ISSN:1051-0761    

DOI:10.2307/1941927

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY

摘要:

The Oregon Transect Ecosystem Research (OTTER) project is a study of ecosystem functions in coniferous forests using the methods of computer modeling, experimental and theoretical remote sensing, and ecological field and laboratory techniques. The study is focused on predicting the major fluxes of carbon, nitrogen, and water, and the factors that dynamically regulate them. The OTTER project was conceived to test two major questions: (1) Can a generalized ecosystem simulation model, designed to use mainly parameters available from remote sensing, predict the functioning of forests across an environmentally variable region? and (2) To what extent can the variables required by this model be derived from remotely sensed data? The scientific objectives and scope of the project demanded that a coordinated effort be made to link ground measurements with remote sensing and modeling requirements. OTTER was selected as a focus for a National Aeronautics and Space Administration (NASA)—sponsored Multi—sensor Aircraft Campaign (MAC; combining NASA aircraft and sensors with those of others) on the basis of experience gained in past ecosystem studies and remote—sensing projects, and the importance of the OTTER objectives to NASA's long—range science goals and plans. Having several independent approaches available, both on the ground and from various remote—sensing platforms, proved valuable in estimating and validating many of the critical variables. This experience and cross comparison should help simplify future studies of a similar nature. Edited data sets from the OTTER project are now available to the scientific community on optical disks or via on—line data banks at NASA (Washington, D.C., USA) and Oregon State University (Corvallis, Oregon, USA).

ISSN:1051-0761    

DOI:10.2307/1941928

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY

摘要:

Due to climate differences, an extreme range in productivity occurs along a 250—km, west—east transect at °44° north latitude in western Oregon, USA, where coniferous evergreen forests dominate. As part of the Oregon Transect Ecosystem Research (OTTER) project, our objective was to evaluate how climate constrains net primary production (NPP) by limiting the utilization of intercepted photosynthetically active radiation (IPAR). The forests measured along the transect intercepted from 22% to 99.5% of the incident PAR. With data collected from recording meteorological stations installed near each site, we defined the hourly conditions when photosynthesis was partly or completely limited by drought, extreme humidity deficits, or frost. From this analysis we calculated that the fraction of incident PAR that could be utilized throughout the year ranged from 92% in the coastal rainforests to<25% in the juniper woodland. NPP varied from 3 to 26 Mg°ha—1°yr—1with the fraction of belowground NPP, estimated from litterfall, increasing from 20% to 60% of the total as the environment becomes harsher. Light—use efficiency (°u) calculated under conditions when the environment did not constrain photosynthesis, averaged 0.8 g/MJ for aboveground NPP and 1.3 g/MJ for total NPP.

ISSN:1051-0761    

DOI:10.2307/1941929

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY

摘要:

Field measurements from the Oregon Transect Ecological Research project (OTTER) were used to validate selected process simulations in the FOREST—BGC ecosystem model. Certain hydrologic, carbon, and nitrogen cycle process simulations were tested in this validation, either comparatively across sites, or seasonally at single sites. The range of simulated ecosystem—process rates across the OTTER sites was large; annual evapotranspiration (ET) ranged from 15 to 82 cm, net photosynthesis (as carbon) from 2.2 to 22.8 Mg/ha, and decomposition (as carbon) from 1.0 to 7.2 Mg°ha—1°yr—1. High correlations between predicted and measured data were found for: aboveground net primary production, R2= 0.82; 100—yr stem biomass, R2= 0.79; and average leaf nitrogen concentration, R2= 0.88. However, correlations for pre—dawn leaf water potential and equilibrium leaf area index (LAI) were much lower, because successful simulation of these variables requires accurate data for soil water—holding capacity. Defining the water—holding capacity of the rooting zone and the maximum surface conductance for photosynthesis and transpiration rates proved to be critical system variables that defied routine field measurement. Although many other processes are simulated in FOREST—BGC, no other processes had repeated field data sets for validations. Problems in parameterizing the model from disparate data sets are also evaluated, with suggestions for using ecosystem modeling in future integrated research programs.

ISSN:1051-0761    

DOI:10.2307/1941930

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY

摘要:

This study tests diurnal climatology assumptions made in the MT—CLIM model by examining two microclimate variables driven by diurnal atmospheric dynamics: incident solar radiation (in kilojoules per square metre), and humidity, expressed as vapor pressure deficit, VPD (in kilopascals). The relative VPD humidity comparison was used to test our hypothesis that night minimum temperatures can function as a surrogate for dew—point temperatures. VPD was chosen as the humidity measure for these tests since plants are more directly sensitive of this measure than relative humidity. For the observed vs. examined vapor pressure deficit models, we obtained coefficients of determination (R2) ranging from 0.66 to 0.84. Incident solar radiation is calculated in the model using an algorithm that relates diurnal temperature amplitude to atmospheric transmissivity, coupled with a potential radiation model to compute diffuse and direct radiation. Correlations for incident solar radiation models indicate generally good agreement, with coefficients of determination ranging from R2= 0.82 to 0.89. These results suggest that MT—CLIM may be a useful way to provide the climatology that many ecological/hydrological models require, particularly for larger scale spatial modeling applications where precise meteorology may not be as important as a good general characterization of the regional climatology.

ISSN:1051-0761    

DOI:10.2307/1941931

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY

摘要:

Remotely sensed data acquired from four remote—sensing instruments on three different aircraft platforms over a transect of coniferous forest stands in Oregon were analyzed with respect to seasonal leaf area index (LAI). Data from the four instruments were corrected for the varying seasonal and geographic atmospheric conditions present along the transect. Strong logarithmic relationships were observed between seasonal maximum and minimum LAI and the simple ratio (SR) (near infrared/red reflectance) calculated from the broad—spectral—band Thematic Mapper Simulator (TMS), as well as from the narrow—spectral—band Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), the Compact Airborne Spectrographic Imager (CASI), and the Spectrom SE590 spectro—radiometer (R2= 0.82—0.97). The TMS SR reached an asymptote at an LAI of °7—8. However, the SE590 and the CASI SR continued to increase up to the maximum LAI of 10.6. The variability of the relationship between the AVIRIS SR and LAI increased at stands with LAIs>7, making a trend in the AVIRIS SR—LAI relationship at LAIs>7 difficult to discern. The SRs of the coniferous forest stands measured by the narrow—spectral—band instruments were higher than they were from the broad—spectral—band TMS. This is attributed partially to the integration of the TMS over a broad wavelength region in the red and more strongly to calibration differences between the sensors. Seasonal TMS SR trends for four time periods for some of the stands deviated from the expected seasonal LAI trends, possibly because of smoke and very low sun angles during some of the acquisition periods. However, the expected SR differences for the seasonal minimum and maximum LAI were observed for all of the sensors for nearly all of the forest stands. This study demonstrates that remotely sensed data from both broad— and narrow—spectral—band instruments can provide estimates of LAI for use in forest ecosystem simulation models to estimate evapotranspiration, photosynthesis, canopy turnover, and net primary production over large areas.

ISSN:1051-0761    

DOI:10.2307/1941932

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY

摘要:

To estimate leaf area index (LAI), intercepted radiation, and other related characteristics of vegetation, ecologists often require separate consideration of the understory and overstory components of vegetation. In the open ponderosa pine (Pinus ponderosa) forests of east—central Oregon, bitterbrush (Purshia tridentata) and manzanita (Arctostaphylos patula) are major understory species. We constructed artificial canopies of these two species and determined whether remotely sensed properties of canopy reflectance might be used to estimate LAI and the fraction of photosynthetically active radiation intercepted (fIPAR). Although the two species differed in their canopy structures and leaf characteristics, they showed similar light extinction coefficients, varying only from 0.52 for bitterbrush to 0.46 for manzanita as derived from the Beer—Lambert Law. The relationship between fIPARand LAI was asymptotic at an LAI of 6 for both species. The normalized—difference vegetation index (NDVI) provided a good linear estimate of fIPAR(R2= 0.86 for manzanita and 0.83 for bitterbrush), and the simple ratio of near infrared to red (SR) permitted a linear estimate of LAI (R2= 0.86 for manzanita and 0.74 for bitterbrush) of this vegetation growing on soils with uniform reflectance properties. Aerial estimates of overstory and understory cover derived from aircraft or satellites provide a basis for assessing the proportional contribution of understory shrub cover to the total vegetation, given that basic relationships between spectral reflectance, LAI, and fIPARhave been established, as in this study.

ISSN:1051-0761    

DOI:10.2307/1941933

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY

摘要:

We examined seasonal changes in canopy chemical concentrations and content in conifer forests growing along a climate gradient in western Oregon, as part of the Oregon Transect Ecosystem Research (OTTER) study. The chemical variables were related to seasonal patterns of growth and production. Statistical comparisons of chemical variables with data collected from two different airborne remote—sensing platforms were also carried out. Total nitrogen (N) concentrations in foliage varied significantly both seasonally and among sites; when expressed as content in the forest canopy, nitrogen varied to a much greater extent and was significantly related to aboveground net primary production (r = 0.99). Chlorophyll and free amino acid concentrations varied more strongly than did total N and may have reflected changes in physiological demands for N. Large variations in starch concentrations were measured from pre— to post—budbreak in all conifer sites. Examination of remote—sensing data from two different airborne instruments suggests the potential for remote measurement of some canopy chemicals. Multivariate analysis of high—resolution spectral data in the near infrared region indicated significant correlations between spectral signals and N concentration and canopy N content; the correlation with canopy N content was stronger and was probably associated in part with water absorption features of the forest canopy. The spectral bands that were significantly correlated with lignin concentration and content were similar to bands selected in the other laboratory and airborne studies; starch concentrations were not significantly related to spectral reflectance data. Strong relationships between the spectral position of specific features in the visible region and chlorophyll were also found.

ISSN:1051-0761    

DOI:10.2307/1941934

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY

摘要:

In this paper, we invert a canopy reflectance model using multispectral satellite data in order to estimate remotely the parameters of crown size, tree count density, cover, foliage biomass, and total standing biomass for nine coniferous forest stands on a transect of western and central Oregon (USA). Issues involved in the inversion of the model are topographic correction, component signature estimation, spatial pattern analysis, and direct biomass estimation. Retrieved parameters correlate well with observed values from ground measurements of the test sites. The model inversion technique is a useful tool for mapping and timber inventory of forests at large scales.

ISSN:1051-0761    

DOI:10.2307/1941935

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY

摘要:

Specific leaf area (SLA) is an important link between vegetation water and carbon cycles because it describes the allocation of leaf biomass per unit of leaf area. Several studies in many vegetation types have shown that canopy SLA is closely related to canopy leaf nitrogen (N) content and photosynthetic capacity. SLA increases as light is attenuated by leaf area down through a plant canopy. It therefore follows that across an individual biome the spatial patterns in canopy—average SLA and leaf N content should be significantly correlated with the spatial patterns in leaf area index (LAI) and canopy transmittance. In this paper, we show that the LAI across the Oregon transect is closely related to canopy—average SLA (R2= 0.82) and leaf N content on a mass basis (R2= 0.80). Canopy—average leaf N per unit area is highly correlated to canopy transmittance (R2= 0.94) across the transect. At any given site, canopy—average SLA and leaf N per unit area do not vary significantly, either seasonally or between different codominant species occupying the same site. The results of this study suggest that the spatial distribution of canopy—average SLA and leaf nitrogen content (and perhaps canopy photosynthetic capacity) can be predicted across biomes from satellite estimates of LAI.

ISSN:1051-0761    

DOI:10.2307/1941936

出版商:Ecological Society of America    

年代:1994

数据来源: WILEY