Browsing by Subject "Plant communities"
Item Effects of repeated early season herbicide treatments of curlyleaf pondweed on native macrophyte assemblages in Minnesota Lakes.(2010-09) Jones, Ajay RobertNon-native invasive species have the potential to cause various problems in small isolated ecosystems, these constraints are exemplified in the small, shallow, lakes of Minnesota. Curlyleaf pondweed (Potamogeton crispus L.) is one of the common occurring and most influential non-native invasive species in Minnesota. Characterized by its early spring growth and early summer senescence, curlyleaf has the ability to negatively affect native macrophyte growth by forming dense monotypic canopies in late spring and releasing nutrients in early summer. Because of the negative impact on natural ecosystems along with the problems curlyleaf can cause for people, there is serious interest in the management of curlyleaf. One management practice is the early season application of herbicides, where curlyleaf is targeted before it is capable of producing turions (propagules) and native plants are unlikely to be affected. We examined the response of native plant communities to spring herbicide treatments of curlyleaf pondweed from 2006 through 2009. Thirteen lakes were examined during our study; ten were treated with herbicide and three were used as nontreatment reference lakes. Plant communities were assessed in the littoral zone with the point intercept method in early spring (before treatment), late spring (after treatment) and mid summer (peak native plant growth). For each survey, approximately 40 random biomass samples were taken in each study lake to estimate plant biomass. To determine changes in native plant frequency and biomass throughout the course of consecutive annual treatments, we compared differences between treated and untreated lakes within years for August surveys and compared August surveys between years for treated or untreated lakes. Additionally, we examined inter-seasonal changes, comparing differences within and between treated or untreated lakes from May to June and June to August in every year. In the reference lakes, curlyleaf persisted at moderate to high frequencies over the four years, and no consistent changes in native plant frequencies were seen. Herbicide treatments proved effective for controlling curlyleaf, which decreased in frequency within 1 month following treatment for each year of the study. The total frequency of occurrence of native plants in August did not decrease in most of the treatment lakes between years. Native macrophyte species richness also showed little change with continued treatment, although shifts in abundance of some species were observed. August native plant biomass increased between 2006 and 2009 in most treatment lakes, whereas native biomass varied in untreated lakes. Much of the change in biomass was attributed to a single species in most treatment lakes. We observed increases of Chara spp. frequency and biomass in most treated lakes. However, multiple years of treatment may be needed to obtain increases in native plant abundance as the largest increases occurred after 3 years of treatment. Early-season lake-wide herbicidal treatments of curlyleaf pondweed can reduce curlyleaf occurrence and density without major harm to native plants. Significant inter-seasonal changes in frequency and biomass were observed in both treated and untreated lakes although differences were not observed between treated and untreated lakes. Native species richness increased from May to June and June to August in both treated and untreated lakes. The frequency of native plants increased between May and June but less so between June and August in both treated and untreated lakes. Conversely, native plant biomass increased from June to August more so than from May to June for both treated and untreated lakes. These findings suggest that early season growth primarily manifests in distribution and colonization, while late season growth results in increased biomass. Similarly, many plant species follow the same patterns as the overall native plants, although other plant species may have different frequency and biomass regimes throughout a single season. Despite the differences in native plant species, we did not see any major inter-seasonal detriment caused by the presence of curlyleaf pondweed in untreated lakes, or positive influence of herbicide treatment in treated lakes. These findings suggest that increases in native plant growth may occur only after several annual treatments.Item Investigation of soil and plant characteristics across a continuum of non-native earthworm invasion in hardwood forests, Tettegouche State Park, MN USA(2013-06) Bennett, Zachary DavidInvasive earthworms cause profound changes in forest floor thickness, soil structure and chemistry, and plant community composition within cold temperate hardwood forests. However, few studies have examined these effects across a continuum of earthworm invasion and in conjunction with canopy disturbance. The research objectives of this thesis were to determine the changes of earthworm invasion on the upper soil horizon's thickness, gravimetric water content, potential horizon field capacity, and available nitrogen and phosphorus; and plant communities in hardwood forest sites within Tettegouche State Park, MN USA. All sites were uneven-aged, unmanaged northern hardwood forests of an approximate age of 225 years. The canopies were dominated by sugar maple and had experienced substantial canopy disturbance (9.7 - 20.5% opening) during an ice storm in spring 2009. Earthworms were sampled in the fall of 2010-2011. Each of the four sites were invaded by differing earthworm assemblages ranging from minimally invaded (1 species and average biomass of 0.1729 AFDgrams/m2) to heavily invaded (5 species and average biomass of 14.12 AFDgrams/m2). In the upper soil horizons O horizon thickness decreased and A horizon thickness increased with increasing earthworm richness and biomass. Mineral soil gravimetric water content was measured biweekly (May-August 2011) but did not differ among sites. Total potential horizon field capacity, including the O horizon, determined that 53-59% of the available water in a 12 cm deep core at field capacity is held in the O horizon. Availability of NO3 was significantly higher in the heavily invaded site compared to all other sites. Plant communities were assessed in the summer of 2009-2011, nonmetric multidimensional scaling was used to analyze the relationship of herbaceous plant species richness and percent cover to environmental variables and that species richness and diversity indices were positively correlated with O horizon thickness and negatively correlated with earthworm richness and biomass. The main conclusions of this study are that 1) moderate canopy disturbance had no affect on soil characteristics, or earthworms and plant communities; 2) earthworm assemblages (richness and biomass) were strongly correlated with changes in forest floor thickness, moisture holding capacity, nitrogen availability and plant community composition in these sugar maple forests, and 3) traditional exclusion of the O horizon when measuring water holding capacity in forest soils should be reconsidered given the large proportion of potential water holding capacity it provides, and is lost when a site is heavily invaded by earthworms. The implications of the loss of the O horizon and the associated loss of water holding capacity on ecosystem functions and biotic communities of hardwood forest systems need to be more fully explored.Item Plants in Prairie Communities(St. Paul, MN: University of Minnesota Extension Service, 1995) Robison, Roy; White, Donald B.; Meyer, Mary H.Item Riparian plant composition, abundance, and structure responses to different harvesting approaches in riparian management zones nine years after treatment in Northern Minnesota, U.S.A.(2010-11) Martin, Michelle AmberI compared riparian plant responses to different harvesting approaches over nine years in Riparian Management Zones (RMZ) in Northern Minnesota. In Chapter 1, I found that tree regeneration in RMZs is greater in partially harvested treatments (60% BA removal) than in unharvested treatments. This was especially true of intolerant tree species, although the shade tolerant species are becoming important in lower strata at year nine post-treatment. In Chapter 2, I found that understory plant community composition and abundance change somewhat over time in partially harvested treatments in comparison to unharvested treatments. This was especially true of woody understory layers, however, less so for the herbaceous layer. In general, the understory plant community shifted toward more shade intolerant and disturbance indicating species. As of nine years post-treatment, partially harvested RMZs balance timber and non-timber management objectives as they increase tree regeneration and do not dramatically alter understory plant communities.