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USGS2021

Climate and Ecological Disturbance Analysis of Engelmann spruce and Douglas fir in the Greater Yellowstone Ecosystem

The effects of anthropogenic climate change are apparent in the Greater Yellowstone Ecosystem (GYE), USA, with forest die-off, insect outbreaks, and wildfires impacting forest ecosystems. A long-term perspective would enable assessment of the historical range of variability in forest ecosystems and better determination of recent forest dynamics and historical thresholds. The objectives of this study were to (1) develop tree-ring chronologies for Engelmann spruce and Douglas fir growing at the study location, (2) correlate the annual ring widths of each species to monthly climate variables, (3) examine the instrumental climate data for regimes shifts in the mean state of variables, and (4) determine when ecological disturbances occurred through a quantification of growth releases. Finally, we discuss both climate-growth relationships and growth releases in the context of climate regime shifts and known forest disturbances. Engelmann spruce and Douglas fir showed some similar climate responses using moving correlation analysis including negative correlations between ring width and June – August current year temperature and previous growing season temperature. Regime shift analysis indicated significant ( p < 0.05) shifts in minimum and maximum GYE temperature in the latter half of the 20th century. Disturbance analysis indicated that both tree species responded to wildfire and insect outbreak events with growth releases in up to 25% of the trees. Disentangling the influence of climate regime shifts and forest disturbances on the climate-growth relationships can be difficult because climate and forest disturbances are intricately linked. Our evidence indicates that regime shifts in monthly climate variables and forest disturbances as recorded by growth releases can influence the ring width response to climate over time. Trees are key to providing a long-term perspective on climate and ecological health across the GYE because they integrate both climate and ecology in their annual ring widths.

Wyoming↗

USGS2024

The efficacy of the semiochemical repellent verbenone to reduce ambrosia beetle attack on healthy and Ceratocystis-infested ‘ōhiʻa trees

The Ceratocystis fungal disease complex, rapid ʻōhiʻa death (ROD), has killed over one million ʻōhiʻa ( Metrosideros polymorpha ), the keystone tree species of Hawaiʻi. The causal fungi can be spread by invasive ambrosia beetles (Coleoptera: Curculionidae) through fungal inoculum found on their bodies and in the frass they produce. Thus, there is a critical need to manage beetle attack on ʻōhiʻa trees to curtail subsequent pathogen spread and disease development. In this experiment at Waiākea Forest Reserve, we tested the potential of the semiochemical repellent, verbenone, in a commercial formulation, to protect healthy and ROD-affected ʻōhiʻa from ambrosia beetle attack in each of the 2022 and 2023 field seasons. Landing rates of ambrosia beetles on healthy and diseased trees were quantified over 16 weeks each year, using sticky traps on ethanol-baited trees that also received either a low (72 g) or high (108 g) dose of verbenone or untreated controls. In addition, we used gas-chromatography mass-spectrometry (GC–MS) to measure verbenone emission over 16 weeks in 2022. We found that the low dose of verbenone is the most effective and economical application to reduce beetle landing on healthy ʻōhiʻa trees and the high dose may be needed to reduce attraction to diseased ʻōhiʻa. Despite a large decrease in verbenone emission levels by week eight, the low dose effectively reduced beetle captures on healthy trees for 14 weeks and the high dose reduced landing rates on diseased trees for 10–14 weeks. Our results indicate verbenone may significantly lower ambrosia beetle attack on ʻōhiʻa, and thus, lead to reduction in the spread of ROD.

Hawaii↗

USGS2026

Millennial-scale climatic and cultural impacts on vegetation and fire at the southern edge of the Rocky Mountains, USA

Mountain forests and woodlands in semiarid regions of the world are threatened by climatic change and other human impacts. In the southwestern USA, climate and culturally driven changes to the structure and fire regimes of dry coniferous forests over recent centuries are well documented by tree-ring archives. However, the roles of climate and people as drivers of millennial-scale changes are less understood. We present a new record of vegetation dynamics and regional fire activity inferred from pollen, microscopic charcoal, and sediment geochemistry from Santa Fe Lake, NM (3532 m a.s.l.), the southernmost natural lake in the Rocky Mountains. Declining elemental intensities (e.g., Ti, Fe, Si) record local deglaciation after 14,000 cal yr BP followed by upslope expansion of trees indicated by increasing Pinus and Picea pollen percentages as the climate warmed during the Late Glacial. Cool, dry growing seasons probably limited the establishment of dense forests until after 12,200 cal yr BP when we hypothesize that Pinus ponderosa (ponderosa pine) expanded regionally (i.e., within 10–100 km) due to continued warming and a possible increase in monsoonal precipitation. Subalpine forests established near Santa Fe Lake by 10,300 cal yr BP as indicated by abundant conifer stomates and increasing Picea and Pinus aristata pollen percentages, which are highest after 5100 cal yr BP. Increasing Juniperus -type, Quercus , and Pinus edulis -type pollen record changes in vegetation belts at lower elevations after 10,300 cal yr BP. Maize pollen, an unambiguous indicator of Puebloan agriculture, first appears at 800 cal yr BP (1150 cal yr CE) and is present through 1600 cal yr CE when Spanish colonization brought cultural upheaval and population loss to local indigenous communities. Regional fire activity, inferred from microscopic charcoal influx, remained relatively constant for most of our record. However, average microscopic charcoal influx more than doubled relative to the rest of the Holocene during the last 2000 years, with the highest influx after 1550 cal yr BP (400 cal yr CE). The increased influx of microscopic charcoal coincides with archaeological evidence for dramatic regional population growth in the northern Rio Grande region and probably reflects extensive cultural burning associated with the development of an agricultural economy. Although climate was an important driver of vegetation change and fire regimes in the mountains of the southwestern USA during the Holocene, our results suggest that human impacts on regional burning during the last 2000 years far exceeded earlier climate-driven variation.

Rocky Mountains↗

USGS2000

Chinese tallow: Invading the southeastern Coastal Plain

Chinese tallow is an ornamental tree with colorful autumn foliage that can survive full sunlight and shade, flooding, drought, and in some cases fire. To horticulturists this kind of tree sounds like a dream, but to ecologists, land managers, and land owners this kind of tree can be a nightmare, especially when it invades an area and takes over native vegetation. Chinese tallow ( Triadica sebifera ), a nonnative tree from China, is currently transforming the southeastern Coastal Plain. Over the last 30 years, Chinese tallow has become a common tree in old fields and bottomland swamps of coastal Louisiana. Several studies at the U.S. Geological Survey's National Wetlands Research Center (NWRC), Lafayette, Louisiana, are aimed at understanding the factors that contribute to Chinese tallow growth, spread, and management. When tallow invades, it eventually monopolizes an area, creating a forest without native animal or plant species. This tree exhibits classic traits of most nonnative invaders: it is attractive so people want to distribute it, it has incredible resiliency, it grows quickly and in a variety of soils, and it is resistant to pests. In the coastal prairie of Louisiana and Texas, Chinese tallow can grow up to 30 feet and shade out native sun-loving prairie species. The disappearing of prairie species is troublesome because less than 1% of original coastal prairie remains, and in Louisiana, less than 500 of the original 2.2 million acres still exist. Tallow reproduces and grows quickly and can cause large-scale ecosystem modification (fig. 1). For example, when it completely replaces native vegetation, it has a negative effect on birds by degrading the habitat. Besides shading out grasses that cattle like to eat, it can also be potentially harmful to humans and animals because of its berries (fig. 2) and plant sap that contain toxins. There is some concern its leaves may shed toxins that change the soil chemistry and make it difficult for other plants to grow.

Fact Sheet↗

USGS2007

Adapting to the reality of climate change at Glacier National Park, Montana, USA

The glaciers of Glacier National Park (GNP) are disappearing rapidly and likely will be gone by 2030. These alpine glaciers have been continuously present for approximately 7,000 years so their loss from GNP in another 25 years underscores the significance of current climate change. There are presently only 27 glaciers remaining of the 150 estimated to have existed when GNP was created in 1910. Mean annual temperature in GNP has increased 1.6°C during the past century, three times the global mean increase. The temperature increase has affected other parts of the mountain ecosystem, too. Snowpacks hold less water equivalent and melt 2+ weeks earlier in the spring. Forest growth rates have increased, alpine treelines have expanded upward and become denser, and subalpine meadows have been invaded by high elevation tree species. These latter responses can be mostly attributed to longer growing seasons and warmer temperatures. Ecosystem modeling of possible future changes in the GNP mountain environments suggest that increased tree growth rates and evapotranspiration will reduce soil moisture and streamflow. The drier forests, with more wood, will burn more frequently and with greater severity, leading to degradation in air quality and increased risk to people and infrastructure. Management of forest fires is an important issue in the arid western United States. In 2003, 13% of GNP’s 4,082 km 2 was burned in three large fires and numerous smaller fires. Managers can accomplish some of their goals, such as preserving threatened wildlife populations, by altering their management of fires. In 2003, intense efforts were successfully made to divert the fires away from valuable grizzly bear ( Ursus arctos horribilis ) habitat that contained huckleberry plants ( Vaccinium spp .) necessary to ensure bear survival through the winter.

Montana↗

USGS2022

Rapid ʻŌhiʻa Death in Hawaiʻi

Ceratocystis lukuohia and Ceratocystis huliohia are two newly recognized fungi that have arrived in Hawai‘i and are causing a serious vascular wilt and canker disease, respectively, of ‘ōhi‘a trees ( Metrosideros polymorpha ), the most common and important tree species in Hawai‘i. Management of these diseases has presented challenges due to unique etiological aspects and the exceptionally pathogenic nature of one of these fungi ( C. lukuohia ) once it gains access to the tree’s vascular tissue. Careful study of the spread of the pathogens has resulted in an understanding of the role of ambrosia beetles and the frass they produce that carries the pathogen, as well as the wounding of trees by many different agents by which the pathogen can access and infect the vascular tissue. A variety control measures are being used. These include a state-of-the-art monitoring program to detect diseased and recently killed trees and molecular biology approaches that can confirm if a given tree was infected by Ceratocystis . Based on monitoring more than one million trees have been estimated as killed by the diseases to date. A major part of the program includes the deployment of a field crew that seeks out and fells large infected ‘ōhi‘a trees as these trees are the main source of most of the infective Ceratocystis -laden frass. Long-term control measures also include fencing of some forests to reduce the amount of wounding to ‘ōhi‘a trees by feral cattle and pigs that allows entry of the fungi and quarantine restrictions to ensure there will be no inter-island movement of the pathogens in ‘ōhi‘a products. Finally, methods are also being developed to restore ‘ōhi‘a forests affected by these diseases by determining effective regeneration practices and developing genetically resistant ‘ōhi‘a stock. Hawai‘i has an active extension program dedicated to providing information on how residents and visitors can contribute to protecting ‘ōhi‘a trees from these diseases. More than 500,000 people have participated in this program. Hawai‘i residents have a very deep appreciation for this tree species and do what they can to help prevent these diseases from destroying more of their most treasured tree species.

Hawai'i↗

USGS2005

Efficacy of immobilizing free-ranging elk with Telazol® and xylazine hydrochloride using transmitter-equipped darts

From January 1999 to April 2002, 14 free-ranging elk were darted with a mixture of Telazol ® reconstituted with xylazine hydrochloride (HCl) in a forested habitat in southwestern Oklahoma and north-central Arkansas. Elk were darted from ground blinds, tree stands, or a vehicle at distances of 14–46 m and were recovered 37–274 m from the dart site. Elk were located using radiotelemetry with 3-cc disposable Pneu-dart ® transmitter darts. Mean±SD dose of Telazol ® and xylazine HCl was 590±192 mg/ml and 276±153 mg/ml, respectively, and mean time to standing after injection of reversal agent was 27 min (range: 1–65 min). The combination of Telazol ® and xylazine HCl successfully immobilized free-ranging elk, and transmitter-equipped darts permitted successful location of sedated elk by two people in areas of dense forest cover. The dose required to sedate elk appeared to vary depending on physiology and behavior, but no drug-induced mortality occurred despite the wide variance in the doses administered. We recommend 500 mg Telazol ® reconstituted with 300 mg xylazine HCl as an initial dose for a ≥200 kg elk. If needed to achieve full sedation, up to 3 additional ml of the mixture may be administered without adverse effects.

Journal of Wildlife Diseases↗

USGS2012

Impacts of climate change on ecosystem services

Key Findings By 2050, climate change will triple the fraction of counties in the U.S. that are at high or extremely high risk of outstripping their water supplies (from 10 percent to 32 percent). The most at risk areas in the U.S. are the West, Southwest and Great Plains regions. Regulation of drinking water quality will be strained as high rainfall and river discharge conditions may lead to higher levels of nitrogen in rivers and greater risk of waterborne disease outbreaks. Climate change will have uneven effects on timber production across the U.S. Recent increases in tree mortality due to disease and pests, and the intensity of fires and area burned will continue to destroy productive forests. On the other hand, in some regions climate change is expected to boost overall forest productivity due to longer growing seasons. There is a better than 50 percent chance that climate change will overwhelm the ability of natural systems to mitigate the harm to people resulting from extreme weather events (such as heat waves, heavy rains, and drought). Vulnerability of people and property in coastal areas is highly likely to increase dramatically – due to the effects of sea-level rise, storm surge, and the loss of habitats that provide protection from flooding and erosion. The areas at greatest risk to coastal hazards in the U.S. are the Atlantic and Gulf coasts. The human communities most vulnerable to climate-related increases in coastal hazards are the elderly and the poor who are less able to respond quickly before and during hazards and to respond over the long term through relocation. Changes in abundance and ranges of commercially important marine fish are highly likely to result in loss of some local fisheries, and increases in value for others if fishing communities and management practices can adapt. In recreation and tourism, the greatest negative climate impacts will continue to be felt in winter sports and beach recreation (due to coastal erosion). Other forms of recreation are highly likely to increase due to better weather, leading to a redistribution of the industry and its economic impacts, with visitors and tourism dollars shifting away from some communities in favor of others. Supporting, regulating, and provisioning ecosystem services all contribute to food security in the United States, and the fate of the nation’s food production are very likely to depend on the interplay of these services and how the agriculture and fishery sectors respond to climate stresses.

Book chapter↗

USGS1995

Pinyon-juniper woodlands

Pinyon-juniper woodlands are one of the largest ecosystems in the Southwest and in the Middle Rio Grande Basin (Fig. 1). The woodlands have been important to the region's inhabitants since prehistoric times for a variety of natural resources and amenities. The ecosystems have not been static; their distributions, stand characteristics, and site conditions have been altered by changes in climatic patterns and human use and, often, abuse. Management of these lands since European settlement has varied from light exploitation and benign neglect, to attempts to remove the trees in favor of forage for livestock, and then to a realization that these lands contain useful resources and should be managed accordingly. Land management agencies are committed to ecosystem management. While there are several definitions of ecosystem management, the goal is to use ecological approaches to create and maintain diverse, productive, and healthy ecosystems (Kaufmann et al. 1994). Ecosystem management recognizes that people are an integral part of the system and that their needs must be considered. Ecological approaches are central to the concept, but our understanding of basic woodland ecology is incomplete, and there are different opinions and interpretations of existing information (Gottfried and Severson 1993). There are many questions concerning proper ecosystem management of the pinyon-juniper woodlands and how managers can achieve these goals (Gottfried and Severson 1993). While the broad concept of ecosystem management generally is accepted, the USDA Forest Service, other public land management agencies, American Indian tribes, and private landowners may have differing definitions of what constitutes desired conditions. Key questions about the pinyon-juniper ecosystems remain unanswered. Some concern the basic dynamics of biological and physical components of the pinyon-juniper ecosystems. Others concern the distribution of woodlands prior to European settlement and changes since the introduction of livestock and fire control. This relates to whether tree densities have been increasing or whether trees are invading grasslands and, to a lesser extent, drier ponderosa pine (Pinus ponderosa) forests. In areas where woodlands were heavily used by American Indians for fuelwood prior to European contact, the advance of pinyon and juniper could represent the slow recovery from intensive use (Samuels and Betancourt 1982). There are numerous questions regarding declines in watershed condition related to changes in pinyon-juniper tree stand densities and to the density and composition of understory vegetation. There are different opinions about proper management of woodland ecosystems. Should these lands be managed for a single resource, such as forage for livestock production, or managed for sustained production of multiple resource products and amenities? Depending on site and stand conditions, the woodlands can produce variable quantities of fuelwood, pinyon nuts, wildlife habitat, forage for livestock, and cover for watershed protection. Management must also consider increasing recreational demands, threatened and endangered species, and protection of archeological sites. Many pinyon-juniper woodland watersheds in New Mexico have unsatisfactory soil and watershed conditions (USDA Forest Service 1993); managers must develop restoration procedures that recognize the value of woodland ecosystems. The concerns, questions, and conflicts surrounding management of pinyon-juniper lands, as well as the ecological foundations of ecosystem management, require that all interested parties reevaluate attitudes toward the woodlands. Ecosystem management goals and concepts recognize diversity. Pinyonjuniper woodlands are diverse, and stand characteristics and site productivities vary. Management objectives and prescriptions must evaluate the potential of each site, and decisions must be based on sound scientific information. This information is often unavailable. Therefore, this paper describes what we do know about the characteristics, distribution, and ecology of pinyon-juniper woodlands, including the effects of natural and human factors, within the southwestern United States and particularly the Middle Rio Grande Basin. It also reviews some past and present management options in this widespread and important vegetation type. The review draws on research and management information from the Rio Grande Basin and from similar areas in the Southwest and adjacent regions. It does not attempt to review all of the relevant literature; additional sources can be found within the articles cited in the References.

General Technical Report↗

USGS2020

The field trip that changed the course of my career

After gobbling down a breakfast of sliced papaya, scrambled eggs, refried beans, and soft flour tacos, we gathered our gear and loaded it into the red zodiac that the station manager had assigned to us. My colleagues and I were headed to a pair of islands off the coast of Belize called Twin Cays, occupied by a unique group of tropical plants and animals adapted to a wet and saline habitat. Our ride from Carrie Bow Cay, home of the Smithsonian Institution’s field station, took about twenty minutes because of the choppy water. As we crossed the three-kilometer stretch from Carrie Bow to Twin Cays, I struggled to keep my seat on the bouncing pontoon and was soon soaked by salt spray. As we neared Twin Cays, the deep blue of the lagoon gave way to the turquoise and pale green colors of the shallow sand flats in the lee of the archipelago. Finally, the zodiac slowed, and we pulled into the calm channel separating the two islands. On either side of the channel was an intimidating tangle of tree trunks, branches, leaves, and aerial roots. The trees leaned out over the water and appeared poised to topple into the sea. However, they were perfectly still in the humid morning air and anchored solidly in place by arching prop roots. I sensed that I had entered an alien world, a waterlogged Terra Incognita that looked, smelled, and sounded like nothing I had ever experienced. As we slowly motored along, I peered more closely at the trees that fringed the shoreline. They had gnarled trunks and twisted branches that supported a canopy of dark green leaves. These trees were red mangroves or Rhizophora mangle, their scientific name, and were the dominant vegetation here. These oceanic mangrove islands were intertidal, which means that the trees were inundated twice a day by the sea. Their intimate relationship with the sea, however, was most apparent along the water’s edge. Long, drop roots plunged from the canopy to dangle in the crystal-clear water. Encrusted on the submerged portions of the mangrove roots were yellow and orange sponges, white and pink anemones, sharp-edged oysters, and feathery-green algae. The mangroves, it turned out, provided the only solid substrate for these sessile creatures. There were also mobile animals that I glimpsed as I leaned over the pontoon to peer into the pellucid water. Tiny fish flashed among the partially submerged roots as each one briefly flipped its body sideways to catch the sun glinting through the water. A school of mangrove snappers swam past the boat and disappeared under the overhanging creekbank, which created a shadowy haven from predators. Ribbons of turtlegrass, uprooted from the nearby reef flat, were draped on mangrove prop roots like green and brown tinsel. As the zodiac floated closer to shore, I spotted a mangrove tree crab, which stealthily crept up a tree trunk. In the distance, I could hear the hectoring cry of an osprey, as well as the periodic cheep-cheep of a mangrove warbler deeper in the forest. A soft breeze carried the faint odor of rotten eggs, which was caused by the microbially mediated production of hydrogen sulfide in the waterlogged soil. This was my first close-up view of Belize’s mangroves. The year was 1985. The movie “Back to the Future” had just premiered, PLO terrorists had hijacked the Italian cruise ship Achille Lauro, five people had died after ingesting cyanide-laced Tylenol, and Microsoft had just released Windows 1.0. I had recently gotten a Macintosh personal computer with 128k of memory (seemed like a lot back then) and was learning how to use Cricket Graph, my first software program. Until that point, I had been creating graphs by hand with ink-filled drawing pens, T-squares, and Letraset dry-transfer sheets. This was a time when the world seemed to be on the verge of dramatic changes—many that would impact me and my career as a scientist.

Book chapter↗

USGS1998

Human versus lightning ignition of presettlement surface fires in costal pine forests of the upper Great Lakes

To recover direct evidence of surface fires before European settlement, we sectioned fire-scarred logging-era stumps and trees in 39 small, physically isolated sand patches along the Great Lakes coast of northern Michigan and northern Wisconsin. While much information was lost to postharvest fire and stump deterioration, 147 fire-free intervals revealed in cross-sections from 29 coastal sand patches document numerous close interval surface fires before 1910; only one post-1910 fire was documented. Cross-sections from the 10 sections with records spanning >150 yr suggest local fire occurrence rates before 1910 ca. 10 times the present rate of lightning-caused fire. Since fire spread between or into coastal sand patches is rare, and seasonal use of the patches by Native people before 1910 is well documented, both historically and ethnographically, ignition by humans probably accounts for more than half of the pre-1910 fires recorded in cross-sections.

American Midland Naturalist↗

USGS2021

Retrospective analysis of estrogenic endocrine disruption and land-use influences in the Chesapeake Bay watershed

The Chesapeake Bay is the largest estuary in the United States and its watershed includes river drainages in six states and the District of Columbia. Sportfishing is of major economic interest, however, the rivers within the watershed provide numerous other ecological, recreational, cultural and economic benefits, as well as serving as a drinking water source for millions of people. Consequently, major fish kills and the subsequent finding of estrogenic endocrine disruption (intersex or testicular oocytes and plasma vitellogenin in male fishes) raised public and management concerns. Studies have occurred at various sites within the Bay watershed to document the extent and severity of endocrine disruption, identify risk factors and document temporal and spatial variability. Data from these focal studies, which began in 2004, were used in CART (classification and regression trees) analyses to better identify land use associations and potential management practices that influence estrogenic endocrine disruption. These analyses emphasized the importance of scale (immediate versus upstream catchment) and the complex mixtures of stressors which can contribute to surface water estrogenicity and the associated adverse effects of exposure. Both agricultural (percent cultivated, pesticide application, phytoestrogen cover crops) and developed (population density, road density, impervious surface) land cover showed positive relationships to estrogenic indicators, while percent forest and shrubs generally had a negative association. The findings can serve as a baseline for assessing ongoing restoration and management practices.

Chesapeake Bay river watersheds↗

USGS2022

Florida and Landsat

More than 21 million people call Florida home, but many more visit the peninsula each year—including a record 131 million in 2019. Residents and tourists enjoy the State’s warm weather and varied attractions amid incredibly diverse biological and natural resources. Numerous lakes and rivers, and 8,400 miles of ocean shoreline, play a prominent role, as do unique habitats like the Everglades, which are home to protected species such as the Florida manatee ( Trichechus manatus latirostris ), American crocodile ( Crocodylus acutus ), and Florida panther ( Puma concolor couguar ). The State also supports cattle, sugarcane, and citrus production—along with nearly one-half of the tree species in the United States. A changing climate is expected to bring rising sea levels and more extreme weather events. In a State where the average elevation is 100 feet above sea level, climate change could affect everything from urban shores and beaches to agriculture and forests. In addition, as cities grow, more land cover tends to shift from natural vegetation to impervious surfaces such as pavement, which can add to environmental risks such as flooding. Landsat can help Florida’s agencies, organizations, and residents monitor the State’s fragile landscapes and plan for a resilient future. Here are just a few examples of how Landsat benefits Florida.

Florida↗

USGS2019

Late-Glacial paleoecology of the Middle Susitna Valley, Alaska: Environmental context for human dispersal

We present here the results of multi-proxy analyses (sediment geochemistry, diatoms, and pollen) from sediment cores collected at four lakes in the middle Susitna Valley, Alaska. These lakes form a transect from the tundra to the boreal forest. The retrieved cores span from ~12,000 cal yr BP to the present, with age control provided by radiometric dates and tephra deposits, some of which are newly identified. Results indicate that deglaciation occurred before 12,000 cal yr BP and that by that time, the lakes were deep, productive, and surrounded by shrub tundra. The lake with the highest sampling resolution indicates a brief climatic reversal ~11,500 cal yr BP with decreased diatom-inferred lake level and lowered lake productivity, and reduced shrub presence. During the early to middle Holocene, all of the sedimentary records provide evidence of climatic amelioration with tree expansion and productive lakes. A middle to late Holocene climatic deterioration with reduced trees and a shallower, less productive lake is also indicated. In addition, the prominent Watana tephra at ~4,000 cal yr BP likely reduced lake productivity and affected the vegetation. Even though the region was relatively productive soon after deglaciation, people did not occupy the region until ~11,000 cal yr BP, about 1000 years later, and then only sparsely. By the middle and late Holocene, the region was more densely populated and this shift in human occupancy presumably reflects changes in resource abundance, especially caribou. Whether the Watana ashfall influenced caribou abundance and thus people, is still under investigation, but given the tephra’s effect on vegetation and lake productivity, it seems likely.

Alaska↗

USGS2021

California and Landsat

California has remarkable geographic diversity, from 1,100 miles of Pacific shoreline to 33 million acres of trees, including its famous redwood forests along the Pacific Coast Highway, U.S. Route 101. And although California’s nickname is “The Golden State," it may also deserve the title of “The Extreme State.” Mount Whitney, the highest peak in the conterminous United States, stands at 14,494 feet above sea level in the Sierra Nevada mountain range. Just 2.5 hours away by car, Death Valley’s Badwater Basin boasts the lowest point in the United States: 282 feet below sea level. Although hundreds of inches of snow fall on Mount Whitney each year, the rainfall in Death Valley, commonly called the hottest place on Earth, averages less than 2 inches. California is the most populous U.S. State with 39 million residents, 26 million of whom live near the coast. It’s also the most agriculturally productive State, raising a variety of fruits, vegetables, nuts, grains, grasses, and flowers in addition to dairy and livestock. Although climate change affects many of these people, production, and places, Landsat can help agencies and residents monitor their landscapes and plan for a resilient future.

California↗

USGS2001

Desertification and a shift of forest species in the West African Sahel

Original field data show that forest species richness and tree density in the West African Sahel declined in the last half of the 20th century. Average forest species richness of areas of 4 km2 in Northwest Senegal fell from 64 ?? 2 species ca 1945 to 43 ?? 2 species in 1993, a decrease significant at p < 0.001. Densities of trees of height ???3 m declined from 10 ?? 0.3 trees ha-1 in 1954 to 7.8 ?? 0.3 trees ha-1 in 1989, also significant at p < 0.001. Standing wood biomass fell 2.1 t ha-1 in the period 1956-1993, releasing CO2 at a rate of 60 kgC person-1 yr-1. These changes have shifted vegetation zones toward areas of higher rainfall at an average rate of 500 to 600 m yr-1. Arid Sahel species have expanded in the north, tracking a concomitant retraction of mesic Sudan and Guinean species to the south. Multivariate analyses identify latitude and longitude, proxies for rainfall and temperature, as the most significant factors explaining tree and shrub distribution. The changes also decreased human carrying capacity to below actual population densities. The rural population of 45 people km-2 exceeded the 1993 carrying capacity, for firewood from shrubs, of 13 people km-2 (range 1 to 21 people km-2). As an adaptation strategy, ecological and socioeconomic factors favor the natural regeneration of local species over the massive plantation of exotic species. Natural regeneration is a traditional practice in which farmers select small field trees that they wish to raise to maturity, protect them, and prune them to promote rapid growth of the apical meristem. The results of this research provide evidence for desertification in the West African Sahel. These documented impacts of desertification foreshadow possible future effects of climate change.

Climate Research↗

USGS2021

Modeling distribution of endemic Bartram’s Bass Micropterus sp. cf. coosae: Disturbance and proximity to invasion source increase hybridization with invasive Alabama Bass

“Bartram’s Bass” Micropterus sp. cf. coosae is endemic to the upper Savannah River basin of the southeastern United States and is threatened by hybridization with invasive Alabama Bass Micropterus henshalli . Bartram’s Bass have been functionally extirpated from reservoirs, and hybrid individuals have been detected in several tributaries. However, the extent of introgression in tributaries is currently unknown. Our objectives were to (1) assess the distribution of Bartram’s Bass, native Largemouth Bass M . salmoides , invasive Alabama Bass, and their hybrids in streams of the upper Savannah River basin and (2) quantify effects of abiotic variables on the distribution of each species. We sampled 154 locations in 2017 and 2018 and assigned genetic identity using hydrolysis probes and microsatellites. We used conditional inference trees to quantify variables affecting the occurrence of each species and hybrids. We observed widespread hybridization across the basin. Pure Bartram’s Bass were collected at 27% (42) of sites, among which only 12 sites contained pure Bartram’s Bass and no other congeners. Thirty sites where pure Bartram’s Bass were collected contained hybrids. In the montane Blue Ridge ecoregion, occurrence of pure Bartram’s Bass was negatively affected by low levels of local-scale developed land cover. In the lower-relief Piedmont ecoregion, pure Bartram’s Bass were positively associated with watershed-scale forest land cover and stream gradient. Distance from a reservoir was positively associated with occurrence of pure Bartram’s Bass in both ecoregions. Pure Bartram’s Bass are likely to occur with high probability in only 16% of nonimpounded stream segments; this represents a conservative estimate, and the true number is likely lower. However, future work accounting for incomplete detection of Bartram’s Bass will help to improve confidence in true extirpations. Conservation efforts may be more successful if implemented on stream segments farther from reservoirs or upstream of dispersal barriers preventing colonization of Alabama Bass.

Georgia, North Carolina, South Carolina↗