JSTOR CITATION LIST Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms & Conditions of Use http://www.jstor.org/about/terms.html For questions, please contact support@jstor.org NUMBER OF CITATIONS : 6 -------------------------------------------------------------------------------- 1. Title: Remote Sensing of Forest Biophysical Structure Using Mixture Decomposition and Geometric Reflectance Models Author(s): Forrest G. Hall; Yosio E. Shimabukuro; Karl F. Huemmrich Source: Ecological Applications, Vol. 5, No. 4. (Nov., 1995), pp. 993-1013. Stable URL: http://links.jstor.org/sici?sici=1051-0761%28199511%295%3A4%3C993%3ARSOFBS%3E2.0.CO%3B2-I Abstract: Using geometric shadow and linear mixture models we develop and evaluate an algorithm to infer several important structural parameters of stands of black spruce (Picea mariana), the most common boreal forest dominant. We show, first, that stand reflectances for this species can be represented as linear combinations of the reflectances of more elemental radiometric components: sunlit crowns, sunlit background, and shadow. Secondly, using a geometric model, we calculate how the fractions of these radiometric elements covary with each other. Then, using hand-held measurements of the reflectances of the sunlit background, sphagnum moss (Sphagnum spp.), and assuming shadow reflectance to be that of deep, clear lakes, we infer the reflectance of sunlit crowns from the geometric shadow model and low-altitude reflectance measurements acquired by a helicopter-mounted radiometer. Next, we assume that the reflectance for all black spruce stands is simply a linear combination of shadow, sunlit crown, and sunlit background reflectance, weighted in proportion to the relative areal fractions of these pixel elements. We then solve a set of linear equations for the areal fractions of these elements using as input helicopter observations of total stand reflectance. Using this algorithm, we infer the values for the areal proportions of sunlit canopy, sunlit background, and shadow for 31 black spruce stands of varying biomass density, net primary productivity, etc. We show empirically and theoretically that the areal proportions of these radiometric elements are related to a number of stand biophysical characteristics. Specifically, the shadow fraction is increasing with increasing biomass density, average diameter at breast height, leaf area index (LAI), and aboveground net primary productivity (NPP), while sunlit background fraction is decreasing. We show that the end member fractions can be used to estimate biomass with a standard error of $\approx$ 2 kg/m$^2$, LAI with a standard error of 0.58, dbh with a standard error of $\approx$ 2 cm, and aboveground NPP with a standard error of 0.07 $\mathrm{kg}\cdot \mathrm{m}^{-2}\cdot \mathrm{yr}$^{-1}$. We also show that the fraction of sunlit canopy is only weakly correlated with the biophysical variables and are thus able to show why a popular vegetation index, Normalized Difference Vegetation Index (NDVI), does not provide a useful measure of these biophysical characteristics. We do show, however, that NDVI should be related to the fraction of photosynthetically active radiation incident upon and absorbed by the canopy. This work has convinced us that a paradigm shift in the remote sensing of biophysical characteristics is in order--a shift away from direct inference of biophysical characteristics from vegetation indices and toward a two-step process, in which (1) stand-level reflectance is approximated in terms of linear combinations of reflectance-invariant, spectrally distinct components (spectral end members) and mixture decomposition used to infer the areal fractions of these components, e.g., shadow, sunlit crown, and sunlit background, followed by (2) the use of radiative transfer models to compute biophysical characteristic values as a function of the end member fractions. 2. Title: Global Primary Production: A Remote Sensing Approach Author(s): Stephen D. Prince; Samuel N. Goward Source: Journal of Biogeography, Vol. 22, No. 4/5, Terrestrial Ecosystem Interactions with Global Change, Volume 2. (Jul. - Sep., 1995), pp. 815-835. Stable URL: http://links.jstor.org/sici?sici=0305-0270%28199507%2F09%2922%3A4%2F5%3C815%3AGPPARS%3E2.0.CO%3B2-G Abstract: A new model of global primary production (GLObal Production Efficiency Model, GLO-PEM), based on the production efficiency concept, is decribed. GLO-PEM is the first attempt to model both global net and gross primary production using the production efficiency approach and is unique in that it uses satellite data to measure both absorption of photosynthetically active radiation (APAR) and also the environmrntal variables that affect the utilization of APAR in primary production. The use of satellite measurements gives global, repetitive, spatially contiguous and time specific observations of the actual vegetation. GLO-PEM is based on physiological principles, in particular the amount of carbon fixed per unit absorbed photosynthetically active radiation $(\varepsilon)$ is modelled rather than fitted using field observations. GLO-PEM is illustrated with the first available year (1987) of the $8\times 8 km$ resolution NOAA/NASA AVHRR land Pathfinder data set. The global net primary production, respiration and $\varepsilon$ values obtained indicate that even the rather simple AVHRR provides a wealth of information relevant to biospheric monitoring. The algorithms and results presented indicate that there are significant possibilities of inferring biological and environmental variables using multispectral techniques that need to be explored if the new generation of satellite remote sensing systems is to be exploited productively. 3. Title: Combining Remote Sensing and Climatic Data to Estimate Net Primary Production Across Oregon Author(s): Beverly E. Law; Richard H. Waring Source: Ecological Applications, Vol. 4, No. 4. (Nov., 1994), pp. 717-728. Stable URL: http://links.jstor.org/sici?sici=1051-0761%28199411%294%3A4%3C717%3ACRSACD%3E2.0.CO%3B2-4 Abstract: A range in productivity and climate exists along an east-west transect in Oregon. Remote sensing and climatic data for several of the Oregon Transect Ecosystem Research Project (OTTER) forested sites and neighboring shrub sites were combined to determined whether percentage intercepted photosynthetically active radiation (%IPAR) can be estimated from remotely sensed observations and to evaluate climatic constraints on the ability of vegetation to utilize intercepted of radition for production. The Thematic Mappers Simulator (TMS) normalized difference vegetation index (NDVI) provided a good linear estimate of %IPAR (R^2 = 0.97). Vegetation intercepted from 24.8% to 99.9% of incident photosynthetically active radiation (PAR), and aboveground net primary production (ANPP) ranged from 53 to 1310 g@?m^-^2@?yr^-^1. The ANPP was linearly related to annual IPAR across sites (R^2 = 0.70). Constraints on the ability of each species to utilize intercepted light, as defined by differential responses to freezing temperatures, drought, and vapor pressure deficit, were quantified from hourly meteorological station measurements near the sites and field physiological measurements. Vegetation could utilize from 30% of intercepted radiation at the eastside semiarid juniper woodland and shrub sites to 97% at the maritime coastal sites. Energy-size efficiency (@d@m), calculated from aboveground production and IPAR modified by the environmental limits, averaged 0.5 g/MJ for the shrub sites and 0.9 g/MJ for the forested sites. 4. Title: Climatic and Biotic Controls on Annual Carbon Storage in Amazonian Ecosystems Author(s): H. Tian; J. M. Melillo; D. W. Kicklighter; A. D. McGuire; J. Helfrich III; B. Moore III; C. J. Vorosmarty Source: Global Ecology and Biogeography, Vol. 9, No. 4. (Jul., 2000), pp. 315-335. Stable URL: http://links.jstor.org/sici?sici=1466-822X%28200007%299%3A4%3C315%3ACABCOA%3E2.0.CO%3B2-1 Abstract: 1 The role of undisturbed tropical land ecosystems in the global carbon budget is not well understood. It has been suggested that interannual climate variability can affect the capacity of these ecosystems to store carbon in the short term. In this paper, we use a transient version of the Terrestrial Ecosystem Model (TEM) to estimate annual carbon storage in undisturbed Amazonian ecosystems during the period 1980-94, and to understand the underlying causes of the year-to-year variations in net carbon storage for this region. 2 We estimate that the total carbon storage in the undisturbed ecosystems of the Amazon Basin in 1980 was 127.6 Pg C, with about 94.3 Pg C in vegetation and 33.3 Pg C in the reactive pool of soil organic carbon. About 83% of the total carbon storage occurred in tropical evergreen forests. Based on our model's results, we estimate that, over the past 15 years, the total carbon storage has increased by 3.1 Pg C (+2%), with a 1.9-Pg C (+2%) increase in vegetation carbon and a 1.2-Pg C (+4%) increase in reactive soil organic carbon. The modelled results indicate that the largest relative changes in net carbon storage have occurred in tropical deciduous forests, but that the largest absolute changes in net carbon storage have occurred in the moist and wet forests of the Basin. 3 Our results show that the strength of interannual variations in net carbon storage of undisturbed ecosystems in the Amazon Basin varies from a carbon source of 0.2 Pg C/year to a carbon sink of 0.7 Pg C/year. Precipitation, especially the amount received during the drier months, appears to be a major controller of annual net carbon storage in the Amazon Basin. Our analysis indicates further that changes in precipitation combine with changes in temperature to affect net carbon storage through influencing soil moisture and nutrient availability. 4 On average, our results suggest that the undisturbed Amazonian ecosystems accumulated 0.2 Pg C/year as a result of climate variability and increasing atmospheric CO$_2$ over the study period. This amount is large enough to have compensated for most of the carbon losses associated with tropical deforestation in the Amazon during the same period. 5 Comparisons with empirical data indicate that climate variability and CO$_2$ fertilization explain most of the variation in net carbon storage for the undisturbed ecosystems. Our analyses suggest that assessment of the regional carbon budget in the tropics should be made over at least one cycle of El Nino-Southern Oscillation because of interannual climate variability. Our analyses also suggest that proper scaling of the site-specific and subannual measurements of carbon fluxes to produce Basin-wide flux estimates must take into account seasonal and spatial variations in net carbon storage. 5. Title: Global Change and Terrestrial Ecosystems: An Initial Integration Author(s): William L. Steffen; John S. I. Ingram Source: Journal of Biogeography, Vol. 22, No. 2/3, Terrestrial Ecosystem Interactions with Global Change, Volume 1. (Mar. - May, 1995), pp. 165-174. Stable URL: http://links.jstor.org/sici?sici=0305-0270%28199503%2F05%2922%3A2%2F3%3C165%3AGCATEA%3E2.0.CO%3B2-I Abstract: We present a framework for integrating GCTE's research programme based on three interacting axes-time, space and applicability. We use the contributed papers from the First GCTE Science Conference to undertake an initial integration of GCTE-type research using this three-axis structure. We assess where progress in being made, where progress is likely to be made in the near future, and where critical gaps exist which require a major effort to eliminate. Elevated $CO_2$ research is one of the most mature areas within GCTE, and provides scope for initial integration along all three axes. Soils, being key to the functioning of all terrestrial ecosystems, provide another excellent opportunity to integrate research along all three axes. A major obstacle to further integration is our lack of understanding of landscape-scale processes, particularly disturbances, and our ability to simulate global change impacts on them. GCTE's Focus 2, Change in Ecosystem Structure, is perhaps best placed to attack many of the gaps that prevent this further integration along space and time scales, and is now entering a rapid development phase; the other Foci also have a major role to play. Integration specifically along the applicability axis is being developed in some areas but requires an enhanced effort to achieve its potential to increase scientific efficiency and effectiveness. The emerging field of global ecology, i.e. ecology at very large space and time scales, is progressing rapidly on the basis of linkages to more traditional ecological research at smaller scales, but requires further interaction with work along the applicability axis. 6. Title: Tropical Secondary Forests Author(s): Sandra Brown; Ariel E. Lugo Source: Journal of Tropical Ecology, Vol. 6, No. 1. (Feb., 1990), pp. 1-32. Stable URL: http://links.jstor.org/sici?sici=0266-4674%28199002%296%3A1%3C1%3ATSF%3E2.0.CO%3B2-J Abstract: The literature on tropical secondary forests, defined as those resulting from human disturbance (e.g. logged forests and forest fallows), is reviewed to address questions related to their extent, rates of formation, ecological characteristics, values and uses to humans, and potential for management. Secondary forests are extensive in the tropics, accounting for about 40% of the total forest area and their rates of formation are about 9 million ha yr$^{-1}$. Geographical differences in the extent, rates of formation and types of forest being converted exist. Secondary forests appear to accumulate woody plant species at a relatively rapid rate but the mechanisms involved are complex and no clear pattern emerged. Compared to mature forests, the structure of secondary forest vegetation is simple, although age, climate and soil type are modifying factors. Biomass accumulates rapidly in secondary forests, up to 100 t ha$^{-1}$ during the first 15 yr or so, but history of disturbance may modify this trend. Like biomass, high rates of litter production are established relatively quickly, up to 12-13 t ha$^{-1}$ yr$^{-1}$ by age 12-15 yr. And, in younger secondary forests (<20 yr), litter production is a higher fraction of the net primary productivity than stemwood biomass production. More organic matter is produced and transferred to the soil in younger secondary forests than is stored in above-ground vegetation. The impact of this on soil organic matter is significant and explains why the recovery of organic matter in the soil under secondary forests is relatively fast (50 yr or so). Nutrients are accumulated rapidly in secondary vegetation, and are returned quickly by litterfall and decomposition for uptake by roots. We propose a model of the gains and losses, yields and costs, and benefits and tradeoffs to people from the current land-use changes occurring in the tropics. When the conversion of forest lands to secondary forests and agriculture is too fast or land-use stages are skipped, society loses goods and services. To avoid such a loss, we advocate management of tropical forest lands within a landscape perspective, a possibility in the tropics because land tenures and development projects are often large. -------------------------------------------------------------------------------- These records have been provided through JSTOR. http://www.jstor.org