-
Coupling of Vegetation Growing Season Anomalies and Fire Activity with Hemispheric and Regional-Scale Climate Patterns in Central and East Siberia
-
An 18-yr time series of the fraction of absorbed photosynthetically active radiation (fAPAR) taken in by
the green parts of vegetation data from the NOAA Advanced Very High Resolution Radiometer
(AVHRR) instrument series was analyzed for interannual variations in the start, peak, end, and length of
the season of vegetation photosynthetic activity in central and east Siberia. Variations in these indicators of
seasonality can give important information on interactions between the biosphere and atmosphere. A
second-order local moving window regression model called the “camelback method” was developed to
determine the dates of phenological events at subcontinental scale. The algorithm was validated by comparing
the estimated dates to phenological field observations. Using spatial correlations with temperature
and precipitation data and climatic oscillation indices, two geographically distinct mechanisms in the system
of climatic controls of the biosphere in Siberia are postulated: central Siberia is controlled by an “Arctic
Oscillation–temperature mechanism,” while east Siberia is controlled by an “El Niño–precipitation mechanism.”
While the analysis of data from 1982 to 1991 indicates a slight increase in the length of the growing
season for some land-cover types due to an earlier beginning of the growing season, the overall trend from
1982 to 1999 is toward a slightly shorter season for some land-cover types caused by an earlier end of season.
The Arctic Oscillation tended toward a more positive phase in the 1980s leading to enhanced high pressure
system prevalence but toward a less positive phase in the 1990s. The results suggest that the two mechanisms
also control the fire regimes in central and east Siberia. Several extreme fire years in central Siberia were
associated with a highly positive Arctic Oscillation phase, while several years with high fire damage in east
Siberia occurred in El Niño years. An analysis of remote sensing data of forest fire partially supports this
hypothesis
VOLUME 20
Located in
Resources
/
Climate Science Documents
-
Coupling snowpack and groundwater dynamics to interpret historical streamflow trends in the western United States
-
A key challenge for resource and land managers is predicting the consequences of climate warming on streamflow and water resources. During the last century in the western United States, significant reductions in snowpack and earlier snowmelt have led to an increase in the fraction of annual streamflow during winter and a decline in the summer. Previous work has identified elevation as it relates to snowpack dynamics as the primary control on streamflow sensitivity to warming. But along with changes in the timing of snowpack accumulation and melt, summer streamflows are also sensitive to intrinsic, geologically mediated differences in the efficiency of landscapes in transforming recharge (either as rain or snow) into discharge; we term this latter factor drainage efficiency. Here we explore the conjunction of drainage efficiency and snowpack dynamics in interpreting retrospective trends in summer streamflow during 1950–2010 using daily streamflow from 81 watersheds across the western United States. The recession constant (k) and fraction of precipitation falling as snow (Sf) were used as metrics of deep groundwater and overall precipitation regime (rain and/or snow), respectively. This conjunctive analysis indicates that summer streamflows in watersheds that drain slowly from deep groundwater and receive precipitation as snow are most sensitive to climate warming. During the spring, however, watersheds that drain rapidly and receive precipitation as snow are most sensitive to climate warming. Our results indicate that not all trends in western United States are associated with changes in snowpack dynamics; we observe declining streamflow in late fall and winter in rain-dominated watersheds as well. These empirical findings support both theory and hydrologic modelling and have implications for how streamflow sensitivity to warming is interpreted across broad regions.
KEY WORDS streamflow trend; hydrologic processes; groundwater processes; climate; warming
Located in
Resources
/
Climate Science Documents
-
Cover Slide Current Climate Science
-
J Brennan
Located in
Resources
/
General Resources Holdings
-
Creating a Mobile Experience for the Explore Natural Communities Website
-
Judy Teague - Senior Ecologist, Allen Ansellmo - Software Engineer, Erin Jones - Vegetation Ecologist, Dave Hauver - Software Engineer Natureserve, Diane Pavek - Research Coordinator, Ann Gallagher - Science Education Coordinator, Urban Ecology Research Learning Alliance, NPS National Capital Region
Located in
National Park Service Spotlights
/
2016 Spotlight on National Park Resources
-
Creating Wetlands: Primary Succession, Water Quality Changes, and Self-Design over 15 Years
-
The succession of vegetation, soil development, water quality changes, and carbon and nitrogen dynamics are summarized in this article for a pair of 1-hectare flow-through-created riverine wetlands for their first 15 years. Wetland plant richness increased from 13 originally planted species to 116 species overall after 15 years, with most of the increase occurring in the first 5 years. The planted wetland had a higher plant community diversity index for 15 years, whereas the unplanted wetland was more productive. Wetland soils turned hydric within a few years; soil organic carbon doubled in 10 years and almost tripled in 15 years. Nutrient removal was similar in the two wetlands in most years, with a trend of decreased removal over 15 years for phosphorus. Denitrification accounted for a small percentage of the nitrogen reduction in the wetlands. The wetlands were effective carbon sinks with retention rates of 1800–2700 kilograms of carbon per hectare per year, higher than in comparable reference wetlands and more commonly studied boreal peatlands. Methane emission rates are low enough to create little concern that the wetlands are net sources of climate change radiative forcing. Planting appears to have influenced carbon accumulation, methane emissions, and macrophyte community diversity.
Located in
Resources
/
Climate Science Documents
-
Crist, Patrick J
-
Located in
Expertise Search
-
Critical slowing down as early warning for the onset of collapse in mutualistic communities
-
Tipping points are crossed when small changes in external conditions cause abrupt unexpected responses in the current state of a system. In the case of ecological communities under stress, the risk of approaching a tipping point is unknown, but its stakes are high. Here, we test recently developed critical slowing-down indicators as early-warning signals for detecting the proximity to a potential tipping point in structurally complex ecological communities. We use the structure of 79 empirical mutualistic networks to simulate a scenario of gradual environmental change that leads to an abrupt first extinction event followed by a sequence of species losses until the point of complete community collapse. We find that critical slowing-down indicators derived from time series of bio- masses measured at the species and community level signal the proximity to the onset of community collapse. In particular, we identify specialist species as likely the best-indicator species for mon- itoring the proximity of a community to collapse. In addition, trends in slowing-down indicators are strongly correlated to the timing of species extinctions. This correlation offers a promising way for map- ping species resilience and ranking species risk to extinction in a given community. Our findings pave the road for combining theory on tipping points with patterns of network structure that might prove useful for the management of a broad class of ecological networks under global environmental change.
resilience | critical transition | mutualism | ecological networks | pollinator decline
Located in
Resources
/
Climate Science Documents
-
Cross-scale Drivers of Natural Disturbances Prone to Anthropogenic Amplification: The Dynamics of Bark Beetle Eruptions
-
Biome-scale disturbances by eruptive herbivores provide valuable insights into species interactions, ecosystem function, and impacts of global change. We present a conceptual framework using one system as a model, emphasizing interactions across levels of biological hierarchy and spatiotemporal scales. Bark beetles are major natural disturbance agents in western North American forests. However, recent bark beetle population eruptions have exceeded the frequencies, impacts, and ranges documented during the previous 125 years. Extensive host abundance and susceptibility, concentrated beetle density, favorable weather, optimal symbiotic associations, and escape from natural enemies must occur jointly for beetles to surpass a series of thresholds and exert widespread disturbance. Opposing feedbacks determine qualitatively distinct outcomes at junctures at the biochemical through landscape levels. Eruptions occur when key thresholds are surpassed, prior constraints cease to exert influence, and positive feedbacks amplify across scales. These dynamics are bidirectional, as landscape features influence how lower-scale processes are amplified or buffered. Climate change and reduced habitat heterogeneity increase the likelihood that key thresholds will be exceeded, and may cause fundamental regime shifts. Systems in which endogenous feedbacks can dominate after external forces foster the initial breach of thresholds appear particularly sensitive to anthropogenic perturbations.
Keywords: thresholds, plant-insect interactions, landscape disturbance, forest management, anthropogenic change
Located in
Resources
/
Climate Science Documents
-
Crowley 1957.pdf
-
Located in
Resources
/
TRB Library
/
COO-CVA
-
Croy, Steve
-
Located in
Expertise Search
