Conservation completes research project at Lake Iowa Park

As summer fades away and we approach fall, let us focus on a research project that our Park Ranger-Naturalist completed along with some help from other Iowa County Conservation staff.

As part of an initiative to perform some science-based research to help steer ICC staff's management decisions in the natural landscapes of our properties, this research project focused on a topic that we deal with a lot — invasive species removal.

… Invasive species are known as species that have invaded into a region that they are not native to, and their presence in an ecosystem has, or eventually will, cause more ecological, economical or human harm than if it were absent.

In our case, we primarily deal with invasive plant species, with our biggest culprits being Amur bush honeysuckle and Autumn Olive.

In this research project, we focused specifically on removal of Amur bush honeysuckle using three different eradication techniques to then determine what technique out of the three is the most effective at reducing honeysuckle density in a given area.

The objective of the study was to compare a physical method of eradication by doing a brush mowing application, a chemical method of eradication by doing a foliar spray application and a combination of a physical and chemical method of eradication by doing a cut-stump application on Amur honeysuckle from a woodland environment at Lake Iowa Park and determine which is the most effective by observing the percent honeysuckle reduction after each eradication method has been administered.

The hypothesis for the study was that the most effective eradication treatment for Amur honeysuckle from the woodlands at Lake Iowa Park would be by cut stump removal.

The study … took place in a three-acre mid-successional Oak-Hickory dominated woodland at Lake Iowa Park just Northwest of Lake Iowa Park Beach.

Here, nine 8-by-8 meter square plots were created. These nine plots were then broken down into three treatment groups, each of which consisted of three subsequent plots for experimental replication.

The treatment groups were … randomly assigned, with one out of the three eradication methods at random and labeled A, B, or C.

Treatment group A was designated as the Foliar spray treatment group in which you use an herbicide designed to kill the targeted species and spray the leaves or foliage of the plant.

Treatment group B was designated as the brush mow treatment group in which you use a forestry brush cutter implement to mow through the targeted species and cut them as low as you can to the ground.

Lastly, treatment group C was designated as the cut-stump treatment group in which you use some sort of cutting tool such as a chain saw, blade power saw, etc. to clean cut through the targeted species at the base of the main stem, and then follow back behind with an herbicide designed to kill the targeted species by painting the fresh, clean-cut stumps with said herbicide.

All honeysuckle stems were counted per each respective plot to get a pre-treatment honeysuckle density measurement. Following treatment, each stem was … again counted for its resprout to get post-treatment density.

It is important to note that two different density measurements were made in the post-treatment density count. One data set we called “resprout,” which counted if a previously treated stem resprouted (did not matter how many stems it resprouted), and the other we called “stems,” that counted each individual new stem that grew from a previously treated stem.

We were able to collect both sets of data for all treatment methods except for the foliar spray treatment due to the fact we did not see any resprout during the allotted time frame for this research project to be completed.

In this instance we were only able to gather data associated with the numbers of previously treated stems with resprout and not for the data associated with the numbers of new stems that grew from a previously treated stem.

Once data was collected, the numbers were … used to determine the percentage of honeysuckle reduction per treatment method. The average percentage of honeysuckle reduction per treatment group was used to compare effectiveness between eradication methods. The results of using both data set collection are as follows.

From the results, we can conclude that our hypothesis was correct. From both data sets, the most effective eradication method was the cut-stump treatment. … It reduced the honeysuckle density on average by 83.7 in the resprout data set and by 73.7% in the stems data set.

Something this study did not take into consideration is the multitude of variables that may influence a land manager’s management decisions.

Again, each of these treatment methods has its own respective advantages and disadvantages and may be either more or less effective depending on individualized managers variables such as access to equipment, site conditions, time, management goals, personal/agency visions and stake holder's best interests.

More studies need to be completed to expand these findings and find further solutions to really get an understanding of what truly is the most effective eradication method for amur honeysuckle that best fits the land manager's goals.

If interested in more information about this study reach out to ghazenfabor@iowacounty.iowa.gov by email.