Wednesday, December 8, 2010

Green Roofs and Exotic Invasive Species - Koelreuteria elegans

Koelreuteria elegans is a species we see sprout across Florida green roofs on a regular basis.

The plant was first brought to the USA from Taiwan as a landscape plant.

Koelreuteria elegans is also know as the Golden Rain Tree and offers bright, stunning colors in the fall and winter months.

Each tree produces numerous seeds during the year.  Seeds are then quickly spread by both birds and water - stormwater runoff.

Once the seeds find organic material, dirt or sand they quickly sprout and send out agressive roots.

The plant is now classified as a Class Two Exotic Invasive species by the Florida Exotic Pest Plant Council.

According to the University of Florida's Center for Aquatic and Invasive Plants, the species is difficult to eradicate and has no know biological control mechanism.

The important factor for green roof designers and owners is realizing this species spreads quickly and should not be used as a green roof plant.  Green roof maintenance procedures should identify juvenile sprout appearances so that they may quickly be removed from the green roofs.

Water and Wind Spread Invasive Plant Seeds
It is probably safe to say that it is not 'If" a Florida Green Roof will sprout a volunteer Golden Rain Tree but "When".

The photo here is of a mature Koelreuteria elegans growing on the bank of a creek in Jacksonville, Florida.  Each year thousands of seeds are dropped and picked up by the flowing water and carried about a half mile to Pottsburg Creek and then the St. Johns River.  Over time this one tree has probably contributed tens of thousands of new Golden Rain Trees along the banks of the St. Johns River - each themselves contributing tens of thousands more.

Green Roofs are situated high in the air, and poised much like the tree in the photo here to spread plant genetic matter across a wide geographic range.

Is is therefore important for the green roof designer and the green roof maintenance staff to understand the ecological implications of the "Right Plant Right Place' concept.

As always, email us with your questions or comments here.

Happy Green Roofing!


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