Annual Diameter Growth Research Articles

Environmental and allometric drivers of tree growth rates in a north Australian savanna

Frequent fire is a feature of the mesic Australian savannas, yet little is known about its effect on tree growth rates. Growth data are critical for the development of demographic models to understand the consequences of different land management regimes. We used generalized linear mixed effects models and information-theoretic multi-model inference to analyse annual diameter growth of adult trees (≥5 cm diameter at breast height, DBH) and saplings (≥1.5 m height and <5 cm DBH) and height growth of juveniles (<1.5 m height) in response to fire, tree size, stand basal area, annual rainfall, and for adult trees, the presence of the introduced Asian swamp buffalo (a potentially growth-limiting herbivore). The analysis was based on two medium-term datasets from natural eucalypt savanna in Kakadu National Park in the Australian monsoonal tropics. One dataset was based on a 7-year experiment examining the effect of buffalo removal during which three fires occurred, and the second was derived from a 4-year study in which three experimental fire treatments (annual early dry season fire, annual late dry season fire and no fire) were imposed. An unplanned, extremely severe fire burnt some of the previously unburnt trees in the final year of this latter experiment, so we considered it as an additional fire treatment. Despite high variance, there was strong evidence for differential effects of the fire treatments on tree growth, and these effects differed among the three size groups. Late and extreme fires resulted in a high proportion of individuals with negative DBH increments (due to burning or shedding of bark, and also to stems being killed and replaced by small stems), and decreased average DBH growth of saplings (−0.17 and −1.38 cm year −1 , respectively— cf . 0.22 cm year −1 for no fire) and adult trees (0.01 and 0.03 cm year −1 , respectively— cf . 0.18 cm year −1 for no fire). Early fires decreased DBH growth of saplings (0.11— cf . 0.22 cm year −1 for no fire) but increased growth of adult trees (0.29— cf . 0.18 cm year −1 ). Height growth of juvenile trees was reduced by early fires (0.01— cf . 0.06 m year −1 for no fire) but was increased by late fires (0.10 m year −1 ), probably because juveniles are physiologically active early in the dry season, but are effectively dormant in the late dry season. When stand basal area was high there was evidence of growth suppression in adults, saplings and juveniles. Growth of adult trees was lower in years with high rainfall and where buffalo were removed, possibly because of increased competition from ground layer vegetation. Our study casts doubt on the sustainability of the frequent, early dry season fires that have become a management goal in much of northern Australia.

Effects of Wind Barrier Protection on Eleven-Year Growth of Black Walnut Seedlings

Abstract Black walnut (Juglans nigra L.) plantings in exposed, open-field sites frequently result in poor seedling growth. The use of artificial wind barriers significantly improved tree growth on such a site in central Michigan on a sandy loam soil, a well-drained Arenic Hapludalfs. The use of a wooden lath (snow fencing) barrier for the first 4 years following planting provided a wind-protected microenvironment that improved the 11-year diameter growth by 60%, and the height growth by 70%, compared to trees grown without the barriers. Annual diameter growth of the protected trees was significantly greater throughout the study, indicating that the barrier effects on growth persisted at least 7 years after the barriers were removed. Trees growing behind the barriers had greater crown and leaf area than those in adjacent exposed plots. The use of existing natural barriers, such as forest edges, fence rows, topography, and tall natural herbaceous vegetation, should be considered when planting trees such as black walnut on exposed sites.

Liana loads and their association with Bertholletia excelsa fruit and nut production, diameter growth and crown attributes

We investigated the association between lianas and Bertholletia excelsa (Brazil nut), a long-lived, emergent tree of significant ecological and economic importance in Amazonia. Our objectives were: (1) to determine the relationship between crown liana load and liana number, basal area, and origin in relation to the B. excelsa host; and (2) to determine the relationship between liana load and B. excelsa fruit and nut production, diameter growth, and crown form, position and area. One hundred and forty trees (≥50 cm dbh) were selected with representatives of 10 diameter classes and four liana load categories. To quantify fruit and nut production, fruit counts and nut fresh weights per tree were measured in 2002 and 2003, and annual diameter growth was quantified using dendrometer bands. Trees with lianas produced significantly fewer fruits and had reduced nut fresh weights than liana-free trees. Trees with the most extensive liana loads (&gt;75% crown coverage) were 10.2 times more likely to have crown forms categorized as less than half-crowns or few branches than trees with reduced liana loads. No statistically significant relationship was found between liana load and tree diameter growth. Results suggest that liana cutting might increase B. excelsa fecundity and commercial nut yields.

Stand structure and growth of Abies magnifica responded to five thinning levels in northeastern California, USA

A 60-year-old red fir stand with 23,950 stems/ha was thinned to five stand densities. Thinning occurred in 1972, 1976, and 1980. Height, dbh, and crown characteristics were measured seven times at 4–7-year intervals from 1972 to 2002. Tree rings were measured retrospectively to determine growth of individual years. Periodic annual increment (PAI) was analyzed for quadratic mean diameter (QMD), height, crown volume, and basal area per ha. We found significant difference for all variables among thinning levels and among measurement periods ( P < 0.002). Trees in heavily thinned plots grew more in height, dbh, and crown volume than trees in lightly thinned plots. The trends were true for the eight tallest trees per plot (=100 trees/ha) for height and dbh. Yet, both total and PAI stand basal area were greater in the lightly thinned plots than in the heavily thinned plots. Thinning intensity accelerated the transformation in diameter distribution from either reverse ‘J’ or skewed shape to a bell-shape. In addition, the heavier thinned plots increased stand vigor and health as indicated by less snow damage and stem deformities than the lighter thinned plots. Annual diameter growth was significantly related to average minimum temperature during the growing season. We conclude that thinning young red fir stands to a wide spacing will enhance stand development and minimize damage to the residual trees.

Effects of lianas on growth and regeneration of Prioria copaifera in Darien, Panama

We conducted a silvicultural experiment to evaluate the effects of lianas on the stem diameter growth of Prioria copaifera (cativo), a valuable timber tree in Panama. Dalbergia brownei, a leguminous liana, is abundant in many riverine P. copaifera-dominated swamp forests in Panama’s easternmost province of Darien, particularly in logged areas. In a forest along the Balsas River, P. copaifera dominated the forest with 96.6% of the total arboreal basal area of 34.8 m 2 ha −1 (trees≥10 cm dbh) while D. brownei comprised 96.9% of the total liana basal area of 3.4 m 2 ha −1 (stems≥1 cm dbh). After classifying liana infestation as severe or minor for the crown of every tree ≥4 cm dbh in six 25 m×25 m plots, we cut all lianas in three randomly chosen plots. Prior to treatment 53% of trees were severely infested, 31% had minor infestation, and 16% were liana-free. During the 5 years after treatment, mean annual diameter growth of cativo trees doubled in plots where all lianas were cut compared to control plots, regardless of severity of prior liana infestation. Prioria regeneration was scarce in heavily vine-infested forest compared to nearby permanent plots in forest with low liana infestation. At a cost of only 16 person-hours ha −1, these results suggest that a small investment in cutting lianas can greatly increase wood production in degraded cativo forests.

Impact of repeated defoliation on jarrah (Eucalyptus marginata) saplings

Summary In Australia, eucalypts frequently suffer defoliation due to insect herbivory or fire. Rapidly-applied ‘shock’ defoliation of eucalypts, characteristic of artificial defoliation experiments, is unusual under natural and plantation conditions, though the exception to this is defoliation by fire. The effect of 15 consecutive annual complete defoliations of jarrah (Eucalyptus marginata Donn ex Smith) saplings on diameter and survival of main stems is described. Within 3 y, this defoliation resulted in almost complete suppression of stem diameter growth. Despite up to 15 y of repeated defoliation, no plants died, although after 15 y about half the defoliated plants had died back to below 30 cm. Low mortality in E. marginata following complete defoliation is in contrast to effects on several other eucalypt species which have been subjected to defoliation experiments. Stem die-back did not appear to be related to less-than-usual winter rainfall in some years. Annual diameter growth of undefoliated plants was not correlated with preceding winter rainfall, probably due to the poor resolution of diameter measurements. The resilience to this defoliation, which is more severe than defoliation encountered in natural conditions, is evidence that understorey jarrah plants are capable of withstanding, for extended periods, defoliation by insects or fire. The degree and frequency of defoliation under current fire management regimes do not appear to threaten the persistence of jarrah saplings. Chronic defoliation by insect pests, while having a detrimental effect on growth, is unlikely to affect the persistence of jarrah saplings.

Spatially aggregated fruiting in an emergent Bornean tree

We investigated the spatial distribution of fruiting in Dryobalanops aromatica (Dipterocarpaceae), a mast-seeding emergent tree that is found in the tropical rain forests of Borneo. Of 393 adults (diameter at breast height (dbh) > 30 cm) in a 52-ha area, 143 (36.4%) individuals fruited. A second-order spatial analysis, based on Ripley's K-function, revealed that fruiting trees were significantly (P < 0.05) aggregated with respect to the total population over distances of 15-115 m. Thus, the spatial distribution of fruiting trees was more aggregated than expected from the adult tree distribution, which itself was aggregated within the study plot. Logistic regression analysis showed that fruiting trees had a significantly greater dbh and were surrounded by more conspecific adults per ha than non-fruiting individuals. Moreover, fruiting trees were found at higher elevations, on steeper slopes, and on sandy rather than clayey soils. In contrast, annual diameter growth, adult density over areas < 1 ha, and slope convexity did not significantly affect fruiting probability. The ratio of seedling (20 cm ≤ h < 60 cm) and sapling (60 cm ≤ h < 300 cm) density to adult density was higher in sites at higher elevations, on steeper slopes, and on sandy soils than that for lower elevations, flat slopes and clayey soils. This suggests that the aggregation of fruiting trees occurred not only at the time of the study, but that it had occurred repeatedly in the past, at the high-elevation, steep-sloped, sandy sites. Thus, site conditions probably affect the dynamics and spatial structure of local populations through differences in fruiting frequency among trees experiencing different site conditions.

Diameter Growth Models Using Minnesota Forest Inventory and Analysis Data

Abstract The Forest Inventory and Analysis (FIA) program of the USDA Forest Service North Central Research Station (NCRS) has begun replacing the 12- to 13-yr periodic inventory cycles for the states in the North Central region with annual inventories featuring measurement of approximately 20% of all plots in each of the 11 states each year. State reports on summaries of the forest resources will be produced every 5 yr. As a method of updating information on plots not visited in the current year, NCRS is developing nonlinear, individual-tree, distance-independent annual diameter growth models for species groups. The models, formulated as the product of an average diameter growth component and a modifier component, were calibrated on Minnesota FIA data from stands that were generally undisturbed, of mixed ages and of mixed species. The dependent variable is annual diameter growth. The independent variables include crown ratio, crown class, stand basal area, stand basal area larger than the subject tree, physiographic class, and latitude and longitude of plot locations. The model predictions at both the individual-tree level and plot level have negligible bias, and the models may be easily recalibrated to include new data sets obtained from the annual inventories. For. Sci. 47(30):301–310.

Resource competition across the crop-tree interface in a maize-silver maple temperate alley cropping stand in Missouri

In order to improve the management of temperate alley cropping, it is important to study the growth and physiological responses of plants arising from competition across the crop-tree interface. Maize (Zea mays L.) was established between rows of seven-year-old silver maple (Acer saccharinum L.) trees in north-central Missouri, USA with four imposed treatments: (1) an unmodified control with a standard rate of N fertilization (179.2 kg N (as NH4NO3) ha−1), (2) trenching with root barrier installed, (3) supplemental fertilization treatment (standard N + 89.6 kg ha−1 N), and (4) a combination of trenching with root barrier and supplemental fertilization. Whereas soil N status had little effect on maize physiology and yield at the interface, competition for soil water was substantial in both years. Without a root barrier, soil water content, predawn and midday water potential, and midday net photosynthesis of maize plants adjacent to the tree row were reduced compared with those of plants in the alley center, but no differences across the maize crop were evident in the presence of a barrier. Grain yield of border row maize plants lacking an adjacent barrier was depressed compared with that for maize plants with a root barrier present (8.42 vs. 6.59 Mg ha−1 in 1997; 5.38 vs. 3.91 Mg ha−1 in 1998). However, the barrier did not completely restore yield to that in the alley center, suggesting that reductions in light near the tree row also limited production. Top ear height showed a similar pattern of response to the presence of a root barrier. Silver maple trees responded to root barrier installation with reduced annual diameter growth and reduced water status on some sample days.

Prediction of Annual Diameter Growth and Survival for Individual Trees from Periodic Measurements

Abstract It is difficult to fit annual tree survival and diameter growth models to data that were measured, not every year, but at some interval. This study aimed to determine suitable methods to obtain parameter estimates for such a system from periodic measurements. Given a system consisting of a tree survival model and a tree diameter growth model, this article presents an iterative method for estimating system parameters. The method involves sequentially updating of the parameters of both models within the growth period. Data from 111 plots from the Southwide Seed Source Study of loblolly pine (Pinus taeda L.) were then used to evaluate this iterative approach against the averaging method that assumes a constant tree survival probability and diameter growth rate during the remeasurement interval. Results indicated that the iterative method out-performed the averaging method in predicting future individual tree survival, diameter growth, and stand basal area. The iterative method was superior because it accounted for the variable rate of diameter growth and tree survival probability as functions of ever-changing stand and tree attributes. For. Sci. 46(1):127-131.

Persistence of suppression effects on peatland black spruce advance regeneration after overstory removal

The persistence of suppression effects on peatland black spruce (Picea mariana (Mill.) BSP) advance regeneration following overstory removal was examined (i) by analyzing post-harvest growth patterns and (ii) by comparing observed post-harvest growth with predictions from an individual-tree growth model. Analysis of growth patterns revealed critical points (inflections or maxima) in annual basal area, diameter, and height growth series, and in specific volume increment. Critical points occurred at different times (ranging from 1 to 29 years after harvest) for different variables and often occurred earlier for trees with greater height at time of harvest. These critical points do not necessarily coincide with the cessation of persisting suppression, however, since post-harvest growth patterns also reflect current influences on growth. The comparison of observed basal area and diameter growth with model predictions isolated persisting suppression effects. The effects of suppression on basal area and diamete...

Effects of Planting Density on Early Growth of Giant Sequoia (Sequoiadendron giganteum)

Abstract Almost no information exists for stocking and growth of young giant sequoia (Sequoiadendron giganteum) plantations. This study measured 2,086 giant sequoia seedlings, planted at true spacings of 7 to 20 ft, over a period of 7 yr. Compared to other species that have been studied, giant sequoia shows remarkably early and extensive effects of intertree competition. Unlike results for other species, spacing substantially affects early height growth of sequoia. A general least squares model showed that crown width, stem diameter, and height increased linearly with the natural log of spacing distance at 4, 5, and 7 yr after planting (all P-values &lt; 0.0001). By 7yr, trees at wide spacing (14-20 ft) were showing 45-78% wider annual diameter growth and 29-67% higher annual height growth than trees at one-half each respective spacing (7-10 ft). Results indicate that for close initial planting densities (7-12 ft spacings), early precommercial thinning (before 7 yr after planting) may be required to avoid intertree competition. West. J. Appl. For. 14(2):65-72.

Management of Intrameatal Vestibular Schwannoma: Microsurgery, Radiosurgery or "Wait and Scan"

The growth of purely intrameatal vestibular schwannoma (VS) was investigated, in the period 1973-96 in a series of 40 patients with 40 unilateral VS. In the present study, the material was analysed and updated. By the end of the observation period (mean 3.6 years), 27 tumours (67.5%) revealed growth and 13 tumours (32%) had no measurable growth. Four growth patterns were observed: (A) 15 tumours (37.5%) exhibited constant growth; (B) 13 tumours (32.5%) had no measurable growth; (C) 8 tumours (20%) revealed growth subsequent to a no-growth period; and (D) 4 tumours (10%) showed different growth patterns during the observation period. The annual diameter growth rate ranged between 00 mm/year and 6.5 mm/year and the mean diameter growth per year was 3.2 mm. The findings of the present study, especially those for group B (the non-growing tumours) and C (tumour growth subsequent to a silent period) bring into question the reliability of the results achieved by radiosurgery, as without any intervention it may be that no tumour growth occurs.

Thinning Improves Growth of Crop Trees in Natural Shortleaf Pine Stands

Abstract Dense, previously unthinned, 24- to 28-yr-old natural shortleaf pine (Pinus echinata Mill.) stands in the Ouachita Mountains of eastern Oklahoma showed good growth responses during the first 5 yr after thinning to three stocking levels̶30, 50 and 70% of full stocking. Residual trees in stands thinned to minimum full stocking (60%) or less appeared to rapidly utilize the additional growing space. Net periodic annual basal area growth averaged 6.7, 7.9, and 8.5 ft2/ac/yr, respectively, for plots thinned to 30, 50, and 70% stocking (PS), but only 4.5 ft2/ac/yr on the unthinned controls due to mortality. Periodic annual diameter growth for trees comprising a dominant stand component averaged 0.42, 0.35, and 0.29 in. on the 30, 50, and 70 PS plots, respectively, and 0.24 in. on the unthinned controls. Periodic annual merchantable volume (3 in. top dob) growth of trees larger than 3.5 in. dbh was not significantly different among the 50 PS, 70 PS, and unthinned control plots, and ranged from 183 to 213 ft3/ac/yr. The excellent growth rates observed during the 5 yr study period exceeded expectations for these sites (SI50= 57) and stand ages, and might be due to the above-normal precipitation received during 4 of the 5 yr. South. J. Appl. For. 20(4):182-187.

Base cation fertilization and liming effects on nutrition and growth of Vermont sugar maple stands

Soil and foliar nutrition, crown condition, and wood growth were measured in three mature sugar maple stands in northern Vermont before and after fertilization with base cations (107 kg ha−1 K, 53 kg ha−1 Ca and 11 kg ha−1 Mg) with or without 3000 kg ha−1 supplemental lime in order to test the effectiveness of such treatments in ameliorating base cation deficiencies in sugar maple (Acer saccharum Marsh.). Pre-fertilization analyses indicated multiple cation deficiencies in these stands, since foliar K, Ca and Mg were all near or below sufficiency standards suggested for sugar maple. Fertilization with cations in addition to liming elevated soil pH from 3.6 to 4.5 in the first year after treatment, and elevated soil pH was maintained over two additional growing seasons along with significantly improved soil Ca and decreased soil Al. Foliar K, Ca and P concentrations were all significantly improved (P < 0.05) compared with controls for the three growing seasons following the first treatment, while only foliar K concentration showed significant improvement in plots treated with the base cation fertilizer without lime. By the third growing season following treatment, trees in limed plots had significantly less crown dieback than controls or trees in plots treated with the base cation fertilizer alone. Diameter growth showed marginal improvement in the plots treated with cations, annual diameter growth increased 200% compared with controls in the limed plots. Despite these positive results, the long term contribution of increased soil pH and soil calcium to soil nutrient pools and root distribution remains to be determined, as does the sustainability of growth increases. We conclude that in northern Vermont sugar maple stands on relatively infertile podzols with low pH, base cation limitations may be especially important in controlling sugar maple tree health or growth, while fertilization to ameliorate base cation deficiencies may be effective only at relatively high base cation addition rates.

Abundance, growth and mortality of very large trees in neotropical lowland rain forest

Very large trees, arbitrarily defined as those over 70 cm diameter above buttresses, account for a major portion of the above-ground biomass in neotropical rain forests. Owing to the scarcity of individuals of a given species and the difficulty of accurate measurement, there are few species-level data on the growth, mortality, and abundance of species that regularly reach emergent status. We report such data for very large individuals from old-growth tropical wet forest at the La Selva Biological Station in the Atlantic lowlands of the Republic of Costa Rica. The landscape-scale abundance of all species reaching over 70 cm diameter was assessed using 515 0.01-ha quadrats located at grid points in a 500 ha area of old-growth forest. In the total sample of 2301 stems 10 cm or more in diameter, very large individuals accounted for 2% of the stems, 23% of the basal area, and 27% of the estimated above-ground biomass. Growth and survival for five species that regularly attain emergent status were measured in a 150 ha area within the 500 ha plot. Survival of 282 very large individuals of the five species was measured over 6 years. The mean annual mortality rate of the total sample was only 0.6% year-1. Mean annual diameter growth increments varied from 1.9 to 5.2 mm year-1 among species, and were negatively correlated with diameter in four of the five species. For a sample of 193 individuals measured over 7 years, growth almost exactly equalled losses in basal area and biomass due to mortality. Because all of these species are regularly recruiting new trees into the over 70 cm diameter class, the amount of biomass in the large-individual size class is increasing over the 150 ha old-growth study area. Historic disturbance and/or current climatic change are hypothesized to account for the increase. We identify lack of standard diameter measurement criteria, and small and potentially unrepresentative plot locations as two problems in assessing the role of very large trees in other neotropical forests. Future studies should sample larger areas; this will increase the generality of the conclusions and will make possible a species-level comparison of the ecology of very large tropical trees.

Forty years of alternative management practices in second-growth, pole-size northern hardwoods. I. Tree quality deveSopment

The effects of six cutting methods on tree quality were observed for 20 years in a northern hardwood stand in Wisconsin. Cutting treatments included an uncut control, three levels of individual tree selection (heavy, medium, and light), crop tree release, and diameter limit. Average annual diameter growth was least in the control treatment (0.13 in./year, 0.33 cm/year) and greatest in the heavy individual tree selection and diameter-limit cuts (0.18 in./year, 0.46 cm/year). Cull in trees in 1992 was significantly higher in the control and diameter-limit treatments. Changes in merchantable height (number of 16-ft (4.9-m) logs) over the period were not significantly different among treatments, but average merchantable heights were significantly greater in the individual tree selection treatments in 1992. Average tree grade increases were significantly better in the medium selection plots than in all other treatments except the crop tree release. Nearly a third of the sawlog-size trees in both the control and diameter-limit treatments were below sawlog grade, significantly more than in the other treatments. Only 2% of the trees in the heavy selection plots were below grade. Tree quality improved the most overall in the medium selection plots. Stand structure in this treatment also most closely matched that recommended by guides developed to sustain yield over long periods of cutting under uneven-aged management.

Structure and dynamics of kanuka (Kunzea ericoidesvar.ericoides) heaths on sand dunes in Bay of Plenty, New Zealand

Abstract The structure, composition, and dynamics of a rare coastal community, kanuka (Kunzea ericoides var. ericoides) shrub- and tree-heaths on sand dunes, were studied on Whale Island and at Thornton, in Bay of Plenty. Both multi-stemmed, semi-prostrate and erect kanuka is present in virtually pure stands on largely unconsolidated dunes on Whale Island, and multi-stemmed, semi-prostrate kanuka in nearly pure stands on consolidated dunes at Thornton. This and other studies indicate that lack of competition (i.e. establishment at low densities) is primarily responsible for the multi-stemmed habit, but interacting environmental (exposure, drought) and genetic factors may also play a part. All communities are floristically poor compared with other woody communities in New Zealand, with only widespread species present and a large proportion of adventives. Mean annual diameter growth was 3.0 mm/yr at Whale Island and 2.8 mm/yr at Thornton; mean annual height growth ranged from 29.8 cm/yr in younger stands (6...

Relationship Between Street Tree Diameter Growth and Projected Pruning and Waste Wood Management Costs

Total pruning time, waste wood stack time, waste wood yield, and average annual diameter growth rates were determined for various diameter classes (4-16 inch; 10- 40 cm) of honeylocust (Gleditsia tricanthos), green ash (Fraxinus pennsylvanica), Norway maple (Acerplatanoides), and littleleaf linden {Tilia cordata). Pruning time increased at a rate of 6 minutes per diameter inch (2.5 cm) and waste wood stack time increased at a rate of 1.5 minutes per diameter inch (1.5 cm) forall species combined. Waste wood yields increase at a rate of 3 pounds per minute pruning for all species combined. Maintenance costs and waste wood yields were higher for honeylocust than for green ash, littleleaf linden, and Norway maple.

Effects of 76 Hz electromagnetic fields on forest ecosystems in northern Michigan: Tree growth

Since 1984, the possible effects of extremely low-frequency electromagnetic (EM) fields generated by a 76 Hz communication antenna on the growth and productivity of four deciduous and one coniferous species have been studied in the Upper Peninsula of Michigan. Results from two research sites are discussed here: one site near an antenna element and a control site located 50 km from the communication system. Growth models for individual tree diameters were developed for northern red oak (Quercus rubra), paper birch (Betula papyrifera), aspen (Populus tremuloides with a few individuals ofP. grandidentata), and red maple (Acer rubrum). A growth model for individual tree height was developed for young red pine (Pinus resinosa). Average differences between the observed and predicted growth were calculated for each growing season and then compared between the study sites and across the study periods to evaluate changes in growth patterns which could be attributed to EM field effects. For aspen and red maple, the results showed a stimulation of diameter growth at magnetic flux density levels of 1 to 7 milliGauss; height growth of red pine was increased at about the same exposure levels. There are no clear indications of an EM field effect on total annual diameter growth for either of the other two species.