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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Hurricane-Induced Rainfall is a Stronger Predictor of Tropical Forest Damage in Puerto Rico Than Maximum Wind Speeds

Projected increases in cyclonic storm intensity under a warming climate will have profound effects on forests, potentially changing these ecosystems from carbon sinks to sources. Forecasting storm impacts on these ecosystems requires consideration of risk factors associated with storm meteorology, landscape structure, and forest attributes. Here we evaluate risk factors associated with damage severity caused by Hurricanes María and Irma across Puerto Rican forests. Using field and remote sensing data, total forest aboveground biomass (AGB) lost to the storms was estimated at 10.44 (±2.33) Tg, ca. 23% of island-wide pre-hurricane forest AGB. Storm-related rainfall was a stronger predictor of forest damage than maximum wind speeds. Soil water storage capacity was also an important risk factor, corroborating the influence of rainfall on forest damage. Expected increases of 20% in hurricane-associated rainfall in the North Atlantic highlight the need to consider how such shifts, together with high speed winds, will affect terrestrial ecosystems.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1980

Landsat analysis of tropical forest succession employing a terrain model

Landsat multispectral scanner (MSS) data have yielded a dual classification of rain forest and shadow in an analysis of a semi-deciduous forest on Mindonoro Island, Philippines. Both a spatial terrain model, using a fifth side polynomial trend surface analysis for quantitatively estimating the general spatial variation in the data set, and a spectral terrain model, based on the MSS data, have been set up. A discriminant analysis, using both sets of data, has suggested that shadowing effects may be due primarily to local variations in the spectral regions and can therefore be compensated for through the decomposition of the spatial variation in both elevation and MSS data.

Barringer, T. H.↗
NASA NTRS1990

Emission of nitric oxide (NO) from tropical forest soils and exchange of NO between the forest canopy and atmospheric boundary layers

Emissions of NO from soils in the Amazon rain forest were measured at 66 locations using an enclosure technique, and continuous vertical profiles of NO and O3 were measured between the ground and 41-m altitude. Fluxes of NO averaged 8.9 (+ or - 1.5) x 10 to the 9th molecules/sq cm per sec from the dominant (yellow clay) soils of the region, with larger fluxes observed from adjacent white sand soils. Fluxes from clay soils were lower by more than a factor of 5 than fluxes observed during the dry season at a nearby site. Low soil emission rates were reflected in lower concentrations of NO at the top of the forest canopy in the wet season, only 30-50 parts per trillion by volume during the daytime. The measured fluxes are consistent with chemical mass balances for NO within the forest canopy, calculated from the NO and O3 profiles taken at night, and with observations of NO between 150 and 5000 m altitude. Measurements of NO emission rates from soil plots fertilized using NaNO3, NH4Cl, or sucrose indicated that a reductive pathway (denitrification) may have been primarily responsible for production of the NO released by both clay and sand soils.

Bakwin, Peter S.↗
NASA NTRS1990

Measurements of reactive nitrogen oxides (NO/y/) within and above a tropical forest canopy in the wet season

Measurements of ambient concentrations of reactive nitrogen oxides were made in the Amazon rain forest, near Manaus, Brazil, continuously at 39 m (above the canopy), and on several days and nights at 19 m (within the canopy). Concentrations were very low, typically 100-700 pptv, except for brief periods when up to 5000 pptv of NO(y) was observed, indicating polluted air from the urban area of Manaus. The forest was a net sink for NO(y) with the NO(y) flux = -7.6 + or - 5.0) x 10 to the 9th molecules/sq cm per sec in unpolluted periods, even though soils emitted NO at a significant rate (8.9 + or - 1.5 x 10 to the 9th molecules/sq cm per sec). The deposition rate for NO(y) appeared to be much larger during the daytime than at night, suggesting that uptake was controlled either by plant processes (stomatal opening) or by supply of reactive components of NO(y) (e.g., HNO3) during the daytime. Implications for regional and global atmospheric chemistry are discussed.

Bakwin, Peter S.↗
NASA NTRS1991

Soil emissions of nitric oxide in a seasonally dry tropical forest of Mexico

Soil emissions of NO were measured at the Chamela Biological Station, Mexico, using soil covers and a field apparatus of NO detection based on CrO3 conversion of NO to NO2 and detection of NO2 by chemiluminescence with Luminol. Mean NO fluxes from forest soils ranged from 0.14 to 0.52 ng NO-N/sq cm/hr during the dry season and from 0.73 to 1.27 ng NO-N/sq cm/hr during the wet season. A fertilized floodplain pasture exhibited higher fluxes, but an unfertilized upland pasture, which represents the fastest growing land use in the region, had flux rates similar to the forest sites. Wetting experiments at the end of the dry season caused large pulses of NO flux, equaling 10 percent to 20 percent of the estimated annual NO emissions of 0.5-1.0 kg N/ha from the forest sites. Absence of a forest canopy during the dry season and the first wet season rain probably results in substantial NO(x) export from the forest system that may be important to regional atmospheric chemical processes. Wetting experiments during the wet season and a natural rain event had little or no stimulatory effect on NO flux rates.

Davidson, Eric A.↗