Princess tree (Paulownia tomentosa)

plants, terrestrial, tier 5

Princess Tree, Paulownia Tree, Empress Tree

Paulownia tomentosa

“A royal pain!”

Family: Scrophulariaceae

History & Introduction

Princess tree is native to Western and Central China where it has been historically grown ornamentally, as well as for its medicinal purposes. It is also highly valued for its timber, especially in Japan where it has been cultivated since the 3rd century B.C. as the wood is used to make traditional ceremonial items.

Princess tree was first introduced to Europe in the 1830s after it was brought back by the Dutch East India Company, and became popularized as a horticultural and landscape tree. It was brought to the US soon after not only due to its attractive purple flowers and large leaves, but as well it was promoted by extension offices as a hopeful export commodity to Japan.

Princess tree has now been cultivated on every continent in the world, often without escaping cultivation. However, due to the similarity in climate and habitat types between princess tree’s native range and that of the north-east US, it has been found invading and rapidly colonizing disturbed sites. More research is needed to quantify the impacts on ecosystem processes.

Identification

Habit: Deciduous tree reaching 105 feet.

Bark: Mature trees have thin, flaky bark; often multi stemmed when growing in open areas. Branches are brittle as the inner pith is hollow and flattened at the nodes. DBH at maturity is 3.9-6.6 feet.

Leaves: Young princess trees can be up to 3ft in length. Mature trees are smaller, between 6-12 inches. Leaves are opposite and broadly ovate, acuminate and cordate in shape. Leaf margins are entire or shallowly lobed, and may be toothed on small plants. On trees that have been mowed or cut leaves may be twice as large.

Flowers: The inflorescence is a large terminal panicle from 6-12” containing tubular, purple flowers 2-2.5 inches in length.

Fruit: Oval 2 part capsule 1-2 inches long. Capsules each have two compartments that contain a single singed seed, 1.5-3mm long. Seeds may last in seed bank up to three years.

Phenology: Flowers bloom late May through early summer.

Habitat

Princess tree can grow in a number of open sunny habitats from roadsides to the edges of forested trails or riversides. It has been found colonizing sites that have recently experienced defoliation events due to leaf eating insects such as spongy moth (Lymantria dispar), as well as sites that have been recently thinned or burned.

Dispersal

Seed can be spred via wind and water. As well, due to its notoriety as a fast growing street tree, it has been sold and spread through the horticultural industry.

Damage and Impact

Due to their hollow branches, princess trees are often brittle and prone to breaking, resulting in large accumulation of plant debris wherever princess trees grow – from forest floors to parking lots. Princess trees often only live to ~70 years. Mature trees are described as structurally unsound and falling trees can be a nuisance for trail and street maintainers, and worse yet a hazard to people and property.

Small seedlings of princess tree can produce leaves large enough to shade out plants growing underneath. While roots can be shallow, they can also grow more deeply and widely. Cutting or mowing princess tree often leads to strong multi stemmed resprouts from the root crown.

Princess tree can mature rapidly, producing flowers within 8-10 years. After flowering, a single tree can produce millions of seeds. The synergy of rapid maturation and prolific seed production allows princess tree to compete with our native native early colonizer tree species and herbaceous plants, and potentially displace the native animals and insects that rely on them. This may result in a reduction in a site’s biodiversity.

Prevention

Do not plant princess tree. Treat princess tree on your property when it is young to prevent further growth and seed formation. Wherever you see princess tree growing in natural areas, please document it in iMapInvasives or iNaturalist. Remember to clean your gear before and after you leave a site to prevent the spread of invasive species like princess tree. After cutting/mowing princess tree, or working in sites with princess tree, remember to clean your equipment to ensure no seeds will be transported.

Control

Chemical control:

The pesticide application rates and usage herein are recommendations based on research and interviews with land managers conducted in the Lower Hudson Prism. When considering the use of pesticides, it is your responsibility to fully understand the laws, regulations and best practices required to apply pesticides in a responsible manner. At times, the pest you seek to treat may not be on a pesticide label, requiring a 2ee exemption from NYSDEC. Always thoroughly read the label of any pesticide and consult the NYSDEC or a licensed pesticide applicator with questions.

Foliar Spray: A 2% solution of glyphosate or triclopyr is effective against princess tree. Repeat application may be necessary during the following growing season. Always read and follow all instructions on the herbicide label.
Cut Stump: For larger trees, apply a 25% solution of glyphosate or 50% solution of triclopyr to the cut stump of princess tree towards the end of the growing season but before leaf senescence.
Basal Bark: A 20% solution of triclopyr applied to the bark of dormant princess tree is somewhat effective in controlling infestations, although this technique is best applied with other strategies, such as a follow-up cut stump

Manual control:

Pulling/digging up: Pulling as a control method is possible only if plants are very young. The entire root must be removed to prevent resprouting.
Mowing: Mowing princess tree is not recommended due to its strong ability to resprout unless performed at regular intervals for several years
Gridling: Girdling princess tree alone will cause princess tree to resprout. Girdle in combination with a basal bark or foliar spray for best results.
Fire: Fire may kill aboveground portions of princess trees, however the intricate root system would likely survive a moderate-severity fire.