Tree Volume Growth Research Articles

Effect of planting density on the development of tree and plantation volume of Populus x euramericana (Dode) Guinier cl. I-214

The effect of plantation density on the stem volume development phases of mean trees of Populus x euramericana (Dode) Guinier, cl. I-214 were studied in the test plantation aged 25 years with two different planting densities 4.25x4.25 m (treatment A) and 6.00x6.00 m (treatment B). The modeling of stem volume growth of mean trees enabled the identification of development phases based on biological laws. Different growth dynamics of mean trees of the clone I-214, depending on plantation density, had a clear effect on the beginning and the end of individual phases, i.e. subphases of development, as well as on the diameters, heights and volumes of mean trees at the end of each phase of volume development.

Impacts of climate change on forest growth: a modelling approach with application to management

The aim of this thesis was to modify and apply a statistical growth and yield model for analysing forest resources and optimal management under a changing climate in Finland. Initially, the structural and functional properties of physiological and statistical growth and yield models were compared under the current climate to assess whether the physiological model could be utilised in the modification of the statistical model (I). Thereafter, the impacts of elevated temperature and CO2 on tree growth were introduced into a statistical growth and yield model with species-specific transfer functions, which were formulated based on data simulated with a physiological model (II-III). These functions were created separately for three main tree species and they described the increase in stem volume growth of trees as a function of elevated temperature and CO2, stand density, competition status of a tree in a stand, geographical location and site fertility type of a stand. This method allowed the internal dynamics of the statistical model to be followed when the impacts of climate change were applied to the volume growth, allocated between diameter and height growth. Finally, this methodology was applied to derive an optimal management solution for a forest region located in eastern Finland under a changing climate by using the large-scale forestry scenario model and National Forest Inventory sample plot data (IV). In model comparisons, it was found that the physiological and statistical models agreed well in terms of relative growth rates regardless of tree species (I). This implies that both models predicted in a similar way the competition within a stand and the effect of position on tree growth. However, the statistical model was less sensitive to initial stand conditions and management than the physiological model. The transfer functions worked reasonably well in the statistical model and the model predictions were logical as regards the differences in productivity between species, sites and locations under current and changing climate (II, III). In these simulations, the volume growth was enhanced less in southern than in northern Finland, where currently low summer temperatures are more limiting to growth. In a regional forestry scenario analyses (IV), the accelerating tree growth under a changing climate increased the maximum sustainable removal of timber at regional level. Changes in optimal forest management were also detected: the proportion of thinnings increased because the stands fulfilled thinning requirements earlier, and the optimisation allocated more cuttings on mineral soils where extraction of wood was cheaper than on peatlands. Altogether, this study presents an attempt to integrate the capabilities of physiological and statistical growth and yield modelling approaches in order to make the latter more responsive to changing environmental conditions. As a result, the statistical model system can be expected to provide more precise predictions for a regional forestry scenario analyses by solving endogenously optimal forest management under a changing climate in

Introducing effects of temperature and CO 2 elevation on tree growth into a statistical growth and yield model

Impacts of elevated temperature and CO 2 on tree growth were introduced into a statistical growth and yield model for Finnish conditions based on corresponding predictions obtained from a physiological growth model. This one-way link between models was made by means of species-specific transfer functions describing the increase in stem volume growth of trees as a function of elevated temperature and CO 2, stand density and the tree's competition status in a stand of Scots pine ( Pinus sylvestris), silver birch ( Betula pendula) and Norway spruce ( Picea abies). This method allows the inner dynamics of the statistical model to be followed when the impacts of temperature and CO 2 elevation on tree growth are introduced into the calculation of volume growth and further allocated between diameter and height growth. In this way compatibility with previous predictions of tree growth by means of statistical models and related model systems under current climatic conditions could be retained. The performance of the statistical model with species-specific transfer functions was evaluated by comparing its predictions with corresponding predictions given by a physiological model under conditions of elevated temperature and CO 2. These calculations revealed that the growth response of individual trees to elevated temperature and CO 2 can be introduced into the statistical model from a physiological growth model with an outcome that results in fairly satisfactory growth responses at the stand level as well.

Growth impacts of Psittacanthus angustifolius Kuijt on Pinus oocarpa Schiede in Honduras

The mistletoe Psittacanthus angustifolius Kuijt (Loranthaceae) severely parasitizes Pinus oocarpa Schiede in southern Mexico and Central America causing growth loss and increased mortality of severely infected trees. The objectives of this study were to use stem analysis to evaluate the impacts of P. angustifolius on P. oocarpa in terms of height and volume growth of individual trees in Honduras and to evaluate a five-class mistletoe rating system for predicting the effects of this mistletoe on the growth of P. oocarpa. Two study sites in Honduras were selected based on incidence and severity of mistletoe infection. Thirteen dominant or codominant trees from each of three true mistletoe rating (TMR) classes: 0, no infection; 2, moderate infection; and 4, severe infection were selected. Stem analysis was conducted on the 78 selected trees to determine their height increment, volume increment, and specific volume increment. To evaluate growth reductions, each infected tree was paired with a healthy tree from the same site by height at time of infection for periodic height increment, age for periodic specific volume increment, and by volume at time of infection for periodic volume increment. To evaluate the mistletoe rating system 95% confidence intervals were constructed to compare means for height and volume increments between mistletoe infection classes for the last year of growth. Growth losses of over 50% were observed in terms of periodic volume increment and periodic specific volume increment during the last 3-year period prior to sampling for trees in TMR class 4 from both sites. Analysis of the effectiveness of the mistletoe rating system for predicting growth losses produced inconsistent results between sites because duration of infection, which was not a component of the rating system, influenced growth losses.

Genetic variation in veneer quality and its correlation to growth in white spruce

This study investigated the genetic variation in veneer quality of white spruce (Picea glauca (Moench) Voss) and its correlation with tree growth and wood density. A total of 270 sample trees from 35 families were harvested from 36-year-old provenance-progeny trials at two sites through a thinning operation. A 36-cm long bolt was collected from each sample tree at an 8-foot (or 2.45 m) height for this veneer quality study. The results indicate that conversion of fast-grown white spruce into veneer and plywood may present some problems. Low wood density, numerous knots, and possibly a high proportion of juvenile wood appear to be major factors contributing to low veneer stress grading, resulting in a production of low-quality veneer. This study also showed that the environmental factors at the two sites played an important role in determining veneer quality and tree radial growth. The narrow-sense heritability for veneer density, veneer modulus of elasticity, and veneer roughness were 0.62, 0.13, and 0.14, respectively. The results revealed considerable phenotypic variation and relatively high additive genetic variation in the veneer modulus of elasticity. The phenotypic and genetic correlations between ring width and veneer density or veneer modulus of elasticity were negative. A positive phenotypic and genetic correlation was found between veneer density and veneer modulus of elasticity. This suggests that selection for tree volume growth in white spruce would lead to a decrease in wood density and veneer stiffness.

The influence of stand development process on the height and volume growth of dominant Fagus sylvatica L. s.l. trees in the central Rhodope Mountains of north-eastern Greece

Summary This study was conducted in pure and mixed Fagus sylvatica L. s.l. stands in the central Rhodope Mountains of north-eastern Greece. Forty dominant beech trees were cut and analysed using a stem analysis technique. The trees came from two different groups (structural types) of stands. The first structural type consists of pure Fagus sylvatica L. s.l. stands and the second consists of Fagus sylvatica‐Pinus sylvestris L. stands. In each structural type some stands are located in good productivity sites and others in medium-productivity sites. Within each structural type the structure of the stands was the result of the same development process. The development process of pure beech stands was entirely different from the development process of beech‐pine stands. The main results of this research indicate that the stand development process, without any interaction with site, influences the height and volume growth of dominant beech trees, at least up to the age of 50 years. The growth environment of Fagus sylvatica‐Pinus sylvestris stands, as a result of their development process, gives a strong competitive advantage to dominant beech trees, to such a degree that the dominant beech trees of Fagus sylvatica‐Pinus sylvestris stands, in sites of intermediate productivity, exhibit practically the same height and at least the same volume, on average, as those of pure Fagus sylvatica stands of good productivity sites, at least up to the age of 50 years.

The zone of influence of paddock trees and the consequent loss in volume growth in young Eucalyptus dunnii plantations

Old paddock trees, retained in young eucalypt plantations for biological conservation, can be assumed to have a circular zone of influence within which the growth of the young trees is reduced. We used a set of non-linear simultaneous equations to model the radius of the zone of influence of old paddock trees and the consequent loss in stand volume growth of young trees in 4-year old Eucalyptus dunnii plantations. For paddock trees with crown radii of 5, 10 and 15 m and a suppression intensity of 0.5, the predicted radius of the zone of influence was 9.04, 23.8 and 42.0 m, and the predicted loss in stand volume growth was 1.3, 8.7 and 27.0% per hectare, respectively. The reduction in volume growth is expected to increase with time because the discrepancies in size between trees in and outside the zone of influence will increase as stands grow and competition for resources intensifies. The reduction in merchantable stand volume is expected to be even greater since some trees within the zone of influence are not expected to reach merchantable size by the end of the rotation. To minimise the loss of productivity while maintaining biodiversity, other alternatives such as offsetting removal of paddock trees by planting more trees in designated retention areas may need to be formulated.

Soil properties under a Pinus radiata - ryegrass silvopastoral system in New Zealand. Part I. Soil N and moisture availability, soil C, and tree growth

Understanding the changes in soil properties in silvopastoral systems is important in regulating the interactions between tree and understorey pastures. In this study, the effects of understorey management on soil mineral N and moisture availability, soil temperature, soil C, and tree growth were investigated in a seven-year-old silvopastoral agroforestry experiment in Canterbury, New Zealand. The systems included understorey treatments of bare ground and ryegrass (Lolium perenne) pasture. Soil mineral N, moisture content, and temperature were monitored from July 1997 to July 1998 in two positions (0.9 and 3.5 m north of tree rows) and two soil depths (0–10 and 10–20 cm). Soil C and N in the 0–10 cm depth were higher in the ryegrass than in the bare ground plots, reflecting the organic C and N input in the ryegrass plots, as well as greater N loss from the bare ground plots in the form of nitrate leaching and/or denitrification. Soil C was higher in the position 0.9 m than 3.5 m away from the tree rows, possibly caused by the greater C input from decomposing fine tree roots and needle litterfall at the 0.9 m position. Soil moisture availability was greater in the bare ground than in the ryegrass plots in the summer. No effect of understorey management on soil temperature was found. Soil nitrate levels were lower in the ryegrass plots and may be limiting when soil moisture supply was adequate. Tree volume growth from winter 1997 to 1998 was significantly greater in the bare ground treatment, reflecting better soil moisture and N supply conditions.

Impact of whole-tree harvesting and compensatory fertilization on growth of coniferous thinning stands

A series of 16 field experiments was established to quantify the growth response of first-thinning stands of Pinus sylvestris and Picea abies to whole-tree harvesting (WTH), and to estimate the need for nutrient compensation. The experiments were undertaken in Finland, Norway and Sweden and represent a wide range of climatic and soil conditions. The biomass and nutrient amounts removed were estimated on the basis of felled sample trees. On average, WTH reduced tree volume growth in both pine and spruce stands (5% and 6%, respectively) during the first 10-year period. The growth reduction was counteracted by fertilization (NPK) and the results indicate that the reduction was an effect of reduced N supply. The inclusion of various site descriptive variables in the linear models did not explain variation in growth response to WTH. Since the growth reductions due to WTH after 10 years were still present, the observation period needs to be extended.

Light absorption and bole volume growth of individual Douglas-fir trees.

Empirical growth and yield models for forest management are evolving toward individual-tree models that are capable of simulating the growth of mixed and uneven-aged stands. Spatially explicit (i.e., distance-dependent) models usually modify the growth of trees by means of competition indices; however, these competition indices rarely simulate the light available for tree growth explicitly. We used tree growth data from an even-aged, unthinned, 50-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand in British Columbia to test the hypothesis that the amount of absorbed light is a good predictor of diameter at breast height, height, and bole volume growth of an individual tree. We also explored the relationships between these variables. A spatially explicit light model was used to simulate photosynthetically active radiation absorbed by individual trees during a growth period (APAR) based on detailed canopy architecture information. For the purpose, we used a weighted leaf area (WLA) that is linearly related to APAR. Because of the integration of light absorption by a tree crown, estimates of WLA were highly correlated with leaf area for dominant trees. For suppressed trees, leaf area was a poor estimator of WLA. The relationship between WLA and bole volume growth was nonlinear, indicating a higher light-use efficiency in suppressed trees than in dominant trees. This relationship was strong enough to be useful for growth modeling. Only height growth of suppressed trees was affected by WLA. We conclude that single-tree WLA can be used as a process-oriented competition index in growth models for forest management.

Loblolly Pine Stand Early Development Under Reserve-Tree Silvicultural Systems in East Texas

Abstract Even-aged reproduction methods retaining reserve trees that persist through the development of the succeeding rotation have been poorly studied in loblolly pine (Pinus taeda L.), yet have potential for satisfying a variety of landowner objectives. Two research sites were established in the East Texas Pineywoods region to examine the development of the regeneration component under five residual basal area densities (0, 10, 20, and 40 ft2/ac with natural regeneration on Site I; 0 and 30 ft2/ac with both natural regeneration and planting on Site II). After 7 yr on Site I and 5 yr on Site II, all reserve-tree methods allowed the development of a sufficient number of trees for producing a new generation beneath the residual overstory. However, suppression of the understory pines was evident, and varied in direct proportion to the basal area of the residual overstory. Volume growth of the residual overstory trees was low on an areal basis due to the death of several large residuals. A trenching experiment showed that the largest effect of the residual overstory on understory development was due to light attenuation rather than competition for soil resources. Advantages offered by reserve-tree methods for loblolly pine have to be assessed in view of the suppressed development of the regeneration. South. J. Appl. For. 24(1):11-16.

Shoot water relations of mature black spruce families displaying a genotype x environment interaction in growth rate. I. Family and site effects over three growing seasons.

Pressure-volume curves were determined for black spruce (Picea mariana (Mill.) BSP) trees from four full-sib families. During the first two years, trees were measured from a plantation on a dry site. In the third year, trees were sampled from the dry site and a wet site. Diurnal measurements of shoot water potential allowed in situ shoot turgor to be estimated in addition to standard water relations traits. Over all years, Female 59 progeny displayed lower osmotic potentials at saturation (Psi(sat)) than Female 63 progeny. Genetic differences in Psi(sat) were similar on both the dry and wet sites. Modulus of elasticity (epsilon) was greater for Female 59 progeny than for Female 63 progeny, producing a compensatory effect resulting in no genetic or site differences in osmotic potential at turgor loss point (Psi(tlp)) or relative water content at turgor loss point (RWC(tlp)). Mean and predawn shoot turgor pressures (P(x) and P(pd)) were higher for Female 59 progeny than for Female 63 progeny and higher at the wet site than the dry site. Genotype x environment trends were observed; compared to Female 63 progeny, Female 59 progeny displayed 9.8 and 5.1% higher P(pd) on the dry and wet sites, respectively, and 3.4 and 9.8% greater P(pd) values in wet and dry years, respectively. Tree volume growth showed no relationship to Psi(tlp) or RWC(tlp), but was correlated with Psi(sat) and P(x); however, the strongest correlation was with P(pd) (r = 0.90).

Growth reduction in harvest-age, coniferous forests with residual trees in the western central Cascade Range of Oregon

To evaluate the relationship of overstory residual trees to the growth of unmanaged young-to-mature understory Douglas fir ( Pseudotsuga menziesii (Mirb.) Franco) and western hemlock ( Tsuga heterophylla (Raf.) Sarg.), the basal area and volume of 14 paired plots with and without residual trees were examined in the Willamette National Forest, Oregon. Residual trees were large survivors of the fires that initiated the understory between 55 and 121 yr ago. Understory stands were naturally regenerated and not managed in any way. High residual tree and understory densities were negatively associated with understory volume. The relation of density of residual trees to total understory and Douglas-fir basal areas and volumes was best described by a negative logarithmic function. The rate of decrease in total understory and Douglas-fir basal areas and volumes per individual residual tree became smaller with increasing residual-tree density. Predicted total understory volume reduction was 23% with five residual trees/ha and 47% with 50 residual trees/ha, averaging 4.6% and 0.9% per residual tree, respectively. After including the estimated volume growth of residual trees since initiation of the understory, stand volume was still 19% lower with five residual trees/ha and 41% lower with 50 residual trees/ha than in stands with no residual trees, averaging a reduction of 38% and 0.8% per residual tree, respectively. In mixed stands of Douglas fir and western hemlock, predicted Douglas-fir basal area and volume declined more rapidly than did total understory basal area and volume when residual-tree densities exceeded about 15 trees/ha. This difference was probably due to the relative shade-intolerance of Douglas fir. Predicted Douglas-fir volume reduction was 13% with five residual trees/ha and 75% with 50 residual trees/ha, averaging 2.6% and 1.5% per residual tree, respectively. The southern aspects had more than 150% the total understory basal area and volume and more than 200% the Douglas-fir volume and basal area of the northern aspects. Lower density and basal area of understory trees, particularly of dominant and codominant Douglas fir, were associated with increasing residual-tree densities. Given the same diameter at breast height (DBH), heights of Douglas fir were not related to residual trees. Regardless of understory age, understory volume was greatest in stands with the lowest understory densities. These results suggest that timber production in unthinned green-tree retention units may be reduced and may depend on the density of leave-trees. Thinning of understory trees is recommended to reduce growth loss from intraspecific competition.

Rate of Sawtimber Volume and Value Growth of Individual Sugar Maple Trees in Managed, Uneven-Aged Stands in the Lake States

Abstract While volume growth of individual sawtimber trees is dependent on changes in diameter and merchantable height, value growth is dependent on these along with changes in tree quality, the quality of logs recovered from the tree, and market prices. For sugar maple and other northern hardwood species, quality development is at least as important as biological growth in determining value growth, making development of silvicultural prescriptions and marking guidelines complex but extremely important for maximizing returns. This paper utilizes projection methods from the literature to develop expected rates of biological and value growth for sugar maple in managed, uneven-aged forests. These rates are presented by 2 in. diameter class and one-half 16 ft log merchantable height classes. Based on the models, the projected rate of biological growth increases with tree diameter and decreases with merchantable height. The rate of value growth generally increases with tree diameter and decreases with merchantable height, but the relationships with tree grade are complex. North. J. Appl. For. 14(2):78-83.

Measuring tree-ring increments on tree bole sections with a video-based robotic positioner.

We report on the design and performance of a system that speeds measurement of radial tree-ring increments on tree stem disks; this method replaces the usual binocular microscope with a video image, and automates the measuring and recording processes. The system was used to measure bole sections cut from stems at various heights to determine volume growth of representative trees in an old-growth ponderosa pine stand. The objective of the measurement system was to speed acquisition of annual growth increments from a large number of disks. A personal computer controls the location of a video camera in a 3-axis positioning system. The operator views the sample on a video monitor and positions the camera over each ring by selecting it with a computer-driven mouse. The computer measures and records the distance that the camera moves between each ring. Task selection is facilitated by menu-driven software that also formats, checks and organizes data files. Measurements have a resolution of 0.026 mm; however, finer resolution could be obtained with a different camera lens. Tests of measurement variability (repeated measurements by individual operators on a single radius) indicated standard errors of 0.006 mm or less for the first measurement sets for four operators. Correlation coefficients among four radii per bole section were as low as 0.66 for a whole tree, suggesting that measurements on single radii may provide poor estimates of radial growth for old trees. This system also offers the potential for automatic ring detection and measurement.

Response of a Scots pine (Pinus sylvestris) stand to application of phosphorus, potassium, magnesium and lime. 3. Foliar nutrient concentrations and stand development

In 1985-88, a 25-yr-old Scots pine forest in Netherlands was limed and fertilized with P, K and Mg in a factoral design. This paper addresses effects of these treatments on foliar nutrient concentrations and tree growth. Stem volume increments of individual trees were measured. Average annual volume growth was estimated to be about 16 msuperscript 3/ha, which may be a slight underestimation. P and K showed increased foliar concentrations immediately after treatment and were the only elements that significantly increased volume growth in 1988-91. Additional annual volume growth of individual trees brought about by P and K corresponded with 0.9 and 2.2 msuperscript 3/ha, respectively. Foliar Mg and Ca increased later and insignificantly reduced and increased volume growth, respectively. Lime and Mg applications tended to lower foliar N. When absolute foliar concentrations and element ratios were compared to Dutch and German standards, it appeared that application of some of these standards in present research would not always have given a fully correct prediction of growth responses to nutrient additions.

Economic assessment of ungulate herbivory in commercial forests of eastern Oregon and Washington, USA

Four forest stands in eastern Washington and Oregon, USA, containing exclosures to prevent or impede ungulate herbivory, were modeled to forecast timber yields and soil expectation values (SEVs) at harvest. Contrasts of ponderosa pine ( Pinus ponderosa Dougl. ex Laws.) growth and yield inside and outside exclosures show that ungulate herbivory may either promote or depress tree volume growth. Projected income from stands with more intensive stocking management and with inclusion of regulated livestock herbivory was higher than that of less intensively managed stands without livestock for scenarios with projected rising stumpage price levels for 2040. Under an assumption of future stumpage prices held constant at 1990 levels, the reverse was true. Ungulate herbivory plus planted stock and prescribed fire in site preparation provided the highest stand value at two sites. Sites without prescribed fire fared better when fenced to prevent livestock or big game herbivory. The results illustrate that ungulate herbivory alone is not the determinant factor of the economic yield of stands, but ungulate herbivory can have substantial impact on site productivity when used in conjunction with prescribed fire, stocking control, and species selection.

Hybrid Aspen Performance and Genetic Gains

Abstract The aspen hybrid breeding program has been active in the Lake States since 1955. This study summarizes long-term performance of aspen hybrids in six locations in Wisconsin and Upper Michigan. Interspecific hybrids of native bigtooth aspen and quaking aspen with other poplar species show improved growth when compared with native aspen species across a range of site quality. Quaking aspen hybrids with Populus tremula (XT-Ta) were the most promising based on growth, wood quality, and disease susceptibility. Individual tree volume growth for the XT-Ta hybrids was more than double that of progeny of pure quaking aspen parents (XT). Other aspen hybrids with P. davidiana, P. alba, and P. canescens parentage exhibited special growth potential on relatively poor and dry-sites, but were susceptible to a bronze leaf disease. Hybridization was more effective in improving aspen growth than breeding within pure species. Hybrid superiority was consistent across a range of site indexes, and showed the greatest potential on high-quality sites. Genetic gains for the XT-Ta hybrids, based on 15-yr height measurements, ranged from 29 to 34% across sites. Gain in volume growth is expected to be over 100%. Short-rotation (20-yr) commercial plantings with aspen hybrids are recommended on low-to medium quality northern hardwood sites. North. J. Appl. For. 10(3): 117-122.

Thinning and Fertilizing Southern Pine Stands of the Lower Coastal Plain: Biological and Economic Effects

Abstract The interaction between thinning and fertilization (nitrogen and phosphorus) was investigated in seven slash pine (Pinus elliottii Engelm. var. elliottii) plantations and one natural loblolly pine (Pinus taeda L.) stand in the lower Coastal Plain of the southeastern United States. Thestands ranged in age from 14-20 years when the 2² factorial (thinning X fertilization) experiments were installed. Significant thinning X fertilization interactions occurred on five tests, but the nature of the interactions was inconsistent. Fertilization responses remained significant8 years after treatment and averaged 35 ft³/ac/yr. Fertilization increased stand volume production in the chip-n-saw product class more frequently than thinning. After 8 years, thinning increased individual tree volume growth by 0.50-3.05 ft³/tree over the controls; however, thinninggenerally decreased both total stand and chip-n-saw volumes at final harvest. Economic effects were examined by determining soil expectation values (SEV) for each thinning and fertilization treatment combination for various rotation lengths using uniform economic assumptions. The treatmentcombination that maximized stand volume production was not always the best financial choice. The increased growth rates due to thinning, fertilization, or both tended to extend the optimal rotation. A 4% real cost of capital with harvest merchandizing of pulpwood and chip-n-saw product classeseconomically favored fertilization over the other treatments. However, increasing the cost of capital (6% real) or merchandizing solely for pulpwood put fertilization at a relative disadvantage. South. J. Appl. For. 16(4):186-193

Soil Nitrogen Mineralization Potential in a Fertilized Loblolly Pine Plantation

Nitrogen deficiency is the most common nutrient deficiency in natural pine (Pinus spp.) stands and plantations of the southern USA. This study was conducted to identify a soil test of available N that correlates well with tree growth volume response to N fertilization. We evaluated the utility of 98-d aerobic incubation for assessing changes in soil N availability resulting from fertilization of a loblolly pine (P. taeda L.) plantation. Results were compared with results from a 30-d incubation and correlated with tree volume growth. Seven months after fertilization with 224 kg N ha−1 as urea, significant increases (P > 0.0312) in N-mineralization potential (Nφ) were found in surface (0–15 cm) soils, but not subsurface (15–50 cm) soils. The increase was also significant in subsequent incubations up to 16 mo after fertilization. A concurrent short-term aerobic-incubation study did not detect significant increases due to fertilization after 7 mo, illustrating the greater sensitivity of the long-term incubation to differences in available N. No differences in Nφ were attributed to P fertilization at 56 kg ha−1, although significant increases occurred when P was included in nutrient leaching solutions in the incubated soils following CaCl2 extraction for inorganic N. Differences in Nφ occurred among seasons, with maximum mineralization occurring in spring and minimum in autumn. Nitrogen-mineralization potential correlated with 2-yr tree volume growth, with the best correlation at the spring sampling date (r = 0.81, P > 0.0002). The linear relationship between volume growth and Nφ was improved with the addition of tree stand stocking as a covariate (r = 0.85). Nitrogen-mineralization potential was also correlated with soil Kjeldahl N, organic C, and exchangeable acidity.