Field studies were conducted during 2003 and 2004 from early June to the end of August, at 20 sites of lower or higher elevation within north-central Pennsylvania, using seedlings of black cherry (Prunus serotina, Ehrh.) and ramets of hybrid poplar (Populus maximowizii×trichocarpa). A linear model was developed to estimate the influence of local environmental conditions on stomatal conductance. The most significant factors explaining stomatal variance were tree species, air temperature, leaf vapor pressure deficit, elevation, and time of day. Overall, environmental factors explained less than 35% of the variation in stomatal conductance. Ozone did not affect gas exchange rates in either poplar or cherry. Ozone-induced foliar injury was positively correlated with cumulative ozone exposures, expressed as SUM40. Overall, the amount of foliar injury was better correlated to a flux-based approach rather than to an exposure-based approach. More severe foliar injuries were observed on plants growing at higher elevations.

The crowns of five canopy dominant black cherry (Prunus serotina Ehrh.), five white ash (Fraxinus americana L.), and six red maple (Acer rubrum L.) trees on naturally differing environmental conditions were accessed with scaffold towers within a mixed hardwood forest stand in central Pennsylvania. Ambient ozone concentrations, meteorological parameters, leaf gas exchange and leaf water potential were measured at the sites during the growing seasons of 1998 and 1999. Visible ozone-induced foliar injury was assessed on leaves within the upper and lower crown branches of each tree. Ambient ozone exposures were sufficient to induce typical symptoms on cherry (0–5% total affected leaf area, LAA), whereas foliar injury was not observed on ash or maple. There was a positive correlation between increasing cumulative ozone uptake (U) and increasing percent of LAA for cherry grown under drier site conditions. The lower crown leaves of cherry showed more severe foliar injury than the upper crown leaves. No significant differences in predawn leaf water potential (ψL) were detected for all three species indicating no differing soil moisture conditions across the sites. Significant variation in stomatal conductance for water vapor (gwv) was found among species, soil moisture, time of day and sample date. When comparing cumulative ozone uptake and decreased photosynthetic activity (Pn), red maple was the only species to show higher gas exchange under mesic vs. drier soil conditions (P < 0.05). The inconsistent differences in gas exchange response within the same crowns of ash and the uncoupling relationship between gwv and Pn demonstrate the strong influence of heterogeneous environmental conditions within forest canopies.

Five-month old hybrid poplar clones NE388 and NE359 were exposed to square-wave 30, 55, and 80 ppb O3 (8 h/day, 7 day/week) under constant high light (HL) and light fleck (LF) during 28 May–29 June 1999, and exposed to 30 and 55 ppb O3 under HL, LF, and constant low light (LL) during 22 May–28 June 2000 within Continuously Stirred Tank Reactors (CSTR) in a greenhouse. Ramets of these two hybrid clones received similar total photosynthetically active radiation (PAR) within the LF and LL treatments. Visible foliar symptoms, leaf gas exchange, and growth were measured. More severe O3 induced foliar symptoms were observed on ramets within the LF and LL treatments than within the HL treatment for both clones. The LF treatment resulted in significantly greater foliar injury than the LL treatment for NE388. The LF and LL treatments generally resulted in lower photosynthetic rates (Pn) for both clones, but did not affect stomatal conductance (gwv); therefore, the ratios of gwv/Pn and the O3 uptake/Pn were greatest in plants grown under the LF treatment, followed by those grown under LL treatment; plants grown under HL had the lowest ratios of gwv/Pn and O3 uptake/Pn. Greater ratios of gwv/Pn and O3 uptake/Pn were consistently associated with more severe visible foliar symptoms. The negative impacts of the LF treatment on growth were greater than those of the LL treatment. Results indicate that not only the integral, but also the pattern of photo flux density, may affect carbon gain in plants. Increased foliar injury may be expected under light fleck conditions due to the limited repair capacity as a result of continuity of O3 uptake while photosynthesis decreases under LL conditions.

The responses of ramets of hybrid poplar (Populus spp.) (HP) clones NE388 and NE359, and seedlings of red maple (Acer rubrum, L.) to ambient ozone (O3) were studied during May–September of 2000 and 2001 under natural forest conditions and differing natural sunlight exposures (sun, partial shade and full shade). Ambient O3 concentrations at the study site reached hourly peaks of 109 and 98 ppb in 2000 and 2001, respectively. Monthly 12-h average O3 concentrations ranged from 32.3 to 52.9 ppb. Weekly 12-h average photosynthetically active radiation (PAR) within the sun, partial shade and full shade plots ranged from 200 to 750, 50 to 180, and 25 to 75 μmol m−2 s−1, respectively. Ambient O3 exposure induced visible foliar symptoms on HP NE388 and NE359 in both growing seasons, with more severe injury observed on NE388 than on NE359. Slight foliar symptoms were observed on red maple seedlings during the 2001growing season. Percentage of total leaf area affected (%LAA) was positively correlated with cumulative O3 exposures. More severe foliar injury was observed on plants grown within the full shade and partial shade plots than those observed on plants grown within the sun plot. Lower light availability within the partial shade and full shade plots significantly decreased net photosynthetic rate (Pn) and stomatal conductance (gwv). The reductions in Pn were greater than reductions in gwv, which resulted in greater O3 uptake per unit Pn in plants grown within the partial shade and full shade plots. Greater O3 uptake per unit Pn was consistently associated with more severe visible foliar injury in all species and/or clones regardless of differences in shade tolerance. These studies suggest that plant physiological responses to O3 exposure are likely complicated due to multiple factors under natural forest conditions.

Measurements of landslide movement made by global positioning system surveys and extensometers over a 3.5-year period show that the Slumgullion landslide in the San Juan Mountains of southwest Colorado moved throughout the monitoring period, but that daily velocities varied on a seasonal basis. Landslide velocities peaked in the early spring and summer in response to snowmelt and summer thunderstorms, respectively. Velocities were slowest in mid-winter when air and soil temperatures were coldest and precipitation was generally low and/or in the form of snow with a low water content. We hypothesize that the seasonal variability in velocities is due to ground-water levels and corresponding pore pressures that decrease when surface water is unavailable or cannot infiltrate frozen landslide material, and increase when surface water from melting snow or rainfall infiltrates unfrozen landslide material. We also suggest that patches of bouldery debris and fractures (created by continuous movement of the landslide) are conduits through which surface water can infiltrate, regardless of the frozen or unfrozen state of the landslide matrix material. Therefore, the availability of surface water is more important than landslide temperature in controlling the rate of landslide movement. This hypothesis is supported by field instrumentation data that show (1) landslide velocities coinciding with precipitation amounts regardless of the depth of freezing of landslide material, (2) spring and annual landslide velocities that were greatest when the depth of freezing was also the greatest, and (3) a rapid (several weeks or less) velocity and pore pressure response to rainfall.The persistent, but seasonally variable movement of the landslide, fits the bathtub model for landslide movement described by Baum and Reid [Baum, R.L., Reid, M.E., 2000. Ground water isolation by low-permeability clays in landslide shear zones. In: Bromhead, E.N., Dixon, N., Ibsen, M.-L. (Eds.), Landslides in Research, Theory and Practice. Proc. 8th Int. Symp. on Landslides, Cardiff, Wales, vol. 1, 139-144]. In their model, the landslide is isolated both mechanically and hydrologically from adjacent materials by low permeability clays. These clays cause the landslide to retain water. Our data support this model by suggesting that pore pressures at the basal landslide surface are always adequate to maintain landslide movement and that any infiltration of water at the surface of the landslide is adequate to rapidly increase landslide velocity. (C) 2002 Elsevier Science B.V. All rights reserved.

Ambient concentrations of tropospheric ozone and ozone-induced injury to black cherry (Prunus serotina) and common milkweed (Asclepias syriaca) were determined in north central Pennsylvania from 29 May to 5 September 2000 and from 28 May to 18 September 2001. Ogawa passive ozone samplers were utilized within openings at 15 forested sites of which six were co-located with TECO model 49 continuous ozone monitors. A significant positive correlation was observed between the Ogawa passive samplers and the TECO model 49 continuous ozone monitors for the 2000 (r=0.959) and 2001 (r=0.979) seasons. In addition, a significant positive correlation existed in 2000 and 2001 between ozone concentration and elevation (r=0.720) and (r=0.802), respectively. Classic ozone-induced symptoms were observed on black cherry and common milkweed. In 2000, initial injury was observed in early June, whereas for the 2001 season, initial injury was initially observed in late June. During both seasons, injury was noted at most sites by mid- to late-July. Soil moisture potential was measured for the 2001 season and a significant positive relationship (P<0.001) showed that injury to black cherry was a function of cumulative ozone concentrations and available soil moisture.

Sixteen black cherry (Prunus serotina, Ehrh.), 10 white ash (Fraxinus americana, L.) and 10 red maple (Acer rubrum, L.) 1-year old seedlings were planted per plot in 1997 on a former nursery bed within 12 open-top chambers and six open plots. Seedlings were exposed to three different ozone scenarios (ambient air: 100% O3; non-filtered air: 98% ambient O3; charcoal-filtered air: 50% ambient O3) within each of two different water regimes (nine plots irrigated, nine plots non-irrigated) during three growing seasons. During the 1998 and 1999 growing season, leaf gas exchange, plant water relations, and foliar injury were measured. Climatic data,ambient- and chamber-ozone-concentrations were monitored. We found that seedlings grown under irrigated conditions had similar (in 1998) but significantly higher gas exchange rates (in 1999) than seedlings grown within non-irrigated plots among similar ozone exposures. Cherry and ash had similar ozone uptake but cherry developed more ozone-induced injury (< 34% affected leaf area, LAA) than ash (<5% LAA), while maple rarely showed foliar injury, indicating the species differed in ozone sensitivity. Significantly more severe injury on seedlings grown under irrigated conditions than seedlings grown under non-irrigated conditions demonstrated that soil moisture altered seedling responses to ambient ozone exposures.

Tropospheric ozone has been identified as the most important regional scale air pollutant across much of eastern United States of America and many areas of Mediterranean climes in southern Europe. Recent field surveys in the northeastern USA and in southeastern Spain have revealed many additional plant species that exhibit symptoms typical of ozone-induced injuries. Objectives of this study were to confirm ozone as the cause of the observed foliar symptoms, determine ozone induced exposure/response relationships, and identify possible bio-indicator species. Thirteen native species of northeastern USA and 27 native species of southeastern Spain were selected for study. Plant species were exposed to ozone within 16 CSTR chambers in a greenhouse during the summer seasons of 2000 and 2001; ozone exposures of 30, 60, 90, and 120 ppb were delivered for 7 h/day, 5 days/week. Results have confirmed that with few exceptions, symptoms observed in the field were induced by exposures to ambient ozone. Species differed significantly in terms of the exposures required for the initiation of visible symptoms and subsequent injury progression.

ABSTRACT Ogawa passive O3 samplers were used in a 13-week study (June 1-September 1, 1999) involving 11 forested and mountaintop sites in north-central Pennsylvania. Four of the sites were collocated with TECO model 49 O3 analyzers. A significant correlation (p < 0.0001) was found for 24-hr average weekly O3 concentrations between the two methodologies at the four sites with collocated monitors. As expected, there were positive relationships between increasing elevation of the sites and increasing O3 concentrations. No O3 exposure patterns were found on a west-to-east or south-to-north basis; however, the area known for lower O3 exposures within a smaller subsection of the study area showed consistently lower O3 exposures. Preliminary results regarding relationships of symptom responses within O3-sensitive bioindicators are also presented with black cherry (Prunus serotina, Elirli.) and common milkweed (Asclepias syriaca, L.) showing clear evidence of increasing injury with increasing O3 exposures. Due to the extremely dry conditions encountered in north-central Pennsylvania during the 1999 growing season, O3-induced symptoms were sporadic and quite delayed until late-season rains during the latter portion of the observation period.

Six sets of 19 GPS observations made between July 1998 and July 1999 show that the Slumgullion landslide in southwest Colorado moved throughout the year, but that daily velocities were highly variable on a seasonal basis.The upper part of the slide reacted more dramatically to seasonal changes than the middle and lower parts.Maximum velocities were up to 10 times greater than minimum velocities on the upper part of the slide and 1.8 to 1.6 times greater on the middle and lower parts of the slide.Maximum velocities occurred between March and May on the lower part of the slide, and between May and July on the middle and upper parts of the slide.Minimum velocities occurred between January and March for 18 of the 19 monitoring points.Annual movements and daily velocities were smallest at the head and toe of the landslide and largest in the central, narrowest part of the landslide.Annual combined horizontal and vertical movement ranged from 0.15 m at the head of the slide to 7.3 m in the neck.Daily velocities ranged from <0.001 m/day to 0.024 m/day.

Measurements of ridge-spreading movements at Bald Eagle Mountain in north-central Colorado were reported in USGS Open-File Report 90-543 for the years 1975-1989. Measurements were renewed in 1997 and 1999 using the Global Positioning System (GPS). Movements are generally away from a ridge-top graben and appear to be concentrated along 3 or 4 trenches with uphill facing scarps that are parallel with slope contours. A point just below the lowest trench has moved the most? a total of 8.3 cm horizontally and slightly downward from 1977 to 1999 relative to an assumed stable point on the periphery of the graben. Movements from 1997 to 1999 are less than 1 cm or within the error of measurement.

Tropospheric ozone is considered as the major pollutant of concern to the health and productivity of forests in the eastern United States and has more recently become of increasing concern within the forests of southern Europe. Recent observations have clearly demonstrated foliar injury symptoms to be occurring on many tree and native plant species within remote forested areas. Several plant genera (and a few species within genera) found in both the forests of Switzerland and the southern coastal region of Spain exhibit field symptoms typical of ambient ozone exposures. Ozone exposures for many species have been conducted under controlled CSTR conditions and within open-top chambers within the study areas. Results have confirmed that the O3-like foliar symptoms as observed under natural forest and open grown conditions for many native tree, shrub, and herbaceous species in Spain and Switzerland are caused by exposures to ambient O3.

During late summer of 1996 and 1997 we examined ozone-induced foliar injury in a plantation of 111 black cherry trees (ramets) comprising 15 clones originating from wild ortets growing in the Allegheny National Forest, Pennsylvania, and the Monongahela National Forest, West Virginia. The experimental plantation was a clonal seed orchard in Centre County, Pennsylvania, started in 1971 using ortet buds grafted onto seedling rootstocks of mixed origin. Clones differed significantly in severity of foliar injury symptoms (F=31.83, p<0.001). One clone (R-12) had significantly more foliar injury with >50% leaf area affected than other clones during both years. In contrast, clone R-14, which is from the same area in northcentral Pennsylvania as R-12, exhibited significantly less injury (LAA<6%). Although ambient O(3) concentrations were similar in both years, foliar injury was significantly greater (15.7%) in 1996 than in 1997 (9.9%). This is probably explained by lower stomatal conductance in 1997 caused by drier and hotter weather patterns in June and July of that year. Despite very different weather patterns and overall levels of injury in 1996 and 1997, mean clonal injury was significantly correlated between both years of assessment (r=0.92, p<0.001). Within tree crowns, foliage in lower and inner crown positions was significantly more injured than foliage in upper and exterior crown positions. There was no evidence of geographically based population differences in sensitivity to foliar O(3) injury. On the contrary, results demonstrate that wild genotypes of proximal geographic origin may differ greatly in sensitivity.

Studies were conducted during the period 1993–1996 to determine the extent of foliar injury on native plant species and black cherry as may be induced by ambient ozone exposures throughout Switzerland. Particular emphasis was placed on determining foliar injury in Canton Ticino (Ti.) situated in the sub-Alpine region of southern Switzerland. Surveys revealed black cherry to be very sensitive exhibiting an adaxial foliar stipple and leaf reddening at higher elevation plots in the southern-most parts of Ti. Open-top chamber investigations confirmed the foliar response as being due to ambient ozone. Surveys of natural vegetation in proximity to air quality monitoring stations throughout the whole of Switzerland revealed many native plants symptomatic with ozone-like foliar injury. Fumigation studies within CSTR chambers are being used to determine ozone-induced exposure/response relationships. Of the species thus far tested, Viburnum lantana, Morus nigra, Betula pendula, Rumex acetosa and Prunus serotina appear most sensitive.

A survey for ozone-induced foliar injury of black cherry was conducted in mid-June 1995 within the Desierto de Los Leones National Park located southwest of Mexico City. Evaluations of the upper and lower tree crowns of 18 trees revealed evidence of significant upper surface stipple, leaf reddening and premature senescence on 72% of the trees. A general survey of an additional 169 trees disclosed that 41% exhibited similar symptoms. A gradient of increasing symptoms with increasing elevation was also evident. For the most part, asymptomatic trees were observed to be situated within well-shaded coves at the lower elevations with very few symptomatic trees present in these areas.

Foliar ozone uptake rates of different-sized black cherry (Prunus serotina Ehrh.) trees were compared within a deciduous forest and adjacent openings in north-central Pennsylvania during one growing season. Study trees included open-grown seedlings and saplings, forest understory seedlings and saplings, and sunlit and shaded portions of mature canopy tree crowns. Instantaneous ozone uptake rates were highest in high-light environments primarily because of higher stomatal conductances. Low ozone uptake rates of seedlings and saplings in the forest understory could be attributed partially to lower average ambient ozone concentrations compared to the canopy and open environments. Among the tree size and light combinations tested, ozone uptake rates were highest in open-grown seedlings and lowest in forest-grown seedlings. Despite lower ozone uptake rates of foliage in shaded environments, ozone uptake per net photosynthesis of foliage in shaded environments was significantly higher than that of foliage in sunlit environments because of weaker coupling between net photosynthesis and stomatal conductance in shaded environments. The potential for greater ozone injury in shaded environments as a result of greater ozone uptake per net photosynthesis is consistent with previous reports of greater ozone injury in shaded foliage than in sunlit foliage.

Ambient concentrations of ozone (O(3)) and carbon dioxide (CO(2)) were measured at locations from the forest floor to the top of the canopy in a deciduous forest at the Moshannon State Forest in northcentral Pennsylvania. O(3) concentrations were measured from May-September for three years (1993-1995) while CO(2) concentrations were measured only during July and August of 1994. O(3) concentrations increased steadily during the day at all locations, peaking during the middle to late afternoon hours. O(3) concentrations then steadily declined to their lowest point, just before dawn. Vertical O(3) concentration gradients varied seasonally and among years. However, O(3) concentrations were highest within the forest canopy and lowest at the forest floor, with an average difference of approximately 13%. Differences in O(3) concentrations between the canopy and forest floor were greatest at night. O(3) concentrations were slightly higher at locations within the canopy than above the canopy. CO(2) concentrations were consistenly higher near the forest floor and were higher above the canopy than within the canopy. CO(2) concentrations were higher at night than during the day at all locations, especially near the forest floor.

Patterns of ozone uptake were related to physiological, morphological, and phenological characteristics of different-sized black cherry trees (Prunus serotina Ehrh.) at a site in central Pennsylvania. Calculated ozone uptake differed among open-grown seedlings, forest gap saplings, and canopy trees and between leaves in the upper and lower crown of saplings and canopy trees. On an instantaneous basis, seedling leaves had the greatest ozone uptake rates of all tree size classes due to greater stomatal conductance and higher concentrations of ozone in their local environment. A pattern of higher stomatal conductance of seedlings was consistent with higher incident photosynthetically-active radiation, stomatal density, and predawn xylem water potentials for seedlings relative to larger trees. However, seedlings displayed an indeterminate pattern of shoot growth, with the majority of their leaves produced after shoot growth had ceased for canopy and sapling trees. Full leaf expansion occurred by mid-June for sapling and canopy trees. Because many of their leaves were exposed to ozone for only part of the growing season, seedlings had a lower relative exposure over the course of the growing season, and subsequently lower cumulative uptake, of ozone than canopy trees and a level of uptake similar to upper canopy leaves of saplings. Visible injury symptoms were not always correlated with patterns in ozone uptake. Visible symptoms were more apparent on seedling leaves in concurrence with their high instantaneous uptake rates. However, visible injury was more prevalent on leaves in the lower versus upper crown of canopy trees and saplings, even though lower crown leaves had less ozone uptake. Lower crown leaves may be more sensitive to ozone per unit uptake than upper crown leaves because of their morphology. In addition, the lower net carbon uptake of lower crown leaves may limit repair and anti-oxidant defense processes.