This is the reply we received from Chris Barber, the “Tree Guy” at Calkins.

In response to concerns about the status of the Class of ’69 Savanna Arboretum, I wanted to give an update on how things are going and provide some more detailed information that you could share with the representatives from the class.

Just to recap our plan for this area, after removing the existing rows of non-native shrubs, we planted 25 potted trees and 125 bare-root saplings and seeded the area with a native prairie/savanna pollinator seed mix.  The tree species were selected to provide the widest variety of native trees that were appropriate for the site conditions, native to Iowa savannas, and tolerant of fire, as it is a necessary component of savanna ecosystem management.  The predominant species for an area like this is a mixture of oak and hickory species which is what we planted along with a few Iowa crabapples.  Ultimately, the target trajectory for this area is to have an area with an open canopy and a diverse mixture of native grasses and wildflowers.  Of course, these are slow-growing tree species that will take many years before the area reaches some semblance of having any tree canopy.  The upside to this is in addition to providing a native ecosystem that is not currently represented at Calkins, these trees are extremely long-lived, and some will be around for the next 15-20 generations to enjoy and learn from.  For perspective, had Jacques Marquette and Louis Jolliet planted acorns as the first Europeans to visit Iowa in 1673, those trees could still be alive today.  We also rerouted our hiking trails to have three separate access points with a memorial sign, educational sign, and benches.

Of the original 25 potted trees, we’ve had 3-4 that have died completely.  Some from initial transplant stress and some probably from a couple of years of extreme drought while they are still establishing good root structure.  There are another 12 that have top-killed but have resprouted.  This is very typical of the oak species that we planted under these conditions.  Under natural conditions, an oak might be top-killed several times from browsing, fire, trampling, drought, etc., before it builds enough roots to shoot up quickly enough to survive whatever nature throws at it.  When this happens, we will let them go, and they typically grow quickly since they have a large root mass proportional to the above-ground mass.

Of the 125 or so bare-root saplings that were planted with tree tubes, approximately 60% have survived the first three years, although the majority of them have top-killed and resprouted.  This is fairly typical of a better-than-average survival rate, especially considering the extreme drought conditions since the time of planting.  At a little over a buck a tree, this is still a very economical way to plant a large number of trees, even though some mortality is expected.

We had also overseeded the area with a native prairie/savanna seed mix containing a mixture of native grasses and wildflower species appropriate for the site.  Since there were some natives on the site already, we decided to inter-seed rather than spray herbicide to kill off the existing vegetation.  The native herbaceous plants have been somewhat slow to establish, which is normal.  We also have some resprouting of the old non-native shrub rows.  This spring, we conducted a prescribed fire to help promote the growth of the native plants and control the non-fire tolerant invasive shrubs.  To mitigate negative impacts on the planted trees, we used a weed eater around each tree to reduce the fuel load and heat.  We also burned the entire area using back burning, where the fire fought against the wind causing it to move slower and reducing heat exposure on the stems.  Unfortunately, fire is not 100% predictable, and having not burned the area since this project started resulted in a higher-than-anticipated dry fuel load and hotter temps than I wanted.  The fire had positive effects on the seeding and invasive shrubs but also a patchwork of negative effects on the trees, although none died as a result of the prescribed fire.  About 5-6 larger trees had lower limbs fire pruned which is natural in a savanna setting, and these trees will suffer no ill effects going forward.  There were also 5-6 that were most likely top-killed but have resprouted.  Some of these also have flexible twigs and appear to re-budding so they may fully recover.  The three that died were dead prior to the prescribed fire.  Of the 65 or so living bare-root saplings, about 60-70% were top-killed due to the prescribed fire and have been resprouted.  We have reinstalled the tree tubes over the resprouts, and I suspect that in 2-3 years’ time, they will surpass the growth of the bare-root saplings that were not top-killed.

I know that was a lot of information to throw at you, but I wanted everyone to have a complete picture of what is going on with the savanna arboretum.  There is money available to replace trees if that is what the class would like to do (we have said yes).  From an ecological standpoint, I think we would be fine without replanting.  I also realize the sentiment behind the memorial and have no issue replacing some if desired.  I’d also be happy to answer any questions.

Chris Barber, The Tree Guy, Calkins