Weak Wooded and Invasive Trees

Certain species of trees naturally have weak wood or grow in such a way that their limbs are prone to failure or breaking off easily. Fast growing trees tend to be weak wooded while slow growing trees tend to be stronger. Some trees have narrow angles where their limbs connect to their trunks. When the angle between a branch and a tree’s trunk is less than 45 degrees, this union is often structurally weak. While stronger tree species may develop weak branch unions, they are much more common in certain species of trees.

Below is a list of tree species known to be weak wooded or prone to limb failures. These conditions generally, make these trees more likely to become a hazard in severe weather. Planting these trees in the urban landscape should be avoided. If you already have these trees growing in your yard, monitor them carefully for signs of stress or weak joints. Consider removing them and replacing them with a more suitable species.

• Silver maple (Acer saccharinum)
• Bradford pear (Pyrus calleryana)
• Red mulberry (Morus rubra)
• Mimosa (Albizia julibrissin)
• Siberian elm (Ulmus pumila)
• Tulip poplar (Liriodendron tulipifera)
• Boxelder (Acer negundo)
• Weeping willow (Salix babylonica)
• White willow (Salix alba)

Invasive trees are those that are not native to an ecosystem and whose introduction is likely to cause harm either to the environment, human health or the economy. Species that grow and reproduce quickly, and spread aggressively are considered invasive. These species should also be avoided when planting a new tree. If these trees are growing on your property, you may want to consider removing them and replacing them with a more desirable species.

While there are hundreds of invasive plants in Maryland, some of the more common tree species found in our area include:

• Bradford pear (Pyrus calleryana)
• Norway maple (Acer platanoides)
• Empress tree (Paulownia tomentosa)
• White mulberry (Morus alba)
• Chinese mulberry (Morus australis)
• Mimosa (Albizia julibrissin)
• Tree of heaven (Ailanthus altissima)
• Siberian elm (Ulmus pumila)
• Sawtooth oak (Quercus acutissima)

With rare exception, the Office of Planning and Zoning will recommend approval of tree permit applications and Historic Preservation Certificates of Approval for any of the trees listed here as either weak wooded or invasive. Please note that both lists are only partial, showing the most common weak or invasive trees in our area. The Office of Planning and Zoning's Urban Forestry webpage has a link to a local native species list and most nurseries can recommend native plant material for your yard.