High-elevation Red Spruce Research Articles

Extracellular Soil Enzyme Activities in High-Elevation Mixed Red Spruce Forests in Central Appalachia, U.S.A.

Anthropogenic emissions have impacted terrestrial forest ecosystem processes in North America since the industrial revolution. With the passage of the Clean Air Act in 1970 in the United States, atmospheric inputs of nitrogen (N) and sulfur (S) into forests in the Appalachian Mountains have declined, which have, potentially, mitigated their effects on processes such as decomposition and nutrient cycling. Activities of microbial extracellular soil enzymes (ESEs) mediate many rate-limiting nutrient transformations in forest soils and play important roles in the decomposition of complex organic compounds. Soils in high-elevation red spruce forests are characterized by low pH and high carbon (C):N ratios and, having historically received extremely high levels of N deposition, may exhibit legacy impacts of deposition on nutrient availability and decomposition. We utilized four sites along a modeled gradient of N deposition in central Appalachia to assess contemporary ESEs in bulk soil under Acer rubrum L., Betula alleghaniensis Britt., and Picea rubens Sarg. in May, June, and July 2016. Increasing N deposition led to increases in organic fraction C and N and decreases in phosphorus (P). Sites receiving higher N also exhibited greater mineral fraction C, N, and P. ESEs were highest in organic fractions with acid phosphatases (AP) exhibiting the highest activity. There was little influence of N deposition on organic fraction ESEs, but strong evidence for a positive relationship between N deposition and activities of AP, β-glucosidases (BG), and chitinase (NAG) in mineral fractions. Species effects on ESEs were present with high AP in organic fractions under spruce and high mineral fraction fungal laccase (LAC) under birch. The sampling season demonstrated little effect on ESEs. ESEs were more strongly influenced by plot-level factors, such as tree species diversity and abundance of ectomycorrhizal (ECM) tree species, than temporal or soil factors or nutrient status related to modeled cumulative N deposition across these sites. Decreases in AP, BG, and NAG activities with greater abundance of broadleaf deciduous species and increases in activities with ECM host abundance indicate that microbial communities driven by these plant functional groups are responsible for the differences in ESEs observed in these high-elevation mixed red spruce stands.

Soil and Tree Nutrient Status of High Elevation Mixed Red Spruce (Picea rubens Sarg.) and Broadleaf Deciduous Forests

Anthropogenic and industrial emissions have resulted in historically high levels of acidic deposition into central Appalachian forests. Despite the reduction in acidic inputs due to legislation curbing industrial emissions in the United States, continued N deposition may impact forest ecosystems. Soil and foliar samples were collected from four high elevation red spruce sites along a modeled gradient of historic N deposition. The three most abundant tree species at all sites, Acer rubrum L., Betula alleghaniensis Britt., and Picea rubens Sarg., were sampled. Bulk soil beneath the canopies of individual trees were collected from the top 15-cm and separated into organic and mineral fractions for analysis. Mehlich-III soil extracts of soil fractions and foliar digests from these trees were subjected to elemental analysis. Soil N concentrations supported the presence of a N deposition gradient: in organic horizon soil fractions, N concentrations were driven by precipitation volume and elevation; whereas in mineral soil fractions, N concentration was explained by modeled N deposition rate and elevation. In organic fractions, significant reductions in Ca, K, and P were evident as N deposition increased, whereas the Ca:Sr ratio increased. Foliar Ca, K, and Sr declined in foliage with increasing N deposition, with concomitant increases in foliar Ca:Sr ratios. Although the three species were sympatric in mixed stands at all four sites, the foliar–soil nutrient associations differed among them across the gradient, indicating differential uptake and cycling of nutrients/metals by these forest tree species.

Spruce-fir forest changes during a 30-year nitrogen saturation experiment

A field experiment was established in a high elevation red spruce (Picea rubens Sarg.) – balsam fir (Abies balsamea) forest on Mount Ascutney Vermont, USA in 1988 to test the nitrogen (N) saturation hypothesis, and to better understand the mechanisms causing forest decline at the time. The study established replicate control, low and high dose nitrogen addition plots (i.e., 0, 15.7 and 31.4kgNH4Cl-Nha−1yr−1). The treatments began in 1988 and continued annually until 2010, but monitoring has continued to present. During the fertilization period, forest floor C:N, net in situ N mineralization, spruce foliar Ca%, and live spruce basal area decreased with increasing N addition, while foliar spruce N% and forest floor net nitrification increased with increasing N addition. The control plots aggraded forest floor N at a rate equal to the sum of the net in situ N mineralization plus average ambient deposition. Conversely, N addition plots lost forest floor N. Following the termination of N additions in 2010, the measured tree components returned to pre-treatment levels, but forest floor processes were slower to respond. During the 30year study, site surface air temperature has increased by 0.5°C per decade, and total N deposition has decreased 5.5 to 4.0kgNha−1yr−1. There have also been three significant drought years and at least one freeze injury year after which much of the forest mortality on the N addition plots occurred. Given that there was no control for the air temperature increase, discussion of the interactive impacts of climate and change and N addition is only subjective. Predicted changes in climate, N deposition and other stressors suggest that even in the absence of N saturation, regeneration of the spruce-fir ecosystem into the next century seems unlikely despite recent region-wide growth increases.

Carbon sources and sinks in high-elevation spruce–fir forests of the Southeastern US

Abstract This paper examines carbon (C) pools, fluxes, and net ecosystem balance for a high-elevation red spruce–Fraser fir forest [Picea rubens Sarg./Abies fraseri (Pursh.) Poir.] in the Great Smoky Mountains National Park (GSMNP), based on measurements in fifty-four 20 m × 20 m permanent plots located between 1525 and 1970 m elevation. Forest floor and mineral soil C was determined from destructive sampling of the O horizon and incremental soil cores (to a depth of 50 cm) in each plot. Overstory C pools and net C sequestration in live trees was estimated from periodic inventories between 1993 and 2003. The CO2 release from standing and downed wood was based on biomass and C concentration estimates and published decomposition constants by decay class and species. Soil respiration was measured in situ between 2002 and 2004 in a subset of eight plots along an elevation gradient. Litterfall was collected from a total of 16 plots over a 2–5-year period. The forest contained on average 403 Mg C ha−1, almost half of which stored belowground. Live trees, predominantly spruce, represented a large but highly variable C pool (mean: 126 Mg C ha−1, CV = 39%); while dead wood (61 Mg C ha−1), mostly fir, accounted for as much as 15% of total ecosystem C. The 10-year mean C sequestration in living trees was 2700 kg C ha−1 year−1, but increased from 2180 kg C ha−1 year−1 in 1993–1998 to 3110 kg C ha−1 year−1 in 1998–2003, especially at higher elevations. Dead wood also increased during that period, releasing on average 1600 kg C ha−1 year−1. Estimated net soil C efflux ranged between 1000 and 1450 kg C ha−1 year−1, depending on the calculation of total belowground C allocation. Based on current flux estimates, this old-growth system was close to C neutral.

Tree growth, foliar chemistry, and nitrogen cycling across a nitrogen deposition gradient in southern Appalachian deciduous forests

The declining health of high-elevation red spruce (Picea rubens Sarg.) and Fraser fir (Abies fraseri (Pursh) Poir.) in the southern Appalachian region has long been linked to nitrogen (N) deposition. Recently, N deposition has also been proposed as a source of negative health impacts in lower elevation deciduous forests. In 1998 we established 46 plots on six sites in North Carolina and Virginia dominated by American beech (Fagus grandifolia Ehrh.), sugar maple (Acer saccharum Marsh.), and yellow birch (Betula alleghaniensis Britt). We evaluated several response variables across an N deposition gradient, including annual basal area growth; foliage percent N, Al, P, K, Mg, and Ca; and forest floor percent N, Mg, and C, pH, and potential net nitrification and N mineralization rates. We found a significant linear relationship between N deposition and basal area growth in sugar maple, but not in American beech or yellow birch. In addition, we found a significant relationship between N deposition and foliar chemistry (foliar %N in all species, foliar Mg/N and %K in sugar maple, and %P in sugar maple and yellow birch). Foliar %N of the three studied species was high relative to values reported in other studies in the United States and Canada. Several forest floor response variables (%N, C/N, pH, Mg/N, and potential net nitrification and N mineralization rates and nitrification/mineralization fractions) were also correlated with N deposition. The correlations between the above response variables and N deposition are consistent with the influence of chronic N deposition on forested ecosystems measured in other regions and suggest that chronic N deposition may be influencing forest structure and chemistry within the southern region.

Variation in overstory nitrogen uptake in a small, high-elevation southern Appalachian spruce-fir watershed

High-elevation red spruce (Picea rubens Sarg.) – Fraser fir (Abies fraseri (Pursh) Poir.) forests of the southern Appalachians exhibit considerable spatial heterogeneity in structure, and possibly in N uptake, because of a combination of natural disturbances and heavy fir mortality caused by infestations of the exotic balsam woolly adelgid (Adelges piceae Ratz). The objectives of this study are to determine spatial variability in tree N uptake in a small high-elevation catchment in the Great Smoky Mountains National Park, compare outcomes among calculation methods, and assess the influence of stand and landscape properties on N uptake. Tree N uptake is estimated for fifty 20 × 20 m plots in the Noland Divide Watershed (NDW). Components considered in the calculations are stem growth, foliage increment, and mortality of spruce, fir, and yellow birch (Betula alleghaniensis Britt.) from 1993 and 1998 stand inventories; throughfall N flux measured in summers 1998 and 1999; litterfall N return for 1 year in a subset of 12 plots; tissue N analyses; and atmospheric N deposition and root turnover estimates from the literature. Overstory N uptake varies spatially within NDW, with a CV of 9–41% depending on the calculation method. Variability among methods is even higher, with an almost 15-fold difference between the smallest and largest average overstory uptake estimate (5 vs. 74 kg·ha–1·year–1). Only 5 and 3 kg·ha–1·year–1of N is sequestered in wood and foliar increment, respectively, while 36 kg·ha–1of N returns annually as aboveground litterfall. Uptake and its components are correlated with measures of stand structure but not with elevation or aspect.

Is there synchronicity in nitrogen input and output fluxes at the Noland Divide Watershed, a small N-saturated forested catchment in the Great Smoky Mountains National Park?

High-elevation red spruce [Picea rubens Sarg.]-Fraser fir [Abies fraseri (Pursh.) Poir] forests in the Southern Appalachians currently receive large nitrogen (N) inputs via atmospheric deposition (30 kg N ha(-1) year(-1)) but have limited N retention capacity due to a combination of stand age, heavy fir mortality caused by exotic insect infestations, and numerous gaps caused by windfalls and ice storms. This study examined the magnitude and timing of the N fluxes into, through, and out of a small, first-order catchment in the Great Smoky Mountains National Park. It also examined the role of climatic conditions in causing interannual variations in the N output signal. About half of the atmospheric N input was exported annually in the streamwater, primarily as nitrate (NO3-N). While most incoming ammonium (NH4-N) was retained in the canopy and the forest floor, the NO3-N fluxes were very dynamic in space as well as in time. There was a clear decoupling between NO3-N input and output fluxes. Atmospheric N input was greatest in the growing season while largest NO3-N losses typically occurred in the dormant season. Also, as water passed through the various catchment compartments, the NO3-N flux declined below the canopy, increased in the upper soil due to internal N mineralization and nitrification, and declined again deeper in the mineral soil due to plant uptake and microbial processing. Temperature control on N production and hydrologic control on NO3-N leaching during the growing season likely caused the observed inter-annual variation in fall peak NO3-N concentrations and N discharge rates in the stream.

Forest Health in North America: Some perspectives on Actual and Potential Roles of Climate and Air Pollution

The perceived health of forest ecosystems over large temporal and spatial scales can be strongly influenced by the frames of reference chosen to evaluate both forest condition and the functional integrity of sustaining forest processes. North American forests are diverse in range, species composition, past disturbance history, and current management practices. Therefore the implications of changes in environmental stress from atmospheric pollution and/or global climate change on health of these forests will vary widely across the landscape. Forest health surveys that focus on the average forest condition may do a credible job of representing the near-term trends in economic value while failing to detect fundamental changes in the processes by which these values are sustained over the longer term. Indications of increased levels of environmental stress on forest growth and nutrient cycles are currently apparent in several forest types in North America. Measurements of forest ecophysiological responses to air pollutants in integrated case studies with four forest types (southern pine, western pine, high elevation red spruce, and northeastern hardwoods) indicate that ambient levels of ozone and/or acidic deposition can alter basic processes of water, carbon, and nutrient allocation by forest trees. These changes then provide a mechanistic basis for pollutant stress to enhance a wider range of natural stresses that also affect and are affected by these resources. Future climatic changes may ameliorate (+ CO2) or axacerbate (+ temperature, + UV-B) these effects. Current projections of forest responses to global climate change do not consider important physiological changes induced by air pollutants that may amplify climatic stresses. These include reduced rooting mass, depth, and function, increased respiration, and reduced water use efficiency. Monitoring and understanding the relative roles of natural and anthropogenic stress in influencing future forest health will require programs that are structured to evaluate responses at appropriate frequencies across gradients in both forest resources and the stresses that influence them. Such programs must also be accompanied by supplemental process -oriented and pattern -oriented investigations that more thoroughly test cause and effect relationships among stresses and responses of both forests and the biogeochemical cycles that sustain them.

Red spruce and loblolly pine nutritional responses to acidic precipitation and ozone

A multidisciplinary research program called Response of Plants to Interacting Stresses (ROPIS) was initiated by the Electric Power Research Institute in 1986 to develop a general mechanistic theory of plant response to interacting air pollutants and other stresses. As part of the program, the individual and combined impacts of acidic precipitation and elevated O 3 on nutritional responses of red spruce ( Picea rubens Sarg.) and loblolly pine ( Pinus taeda L.) were evaluated. Red spruce saplings were exposed to charcoal filtered, non-filtered, 1·5 times ambient or twice ambient levels of O 3 in combination with rain pH treatments of 3·1, 4·1, or 5·1 for 4 years. Similarly, loblolly pine seedlings were exposed to subambient, ambient or twice ambient O 3 levels in combination with acidic precipitation treatments of pH 3·8 or 5·2 for 3 years. Cation leaching was accelerated in the pH 3·1 rain treatment in the red spruce study, driven by atmospheric inputs of H + and SO 4 2−. Subsequent decreases in soil pH, exchangeable pools of Ca 2+ and Mg 2+, and increases in exchangeable Al 3+ in the organic horizon were observed. Calcium and Mg 2+ fluxes in throughfall of red spruce were also enhanced at pH 3·1, and foliar concentrations of Mg 2+ were reduced. In contrast, soil pH and nutrient concentrations as well as foliar leaching in the loblolly pine study were not significantly affected by either the pH 3·8 or 5·2 rain treatments. Ozone exposure had no effect on throughfall or soil solution ionic flux for either species. Results indicate that ambient rainfall acidities are not likely to affect the nutritional status of loblolly pine. High elevation red spruce forests, however, could be impacted by acidic deposition via enhanced soil acidification, leading to Al 3+ mobilization and reduced availability of important base cations as well as increased foliar leaching.

Cloudwater and Ozone Effects upon High Elevation Red Spruce: A Summary of Study Results from Whitetop Mountain, Virginia

AbstractThis paper integrates the results of a number of studies on the effects of cloudwater and ozone (O3) on red spruce (Picea rubens Sarg.) seedlings, saplings, and mature trees at Whitetop Mountain, VA, over a 3‐yr period. These investigations consisted of (i) seedling chamber exclusion studies, (ii) mature tree branch chamber exclusion studies, and (iii) field experiments comparing responses of seedlings, saplings, and mature trees. The studies included treatments that: (i) excluded clouds and O3 (COE), (ii) excluded clouds and had ambient O3 (CE), and (iii) exposed plants to both clouds and O3 either with (CC) or without (AA) chambers. Seedlings and mature branches in the various treatments were compared with respect to growth rates, gas exchange rates, foliar nutrition, and chlorophyll and wax content. Soil solution, throughfall, and foliar responses of mature trees near the summit, receiving differing amounts of cloud exposure (low cloud and high cloud sites) were also monitored. Ozone was found to have minimal effects on the parameters measured, whereas cloudwater exposure was found to have adverse effects on several response parameters. Chambered seedlings that were exposed to cloudwater (AA and CC), and mature trees at the high cloud site had significantly lower foliar Ca and Mg concentrations than their counterparts, which were protected from exposure (seedlings) or received low cloud exposure (mature). A 3 to 5°C increase in cold tolerance was also measured in seedlings from which cloudwater was excluded. These findings suggest that cloudwater‐mediated effects are currently having a negative impact on the health of red spruce, and may be involved in red spruce decline in the eastern USA.

Effects of ammonium on elemental nutrition of red spruce and indicator plants grown in acid soil

Abstract Decline of high elevation red spruce (Picea rubens Sarg.) forests in the northeastern United States has been related to Ca and Mg deficiencies induced by input of air‐borne nitrogenous nutrients into the forest ecosystem. This research investigated the effects of N nutrition on mineral nutrition of red spruce and radish (Raphanus sativus L.), as an indicator plant, grown in acid forest soil. Red spruce and radishes in the greenhouse were treated with complete nutrient solutions with 15 mM N supplied as 0, 3.75, 7.5, 11.25, or 15 mM NH4 + with the remainder being supplied as NO3. Growth of each species was chlorotic and stunted by increased NH4 + in the nutrient solution. Increasing NH4 + from 0 to 15 mM depressed soil pH by about 1 unit (from 4.5 to an average of 3.5). Accumulation of N, K, Ca, and Mg by each species was restricted as the proportion of NH4 + increased, although the magnitude of these restrictions were small. The restrictions in growth were attributed directly to NH4 + toxicity an...

Red spruce bud mortality at Whiteface Mountain, New York

Terminal bud mortality for shoots produced between 1982 and 1989 was measured for midcanopy branches of mature red spruce trees (Picea rubens Sargent) at two elevations on Whiteface Mountain, New York, U.S.A. Average terminal bud mortality ranged from 15 to 45% in different years, and there was no evidence for a biotic cause of bud mortality. Between branches on different trees, there was a negative correlation between frequency of terminal bud mortality for shoots produced between 1987 and 1989 and the percent change in current-year foliage biomass between 1987 and 1990. Branches with a high frequency of terminal bud mortality also tended to have a high proportion (> 50%) of 1990 shoots developed on adventitious branchlets. In late November 1990, terminal buds from most trees at 710–1120 m elevation were susceptible to freezing injury between −31 and −38 °C when cooled at 4 °C/h under laboratory conditions. Typical winter minimum temperatures at 700–1100 m elevation on Whiteface Mountain are within this range. In a recent controlled study of red spruce seedlings, high foliar nitrogen was associated with an increased risk of freezing injury to terminal buds in autumn. We found that red spruce on Whiteface Mountain had higher foliar nitrogen levels compared with red spruce at a much lower elevation in Maine. Based on these results, we advocate further research on the relationship between foliar nitrogen and bud freezing sensitivity in high elevation red spruce. Key words: Picea rubens, red spruce, bud mortality, freezing injury, nitrogen, red spruce decline.

Temperature increase accelerates nitrate release from high-elevation red spruce soils

One possible consequence of predicted increases in global temperature is an increase in soil organic matter decomposition rates and (or) nitrification rates. In nitrogen-saturated ecosystems, such a change could lead to an increase in nitrate production, since much of the ammonium released from decomposition of organic matter would be converted to nitrate rather than taken up by plants or microorganisms. In a high-elevation red spruce (Picearubens Sarg.) stand, soil at 15 cm below the surface of the sunny and shaded sides of a recent clearing were found to exhibit a significant temperature differential (Δ = 1.2 °C, p < 0.01). Soil solutions collected at 15 cm from the warmer, sunny side over an 18-month period had higher (p < 0.01) mean concentrations of nitrate (71% greater), Mg (58% greater), and Al (24% greater) than those from the shaded side. Fluxes of nitrate and Mg were 30–33% higher on the sunny side of the clearing (p = 0.10, p < 0.01, respectively). If global climate changes result in accelerated releases of nitrate that are widespread in high-elevation spruce–fir forests, elevated Al levels and (or) base cation leaching losses may result, with possible negative consequences for forest health.

A comparison of red spruce and balsam fir shoot structures.

I compared the shoot structures of high-elevation red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea (L.) Mill.). Needle widths, thicknesses and perimeters were measured to estimate total leaf areas from measured projected leaf areas. Measured needle perimeter/needle width ratios differed significantly from estimated ratios that assumed needles were either rhomboidal or elliptical in cross section. The vertical and horizontal silhouette shoot area to total leaf area ratios (STAR(v) and STAR(h)) of the two species were negatively correlated with needle packing and canopy height. Red spruce had higher values of STAR(v) than balsam fir at each canopy height, but STAR(v) declined with canopy height at a similar rate in the two species. The STAR(h) values of the two species did not differ significantly at a given canopy height. Needle packing increased with canopy height at the same rate in the two species. Needle weight increased in red spruce and decreased in balsam fir with increased needle packing, but showed no significant dependence on canopy height. Red spruce had higher values of STAR(h) than balsam fir at low values of needle packing, but STAR(h) values converged at high values of needle packing. The generally comparable values of STAR, along with similar needle diameters, may imply that red spruce and balsam fir have similar collection efficiencies of wet and dry particles. Measurements of STAR may be used to estimate leaf area indices (LAI) more accurately when using indirect techniques.

Seasonal variation in nitrate reductase activity in needles of high-elevation red spruce trees

To assess seasonal and site variation in foliar nitrate reductase activity and its utility as a biochemical marker for the uptake of nitrogen oxide pollutants in high-elevation forests, we measured nitrate reductase activity in current-year needles of red spruce (Picearubens Sarg.) saplings at two high-elevation stands (1935 and 1720 m) in the Great Smoky Mountains, North Carolina. Measurements spanned two growing seasons between September 1987 and September 1988. Nitrate reductase activity peaked near 60 nmol•g−1•h−1 at both sites in September and October 1987 and August 1988 and declined 80% in November 1987 and 65% in September 1988. Although nitrate reductase activity was 30% greater in saplings at the higher site relative to the lower site in September and October 1987, activity dropped to approximately 10 nmol•g−1•h−1 at both sites in November 1987. No differences among sites were evident the following year. Comparing deposition of nitric acid vapor at a nearby site to nitrate reductase activity suggests that needle nitrate reductase activity is not an unequivocal marker for foliar uptake of nitrogen oxides during air pollutant episodes. The changes in soil nitrate levels in this system provide preliminary evidence that foliar nitrate assimilation may, in part, include nitrate taken up from the soil, as the highest activity occurred during periods of higher A-horizon nitrate concentrations in 1988. These measurements of nitrate reductase activity suggest that red spruce are capable of assimilating nitrate in foliage in the field and that the nitrate assimilation capacity varies throughout the year.

Water holdup capacity and residence time of red spruce and balsam fir branches

This study examined the throughfall dynamics of high-elevation red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] branches. A site was established at an elevation of 1160 m on Mt. Washington, New Hampshire, USA, and branches were collected from the canopies of mature trees. Throughfall water dynamics of branches collected in September 1988 and March 1989 were determined using a fluorescent tracer in an artificial precipitation apparatus. Water holdup capacities of spruce and fir branches from different canopy positions were similar. Spruce retained more water per unit area than fir. For rain, a three-compartment model that was used to analyze water dynamics showed that the bulk of water initially on the branch experienced very slow turnover, while intercepted water left the branch quickly. There did not appear to be any difference in throughfall dynamics between spruce and fir. Our results suggest that the initial composition of rain and mobilized dry deposition will influence the composition of water in contact with the branch for a relatively long time, as branch water composition will respond slowly to changes in precipitation composition. These predictions require field testing where sequential sampling of throughfall and precipitation occurs on a time scale equivalent to 0.1–0.2 mm of precipitation.

Tests of the use of net throughfall sulfate to estimate dry and occult sulfur deposition

Throughfall and stemflow measurements taken in a mature high elevation red spruce stand, and precipitation measurements made in a nearby clearing, were used to calculate weekly net throughfall (=throughfall + stemflow - precipitation) sulfate deposition and net throughfall volume in the stand over a 20-week period. The study fortuitously was divisible into a low cloudwater deposition period, during which precipitation volumes generally exceeded throughfall volumes, and a high cloud period, during which the reverse was true. Weekly cloudwater deposition volume was estimated independently from continuously recorded cloudwater collections by an artificial tree located on an elevated platform in the clearing. Weekly net throughfall volume correlated well with cloudwater deposition volume ( r = +0.86). Precipitation accounted for only 25% of the throughfall sulfate collected throughout the study and only 15% of that collected during the high cloud period, as net throughfall sulfate was 2.4 times greater during the high cloud period than during the low cloud period. Weekly estimates of cloudwater sulfate deposition correlated well ( r = +0.74) with measures of net throughfall sulfate during the high cloud period. Dry deposition models were used to estimate weekly dry S deposition; weekly estimates of the wash-off of this dry deposition also correlated well ( r = +0.76) with net throughfall sulfate during the low cloud period. During the high cloud period, estimates of cloudwater S plus dry S deposition accounted for 67% of the sulfate collected in net throughfall; however, during the low cloud period only 55% of net throughfall sulfate was accounted for. The low percentage of sulfate accounted for during the low cloud period suggests that the dry models were underestimating S deposition. Possible reasons for underestimation include failure to consider fully topographic complexity and edge effects, underestimates of surface wetness, and the possibility of canopy sources of sulfate (foliar leaching). These results support the use of throughfall sulfate measurements as gross estimates of (1) total S deposition, (2) total dry S deposition (using net throughfall in environments where cloudwater deposition accounts for less than 5% of total sulfate deposition) and/or (3) total cloud S deposition (subtracting precipitation and dry inputs from total throughfall sulfate in high cloud environments).

Modeling the Effect of Winter Climate on High-Elevation Red Spruce Shoot Water Contents

Abstract During the winter of 1989-90, meteorological towers were erected at two sites (880 and 1010 m elevation) within the spruce-fir zone on Mt. Moosilauke, New Hampshire. Hourly means of temperature, wind velocity, relative humidity, and solar radiation were collected and stored on data loggers. Previous-year shoots were collected from four spruce trees at each site on a weekly basis, and their relative water contents (RWC) were determined. Measured meteorological parameters were used to simulate changes in the RWC of previous-year spruce shoots through the winter. Our model suggests that shoot water is replenished throughout the winter, presumably from water stored in older woody structures or by root uptake. Recharge was defined to be directly dependent on shoot water saturation deficit (WSD = 100% - RWC), with a temperature cutoff of -4°C. The predicted output of the model generally followed measured RWC. According to our model, periods of high transpiration were associated with low relative humidities, sometimes accompanied by high temperatures and high levels of radiation. Our results suggest that winter water relations in spruce are governed by a balance between transpirational losses, which are primarily dependent upon meteorological conditions, and the rate of recharge, which is dependent on shoot water potential, temperature and perhaps soil water availability. For. Sci. 37(6):1567-1580.

Winter desiccation and solar radiation in relation to red spruce decline in the northern Appalachians

Exposure to direct solar radiation was correlated with needle death within individual high-elevation red spruce (Picearubens Sarg.) shoots following winter injury episodes at six sites in 1980 and 1989. We observed extensive visible needle damage to red spruce in northern New England between March and May of 1989 and determined that it was preceded by desiccation. In an independent growth chamber experiment, red spruce needles were heated to above freezing when exposed to strong illumination in calm subfreezing air. Rapid needle cooling occurred when the radiation load was suddenly reduced at the end of each light period, and needles desiccated severely within 10 days. These separate observations are consistent with three hypotheses: injury results from (i) desiccation, (ii) rapid needle cooling, (iii) freezing injury caused by a reduction in cold hardiness due to solar heating. These three mechanisms are not necessarily mutually exclusive.

Seasonal patterns of photosynthesis and respiration of red spruce saplings from two elevations in declining southern Appalachian stands

Exploratory studies were initiated at two high-elevation red spruce (Picearubens Sarg.) stands in the Great Smoky Mountains of western North Carolina to document the magnitude and physiological basis of differences in tree growth at the two sites. Increment core data indicate that conditions have become relatively less favorable for mature trees at the upper site during the past 20 years and that annual height growth of sapling trees has been 40% less at that site compared with a similar site at an elevation 215 m lower. Seasonal measurements of net photosynthesis and dark respiration rates of saplings indicated that differences in sapling growth rates at the upper site were associated with increases in dark respiration and less favorable net photosynthesis:dark respiration ratios. Basal diameter increment was most closely associated with differences in current net photosynthesis rates among trees at the upper site, whereas height and diameter growth of the upper canopy related most closely to the net photosynthesis rate among lower-elevation trees. Reduced foliar calcium and magnesium, reduced foliar chlorophyll, increased foliar aluminum, and low ratios of calcium:aluminum were found at the upper site. Tissue and soil aluminum levels that are in the range of those associated with aluminum toxicity to red spruce provide a preliminary indication that current high atmospheric inputs of the strong anions SO4 and NO3 to acidic soils may be adversely affecting growth and physiology of trees at the high-elevation site.