Crown Vigor Research Articles

Predictors of street tree survival in Philadelphia: Tree traits, biophysical environment, and socioeconomic context

Street trees are highly visible components of the urban forest, providing ecosystem services to city residents, but tree mortality can result in a loss of these essential benefits. Here, we focus on how street tree survival in Philadelphia, Pennsylvania (US) has been influenced by 1) tree traits and attributes, 2) the local biophysical environment, and 3) socioeconomic context. We used a longitudinal monitoring approach with a 6-year time interval and 103 randomly-located, fixed-length permanent plots, containing a range of tree size classes, to assess street tree survival rates, predictors of survival, and the balance of tree losses and gains. Street trees surveyed in this study experienced an annual mortality rate of 3.68% and followed a Type III mortality curve, with the highest annual mortality rates in the smallest size class. On the surveyed plots, there was a net decrease of live trees over the study period (2657 to 2542; 4.33% decline). Multivariate logistic regression revealed significant associations between street tree survival and tree crown vigor, species traits (expected mature stature and drought tolerance), site type, land use type, % impervious surface in a 15 m buffer, parcel-level demolition events, % of residents in poverty, % unoccupied households, and % renter-occupied households. Additionally, the final model included a multiplicative interaction term between crown vigor and tree size with separation in pattern of small (DBH < 7.6 cm) from larger (DBH ≥ 7.6 cm) trees. Our findings suggest that targeted management interventions may enhance overall street tree survival, such as focusing on small trees, as well as trees in sidewalk cut-outs, commercial or industrial areas, or near demolition activity. Longitudinal monitoring studies such as ours provide valuable information about how urban forest systems change over time, with assessments that are valuable for management by municipal foresters and other street tree stewards.

Factors associated with bark beetle infestations of Colorado Plateau ponderosa pine using repeatedly-measured field plots

Decades of research have brought increasing focus to the biotic and abiotic factors associated with bark beetle infestation of North American conifers. Information is lacking, however, regarding beetle-caused mortality for ponderosa pine of the Colorado Plateau. From 1995 to 2019, we installed and periodically remeasured permanent plots in this forest type with a goal of identifying factors related to infestation probability including tree and stand characters, and abiotic factors such as temperature and precipitation. Forty-eight sites were distributed throughout the Colorado Plateau, each with two transects of 10 contiguous ∼ 0.04 ha circular plots. Stand and tree conditions were measured or interpolated for each year from plot establishment in 1995 until the final measurements in 2019. Temperature, precipitation, and other abiotic conditions were estimated from Daymet interpolations. We used a generalized linear mixed model to identify significant explanatory variables resulting in the best accuracy of predicting stem-level bark beetle-caused pine mortality. Tree and stand conditions were found related to the probability of infestation. Pines >15.2 cm dbh were more likely to become infested compared to pines below that threshold; no relationship was found above that breakpoint. Similarly, stems 80–180 years old had elevated probability of infestation compared to stems < 80 years; stems > 180 years were intermediate. Pines with poor crown vigor (low crown volume, suppressed or intermediate canopy position) were more likely to become infested compared to pines with good crown vigor (high crown volume, dominant or open grown canopy position). Pine basal area (BA), a surrogate for intra-species competition, was positively related to probability of infestation. Pine BA infested the previous year, a surrogate for beetle population size, was also positively related to probability of infestation. Several drought- and precipitation-related variables resulted in similar model accuracy. Best model fit among these, by a slight margin, was contemporaneous climate water deficit (CWD), a measure of plant water stress, summed from April-August. Increasing CWD was associated with increased probability of infestation. Finally, counts of days above 16 °C the previous year were negatively related to infestation probability. That is, relatively warm weather during the previous year was associated with reduced beetle success, possibly because it can result in fractional beetle life cycles that disrupt synchronized attacks on new hosts or leave overwintering brood in less cold hardy life stages.

Assessing Role of Drought Indices in Anticipating Pine Decline in the Sierra Nevada, CA

Tree mortality in Sierra Nevada’s 2012–2015 drought was unexpectedly excessive: ~152 million trees died. The relative performance of five drought indices (DIs: SPEI, AI, PDSI, scPDSI, and PHDI) was evaluated in the complex, upland terrain which supports the forest and supplies 60% of Californian water use. We tested the relative performance of DIs parameterized with on-site and modeled (PRISM) meteorology using streamflow (linear correlation), and modeled forest stand NDVI and tree basal area increment (BAI) with current and lagged year DI. For BAI, additional co-variates that could modify tree response to the environment were included (crown vigor, point-in-time rate of bole growth, and tree to tree competition). On-site and modeled parameterizations of DIs were strongly correlated (0.9), but modeled parameterizations overestimated water availability. Current year DIs were well correlated (0.7–0.9) with streamflow, with physics-based DIs performing better than pedologically-based DIs. DIs were poorly correlated (0.2–0.3) to forest stand NDVI in these variable-density, pine-dominated forests. Current and prior year DIs were significant covariates in the model for BAI but accounted for little of the variation in the model. In this ecosystem where trees shift seasonally between near-surface to regolithic water, DIs were poorly suited for anticipating the observed tree decline.

Effects of Girdling Intensity, Pruning Season and Thinning on Tree Growth, Crown Vigor and Wound Recovery in Japanese Larch

To ensure sustainable forestry, it is important to establish efficient management procedures for seed orchards. We evaluated the effects of thinning, pruning season and girdling intensity on tree growth and vigor in an old Larix kaempferi seed orchard. Even after four years, tree size (crown width and tree height) increased, resulting in light intensity of an un-thinned class decreasing. Thinning counteracted the decrease in light intensity associated with tree growth, but it had no effect on promoting tree growth. Tree crown status was scored based on vigor and health. No significant difference in crown vigor was observed between unpruned and winter-pruned trees, but the summer-pruning class showed significantly lower vigor. Five years after girdling, trees with low and moderate girdling levels maintained high crown vigor, similar to intact trees, while the crown vigor of trees subjected to severe girdling was significantly lower. This is the first study to quantitatively model trends in remaining girdling depth over time, and to show that the half decay period was ca. 2–3 years. Our findings suggested that management procedures that combine moderate-level girdling, winter pruning and thinning to maintain rPPFD at 50% are well-suited to balancing tree vigor and reproduction in seed orchards.

Monitoring Fine-Scale Forest Health Using Unmanned Aerial Systems (UAS) Multispectral Models

Forest disturbances—driven by pests, pathogens, and discrete events—have led to billions of dollars in lost ecosystem services and management costs. To understand the patterns and severity of these stressors across complex landscapes, there must be an increase in reliable data at scales compatible with management actions. Unmanned aerial systems (UAS or UAV) offer a capable platform for collecting local scale (e.g., individual tree) forestry data. In this study, we evaluate the capability of UAS multispectral imagery and freely available National Agricultural Imagery Program (NAIP) imagery for differentiating coniferous healthy, coniferous stressed, deciduous healthy, deciduous stressed, and degraded individual trees throughout a complex, mixed-species forests. These methods are first compared to assessments of crown vigor in the field, to evaluate the potential in supplementing this resource intensive practice. This investigation uses the random forest and support vector machine (SVM) machine learning algorithms to classify the imagery into the five forest health classes. Using the random forest classifier, the UAS imagery correctly classified five forest Health classes with an overall accuracy of 65.43%. Using similar methods, the high-resolution airborne NAIP imagery achieved an overall accuracy of 50.50% for the five health classes, a reduction of 14.93%. When these classes were generalized to healthy, stressed, and degraded trees, the accuracy improved to 71.19%, using UAS imagery, and 70.62%, using airborne imagery. Further analysis into the precise calibration of UAS multispectral imagery, a refinement of image segmentation methods, and the fusion of these data with more widely distributed remotely sensed imagery would further enhance the potential of these methods to more effectively and efficiently collect forest health information from the UAS instead of using field methods.

Liming still positively influences sugar maple nutrition, vigor and growth, 20 years after a single application

Despite the decrease in acid deposition observed over the last decades, the health of sugar maple (SM; Acer saccharum Marshall), a species known as sensitive to base cation availability, is still a concern in many areas of northeastern North America. Twenty years after a single application of dolomitic lime, a widely available soil amendment, the effect of liming was evaluated on SM nutrition, vigor and growth in a declining stand affected by acid deposition. Lime doses of 0–50 t·ha−1 were applied over a 5 m radius around each selected tree. This experiment is unique in that it monitors the effects of doses that are economically feasible (“lower doses”; 0, 0.5, 1, 2 and 5 t·ha−1) and of higher ones (10, 20, 50 t·ha−1). We found that lime still had a positive effect on all variables studied after 20 years. In addition, SM nutrition, stem growth and crown vigor improved as lime dose increased. On average, foliar Ca and Mg concentrations increased by 35% and 46% for trees that received the 2 and 5 t·ha−1 doses, respectively, and by as much as 70% and 95% for those that received the 50 t·ha−1 dose. Crown dieback decreased from 44% for the control trees to less than 5% for those that received lime doses ≥5 t·ha−1. Basal area increment increased by 93% and 144% for trees that received lower and higher doses, respectively, compared to non-limed trees. Results indicate that a lime dose of approximately 5 t·ha−1, which is both potentially economic and operationally feasible, can have a beneficial effect on SM nutrition, vigor and growth for at least 20 years on such acidic and base-poor soils. Preserving SM tree health in this changing world is important to ensure its sustainability in maple forests.

The vegetation structure and condition of contracting lowland habitat for Leadbeater's possum (Gymnobelideus leadbeateri)

Lowland Leadbeater’s possums are on a trajectory to extinction, with fewer than 40 individuals surviving in the wild. Quantification of the vegetation characteristics of their occupied habitat is urgently needed to inform strategies to conserve this genetically distinct population. We surveyed the canopy and midstorey vegetation at all remaining (nine) occupied territories and eleven abandoned territories in lowland swamp forest at the Yellingbo Nature Conservation Reserve. For each territory we quantified canopy and midstorey stem density, basal area (total and live) and vegetation condition (percentage live basal area, tree crown vigour and plant area index) within a 50-m radius of known den locations. The canopy at all locations was dominated by mountain swamp gum (Eucalyptus camphora), with most occupied sites supporting dense midstorey dominated by paperbarks, either Melaleuca squarrosa or Melaleuca ericifolia. Occupied territories had higher stem densities and better vegetation condition than abandoned territories. Stem density alone was able to predict occupancy vis-à-vis abandoned sites with a high (80%) degree of accuracy. Lowland Leadbeater’s possums occupy swamp forests characterised by high stem density, particularly in the midstorey, structural complexity and healthy vegetation. These findings can help guide habitat restoration and translocation projects currently underway to expand the area of lowland habitat for this critically endangered species.

Phytophthora Species Detected in Two Ozark Forests with Unusual Patterns of White Oak Mortality.

Widespread decline and mortality of white oaks (Quercus alba) occurred in Missouri Ozark forests between 2011 and 2017. Symptoms included rapid crown death with bronzing of leaves, retention of dead leaves, crown dieback and thinning, and loss of large limbs within one year of death. Decline and mortality were associated with hillside drainages and fit descriptions of European oak forests predisposed to decline by pathogenic Phytophthora species. A survey was performed at two locations in 2014 and 2015 to assess the distribution of dead and declining white oaks, and the occurrence and distribution of Phytophthora species. Multiple Phytophthora species were detected, including P. cinnamomi, P. cactorum, P. europaea, and P. pini. P. cinnamomi was the most common and widely distributed species among plots at both locations. The detection of P. cinnamomi at the base of white oaks was not associated with poor crown vigor. However, more quantitative survey techniques are necessary to clearly evaluate this relationship. P. cinnamomi kills fine roots of white and red oaks in North America and has been associated with the decline of white oaks in the United States (Ohio) and other countries. Further studies are needed to determine the importance of P. cinnamomi in oak decline within the Ozark highlands.

Monitoring Young Tree Survival with Citizen Scientists: The Evolving Tree Checkers Program in Philadelphia, PA

Citizen science programs are not static; they change over time in response to new program priorities and emerging technologies, as well as to improve work flow for program staff and volunteers. In this article, the authors present a case study of an evolving urban forestry citizen science program at the Pennsylvania Horticultural Society, a nonprofit organization in Philadelphia, Pennsylvania, U.S. The Tree Checkers program involves tree stewards recording data each summer about recently planted tree survival, growth, crown vigor, and maintenance, while also engaging their neighbors to encourage proper tree care. The program began in 2011, but changed in 2016 to use a new online data collection tool that was integrated into a larger tree data management system. Tree Checkers has also shifted to be more focused on rigorous data to report program performance and share information with researchers, whereas the earlier years of Tree Checkers were centered on enabling and encouraging neighborhood tree stewards to plan for tree care. A recent data quality evaluation showed that volunteer data was reasonably consistent with data reported by more experienced interns for tree survival, vigor, and trunk measurements, but stewardship variables were not interpreted and recorded consistently. By making rigorous data more central to Tree Checkers, program staff also sought to institutionalize monitoring within the organization, allowing for direct comparisons of outcomes year-to-year. The authors close with lessons learned that are relevant to other organizations seeking to create or enhance outcomes monitoring programs with citizen scientists.

The role of charcoal disease and wood borers on Quercus brantii Lindl. decline under different physiographical conditions

Oak decline is an expression describing death and drying up of oak trees. The present research evaluated the relationship between various geographical directions and altitude and some factors predisposing Persian oak (Quercus brantii Lindl.) decline, such as charcoal disease and oak wood boring insects in a 100 hectares area of the Shurabad forests in Lorestan Province of Iran. A 200 by 200 m sampling network was first designed on a regular-random (systematic) basis, and the trees were sampled from 1500-m2 circular plots. Information including hillside direction, altitude, infection site (on tree crown or on trunk), type of infection (charcoal disease or wood borers), crown vigor, and heights of the infection sites on the trees was recorded in each sample plot. Results indicated the significant relationships of infection type and severity with altitude, geographical direction, slope, and location of the sample plot at the significance level of 5%. Wood borers were the most common cause of infection. There was very little attack by charcoal disease in the study area. Most diseased trees were in the valley, in a northerly direction, at the 1101–1150 m elevation class and the 41–50% slope class. There were very few healthy trees in the study area, and most of them were on the ridges, in a southwesterly direction, at the 1151–1200 m altitude class and the 11–20% slope class.

Precommercial release thinning of potential Acacia koa crop trees increases stem and crown growth in dense, 8-year-old stands in Hawaii

An 8-year-old dense monotypic stand of naturally regenerated koa (Acacia koa A. Gray) on the Island of Hawaii was selected to determine the effects of precommercial release thinning, phosphorous (P) fertilization and herbaceous weed control on growth of potential crop trees over approximately 30months. Thinning consisted of cutting down all stems within a 4.5-m radius of the crop tree. Phosphorus was added at a rate of 300kgha−1 over two years. Herbaceous weeds were sprayed once with imazapyr, a broad-spectrum herbicide. Thinning alone or in combination with P fertilization significantly increased stem diameter increment and allometric estimates of the growth of leaf area and aboveground biomass. There was no significant increase in stem diameter, leaf area or biomass in the absence of thinning. Within the thinned treatment, P fertilization resulted in significant increases in tree height over time. Herbaceous weed control had no effect on tree growth. The atmospherically resistant vegetation index (ARVI), which was derived from spectral analyses of high-resolution satellite imagery (GeoEye1), was significantly higher for thinned than unthinned trees 25months after study initiation, suggesting greater light absorbance and a possible explanation for overall greater growth of thinned trees. When considered with results from previous studies, these findings indicated that crop tree selection and precommercial release thinning in dense, even-aged koa stands should be done early in stand development to prevent loss of crown vigor and growth potential. Additional interventions like P fertilization or herbaceous weed control may not be necessary until trees are older or site conditions suggest important soil resource limitations.

Long‐term impact of protected colonial birds on a jeopardized cork oak population: conservation bias leads to restoration failure

Summary Conservation bias towards flagship species sometimes threatens other species of chief concern. Long‐term studies of potential harm by favoured species on other sensitive species, though seldom adopted, are required to fairly evaluate the suitability of management and restoration efforts. We illustrate the potential detrimental outcomes of conservation biased towards birds by investigating the long‐term (1963–2009) impact of a large waterbird colony (up to 13 000 pairs) on a remnant cork oak Quercus suber population at a World Biosphere Reserve in south‐western Spain (the Doñana National Park). To this end, we compared changes in performance (growth, crown vigour and survival) of oaks occupied and unoccupied by the waterbird colony. After 46 years of occupation, the risk of death to centenarian oaks in the area occupied by the colony was over twofold higher than for trees outside the area. Non‐centenarian planted and naturally regenerated oaks showed similar trends, leading to restoration failure. Synthesis and applications. Our long‐term study reveals that waterbirds and centenarian oaks cannot coexist, at the most local scale, but they can at a regional scale including within the Doñana area. We propose immediate planting efforts in suitable colony‐free areas, while managers evaluate the feasibility of relocating colonial waterbirds to an alternative location. To preserve the Doñana oak genetic pool, such reforestation should be accomplished using local seeds and seedlings. New trees should not be planted in close proximity of colony‐occupied trees since it significantly reduces their survival. Doñana stakeholders should both overcome current conservation bias in favour of birds and enter into a process of settlement to best preserve the overall biodiversity of the system.

Changes in stand structure and tree vigor with repeated prescribed fire in an Appalachian hardwood forest

Without large scale disturbances to alter forest structure and open the canopy, historically oak-dominated forests of the central and Appalachian hardwood regions of eastern North America are shifting to dominance by shade-tolerant, ‘mesophytic’ species. In response, prescribed fire is applied with increasing frequency and spatial extent to decrease non-oak species and promote dominance of oak species. However, relatively few studies have examined impacts of repeated fire to forest structure and tree vigor across multiple years and varied terrain. In this study, we examined tree vigor, tree mortality, and stand structure in response to different burn treatments: Frequent (burned 4 times in eight years), Less Frequent (burned 2 times in eight years), and Fire-Excluded. We hypothesized that fire-driven decreases in stem density and basal area would be greatest for small size classes, especially of shade-tolerant species on drier landscape positions, and would increase with burn frequency and fire temperature. We expected trees surviving fire to exhibit increased crown vigor over time since fire. Prescribed fire effects depended on tree size-class and landscape position. About 60% of surviving midstory trees (10–20cm diameter at breast height (DBH)) and 25% of overstory trees (⩾20cm DBH) on sub-xeric and intermediate landscape positions experienced crown dieback. Fire-Excluded sites had fewer trees with crown dieback (11–28% across size classes) compared to burned sites (21–87%). Throughout the duration of the study, midstory and overstory maples had significantly greater likelihood of increased crown dieback compared to oaks. Paradoxically, midstory maples had a higher survival probability than similarly-sized oaks, while overstory maples had lower survival than overstory oaks. The greatest reductions in density and basal area occurred in saplings (trees 2–10cm DBH) and midstory trees on sub-xeric and intermediate (but not sub-mesic) landscape positions. Both Less Frequent and Frequent burning reduced density and basal area of sapling and mid-story shade-tolerant species, but also of mid-story chestnut oaks. Individual tree mortality was positively correlated with char height after the first burn regardless of burn frequency. A large and significant initial sprouting response to fire dissipated over time and with repeated burning. Future assessments of mortality and vigor of residual trees following fire are essential for evaluating the long-term effectiveness of prescribed fire management in shifting species composition away from ‘mesophytic’ species and toward oaks, and could help guide management choices regarding repeated prescribed burning.

Evaluation of Cleanings to Maintain Oak Forests on the Allegheny National Forest

Ten-year results for an administrative study on the Allegheny National Forest (ANF) that examined their cleaning (precommercial thinning) prescriptions and standards for success in maintaining oak (Quercus spp.) composition in young stands and maintaining oak stems in a competitive position are presented. Two studies were installed. One study was in a 25- to 30-year-old stand where we released intermediate and suppressed oak species, in particular white oak (Quercus alba), to see if they would survive and improve in crown class. The other study was installed in two 16-year-old stands where cleanings using crown-touching crop-tree release treatments were done, with untreated control plots reserved. A total of eight treated and eight control plots in two stands were examined. In the first study, mortality of white oaks in the lower canopy (intermediate or overtopped) was 83 and 39% in control versus treated areas, respectively. The cleaning treatments were successful in keeping trees alive, but crown vigor declined and no trees increased in crown class. In the second study, the mortality of crop trees was 15 and 2% in control versus treated stands, respectively. The proportion (number of stems) of crop trees of all species in the upper canopy (dominant or codominant) dropped 22% versus 1% for control versus treated trees over the 10 years. Stand-level oak composition in control stands was 11.3% of basal area after 10 years (11.7% initially). In treated stands, it was 18.3% of basal area after 10 years (10.7% initially), a 71% increase in oak. The treatments successfully increased survival, growth, and composition of oak.

Effects of two types of Ca fertilizer on sugar maple nutrition, vigor and growth after 7 years

Sugar maple (Acer saccharum Marsh., hereafter SM) dieback has been of concern in many stands of northeastern North America for decades. In acidic, base-poor forest soils, this phenomenon has often been attributed to calcium (Ca) deficiency. Corrective measures such as dolomitic lime addition (CaMg(CO3)2) have been tested to restore SM vitality in these ecosystems. However, few studies have evaluated the effect of Ca addition alone on SM. Furthermore, liming experiments have showed that the Mg content of lime could induce a nutritional antagonism which hinders potassium (K) uptake. This may have limited the response of SM to dolomitic lime application. To address these issues, two calcium fertilizers with negligible Mg content (CaCO3 and CaSO4·2H2O) were applied at rates of 1, 2 and 4tCaha−1 on SM trees. After 7years, foliar Ca nutrient concentrations of treated trees increased in both Ca treatments, reaching published concentration ranges for healthy SM trees. These increases were greater than those observed after a similar period in two nearby experiments in which CaMg(CO3)2 and CaCO3 were used at comparable or lower doses. Also, no nutrient antagonism was detected in the present study. Tree crown vigor and basal area growth were improved by the Ca treatments, but the magnitude of the growth response for trees treated with the CaCO3 fertilizer was far less than in the other nearby experiment where CaCO3 was also used. This strongly suggests that Mg nutrition is not a limiting factor in this ecosystem. The comparatively lower growth response of trees to Ca treatments in this study is unclear, but better growth conditions at the studied site, compared to the two other nearby experiments, may have played a role in this phenomenon. Long-term monitoring of these experiments seems warranted to clarify these issues.

Effects of Acidic Deposition and Soil Acidification on Sugar Maple Trees in the Adirondack Mountains, New York

We documented the effects of acidic atmospheric deposition and soil acidification on the canopy health, basal area increment, and regeneration of sugar maple (SM) trees across the Adirondack region of New York State, in the northeastern United States, where SM are plentiful but not well studied and where widespread depletion of soil calcium (Ca) has been documented. Sugar maple is a dominant canopy species in the Adirondack Mountain ecoregion, and it has a high demand for Ca. Trees in this region growing on soils with poor acid-base chemistry (low exchangeable Ca and % base saturation [BS]) that receive relatively high levels of atmospheric sulfur and nitrogen deposition exhibited a near absence of SM seedling regeneration and lower crown vigor compared with study plots with relatively high exchangeable Ca and BS and lower levels of acidic deposition. Basal area increment averaged over the 20th century was correlated (p < 0.1) with acid-base chemistry of the Oa, A, and upper B soil horizons. A lack of Adirondack SM regeneration, reduced canopy condition, and possibly decreased basal area growth over recent decades are associated with low concentrations of nutrient base cations in this region that has undergone soil Ca depletion from acidic deposition.

Factors influencing loblolly pine stand health in Fort Benning, Georgia, USA

Loblolly pine (LBP; Pinus taeda L.) stands provides two-thirds of the existing federally protected red-cockaded woodpecker (RCW; Picoides borealis) habitat in Fort Benning, Georgia, USA. However, LBP in this area is suspected to face a forest decline issue, which may risk the sustainability of the RCW population. Land managers are attempting to convert LBP stands to longleaf pine (Pinus palustris Mill.), which once dominated the landscape, however the transition has to be gradual so current RCW habitat is maintained until longleaf pine stands sufficiently support RCW populations. It is critical to identify environmental factors influencing LBP health and convert LBP stands under poor environment to longleaf pine first. We installed 90 plots (30 × 30 m2) in mature (>38 years) loblolly pine forests and measured aspect, slope, soil texture, soil (pH, organic matter, cation exchange capacity, and exchangeable phosphorus, potassium, magnesium, and calcium) and foliar (nitrogen and phosphorus) nutrient, diameter at breast height, light exposure, and crown vigor class (CVC; 1 = good, 2 = fair, and 3 = poor). Stand age, site index, and burning and thinning history were retrieved from existing inventory data. Our results show that site index was the main factor in determining LBP health. Site index showed significant correlation with percentage of LBP in CVC1 (p = 0.04) and CVC3 (p = 0.07). Percentage of LBP in CVC3 tended to decrease as soil texture became finer. Poorer site index and coarser soil likely resulted in water stress during periods of drought leading to higher %CVC3 LBP. Based on these results, conversion to longleaf pine should start from LBP stands on coarser soil (or lower site index) at Fort Benning.

The Status of White Oak (Quercus alba) Trees at the Gordon Natural Area, Chester County, Pennsylvania

ABSTRACT A field study was conducted in 2007 and 2008 to assess the population, distribution, size, and health status of white oak (Quercus alba L.) trees found in a forest at the Gordon Natural Area preserve in Chester County, Pennsylvania. A sweep survey was used to locate each oak, and then geographic coordinates, diameter at breast height (DBH), and crown vigor, were determined for each tree. Twenty-three trees were encountered in all, indicating a low density of &amp;lt; one tree per hectare, which was much lower than that of other co-occurring late successional species. Trees exhibited both clumped and linear distributions, likely resulting from acorn caching and past use of the species as a border around now reforested farmland. Trees were spread across most DBH size classes with a mean DBH = 57.4 cm. Most trees were relatively large and none occurred below 25 cm. Most trees were also healthy, though some were unhealthy. Overall, results suggest that white oak is an uncommon but widely dispersed species at the preserve, with a relatively healthy, but aging, population. Given these results, more studies of the species at the preserve are warranted, including new and periodic assessments of its recruitment status and canopy tree health, to better manage and ensure that white oak continues to have a presence in this forest and the region.

Soil and sugar maple response 15 years after dolomitic lime application

Dolomitic lime (CaMg(CO3)2) was applied in 1994 at rates of 0–50Mgha−1 to sugar maples (SMs) (Acer saccharum Marsh.) in a base-poor and declining northern hardwood stand subjected to a high level of acid deposition in Quebec. The soil chemistry and the SM nutrition, growth, crown vigor, and regeneration status were evaluated 15years after treatment. The soil chemical properties still responded strongly to lime after 15years. Similarly, the foliar Ca and Mg concentrations were still higher for treated trees relative to the control trees. After 15years, the mean crown dieback of trees decreased quadratically with the lime rate, from 39% for the control trees to a value of 1–3% for the lime rates of 5Mgha−1 and higher. Additionally, the stem basal area increment for the limed trees was nearly double that of the unlimed trees in 2009. The lime application was also beneficial to the SM regeneration. The overall SM seedling density increased with the lime rate, being nearly twice as much in the 50Mgha−1 (32 seedlings m−2) compared with the controls (16 seedlings m−2). The proportion of the SM seedlings to all of the other species increased quadratically from 22% in controls to more than 55% in the 5–50Mgha−1 treatments. In contrast, the proportion of competitive species decreased quadratically with the lime rate, including American beech (Fagus grandifolia Ehrh.) for which the proportion in the treated plots (24%) was nearly half the proportion observed in the controls (46%). However, increase in stem density of regeneration and canopy closure in response to lime application limit the development of the regeneration which did not benefit in terms of diameter and height. These results show that a single lime addition has long-term beneficial effects on the soil chemistry and the SM nutrition, vigor, growth, and regeneration in base-poor and declining northern hardwood stands. Moreover, the results confirm that liming is an essential tool to restore the SM representation and health in acidic and base-poor soils.

The Relationship Between Structural Root Depth and Vigor of Urban Trees

The prevalence of deep root systems on urban trees has been well documented, but the consequences are not well understood. The relationship between structural root depth and vigor of street trees was investigated in Greensboro, North Carolina; Snoqualmie, Washington; and Glen Ellyn, Illinois, United States. Regression analysis was used to explore the relationship between root depth and crown vigor, trunk diameter growth, and trunk condition as indicators of tree performance. The average depth of structural roots for most species was less than three centimeters. However, in 10 of the 14 species included in the study, the structural roots of 20%–60% of the individual trees were more than eight centimeters deep. Regression analysis showed a significant relationship between root depth and indicators of tree performance for Acer rubrum, Quercus bicolor, Fraxinus oxycarpa, and Tilia cordata, but no relationship was identified for other species measured. Root depth explained less than half of the reduction in tree performance of these species, however, and is apparently only one of several factors affecting the growth of street trees.