Regional-scale Patterns Research Articles

Sensitivity of boreal forest regional water flux and net primary production simulations to sub‐grid‐scale land cover complexity

We use a general ecosystem process model (BIOME‐BGC) coupled with remote sensing information to evaluate the sensitivity of boreal forest regional evapotranspiration (ET) and net primary production (NPP) to land cover spatial scale. Simulations were conducted over a 3 year period (1994–1996) at spatial scales ranging from 30 to 50 km within the BOREAS southern modeling subarea. Simulated fluxes were spatially complex, ranging from 0.1 to 3.9 Mg C ha−1 yr−1 and from 18 to 29 cm yr−1. Biomass and leaf area index heterogeneity predominantly controlled this complexity, while biophysical differences between deciduous and coniferous vegetation were of secondary importance. Spatial aggregation of land cover characteristics resulted in mean monthly NPP estimation bias from 25 to 48% (0.11–0.20 g C m−2 d−1) and annual estimation errors from 2 to 14% (0.04–0.31 Mg C ha−1 yr−1). Error was reduced at longer time intervals because coarse scale overestimation errors during spring were partially offset by underestimation of fine scale results during summer and winter. ET was relatively insensitive to land cover spatial scale with an average bias of less than 5% (0.04 kg m−2 d−1). Factors responsible for differences in scaling behavior between ET and NPP included compensating errors for ET calculations and boreal forest spatial and temporal NPP complexity. Careful consideration of landscape spatial and temporal heterogeneity is necessary to identify and mitigate potential error sources when using plot scale information to understand regional scale patterns. Remote sensing data integrated within an ecological process model framework provides an efficient mechanism to evaluate scaling behavior, interpret patterns in coarse resolution data, and identify appropriate scales of operation for various processes.

Upper-level steering flow and continental anticyclones on the central Gulf Coast of the United States

In a previous paper, trends in weather types dominated by continental anticyclones over the central Gulf Coast of the United States were analyzed. These events were found to be decreasing in frequency from 1961 to 1989. Magnitudes of some individual surface atmospheric variables during these events also changed significantly over this period even though the air masses represented did not change significantly. In this paper, the geography of 500 hPa height variability and steering flow patterns are examined in periods preceding such events in New Orleans in order to explain the forcing mechanisms that may be producing the observed frequency and intensity changes. Results indicate that the meridional gradient of atmospheric mass between the subtropics and extratropics may have increased over time, and consequently the increased zonal flow may have contributed to the relative paucity of continental anticyclone days in recent years. The zonality/meridionality of the flow and the extent of the circumpolar vortex over the region both appear to be related to the observed frequency shift. Furthermore, variability in the 500 hPa flow appears to be linked to the surface weather variability that was previously observed. These results are important in identifying the degree of scale interaction between upper-level, hemispheric-scale flow and local- to regional-scale surface weather patterns. © 1998 Royal Meteorological Society

Regional Gradient Analysis and Spatial Pattern of Woody Plant Communities of Oregon Forests

Knowledge of regional-scale patterns of ecological community structure, and of factors that control them, is largely conceptual. Regional- and local-scale factors associated with regional variation in community composition have not been quantified. We analyzed data on woody plant species abundance from 2443 field plots across natural and seminatural forests and woodlands of Oregon to identify and quantify environmental, biotic, and disturbance factors associated with regional gradients of woody species composition; to examine how these factors change with scale (geographic extent) and location; and to characterize and map geographic patterns of species and environmental gradients. Environmental correlates of species gradients, species diversity patterns, and the spatial patterning of woody plant communities varied with geographic extent and location. Total variation explained (TVE) by canonical correspondence analyses (CCAs) was 9–15% at three hierarchical geographic extents: the entire state, two half-states, and five subregions. Our high level of unexplained species variation is typical of vegetation gradient analyses, which has been attributed to landscape effects, stochastic processes, and unpredictable historical events. In addition, we found that TVE in canonical correspondence analysis is confounded by sample size. Large numbers of plots and species, as in our study, are associated with lower TVEs, and we propose a mechanism for this phenomenon. Climate contributed most to TVE (46–60%) at all locations and extents, followed by geology (11–19%), disturbance (6–12%), and topography (4–8%). Seasonal variability and extremes in climate were more important in explaining species gradients than were mean annual climatic conditions. In addition, species gradients were more strongly associated with climatic conditions during the growing season than in winter. The dominant gradient at the state scale was from the lower elevation, moderate, maritime climate along the coast to the higher elevation, drier, continental climate of eastern Oregon. The second canonical axis followed a gradient from the warm, dry, growing seasons of the western interior valleys and eastern Cascade Range to the cooler, wetter mountainous areas. Geologic variables were most strongly correlated with axis 3, and measures of local site and disturbance with axis 4. For most of the state, our findings on the associations of disturbance factors with species gradients were inconclusive due to confounding of land ownership patterns, disturbance histories, and elevation in our sample. Near the coast, where gradients were not confounded, clear-cutting and stand age accounted for only 2 and 1% of TVE, respectively, in partial CCA. Ordinations of our long, regional gradients were influenced more by species presence than by abundance, and few woody species have been totally eliminated from sites by clear-cutting. Within Oregon and for the range of geographic extents we examined, variation in the environmental correlates of species gradients was more strongly associated with geographic location than with geographic extent, although topographic factors explained slightly more variation at smaller geographic extents. The greatest subregional contrast in vegetation character was between eastern and northwestern Oregon, and the Klamath subregion was intermediate. In the drier climate of eastern Oregon, community structure varied at a finer spatial scale, and climatic and topographic moisture were more strongly associated with species gradients than in the moister areas of western Oregon. Topographic effects were weakest and climatic effects strongest near the coast, where climate is moderate. Alpha and gamma diversity were greater in western Oregon, but beta diversity was greater in eastern Oregon and greater for shrubs than for trees. Our findings supported a conceptual model of multiscaled controls on vegetation distribution, and the related notion that local community structure is the result of both regional- and local-scale processes. Despite strong ecological contrasts within the region, we were able to synthesize species–environment relations at the regional level. This suggests that apparent conflicts among local vegetation studies can be explained by real ecological differences among places.

REGIONAL GRADIENT ANALYSIS AND SPATIAL PATTERN OF WOODY PLANT COMMUNITIES OF OREGON FORESTS

Knowledge of regional-scale patterns of ecological community structure, and of factors that control them, is largely conceptual. Regional- and local-scale factors associated with regional variation in community composition have not been quantified. We analyzed data on woody plant species abundance from 2443 field plots across natural and seminatural forests and woodlands of Oregon to identify and quantify environmental, biotic, and disturbance factors associated with regional gradients of woody species composition; to examine how these factors change with scale (geographic extent) and location; and to characterize and map geographic patterns of species and environmental gradients. Environmental correlates of species gradients, species diversity patterns, and the spatial patterning of woody plant communities varied with geographic extent and location. Total variation explained (TVE) by canonical correspondence analyses (CCAs) was 9–15% at three hierarchical geographic extents: the entire state, two half-states, and five subregions. Our high level of unexplained species variation is typical of vegetation gradient analyses, which has been attributed to landscape effects, stochastic processes, and unpredictable historical events. In addition, we found that TVE in canonical correspondence analysis is confounded by sample size. Large numbers of plots and species, as in our study, are associated with lower TVEs, and we propose a mechanism for this phenomenon. Climate contributed most to TVE (46–60%) at all locations and extents, followed by geology (11–19%), disturbance (6–12%), and topography (4–8%). Seasonal variability and extremes in climate were more important in explaining species gradients than were mean annual climatic conditions. In addition, species gradients were more strongly associated with climatic conditions during the growing season than in winter. The dominant gradient at the state scale was from the lower elevation, moderate, maritime climate along the coast to the higher elevation, drier, continental climate of eastern Oregon. The second canonical axis followed a gradient from the warm, dry, growing seasons of the western interior valleys and eastern Cascade Range to the cooler, wetter mountainous areas. Geologic variables were most strongly correlated with axis 3, and measures of local site and disturbance with axis 4. For most of the state, our findings on the associations of disturbance factors with species gradients were inconclusive due to confounding of land ownership patterns, disturbance histories, and elevation in our sample. Near the coast, where gradients were not confounded, clear-cutting and stand age accounted for only 2 and 1% of TVE, respectively, in partial CCA. Ordinations of our long, regional gradients were influenced more by species presence than by abundance, and few woody species have been totally eliminated from sites by clear-cutting. Within Oregon and for the range of geographic extents we examined, variation in the environmental correlates of species gradients was more strongly associated with geographic location than with geographic extent, although topographic factors explained slightly more variation at smaller geographic extents. The greatest subregional contrast in vegetation character was between eastern and northwestern Oregon, and the Klamath subregion was intermediate. In the drier climate of eastern Oregon, community structure varied at a finer spatial scale, and climatic and topographic moisture were more strongly associated with species gradients than in the moister areas of western Oregon. Topographic effects were weakest and climatic effects strongest near the coast, where climate is moderate. Alpha and gamma diversity were greater in western Oregon, but beta diversity was greater in eastern Oregon and greater for shrubs than for trees. Our findings supported a conceptual model of multiscaled controls on vegetation distribution, and the related notion that local community structure is the result of both regional- and local-scale processes. Despite strong ecological contrasts within the region, we were able to synthesize species–environment relations at the regional level. This suggests that apparent conflicts among local vegetation studies can be explained by real ecological differences among places.

Extreme temperature days in the south-central United States

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 08:151-162 (1997) - DOI: https://doi.org/10.3354/cr008151 Extreme temperature days in the south-central United States Henderson KG, Muller RA Extreme temperature days in the south-central United States can have significant impacts on energy demand, agriculture, and human comfort. In this paper an extreme day is defined as a day that exceeds 1 standard deviation of the long-term average temperature for that day. Using this methodology, similar numbers of extreme days are found to occur in each season. Sixteen stations are selected from the Historical Climate Network Daily (HCN/D) record to represent conditions across a 6-state region. Significant interseasonal and interannual variability are found in the time-series of extreme days at all stations. In winter approximately 10 to 15 warm and cold days occur each year. However, neither type of event persists for long periods of time. This pattern is indicative of the vigorous atmospheric circulation that moves fronts and air masses through the midlatitudes during this season. Winters with a high frequency of cold days are associated with large-scale meridional circulation over North America, while zonal flow in winter produces more frequent warm days. In summer cold days occur regularly each year but cold events are short-lived. Warm events, however, follow a very different pattern. Warm day frequency is much more variable in the summer, and warm events tend to persist for longer periods of time when they do occur. Large-scale circulation differences between summers with frequent warm and cold days are weak, indicating that regional-scale patterns of subtropical flow and the expansion of the Atlantic Subtropical High are most likely important forcing factors in summer. Over this century there is a long-term trend toward more frequent cold days in all seasons. However, this trend may be reversing in the past decade. Extreme temperature · Climate variability · South-central United States Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 08, No. 2. Publication date: May 08, 1997 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 1997 Inter-Research.

Atmospheric Deposition of Nutrients and Pollutants in North America: An Ecological Perspective

Research on air pollution and acidic deposition during the last 15 yr has greatly increased our knowledge of the rates and the processes of atmospheric deposition. The invigoration of the field has been a direct result of interchange and cooperation among ecosystem ecologists, micrometeorologists, and plant physiological ecologists who each approach the study of atmospheric deposition from different perspectives. This has led to the widespread realization among ecologists of the importance of dry and cloud deposition and the introduction of new methods to estimate these fluxes. In this paper I summarize the current understanding of atmospheric deposition processes, measurement methods, and patterns of deposition in North America. Dry deposition measurements are still highly uncertain in most cases, and methodology is still an active area of research and debate, but it seems clear that ecologists will require a suite of different methods to evaluate dry deposition fluxes of the various elements important to ecosystems. Standard model formulations have been developed for estimating dry and cloud deposition, and these models are finding wide use in flux estimation at sites where direct measurements are unavailable. National monitoring networks for wet and dry deposition have been established and are providing information on continental— and regional—scale patterns. Research has demonstrated that deposition rates are increased substantially at high—elevation sites by enhancement of wet, dry, and especially, cloud deposition. Patterns of O3 exposure are also different at high—elevation sites. The deposition of O3, while mechanistically similar to that of other gases, has been treated differently in the ecological and botanical literature because of its direct phytotoxicity at ambient concentrations in industrialized areas. Current efforts in ozone exposure research involve determining appropriate exposure indices for interpreting biological responses and coupling models of atmospheric transport with models of ozone disposition within the plant.

Aspects of Regional-Scale Flows in Mountainous Terrain

Abstract Mountaintop data from remote stations in the central Rocky Mountains have been used to analyze terrain-induced regional (meso-β to meso-α) scale circulation patterns. The circulation consists of a diurnally oscillating wind regime, varying between daytime inflow toward, and nocturnal outflow from, the highest terrain. Both individual case days and longer term averages reveal these circulation characteristics. The persistence and broadscale organization of nocturnal outflow at mountaintop, well removed from valley drainage processes, demonstrates that this flow is part of a distinct regime within the hierarchy of terrain-induced wind systems. The diurnal cycle of summertime convective storm development imparts a strong influence upon regional-scale circulation patterns. Subcloud cooling processes, associated with deep moist convection, alter the circulation by producing early and abrupt shifts in the regional winds from an inflow to outflow direction. These wind events occur frequently when moist ...