Sunday, April 19, 2009

The Spread of Holly Needs to be Checked

The bright red berries and pointed leaves are synonymous with peace and love of the holidays, but the rest of the year, Holly has become an invasive pest. In some areas of the Northwest U.S. and Western Canada, it is a crop much like our local Noble Fir but Holly is not native to the region and like many invasive species enjoys the ingredients it needs for success as well anonymity from natural predators.

Holly is quickly becoming an invader of Northwest Forests such as this small population in the Old Growth Forest at Lewis & Clark State Park.

In my work with invasive species, I hear many home and property owners complain about the plant as they tried to remove it from their yards. Like many invasive species, it reproduces in more than one way. Seeds are dispersed by birds which accounts for small populations well away from the parent plant. The trees also spread by “suckering” and “layering“. Suckering is the reproduction of a plant by shoots that arise from an existing root system. Layering is when the plant grows roots where stems touch the ground. Take a look through any of our local forests or reproduction lands and you will find small populations of Holly growing in areas devoid of solar radiation or in full sunlight.

While it is not listed on the Washington State list of noxious weeds, many other states and provinces are waging formal battles with the plant. English holly has become a serious pest in state and national parks like Olympic. Urban parks and arboretums in Portland, Seattle and Vancouver B.C. all have ongoing programs to eliminate the plants. More locally, The Friends of Seminary Hill in Centralia are slowly confronting the invaders along with Ivy in the Seminary Hill Natural Area.

On a recent hike, I also noticed a small population in the old growth loop at Lewis and Clark State Park near Toledo.

Holly is effectively controlled is by removing the entire tree and the entire root system, and then physically removing the tree and its branches out of the woods. A holly branch, if left on the ground, will grow roots and continue to thrive. Lopping off or cutting down Holly trees does nothing to the root system, and the plant easily sprouts new shoots and continues to grow.

I would employ the knowledge of a licensed professional or the local noxious weed control board and apply pesticide to the stump of a freshly cut holly bush or tree.

Holly has its uses, but like most invasive species, its presence is having unintended consequences on the natural system of our area. It is crowding out native plants and in some cases, physically impairs our movement in our own yards with its stiff, protruding leaves. Care has to be taken as even the best of intentions can make this plant more aggressive and difficult to treat.


Mossy Mom said...

I did not know that holly was invasive. I have two of them in my yard. I had to trim them so I could mow the lawn around them without getting hurt.

Gregg P said...

I think that is true that many people, even some of the most knowlegeable about native vegetation. I have found holly in all over Olympic National Park due to the method of spread. Birds eat the seed where people have the plant in domestic situations then go poop them out anywhere....even on our most protected lands and it takes over the forest floor...out competing native plants on the forest floor.

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