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Starlings; the primary dispersers of Invasive Pear trees (Pyrus calleryana)
Invasive European Starlings are a dominant species in metropolitan landscapes which also is where Callery Pear varieties are most concentrated in landscape plantings. In the fall you’ll notice the starlings gather in large flocks of hundreds to thousands consuming in mass; Callery Pear fruits, Amur Honeysuckle berries, and also stripping native food sources clean such as Poison Ivy fruits and Eastern Red Cedar fruits that native birds prefer.
When you see fields, vacant land, and unmowed pastures of pears and honeysuckle establishing; consider what birds utilize these non-native plant dominated open environments?
You may see a killdeer, a native sparrow species or possibly a meadowlark if the field is large and diverse enough, but none of these birds eat Callery Pear fruits. The single species of native bird that likely contributes to a small amount of dispersion of Callery pear fruits into open environments is the American Robin, who do utilize these open environments, but never with the flock quantity or consumption quantity of the invasive starling flocks that strip the large majority these trees clean during their murmuration season. Robins do mass-consume fruits, but with the exception of ornamental crabapples and a few callery pear fruits, their consumption and dispersion is nearly purely of native plant fruits.
Starling foraging patterns of mass shrub/tree/vine fruit stripping followed by field/pasture ground foraging make them uniquely adept foresters of trees, shrubs, and vines. Unfortunately on this continent, they’re creating invasive plant thickets/woodlands.
In the fall, European Starlings alternate between Tree/Shrub fruit foraging to ground foraging in lawns, fields, prairies, and farm fields that become invaded by whatever tree/shrub species they eat in mass if left unmown and/or unburned. Since the introduction of Callery Pears, Starlings have a new favorite item on the menu.
Unmowed/Unburned Open Environments are most Suceptible to Pear Invasion
The invasive tree/shrub fruit stripping proceeded by ground foraging allows for mass depositing of invasive plant seeds into vacant land/fields, farmland, lawns, and pastures which is how unmowed fields turn into even-aged stands of Callery pears and Amur Honeysuckle. This pattern also forms a management tactic for preventing Callery invasion. Keeping fields, vacant land, lawns, and pastures mowed at least once 1 year, preferably during the dormant season prevents woody plant invasion of all kinds. Where native prairies are established and prescribed burns are possible; burns can replace the annual once a year mowing. Missing just 2 or 3 years straight of mowing or burning one of these open environments can allow Callery pears to grow thick enough to damage some bush hogs. By year 5 of no mowing most bush hogs and tractor mowers can’t handle mowing an acre of 3” to 4” thick pear trunks. So, how do we manage these open environments in a way that fosters biodiversity while excluding Callery Pear Invasion?
It is thought that native thickets are prone to invasion due to remnant populations often being draped in invasive plants, but this is a misinterpretation of the landscape. Most often native thickets are limited to artificial edges where they can’t form an interior as pictured above. When native thickets are allowed to form continuous unfragmented communities within open landscapes, they close the niche to invasive woody plants like this Quapaw Wild Plum (Prunus hortulana) is demonstrating.
Cultivating Biodiversity While Closing the Open Environment from Callery Pear INVASION
This land management prescription is only for the pasture/field/prairie/vacant environments that are quickly turning into Callery Pear Forests.
Forming Continuous, Unfragmented Native Thicket
1. After Callery Pear/Honeysuckle removal; establish a native a mix of colonizing native thicket species and non-colonizing native thicket species to be managed as continuous un-fragmented thicket. As you can see in the Quapaw Wild Plum (Purnus hortulana) picture above, when native thicket species are allowed to establish continuously they form highly competitive interiors that are resistant to invasive plant invasion; though edges of thickets will always need some periodic management. Failure to create a continuous thicket will lead to invasive plant invasion throughout the native thicket, the niche needs to be closed and stabilized through unimpeded native thickets growth wherever the land won’t receive an annual mowing or burn. Good news is these native thicket species are perpetually trying to form this dwarf forest, and if they’re allowed to, they will. See the short list of colonizing thicket species and non-colonizing thicket at the end of the post.
Wrapping Annually Mowed or Burned Native Meadow/Prairie around the Native Thickets
2. If the land can be mowed or burned, establish a native prairie/meadow around the native thicket species. The more diverse the native prairie with competitive grasses and long lived prairie wildflowers, the more resistant the meadow/prairie will be to pear invasion. But as along as you’re sticking to mowing it once a year in the dormant season, then the make up of the native meadow/prairie matters less as the mowing will prevent pear invasion. On the other hand, the prairie grasses are necessary to create hot enough fires to burn back pear invasion. We don’t recommend burning the meadow/prairie until 10 years after the thicket species are planted so that the thickets have enough time to create dense enough colonies to resist fire damage. Fire is also non-selective where as mowing operator can mow around new native colonial thicket suckers allowing the thicket species to expand their footprint. The goal of the management plant should be to create a combination of continuous large islands of thickets in combination with annually mowed or burned native prairie/meadow to foster good ecological value and invasive plant resistance through a fully occupied and competitive native plant environment.
Here’s a list of colonizing and non-colonizing Native thicket species; plant them on 18-22 foot centers. Check to see if they’re native to your region before selecting them and chose 2 Colonizing species per 1 non-colonizing species for most effective land coverage. The exact thicket species selection ultimately should be determined by the characteristics of your site which often requires a native plant-skilled professional to determine.
Alternative to Planting Native Thickets:
Plant Native Meadows/Native Prairie on the site of the open field/pasture, and mow this landscape once a year in the winter time to prevent Callery Pear invasion. Spaced out Native Trees in the field will add to biodiversity value of the land and can easily be mowed around.
Native Colonial Thicket Species (Space Eaters/Niche Closers)
Wild Plum species; Sumac Species, Roughleaf Dogwood, Gray Dogwood, Chokecherry, Rusty Blackhaw Viburnum, Devil’s Walking Stick, American Hazelnut, Prickly Ash
Non-Colonial Thicket Species
Wafer Ash, Hawthorn Species, Eastern Redbud, Silky Dogwood, Arrowwood Viburnum, Native Crabapple species (i.e. Malus coronaria), Native Roses