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From Swamps to Deserts, From Habitat Disturbance to Recovery, USGS Scientists Highlight Their Research
Released: 8/4/2002

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Catherine Puckett 1-click interview
Phone: 707-442-1329

Gloria Maender
Phone: 520-670-5596

Lighting a Fire under Exotic Plant Invaders: Restoring fire to coniferous forests after a century of fire suppression is being widely considered throughout the Western United States. While fire was historically a natural ecosystem process in these forests, it is being returned to a landscape that now has alien plants often poised for colonization after any disturbance, including natural fires. In the Sierra Nevada, researchers have clear evidence that high-intensity fires assist the invasion process if alien seed sources are nearby. Additionally, mechanical manipulation of fire fuels, such as clearing fuel breaks, may create "invasive corridors" that can carry alien species into uninfested wildland areas. Fuel breaks also assist in maintaining seed banks for alien annual plants, which readily burn and perpetuate the cycle of invasion. Learn more about "Impact of fire management practices on invasive plants," presented by Jon Keeley on Tues., Aug. 6 at 3:05 p.m. in the Turqoise Meeting Room, TCC, or by calling him at 559-565-3170.

Using Fire to Thin Understory in Old-Growth Forests: More than a century of fire suppression in the Sierra Nevada has resulted in accumulation of surface fuels and higher densities of small trees, increasing the potential for large, destructive crown fires. Resource managers are using prescribed fire to thin stands, reduce fuel loads, and restore natural forest structure and process. However, some researchers and land managers are concerned that the long fire-free interval in these forests may result in unnaturally high fire intensity, leading to excessive mortality of large overstory trees. To determine patterns of tree death in response to the reintroduction of fire, USGS scientists used prescribed fire on test plots that had not burned in more than 100 years. Preliminary results show that initial death of trees was locally high in places where fire intensity was greatest, but patchy overall, despite the large amounts of accumulated fuels from the many years of no fires. Prescribed fire killed only a small percentage of the largest trees, yet successfully removed many of the small trees that contribute to increased danger of severe wildfire. In a forest’s natural fire regime, not all fires are of the same intensity, which means that there is a varied and ecologically important pattern of tree deaths, as happened in these test fires. Learn more about "Tree mortality following reintroduction of fire to an old growth mixed conifer forest," presented by Eric Knapp on Aug. 8 at 11:15 a.m. in the Mohave Meeting Room, TCC, or by calling him at 559-565-3175.

How Fire and Other Disturbances Influence Plant Invasions: Regeneration of many native plant species depends on natural disturbances such as fire. Yet researchers and land managers also recognize that this fire disturbance now creates the opportunity for non-native species to colonize otherwise intact ecosystems. How are land managers to know which types of disturbance, when combined, may hinder or increase invasion? These issues are important to managers who must make decisions regarding how to control or use fire and other types of disturbance as part of landscape management. Learn more about "Fire and other forms of disturbance: are they similar and do they have similar effects on invasive plants," presented by Matt Brooks on Tues., Aug. 6 at 1:10 p.m. in the Turqoise Meeting Room, TCC, or by calling him at 702-914-2206 x225.

A Desert Not Forever? Several species of invasive exotic plants that are now widely dispersed across the Mojave Desert have the potential to increase the frequency of wildfires, enable fires to spread over large areas, and increase the desert’s susceptibility to future fires. The effects of a single desert fire may persist for 50 years, or more. In some areas, repeated burning has eliminated perennial plants and converted native desertscrub into annual exotic grasslands, perhaps irreversibly, under the current climate regime. USGS scientists are developing models to predict how some Mojave Desert habitats may be affected in the future by increased fire, exotic plant invasions and climate change. Learn more about "Fire and exotics in the Mojave Desert: an irreversible change?" presented by Dustin Haines on Tues., Aug. 6 at 10:30 a.m. in the Maricopa Meeting Room, TCC, or by calling him at 702-914-2206 x232.

Desert Fires Rob the Bank: Seeds from annual plants naturally accumulate in seed "banks" in the Mojave Desert and persist until conditions are favorable for the next plant cycle. Fluctuations in plant populations are reflected in the seed bank, particularly when severe disturbances such as fire occur. Scientists conducting experiments to examine how fire and seed-eating ants and rodents affect desertscrub seed banks, have found that fire, not seed-eaters, affects seed bank dynamics, reducing native seed diversity and density. High-intensity or sequential fires in combination with alien annual grass invasions may even be capable of driving native seeds banks toward local extinctions. Learn more about "Seed bank variation in Mojave desertscrub relative to wildfire, granivores and invasive species," presented by Todd Esque on Tues., Aug. 6 at 10:00 a.m. in the Graham Meeting Room, TCC, or by calling him at 702-914-2206 x226.

Seed Banks, But No Seeds: Farmed fields that were once baldcypress swampland tend to lack living seeds of almost all woody species including trees, shrubs and vines, making restoration of them more difficult than many other types of wetlands. The tendency of woody species to be lost quickly from the seed bank (stored seed in the soil) of farmed fields is probably mostly due to the inherent short-lived nature of the seeds and the hydrologic changes associated with drying fields for farming. The lack of woody species in farmed fields means that restorationists must find ways to reconnect aquatic dispersal of woody species to the target restoration site (e.g., via flood pulsing). Alternatively, woody species can be planted, but this practice has thus far failed to create high-diversity swamps. Learn more at "Regional spatial patterns of seed banks of bald cypress swamps at the northern extreme of the Mississippi Alluvial Valley," presented by Beth Middleton on Thurs., Aug. 8 at 2 p.m. in the Gila Meeting Room, TCC, or call her at 337-266-8618.

Double Whammies and Silver Linings — Wildland Fire and Invasive Plants: As wildfires rage across many areas of the country this summer, we are reminded of the importance of fire as a natural phenomenon. Now there is increased interest in the longer-term effects of fire, as national efforts are mounted to combat the spread of invasive species. The potential exists for both positive and negative effects of fire on invading species through a complex web of interaction. Knowledge of these interactions may serve to aid land managers in their efforts to eradicate invaders that are fire-intolerant and avoid the incidental spread of fire-resistant species. Learn more about "A general conceptual model of the interactions between invasives and fire: current status and future directions," presented by Jim Grace on Tues., Aug. 6 at 2:25 p.m. in the Turquoise Ballroom, TCC, or by calling him at 377-266-8632.

Restoring Livestock Watering Sites in the Mojave Desert: Domestic livestock have grazed the Mojave Desert for more than 150 years. Recently, land management agencies have reduced grazing and focused efforts on restoring degraded rangelands. Assessments of plant community changes caused by grazing have been lacking, however, for the central Mojave Desert. To fill this need so that managers can better define restoration objectives, USGS scientists assessed grazing disturbance associated with livestock watering sites in a recently closed grazing allotment. Their findings suggest that grazing impacts on plant communities are greatest from about 55 to 220 yards away from watering sites. Learn more about "Plant community structure associated with livestock watering sites in the central Mojave Desert," presented by John Matchett on Fri., Aug. 9 at 9:45 a.m. in the Graham Meeting Room, TCC, or by calling him at 702-914-2206 x229.

Improving Tools for Fire Managers: Tree death is one of the most obvious and important effects of forest fires. Predicting which trees will die following a fire is difficult, and land managers need a better understanding of tree death processes to assess how fire might affect natural landscapes. New USGS research shows that the death process for burned and unburned trees is not fundamentally different. The research demonstrates that the overall health of a tree, as measured by the tree’s growth rate, indicates its resistance to fire-caused damage, much the same as tree health indicates a tree’s resistance to other stressors, such as insects and fungi. This information will aid managers planning prescribed burns or post-fire restoration operations. Learn more about "Searching for a general model of tree death in burned and unburned stands," presented by Phillip van Mantgem on Wed., Aug. 7 at 10:30 a.m. in the Apache Meeting Room, TCC, or by calling him at 559-565-3179.

Disturbance and Climate Change Can Spoil the Soil: Biological soil crusts are a dominant feature in arid and semi-arid ecosystems, displaying many different ecological roles. Land use, invasive plants and climate change can strongly affect them. Soil surface disturbance and dominance by invasive plants result in loss of lichens and mosses, leaving cyanobacteria dominating the soil surface. This loss reduces soil stability, carbon and nitrogen contributions, surface temperatures and soil water retention times. Climate change will differentially affect crust species and thus change species composition. These changes can alter nutrient cycles, soil moisture and soil temperatures, having ramifications throughout the soil food webs and attendant nutrient cycles. Learn more about which of these factors is most likely to influence recovery and restoration of biological soil crusts at "Biological soil crusts: effects of global change on ecosystem roles and restoration" presented by Jayne Belnap on Thurs., Aug. 8, at 1:30 p.m. in the Leo Rich Theatre, TCC, or by calling her at 435-719-2333.

Got Calcium? High levels of nitrogen in the soil contribute to rapid tree growth and intensive short-rotation forestry in conifer forests of the Oregon Coast Range. Yet nutrient losses that accompany tree harvest may affect long-term nutritional balances. Over the past decade, substantial reductions in forest growth and integrity have occurred in some areas. Nitrogen-rich sites may lose calcium over time because of rapid tree growth, forest harvest and nutrient leaching. The preliminary results of a study using soil and leaf data from 22 randomly selected Douglas-fir plantations indicate that sites with high levels of nitrogen in the soil have low levels of calcium and magnesium. Learn more about "Forest harvest, N saturation, and potential base cation depletion in coastal Oregon forests," presented by Steven Perakis on Mon., Aug. 5 at 1:30 p.m. in the Grand Ballroom Central, Radisson, or by calling him at 541-758-8786.

Fossil Middens Rat on History of Pinyon Pines: The last 50,000 years of biogeographic history of pinyon pines are well documented by the abundant needles and seeds found in fossil packrat middens throughout the Western United States. A study of the middens suggests that natural plant distributions may take many thousands of years to adjust to a period of warming climate such as that expected during the next 100 years. For example, as the climate warmed at the end of the Ice Age (about 11,000 years ago), Pinus edulis expanded its range northward from Arizona and New Mexico. This pinyon pine species did not reach its present northern and eastern limits in Colorado, however, until the last 1,000 years. Learn more about "The biogeographic histories of Pinus monophylla and Pinus edulis," presented by Kenneth Cole on Mon., Aug. 5 at 1:30 p.m. in the Graham Meeting Room, TCC, or by calling him at 928-556-7466, ext. 230.

Vegetation in Severely Disturbed Sites in the Mojave Desert Can Recover Naturally: Scientists studying disturbances that occurred 10-93 years ago in utility corridors, military training camps, and abandoned mining towns, are finding that native perennial species can reestablish after disturbance without any help from humans. There is high variability in species composition of initial recolonizers, but total perennial plant cover, regardless of species composition, may recover in less than 100 years. Several thousand years, however, may be needed for the species composition to be the same as that before disturbance. The life history of colonizing species provides a framework to understand and project the recovery trajectory for a disturbed site. Climate change, increased carbon dioxide in the atmosphere and introduction of invasive exotic species may confound such predictions of a natural recovery trajectory. Learn more about "Natural recovery of perennial vegetation in severely disturbed sites in the Mojave Desert" presented by Kathryn Thomas on Tues., Aug. 6 at 9:30 a.m. in the Maricopa Meeting Room, TCC, or by calling her at 928-556-7466, ext.235.

Just How Tough Are These Crusts? Biological soil crusts, a community of lichens, mosses, and cyanobacteria found on soil surfaces, are an essential component of arid and semi-arid ecosystems. They are important for soil stability, decreasing sediment loss from both wind and water erosion. They provide fixed nitrogen and decrease surface reflection. Mojave Desert crusts are easily damaged or destroyed by soil surface disturbances such as livestock grazing, off-road recreational vehicles, and military training exercises. Land managers need the ability to distinguish surfaces on the basis of resistance to disturbance, as well as expected recovery times after disturbance. Initial studies in the Mojave Desert show that within a given climate regime, resistance to disturbance is best predicted by soil texture, and that crusts require more than a century for recovery if significant shearing occurs. Learn more about how to predict where crusts are and more about "Resistance and resilience of biological soil crusts to soil surface disturbance in the Mojave Desert," presented by Susan Phillips on Tues., Aug. 6 at 8:50 a.m. in the Maricopa Meeting Room, TCC, or by calling her at 435-719-2337.

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