Ecological Interactions and Biological Control

By David A. Andow; David W. Ragsdale et al. | Go to book overview
Save to active project

ble for several of the programs, but there are other parameters that are equally valid measures of the success of biocontrol programs. For example, knapweed increases surface runoff and stream sedimentation ( Lacey et al. 1989), and there is a suggestion that it reduces ponderosa pine regeneration. Both of these could have been used as project objectives. A concern with leafy spurge is that it is displacing the western prairie fringed orchid (Plantanthera praeclara), of which there are about 2,000 plants in North Dakota ( Federal Register 1989). Hence the objective of the U.S. Forest Service group responsible for managing the main orchid populations should be to maintain or increase it. The Canadian Department of National Defense is concerned with spurge at Shilo, Manitoba, because it does not bind the sandy soil, so the area is subject to wind erosion after tank exercises. Biocontrol success would be an increase in the root mat near the surface as grass replaces spurge. Military authorities are also concerned with the maintenance of native plant communities and being a good neighbor to surrounding farmers, both of which have to be measured in other terms. One of the government of Saskatchewan's goals for the leafy spurge biocontrol program is the elimination of an annual $150,000 subsidy for its chemical control; the results achieved are sufficiently encouraging that this subsidy has already been withdrawn, so this goal has been met. The point is that each of these objectives needs to be measured in terms other than weed reduction, and many weed biocontrol projects are not taking this final step.


The impact of biocontrol agents--such as degree of defoliation or reduction in weed population vigor--on their target weed is not linearly related to the benefits of weed biocontrol, such as forage yield. Indeed, the benefits are usually not studied because they are not established because project goals.

Monitoring weed biocontrol projects is difficult because many parameters must be followed and the effects do not necessarily occur where and when they are expected. The system suggested is to divide the project into the following steps, each with its own goal, to be investigated in sequence: agent establishment, intensity of agent attack, impact of the agent on the weed, and project benefits. Many projects are terminated with an assessment of the agent impact on the weed, which is done by clipping or sorting vegetation inside and outside the agent area. However, satisfactory results can usually be obtained with much less effort with Daubenmire's approach for assessing plant species cover. This is not the end of a project, since the benefits of reducing weed cover have to be measured in other terms, such as forage yield, reduced erosion, reduced herbicide use, and the protection of rare species. These are the benefits that justify starting a biocontrol project, and they vary with each weed species.


I gratefully acknowledge the assistance of Alan Sturko of the British Columbia Forest Service for collecting samples and providing data from Daubenmire transects,


Notes for this page

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
Loading One moment ...
Project items
Cite this page

Cited page

Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

Cited page

Bookmark this page
Ecological Interactions and Biological Control
Table of contents

Table of contents



Text size Smaller Larger
Search within

Search within this book

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

While we understand printed pages are helpful to our users, this limitation is necessary to help protect our publishers' copyrighted material and prevent its unlawful distribution. We are sorry for any inconvenience.
Full screen
/ 340

matching results for page

Cited passage

Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

Cited passage

Welcome to the new Questia Reader

The Questia Reader has been updated to provide you with an even better online reading experience.  It is now 100% Responsive, which means you can read our books and articles on any sized device you wish.  All of your favorite tools like notes, highlights, and citations are still here, but the way you select text has been updated to be easier to use, especially on touchscreen devices.  Here's how:

1. Click or tap the first word you want to select.
2. Click or tap the last word you want to select.

OK, got it!

Thanks for trying Questia!

Please continue trying out our research tools, but please note, full functionality is available only to our active members.

Your work will be lost once you leave this Web page.

For full access in an ad-free environment, sign up now for a FREE, 1-day trial.

Already a member? Log in now.

Are you sure you want to delete this highlight?