Browsing by Subject "Ecosystem"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Effects of site and climate characteristics on forest invasibility by non-native plants in the Midwest.
    (2010-07) Kurtz, Cassandra Marie
    Non-native invasive plant (NNIP) species can have significant effects on forest regeneration, structure, biodiversity, and wildlife habitat, costing billions of dollars annually. Understanding how NNIPs in the Midwest may spread in the future requires understanding their response to site and climate characteristics. Current research suggests climate change may influence invasive plant presence and spread. In this study, I modeled the relationship between invasive species presence, site characteristics (e.g. disturbance, live tree volume, city distance, edge distance, physiography, and type of water [e.g. streams] present on plot), and climate (annual average number of days the temperature is ≥ 90˚F and annual average number of days the temperature is ≤ 32˚F) for five non-native invasive plants (multiflora rose [Rosa multiflora], common buckthorn [Rhamnus cathartica], non-native bush honeysuckles [Lonicera spp.], garlic mustard [Alliaria petiolata], and reed canary grass [Phalaris arundinacea]) sampled by the USDA Forest Service’s Forest Inventory and Analysis program in seven Midwestern states for 2005-2006 Species’ response to site and temperature predictors varied due to trait differences such as shade tolerance and moisture affinity. For most species, presence was positively related to biotic disturbance (disease(s) and/or animal(s)) and mesic physiography and negatively related to distance from a city or a nonforest edge. The best predictor for the presence of NNIPs was annual average number of days the temperature is ≤ 32˚F, with all five species presence correlated with the annual average number of days the temperature is ≤ 32˚F. Understanding the effect of site characteristics and climate on NNIP distribution provides insights into important drivers of species presence at a regional scale and allows land managers, scientists, and concerned citizens to predict invasion risk and future ecosystem response.
  • Thumbnail Image
    Item
    Grasslands and Brushlands of the Oak Savanna Region of Minnesota as Biomass Feedstock Sources
    (2010-01) Gillitzer, Peter Andrew
    Abstract summary not available.
  • Thumbnail Image
    Item
    Hierarchical Influences of Channel, Riparian And Landscape Features on Coarse Woody Debris in Low-gradient, Midwestern Streams
    (University of Minnesota Duluth, 1998) Johnson, Lucinda B; Host, George E; Richards, Carl
    Coarse woody debris is an important component of many small to medium streams, directly influencing stream geomorphology as well as many ecosystem properties and processes (reviewed by Harmon, et al. 1984, Gregory and Davis 1992, Gurnell, et al. 1995; Table 1). Woody debris exerts control over the structure of aquatic habitats by impeding flow, thereby increasing flow heterogeneity in the channel, influencing the pool-riffle sequence, erosional processes, channel dimensions, and deposition and retention of sediment and organic matter. Habitats created by CWD are varied, including plunge pools, backwaters and eddies, as well as the interstices of debris dams and individual logs (O’Connor 1991). These habitats are critical for fish as well as invertebrate species, providing flow and predation refugia for fish, oviposition and pupation sites, a feeding platform for invertebrates, and a substrate for biofilm production (Sedell et al. 1988, Shearer and Webster 1988)). The structure and dynamics of physical habitat in streams (Southwood 1977) and potential sources of colonizers (Gore 1982) regulate the composition and function of stream communities. Increased retention of particulate organic matter and production of FPOM from decomposing logs alters nutrient fluxes through the biota and subsequently influences the functional response of the fish and invertebrate communities within the stream (Minshall et al. 1982, Sedell et al. 1988). In response to changes in organic matter storage, functional responses of invertebrate communities, taxa abundance, and production have been reported to vary between erosional and depositional habitats, as well as between reaches with and without debris dams (Molles 1982, Smock et al. 1982, 1989), or logs (Wallace et al. 1995). In regions with unstable substrates, snags support a large proportion of the insect biomass and production (Benke, et al. 1984, Smock, et al. 1985). In many regions of the United States coarse woody debris was historically a prominent feature in streams, such that logjam s stretched for kilometers on both small and larger streams (Swanson, et al. 1976, Triska 1984, Maser and Sedell 1995). Debris removal was initiated to provide unobstructed waterways for navigation and transportation of harvested logs. In 1776 the U.S. Congress appropriated money to clear driftwood from streams and rivers to improve navigation, beginning with the Mississippi River. Removal of woody debris in rivers remains an active role of the U.S. Army Corps of Engineers (Harmon, et al. 1986), and is one of the primary roles of County Drain Commissioners (locally elected officials charged with creation and maintenance of an extensive network of drainage ditches) in the state of Michigan. Geomorphic features, to some degree, have regulated the original vegetation of the landscape (Grimm 1984, Host and Pregitzer 1992), as well as the historical and current land use/land cover patterns within the region. Many land management practices directly and indirectly influence the abundance of coarse woody debris (CWD) in streams. Alteration of the hydrologic regime resulting from stream channelization, wetland filling, or urbanization frequently results in increased bank erosion, one of the primary mechanisms of CWD input to streams in non-mountainous regions (Keller and Swanson 1979; Davis and Gregory 1994). Especially in small to medium-sized streams, forest management alters the species composition, number, and size distribution of trees in the upland, and thus dramatically modifies the potential source and input rates of CWD to streams (Bilby 1984, McDade et al. 1990, Gumell, et al. 1995, Fetherston et al. 1995). In agricultural and suburban regions potential sources of woody debris as well as the stream retention capacity are altered by management practices such as grazing, landscaping, riparian vegetation thinning or removal, dredging and channelization. The riparian zone and the land-water ecotone mediate inputs of sediment, nutrients, and particulate organic matter to streams, in addition to providing other important ecosystem functions (Gregory, et al. 1991). Coarse woody debris produced in the riparian zone by fire, disease, insect damage, ice/snow loading, and wind-throw represents the potential source for the stream (Keller and Swanson 1979). Processes such as mass soil wasting, bank undercutting and erosion, and flooding transport this material into the stream. In some systems beaver may be the primary vector transporting large volumes of CWD to the channel (Naiman, et al. 1986, Maser and Sedell 1995). The processes controlling CWD input to streams are influenced locally by tree species, stand age, soil stability, and human intervention (e.g., forest harvest and riparian zone clearing), and regionally by geology, climate, valley geomorphology and land use patterns. Since CWD fundamentally influences both the structure and function of many streams, identifying the myriad of factors that regulate its abundance and distribution is essential for understanding how many aspects of stream ecosystems are regulated. Many studies have examined the role of coarse woody debris in high- and low-gradient catchments (Table 1). However, few studies have attempted to quantify the relationship between landscape factors and the observed patterns in CWD abundance and distribution in low gradient systems, particularly in landscapes that are not dominated by forests. Landscape-scale factors such as land use patterns and surficial geology influence the abundance of woody debris found in stream channels (Ralph et al. 1994; Richards, et al. 1996) and undoubtedly also play a role in mediating the impact of disturbance events that influence the export of CWD and smaller organic matter fragments. By examining the factors influencing large woody debris at a range of spatial scales, the extent to which local and regional factors regulate the abundance and distribution of CWD can be discriminated. The goals of this paper are to: 1) characterize the abundance, size, and distribution of CWD in low gradient streams in developed landscapes; 2) quantify the relative influence of reach- and catchment-scale factors on the abundance and distribution of CWD.
  • Thumbnail Image
    Item
    Mapping Lake Trout Spawning Habitat Along Minnesota's North Shore
    (University of Minnesota Duluth, 1999) Richards, Carl; Bonde, John; Schreiner, Don; Selgeby, James; Cholwek, Gary; Yin, K. Karen
    Lake Superior's surface covers more area than any other body of fresh water in the world. While it is the largest of the Great Lakes, less is known about it than any of the other lakes in the chain. Lake Superior supports a variety of life and its nearshore area is vital to its overall ecosystem as well as to many fish species that inhabit the lake. Lake trout (Salvelinus namaycush) have historically been the top predator in the Lake Superior fish community and are the primary species caught by anglers. Lake trout are well adapted to the cold, clear, infertile waters of Lake Superior and generally require boulder and cobble substrates at depths less than 30 meters for spawning and early survival of eggs and fry (Marsden et al., 1995). An important component of lake trout management in Lake Superior has been the protection of known spawning areas. Stocking suitable habitat with hatchery reared lake trout is a management strategy based on the belief that adult fish returning to these areas will have increased early survival of eggs and fry. Biologists also believe that early life stages of lake trout stocked on appropriate spawning substrates will imprint and re-colonize these spawning areas more quickly than if left to normal population expansion (Krueger et al., 1986). These approaches require site specific knowledge of the distribution and areal extent of bathymetric features and substrate type so that efforts can be concentrated in specific areas where success is likely. An important information need, discussed in the Fisheries Management Plan for the Minnesota Water of Lake Superior (MNDNR 1995), is the identification and quantification of lake trout spawning habitats. Unfortunately, detailed maps of Lake Superior's benthic habitats sufficient for identifying potential lake trout spawning habitats are largely nonexistent in Minnesota waters. With the exception of embayments and ports extensively used for shipping, contemporary bathymetric maps of the lake are built from data consisting of a few depth measurements per square kilometer. While these maps are sufficient for describing the general shape of the lake 's bottom for general navigation purposes, they are insufficient to depict detailed fish habitat. Furthermore, the substrate of the lake is largely unknown. When looking out over any large body of water, it is difficult to tell what might lie underneath. The shoreline geology can provide a clue, but what is on shore is not always the same as what lies a few hundred meters, or even just a few meters, offshore. Very few systematic surveys of substrate type have been conducted and no maps exist. To date, the long length of the shoreline and cost associated with conducting such surveys have prohibited extensive surveys. Even mapping just a square kilometer of near shore area with traditional methods would have been a major undertaking.