Mark J. Renz

Using habitat suitability models to target invasive plant species surveys

Managers need new tools for detecting the movement and spread of nonnative, invasive species. Habitat suitability models are a popular tool for mapping the potential distribution of current invaders, but the ability of these models to prioritize monitoring efforts has not been tested in the field. We tested the utility of an iterative sampling design (i.e., models based on field observations used to guide subsequent field data collection to improve the model), hypothesizing that model performance would increase when new data were gathered from targeted sampling using criteria based on the initial model results. We also tested the ability of habitat suitability models to predict the spread of invasive species, hypothesizing that models would accurately predict occurrences in the field, and that the use of targeted sampling would detect more species with less sampling effort than a nontargeted approach. We tested these hypotheses on two species at the state scale (Centaurea stoebe and Pastinaca sativa) in Wisconsin (USA), and one genus at the regional scale (Tamarix) in the western United States. These initial data were merged with environmental data at 30-m2 resolution for Wisconsin and 1-km2 resolution for the western United States to produce our first iteration models. We stratified these initial models to target field sampling and compared our models and success at detecting our species of interest to other surveys being conducted during the same field season (i.e., nontargeted sampling). Although more data did not always improve our models based on correct classification rate (CCR), sensitivity, specificity, kappa, or area under the curve (AUC), our models generated from targeted sampling data always performed better than models generated from nontargeted data. For Wisconsin species, the model described actual locations in the field fairly well (kappa = 0.51, 0.19, P < 0.01), and targeted sampling did detect more species than nontargeted sampling with less sampling effort (chi2 = 47.42, P < 0.01). From these findings, we conclude that habitat suitability models can be highly useful tools for guiding invasive species monitoring, and we support the use of an iterative sampling design for guiding such efforts.

Developing cost-effective early detection networks for regional invasions

Early detection and rapid response (EDRR) seek to control or eradicate new invasions to prevent their spread, but effective EDRR remains elusive due to financial and managerial constraints. As part of the Great Lakes Early Detection Network, we asked stakeholders to indicate their needs for an effective EDRR communication tool. Our results led to the development of a website with five primary features: (1) the ability for casual observers to report a sighting; (2) a network of professionals to verify new sightings; (3) email alerts of new sightings, including data from all data providers across the region; (4) maps of species distributions across data providers; and (5) easy communication channels among stakeholders. Using results from our stakeholder discussions, we provide a cost-effective framework for online EDRR networks that integrate data and develop social capital through a virtual community. This framework seeks to provide real-time data on current species distributions and improve across jurisdictional collaboration with limited oversight.

The Effects of Increasing Grazing Height on Establishment of Pasture Weeds in Management-Intensive Rotationally Grazed Pastures

Abstract Weeds can infest management-intensive grazed pastures and impact forage quantity, forage quality, and animal health. Common burdock, plumeless thistle, and Canada thistle are three common pasture weeds in the midwestern United States that are managed to avoid these impacts. Experiments were established at two sites to determine if increasing grazing heights from fall through summer would reduce emergence and survival of burdock, plumeless thistle, and Canada thistle seedlings. Five simulated grazing heights (5, 10, 15, and 20 cm and a not-clipped treatment) were implemented in October 2008 and repeated in May through August. Density of all species was reduced from May to September, with reductions ranging from 65 to 78%, regardless of treatment. Treatments that left at least 15 cm of residual grass had reduced densities of burdock and Canada thistle compared to the 10-cm treatment. Regression analysis demonstrated that reduction in burdock and summed planted weed density was related to increased intercepted photosynthetically active radiation from forage in April. However, total biomass yield was reduced up to 60% when grazing heights were increased from 5 to 20 cm, although differences were only observed at the fall and early spring grazing events. Relative forage quality (RFQ) was similar across treatments, except at the third grazing event for which the 15 and 20-cm treatments had reduced RFQ compared with other treatments. Results suggest that increasing grazing heights can reduce emergence and survival of burdock and Canada thistle but can also result in a reduction in forage quantity in the fall and early spring. Nomenclature: Canada thistle, Cirsium arvense (L.) Scop.; common burdock, Arctium minus Bernh.; plumeless thistle, Carduus acanthoides L.

Effects of Giant Foxtail (Setaria faberi) and Yellow Foxtail (Setaria pumila) Competition on Establishment and Productivity of Switchgrass

Abstract Switchgrass is a potential feedstock for cellulosic bioenergy production. Weed competition from annual grass during the establishment year can reduce switchgrass establishment and resulting productivity, but the relationship between early season grass densities and outcomes of competition are not well understood. We measured how a range of giant and yellow foxtail densities in the establishment year influenced switchgrass establishment and resulting productivity in the first production year (second year of the growing season). In two of the three site–yr more than four foxtail plants m−2 reduced switchgrass plant densities below documented thresholds of establishment success. A lesser effect of foxtails in the third site–year suggested that higher switchgrass emergence rates reduced foxtail competitive ability during establishment. Effects on yield were consistent over the three site–yr. The yield (10.96 Mg ha−1 ± 0.77) decreased rapidly as foxtail density increased. One foxtail plant m−2 reduced switchgrass yield in the first production year by 25%, and yield loss was 90% or greater at densities > 50 foxtail plants m−2. Although switchgrass can establish in the presence of foxtail competition, these weed species should be controlled to maximize yields in the first production year. Nomenclature: Giant foxtail, Setaria faberi Herrm.; yellow foxtail, Setaria pumila (Poir.) Roemer & J.A. Schultes; switchgrass, Panicum virgatum L.

Native Forb Establishment following Application of Aminopyralid or Clopyralid

Interest exists in planting mixed forb—grass prairies in the midwestern United States. Aminopyralid or clopyralid can be used to suppress competition from invasive plants prior to seeding prairies. As these active ingredients are known to persist, concern exists that reductions in forb establishment could occur. We tested whether common midwestern forb species could tolerate an application of aminopyralid or clopyralid alone or in combination the summer prior to seeding, and whether fall dormant or spring seeding date influenced establishment. This experiment was performed in Beresford, SD, and Arlington, WI, where aminopyralid (54 or 123 g ae ha-1), clopyralid (237 and 420 g ae ha-1), or aminopyralid + clopyralid (54 + 237 g ae ha-1) were applied to a prepared seedbed in July of 2009. Ten forbs were seeded in November 2009 as a dormant seeding and in April 2010 as a spring seeding at both locations, and establishment was assessed 12 and 24 mo after treatment (MAT). Results were site and species specific. Time of seeding was an important driver of plant counts at both locations 12 and 24 MAT. In Wisconsin at 12 MAT, 60% of species studied exhibited higher counts in the spring seeding. This trend persisted in some, but was not consistent across all 10 species. In South Dakota, 80% of species studied had higher counts at 12 and 24 MAT, but differences were species specific and often differed from those studied in Wisconsin. Those species that had higher counts in spring seeding at 12 MAT, maintained higher counts at 24 MAT. Forbs planted in plots treated with herbicides did not differ from plots left untreated at either location. Results suggest native forbs typically seeded in the upper Midwest can tolerate these herbicides when applied at least 4 mo prior to seeding. Nomenclature: Aminopyralid; clopyralid.

Managing Field Bindweed in Sorghum-Wheat- Fallow Rotations

Abstract Infestation of field bindweed ( Convolvulus arvensis L.) on farms in the semiarid, Southern High Plains is widespread and has led to significant reductions in crop productivity throughout the region. A 3-year study was conducted in a wheat ( Triticum aestivum L.)-sorghum [ Sorghum bicolor (L.) Moench]-fallow rotation at two locations to investigate the long-term suppression of field bindweed with chemical methods. Specifically, the effects of one, two, and three years of fall-applied herbicides on bindweed populations were of interest. Chemical treatments used at each location were: quinclorac (0.28 and 0.43 kg/ha); quinclorac + 2,4-D (0.28 + 0.56 kg/ha); dicamba (1.12 kg/ha); and metsulfuron (0.021 kg/ha). Results indicate that the third year of herbicide application may be critical in effectively suppressing field bindweed for more than one year. There were no differences among herbicide treatments between one and two years of application by the third year. All herbicides containing quinclorac and dicamba significantly reduced bindweed populations the following spring after application; metsulfuron alone was not considered effective in either short- or long-term suppression. Field bindweed control may be reduced when 3-year herbicide program begins following a fallow period without any tillage or crop competition.