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Wildfire effects on permafrost and soil moisture in spruce forests of Interior Alaska

Journal of Forestry Research 2020年第2期31卷 553-563页

作者： christopher potter Charles Hugny NASA Ames Research Center Moffett FieldCA 94035USA Interior Alaska Wilderness Consultants NenanaAKUSA

In the summer of 2015,hundreds of forest fires burned across the state of *** uncontrolled wildfires near the town of Tanana on the Yukon River were responsible for the largest portion of the area burned *** July 2017,field measurements were carried out in both unburned and burned forested areas nearly adjacent to one another,all within 15 miles of the village of *** surveys were used to first visually verify locations of different burn severity classes,(low,moderate,or high),estimated in 2016 from Landsat images(collected before and after the 2015 Tanana-area wildfires).Surface and soil profile measurements to 30-cm depth at these same locations were collected for evidence of moss layer and forest biomass *** temperature and moisture content were measured to 30-cm depth,and depth to permafrost was estimated by excavation wherever *** thermal infra-red images of the soil profiles were taken at each site location,and root-zone organic layer samples were extracted for further chemical *** supported the hypothesis that the loss of surface organic layers is a major factor determining post-fire soil water and temperature changes and the depth of permafrost *** the most severely burned forest sites,complete consumption of the living moss organic layer was strongly associated with both warming at the surface layer and increases in soil water content,relative to unburned forest *** temperatures at both 10-cm and 30-cm depths at burned forest sites were higher by 8-10C compared to unburned *** 15 cm,temperatures of unburned sites dropped gradually to frozen levels by 30 cm,while soil temperatures at burned sites remained above 5C to 30-cm *** water content measured at 3 cm at burned sites was commonly in excess of 30%by volume,compared to unburned *** strong correlation between burn index values and depth to permafrost measured across all sites sampled in July 2017 showed tha

关键词： Alaska Landsat Permafrost RdNBR Soil temperature Soil water Wildfire

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Landsat Time Series Analysis of Vegetation Changes in Solar Energy Development Areas of the Lower Colorado Desert, Southern California

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Journal of Geoscience and Environment Protection 2016年第2期4卷 1-6页

作者： christopher potter CASA Systems 2100 Los Gatos California USA

Land cover change from renewable energy development in southern California is receiving increasing attention due to potential impacts on protected area conservation, endangered species, and greenhouse gas emissions. This study was designed to quantify and map, for the first time, variations desert vegetation canopy density and related growth rates using 30 consecutive years of Landsat satellite image data across the Lower Colorado Desert. The time-series for mean normalized difference vegetation index (NDVI) values sampled from each of the three major land cover types (shrubland, barren sand dune, and developed urban) showed no significant positive or negative trend in vegetation canopy density. Three periods of significant decrease in NDVI were detected during the drought periods of 1989-1990, 2002-2003, and 2013-2015, indicating that annual precipitation has been the main controller of shrubland canopy growth and green cover. Shrubland canopy cover has been relatively stable in renewable energy development zones since the mid-2000s. NDVI change in the period after nearly all southern California solar energy developments were initiated (post-2010) could be attributed largely to topographic water flow pathways through canyons and desert washes, both in and around all solar energy development zones.

关键词： Landsat Shrubland Solar Energy Development Lower Colorado Desert DRECP

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Regional Analysis of NASA Satellite Greenness Trends for Ecosystems of Arctic Alaska

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International Journal of Geosciences 2014年第9期5卷 997-1006页

作者： christopher potter Mail Stop 232-21 Moffett Field USA

Trends in the growing season MODerate resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) time-series were analyzed for the period from 2000 to 2010 to understand landscape-level patterns of vegetation change in ecosystems of arctic Alaska. We compared datasets for vegetation cover types, wetland cover classes, wildfire boundaries since the 1940s, permafrost type, and elevation to identify the most likely combination of factors driving regional changes in habitat quality and ecosystem productivity. Approximately 57% of all arctic ecosystem areas in Alaska were detected with significant (p < 0.05) positive or negative MODIS growing season EVI trends from 2000 to 2010. Nearly all (99%) of these ecosystem areas (covering 178,050 km2) were detected with significant positive growing season EVI trends. The vast majority of the arctic Alaska region detected with significant positive growing season EVI trends was classified as upland tundra cover, although non-forested wetlands (marshes, bogs, fens, and floodplains) were co-located on 8% of that area. Herbaceous wetlands were co-located on 55% of the total area detected with significant negative growing season EVI trends, mostly on the arctic coastal plain and foothills. This evidence supports the hypothesis that temperature (warming) has markedly enhanced the rates of upland tundra vegetation growth across most of arctic Alaska over recent years.

关键词： MODIS EVI Arctic Tundra Wetlands Wildfire Alaska

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Net primary production and carbon cycling in coast redwood forests of central California

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Open Journal of Ecology 2012年第3期2卷 147-153页

作者： christopher potter NASA Ames Research Center Mountain View USA

A simulation model to estimate net primary productivity (NPP) has been combined with in situ measurements of soil carbon dioxide (CO2) emissions and leaf litter pools in three coast redwood forest stands on the central California coast. Monthly NPP was predicted from the CASA model using 250-meter resolution vegetation index (VI) inputs. Annual NPP was predicted to vary from 380 g·C·m-2·yr-1 to 648 g·C·m-2·yr-1 at central coast redwood sites over the years 2007 to 2010. Measured soil respiration rates at between 0.5 to 2.2 g·C·m-2·d-1 were slightly below the range of measurements previously reported for a second-growth mixed (redwood and Douglas-fir) conifer forests. Although warm monthly temperatures at the southern-most redwood forest sites evidently results in elevated stress levels to sustained redwood growth into the dry summer months of June and July, these redwood stands appear to sequester CO2 from that atmosphere into forest biomass for a net positive ecosystem carbon balance each year.

关键词： Carbon Forest Ecosystems Remote Sensing MODIS

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Landscape Patterns of Vegetation Canopy Regrowth Following Wildfires in the Sierra Nevada Mountains of California

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Open Journal of Forestry 2015年第7期5卷 723-732页

作者： christopher potter NASA Ames Research Center Moffett Field USA

Rapid recovery of pioneer shrub and forest patch cover can reduce soil erosion, nutrient runoff and degradation of stream habitats, and promote small mammal and avian biodiversity following stand-replacing wildfires. Landsat imagery from the past 25+ years was analyzed to understand patterns and rates of vegetation recovery, focusing on high burn severity (HBS) patches, within wildfire areas dating from the late 1940s in the Sierra-Nevada region of California. Normalized difference vegetation index (NDVI) levels indicative of recovered woody cover within HBS areas were analyzed starting in 1985 to quantify regrowth of patch dynamics. Analysis of landscape metrics showed that the percentage of total HBS area comprised by the largest patch of recovered woody cover was relatively small in all fires that occurred since 1995, but increased rapidly with time since fire. Patch complexity of recovered woody cover decreased notably after more than 50 years of regrowth, but was not readily associated with time for fires that occurred since the mid 1990s. Patch complexity of dense woody cover was consistently high in fires after 1995 and increased with the elevation of HBS areas. The aggregation level of patches with recovery of woody cover increased steadily with time since fire. The study approach using satellite remote sensing can be expanded to assess the consequences of stand-replacing wildfires in all forests of the region.

关键词： Landsat Forest Wildfire Regrowth Disturbance Sierra Nevada California

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Geographic Analysis of Burn Severity for the 2013 California Rim Fire

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Natural Resources 2014年第11期5卷 597-606页

作者： christopher potter NASA Ames Research Center Moffett Field CA USA

Analysis of Landsat imagery was applied to classify burn severity within the 2013 Rim Fire area using the relative difference normalized burn ratio (RdNBR). Results showed 53,220 ha in the High Burn Severity (HBS) class and another 34,214 ha in the Moderate Burn Severity (MBS) class. Within Yosemite National Park, 12,084 ha were detected by RdNBR analysis in the HBS class and another 11,089 ha in the MBS class. The most typical ecosystem habitat detected within the HBS class was Ponderosa pine—Mixed Conifer forest, between the elevations of 1000 and 2000 meters or on slopes between 5 and 30 percent. Most of the HBS areas were located in areas where high levels of pre-fire fuels were quantified by 2013 Landsat vegetation index (NDVI) values between 500 and 800. The Low Burn Severity (LBS) class covered a higher fraction of areas where the duration since last fire (YSF) was less than 25 years, compared to the HBS class, which covered a higher fraction of areas where the YSF was greater than 60 years.

关键词： Wildfire California Burn Severity Landsat Remote Sensing

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Ten Years of Vegetation Change in Northern California Marshlands Detected Using Landsat Satellite Image Analysis

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Journal of Water Resource and Protection 2013年第5期5卷 485-494页

作者： christopher potter NASA Ames Research Center Moffett Field USA

The Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) methodology was applied to detect changes in perennial vegetation cover at marshland sites in Northern California reported to have undergone restoration between 1999 and 2009. Results showed extensive contiguous areas of restored marshland plant cover at 10 of the 14 sites selected. Gains in either woody shrub cover and/or from a recovery of herbaceous cover that remains productive and evergreen on a year round basis could be mapped out from the image results. However, LEDAPS may not be highly sensitive changes in wetlands that have been restored mainly with seasonal herbaceous cover (e.g., vernal pools), due to the ephemeral nature of the plant greenness signal. Based on this evaluation, the LEDAPS methodology would be capable of fulfilling a pressing need for consistent, continual, low-cost monitoring of changes in marshland ecosystems of the Pacific Flyway.

关键词： Landsat Marshland Vegetation Wetlands Regrowth Restoration

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Vegetation Regrowth Following Wildfires in the Santa Cruz Mountains of Northern California Monitored Using Landsat Satellite Image Analysis

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Open Journal of Forestry 2016年第2期6卷 82-93页

作者： christopher S. potter NASA Ames Research Center Moffett Field CA USA

The Santa Cruz Mountain range in northern California is a coastal landscape with a history of extensive forest logging and frequent large wildfires that have recently destroyed numerous residential structures at the wildland interface. Results from Landsat satellite image time-series analysis since 1984 of the study area within the Los Gatos Creek and Corralitos Creek watersheds showed that none of the severe drought periods since the 1980s have notably inhibited rapid tree and shrub regrowth rates on steep hill slopes burned recently by the 1985 Lexington Fire and the 2008 Summit Fire. In high burn severity areas of both fires, post-fire vegetation types showed a marked increase in shrub cover, mainly at the expense of evergreen tree cover. Most of these low (-1 of standing woody biomass on the burned areas. This study is the first of its kind to utilize a full 30-year record of Landsat vegetation index data to monitor tree and shrub regrowth after stand-replacing wildfires in California.

关键词： Landsat California Santa Cruz Mountains Forest Shrub Wildfire Drought NDVI

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Vegetation regrowth trends in post forest fire ecosystems across North America from 2000 to 2010

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Natural Science 2012年第10期4卷 755-770页

作者： Shuang Li christopher potter NASA Ames Research Center Moffett Field USA

The goal of this study was to determine whether climate has affected vegetation regrowth over the past decade (2000 to 2010) in post-fire forest ecosystems of the United States and Canada. Our methodology detected trends in the monthly MODerate resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) timeseries within forest areas that burned between 1984 and 1999. The trends in summed growing season EVI (composited to 8 km spatial resolution) within all burned area perimeters showed that nearly 1.6% post-fire forest area declined in vegetation greenness cover significantly (p < 0.05) over the past decade. Nearly 62% of all post-fire forest area showed a non significant EVI regrowth trend from 2000 to 2010. Regression results detected numerous significantly negative trend pixels in post-fire areas from 1994-1999 to indicate that forest regrowth has not yet occurred to any measurable level in many recent wildfire areas across the continent. We found several noteworthy relationships between annual temperature and precipitation patterns and negative post-fire forest EVI trends across North America. Change patterns in the climate moisture index (CMI), growing degree days (GDD), and the standardized precipitation index (SPI) were associated with post-fire forest EVI trends. We conclude that temperature warming-induced change and variability of precipitation at local and regional scales may have altered the trends of large post-fire forest regrowth and could be impacting the resilience of post-fire forest ecosystems in North America.

关键词： MODIS EVI Post-Fire Forest Regrowth Climate Change North America

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Monitoring of Net Primary Production in California Rangelands Using Landsat and MODIS Satellite Remote Sensing

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Natural Resources 2012年第2期3卷 56-65页

作者： Shuang Li christopher potter Cyrus Hiatt California State University Monterey Bay Seaside USA Henan University College of Environment and Planning Kaifeng Henan China NASA Ames Research Center Moffett Field USA

In this study, we present results from the CASA (Carnegie-Ames-Stanford Approach) model to estimate net primary production (NPP) in grasslands under different management (ranching versus unmanaged) on the Central Coast of California. The latest model version called CASA Express has been designed to estimate monthly patterns in carbon fixation and plant biomass production using moderate spatial resolution (30 m to 250 m) satellite image data of surface vegetation characteristics. Landsat imagery with 30 m resolution was adjusted by contemporaneous Moderate Resolution Imaging Spectroradiometer (MODIS) data to calibrate the model based on previous CASA research. Results showed annual NPP predictions of between 300 - 450 grams C per square meter for coastal rangeland sites. Irrigation increased the predicted NPP carbon flux of grazed lands by 59 grams C per square meter annually compared to unmanaged grasslands. Low intensity grazing activity appeared to promote higher grass regrowth until June, compared to the ungrazed grassland sites. These modeling methods were shown to be successful in capturing the differing seasonal growing cycles of rangeland forage production across the area of individual ranch properties.

关键词： Grasslands MODIS Landsat California Net Primary Production

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