Jones J.A.,Oregon State University |
Creed I.F.,University of Western Ontario |
Hatcher K.L.,Oregon State University |
Adams M.B.,Us Forest Service Usfs Northern Research Station |
And 19 more authors.
BioScience | Year: 2012
Analyses of long-term records at 35 headwater basins in the United States and Canada indicate that climate change effects on streamflow are not as clear as might be expected, perhaps because of ecosystem processes and human influences. Evapotranspiration was higher than was predicted by temperature in water-surplus ecosystems and lower than was predicted in water-deficit ecosystems. Streamflow was correlated with climate variability indices (e.g., the El Niño-Southern Oscillation, the Pacific Decadal Oscillation, the North Atlantic Oscillation), especially in seasons when vegetation influences are limited. Air temperature increased significantly at 17 of the 19 sites with 20-to 60-year records, but streamflow trends were directly related to climate trends (through changes in ice and snow) at only 7 sites. Past and present human and natural disturbance, vegetation succession, and human water use can mimic, exacerbate, counteract, or mask the effects of climate change on streamflow, even in reference basins. Long-term ecological research sites are ideal places to disentangle these processes. © 2012 by American Institute of Biological Sciences. All rights reserved.
Vicca S.,University of Antwerp |
Bahn M.,University of Innsbruck |
Estiarte M.,Global Ecology Unit |
Van Loon E.E.,University of Amsterdam |
And 50 more authors.
Biogeosciences | Year: 2014
As a key component of the carbon cycle, soil CO2 efflux (SCE) is being increasingly studied to improve our mechanistic understanding of this important carbon flux. Predicting ecosystem responses to climate change often depends on extrapolation of current relationships between ecosystem processes and their climatic drivers to conditions not yet experienced by the ecosystem. This raises the question of to what extent these relationships remain unaltered beyond the current climatic window for which observations are available to constrain the relationships. Here, we evaluate whether current responses of SCE to fluctuations in soil temperature and soil water content can be used to predict SCE under altered rainfall patterns. Of the 58 experiments for which we gathered SCE data, 20 were discarded because either too few data were available or inconsistencies precluded their incorporation in the analyses. The 38 remaining experiments were used to test the hypothesis that a model parameterized with data from the control plots (using soil temperature and water content as predictor variables) could adequately predict SCE measured in the manipulated treatment. Only for 7 of these 38 experiments was this hypothesis rejected. Importantly, these were the experiments with the most reliable data sets, i.e., those providing high-frequency measurements of SCE. Regression tree analysis demonstrated that our hypothesis could be rejected only for experiments with measurement intervals of less than 11 days, and was not rejected for any of the 24 experiments with larger measurement intervals. This highlights the importance of high-frequency measurements when studying effects of altered precipitation on SCE, probably because infrequent measurement schemes have insufficient capacity to detect shifts in the climate dependencies of SCE. Hence, the most justified answer to the question of whether current moisture responses of SCE can be extrapolated to predict SCE under altered precipitation regimes is "no" - as based on the most reliable data sets available. We strongly recommend that future experiments focus more strongly on establishing response functions across a broader range of precipitation regimes and soil moisture conditions. Such experiments should make accurate measurements of water availability, should conduct high-frequency SCE measurements, and should consider both instantaneous responses and the potential legacy effects of climate extremes. This is important, because with the novel approach presented here, we demonstrated that, at least for some ecosystems, current moisture responses could not be extrapolated to predict SCE under altered rainfall conditions. © Author(s) 2014.
Saunders M.R.,Purdue University |
Fraver S.,USFS Northern Research Station |
Wagner R.G.,University of Maine, United States
Silva Fennica | Year: 2011
Both nutrient concentrations and pre and post-harvest pool sizes were determined across down woody debris decay classes of several hardwood and softwood species in a long-term, natural disturbance based, silvicultural experiment in central Maine. Concentrations of N, P, Ca, Mg, Cu, Fe, and Zn generally increased 2- to 5-fold with increasing decay class. Concentrations of Mn, Al and B did not differ among decay classes, while K decreased by 20-44% from decay class 1 to class 4. C:N-ratios declined with increasing decay class, while N:P-ratios increased from decay class 1 to 2 and then plateaued with further decay. Within decay classes, softwoods generally had lower nutrient concentrations and higher C:N-ratios than hardwoods; N:P-ratios did not differ between hardwoods and softwoods. Although gap harvesting increased the size of the overall down woody debris nutrient pools, mostly through a large pulse of decay class 1 material, harvesting generally reduced the nutrients held in advanced decay classes. Pre-harvest down woody debris pools for N, P, K and Ca were 11.0, 0.6, 2.1 and 21.1 kg ha-1, respectively, while postharvest were 20.0, 1.3, 6.2 and 46.2 kg ha-1, respectively. While the gap-based silvicultural systems sampled in this study doubled the size of the pre-harvest, downed woody debris nutrient pools, the post-harvest pools were estimated to be only 3.2-9.1% of aboveground nutrients.
Ponce G.,University of Arizona |
Moran S.,U.S. Department of Agriculture |
Huete A.,University of Arizona |
Huete A.,University of Technology, Sydney |
And 14 more authors.
34th International Symposium on Remote Sensing of Environment - The GEOSS Era: Towards Operational Environmental Monitoring | Year: 2011
According to Global Climate Models (GCMs) the occurrence of extreme events of precipitation will be more frequent in the future. Therefore, important challenges arise regarding climate variability, which are mainly related to the understanding of ecosystem responses to changes in precipitation patterns. Previous studies have found that Above-ground Net Primary Productivity (ANPP) was positively related to increases in annual precipitation and this relation may converge across biomes during dry years. One challenge in studying this ecosystem response at the continental scale is the lack of ANPP field measurements over extended areas. In this study, the MODIS EVI was utilized as a surrogate for ANPP and combined with precipitation datasets from twelve different experimental sites across the United States over a 10-year period. Results from this analysis confirmed that integrated-EVI for different biomes converged toward common precipitation use efficiency during water-limited periods and may be a viable surrogate for ANPP measurements for further ecological research.
Reinhart K.O.,U.S. Department of Agriculture |
Reinhart K.O.,Indiana University |
Royo A.A.,USFS Northern Research Station |
Kageyama S.A.,U.S. Department of Agriculture |
Clay K.,Indiana University
Acta Oecologica | Year: 2010
Canopy disturbances such as windthrow events have obvious impacts on forest structure and composition aboveground, but changes in soil microbial communities and the consequences of these changes are less understood. We characterized the densities of a soil-borne pathogenic oomycete (Pythium) and a common saprotrophic zygomycete (Mortierella) in nine pairs of forest gaps created by windthrows and adjacent forest understories. We determined the levels of Pythium necessary to cause disease by performing pathogenicity experiments using two Pythium species, a range of Pythium densities, and two common tree species (Acer rubrum and Prunus serotina) from the study sites. Three years post-disturbance, densities of Mortierella remained suppressed in soil from forest gaps compared to levels in intact forest understories while varying across sites and sampling dates. Pythium were infrequently detected likely because of soil handling effects. Expression of disease symptoms increased with increasing inoculum density for seedlings of P. serotina with each Pythium spp. having a similar effect on this species. Conversely, A. rubrum appeared resistant to the two species of Pythium. These results suggest that Pythium densities at sites where they were detected are sufficient to cause disease and possibly affect establishment of susceptible species like P. serotina. Because early seral environments have lower loads of the saprotrophic Mortierella, pathogen loads may follow a similar pattern, causing susceptible species to establish more frequently in those habitats than in late-seral forests. Forest disturbances that alter the disease landscape may provide an additional mechanism for explaining succession of temperate forests in addition to the shade-tolerance paradigm. © 2010.
Jurgensen M.,Michigan Technological University |
Tarpey R.,Michigan Technological University |
Pickens J.,Michigan Technological University |
Kolka R.,USFS Northern Research Station |
Palik B.,USFS Northern Research Station
Soil Science Society of America Journal | Year: 2012
The effects of long-term silvicultural thinning on soil C and N content are not well known. We evaluated the impact of periodic thinnings on soil C and N pools in a 134-yr-old red pine (Pinus resinosa Ait.) forest in Minnesota, and a 104 yr-old northern hardwood forest in Wisconsin. The red pine stands had five thinning regimes (13.8, 18.4, 22.7, 27.6, 32.1 m 2 ha -1 residual basal area [BA]), which were cut five or seven times over 46 yr. The northern hardwood stands had three residual basal area treatments (13.8, 17.2, 20.6 m 2 ha -1) that were thinned five times over 50 yr. Our results showed that the heaviest-thinned (13.8 m 2 ha -1) and uncut control red pine stands had higher C and N contents in the mineral A horizon, as compared to the other four thinning treatments. Multiple thinning did not affect C and N pool size in the forest floor and surface mineral soil (30-cm depth) in either red pine or hardwood stands. Within stand BA variability was positively correlated to C and N pools in the forest floor of the lightly-thinned (32.1 m 2 ha -1) red pine treatment, but was negatively correlated to C and N pools in the A horizon. Our study and the literature indicate that stem-only removal for wildfire risk reduction and bio-energy production would have little impact on total soil C and N pools. However, more information is needed on the effects of whole-tree thinning regimes on soil C and nutrient contents. © Soil Science Society of America.