Concentrations of up to 14 elements were determined from increment cores by proton-induced X-ray emission for dated series of annual rings of plantation Liriodendrontulipifera L. All trees were treated in 1965 with 841, 224, and 280 kg/ha of elemental N, P, K, respectively, and with either 0, 1683, or 3366 kg/ha of elemental Ca applied as pulverized agricultural limestone. Intraring elemental concentrations were not significantly different between earlywood and late-wood. Statistical variability of proton-induced X-ray emission elemental determinations was greatest for Al, Si, Cl, Cu, and Zn; concentrations of P, K, Ca, Mn, and Sr were least variable. Estimated standard errors among cores within trees averaged less than those among trees on a uniform site. Element mobility was tested in xylem core samples taken in 1965 and 1986. Liming significantly increased P, S, K, Ca, and Zn and decreased Mn in pre-1965 xylem. Retroactive liming effects were not detected for Mg, Al, Fe, Sr, or Ba; liming responses of Si, Cl, and Cu were unclear. Significant differences in elemental concentration independent of liming were detected between the 1965 and 1986 sampling times for P, K, Ca, Mn, Zn, Sr, and Ba. Of these, differences in P, K, and Mn may be due largely to heartwood formation between sampling times. Exchangeable Ca and Mg, followed by pH, were the most important soil variables in significant regressions with xylem elemental concentrations; only weak relationships were found with foliar elemental concentrations. Concentrations of Al, Si, Fe, and Cu in L. tulipifera xylem could be useful biomonitors of soil chemical changes by virtue of their apparent immobility; other elements, particularly S and Sr, may also be useful. However, expected time trends, especially as they pertain to heartwood formation, should be taken into account for each element.

No abstract

No abstract

¥ O 3 + CO 2 had a stimulatory effect on yearly basal area growth increment after two seasons, significant increases in shoot and root biomass ( ~ 60% increase relative to all others) were not detected until the fifth season. After five seasons, the yearly basal area growth increment of saplings exposed to 1·5 ¥ ¥ ¥ ¥ O 3 + CO 2 -air increased by 41% relative to all others. Based on this multiyear study, it appears that chronic O 3 effects on yellowpoplar growth are limited and slow to manifest, and are consistent with previous studies that show yellow-poplar growth is not highly responsive to O 3 exposure. In addition, these results show that enriched CO 2 may ameliorate the negative effects of elevated O 3 on yellow-poplar shoot growth and root biomass under field conditions.

Understanding differences in physiological and growth strategies in low-light environments among upland oak species may help managers address the challenges of oaks’ poor regeneration. Gas exchange and chlorophyll content were measured for northern red oak ( Quercus rubra L.), chestnut oak ( Quercus prinus L.), and white oak ( Quercus alba L.) germinants grown at 25%, 18%, and 6% of full sun in one of two native forest soil mixes for two summers. Northern red and chestnut oak photosynthesis at saturating light (Amax, mass) increased by 23%–36% as light levels increased from 6% to 25% of full sun, while white oak Amax, mass declined by 20% and plateaued at 18% of full sun. White oak light compensation point is representative of deep shade (7.2 µmol·m–2·s–1), while northern red and chestnut oak averaged 17.8 µmol·m–2·s–1. Total chlorophyll content increased as light levels decreased for all species. Of the three species, the slow-growing white oak seedlings appeared to be more efficient in utilizing light than northern red or chestnut oak seedlings. This suggests no additional benefits to increasing light above that typically found in a light shelterwood cut; however, it is crucial to control faster-growing competing vegetation.

Northern red oak ( Quercus rubra L.) seedling growth has been extensively studied. White oak ( Quercus alba L.) and chestnut oak ( Quercus prinus L.), however, are far less investigated despite their importance among upland oak species in eastern North American forests. We characterized white and chestnut oak seedling response to light and available soil nutrients while using northern red oak as a benchmark. Germinants were grown within one of three shade treatments (25%, 18%, and 6% of full sun) in one of two native forest soil mixes over two growing seasons. Leaf area, shoot mass, and root mass of all three species showed positive growth responses to increasing light. Growth and biomass were higher for all species grown in the more nutrient-rich forest soil, but chestnut oak displayed the greatest positive responses to the higher nutrient levels. White oak seedlings were the slowest growers and demonstrated the most root-centered growth, with root to shoot ratios almost twice that of either chestnut or northern red oak seedlings. The oak species evaluated here responded differently to changes in resource availability. Our study demonstrates the differential response of upland oaks to low light and nutrients. These differences need consideration when developing oak management prescriptions for specific oaks.

The chronic effects of ozone (O 3 ) alone or combined with elevated carbon dioxide (CO 2 ) on the foliar physiology of unfertilized field-grown yellowpoplar (Liriodendron tulipifera L.) seedlings were studied from 1992 to 1996. Within open-top chambers, juvenile trees were exposed to the following: charcoal-filtered air (CF); 1 ambient ozone (1XO 3 ); 1.5 ambient ozone (1.5XO 3 ); 1.5 ambient ozone plus 700 ppm carbon dioxide (1.5XO 3 +CO 2 ); or chamberless open-air (OA). Seasonal 24-h mean ambient O 3 concentrations ranged from 32 to 46 ppm over the five seasons. Averaged over 5 years, midseason net photosynthesis at saturating light (A sat ) was reduced by 14% (P=0.029) and stomatal conductance (g s ) was reduced, albeit non-significant, by 13% (P =0.096) in upper canopy foliage exposed to 1.5XO 3 -air relative to CF controls. There were no significant differences over the 5 years in A sat and g s between trees grown in 1XO 3 -and 1.5XO 3 -air. Our results support the hypothesis that the magnitude of O 3 effects on A sat and g s decreases as saplings age. When averaged over the five seasons of exposure, total chlorophyll concentration (chl) was not significantly affected by exposure to elevated O 3 ; however, in 1.5XO 3 +CO 2 -air, foliar chl was reduced by 33% relative to all others (P<0.001). In 1.5XO 3 +CO 2 -air, A sat was 1.4-1.9 times higher (P<0.001) and g s was 0.7 times lower (P=0.022) than all others. O 3 uptake in juvenile trees exposed to elevated O 3 plus elevated CO 2 (1.5XO 3 +CO 2 -air) was most comparable to trees exposed to ambient air (1XO 3 ) throughout the study. These findings suggest that elevated CO 2 may minimize the negative effects of O 3 by reducing O 3 uptake through decreased stomatal conductance.

FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes.