Activity - Inventory and Sampling Weeds

Skills: Observing, Classifying, Recording data, Interpreting data.
Activity - Inventory and Sampling Weeds - Articles

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Introduction:

To understand the impact of weeds on a habitat, weed infestations can be sampled and possibly mapped. If your goal is to manage the weeds, sampling and mapping gives you valuable information on what IPM tactics you will use and when to use them.

The goal of sampling is to get an accurate estimation of the potential weed population in a given area. This means, the sampling technique must adequately represent the whole area you are considering. For example, in a farm field, you do not just sample on the edge of the field because this would give you an inaccurate estimate of what is going on in the whole field. Mapping of where exactly the weeds are may allow you to spot treat rather than do something on the whole field.

Your goal in sampling may be understanding of the species composition of an area or gaining information in order to make management decisions. The type of sampling used will depend on what you want to know and what environment you are sampling in. For example, for farm situations, there are established "economic thresholds" of tolerance for weeds. Above that level, the weeds will cost the farmer money if he or she does not do something to knock them back. Also, the sampling technique for a wetland (see later sections) is not the same as for a field or turf grass area.

Learning Objectives:

1. Try and compare sampling techniques for weeds
2. Learn plant identification
3. Learn factors involved in management decisions based on sampling information
4. Discover the concepts of species diversity and distribution within habitats

Materials Needed:

• paper and/or data sheets
• long tape measures to set up transects
• meter square*
• weed ID books or charts
• hand lens
• zip lock bags if specimens are to be brought back for ID

* a meter square is basically a frame that is 1 meter on each side. This can be made of wood, PVC, or measured on the spot. Having a frame you can pack around with you is easiest and quickest.

Timeline:
Depends upon how in-depth. One to several class periods, or partial or all day field activity.

Procedures:

1. Select several environments in which to sample weeds. Start with someplace easy such as a lawn.

2. Lay out a transect across the environment and predetermine at what distance intervals you will stop and sample.

3. Transect method - at each predetermined point on the transect, stop and write down the plant species touching or closest to each side of the tape at the stopping point. Do this until all points are sampled.

4. Quadrat square method - go back and stop again at the same points. This time, set the corner of the quadrat square down at the stopping point parallel to the tape. Inside the square, see how many different plant species you can find. List them. Make an estimate of what percent of the ground within the quadrat is covered by each of the species. Determine if the plant species are evenly distributed or clumped.

Data collection:

See attached data sheets.

Transect method - list species found at each interval as described above. You can also take measurements like plant height, stage of growth or other factors that are relevant in that habitat.

Quadrat method - list all plant species found inside quadrat with % cover

Analysis:

Compare the effects of using the transect method vs. the quadrat square method

  • which was more time consuming?
  • did they give similar estimates of weed diversity and abundance?
  • which of the techniques would be most useful in which habitats?

Discussion:

What did the results of sampling tell you about the characteristics of the weeds you found?
Were there areas within the habitat that some species seemed to thrive, while others did not?
Why might this be?
If you were to make some decisions about managing these weeds, which IPM tactics might you consider?