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One of the most common questions we are asked is whether the Empress Splendor tree is invasive. The fast growth rate of the tree naturally leads to this question.

The Empress Splendor comes from the genus Paulownia. It is grown around the world with common names including Empress, Princess, Foxglove, and Kiri tree. These trees are grown and loved for enjoyment and shade in gardens, and for lumber on tree farms.

Unfortunately, popular internet search results on Paulownia are most often lead to the P. tomentosa, the only species of Paulownia that is on an invasive species list. There are at least 8 other species of Paulownia that are not invasive, including the P. fortunei and P. elongata planted by World Tree. This causes a lot of confusion and many assume the invasive qualities attributed to the tomentosa apply to all of the species, which we demonstrate here is not the case.

Here we summarize the evidence that they pose little threat to local ecosystems, particularly in controlled environments.

Background:

1. World Tree does not grow or plant any invasive species.

The genus Paulownia consists of at least 9 species or varieties. Only one of these, the tomentosa, is on the USDA invasive species list. The Empress Splendor trees created and planted by World Tree are grown from tissue culture gathered from the species fortunei and elongata, which are not listed as invasive.

2. The one species of Paulownia listed as invasive in fact shows little evidence of being invasive.

All species of Paulownia, including the tomentosa, fortunei, and elongata, produce many small, winged seeds which can scatter widely, yet they are proven to have low rates of germination and seedling survival unless under ideal conditions. They require an abundance of light in cleared areas, and are sensitive to water and temperature variations. They also exhibit low survival rates compared to many other naturalized trees, therefore posing little threat to local trees or other plants.

It is also noteworthy that no species of Paulownia are listed as being invasive in China, Latin America, nor the European Union, all areas where the trees are grown extensively in controlled plantation environments and ornamentally in garden environments.

3. World Tree’s Eco-Tree Farms are highly controlled environments.

World Tree closely monitors and conducts annual tree audits on the Empress trees grown on our 150+ farms in North and Latin America. We grow the trees for maximum health and rates of growth. Any signs of spreading or other potentially negative impacts on local ecosystems outside of the farm boundaries are dealt with immediately, but to date, we have not witnessed this behavior on any of our farms.

Below is a list of research reports and scientific evidence that together build the case that the Empress Splendor (Paulownia) tree should not be considered invasive.

A Case for the Non-Invasiveness of Paulownia
World Tree Research Report (2020)

The report provides a summary of the science and other evidence that disputes the invasive label given to all Paulownia species. The seeds are very difficult to germinate and seedlings have low survival rates in less than ideal environments. Most are grown in controlled environments on tree farms around the world where any signs of spreading or other invasive behavior are dealt with immediately.

Paulownia – Invasive or Not?
Morgane Gillard (2020)

Gillard is a plant ecologist and science writer with a specialty in invasive species. In this report, she goes into detail as to what constitutes an invasive species. She concludes that although Paulownia tomentosa is considered invasive, the two species planted by World Tree, elongata and fortunei, do not demonstrate the necessary characteristics to classify them as invasive.

Paulownia: A Stifled Agricultural Resource
American Paulownia Association Newsletter, Paul Sutton (Feb 2016)

Well-researched and referenced article making the case that the Paulownia tomentosa tree species does not meet all the normal criteria of an invasive species and should therefore be removed from the invasive species list until more research can be done.

The following research reports and scientific evidence continue to build the case that the Empress Splendor (Paulownia) tree should not be considered invasive.

Ornamental, crop or invasive? The history of the Empress tree (Paulownia) in the USA
Forests, Trees and Livelihoods, Whitney Adrienne Snow (2014)

The author argues that although the Paulownia tomentosa may be considered invasive, the Paulownia elongata is not, although its popularity has suffered because of the bad reputation of its cousin. She also makes the case that “invasive” and “non-native” are distinct classifications and should not be confused. The elongata has many fans including former President Jimmy Carter, who has promoted the trees’ potential not only for its sustainable timber, but also for use as a biofuel, biomass, and carbon capture.

Survivorship, attained diameter, height and volume of three Paulownia species after 9 years in the southern Appalachians
USDA Forest Service, Erik C. Berg, Stanley J. Zarnoch, W. Henry McNab (2019) 

The study compares the survival and growth rates of Paulownia elongata, fortunei, and tomentosa in unmanaged forests of the southern Appalachian Mountains over a 9-year period. The combined survival rate was only 27.3%, likely due to inclement weather events, with the tomentosa having the lowest rate (21%). In another study, the tomentosa showed a survival rate of only 11% to 27% in controlled areas after 7 years. These findings suggest the Paulownia does not survive well in places where it does not receive adequate light, care, and attention, making the chances of it becoming invasive slim. It grows best in managed plantations.

Tree Crops for Marginal Farmland – Paulownia
University of Tennessee Extension, Wayne K Clatterbuck and Donald G. Hodges (2004)

Paulownia is one tree type cited as being suitable for planting on marginal farmland in the Southeast. The report also states that although it is categorized as an “invasive exotic” (p. 8), it is suspect that it is invasive. This is due to many characteristics including the fact the seeds are difficult to germinate and do not survive unless under very specific soil conditions, and rarely in fields. Also, its deep taproot does not compete with other trees or plants and requires high sun exposure to keep growing. These are not characteristics of invasive plants.

Paulownia in China: Cultivation and Utilization
Chinese Academy of Forestry Staff, Zhu, et al. (1986)

This report is cited extensively in other studies on Paulownia. It makes the case that although Paulownia seeds are small, winged, and plentiful, germination and seedling growth require intensive light to grow and survive (p. 24).

Sustainable Capital Group Panama S.A. – Commercial Reforestation with Paulownia and Carbon Dioxide Capture in Chepo District, Panama
Rainforest Alliance – SmartWood Program, Edwin Alpizar and Jared Nunery (2011)

The study concluded that the Paulownia tree is an ecologically sound tree for the purposes of reforestation and carbon sequestration. It did not see any signs of invasiveness.

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