Tree Throw, Soil Production, and Disturbance Ecology: A Model Illustrating a Coupling Between the Geosphere and the Biosphere
The question of the acoustic impact of a falling tree is best left to the philosophers. However, geologists know that when a tree falls over, it displaces significant quantities of soil and if the tree is anchored into bedrock, large clasts may be ripped out of the ground. Indeed, tree throw may be the dominant agent of physical weathering in forests and likely leads to high rates of soil production. Because this process is dependent on tree density and because stand density, itself, is dependent on soil thickness, a coupled system materializes between bedrock erosion, soil production, and forest development. This system is explored with a numerical model that provides some interesting results. 1) A humped relationship between soil depth and soil production emerges naturally from this coupled system. 2) The soil production rate on a bedrock surface decreases with the size of the bedrock surface. 3) Soil is not produced uniformally across a hillslope but forms in patches that then spread out. In addition, other examples will be given to answer the question "What is Biogeoscience?" The role of vegetative ash in accelerating post-fire erosion rates will described as well as the role of biotic crusts in armoring soils against wind erosion.
Eco-Hydrology From Space: How Satellites Can Be Harnessed To Assess Human Impacts On The Trophic Status Of Lakes In Forested Landscapes
The recent proliferation of spatially and temporally extensive geospatial datasets (e.g., Radarsat, Landsat) has created research opportunities into the characterization of eco-hydrological processes and patterns across Canada's vast forests. Herein, we demonstrate how these space based sensors can be used to establish the hydrologic controls on the range of natural variability (RNV) of lake trophic status and to assess thresholds in disturbance related to human activities that lead to the exceedance in RNV (i.e., lake trophic status that is outside the RNV). We focus on two lake districts in the boreal forest. One is on the western Boreal Plain, where average annual precipitation (P) is less than potential evapotranspiration (PET) (P<PET) and hydrology is characterized by complex surface and subsurface hydrologic interactions. The other is on the eastern Boreal Shield where P>PET and hydrology is characterized by simpler surface hydrologic dynamics. In each of these lake districts, we use Radarsat and Landsat imagery to map surface/near surface hydrologic flow paths (the conveyors of nutrients to and from lakes) and lake trophic status. We establish the RNV of trophic status in landscapes with minimal human presence and compare this to the trophic status of lakes where there is a significant human footprint caused by forest management activities. By building statistical models that account for differences in climate and hydrologic pathways within basins contributing to a lake, we are able to evaluate how much disturbance in forest hydrology is needed to result in a fundamental change in nutrient loading to the lakes and ultimately lake trophic status. We conclude that satellite sensors can assist in the establishment of realistic reference conditions against which effects of forest management activities on lake trophic status can be assessed and management targets can be established.
Wildfires, mountain pine beetle and large-scale climate in Northern North America.
Research on the interactions between biosphere and atmosphere and ocean/atmosphere dynamics, concretely on the coupling between ecological processes and large-scale climate, is presented in two studies in Northern North America: the occurrence of large lightning wildfires and the forest area affected by mountain pine beetle (Dendroctonus ponderosae, MPB). In both cases, large-scale climatic patterns such as the Pacific Decadal Oscillation (PDO) and the Arctic Oscillation (AO) operate as low and low and high frequency frameworks, respectively, that control the occurrence, duration and spatial correlation over large areas of key local weather variables which affect specific ecological processes. Warm PDO phases tend to produce persistent (more than 10 days long) positive mid-troposphere anomalies (blocking highs) over western Canada and Alaska. Likewise, positive (negative) AO configurations increase the frequency of blocking highs at mid (high) latitudes of the Northern Hemisphere. Under these conditions, lack of precipitation and prevailing warm air meridional flow rapidly dry fuel over large areas and increase fire hazard. The spatiotemporal patterns of occurrence of large lightning wildfire in Canada and Alaska for 1959-1999 were largely explained by the action and possible interaction of AO and PDO, the AO being more influential over Eastern Canada, the PDO over Western Canada and Alaska. Changes in the dynamics of the PDO are linked to the occurrence of cold winter temperatures in British Columbia (BC), Western Canada. Reduced frequency of cold events during warm PDO winters is consistent with a northward-displaced polar jet stream inhibiting the outflow of cold Arctic air over BC. Likewise, the AO influences the occurrence of winter cold spells in the area. PDO, and to a lesser degree AO, were strongly related to MPB synchrony in BC during 1959-2002, operating through the control of the frequency of extreme cold winter temperatures that affect MPB larvae survival. The onset of a warm PDO phase in 1976 1) increased (decreased) the area burnt by wildfire in the Canadian Boreal Forest (BC) by increasing (decreasing) the frequency of blocking highs in the area, and 2) favored MPB outbreaks in BC by reducing the occurrence of extremely low winter temperatures. Likewise, the exceptionally high and persistent AO values of the late 1980s and 1990s increased area burned in Eastern Canada and MPB activity in the southern and northern parts of BC. A possible recent PDO phase shift may largely reverse these trends.
Foredune Vegetation Variability, Gulf County, Florida
This study examines the relationship between a variety of foredune types with different exposures to wave and wind energy, and long-term erosion/accretion rates, and the associated variations in vegetation species and percentage cover. Surveys were conducted over 1 m2 continuous quadrats from the start of beach vegetation to the base of the foredune's lee side. The presence/absence, and percent cover were used to compare species similarity, richness and diversity for each profile location. Results show that taller foredunes have greater species richness and diversity, despite the close proximity to the water's edge on slightly eroding shorelines. The climax species found only on the crest and lee side of these dunes highlight the loss of seaward foredune material, as evidenced in historical records. Prograding beaches have much lower foredunes which are dominated by pioneer species (eg. Uniola paniculata,) which only build the foredune until a new seaward vegetation line appears, and inicipient ridges may form. The succulent plant Ipomoea imperati is more predominant on south facing shorelines which is identified as having higher wave energies, and are therefore subject to increased salt spray. This species builds characteristically, lower foredune ramps until pioneering grass species can germinate and build taller foredunes at these locations.
An Estimation of the Lagrangian Length Scale Within a Plant Canopy
Studies of greenhouse gas fluxes of various plant communities have advanced the understanding of bulk interactions between the atmosphere and ecosystems. Micrometeorological instrumentation is currently unable to resolve scalar sources and sinks within plant canopies. Analytical Lagrangian analyses capable of predicting concentration profiles from known source distributions provide the opportunity to calculate source/sink distributions through inverted forms of these equations. Source profiles of carbon dioxide, ammonia, heat, and water vapour within canopies calculated using inverse Lagrangian models produce logical results. However, uncertainties concerning estimates of the essentially immeasurable Lagrangian length scale (LL), a key input, impede the practicality of this method. Small errors in suggested parameterizations of LL can lead to irrational predictions of source distributions. The present study seeks to evaluate LL within an agricultural canopy by using field measurements to constrain the Warland-Thurtell (2000) Lagrangian equation. Measurements of net CO2 flux, soil CO2 flux, and in-canopy profiles of CO2 concentrations taken in a cornfield in 2008 provided the information required to solve for LL. Comparing these optimized values of LL to those predicted by models, along with previous information on the structure of in-canopy turbulence, will improve the overall understanding of Lagrangian length scales, and help to improve source distribution predictions.