by subalpine fir (Abies lasiocarpa), lodgepole pine (Pinus contorta) and interior spruce (Picea glauca × engelmanii). Using maximum likelihood methods, we quantified crown radius and length as functions of tree size and competition, estimated by the species identity and spatial arrangement of neighboring trees. Tree crown size depended on tree bole size in all species. Given low levels of competition, pine displayed the widest, shortest tree crowns compared to the relatively long and narrow crowns found in spruce and fir. Sensitivity to crowding by neighbors declined with increasing tree height in all but the pine crown radius model. Five of the six selected best models included separate competition coefficients for each neighboring tree species, evidence that species generally differ in their competitive effects on neighboring tree crowns. The selected crown radius model for lodgepole pine, a shade-intolerant species, treated all neighbors as equivalent competitors. In all species, competition from neighbors exerted an important influence on crown size. Per-capita effects of competition across different sizes and species of neighbors and target trees varied, but subalpine fir generally displayed the strongest competitive effects on neighbors. Results from this study provide evidence that species differ both in their response to competition and in their competitive influence on neighbors, factors that may contribute to maintaining coexistence.     

Canopy gap characteristics and their implications for management in the temperate rainforests of southeast Alaska

In the coastal temperate rainforests of southeast Alaska, much progress has been made in describing landscape-level natural disturbances and formulating management systems that emulate those disturbances. Little is known, however, concerning canopy gaps, the dominant form of natural disturbance in the region. During June–August, 1991–1993, we characterized canopy gap patterns and dynamics at three sites in the western hemlock/blueberry/shield fern plant association in the northern portion of the Tongass National Forest.Forest area in canopy gaps ranged from 5.8 to 12.6% and averaged 8.7%. The proportion of forest area in expanded gaps ranged from 18.1 to 43.9% and averaged 27.4%. Gap and gapmaker (tree whose death or crown displacement results in the creation or expansion of a canopy gap) characteristics were generally similar among sites. The majority of canopy gaps were <50 m² in area, had a D/H ratio <0.50, were created from the death of one or two gapmakers, and had experienced gap expansion. The majority of expanded gap areas were <200 m². Gapmakers were usually snapped, had recently died (<20 years ago), and tended to be larger in diameter than surrounding overstory trees. Species composition of gapmakers was similar to surrounding overstory trees. A substantial amount of gap infilling takes place between 20 and 80 years following tree death, but gaps, or portions of gaps, can persist for >80 years. Forest turnover time was estimated to range from 230 to 920 years, and average 575 years. Canopy residence time was estimated to range between 210 and 840 years, and averaged 525 years.To emulate canopy gap dynamics in the plant association studied, forest managers should: (1) maintain a small proportion of a stand in openings within an otherwise undisturbed canopy; (2) use a combination of single tree selection and small group selection systems; (3) re-enter stands every 20–80 years; (4) select larger than average diameter crop trees in proportion to the species composition of the stand; (5) minimize soil disturbance and (6) select crop trees during re-entry so that the creation of new gaps and the expansion of old gaps is accomplished in approximately equal proportions.     

Extending sapwood — Leaf area relationships from stems to roots in Coast Douglas-fir

? Studies of allometric relationships between leaf area and the cross-sectional area (CSA) of sapwood in the stem have shed light on the structural and functional relationships between water-conducting and photosynthetic tissues.

? The purpose of this study was to test whether sapwood-leaf area relationships could be extended from stems to roots in coast Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Twelve trees were felled, their stumps were excavated, and the CSA of sapwood and heartwood were estimated for individual roots, entire root systems, and stem section.

? Root sapwood CSA was greater than sapwood CSA throughout the stem, and the ratio of leaf area to sapwood CSA (A _l :A _s ) was accordingly lower for root sapwood. The relationship between sapwood CSA and leaf area was more variable in roots and at groundline compared to crown base. Root A _l :A _s decreased with relative tree height (tree height/mean stand height).

? The strong allometric relationship between leaf area and the CSA of sapwood in the stem generally holds when extended to roots. The greater CSA of sapwood in roots versus stems may reflect differences in their roles in supporting the tree.

     

日本山口的一些景观树对2006、2007年干旱和高温事件的响应

本文依据1967-2007年间的气象资料,对日本山口市的极端天气事件进行了分析,主要用像素分析和光谱分析法对景观树的响应进行了调查研究.结果表明,经过干热、多风的2007年夏季之后,山口市的许多景观树对这些极端天气事件的响应趋于缩减其叶面积和减少辐射能的吸收.一些景观树种出现树叶早期变色或脱落,在许多不利条件下栽培的四照花(Cornus kousa)树上发生叶边叶缘焦枯症状.像素分析结果表明,四照花样树的叶面积平均焦枯率达41.6%,山茶花2007年花季的花量也明显少于2006年.对偏冠变色的美国枫香(Liquidambar styraciflua)树进行的微分分析表明,其树冠颜色呈逻辑斯蒂函数式变化.这表明即使在湿润的山口市,持续的高温少雨天气对一些不利条件下栽植的敏感景观树也是有害的.