This article was originally conversation.
Speaking of spring, many people think of flowers and trees in full bloom. Also, if you live in the Northeast, Midwest, or South of the United States, you’ve probably seen medium-sized trees with long branches covered in tiny white flowers – Callery pear (Pyrus calleryana).
For decades, the Karely pear, which comes in a variety of varieties, including ‘Bradford’ pear, ‘Aristocrat’ and ‘Cleveland Select’, has been one of the most popular trees in the United States for ornamental planting. But today invasive species. land manager and plant ecologist like me We are working to eradicate it in order to protect biodiversity in its natural habitat.
As of 2023, Sell, Plant or Grow Callery Pears Ohio. A similar ban is south carolina and pennsylvania 2024. north carolina and Missouri If a resident cuts down a Callery Pear Tree on their property, they will be given a free native tree.
How did this once-high-demand tree become “weed of the week“? The devil lurks in the biological details.
Botanists brought curry pears to America from Asia early 1900sThey deliberately bred garden varieties to enhance their ornamental qualities. In doing so, they created an arboriculture prodigy.as the New York Times Observed in 1964:
“Few trees have all the desirable characteristics, but the Bradford ornamental pear comes extraordinarily close to the ideal.”
The modern variety of Callery pear bursts with white flowers in spring followed by dark green foliage in summer before turning deep red and maroon in fall. They are also very tolerant of urban soils. highly compressed and hard to get roots. The tree shape is rounded and grows quickly, making it suitable for planting side by side on roads and road shoulders.
Callery pear trees were very popular in residential settings during the post-World War II suburban development boom. City street tree of the yearBut the breeding process that created this variety and other varieties of Callery pears had unintended consequences.
Clones to produce American originals
To ensure that each Callery pear tree had bright flowers, red foliage, and other desirable characteristics, gardeners created identical clones in the following manner. a process known as transplantation: Creates saplings from cuttings of trees with desired properties.
This approach eliminated the nasty complexity of mixing genes during sexual reproduction and ensured that each tree, when mature, would have the traits desired by homeowners. All trees of a particular variety were genetically identical clones.
Grafting also meant that karelinashi trees could not bear fruit. fertilize their flowers with their own pollenIn contrast, Callery pears are self-incompatible: the pollen of an individual tree cannot fertilize the flowers of that tree. so they are effectively the same tree.
If a tree cannot bear fruit, it cannot disperse in its natural habitat. Horticulturalists and landscapers have considered it perfectly safe to plant Callery pear near natural habitats such as prairies, as the species is locked in place by its reproductive biology. However, the tree breaks free from its isolation and spreads its seeds far and wide.
Botanist at the University of Cincinnati Teresa Curry and colleagues found that when gardeners tinkered with Callery pears to create new versions, they made the individuals sufficiently different. escape the fertilization barrierIf there are only ‘Bradford’ pear trees in the neighborhood, they cannot produce fruit, but if someone adds ‘Aristocrat’ pears to the garden, these two varieties can fertilize each other and produce fruit.
Wild populations of trees were established when pear trees in gardens and parks began laying seeds in nearby areas. there is.
Callery pear is surprisingly fertile in today’s landscape. The abundant flowering that horticulturists intentionally bred into these cultivars has now resulted in enormous quantities of pears being harvested each year. and then fly to excrete the seeds in their natural habitat. Most problematic invasive species in the eastern United States.
Like other invasive species, pears keep native species out.Old curry seedlings spreads from the edge of the habitat into the grasslandshas the advantage of being able to dominate the site.
of my labwe found that karelinashi leaves very early in the spring and sheds the leaves in late autumn. Absorbs more sunlight than native speciesAlso during the invasion these trees change the soil Releases chemicals that inhibit the germination of native plants.
Carolina is very resistant to natural disturbances.when in fact My graduate student Meg Maloney tried to kill a tree with predetermined fire or pending Liquid nitrogen Directly on the stump after cutting down the tree, her efforts failed. Instead, the trees sprouted aggressively and seemingly gained strength.
When pears escape into the wild, the seedlings very sharp and hard thorns It can even puncture shoes and tires. This makes trees a threat not only to those who work in the area, but also to native plants. Another troubling factor is that when Callery pears bloom, strong smell something that many people find offensive.
the current, Apply herbicide directly Callery pear intrusion is the only known control. However, trees are successful at spreading, so poisoning a sapling may only create space for other Callery saplings to settle. It is unclear how they can escape the confounding ecological cycles of , herbicide application, and reinvasion.
Banned but not gone
in response to work by Ohio Invasive Plant Council and other experts say Ohio has taken an extraordinary step. Callery pear ban To deter ecosystem encroachment into natural habitats. However, trees are common in residential areas across the state and have established active populations in their natural habitat. In order to maintain it, it will work well into the future.
Meanwhile, homeowners can help. The gardener says that anyone who has her Callery pears on his property remove and replace It is not an alien species.Few trees have all the necessary attributes, but many Native forest It has visually appealing features and does not threaten your local ecosystem.
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