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Inventory and Monitoring
Line graph depicting vegetation change over time
It is important for managers to be aware of land conditions and track changes that are occurring. The first step is to conduct an inventory of the plant species to establish a baseline for comparison. It is best to record both if they are present and where they occur. Inventory and monitoring help identify new or spreading weed populations and evaluate the success of control techniques.

Data are obtained by taking samples of the study area. Sampling can be repeated and compared to monitor changes in vegetation over time. Photographs can also provide insightful clues about vegetation changes when taken from the same location at different times.

There are three main types of data obtained through sampling. These are density, frequency, and cover. Each one measures different aspects of the plant community.

Two range technicians taking samples

Density data
Density is an estimate of the number of plants in a given area. In order to take density measurements, managers must determine what to count as an individual plant. This may seem strange, but with vegetative reproduction, “individual” plants can share common roots or stems. Plants are recorded by species, and this provides a relative abundance of the different species. Collecting density data is very time intensive.

Frequency data
This is more coarse than density data and easier to obtain. It simply measures whether or not a particular plant species occurs within a sample area. Frequency data is usually expressed as a percentage. An example might be, “rush skeletonweed occurred in 35% of the sample plots.” This presence or absence approach can work to track plant introductions, and roughly identify species that are increasing or decreasing.

Pictuer of different types of cover

Cover data
Cover can be anything from rocks to plants or leaf litter that covers the soil surface. It relates to the amount of protection against soil erosion. Emphasis is usually placed on the amount of cover provided by different plant species. Two types often measured are basal and canopy cover. Basal cover measures only the part of the plant coming out of the ground. Canopy cover includes a projection of all the leaves and branches...essentially the area of ground hidden while looking directly down on a plant. A statement about cover data might be, “Sagebrush provided 30% of the site cover while cheatgrass covered 45%. The remaining 25% was comprised of rocks or bare soil.”

New technology
Relatively new technologies, such as Remote Sensing (RS), Global Positioning Systems (GPS), and Global Information Systems (GIS), can make inventory and monitoring for invasive weeds much easier and efficient. These three technologies are often integrated, and are powerful tools for tracking weeds.

Image of how remote sensing works

The most common forms of RS used in weed control are images of vegetation types obtained from aircraft and satellites. RS can also be used to map large-scale weed invasions.

Two people in the field collecting GPS data

GPS technology uses satellites to pinpoint locations on earth. With this, managers can record and map invaded sites for control measures and tracking weed populations.

Image of several map layers that are used in GIS analysis

GIS uses computers to create maps with layers of different landscape features such as soil types, rivers, vegetation types, and elevation. This can help reveal important clues about what areas are most vulnerable to weed invasion.

-Density data photo: Loren St. John.
-Cover data photo: Southwest Regional Gap Analysis Project. Field site database. (http://earth.gis.usu.edu/swgap/trainingsites.html, 18 October 2006).
-New technology photos: Public domain.

Text references:
-Colorado Natural Areas Program. 2000. Creating an integrated weed management plan: A handbook for owners and managers of lands with natural values. Colorado Natural Areas Program, Colorado State Parks, Colorado Department of Natural Resources; and Division of Plant Industry, Colorado Department of Agriculture. Denver, Colorado. 349 pages.
-DiTomaso, J.M. 2000. Invasive weeds in rangelands: Species, impacts, and management. Weed Science. Vol. 48 No. 2 pp. 255-265.
-Guidelines for coordinated management of noxious weeds: Development of weed management areas. Center for Invasive Plant Management. Available: (http://www.weedcenter.org/management/guidelines/tableofcontents.html 17 October 2006).
-University of Nevada Reno. Cooperative Extension. Fact sheet 96-12. Available:(http://www.unce.unr.edu/publications/FS96/FS9612.pdf 17 October 2006).