A vast number of wildlife species rely on acorns for food. As the source of acorns, oak trees are vital to sustaining populations. Acorns provide nutritious food during fall and winter when other sources are scarce.
Individual oak trees can take up to 30 years to produce acorns, but mast crops are variable. Some oak trees may not produce many acorns. Production factors include pollination, frost, and drought. RPM (Root Production Method®) has led to increased production of acorns, or mast, in swamp white oaks.
Swamp White Oak Acorn Output
Greater, earlier mast production benefits native wildlife.
Planted 18- to 24-month-old swamp white oak RPM seedlings produced acorns each year. Acorn production occurred on these seedlings in each of their first four years. Some (3.5%) of the 2,522 RPM seedlings produce acorn in their first year in the field.
Most of the production (60%) occurred in oaks from 19-liter containers. Acorn production was also seen in 11-liter container RPM trees. During the first four years in the field, average RPM acorn production increased from 4.3 to 12.5 acorns per tree. Some individual trees were able to produce up to 125 acorns.
There is correlation between the seedlings’ planting size and first year acorn production. Probability relates to seedling height and basal diameter at planting. For example, the probability is 2% for a 1.5m RPM seedling with a basal diameter of 1.8cm. The percentage is 15% for a 2.5 basal diameter tree of similar height.
Consistent, early production of acorns was surprising. Open-grown oaks do not begin producing for 20-30 years. No bareroot oak seedlings have produced acorns after only four growing seasons.
It is worth noting that RPM trees are still susceptible to outside variables. Rabbit girdling in year two caused shoot dieback in the natural vegetation field. This took the RPM trees out of production. Production did rise in years three and four as more trees came into production. The location of most acorn-bearing trees was in redtop grass fields.
Summary Findings of Acorn Production
Planting large RPM® (Root Production Method®) seedlings in a redtop grass ground cover appears best for restoring acorn production in agricultural floodplains.
What is RPM®?
Root Production Method®, or RPM, enhances the survivability of trees planted on challenging sites. Field planting of RPM seedlings has been used in Midwestern agricultural floodplains. Studies of RPM-produced wetland species evaluated their superior survival, growth rates, and natural regeneration. Studies compared RPM seedling results to traditional field-grown seedlings and bare-rooted practices.
Our research proves RPM trees have higher survivability rates. RPM trees also grow, flower, and fruit up to two times faster than those produced with other methods.
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