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At least 181 records · Page 10Linked to original sources
USGS2013

Projecting the land cover change and its environmental impacts in the Cedar River Basin in the Midwestern United States

The physical surface of the Earth is in constant change due to climate forcing and human activities. In the Midwestern United States, urban area, farmland, and dedicated energy crop (e.g., switchgrass) cultivation are predicted to expand in the coming decades, which will lead to changes in hydrological processes. This study is designed to (1) project the land use and land cover (LULC) by mid-century using the FORecasting SCEnarios of future land-use (FORE-SCE) model under the A1B greenhouse gas emission scenario (future condition) and (2) assess its potential impacts on the water cycle and water quality against the 2001 baseline condition in the Cedar River Basin using the physically based soil and water assessment tool (SWAT). We compared the baseline LULC (National Land Cover data 2001) and 2050 projection, indicating substantial expansions of urban area and pastureland (including the cultivation of bioenergy crops) and a decrease in rangeland. We then used the above two LULC maps as the input data to drive the SWAT model, keeping other input data (e.g., climate) unchanged to isolate the LULC change impacts. The modeling results indicate that quick-response surface runoff would increase significantly (about 10.5%) due to the projected urban expansion (i.e., increase in impervious areas), and the baseflow would decrease substantially (about 7.3%) because of the reduced infiltration. Although the net effect may cause an increase in water yield, the increased variability may impede its use for public supply. Additionally, the cultivation of bioenergy crops such as switchgrass in the newly added pasture lands may further reduce the soil water content and lead to an increase in nitrogen loading (about 2.5% increase) due to intensified fertilizer application. These study results will be informative to decision makers for sustainable water resource management when facing LULC change and an increasing demand for biofuel production in this area.

Environmental Research Letters↗
USGS2009

Climatic effects of 30 years of landscape change over the Greater Phoenix, Arizona, region: 1. Surface energy budget changes

This paper is part 1 of a two-part study that evaluates the climatic effects of recent landscape change for one of the nation's most rapidly expanding metropolitan complexes, the Greater Phoenix, Arizona, region. The region's landscape evolution over an approximate 30-year period since the early 1970s is documented on the basis of analyses of Landsat images and land use/land cover (LULC) data sets derived from aerial photography (1973) and Landsat (1992 and 2001). High-resolution, Regional Atmospheric Modeling System (RAMS), simulations (2-km grid spacing) are used in conjunction with consistently defined land cover data sets and associated biophysical parameters for the circa 1973, circa 1992, and circa 2001 time periods to quantify the impacts of intensive land use changes on the July surface temperatures and the surface radiation and energy budgets for the Greater Phoenix region. The main findings are as follows: since the early 1970s the region's landscape has been altered by a significant increase in urban/suburban land area, primarily at the expense of decreasing plots of irrigated agriculture and secondarily by the conversion of seminatural shrubland. Mean regional temperatures for the circa 2001 landscape were 0.12??C warmer than the circa 1973 landscape, with maximum temperature differences, located over regions of greatest urbanization, in excess of 1??C. The significant reduction in irrigated agriculture, for the circa 2001 relative to the circa 1973 landscape, resulted in dew point temperature decreases in excess of 1??C. The effect of distinct land use conversion themes (e.g., conversion from irrigated agriculture to urban land) was also examined to evaluate how the most important conversion themes have each contributed to the region's changing climate. The two urbanization themes studied (from an initial landscape of irrigated agriculture and seminatural shrubland) have the greatest positive effect on near-surface temperature, increasing maximum daily temperatures by 1??C. Overall, sensible heat flux differences between the circa 2001 and circa 1973 landscapes result in a 1 W m -2 increase in domain-wide sensible heating, and a similar order of magnitude decrease in latent heating, highlighting the importance of surface repartitioning in establishing near-surface temperature trends. In part 2 of this study, we address the role of the surface budget changes on the mesoscale dynamics/thermodynamics, in context of the large-scale environment. Copyright 2009 by the American Geophysical Union.

Journal of Geophysical Research D: Atmospheres↗
USGS2016

Comparing three approaches of evapotranspiration estimation in mixed urban vegetation; field-based, remote sensing-based and observational-based methods

Despite being the driest inhabited continent, Australia has one of the highest per capita water consumptions in the world. In addition, instead of having fit-for-purpose water supplies (using different qualities of water for different applications), highly treated drinking water is used for nearly all of Australia’s urban water supply needs, including landscape irrigation. The water requirement of urban landscapes, and particularly urban parklands, is of growing concern. The estimation of ET and subsequently plant water requirements in urban vegetation needs to consider the heterogeneity of plants, soils, water and climate characteristics. Accurate estimation of evapotranspiration (ET), which is the main component of a plant’s water requirement, in urban parks is highly desirable because this water maintains the health of green infrastructure and this in turn provides essential ecosystem services. This research contributes to a broader effort to establish sustainable irrigation practices within the Adelaide Parklands in Adelaide, South Australia.

Remote Sensing↗
USGS1997

A self-modifying cellular automaton model of historical urbanization in the San Francisco Bay area

In this paper we describe a cellular automaton (CA) simulation model developed to predict urban growth as part of a project for estimating the regional and broader impact of urbanization on the San Francisco Bay area's climate. The rules of the model are more complex than those of a typical CA and involve the use of multiple data sources, including topography, road networks, and existing settlement distributions, and their modification over time. In addition, the control parameters of the model are allowed to self-modify: that is, the CA adapts itself to the circumstances it generates, in particular, during periods of rapid growth or stagnation. In addition, the model was written to allow the accumulation of probabilistic estimates based on Monte Carlo methods. Calibration of the model has been accomplished by the use of historical maps to compare model predictions of urbanization, based solely upon the distribution in year 1900, with observed data for years 1940, 1954, 1962, 1974, and 1990. The complexity of this model has made calibration a particularly demanding step. Lessons learned about the methods, measures, and strategies developed to calibrate the model may be of use in other environmental modeling contexts. With the calibration complete, the model is being used to generate a set of future scenarios for the San Francisco Bay area along with their probabilities based on the Monte Carlo version of the model. Animated dynamic mapping of the simulations will be used to allow visualization of the impact of future urban growth.

Environment and Planning B: Planning and Design↗
USGS2023

Potential effects of climate change on Ambystoma barbouri (streamside salamander)

Ambystoma barbouri (streamside salamanders) are stream-breeding mole salamanders that rely on seasonally intermittent, fishless streams for egg and larval development but are primarily fossorial as adults. Climate-driven changes are likely to alter streamflow duration, peak, and seasonality within the range of A. barbouri , reducing reproductive habitat and larval survival. Although future changes in precipitation volume within the geographic range of A. barbouri are uncertain, in the next 90 years, increasing temperatures will likely increase potential evapotranspiration. Decreasing ratio of precipitation to potential evapotranspiration will likely shorten flow duration for intermittent streams, potentially causing earlier stream dry downs before larval metamorphosis. Increased temperatures may also shorten developmental periods buffering A. barbouri larvae from the effects of increased stream no-flow days. Additionally, precipitation in the future will increasingly fall in heavy rainfall events. Heavy rain and subsequent flooding during early larval stages may displace A. barbouri larvae from fishless pools into downstream reaches with vertebrate predators that can reduce survival. Finally, agriculture and urban land cover may amplify the stresses of climate change on A. barbouri , altering reproductive habitat and reducing survival of larval, juvenile, and adult life stages.

Illinois, Indiana, Kentucky, Ohio, Tennessee, West↗
USGS2018

Increasing soil organic carbon to mitigate greenhouse gases and increase climate resiliency for California

Rising air temperatures are projected to continue to drive up urban, agricultural, and rangeland water use, straining both surface and groundwater resources. Scientific studies have shown that managing farms, ranches, and public lands to increase soil carbon can increase soil waterholding capacity and increase hydrologic benefits such as increased baseflows and aquifer recharge, reduced flooding and erosion, and reduced climate-related water deficits. Coincident improvements in forage and crop yields are also indicated, while simultaneously sequestering carbon, reducing atmospheric greenhouse gases and mitigating climate change. This study was developed to consider the multiple benefits of increasing the organic matter content of soils across California’s working lands. Study results indicate that a one-time ¼” application of compost to rangelands can lead to carbon sequestration rates in soils that are maximized after approximately 15 years, and more than offset greenhouse gas emissions stimulated by the compost addition for at least five decades longer. Modeled increases in total soil organic matter of 3% enhanced hydrologic benefits across 97% of working lands, and reduced climate change impacts. Economic valuation indicated all benefits increasing over time, demonstrating a large potential for the California carbon market to support incentives in regionalizing the impacts in the coming decades. Socioeconomic and related land use pressures pose barriers to implementing management practices to increase soil organic matter by driving conversion of rangeland to urban or to more greenhouse-gas emission intensive agriculture. Results can be effectively used with land use change scenarios to identify where on California’s working lands hydrologic benefits of soil organic matter enhancement coincide with development risk, highlighting counties in California in which there may be resilience to climate change when strategic soil management and land conservation are combined.

California↗
USGS2025

Ecosystems

The Fifth National Climate Assessment updates the evidence regarding how climate change influences ecosystems, biological diversity, and the implications for changes to critical ecosystem services—as noted in the key messages above (McElwee et al., 2023). Large-scale transformational changes to ecosystems are occurring, including—but not limited to—land-use conversion, hydrological alteration, and fire regimes. Implications of such transformational change include ecosystem capacity to maintain biological diversity and ecosystem services, impacting recreational opportunities (e.g., hunting and fishing, birding, ecotourism) and agriculture production (McElwee et al., 2023). A central tenet of the Fifth National Climate Assessment regarding ecosystems was the shifts to alternative states and how the Resist-Accept-Direct (RAD) framework may guide the adaptive management of ecosystems moving forward (Lynch et al., 2022). Nebraska is in the northern Great Plains, where extremes in climate and resulting ecosystem processes are experienced (Knapp et al., 2023). Pressures on ecosystems to provide essential services, including healthy soil and water to benefit humans and animals, will inevitably impact economic development, urban and rural communities, and fish and wildlife populations as climate change continues (Knapp et al., 2023). All ecosystems will be impacted in Nebraska, but aquatic systems—wetlands, aquifers, lakes, streams, and rivers—may be most impacted, given the scarcity of water as human demand (i.e., agriculture and a growing population) persists and increases (Bathke et al., 2014). Major knowledge gaps remain regarding how fish and wildlife populations will persist in changing environments. Past changes, including large-scale land conversion, water delivery systems, and water storage (construction of reservoirs), suggest that some species can adapt to novel environments and shift distributions. However, many more species may be maladapted to the expected changes in climate. Species may be unable to move to suitable habitats, and biological constraints under rapidly changing conditions may impede adaptation— resulting in extirpation and potential extinction. Further, changing conditions open multiple pathways for invasive species and novel diseases, impacting native fish populations, wildlife populations, and human health.

Nebraska↗
USGS2020

Mitigation ponds offer drought resiliency for western spadefoot (Spea hammondii) populations

Synergistic effects of habitat loss, drought, and climate change exacerbate amphibian declines. In southern California urbanization continues to convert natural habitat, while prolonged drought reduces surface water availability. Protection of biodiversity may be provided through mitigation; however, the long-term effectiveness of different strategies is often unreported. As a mitigation measure for building a new development within occupied Spea hammondii (western spadefoot) habitat in Orange County, California, artificial breeding pools were constructed at two off-site locations. Spea hammondii tadpoles were translocated from the pools at the development site to two off-site locations in 2005–2006. We conducted surveys a decade later (2016) to determine if S. hammondii were persisting and breeding successfully at either the original development site or the human-made pools at the two mitigation sites. We also verified hydroperiods of any existing pools at all three locations to see if any held water long enough for successful S. hammondii recruitment through metamorphosis. During our study, no pooling water was detected at two of three main sites surveyed, and no S. hammondii were observed at these locations. Twelve of the 14 pools created at only one of the two mitigation sites held water for over 30 d, and we detected successful breeding at seven of these pools. Recruitment in some mitigation ponds indicated that S. hammondii habitat can be created and maintained over 10+ yr, even during the fifth year of a catastrophic drought. Therefore, this may also serve as a conservation strategy to mitigate climate change and habitat loss.

California↗
USGS2023

Integrating urban water fluxes and moving beyond impervious surface cover: A review

Though urban areas represent a small fraction of global land cover, they have an outsized impact on hydrological processes. Within these areas, the pathways that water follows are fundamentally transformed by the disturbance of soils, land cover, vegetation, topography, and built infrastructure. While progress has been made across many cities to quantify interactions between hydrological processes and the urban environment, many fundamental questions remain unanswered. In this article, we review the state of urban hydrologic science, with an eye towards identifying gaps in our understanding of how water flows through built landscapes. Our review focuses on key topics within urban hydrology related to water quantity, including runoff and streamflow generation, soils and soil water, groundwater, vegetation, and climate. We also describe some of the challenges and opportunities within the field of urban hydrology that we envision will drive future work and collaboration.

Journal of Hydrology↗
USGS2001

Nutrient transport to the Swan - Canning Estuary, Western Australia

Catchment nutrient availability in Western Australia is primarily controlled by the disposal of animal waste and the type and rate of fertilizer application, particularly on the relatively narrow (~25 km wide), sandy coastal plain. Nitrogen (N) and phosphorous (P) concentrations and fluxes during the wet season of 15 tributaries, including four urban drains to the Swan-Canning Estuary, were evaluated from 1986 to 1992 and additionally concentrations only were evaluated throughout the year from 1993 to 1996. Concentrations of filtered reactive P (FRP) and total P (TP) were generally low, with the volume-weighted means for all sites being 0.06 mg 1-1 and 0.12 mg 1-1 respectively. The urban drains had higher TP concentrations (volume-weighted mean of 0.21 mg 1-1) than the streams (0.12 mg 1-1), with the high concentrations associated with particulate matter. Total inorganic N (TIN, NH4N plus NO3N) and total N (TN), which is of interest to eutrophic status of the N-limited estuary, were likewise low, compared with other developed areas having a similar climate. Both TIN and TN were higher in the urban drains (0.76 mg 1-1 and 1.5 mg 1-1 respectively) than the streams (0.31 mg 1-1 and 1.2 mg 1-1 respectively). The Avon River, which drains 98.5% of the 121 000 km2 catchment area, contributes most of the N (0.03 kg ha-1 year-1 or 65%) and a high percentage of the P (<0.01 kg ha-1 year-1 or 32%) to the estuaries. The Avon River nutrient fluxes are much less than other tributaries closer to the estuary. The coastal plain receives significantly higher rainfall (1,200 mm year-1) and has more intense horticulture and animal production than inland areas (<300 mm year-1). Annual rainfall is seasonal, occuring primarily from May through December. The surficial aquifers on the coastal plain generally are sandy with a low nutrient retention capacity, and rapidly transmit soluble and colloidal material in subsurface flow. Ellen Brook, on the coastal plain, drains pastures treated with superphosphate and has the highest FRP (0.51 mg 1-1), TP (0.7 mg 1-1) and TN (2.1 mg 1-1) of any tributary to the estuary. The coastal plain is also undergoing urbanization, particularly in areas adjacent to the estuary. Nutrients are subsequently available for transport during the onset of seasonal wet weather. Perennial baseflow from urban areas is an important source of nutrients. Water yield from the urban areas was high, being as much as 50% of annual rainfall. The timing of the nutrients delivered by the tributaries may be an important control on estuarine ecology. Copyright ?? 2001 John Wiley and Sons, Ltd.

Hydrological Processes↗
USGS2011

Interdisciplinary environmental project probes Chesapeake Bay down to the core

Interrelated environmental concerns about Chesapeake Bay are being addressed in an interdisciplinary project using paleoecological and geochemical records from sediment cores to investigate Holocene climate and human encroachment. The research is looking at interannual through millennial-scale variability of bay salinity, sediment accumulation, and dissolved oxygen, temperature, and faunal and floral trends. Current and planned research is expected to result in better restoration strategies by improving our understanding of the linkages between the bay's ecosystem, climate, and land use. Chesapeake Bay, the United States' largest and most productive estuary, faces several complex environmental issues, including eutrophication and anoxia in the main channel and tributaries, high turbidity and rates of sedimentation, outbreaks of the toxic dinoflagellate Pfiesteria piscicida , and coastal erosion and submergence tied to sea-level rise. Such problems often are attributed to human activities in the bay's watershed, including pollution, urbanization, and deforestation, but it now is recognized that climatic factors also strongly influence bay salinity, temperature, and water quality.

Chesapeake Bay watershed↗
USGS2009

Seasonal source-sink dynamics at the edge of a species' range

The roles of dispersal and population dynamics in determining species' range boundaries recently have received theoretical attention but little empirical work. Here we provide data on survival, reproduction, and movement for a Virginia opossum (Didelphis virginiana) population at a local distributional edge in central Massachusetts (USA). Most juvenile females that apparently exploited anthropogenic resources survived their first winter, whereas those using adjacent natural resources died of starvation. In spring, adult females recolonized natural areas. A life-table model suggests that a population exploiting anthropogenic resources may grow, acting as source to a geographically interlaced sink of opossums using only natural resources, and also providing emigrants for further range expansion to new human-dominated landscapes. In a geographical model, this source-sink dynamic is consistent with the local distribution identified through road-kill surveys. The Virginia opossum's exploitation of human resources likely ameliorates energetically restrictive winters and may explain both their local distribution and their northward expansion in unsuitable natural climatic regimes. Landscape heterogeneity, such as created by urbanization, may result in source-sink dynamics at highly localized scales. Differential fitness and individual dispersal movements within local populations are key to generating regional distributions, and thus species ranges, that exceed expectations. ?? 2009 by the Ecological Society of America.

Ecology↗
USGS2004

The Colorado Plateau: cultural, biological, and physical research

Stretching from the four corners of Arizona, New Mexico, Colorado, and Utah, the Colorado Plateau is a natural laboratory for a wide range of studies. This volume presents 23 original articles drawn from more than 100 research projects presented at the Sixth Biennial Conference of Research on the Colorado Plateau. This scientific gathering revolved around research, inventory, and monitoring of lands in the region. The book's contents cover management techniques for cultural, biological, and physical resources, representing collaborative efforts among federal, university, and private sector scientists and land managers. Chapters on cultural concerns cover benchmarks of modern southwestern anthropological knowledge, models of past human activity and impact of modern visitation at newly established national monuments, challenges in implementing the 1964 Wilderness Act, and opportunities for increased federal research on Native American lands. The section on biological resources comprises sixteen chapters, with coverage that ranges from mammalian biogeography to responses of elk at the urban-wildland interface. Additional biological studies include the effects of fire and grazing on vegetation; research on bald eagles at Grand Canyon and tracking wild turkeys using radio collars; and management of palentological resources. Two final chapters on physical resources consider a proposed rerouting of the Rio de Flag River in urban Flagstaff, Arizona, and an examination of past climate patterns over the Plateau, using stream flow records and tree ring data. In light of similarities in habitat and climate across the Colorado Plateau, techniques useful to particular management units have been found to be applicable in many locations. This volume highlights an abundance of research that will prove useful for all of those working in the region, as well as for others seeking comparative studies that integrate research into land management actions.

Utah;Colorado;Arizona;New Mexico↗
USGS2008

The California Clapper Rail and multispecies recovery planning

The California clapper rail (Rallus longirostris obsoletus) lives in remnant tidal marshes of San Francisco Bay, where less than 20 percent of the historic tidal wetlands remain. Listed as an endangered species in 1970 by the Fish and Wildlife Service (FWS), this enigmatic bird faces a myriad of threats, including habitat loss due to urban encroachment, sea-level rise caused by climate change, alteration of native habitats by invasive plants, non-native predators, and exposure to mercury and other pollutants. The FWS is in the process of revising the existing recovery plan for California clapper rails and is including the rail in a multispecies recovery plan directed towards imperiled salt-marsh ecosystems. Sound scientific information is critical to the success of any recovery plan, but even more so when dealing with complex multiple-species interactions within an ecosystem.

Endangered Species Bulletin↗
USGS1980

Effects of urbanization on the water quality of lakes in Eagan, Minnesota

Water-quality characteristics of 17 lakes and ponds in the city of Eagan were described from data collected from 1972 through 1978. The data showed that differences in water quality between lakes were related to differences in the percentage of urbanization. However, water-quality variations within each lake were affected more by climatic variations than by land-use changes during that period. Dissolved solids, alkalinity, and chloride concentrations varied most in lakes with urbanized watersheds, in lakes with outlets, and in lakes less than 6 feet deep. Certain lakes without outlets showed an increase in chloride during the study, caused in part by urbanization but intensified by drought conditions of 1976-77. Fifteen of the lakes studied are less than 10 feet deep and frequently mix during open water. These lakes are highly eutrophic, primarily because of high nutrient loading and recycling of nutrients. Holland and Fish Lakes, with depths of 52 and 30 feet, respectively, were the least eutrophic. These lakes limit continuous recycling of nutrients from bottom materials to water surface by thermal stratification and entrapment of nutrients in the hypolimnion. Three phosphorus-prediction models developed during the study are applicable to shallow (less than about 12 feet), nonstratifying lakes and ponds. The data base was not sufficient to select an appropriate model to predict the effects of future loading from continuing urbanization on the deeper lakes.

Minnesota↗
USGS2005

Urbanization effects on stream habitat characteristics in Boston, Massachusetts; Birmingham, Alabama; and Salt Lake City, Utah

Relations between stream habitat and urban land-use intensity were examined in 90 stream reaches located in or near the metropolitan areas of Salt Lake City, Utah (SLC); Birmingham, Alabama (BIR); and Boston, Massachusetts (BOS). Urban intensity was based on a multi-metric index (urban intensity index or UII) that included measures of land cover, socioeconomic organization, and urban infrastructure. Twenty-eight physical variables describing channel morphology, hydraulic properties, and streambed conditions were examined. None of the habitat variables was significantly correlated with urbanization intensity in all three study areas. Urbanization effects on stream habitat were less apparent for streams in SLC and BIR, owing to the strong influence of basin slope (SLC) and drought conditions (BIR) on local flow regimes. Streamflow in the BOS study area was not unduly influenced by similar conditions of climate and physiography, and habitat conditions in these streams were more responsive to urbanization. Urbanization in BOS contributed to higher discharge, channel deepening, and increased loading of fine-grained particles to stream channels. The modifying influence of basin slope and climate on hydrology of streams in SLC and BIR limited our ability to effectively compare habitat responses among different urban settings and identify common responses that might be of interest to restoration or water management programs. Successful application of land-use models such as the UII to compare urbanization effects on stream habitat in different environmental settings must account for inherent differences in natural and anthropogenic factors affecting stream hydrology and geomorphology. The challenge to future management of urban development is to further quantify these differences by building upon existing models, and ultimately develop a broader understanding of urbanization effects on aquatic ecosystems.

American Fisheries Society Symposium↗
USGS2004

Global climate change and wildlife in North America

It is widely accepted by the scientific community that the earth, which has always experienced climate variation, is now undergoing a period of rapid climate change that is enhanced by anthropogenic atmospheric carbon enrichment during the past 100 years. These climatic changes are accelerating and projections for the next 100 years indicate extensive warming in most (but not all) areas, changing patterns of precipitation, and a significant acceleration of sea level rise. Other likely components of ongoing climate change include changes in season lengths, decreasing range of nighttime versus daytime temperatures, declining snowpack, and increasing frequency and intensity of severe weather events. The many components of climate change, and especially the unprecedented rapid rate of change, are just as important as increasing temperatures. Wildlife species are closely adapted to their environments and readily respond to climate variation. However, as discussed in this technical review, the climate change now underway has extensive potential to affect wildlife throughout North America, either directly or indirectly through responses to changing habitat conditions. When considered in combination with other factors (e.g., pollution, ozone depletion, urbanization, etc.), the potential effect is even greater. The effects of climate change on populations and range distributions of wildlife are expected to be species specific and highly variable, with some effects considered negative and others considered positive. In North America the ranges of habitats and wildlife are predicted to generally move northward as temperatures increase. Variations in this overall pattern will be dependent upon specific local conditions, changing precipitation patterns, and the response of different species to different components of climate change. It follows that the structure of plant–animal communities will also change. Ignoring climate change is likely to increasingly result in failure to reach wildlife management objectives. Wildlife managers need to become knowledgeable about climate change, ways to cope with it, and ways to take advantage of it. Management options currently available include protecting coastal wetlands to allow for sea level rise, reducing the risks to wildlife from potential catastrophic events, adjusting yield and harvest models, accounting for known climatic variations, and taking climate change into consideration when selecting the location and other characteristics of conservation areas. Wildlife managers also need to expect the unexpected and reduce nonclimate stressors on ecosystems. Overall, wildlife managers can minimize negative impacts to wildlife and take advantage of positive aspects by planning ahead and employing adaptive management.

Technical Review↗
USGS2013

Regional demographic trends from long-term studies of saguaro ( Carnegiea gigantea ) across the northern Sonoran Desert

Ten saguaro ( Carnegiea gigantea ) populations in the northern Sonoran Desert were monitored from 1959 to 2005 to discriminate how climate influences plant growth, abundance, reproductive potential, survivorship, age structure and regeneration trends. Thousands of saguaros were measured to determine site-specific growth rates and survivorship through time. Observed growth rates were used to predict the ages of saguaros and reconstruct local and regional regeneration patterns back to the late 18th century. Both growth rates and degree of branching generally tracked temperature and moisture gradients. Site-specific age-height models explained 89-97% of variance in observed ages, with a slope of nearly one. Regeneration was more consistent at sites in the western (hotter/drier) than eastern (cooler/wetter) sites, which exhibited clear multidecadal variability in regeneration rates. Averaged across the region, saguaro regeneration rates were highest from 1780 to 1860, coincident with wet conditions and high Pinus ponderosa recruitment in the highlands. Milder and wetter winters and protection from livestock grazing likely promoted late 20th century regeneration surges at some sites. Predictions of saguaro population dynamics in the 21st century likely will be confounded by the saguaro's episodic and asynchronous regeneration, continued urbanization, ongoing grass invasions and associated wildfires, and changing climate.

Arizona↗