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The development of water resources to satisfy urban water needs has had serious impacts on freshwater ecosystem integrity and on valuable ecosystem services, but positive trends are emerging that point the way toward a solution. We demonstrate this through case studies of water resource development in and around five large urban areas: Los Angeles, Phoenix, New York, San Antonio, and Atlanta. Providing freshwater ecosystems with the water flows necessary to sustain their health, while meeting the other challenges of urban water management, will require greatly increased water productivity in conjunction with improvements in the degree to which planning and management take ecosystem needs into account. There is great...
The rate of future climate change is likely to exceed the migration rates of most plant species. The replacement of dominant species by locally rare species may require decades, and extinctions may occur when plant species cannot migrate fast enough to escape the consequences of climate change. Such lags may impair ecosystem services, such as carbon sequestration and clean water production. Thus, to assess global change, simulation of plant migration and local vegetation change by dynamic global vegetation models (DGVMs) is critical, yet fraught with challenges. Global vegetation models cannot simulate all species, necessitating their aggregation into plant functional types (PFTs). Yet most PFTs encompass the full...
We have employed herbarium specimens, historical records and molecular techniques in reconstructing the introduction and spread of Bromus tectorum L. (or Anisantha tectorum [L.] Nevski [Stace 1997]) (Figure 1) into North America and other portions of the grass's naturalized ranges (Novak et al. 1991, Novak and Mack 1993, Novak et al. 1993). We summarize in this article a portion of our findings from this ongoing effort. Published in Bioscience, volume 51, issue 2, on pages 114 - 122, in 2001.
Categories: Publication; Types: Citation, Journal Citation; Tags: Bioscience
Water controls the dynamics of terrestrial ecosystems directly, as a resource for the biota, and indirectly, as a driver for abiotic processes on the Earth's surface, in the atmosphere, and belowground. The biota, in turn, modulate several hydrological processes and the rate of the water cycle. Here we review recent advances related to fundamental processes and feedbacks emerging from the interactions among hydrologic processes and ecosystems, with a particular focus on soil moisture dynamics and river flow. Most terrestrial vegetation interacts with hydrological processes through the soil-water balance, which is affected by soil properties, random climate drivers, and feedbacks with the biota. River flow enhances...
How many cows can western public rangelands accommodate? If extreme environmentalists and ranchers had to concur on a response, it would be as difficult as answering "How many angels can dance on the head of a pin?" The battle cry of supporters of the environmental group Earth First! is "Cattle free by '93''; they argue that chomping cattle are the scourge of western ranges and that grazing has been the major force repainting the ecological picture of the west. They reason that damage caused by cattle to the riparian corridors and upland regions, and the effects of that damage on plants and wildlife, is reason enough to completely bar cattle from public ranges. Many ranchers view any prohibitions on grazing as an...
Categories: Publication; Types: Citation, Journal Citation; Tags: BioScience
Photosynthetic assimilation of atmospheric carbon dioxide by land plants offers the underpinnings for terrestrial carbon (C) sequestration. A proportion of the C captured in plant biomass is partitioned to roots, where it enters the pools of soil organic C and soil inorganic C and can be sequestered for millennia. Bioenergy crops serve the dual role of providing biofuel that offsets fossil-fuel greenhouse gas (GHG) emissions and sequestering C in the soil through extensive root systems. Carbon captured in plant biomass can also contribute to C sequestration through the deliberate addition of biochar to soil, wood burial, or the use of durable plant products. Increasing our understanding of plant, microbial, and...
Climatic changes are predicted to significantly affect the frequency and severity of disturbances that shape forest ecosystems. We provide a synthesis of climate change effects on native bark beetles, important mortality agents of conifers in western North America. Because of differences in temperature-dependent life-history strategies, including cold-induced mortality and developmental timing, responses to warming will differ among and within bark beetle species. The success of bark beetle populations will also be influenced indirectly by the effects of climate on community associates and host-tree vigor, although little information is available to quantify these relationships. We used available population models...
Transitions between atmosphere and soil, and between soil and roots, are two examples of small-scale boundaries across which the nutrient, water, and gas dynamics of ecosystems are modulated. Most atmospheric inputs to ecosystems have to pass through the soil; thus, the atmosphere?soil boundary influences the type and amount of materials and energy entering the soil. Belowground plant inputs occur through the rhizosphere, the zone of soil immediately adjacent to the root. This soil boundary layer affects root inputs to soil and root extraction of water and nutrients from soil. We discuss how water, carbon, nitrogen, and oxygen dynamics are affected by atmosphere?soil and soil?root boundaries and how light, soil...
In the western United States vast acreages of land are exposed to low levels of atmospheric nitrogen (N) deposition, with interspersed hotspots of elevated N deposition downwind of large, expanding metropolitan centers or large agricultural operations. Biological response studies in western North America demonstrate that some aquatic and terrestrial plant and microbial communities are significantly altered by N deposition. Greater plant productivity is counterbalanced by biotic community changes and deleterious effects on sensitive organisms (lichens and phytoplankton) that respond to low inputs of N (3 to 8 kilograms N per hectare per year). Streamwater nitrate concentrations are elevated in high-elevation catchments...
Osvel Hinojosa Huerta paddles his canoe across the Cienega de Santa Clara one bright, warm fall day. The cienega, a 14,000-acre lake and marshland, lies near where the Colorado River flows into the Gulf of California in Mexico. Thick rows of cattails and tasseltopped reeds line the shore, providing habitat for the endangered Yuma clapper rail. The cienega’s shallow waters hold tilapia, catfish, carp, and largemouth bass, as well as desert pupfish, another endangered species. Overhead appear widgeons, cormorants, terns, pelicans, and herons. “This is the largest wetland in the delta,� says Hinojosa, a PhD candidate in wildlife biology at the University of Arizona in Tucson and director of Sonoran Desert conservation...
The Ahakhav Preserve is one of several places on the Colorado River and its tributaries south of Lake Mead where government agencies, Indian tribes, private groups, and individual landowners are seeking to recreate at least a portion of the former riparian ecosystem. Efforts are under way or planned to restore the native flora at selected sites and to bolster the population of native Colorado River fish decimated by a changed river and the introduction of new species. Further, a coalition of government agencies and private companies in three states is developing a controversial multispecies conservation plan for the river and its endangered wildlife. Published in BioScience, volume 51, issue 12, on pages 998 - 1003,...
Physical ecosystem engineers are organisms that physically modify the abiotic environment. They can affect biogeochemical processing by changing the availability of resources for microbes (e.g., carbon, nutrients) or by changing abiotic conditions affecting microbial process rates (e.g., soil moisture or temperature). Physical ecosystem engineers can therefore create biogeochemical heterogeneity in soils and sediments. They do so via general mechanisms influencing the flows of materials (i.e., modification of fluid dynamic properties, fluid pumping, and material transport) or the transfer of heat (i.e., modification of heat transfer properties, direct heat transfer, and convective forcing). The consequences of physical...
Billions of dollars are being spent in the United States to restore rivers to a desired, yet often unknown, reference condition. In lieu of a known reference, practitioners typically assume the paradigm of a connected watercourse. Geological and ecological processes, however, create patchy and discontinuous fluvial systems. One of these processes, dam building by North American beavers (Castor canadensis), generated discontinuities throughout precolonial river systems of northern North America. Under modern conditions, beaver dams create dynamic sequences of ponds and wet meadows among free-flowing segments. One beaver impoundment alone can exceed 1000 meters along the river, flood the valley laterally, and fundamentally...