Cottonwoods going dormant, what a year!

Who would have guessed what a whirlwind year of cottonwoods this turned out to be. We've been blown away by enthusiasm and support. 

We have some preliminary results to share, but first here's a quick refresher on the project this year.

At Lilydale with partners planning the cottonwood experiment


I worked with closely with staff from St. Paul Parks and Recreation and the National Park Service as well as researchers associated with the University of Minnesota to design a cottonwood planting experiment that will help us determine the best way for public landowners to plant them in the national park. We went out in the dead of winter to evaluate planting sites and start planning. Special thanks to US Army Corps of Engineers.

Implementing the project was a blast! Volunteers were out in the dead of winter collecting cuttings with foresters from the Army Corps of Engineers and rangers from the National Park Service. We teamed up with the City of St. Paul's Parks and Recreation to plant cottonwoods at Lilydale Regional Park with the help of city employees, a youth crew and volunteers.





Measuring height of plants



Counting leaves to measure vigor

Then youth from Urban Roots helped collect data so we can start answering questions:

1. Do planted cottonwoods grow best in forest openings or fields?
2. Are the cottonwoods sufficiently shielded from deer browse when they're in fencing, tree tubes, or left exposed?


For each of those questions we also looked at whether this was true for trees planted from seed and as unrooted and rooted cuttings. 

The tree in the foreground was unprotected
and clearly has fewer leaves than the tree
directly in front of a tree tube in the
background that was pulled out of the tube


None of the seeds germinated and produced seedlings. This was not surprising because if they would have been successful we would not be worried about their populations. We will study cottonwood germination further next spring.

The cuttings we collected last winter show no visible signs of growth. This is because they started out simply as sticks without roots. Trees need roots before they can begin growing leaves and twigs. By the end of the season these trees had produced roots, so they'll be ready to leaf out next spring. We will be able to compare unrooted and rooted cutting growth next year.

Since the seeds and unrooted cuttings did not grow but the rooted cuttings did, the data shown for this year is only for rooted cuttings. 


Rooted cuttings that were protected by tubing or fencing had more new stem growth at the end of the summer and did not show signs of deer browse. It is likely that the deer eating new growth on the trees that had no fencing or tubing to protect them is the cause.


Only the trees with no form of protection were browsed.

Rooted cuttings grew more stem and leaves when growing in tubing. Those in fencing were in second place for growth an leaves and those without fencing grew the least, likely due to browsing pressure.




Trees in the field grew vigorously

 
We found that rooted cuttings growing in the field grew more in terms of amount of new growth and number of leaves produced. The trees in the field grew nearly twice as much new stem as those in the forest. Leaf production wasn't dramatically different, but more did grow on field trees. 

It will take another year or two of data to confirm these findings but this year's data yields a few preliminary findings that suggest what conditions make cottonwood plantings most successful: 

1. Cottonwoods showed less growth at the end of the season when they were not protected from deer. Of the protected trees, those with tubing grew the most.
2. Cottonwoods grown in fields grew more than those in the forest.

We will monitor the plots though August 2016 and draw final conclusions then. At that time, we will be more confident in our conclusions  because we will have data from more growing seasons and sites. 

The cottonwood trees are going dormant after a busy year, but the project is not. The McKnight Foundation gave the Mississippi River Fund a grant to keep this work going after my Minnesota GreenCorps position ended. This means I'm spending the winter working with the Minneapolis Park and Recreation Board and Three Rivers Park District to organize a cottonwood planting at North Mississippi Regional Park in Minneapolis, and working with the National Wildlife Federation to identify other areas along the river that need cottonwood restoration.