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Ecologists have individualistic perspectives on how nature works because our personal interests in nature (plants, birds, soils) subsequently become modified by our encounters with teachers, historical events, individuals, and ideas. I suspect that, upon reflection, most of us could name a dozen or so persons, courses, papers or books that have had a special influence on our career trajectories. The ESA Bulletin’s editor, through this Paper Trail series, has given us the opportunity to reflect upon particularly influential papers as a way for us to understand the intellectual fabric of our discipline. This is especially germane on the eve of ESA’s Centennial. I describe here a seminal paper that shaped my thinking which has led, in turn, to other developments in ecology.

A survey was distributed to members of the Ecological Society of America in 2014, which asked respondents to rate the usefulness of 131 of the most common, current ecological concepts. As part of the survey, key demographic and professional information was requested from respondents, including age, gender, education level, sector of employment, and primary area (i.e., domain) of interest in ecology. This paper reports how those factors interacted and affected concept ratings. Comprehensive analysis revealed many significant patterns. Among these, we discovered that concept ratings almost invariably increased with age, often dramatically. Also, there was a very strong tendency for males to rate concepts, in general, higher than did females, but the magnitudes of these differences were small. Furthermore, there was a significant gulf between the academic and government employment categories, characterized by academic respondents having rated most concepts higher. This research is important to the ecological community as a quantitative description of the kinds of variation existing among its constituents in terms of types and degrees of concept utility. Self‐knowledge is critical for understanding the discipline and for advancing its educational, research, and environmental initiatives.

This article reports the results ofa survey of 1215 nonstudent Ecological Society of America (ESA) members. The results pertain to three series of questions designed to assess ecologists' engagement in various advocacy activities, as well as attitudes on the relationship between environmental advocacy, values, and science. We also analyzed the effects of age, gender, and employment categories on responses. While many findings are reported, we highlight six here. First, ecologists in our sample do not report particularly high levels of engagement in advocacy activities. Second, ecologists are not an ideologically unified group. Indeed, there are cases of significant disagreement among ecologists regarding advocacy, values, and science. Third, despite some disagreement, ecologists generally believe that values consistent with environmental advocacy are more consonant with ecological pursuits than values based on environmental skepticism. Fourth, compared to males, female ecologists tend to be more supportive of advocacy and less convinced that environmentally oriented values perturb the pursuit of science. Fifth, somewhat paradoxically, ecologists in higher age brackets indicate higher engagement in advocacy activities as well as a higher desire for scientific objectivity. Sixth, compared to ecologists in other employment categories, those in government prefer a greater separation between science and the influences of environmental advocacy and values.

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.

“Ecological topology” has recently been highlighted as a “frontier of ecology,” yet the term “ecological topology” only occasionally appears in the literature. On the other hand, the term “topology” appears in a variety of publications in this and other ecologically oriented journals, but its use is varied and applied to a wide cross-section of ecological problems. These variable usages suggest that topology does not have a common meaning to all ecologists. Part of this confusion results from the fact that topological ways of seeing nature are both formally derived from mathematical origins, and informally derived from non-mathematical conceptualizations. Interestingly, parallels occur between both mathematically originated and conceptually originated topology with respect to object-oriented, network topologies (formally derived from Eulerian mathematics), and field-oriented, manifold topologies (formally derived from Poincareian mathematics). Topological ways of understanding nature and addressing both theoretical and applied problems have served ecology well in the past, but this approach will be improved with a better, more unified understanding among ecologists as to the variety of meanings found and practiced in the science.

Redistribution of snow by wind is a defining feature of the physical environment in high-elevation upper treeline and alpine landscapes where most precipitation is snow and wind speeds are frequently high. In these landscapes, snow, wind, topography, and vegetation interact to produce a pattern of snow deposition where wind-driven snow is eroded from exposed areas and deposited on the lee sides of hills, trees, rocks, and other obstructions. During winters on Libby Flats, a broad, high-elevation ridge located in southeastern Wyoming, USA, snow is heterogeneously distributed with snow depths ranging from 0.1 to 7 m over a lateral span of a few meters. Snow depth variations are principally controlled by the aerodynamic influence of trees on wind, with the deepest drifts forming on the lee sides of krummholz patches and ribbon forests. While precipitation varied from year to year, spatial patterns of snow scouring, drifting, and snowmelt were nearly identical. This characteristic and chronic pattern alters ecosystem structure (e.g., plant species distributions and soil characteristics) and function (e.g., decomposition, primary production, nutrient cycling, and water balance). To better comprehend and predict how ecosystem structure and function change with respect to snow distribution in treeline ecotones, an understanding of the snow transport process, ablation, and subsequent water distribution is required. Since snow accumulation and melt are difficult to observe spatially, we adapted and validated snow transport and land surface models to simulate the heterogeneous snow distributions produced during three consecutive water years (1998–2000). Comparisons of field measurements with model predictions indicate that the linked models generally mimicked the temporal and spatial characteristics of snow accumulation, redistribution, and ablation on Libby Flats. However, considerable modelled and observed discrepancies were associated with shallow or deep snow depths. Model agreement with observations could be improved with higher temporal resolution meteorological data, better resolved terrain and vegetation data, and model improvements.

A map of the vegetation of the Catskill Park, NY, was created using multi-temporal Landsat Thematic Mapper TM data and ancillary spatial data to support ecological studies in Catskill watersheds. The map emphasizes forest types defined by dominant tree species and depicts 24 vegetation classes. Mapping included a series of supervised classifications in a decision tree framework that allowed forest types to be distinguished using spectral characteristics and other environmental relationships (e.g., landscape position, elevation). Traditional contingency table analysis (based on limited ground sampling) suggests overall map accuracy ranging from 28% to 90%, depending on the level of aggregation of the original 24 map classes. Fuzzy accuracy assessment based on the same ground data suggests a 71% level of acceptable classification. The map indicates that maple-dominated forests are predominant in the Catskill region, but that beech and birch-dominated forests become more important at higher elevatio...

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.

A variety of transport processes operate within the biosphere at all temporal and spatial scales. Temporary events or chronic conditions, both scale-dependent, instigate the transport of entities having material, energetic, or informational properties via several different transport vectors. The fluxes and influences imparted by these transport phenomena shape the physical environment, underlie gene flow, facilitate animal communication, and constrain the nature of local systems. These transport phenomena have been highly altered in the last century as humankind has become an ever more potent force in the earth system. As a result, issues of environmental and earth system science are, to a considerable extent, aspects of transport phenomena. A general appreciation for transport phenomena, broadly defined, is vital to gaining an appropriate perspective on the fluid nature of the earth system and to defining system structure and function through present and past events.

Annual brome grasses, Bromus japonicus and B. tectorum, are common exotic plants in the northern mixed grass prairies of North America. As annuals, the bromes die following seed set in late spring, creating a functional difference between them and native perennial grasses because perennials continue to maintain live shoots into the summer and root systems throughout the year. Our objective was to investigate how this functional difference alters ecosystem properties over the growing season, including soil moisture content, quantity of plant biomass, litter accumulation and aboveground litter decomposition. We conducted an experiment in which the annual bromes were removed from treatment plots to compare with adjacent reference plots. While this experiment served as a direct test for brome impacts, observational plots also were sampled to determine if impacts were apparent in an unmanipulated system. A litter bag experiment was conducted to evaluate impacts of brome grasses on decomposition. Experimental removal of brome grasses led to more biomass both above- and belowground at the end of the growing season, and high brome observational plots averaged 28% less aboveground biomass and 40% less belowground biomass than low brome plots. In contrast, removal of brome grasses did not produce a consistent impact on soil moisture content between sites or among months, and none of measurable impacts from the removal experiment were significant in the observational study. Bromes slowed decomposition of aboveground litter at both sites. However, the overall impact on litter accumulation was only significant at one site, where brome removal reduced surface litter in the latter half of the growing season and high brome observational plots averaged 36% more litter than low brome plots. This study demonstrates how the brome functional type alters several properties in an ecosystem traditionally dominated by perennial grasses.

High-elevation areas in the Rocky Mountain treeline ecotone exhibit heterogeneous snow distribution resulting from interactions among topography, vegetation, and wind. Our study area-Libby Flats-is a gently arched ridge at 3200 m a.s.l. in the Medicine Bow Mountains, Wyoming. The Libby Flats snow season (October-May) features sub-freezing temperatures, abundant snow, and strong westerly winds (averaging 10 m s-1). While relief is gentle on Libby Flats, it, together with islands of krummholz and flagged trees, produces snow depths ranging from 0 to 7 m. These variable snow depths have important feedbacks on the occurrence of trees and vegetation, as well as direct controls on ecosystem properties. To better understand the factors controlling these interactions, snow distribution patterns were measured and modeled over a 6.25 km2 area on Libby Flats during the 1997-98 snow season. Snow-depth observations during the snow season were compared with results from the SnowTran-3D model. These tests demonstrated that the model closely reproduces the observed snow distribution patterns and adequately represents snow depths at a 5 m spatial resolution on Libby Flats. Simulation experiments demonstrate the relative importance of wind speeds, precipitation, and vegetation in the natural system.

Remote agricultural lands, which include wildlife habitat, angling opportunities and scenic vistas, command higher prices per hectare in Wyoming than those whose landscape is dominated by agricultural production. Geographic information systems (GIS) data are used to measure recreational and scenic amenities associated with rural land. A hedonic price model is specified with GIS measures. It is used to estimate the impact of amenity and agricultural production land characteristics on price per acre for a sample of Wyoming agricultural parcels. Results indicate that the specification performed well across several functional forms. The sampled land prices are explained by the level of both environmental amenities as well as production attributes. Statistically significant amenity variables included scenic view, elk habitat, sport fishery productivity and distance to town. This analysis permits a better estimation of environmental amenity values from hedonic techniques. Improved estimation of amenity values is vital for policies aimed at open space preservation, using agricultural conservation easements and land use conflict resolution.

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

The annual brome grasses, Bromus japonicus and B. tectorum, are common invaders of the Northern Great Plains. Our objective was to determine if these exotic plants were positively or negatively associated with particular plant species or functional types in a prairie/pine ecotone at Wind Cave National Park, South Dakota. We addressed this issue by sampling at two spatial scales—the landscape scale and the site scale. For the landscape we evaluated species associations across a 3800 ha ecotone using 90 transects. Annual bromes were positively associated with C3 grasses, particularly Agropyron smithii and Stipa viridula, in addition to the shrub Symphoricarpos occidentalis. Annual bromes were negatively associated with trees, C4 grasses, particularly A. gerardii, Bouteloua curtipendula and Schizachyrium scoparium, as well as the shrub Rhus aromatica. For the site scale we assessed relationships at a finer resolution within two 1 ha stands of grassland vegetation. Annual bromes were negatively assoc...

Nitrous oxide (N2O) and nitric oxide (NO) are important atmospheric trace gases participating in the regulation of global climate and environment. Predictive models on the emissions of N2O and NO emissions from soil into the atmosphere are required. We modified the CENTURY model (Soil Sci. Soc. Am. J., 51 (1987) 1173) to simulate the emissions of N2O and NO from tropical primary forests in the Atlantic Zone of Costa Rica at a monthly time step. Combined fluxes of N2O and NO were simulated as a function of gross N mineralization and water-filled pore space (WFPS). The coefficients for partitioning N2O from NO were derived from field measurements (Global Biogeochem. Cycles, 8 (1994) 399). The modified CENTURY was calibrated against observations of carbon stocks in various pools of forest ecosystems of the region, and measured WFPS and emission rates of N2O and NO from soil to the atmosphere. WFPS is an important factor regulating nutrient cycling and emissions of N2O and NO from soils making the accuracy of the WFPS prediction central to the modeling process. To do this, we modified the hydrologic submodel and developed a new method for the prediction of WFPS at the monthly scale from daily rainfall information. The new method is based on: (1) the relationship between monthly rainfall and the number of rainfall events, and (2) the relative cumulative frequency distribution of ranked daily rainfall events. The method is generic and should be applicable to other areas. Simulated monthly average WFPS was 0.68±0.02 — identical with the field measurement average of 0.68±0.02 from the annual cycle observed by Keller and Reiners (Global Biogeochem. Cycles, 8 (1994) 399). Simulated fluxes of N2O and NO were 52.0±9.4 mg-N m−2 month−1 and 6.5±0.7 mg-N m−2 month−1, respectively, compared with measured averages of 48.2±11.0 mg-N m−2 month−1 and 7.1±1.1 mg-N m−2 month−1. The simulated N2O/NO ratio was 11.2±1.9 compared with the measured value of 10.9±4.7. WFPS is the dominant determinant of the fraction of gross N mineralization that is emitted from the soil as N2O and NO. If WFPS were not limiting during part of the year, this fraction would be 4.2%. With some periods of lower WFPS, the realized fraction is 2.2%. Because of the strong relationships between N2O and NO emission rates and rainfall and its derivative, WFPS, these moisture variables can be used to scale up nitrogen trace gas fluxes from sites to larger spatial scales.

Nitrous oxide (N2O) and nitric oxide (NO) are among the trace gases of concern because of their importance in global climate and atmospheric chemistry. Modeling techniques are needed for simulating the spatial and temporal dynamics of N2O and NO emissions from soils into the atmosphere. In this study, we modified the ecosystem model CENTURY to simulate changes in N2O and NO soil emissions through the process of converting tropical moist forests to pastures in the Atlantic Lowlands of Costa Rica. Measurements of water-filled pore space (WFPS) and fluxes of N2O and NO from a chronosequence of pastures were used for calibration and testing of the model. It was found that the N2O + NO - WFPS and N2O:NO - WFPS relationships as developed from primary forests could be generalized to the chronosequence of pastures and other land use systems in the region. Modeled net increases (compared to primary forests) in total N2O and NO production after conversion from forest to pasture were 514 kg N ha(-1) during the first 15 years under normal field conditions. The nitrogen loss in the form of N2O and NO during the first 15 years could range from 401 to 548 kg N ha(-1), depending on the amounts of forest residue remaining on pasture sites. N2O-N accounted for 90% of the gas fluxes, while NO-N accounted for 10%. Sensitivity analysis indicated that the impacts of forest-pasture conversion on N2O and NO emissions from soil into the atmosphere were complex, depending on the initial conditions of the forest-derived pastures, management practices, soil physical and chemical conditions and their changes over time, N availability, and climate. It is therefore important to incorporate the spatial and temporal heterogeneities of those controlling factors in estimating regional and global N2O and NO emissions from soils into the atmosphere. [References: 37]

A Landsat Thematic Mapper (TM) based digital land cover map has been created for the state of Wyoming, USA, at moderate spatial (l-km2 minimum mapping unit) and high typal (41 land cover types) resolution as part of the Wyoming Gap Analysis Program (WGAP). This map presents opportunities for regional characterization of land cover, especially vegetation, and for examination of ecological phenomena that manifest themselves over large areas. Using the digital land cover data, we describe Wyoming vegetation and examine positions of three prominent physiognomic transitions in Wyoming: the elevation of upper and lower treeline, and the position of the biogeographic boundary between shruband grass-dominated vegetation. By area, the three leading land cover types in Wyoming are Artemisia tridentata ssp. wyomingensis sagebrush (33.4 %), mixed grass prairie (17.5 %) and Pinus contorta forest (6.5 %). Average upper-treeline elevation in Wyoming is 2947 m, and decreases with increasing latitude at an average rate of about 0.5 m/km, less than the rate of about 0.9 m/km reported by Peet (1978) for a gradient from Mexico to Canada. Lower-treeline occurs at an average elevation of 2241 m, and decreases with increasing latitude and with southerly aspect. In Wyoming, shrub-dominated communities are more likely to occur than grass-dominated communities as summer precipitation decreases below 282 mm. All of these relationships are subtle, and it appears that for particular areas, local factors are more important than regional climatic trends in explaining the position of phytogeographic boundaries.

The effect of converting lowland tropical rainforest to pasture, and of subsequent succession of pasture lands to secondary forest, were examined in the Atlantic Zone of Costa Rica. Three replicate sites of each of four land-use types representing this disturbance-recovery sequence were sampled for changes in vegetation, pedological properties, and potential nitrogen mineralization and nitrification. The four land-use types included primary forest, actively grazed pasture (10-36 yr old), abandoned pasture (abandoned 4-10 yr) and secondary forest (abandoned 10-20 yr). Conversion and succession had obvious and significant effects on canopy cover, canopy height, species composition, and species richness; it appeared that succession of secondary forests was proceeding toward a floristic composition like that of the primary forests. Significant changes in soil properties associated with conversion of forest to pasture included: (1) a decrease in acidity and increase in some base exchange properties, (2) and increase in bulk density and a concomitant decrease in porosity, (3) higher concentrations of NH[sub 4][sup +], (4) lower concentrations of NO[sub 3][sup [minus]], (5) lower rates of N-mineralization, and (6) in some cases, lower rates of nitrification. Chemical changes involving cations associated with conversion from forest to pasture indicated increases in soil fertility under the pasturemore » regimes, while changes associated with nitrogen indicated decreases in fertility. Physical changes in density and porosity were deleterious with respect to infiltration, percolation, aeration, and, ultimately, erodability. Beyond the practical aspects of land management, many of these changes are very important to carbon and nitrogen cycling and to the emission and consumption of biogenic trace gases.« less

Watershed 2 of the Hubbard Brook Experimental Forest was experimentally deforested in the winter of 1965-1966, and subsequent plant regeneration was suppressed by herbicide application until the 1969 growing season. Changes in species structure, plant abundance, aboveground primary productivity and biomass, and aboveground nutrient pools were recorded on 70 permanent plots distributed across the watershed during 1, 2, 3, 5, 11, and 20 yr of subsequent succession. Species richness increased rapidly over time but equitability and the Shannon-Wiener diversity index declined with succession. Plant densities of herb, shrub, sapling, and tree strata increased, then decreased, in successive waves as the vegetation increased in height. Basal area (stems >5.1 cm dbh) initially increased exponentially, then linearly after the 5th yr to attain a total of 18.7 m2/ha by the 20th yr. Primary productivity also increased exponentially at first, but then increased linearly through the 20th yr at which time annual aboveground primary productivity was 20 Mg/ha. Aboveground biomass increased linearly after the 5th yr until by the 20th yr it was 52 Mg/ ha, 38% of the reference forest biomass. Aboveground nutrient pools of some elements accumulated faster than biomass by the 20th yr when calculated as percentages of the 55-yr-old reference forest pools and biomass. These included: potassium-52%, phosphorus-44%, magnesium-42%. Others accu- mulated more slowly than biomass: sulfur-32%, and nitrogen and calcium each-29%. While recovery rate on Watershed 2 was delayed in the first decade of regrowth, and composition was somewhat altered because of the 3-yr suppression, this forest nevertheless displayed a vigorous capacity for regeneration after suppression ceased.

[1] Measurements of net CO2 flux density (μmol m−2 s−1) from a high elevation, sagebrush steppe community in southeastern Wyoming (USA) were compared quantitatively among four different instrument systems (leaf cuvette and 1 m2 community chamber for gas exchange measurements; tower and aircraft eddy covariance systems) by minimizing spatial and temporal variability. Ground-based flux measurements were recorded at an intensive site located near the midpoint and directly beneath an approximate 20-km flight transect. A high degree of homogeneity in plant species composition, density, cover, and the amount of leaf area per unit ground area, as well as little topographic variability, was measured at the intensive site and along the flight transect. Flux measurements were compared on days with relatively high and low soil moisture availability (predawn plant water potentials >−0.8 MPa and

[1] Mean midday values of eddy covariance CO2 flux and absorbed photosynthetically active radiation (APAR), derived from solar irradiance and normalized difference vegetation index (NDVI), were measured from May to September 1999 with an aircraft at 60–90 m above ground level over three different ecosystems dominated by native plant species in southeastern Wyoming (mixed conifer forest, mixed short-grass prairie, and sagebrush shrubland). The midday net CO2 uptake at each site followed seasonal trends, with summer values occurring later over the forest than over the other sites. At the landscape scale, linear relationships were observed between CO2 uptake and APAR for the grassland and shrubland, with increasing APAR leading to increasing CO2 uptake. Over the forest, however, the CO2 uptake was only weakly related to APAR, but an additional linear relationship with infrared surface temperature (TIR) implied that respiration may have been more important than APAR in determining net CO2 uptake by the forest. The regression slope for net CO2 uptake versus APAR for the grassland data agreed with those from other observations.

Much is inferred, but little is actually known, about how ecologists view themselves and what they value as scientists. We investigated these attitudes as part of a survey of non-student, U.S.-addressed members of the Ecological Society of America. The part of the survey reported in this paper requested ratings of 15 possible traits of a good ecologist. These traits embodied values associated with religious principles, aesthetics, caring for nature, and epistemic competence (via professional proficiency). The survey was completed by 20% of the potential respondent pool of 6,083 ecologists. The resulting trait scores were analyzed with respect to age, gender, level of education, nature of employment, primary domain of inquiry, principle method of analysis, and source of greatest professional satisfaction. Respondents ranked traits associated with professional proficiency highest and religious principles lowest. Reactions to ethical and aesthetic traits were mixed. With increasing age, rankings for ethical and aesthetic traits increased while scores for some aspects of epistemic proficiency declined. Gender effects were few. Ecologists with BA/BS or MA/MS degrees scored aesthetic and pro-social traits higher and epistemic proficiency traits lower than did PhD degree-holding respondents. Ecologists employed by government, business, or non-profits had uniquely different scoring spectra from one another and from the entire pool. Characterization of values held by ecologists classified by various domains of inquiry, primary methods of analysis, or sources of greatest professional satisfaction was complex. Particularly intriguing was that those who worked in the ecosystem domain, who used modeling and meta-data analysis as methods, or who received the most professional satisfaction from these same activities, exhibited strong support for several epistemic proficiency-related traits, while being relatively negative about traits in the aesthetic and nature-caring categories. These results put some empirical substance and conceptual structures behind perceptions that distinct subcultures exist in U.S. ecology. These results are relevant in three ways. First, they provide a framework by which individual ecologists may become aware of the motivations that drive them, the values that shape their attitudes, and the source and meaning of their professional priorities. Second, these results challenge mentors to be mindful of how they guide young ecologists in the development of their own values and priorities. Third, these results inform the leadership of professional organizations of the range and variation of positions that their member hold and that are relevant to initiatives the leadership may which to promote.

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.

MEASUREMENTS of the flux of nitrous oxide―an important green-house gas―from recently formed pasture in the Amazon basin have shown a threefold increase relative to the flux from the original forest soil1. Based on these measurements, Luizao et a1.1 esti-mated that present rates of conversion from forest to pasture supply up to 1 Tg of N2O—N to the atmosphere each year, corresponding to ≤25 % of the current imbalance between sources and sinks of this gas. But this estimate assumes that such conversion produces elevated fluxes that remain constant in time. To assess the validity of this assumption, we present measurements of tracegas fluxes from Costa Rican pastures of varying ages. Nitrogen oxide fluxes peak during the first ten years after conversion, but decline thereafter to values that are even lower than the original forest fluxes. We conclude that previous studies have overestimated the contribution of pastures to the global budget of nitrous oxide, and that accurate predictions of soil-atmosphere tracegas fluxes will require a detailed knowledge not only of current land use, but also of landuse history.

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.

[1] The humid tropical zone is a major source area for N2O and NO emissions to the atmosphere. Local emission rates vary widely with local conditions, particularly land use practices which swiftly change with expanding settlement and changing market conditions. The combination of wide variation in emission rates and rapidly changing land use make regional estimation and future prediction of biogenic trace gas emission particularly difficult. This study estimates contemporary, historical, and future N2O and NO emissions from 0.5 million ha of northeastern Costa Rica, a well-documented region in the wet tropics undergoing rapid agricultural development. Estimates were derived by linking spatially distributed environmental data with an ecosystem simulation model in an ensemble estimation approach that incorporates the variance and covariance of spatially distributed driving variables. Results include measures of variance for regional emissions. The formation and aging of pastures from forest provided most of the past temporal change in N2O and NO flux in this region; future changes will be controlled by the degree of nitrogen fertilizer application and extent of intensively managed croplands.

The fluxes of water and chemicals in throughfall and stemflow of three subalpine balsam fir forests of New Hampshire, USA were measured. The three fir stands were highly dissimilar in structural characteristics, serving as a test of the importance of stand structure on these fluxes. The sum of throughfall and stemflow water exceeded incident precipitation by more than 18 to 29%. This difference was attributed to the unmeasured input of cloud droplets impacted on canopy surfaces. The principal effect of stand structure was a positive relationship between stand density and stemflow. The flux of NH+4, Na+, SO=4 and Cl− in stemflow was also significantly higher in the most dense stand. The fir canopy effects on capture and chemical alterations of elements were compared with analogous behavior of a nearby deciduous forest. There were several major contrasts, the most striking of which was a flux/canopy pool ratio (leachability index) in the hardwood canopy ranging from two to 32 times higher than in the fir canopy.

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

Changes in species composition, cover, biomass, and elemental pools in space and time were determined for epiphytic lichens associated with balsam fir (Abies balsamea (L.) Mill.) forests on Mt. Moosilauke, New Hampshire, USA. Thirty-three species of epiphytic lichens were present; none was able to fix atmospheric nitrogen. Between 45 and 94% of the total lichen flora occurred in any given stand. Hypogymnia physodes, H. krogii, Bacidia chlorococca, Platismatia glauca, Hypotrachyna revoluta, and Parmelia saxatilis were the leading dominants in all stands and accounted for 74-93% of the bole cover. Each species exhibited an individualistic pattern of vertical distribution. Lichen cover was least in the lower part of the bole (

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.

A systematic examination of nitrogen cycling in disturbed forest ecosystems demonstrates that eight processes, operating at three stages in the nitrogen cycle, could delay or prevent solution losses of nitrate from disturbed forests. An experimental and comparative study of nitrate losses from trenched plots in 19 forest sites throughout the United States suggests that four of these processes (nitrogen uptake by regrowing vegetation, nitrogen immobilization, lags in nitrification, and a lack of water for nitrate transport) are the most important in practice. The net effect of all of these processes except uptake by regrowing vegetation is insufficient to prevent or delay losses from relatively fertile sites, and hence such sites have the potential for very high nitrate losses following disturbance.

Vitousek & Reiners (158) have suggested that change in net ecosystem production is a major determinant of the balance between inputs and out­ puts of elements in terrestrial ecosystems. They argued that in the course of primary succession element outputs are initially relatively high (approx­ imating inputs), that they then drop to a minimum because of element accumulation in biomass and detritus when net ecosystem production is highest, and that eventually output rates rise again approximately to equal inputs in late succession when net ecosystem production approaches zero (Figure 1). In most cases of secondary succession, net ecosystem production is negative immediately following disturbance, and in such cases output rates can exceed input rates. The probable importance of change in net ecosystem production is supported in particular by observations of higher element outputs from later successional ecosystems (22, 90, 1'57-159) and

The controls of potential nitrogen mineralization, nitrate production, and nitrate mo- bilization in a wide range of forest ecosystems were investigated through a combination of field and laboratory experiments. Trenched plot experiments were performed in 17 forests, and laboratory incubation studies of potential ammonium and nitrate production were made on soils from 14 of these sites. The site with the greatest potential for nitrate production in the laboratory was a New Hampshire northern hardwoods forest. Several other sites, including New Hampshire balsam fir, Indiana maple- beech, New Mexico aspen, and Oregon western hemlock forests, also had high potential nitrate production. All of these sites also had rapid nitrate movement to below the rooting zone following trenching in the field. Of nine processes which could be important in preventing or delaying solution losses of nitrate from disturbed forests, two appeared most important among the forests we examined. Low net nitrogen mineralization (caused by either nitrogen immobilization or low gross nitrogen mineralization) and lags in nitrification (probably caused by either low initial populations of nitrifying bacteria or the allelochemic inhibition of nitrification) were identified as important in several sites and in different regions. A direct relationship between the amount of nitrogen in annual litterfall and the proportion of forest floor nitrogen mineralized in laboratory incubations was observed, suggesting that refractory organic nitrogen compounds are produced in nitrogen-poor sites. An inverse relationship was found between the amount of nitrogen in litterfall in these and other sites and the carbon:nitrogen ratio of that litterfall, suggesting that the immobilization capacity of litter is increased in nitrogen-poor sites. The presence and length of lags in nitrification were inversely correlated with the mean concentration of mineral nitrogen in mineral soil. These patterns suggest that nitrogen retention within disturbed forest ecosystems can be caused by low nitrogen availability prior to disturbance.

The capture efficiencies of balsam fir [Abies balsamea (L.) Mill] canopy components for monodisperse glycerin droplets were measured in a low-speed wind tunnel. Droplets were produced at sizes and wind speeds typical of cloudy conditions in a windy, subalpine environment. Capture efficiencies (CE) were evaluated on the basis of the Stokes number (STK) (an inertia parameter). Regression analyses produced a cubic equation relating CE to the independent variable, STK, with an R2 of 0.78. The data demonstrated a decline in CE when STK > 10, a departure from current theory. Droplet re-entrainment is suggested as a possible cause for this behavior. The utility of these data for modeling cloud droplet deposition is discussed.

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.

Atmospheric depositions of water, calcium, magnesium, sodium, potassium, and lead were measured in an Abies balsamea krummholz ecosystem in New Hampshire, U.S.A. Two types of collectors were used. Open buckets captured rainout, washout, and sedimentation (bulk precipitation), while buckets with attached artificial conifer foliage collected intercepted aerosols and cloud droplets as well as bulk precipitation. Water catchment averaged 4.5 times greater in the foliar collectors than in open buckets, and calcium, magnesium, sodium, potassium, and lead deposition averaged 8.3, 6.0, 4.9, 5.7, and 5.5 times greater, respectively, in the foliar collectors. Most of the increase in foliar collectors was due to higher volume catchment but some concentration enrichment through interception was also contributory. These data cannot be extrapolated to elemental deposition per unit area without correcting capture efficiency of collectors to that of natural vegetation. These data do strongly suggest, however, that in areas of high wind and frequent exposure to clouds or fog, such as in montane areas of New England, measurements of total elemental deposition require an evaluation of interception as well as bulk precipitation.

Vegetation structure and dynamics of the upper subalpine or fir zone were studied in the White Mountains of New Hampshire. The fir zone extends from 1220 m, the approximate upper limit of Picea rubens occurrence, to treeline (°1450 m) where it is usually represented by a low krummholz. Live tree density in the part of the zone in which trees are >2 m tall averages 5000 stems/ha. Eighty—four percent of these are Abies balsamea, and most of the rest are Betula papyrifera var. cordifolia. Basal area averages 30 m2/ha; canopy height averages 6.8 m. Stands tend to be dominated by discrete age classes. Tree ages range up to 111 yr (average 55 yr). Fir zone vegetation is subject to a number of processes that lead to a hierarchical set of overlapping patterns. Elevation and wind exposure produce general, or first—order, patterns over the landscape, e.g., canopy height decreases with elevation and exposure. Overlying this general pattern are a series of second—order patterns. Two acute disturbance factors–hurricanes and avalanches–have stamped discrete impressions over the general pattern. Other, more endogenously generated patterns, marks the landscape with more subtle textures. These patterns include fir waves, broken gaps, strips, and glades. A conceptualization of vegetation as a hierarchical series of overlapping patterns is an extension of Watt's view of vegetation dynamics and bears important ecological implications.

The ecosystem level of ecological research is fraught with conceptual difficulties that have contributed to faltering progress in theoretical development. An acceptance of multiple models for different aspects of ecosystems may assist in reducing this confusion. Two complementary models of ecosystems are suggested: the first based on energy, the second based on matter. Whereas the first follows from the second law of thermodynamics, the second complementary model derives from the chemical stoichiometry of the biota. These models can be developed independently but have many points of interaction. These points yield another series of predictions and hypotheses. While these complementary models serve as theoretical structures for much of the body of ecosystem concepts, they are not adequate by themselves. Other complementary models, perhaps centered on explicit linkages at the population and community levels, are necessary.

When sunlight passes through openings in leaf or overstory plant canopies, strong penumbral effects (e.g., penumbral light-spreading) can result in major changes in the total sunlit area, the irradiance level, and exposure duration at the incident surface. These effects are based on well-known optical principles whereby light that originates from a non-point source (e.g., sunlight) and passes through a circular aperture will project an image composed of a bright center portion (numbra) circumscribed by a shadow-edge (penumbra). A hypothetical opening diameter (G) and distance to the incident surface (D) was expressed as the ratio G/D (= GDR) and used to quantify changes in the projected sun spot diameter (Gp) and area (Gparea), and the relative irradiance levels and durations of the numbra and penumbra. When GDR was 80% of the exposure period. Beyond a GDR of 0.05, pen- umbral effects were negligible. Definitions of a sunfleck, sunpatch, gap, and clearing are proposed based on the specific sunlight regimes generated by the corresponding GDR values. These penumbral and latitudinal effects on sunlight penetration through canopy openings are discussed for a variety of leaf canopy and forest overstory types using rep- resentative gap sizes and vegetation heights.

velopment of ecosystems were presented in Odum's very important paper, "The Strategy of Ecosystem Development" (1969). This series of hypotheses has helped to organize thinking on ecosystem dynamics and to focus further research. In this paper, we wish to examine one of these hypotheses, which suggests that as ecosystems mature their ability to conserve nutrients increases. Our objective is to show through logical examination of characteristics of succession, and through presentation of critical field data, that this hypothesis cannot be stated quite so simply. We also intend to show that uncritical utiliza

Decay of balsam fir (Abies balsamea) boles was examined in an upper subalpine forest of the White Mountains, New Hampshire, USA. Fifty percent of the initial mass was lost in 23 yr; 90% was lost in 77 yr. High decay rates were attributed to the small diameters of the boles, ample moisture, and a nitrogen-rich environment. Average dead wood mass in this forest was 4.9 kg/M2, representing 25% of the sum of dead wood, live plant biomass, and forest floor organic matter. Changes in density and moisture and in the concentrations and content of various chemical com- ponents of the boles were traced over the decay sequence. Changes in the content of cellulose, lignin, carbon and sodium followed loss of mass during decay. Contents of calcium, magnesium, potassium and phosphorus decreased faster than loss of mass in the early stages of decay. Much of this initial loss was acribed to sloughing of nutrient-rich bark which in these small boles comprised 13% of dry mass. Later in decay, the loss rates of calcium, magnesium and potassium were about the same or slightly less than the loss rate of mass. After a steep initial drop, phosphorus content of the boles remained approximately constant between years 12 and 33. Thereafter the loss rate paralleled loss of mass. Nitrogen content was approximately constant in the first 33 yr after which it declined in parallel with loss of mass.