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This paper demonstrates the ways and degrees to which contemporary, U.S.-based, employed or retired ecologists aggregate into guild-like groups on the basis of their valuations of 15 professional traits. Principle components analysis of survey data from 904 Ecological Society of America respondents led to five emergent factors from the 15 traits: `enjoying nature,' `preserving nature,' `questing for knowledge,' `possessing epistemic expertise,' and `accepting religious foundations for valuing nature.' Subsequent cluster analysis on these factors yielded four groups of respondents we designated as `youthful relativists,' `older naturalists,' scientific objectivists,' and `optimistic traditionalists.' Surprisingly, the majority of respondents were negative about the `enjoying nature,' or `preserving nature' factors, a matter for further exploration. Also, differential levels of doubt existed as to the maintenance of objectivity during the practices of research, and especially in participation in environmental issues.

Clearcutting is a common silvicultural practice in the deciduous forests of northern New England. Subsequent regrowth is usually rapid, largely due to regenerative capacities of successional plants, particularly pin cherry (Prunus pensylvanica L.). The forest cover of an experimental watershed (W2) in Hubbard Brook Experimental Forest, NH was clearcut and then treated with herbicides for 3 years to prevent regrowth. This experimental treatment delayed plant growth and caused extensive nutrient losses from the watershed-ecosystem, thereby diminishing factors normally promoting revegetation. This article addresses the question of whether, or to what degree, resilience, defined here as the trajectory of recovery back to a prior state following a perturbation, was reduced by this treatment. Performance metrics for resilience were aboveground net primary productivity (ANPP) and biomass accumulation. Data collected over seven intervals for the first 31 years of regrowth show that a primary component of resilience—pin cherry density—was reduced, and that ANPP and biomass accumulation were initially below normal compared with other clear-cut sites. After approximately a decade of regrowth, however, trajectories for both ANPP and biomass fell within the lower margins of variability measured in other regional examples.

Carbon sequestration was estimated a northern mixed-grass prairie site and a sagebrush–steppe site in southeastern Wyoming using an approach that integrates remote sensing, CO2 flux measurements, and meteorological data. Net ecosystem exchange (NEE) of CO2 was measured using aircraft and ground flux techniques and was linearly related to absorbed photosynthetically active radiation (APAR). The slope of this relationship is the radiation use efficiency (ɛ = 0.51 g C/MJ APAR); there were no significant differences in the regression coefficients between the two sites. Furthermore, ecosystem chamber measurements of total respiration in 1998 and 1999 were used to develop a functional relationship with daily average temperature; the Q10 of the relationship was 2.2. Using the Advanced Very High Resolution radiometer. Normalized Difference Vegetation Index and meteorological data, annual gross primary production and respiration were calculated from 1995 to 1999 for the two sites. Overall, the sagebrush–steppe site was a net carbon sink, whereas the northern mixed-grass prairie site was in carbon balance. There was no significant relationship between NEE and APAR for a coniferous forest site, indicating this method for scaling up CO2 flux data may be only applicable to rangeland ecosystems. The combination of remote sensing with data from CO2 flux networks can be used to estimate carbon sequestration regionally in rangeland ecosystems.

Annual brome grasses, Bromus japonicus and B. tectorum, are common invaders of northern mixed-grass prairie, and have been shown to alter the structure and function of prairie ecosystems, including plant biomass production and litter decomposition. To build on previous findings, our objective was to model the impact of annual brome grasses on soil organic carbon storage as a step towards forecasting ecological change. Specifically, we measured differences in carbon storage between patches dominated by annual bromes and perennial grasses, in addition to evaluating key plant functional characteristics that impact carbon storage. Using the CENTURY model, we simulated high- and low-brome vegetation based on differences in functional characteristics, allowing us to extrapolate the findings from the field study across a broader time scale. We sampled a prairie site in 1996 and 1997 to quantify differences between the high- and low-brome cover plots. High-brome plots averaged 40% brome cover, while the low-brome plots averaged 1% brome cover. We found differences in functional attributes for growth characteristics and litter quality, as well as minor differences in edaphic variables between the plots. Based on field measurements, more soil organic carbon was stored under high-brome vegetation than low-brome, but the differences were not statistically significant. Results from model simulations were consistent with field measurements, and suggested that this prairie ecosystem was not significantly impacted by the functional differences between high- and low-brome vegetation for the first 50 years after the brome invasion under historical management and climate. However, the model results also showed that the differences in soil organic carbon storage continue to diverge after 50 years and consequently could be significant in the future.

A synthesis of the biogeochemistry of S was done during 34 yr (1964-1965 to 1997-1998) in reference and human-manipulated forest ecosystems of the Hubbard Brook Experimental Forest (HBEF), NH. There have been significant declines in concentration (0.44 mol/liter-yr) and input (5.44 mol/ha-yr) of SO4 in atmospheric bulk wet deposition, and in concentration (0.64 mol/liter-yr) an d output (3.74 mol/ha-yr) of SO4 in stream water of the HBEF since 1964. These changes are strongly correlated with concurrent decreases in emissions of SO2 from the source area for the HBEF. The con- centration and input of SO4 in bulk deposition ranged from a low of 13.1 mol/liter (1983-1984) and 211 mol/ha-yr (1997-1998) to a high of 34.7 mol/liter (1965-1966) and 479 mol/ha-yr (1967-1968), with a long-term mean of 23.9 mol/liter and 336 mol/ha-yr during 1964-1965 to 1997-1998. Despite recent declines in concentrations, SO4 is the dominant anion in both bulk deposition and stream water at HBEF. Dry deposition is difficult to measure, especially in mountainous terrain, but was estimated at 21% of bulk deposition. Thus, average total atmospheric deposition was 491 and 323 mol/ha-yr during 1964-1969 and 1993-1998, respectively. Based on the long-term 34 S pattern associated with anthro- pogenic emissions, SO4 deposition at HBEF is influenced by numerous SO2 sources, but biogenic sources appear to be small. Annual throughfall plus stemflow in 1993-1994 was estimated at 346 mol SO4 /ha. Aboveground litterfall, for the watershed-ecosystem averaged about 180 mol S/ha-yr, with highest inputs (190 mol S/ha-yr) in the lower elevation, more deciduous forest zone. Weathering release was calculated at a maximum of 50 mol S/ha-yr. The concentration and output of SO4 in stream water ranged from a low of 42.3 mol/liter (1996-1997) and 309 mol/ha-yr (1964-1965), to a high of 66.1 mol/liter (1970-1971) and 849 mol/ha-yr (1973-1974), with a long-term mean of 55.5 mol/liter and 496 mol/ha-yr during the 34 yrs of study. Gross outputs of SO4 in stream water consistently exceeded inputs in bulk deposition and were positively and significantly related to annual precipitation and streamflow. The relation between gross SO4 output and annual streamflow changed with time as atmo- spheric inputs declined. In contrast to the pattern for bulk deposition concentration, there was no sea- sonal pattern for stream SO4 concentration. Nevertheless, stream outputs of SO4 were highly sea- sonal, peaking during spring snowmelt, and producing a monthly cross-over pattern where net hydro- logic flux (NHF) is positive during summer and negative during the remainder of the year. No significant elevational pattern in streamwater SO4 concentration was observed. Mean annual, volume-weighted

A synthesis of the biogeochemistry of K was conducted during 1963–1992 in the reference and human-manipulated watershed-ecosystems of the Hubbard Brook Experimental Forest (HBEF), NH. Results showed that during the first two years of the study (1963–65), which coincided with a drought period, the reference watershed was a net sink for atmospheric inputs of K. During the remaining years, this watershed has been a net source of K for downstream ecosystems. There have been long-term declines in volume-weighted concentration and flux of K at the HBEF; however, this pattern appears to be controlled by the relatively large inputs during the initial drought years. Net ecosystem loss (atmospheric deposition minus stream outflow) showed an increasing trend of net loss, peaking during the mid-1970s and declining thereafter. This pattern of net K loss coincides with trends in the drainage efflux of SO4 2− and NO3 −, indicating that concentrations of strong acid anions may be important controls of dissolved K loss from the site. There were no long-term trends in streamwater concentration or flux of K. A distinct pattern in pools and fluxes of K was evident based on biotic controls in the upper ecosystem strata (canopy, boles, forest floor) and abiotic controls in lower strata of the ecosystem (mineral soil, glacial till). This biological control was manifested through higher concentrations and fluxes of K in vegetation, aboveground litter, throughfall and forest floor pools and soil water in the northern hardwood vegetation within the lower reaches of the watershedecosystem, when compared with patterns in the high-elevation spruce-fir zone. Abiotic control mechanisms were evident through longitudinal variations in soil cation exchange capacity (related to soil organic matter) and soil/till depth, and temporal and disturbance-related variations in inputs of strong-acid anions. Marked differences in the K cycle were evident at the HBEF for the periods 1964–69 and 1987–92. These changes included decreases in biomass storage, net mineralization and throughfall fluxes and increased resorption in the latter period. These patterns seem to reflect an ecosystem response to decreasing rates of biomass accretion during the study. Clearcutting disturbance resulted in large losses of K in stream water and from the removal of harvest products. Stream losses occur from release from slash, decomposition of soil organic matter and displacement from cation exchange sites. Elevated concentrations of K persist in stream water for many years after clearcutting. Of the major elements, K shows the slowest recovery from clearcutting disturbance.

Nitrous oxide production was measured in intact cores taken from active pasture and old-growth forest Inceptisols in the Atlantic Lowlands of Costa Rica. Following additions of aqueous KNO3 or glucose, or the two combined amendments, the cores were incubated in the laboratory to determine if N2O production rates were either N-limited or C-limited in the two land use types. Differences in rates of denitrification (N22O + N2 production) among amended forest and pasture soils were determined by addition of 10% C2H2. The forest soils were relatively insensitive to all amendment additions, including the acetylene block. Forest N2O production rates among the treatments did not differ from the controls, and were consistently lower than those of the pasture soils. With the addition of glucose plus nitrate to the forest soils, production of N2O was three times greater than the controls, although this increase was not statistically significant. On the other hand, the pasture soils were definitely nitrogen-limited since N2O production rates were increased substantially beyond controls by all the amendments which contained nitrate, despite the very low N level (5 mg N kg−1 soil) relative to typical fertilizer applications. With respect to the nitrate plus glucose plus acetylene treatment, denitrification was high in the pasture soils; N2O production in the presence of C2H2 was 150% of the rate of N2O production measured in the absence of the acetylene block. The results are discussed in relation to the effects of agricultural land use practices and subsequent impacts of disturbance on N2O release.

Soil nitrogen transformations and nitrous oxide fluxes were measured in a range of sagebrush steppe ecosystems in south-central Wyoming. Net nitrate production, measured in laboratory incubations, was highest in the ecosystem type dominated by Artemisia tridentata ssp. vaseyana, especially early in the growing season. Fluxes of nitrous oxide, measured in closed chambers and analyzed by gas chromatography, also tended to be higher in the same type, but only for short periods in the spring. Thereafter, all nitrous oxide fluxes were low and did not differ consistently among types. Estimated average annual fluxes for three Artemisia ecosystem types (dominated by Artemisia tridentata ssp. vaseyana, Artemisia tridentata ssp. wyomingensis, and Artemisia nova) were 0.32, 0.23 and 0.13 kg N2O-N ha−1 y−1 repsectively. Average annual flux, weighted by the areal extent of these and other vegetation types in the region, was approximately 0.21 kg N2O-N ha−1y−1. Assuming this landscape is representative of sagebrush steppe, we calculate a flux of 9.5 × 109 g y−1 of N2O-N from U.S. sagebrush steppe, and a flux of 1.1 × 1011 g y−1 of N20-N from analogous desert and semi-desert shrublands of the world.

Five canopy components of subalpine balsam fir forests (branches with young needles, branches with old needles, non-foliated twigs, lichen-covered twigs, and boles) were treated with simulated rain to test the influence of these components on throughfall and stemflow chemistry. Effects on the fluxes of potassium, sodium, hydrogen, sulfate, nitrate and ammonium ions by the canopy components were tested in relation to rain application rate, duration of rain, and time since the last rain. Interactions between ionic behavior and components were complex. In general, the ionic behavior ranged from high levels of net efflux to mixed influx-efflux to high levels of influx in the order: sulfate, potassium, sodium, nitrate, hydrogen, ammonium. In cases in which application rates produced significantly different results, net flux rates increased with application rate. Branch components mostly ranged from low flux rates (either influx or efflux) to high rates according to the order: young needles

Canopy gap area/age distributions and growth mechanisms were examined in a virgin subalpine forest in the White Mountains, New Hampshire, USA. The gap area distribution was negative exponential in form. Whithin gap tree ages varied widely in response to stepwise gap expansion caused by windthrow of peripheral trees or death of standing mature Picea rubens at gap edges. As a consequence, the density of small gaps may have been underestimated and the density of large gaps overestimated. The estimates of canopy turnover time, 303 yr, and of patch birth rate on an area basis, 3.3×10-3 ha new patches/ha land area/yr, were not affected by the gap expansion phenomenon. However, any estimate of patch birth rate as numbers of new patches formed per year would have been too low. Because of increasingly widespread Picea death, the patch area/age distribution of this forest may not currently be in steady-state.

Mountain big sagebrush steppes in Wyoming have strong spatial patterning associated with topography. We describe the spatial variability of vegetation in a sagebrush steppe, and test the relationship between topography and vegetation using canonical correlation. Results of the analysis suggest that the main control over vegetation distribution in this system is wind exposure. Exposed sites are characterized by cushion plant communities and Artemisia nova, and less exposed sites by the taller sagebrush species Artemisia tridentata ssp. vaseyana. Topographic depressions and leeward slopes are characterized by aspen stands and nivation hollows. Measurements of soil microclimate suggest that a major influence of topographic position on vegetation is snow redistribution and its effect on soil moisture and temperature.

Laboratory incubations of15N-amended soils from a sagebrush steppe in south-central Wyoming indicate that nutrient turnover and availability have complex patterns across the landscape and between microsites. Total and available N and P and microbial C and N were highest in topographic depressions characterized by tall shrub communities. Net and gross N mineralization rates and respiration were also highest in these areas, but microbial efficiencies expressing growth relative to respiration cost were highest in soils of exposed ridgetop sites (prostrate shrub communities). Similar patterns occurred between shrub and intershrub soils, with greater nutrient availability under shrubs, but lower microbial efficiencies under shrubs than between. Surface soils had higher soil nutrient pools and N mineralization rates than subsurface soils, but N and C turnover and microbial efficiencies were lower in those surface soils. All soils decreased in respiration, mineralization, and immobilization rates during the 30-day incubation period, apparently approaching a steady-state substrate use. Soil microbial activity of the high organic matter accumulation areas was apparently more limited by labile substrate.

This paper presents a model of water flux and throughfall concentrations of K+ and NH 4 + in a subalpine balsam fir forest. The model is based on a multi-layer submodel of hydrologic flow. Cloud water deposition and evaporation are incorporated as separate submodels. Chemical exchange is parameterized with diffusion resistances and internal foliar concentrations determined from leaching experiments on isolated canopy components. The model is tested against within-storm throughfall measurements and found to agree reasonably well in most instances. Some specific departures from observed data are noted, of which some can be explained. Differences between observed and modeled concentrations of K+ early in the storm events suggest that pre-storm conditions, which were not modeled, are important in controlling the chemical exchange. Responses of throughfall chemistry to changes in rain rate, rain concentration, and stand surface area index (SAI) were investigated by simulation with the model. Increasing rain rates increased leaching of K+ and uptake of NH 4 + . Increasing concentrations of K+ in rain decreased slightly the amount of K+ leached, but increasing concentration of NH 4 + in rain increased NH 4 + uptake proportionately. Increasing canopy SAI increased the leaching of K+ and the uptake of NH 4 + , with the pattern of the increase dependent on rain rate.