Publications Published in Ecological Applications

1. Carbon Sequestration in California Agriculture, 1980-2000. Kroodsma, David A.; Field, Christopher B..
   Ecological Applications: 2006
   Notes
   To better understand agricultural carbon fluxes in California, USA, we estimated changes in soil carbon and woody material between 1980 and 2000 on 3.6 X 10^6 ha of farmland in California. Combining the CASA (Carnegie-Ames-Stanford Approach) model with data on harvest indices and yields, we calculated net primary production, woody production in orchard and vineyard crops, and soil carbon. Over the 21-yr period, two trends resulted in carbon sequestration. Yields increased an average of 20%, corresponding to greater plant biomass and more carbon returned to the soils. Also, orchards and vineyards increased in area from 0.7 X 10^6 ha to 1.0 X 10^6 ha, displacing field crops and sequestering woody carbon. Our model estimates that California's agriculture sequestered an average of 19 g C∙m‾²∙yr‾¹ . Sequestration was lowest in non-rice annual cropland, which sequestered 9 g C∙m‾²∙yr‾¹ of soil carbon, and highest on land that switched from annual cropland to perennial cropland. Land that switched from annual crops to vineyards sequestered 68 g C∙m‾²∙yr‾¹ and land that switched from annual crops to orchards sequestered 85 g C∙m‾²∙yr‾¹ . Rice fields, because of a reduction in field burning, sequestered 55 g C∙m‾²∙yr‾¹ in the 1990s. Over the 21 years, California's 3.6 X 10^6 ha of agricultural land sequestered 11.0 Tg C within soils and 3.5 Tg C in woody biomass, for a total of 14.5 Tg C statewide. This is equal to 0.7% of the state's total fossil fuel emissions over the same time period. If California's agriculture adopted conservation tillage, changed management of almond and walnut prunings, and used all of its orchard and vineyard waste wood in the biomass power plants in the state, California's agriculture could offset up to 1.6% of the fossil fuel emissions in the state.
   
   
   
2. Changes in an Assemblage of Temperate Reef Fishes Associated with a Climate Shift. Sally J. Holbrook; Russell J. Schmitt; John S. Stephens, Jr..
   Ecological Applications: 1997
   Notes
   Substantial changes have occurred in assemblages of near shore reef fishes in the Southern California Bight during the past two decades. At two sites off Los Angeles, California , species richness of reef fishes fell 15-25%, and composition shifted from dominance by northern to southern species. Additionally, by 1993, 95% of the fish species had declined in abundance by an average of 69%. Concurrent declines of similar magnitude were observed for several trophic levels of the benthic ecosystem farther north at Santa Cruz Island where populations of surfperches (Pisces: embiotocidae), the standing stock of their crustacean prey, and the biomass of understory microalgae all declined by ~80%. Abundance of fishes fell because declining recruitment of age-0 fish was insufficient ot compensate for losses of older age classes. Annual levels of recruitment of age-0 fishes at all reefs examined fell more than one order of magnitude over two decades and was correlated among years with a broad indicator of Bight-wide productivity, the biomass of macrozooplankton in the California Current. Lower productivity if the coastal marine ecosystem, associated with a climate regime shift in 1976-1977, likely caused large, but unforeseen, impacts on population abundances and trophic structure in near shore benthic communities.
   
   
   
3. Declines of the California red-legged frog: Climate, UV-B, habitat, and pesticides hypotheses. Davidson, C.; Shaffer, H. B.; Jennings, M. R..
   Ecological Applications: 2001
   Notes
   The federally threatened California red legged frog (Rana aurora draytonii) has disappeared from much of its range for unknown reasons. We mapped 237 historic locations for the species and determined their current population status. Using a geographic information system (GIS), we determined latitude, elevation, and land use attributes for all sites and analyzed the spatial pattern of declines. We then compared the observed patterns of decline to those predicted by the climate change, UV-B radiation, pesticides, and habitat alteration hypotheses for amphibian decline. Declines were not consistent with the climate change hypothesis but showed a strong positive association with elevation, percentage upwind agricultural land use, and local urbanization. These results apply to patterns of decline across the entire range of R. a. draytonii in California, as well as within geographic subregions. The elevational gradient in declines is consistent with the UV-B hypothesis, although the UV-B hypothesis also predicts a north-to-south gradient in declines, which we did not observe. The association of declines with the amount of upwind agricultural land use strongly suggests that wind-borne agrochemicals may be an important factor in declines. This association was most pronounced within the Central Valley-Sierra region, where other studies have documented both transport and deposition of pesticides to the Sierra Nevada and the presence of pesticide residues in the bodies of congeneric (Rana muscosa) and more distantly related (Hyla regilla) frog species.
   
   
   
4. Global Warming and soil Microclimate: Results from a meadow-warming experiment. Harte, John; Torn, Margaret S; Chang, Fang-Ru; Feifarek, Brian; Kinzig, Ann P; Shaw, Rebecca; Shen, Karin.
   Ecological Applications: 1995
   Notes
   We used overhead infrared radiators to add a constant increment of {approx}15 W/m{sup 2}, over 2 yr, to the downward heat flux on five 30-m{sup 2} montane meadow plots in Gunnison County, Colorado, USA. Heating advanced snowmelt by {approx}1 wk, increased summer soil temperatures by up to 3{degrees}C, and reduced summer soil moisture levels by up to 25% compared to control plots. Soil microclimate response to heating varied with season, time of day, weather conditions, and location along the microclimate and vegetation gradient within each plot, with the largest temperature increase observed in daytime and in the drier, more sparsely vegetated zone of each plot. Day-to-day variation in the daily-averaged temperature response to heating in the drier zone was negatively correlated with that in the wetter zone. Our experimental manipulation provides a novel and effective method for investigating feedback processes linking climate, soil, and vegetation.
   
   
   
5. The Role of Climate Change In Interpreting Historical Variability . Constance I. Millar; Wallacew B. Woolfenden.
   Ecological Applications: 1999
   Notes
   Significant climate anomalies have characterized the last 1000 yr in the Sierra Nevada, California, USA. Two warm, dry periods of 150- and 200-yr duration occurred during AD 900-1350, which were followed by anomalously could climates, known as the Little Ice Age, that lasted from AD 1400 to 1900. Climate in the last century has been significantly warmer. Regional biotic and physical response to these climatic periods occurred. Climate variability present challenges when interpreting historical variability, including the need to accommodate climate effects when comparing current ecosystems to historical conditions, especially if comparisons are done to evaluate causes (e.g., human impacts) of differences, or to develop models for restoration of current ecosystems. Many historical studies focus on "presettlement" periods, which usually fall within the Little Ice Age. Thus, it should be assumed that ecosystems inferred for these historical periods responded to different climates that those at present, and management implications should be adjusted accordingly. The warmer centuries before the Little Ice Age may be a more appropriate analogue to the present, although no historic period is likely to better as a model than an understanding of what conditions would be at present without intervention. Understanding the climate context of historical reconstruction studies, and adjusting implications to the present, should strengthen the value of historical variability research to management.