Tree Size Distribution Research Articles

Competition, mortality, and development of spatial patterns in two Cantabrian populations of <i>Fagus sylvatica</i> L. (Fagaceae)

In this paper the spatial patterns of size and mortality of European beech ( Fagus sylvatica L.) were analy sed in two deciduous forest plots of Northern Spain. ?i general terms, radial growth of F. sylvatica yields a direct relationship with size and an inverse relation with intraspecific competition while tree mortality seems be related to intraspecific competition. In the overall even-aged population, a lack of a recognisable structure in tree-size distribution, a small-scale regularity of survivors, and a regular pattern of dominant trees was noticed. This is a consequence of intense intraspecific competition at local level. In the old-growth plot, the wide repulsion between small and large beeches yields a specific spatial structure in tree-size distribution, showing even-sized groups of trees in different stages. Mortality in this plot occurs mainly within the dense group of small trees, which produces a broad regular pattern among the live beech trees. The random spatial pattern of dominant beeches seems to be characteristic of old-growth forests and could be a consequence of either self-thinning processes or exogenous factors.

A new method for modeling the heterogeneity of forest structure

Despite the critical ecological roles of structural complexity, ecologically relevant quantitative measures of structural complexity that allow comparisons among forest stands are still lacking. The objective of this study was to develop a method that allows comparisons of structural heterogeneity among stands. To encompass a broad range of potential structural complexities, we simulated three spatial point patterns each for tree-size distributions from five inventoried natural stands. Forest structure was modeled and analyzed by simulating point patterns of trees and constructing triangular networks to connect neighboring tree tops to one another. This method is based on the concept of spatial tessellation of tree positions, where point patterns are converted into 2-dimensional nearest neighbor triangles. A structural complexity index (SCI) was defined as the sum of the areas of 3-dimensional triangles (with x, y, and z coordinates) divided by the sum of the areas of 2-dimensional triangles. Vertical gradients were defined as the maximum size difference among the trees forming a triangle, that is, the greater the difference, the greater the structure and the larger the SCI value. Patch-types were defined as classes of structural gradients at different positions within the canopy. More patch-types are also indicative of more structurally heterogeneous stands. Both the SCI and the number of patch-types and patch-size heterogeneity related closely to conventional descriptors of forest structure. While the number of patch-types and patch-type heterogeneity related more to the vertical component of structural complexity, SCI integrated well with both the vertical and horizontal structure. SCI and the concept of patch-types complement one another and can be used to quantitatively compare the structure of different stands. The applicability of this modeling approach in characterizing the structural heterogeneity of forests across spatial scales is discussed.

Application of volume growth and survival graphs in the evaluation of four process-based forest growth models.

Volume growth and survival (VGS) graphs, which show volume growth rate and risk of mortality for individual trees (or tree size classes), have been proposed as a tool for assessing the validity of models that describe the development over time of tree size distributions within forest stands. We examined the utility of the VGS method in evaluating four process-based models. The performance of the models FORSKA, 4C, MORG, and PipeQual is analyzed against long-term data from a Scots pine stand in Evo, Finland, and the models FORSKA and 4C are also assessed with respect to data from a beech stand in Fabrikschleichach, Germany. Comparison of the measurement-based VGS graphs with those produced from the model-based data shows that although the models yield similar stand-level predictions, they can differ widely in their projections of individual tree growth and size distributions. Examination of the discrepancies between models and data in the context of the VGS graphs reveals several areas in which the models could be improved. We conclude that the method is useful in model evaluation, especially if used in combination with indicators of stand structure, such as the height/diameter ratio.

Volume growth and survival graphs: a method for evaluating process-based forest growth models

We investigated the relationships within forest stands between tree size and (a) stem volume growth rate and (b) risk of mortality for individual trees. Values of both x and y variables were plotted relative to the largest value in the stand. We refer to the resultant presentations as relative volume growth and relative survival graphs (VGSs). A pair of VGSs can be produced readily from an individual-tree growth model. It can also be constructed from consecutive sets of field measurements. Comparison of VGSs derived from model and measurement data provides a test of the validity of the components of the growth model. We have analyzed VGSs based on measurement data for Scots pine (Pinus sylvestris L.) in central Finland and for beech (Fagus sylvatica L.) in southern Germany. The graphs based on measurement data varied as a consequence of differences in competition, stand management, and tree species. We analyzed the relationship between VGSs and stand dynamics using a simple growth model. We found that different features of the VGSs imply characteristic tree size distributions in subsequent years. Thus, we conclude that if the VGSs generated by a model do not correspond to those based on field measurements, the model cannot be relied on to reproduce the development of tree-size distribution correctly. Relative growth and survival graphs thus provide a tool for evaluating complicated growth models.

Utilizing Local Variance of Simulated High Spatial Resolution Imagery To Predict Spatial Pattern of Forest Stands

Spatial pattern, defined as the distribution of individuals in space, is an important characteristic of forest stands. It provides an insight into the allocation of above- and below-ground resources to a tree, as well as reflecting the stand history, microclimate, and competition between different species over time. The spatial arrangement of trees can be described as random, aggregated, or regular with a number of statistics existing that characterize the spatial pattern of a given tree population. High spatial resolution remote sensing is an obvious tool to facilitate the measuring and monitoring of spatial patterns in forest stands. Remote sensing imagery provides detailed information about forest structure while still allowing large areas of forest to be mapped and monitored. The increased availability of high resolution imagery coupled with improvements in scene processing and interpretation techniques allow additional information, such as texture, to be extracted from this type of imagery. In this paper the spatial pattern of trees within a forest stand is related to high spatial resolution imagery. This relationship is developed using a technique that relates scene texture variance to a statistic describing spatial pattern. The technique was tested on a number of simulated remote sensing scenes by systematically varying the size and spatial distribution of trees using a geometric-optical model. Results indicate that it is theoretically possible to derive the spatial pattern of trees within a high spatial resolution forested scene provided crown size is estimated a priori. It is also likely that the total projected foliage cover of the canopy will affect the ability to predict spatial distribution based on texture variance. It was concluded that the spatial pattern of trees within a scene can play a vital role in the amount and degree of variation existing within imagery. It is important to consider the implications of these type of relationships when developing variance-based models of forest structure.

How much do local factors matter for predicting transient ecosystem dynamics? Suggestions from permafrost formation in boreal peatlands

With rapid climate warming, ecosystems will probably exhibit complex dynamics because local factors and life history attributes of species mediate the effects of regional climate change. To assess the relative importance of local vs. regional processes on permafrost formation in boreal peatlands, I sampled for permafrost and factors affecting its formation in 38 collapse scars across a 4 °C mean annual temperature (MAT) gradient in the discontinuous permafrost zone of northern Manitoba, Canada. Three complimentary approaches were used to model factors important to permafrost formation at both local and regional scales. In the first analysis, a mechanistic, spatial model of permafrost formation was developed as a function of Picea mariana size and proximity. In the second approach, permafrost formation was modelled as a function of two local factors, diameter of Picea mariana trees and emergent organic matter depth, and the regional factor, mean annual temperature (MAT). Finally, published aerial photography data were used to determine whether the proportion of bogs with permafrost changes across a MAT gradient. Results show that permafrost formation in boreal permafrost peatlands is best described as a locally driven process within regional climatic constraints. At local scales of 1–2 meters, the spatial and size distributions of trees controlled the spatial distribution of permafrost. At regional scales, tree size was a significantly better predictor than emergent organic matter or MAT. These results suggest that transient models of discontinuous permafrost based only on climate may poorly predict changes in vegetation and permafrost.

Overstory influences on herb and shrub communities in mature forests of western Washington, U.S.A.

Understanding the relationships between forest overstory and understory communities is essential for predict - ing changes in the abundance and distribution of understory plants through successional time and in response to forest management. We used correlation analysis, multiple regression, and nonparametric models to explore the relationships between overstory characteristics (canopy cover, stand density, and tree-size distributions) and the abundance of species in the herb and shrub layers in mature forests of western Washington. Overstory variables explained >50% of the varia- tion in the mean response of total shrub cover and ca. 50% of the variation in cover of Acer circinatum Pursh (the most common shrub species) and late-seral herbs (species reaching their greatest abundance in late-successional for - ests). Stronger relationships (80-90% variance explained) were found between overstory variables and the maximum cover of total shrubs, A. circinatum, total herbs, and each of three functional groups of herbaceous species. These em- pirical relationships represent both direct resource limitations and time-dependent responses for which overstory charac - teristics may be surrogates. Models of maximum abundance yielded the most consistent results, suggesting the relative importance of different overstory variables as limiting factors for understory response, although these limiting factors have different effects on plants with different life-history strategies. Resume : Pour predire les changements dans l'abondance et la distribution des plantes du sous-bois au cours de la suc- cession et en reponse a l'amenagement forestier, il est essentiel de comprendre les relations entre l'etage forestier do- minant et les communautes du sous-bois. Les auteurs ont utilise l'analyse de correlation, la regression multiple et les modeles non parametriques pour explorer les relations entre les caracteristiques de l'etage dominant (recouvrement de la canopee, densite du peuplement, distributions de la dimension des arbres) et l'abondance des especes dans les strates

Structure and recent recruitment at alpine forest-pasture ecotones in the Spanish central Pyrenees

Treeline ecotones are intensively studied to quantify the response of vegetation to environmental changes. We describe here the size, growth-form, and spatial distribution of trees in two alpine forest-pasture ecotones located in the Central Pyrenees (Ordesa and Tessó), dominated by Pinus uncinata Ram. and little affected by anthropogenic disturbances during the last century. Total variation of tree data was partitioned into spatial, environmental, combined, and unexplained components. The influence of understory plants on P. uncinata recruitment was assessed using cover data and detrended canonical correspondence analysis (DCCA). Climatic effects on recent recruitment were also investigated at Tessó. Most individuals at Ordesa were multistemmed and shrubby (krummholz). Krummholz and seedlings showed significant spatial correlation. The spatial component of variation of tree data was greater at Ordesa (26%) than at Tessó (4%). DCCA revealed a significant effect of elevation on the spatial segregation of the size and growth-form classes across both ecotones. At Tessó, recruitment was concentrated close to the treeline, where the cover of the dominant understory shrub (Rhododendron ferrugineum) decreased. The abundance of young individuals in the upper part of this ecotone might produce a future upward displacement of treeline. During the last 60 years, the important episodes of recruitment at Tessó were favoured by wet and warm springs and summers. Ordesa showed a clear spatial trend of distribution of P. uncinata individuals. Most individuals were krummholz, located at greater elevation. Recruitment was associated with krummholz type vegetation, which could buffer seedlings (nurse effect) from the harsh environment and thereby favour the establishment of seedlings.

Dynamics of snags in aspen-dominated midboreal forests

This research focuses on the dynamics of snags within aspen-dominated ( Populus tremuloides Michx.) boreal forests within Alberta. Data from Alberta Lands and Forest Service permanent sample plots (PSP) were analyzed to determine densities, size distributions, input rates, falldown rates, and longevity patterns of snags (≥10 cm DBH). The mean density of snags in 20 to 39-yr-old stands was 18.1 snags per ha increasing to 61.6–99.8 snags per ha in stands up to 100+ yrs. In general, size distributions of trees and snags exhibited a reversed J-shaped size distribution. In stands <40 yrs of age, size distributions of snags lagged behind trees. However, as the stand aged and self-thinning of small trees was supplemented by the death of canopy codominants, the size distribution of snags began to increasingly overlaps with that of trees. Overall snag input rates varied from 0.08–8.2% of trees per annum, larger values were associated with older stands and/or smaller trees. Snag falldown rates varied from 9–21% of snags per annum depending upon stand age. Falldown rates exhibited a U-shaped pattern with rates decreasing in 60 to 79-yr-old stands. Snag longevity patterns exhibited a negative sigmoidal shape with an initial period of relative stability for approximately 5 yrs after death, afterwards the probability of falldown increased with a greatest falldown occurring between 10 to 20 yrs after death.

Structural heterogeneity and spatial autocorrelation in a natural mature Pinus sylvestris dominated forest

The tree species composition, vertical stratification and patterns of spatial autocorrelation at the tree and quadrate (25 × 25 m) scales were studied in a natural mature PinuS sylvestris dominated forest in eastern Finland. For the analyses we mapped the locations and dimensions of trees taller than 10 m in a 9 ha (300 × 300 m) area, and within this area we mapped all trees taller than 0.3 m on a core plot of 4 ha (200 × 200 m). The overall tree size distribution was bimodal. the dominant layer and the understory forming the peak frequencies. Pinus sylvestris dominated the main canopy, together with scattered Betula pendula and Picea abies. Alnus incana, Populus tremula, Salix caprea, Sorbus aucuparia and Juniperus communis occurred only in the under‐ and middlestories. Autocorrelation analysis (semivarianee) of tree size variation revealed spatial patterns, which were strongly dependent on the size of trees included in the analysis. When all living trees, including the understory regeneration, were taken into account, the autocorrelation pattern ranged up to 35 m inter‐tree distances, reflecting the spatial scale of understory regeneration patches. Competitive interaction among middle‐ and upperstory trees (height&gt;10 m) had contrasting effects on autocorrelation pattern depending on spatial scale. At the fine scale, dominant trees suppressed their smaller close neighbors (asymmetric competition), which was shown as increased tree size variation at small inter‐tree distances (&lt;2 m). At slightly larger inter‐tree distances, specifically among large trees of similar size, competition was more symmetrical, which resulted in decreased tree size variation at these inter‐tree distances (3–4 m). This effect was seen most clearly in the dominant trees, there being a clear autocorrelation pattern in tree size up to inter‐tree distances of ∼4 m. At the quadrate scale (25 × 25 m) the analysis revealed high local variation in structural characteristics such as tree height diversity (THD), tree species diversity (H) and autocorrelation of tree height. The analysis suggests that naturally developed P. sylvestris forests exhibit complex small‐scale patterns of structural heterogeneity and spatial autocorrelation in tree size. These patterns may be important for stand‐scale habitat diversity and can have aggregated effects on ecosystem dynamics at larger spatial scales though their influence on the spread of disturbance and regeneration after disturbance.

Diameter and height distributions in genetically improved Pinus radiata

Diameter and height distributions for Pinus radiata D. Don trees grown from seed lots representing a range of genetic improvement were compared at midrotation (age 14 or 15) in seven large-plot trials at six sites. In one of the trials, comparisons were made at year 5 and annually from age 8 to 16. These are the first data from plantation conifers comparing tree size distributions of commercially planted seed lots. Differences among seed lots for quadratic mean diameter and mean height were statistically significant and generally reflected the expected level of genetic improvement. Standard deviation, skewness, and kurtosis were not significantly different among seed lots. However, diameter distributions of higher rated seed lots sometimes appeared very slightly more skewed to the right and flatter than the lower rated seed lots, a similar tendency observed as stands age. Models used to predict diameter distribution from stand parameters are not likely to require modification for genetically improved seed lots.

Canopy transpiration from a boreal forest in Sweden during a dry year

Estimation of areal evapotranspiration is crucial for the parameterization of the soil-vegetation-atmosphere interface in climate models and for the assessment of land-use changes on water resources. Present knowledge on how areal forest evapotranspiration depends on forest species composition and age is insufficient. In this study, transpiration of 50- and 100-year-old coniferous stands was estimated on the basis of sap-flow measurements on 24 trees, 12 in each stand. The measured samples represented the size distribution of Pinus sylvestris and Picea abies trees. Daily canopy transpiration ( E Q) was scaled from individual tree flow rates using the quotients of stem circumferences of the sample trees to those of the stands. E Q was used in a rearranged Penman equation to deduce a potential canopy conductance, valid for non-limiting soil-water conditions, from a period when soil-water storage was not limiting transpiration. This enabled quantification of the seasonal transpiration deficit, which in both stands reached at least one fifth of the total potential transpiration over the growth season. The estimated fluxes of E Q were low with a maximum daily value of about 2.8 mm in the 50-year-old stand. For dry-weather days, E Q was well correlated to daily sums of stand evapotranspiration estimated from eddy-correlation measurements. Responses to drought were species specific. Transpiration in pines from the 50-year-old stand was less affected by drought relative to spruce or older pine trees, which was also reflected by stem increment during the season.

ROADSIDE TREES IN URBAN HONG KONG: PART III TREE SIZE AND GROWTH SPACE

Summary The dimensions of the entire population of 19,154 street trees in urban Hong Kong had been measured in the field in a recent census. The same study also collected detailed data on the dimensions of the roadside growth space of individual trees. The results yield useful information on tree-size distribution, and its relationship with species composition, changing species preference over the years, and projected long-term arboreal character of the city. The immediate roadside environment of the trees was analyzed in terms of dimensions and types of growth space to highlight their association with tree size. The interpretations provide hints for tree managers to modify species choice with reference to attainable size and in comparison with the geometry of the planting sites. The need to take into account the ground truth in the planning and management of roadside trees in a cramped environment is emphasized

Effect of CPPU and NAA on Fruit Growth and Cropping of Redchief `Delicious'

NAA is commonly used for fruit thinning of apples. However, with spur-type `Delicious' fruit, size may be less than expected based on the remaining crop load. Attempts to enhance fruit size on NAA-thinned trees with benzyladenine (BA) resulted in an interaction causing an increase in small (≤64 mm) fruit. CPPU [N-(2-chloro-4-pyridinyl)-N'-phenylurea], a highly active cytokinin in promoting parthenocarpy and growth of a number of fruit, was evaluated alone and with NAA for its effects on cropping and fruit growth in Redchief `Delicious'. High-volume sprays of CPPU were applied at 0, 2.5, 5, and 10 mg·L–1 to 13-year-old trees at 7.26 mm king fruit diameter. NAA was applied at 15 mg·L–1 with and without CPPU at 5 mg·L–1. Each treatment consisted of a single tree replicated four times. Response was evaluated by determining yield per tree and fruit size distribution at harvest. CPPU increased the amount of large (≥70 mm) fruit produced without significantly reducing yield. The amount of large fruit produced was 35, 71, 91 and 85 kg/tree for the nonthinned control (NTC) and CPPU at 2.5, 5, and 10 mg·L–1, respectively. NAA (15 mg·L–1) reduced yield by 39 kg/tree and increased amount of large fruit by 44 kg/tree. When CPPU (5 mg·L–1) was oversprayed with NAA (15 mg·L–1), yield was reduced by 30 kg/tree, and amount of large fruit was increased by 56 kg/tree compared to the NTC. The interaction was not significant for yield but was significant (P = 0.01) for amount of large fruit produced. Seed content was significantly reduced by NAA and CPPU, the effect being greater for NAA and in small (51 to 56 and 57 to 63 mm) than in large (76 to 82 mm) fruit. These data showing no significant inhibition of fruit growth with a combination of NAA and CPPU in Redchief `Delicious' are in contrast with findings for a related cytokinin, BA, where fruit growth was depressed significantly when combined with NAA.

Modeling the regeneration of oak stands in the Missouri Ozark Highlands

This paper describes a method for modeling the regeneration of even-aged oak stands in the Ozark Highlands of southern Missouri. The approach is based on (i) a growth model that is applicable to both oak sprouts and advance reproduction and (ii) a method for probabilistically estimating future size distributions of trees. The modeling method is illustrated using sprouting frequency, survival, and 5th-year height data for stump sprouts of five oak species. To consider the large residual variation in estimates of future sprout heights, nonlinear regression estimates of heights and their prediction errors are simultaneously used to estimate the probability that a sprout originating from a parent tree of a given species and diameter will grow into a specified 5th-year height class. To account for sprouting and survival failures, those probabilities are multiplied by logistic regression estimates of the probability that a parent tree will produce a sprout that survives to age 5. The resulting joint probabilities facilitate predicting future height distributions of surviving sprouts when the model is applied to a preharvest inventory of overstory trees.

Environmental regulation of xylem sap flow and total conductance of Larix gmelinii trees in eastern Siberia.

Xylem sap flow and environmental variables were measured on seven consecutive midsummer days in a 130-year-old Larix gmelinii (Rupr.) Rupr. forest located 160 km south of Yakutsk in eastern Siberia, Russia (61 degrees N, 128 degrees E, 300 m asl). The site received 20 mm of rainfall during the 4 days before measurements, and soil samples indicated that the trees were well watered. The tree canopy was sparse with a one-sided leaf area index of 1.5 and a tree density of 1760 ha(-1). On a clear day when air temperature ranged from 9 to 29 degrees C, and maximum air saturation deficit was 3.4 kPa, daily xylem sap flux (F) among 13 trees varied by an order of magnitude from 7 l day(-1) for subcanopy trees (representing 55% of trees in the forest) to 67 l day(-1) for emergent trees (representing 18% of trees in the forest). However, when based on xylem sap flux density (F'), calculated by dividing F by projected tree crown area (a surrogate for the occupied ground area), there was only a fourfold range in variability among the 13 trees, from 1.0 to 4.4 mm day(-1). The calculation of F' also eliminated systematic and large differences in F among emergent, canopy and subcanopy trees. Stand-level F', estimated by combining half-hourly linear relationships between F and stem cross-sectional area with tree size distribution data, ranged between 1.8 +/- 0.4 (standard deviation) and 2.3 +/- 0.6 mm day(-1). These stand-level F' values are about 0.6-0.7 mm day(-1) (30%) larger than daily tree canopy transpiration rates calculated from forest energy balance and understory evaporation measurements. Maximum total tree conductance for water vapor transfer (G(tmax), including canopy and aerodynamic conductances), calculated from the ratio of F' and the above-canopy air saturation deficit (D) for the eight trees with continuous data sets, was 9.9 +/- 2.8 mm s(-1). This is equivalent to a leaf-scale maximum stomatal conductance (g(smax)) of 6.1 mm s(-1), when expressed on a one-sided leaf area basis, which is comparable to the published porometer data for Larix. Diurnal variation in total tree conductance (G(t)) was related to changes in the above-canopy visible irradiance (Q) and D. A saturating upper-boundary function for the relationship between G(t) and Q was defined as G(t) = G(tmax)(Q/[Q + Q(50)]), where Q(50) = 164 +/- 85 micro mol m(-2) s(-1) when G(t) = G(tmax)/2. Accounting for Q by excluding data for Q < Q(85) when G(t) was at least 85% of G(tmax), the upper limit for the relationship between G(t) and D was determined based on the function G(t) = (a + blnD)(2), where a and b are regression coefficients. The relationship between G(t) and D was curvilinear, indicating that there was a proportional decrease in G(t) with increasing D such that F was relatively constant throughout much of the day, even when D ranged between about 2 and 4 kPa, which may be interpreted as an adaption of the species to its continental climate. However, at given values of Q and D, G(t) was generally higher in the morning than in the afternoon. The additional environmental constraints on G(t) imposed by leaf nitrogen nutrition and afternoon water stress are discussed.

Initiation of a New Woodland Type on the Texas Coastal Prairie by the Chinese Tallow Tree (Sapium sebiferum (L.) Roxb.)

BRUCE, K. B., G. N. CAMERON (Department of Biology, University of Houston, Houston, Texas 77204) AND P. A. HARCOMBE (Department of Ecology and Evolutionary Biology, Rice University, Houston, Texas 77251). Initiation of a new woodland type on the Texas Coastal Prairie by the Chinese tallow tree (Sapium sebiferum (L.) Roxb.). Bull. Torrey Bot. Club 122:215-225. 1995.-The chronosequence method (stand ages 0-20 years) was used to study the invasion of the Upper Coastal Prairie of Texas by the Chinese tallow tree and to learn whether this exotic plant would be replaced by native woodland species. This invasion marked a dramatic transformation of community structure. Dominance of life forms shifted rapidly (< 10 years to canopy closure) as graminoids and forbs were replaced by trees and shrubs during succession. Size-frequency distributions of the trees showed that stands were not even-aged. Many stands in the oldest three age classes exhibited descending monotonic tree size distributions. Because Chinese tallow produces seeds soon after establishment, it seems likely that the rapid increase in density was the result of initial trees acting as seed sources. The most common native trees that appeared in the survey were generally small-seeded inhabitants of local riparian areas, e.g., hackberry (Celtis laevigata), elm (Ulmus americana), green ash (Fraxinus pensylvanica), and yaupon (Ilex vomitoria). Low densities of these species indicated slow invasion rates compared to that of tallow. Currently, stands are virtually monospecific. However, the non-tallow species showed a significant increase in density with stand age which suggests that these woodlands may become more diverse in the future.

Field evidence for infra-specific competition between trees

An investigation of patterns in the spatial and size distribution of trees in single species stands is described. Three widely used indicators of competition are produced from these field measurements, and used to evaluate if competition between the trees has occurred. The fieldwork can be carried out at any time of year, and is suitable for both class and small group projects.

Dependence of the aboveground respiration of hinoki cypress (Chamaecyparis obtusa) on tree size.

Nighttime respiration was measured at monthly intervals over one year on the aboveground parts of five sample trees in an 8-year-old hinoki cypress (Chamaecyparis obtusa (Sieb. et Zucc.) Endl.) stand, by an enclosed standing-tree method. The respiration rate rose rapidly from early spring to a maximum in June, and decreased abruptly in July and then gradually toward autumn and winter. The seasonal change in the respiration rate was synchronized with stem volume increment rather than with monthly mean air temperature. The respiration rate, r, of individual trees increased with increasing tree dimensions, such as stem volume, v(S), and stem girth at the base of the live crown, G(B). The dependence of respiration rate on tree size was successfully represented by a power function. The r - v(S) dependence was rather stronger than the r - G(B) (2) dependence, especially toward the end of the growing season (from July to September). The observed respiration rate was almost the same as the respiration rate corrected for the monthly mean air temperature. The annual respiration of individual trees was directly proportional to their phytomass or to its increment. Although the annual respiration of individual trees decreased proportionally to the square root of the leaf mass, it decreased abruptly in the range close to the smallest sample tree. Combining the monthly relationship between respiration rate and stem volume with the tree size distribution in the stand, the stand aboveground annual respiration was estimated to be 20.4 Mg CO(2) ha(-1) year(-1) (= 12.5 Mg dry mass ha(-1) year(-1)) for an aboveground biomass of 17.4 Mg ha(-1) with an annual increment of 6.51 Mg ha(-1) year(-1), i.e., the stand aboveground annual respiration amounted to the equivalent of 72% of the biomass or to almost twice the biomass increment.

Disaggregating Stand Volume Growth to Individual Trees

Abstract A disaggregation function, relative size-growth (RSG), was proposed and developed for interior Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn] Franco) to distribute stand volume growth to a list of individual trees. The RSG function was formulated as a quadratic equation relating relative tree growth to relative tree size in a stand. The shape of the RSG function was linear, convex, or concave depending on initial stand conditions and structure. A recursive system of equations was developed to predict the three coefficients of the RSG function using initial stand density, mean tree size, and coefficient of variation of tree size distribution as predictor variables. This disaggregation function determines within-stand growth of individual trees and simulates stand development and dynamics. The RSG function provides a biologically based link between whole-stand and individual tree resolution models. FOR. SCI. 39(2):295-309.