Survey and Mapping of Invasive Species Population in Highways' Rights-of-Way by Absence-Presence Sampling Methods
Invasive Species/Vegetation Management
By law, Departments of Transportation are required to control noxious weeds along highway rights-of-way (ROWs). Beginning 2000, District 4 (D4) of Minnesota Department of Transportation (Mn/DOT) adopted a survey design consisting of n= 7, 3-mile segments to quantify infestations of Canada thistle (Cirsium arvense (L.)(Scop.), leafy spurge (Euphorbia esula L.) and poison ivy (Toxicodendron radicans) in chosen regions of the district. In 2004 and 2005, a second survey design was added to see if stratification by ecozone in D4, and greater numbers of smaller size segments could improve the survey precision. The analysis of data recorded in the surveys using the two sampling designs showed insignificant differences (? = 0.05) between means. However, precision was noted to be much greater in all cases with the 1/4-mile plan at the sub-districts level. Further, weed abundances were found to vary substantially among ecological zones (? = 0.05). When the1/4-mile segments data were used in a re-sampling to test the hypothesis that 'further improvements in precision and sampling efficiency are possible with even shorter segments', the results proved the hypothesis. Based on these results, a second hypothesis, that shorter segments should reduce inspection costs, increase sample sizes, improve precision, and allow conversion from an area-measurement approach to one based on presence or absence of chosen weeds in selected segments was tested in surveys conducted 2007. Preliminary analysis of data sets recorded in surveys using two different short segment lengths (225ft and 14ft) have revealed the need for multi-season surveys to obtain sufficient data improve our confidence in the conclusions regarding use of short segments in absence-presence surveys.
We propose to conduct absence-presence surveys in multiple Mn/DOT management sub-districts for a minimum of two seasons using the shortest (14ft) segments. Analysis of the data would help answer the question on the application of short sampling units (less than 15 feet long) in absence-presence survey for evaluation of species infestations along highways' rights-of-ways, cheaply and with required precision. This study would also allow for conclusions regarding application of the methodology statewide, and nationally.
Use of these methods would benefit the users in terms of the reduced time required to perform weed population surveys, and the increased precision of the population estimates. This increased precision will lead to improved decisions for weed control, and thereby bringing about reduced overall cost of weed control.
Caleb N Arika, University of Minnesota, Telephone: (612)625-9799
May 13, 2008
- items posted in the last 7 days (30 days for TERI)