Under a changing climate, devising strategies to help stakeholders adapt to alterations to ecosystems and their services is of utmost importance. In western North America, diminished snowpack and river flows are causing relatively gradual, homogeneous (system-wide) changes in ecosystems and services. In addition, increased climate variability is also accelerating the incidence of abrupt and patchy disturbances such as fires, floods and droughts. This paper posits that two key variables often considered in landscape ecology—the rate of change and the degree of patchiness of change—can aid in developing climate change adaptation strategies. We use two examples from the “borderland” region of the southwestern United States and northwestern Mexico. In piñon-juniper woodland die-offs that occurred in the southwestern United States during the 2000s, ecosystem services suddenly crashed in some parts of the system while remaining unaffected in other locations. The precise timing and location of die-offs was uncertain. On the other hand, slower, homogeneous change, such as the expected declines in water supply to the Colorado River delta, will likely impact the entire ecosystem, with ecosystem services everywhere in the delta subject to alteration, and all users likely exposed. The rapidity and spatial heterogeneity of faster, patchy climate change exemplified by tree die-off suggests that decision-makers and local stakeholders would be wise to operate under a Rawlsian “veil of ignorance,” and implement adaptation strategies that allow ecosystem service users to equitably share the risk of sudden loss of ecosystem services before actual ecosystem changes occur. On the other hand, in the case of slower, homogeneous, system-wide impacts to ecosystem services as exemplified by the Colorado River delta, adaptation strategies can be implemented after the changes begin, but will require a fundamental rethinking of how ecosystems and services are used and valued. In sum, understanding how the rate of change and degree of patchiness of change will constrain adaptive options is a critical consideration in preparing for climate change.
Long-term change in perennial vegetation along the Colorado River in Grand Canyon National Park (1889-2010)
Long-term monitoring data for perennial vegetation are difficult to obtain (Webb et al. 2009), particularly in remote terrain. Climate change and other anthropogenic influences have impacts on these isolated areas, and managers require scientific evaluations of landscape changes to make informed decisions about whether restoration or mitigation strategies are needed to ensure that resources remain intact for future generations. At the bottom of Grand Canyon (Arizona), the Colorado River winds about 450 km (280 miles) through a narrow, canyon-bound river corridor sustaining desert and riparian vegetation on substrates ranging from bedrock to river sandbars, creating a challenging environment for change-detection monitoring techniques (Belnap et al. 2008).
A quantitative food web approach for estimating selenium flux in the Colorado River in Grand Canyon
Tamarix spp. are introduced shrubs that have become among the most abundant woody plants growing along western North American rivers. We sought to empirically test the long-held belief that Tamarix actively displaces native species through elevating soil salinity via salt exudation. We measured chemical and physical attributes of soils (e.g., salinity, major cations and anions, texture), litter cover and depth, and stand structure along chronosequences dominated by Tamarix and those dominated by native riparian species (Populus or Salix) along the upper and lower Colorado River in Colorado and Arizona/California, USA. We tested four hypotheses:
The rate of salt accumulation in soils is faster in Tamarix dominated stands than stands dominated by native species,
The concentration of salts in the soil is higher in mature stands dominated by Tamarix compared to native stands,
Soil salinity is a function of Tamarix abundance, and
Available nutrients are more concentrated in native-dominated stands compared to Tamarix-dominated stands.
We found that salt concentration increases at a faster rate in Tamarix-dominated stands along the relatively freeflowing upper Colorado but not along the heavily regulated lower Colorado. Concentrations of ions that are known to be preferentially exuded by Tamarix (e.g., B, Na, and Cl) were higher in Tamarix stands than in native stands. Soil salt concentrations in older Tamarix stands along the upper Colorado were sufficiently high to inhibit germination, establishment, or growth of some native species. On the lower Colorado, salinity was very high in all stands and is likely due to factors associated with floodplain development and the hydrologic effects of river regulation, such as reduced overbank flooding, evaporation of shallow ground water, higher salt concentrations in surface and ground water due to agricultural practices, and higher salt concentrations in fine-textured sediments derived from naturally saline parent material.
Restoration of the razorback sucker in the Colorado River, southwestern United States
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Proceedings of the World River Conference, November 19-20, Gifu, Japan
Although it's been around for tens of thousands of years, Xyrauchen texanus, or the razorback sucker, is a fish few people recognize. Once abundant in the turbulent and unpredictable Colorado River, the razorback sucker is now restricted to a few remnant populations, the largest being found in Lake Mohave, Arizona-Nevada. Habitat loss due to channelization and reservoir construction, along with competition and predation by over 40 introduced fish species in the Basin, led to the listing of the razorback sucker as an endangered species in 1991...
Fish introduction impacts on fisheries and water quality
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21st Annual National Conference Enhancing the States’ Lake Management Programs, Chicago, Illinois, April 29-May 2, 2008