Anyone who has a walnut or oak tree on their property knows that leaves aren’t the only things that fall to the ground at this time of year.
For many Ozarks families, gathering black walnuts and selling them at local hulling stations is a way to make money from a cash crop that’s literally at their feet. For those with oak trees in their yards, now is when those final lawn-cutting jobs are going to be noisier and perhaps a bit harder on mower blades as they cut through the fallen acorns.
However, to area wildlife, the nut drop that’s now underway has much greater significance. The nuts – collectively known as hard mast – that are falling now are factors that will help determine survival over the winter and propagation success next spring.
“Hard mast is an important fall and winter food source for many species of wildlife, particularly in the heavily forested portions of the state,” said Missouri Department of Conservation (MDC) Research Silviculturist Megan Buchanan. “Fluctuations in mast production can exert a strong influence on wildlife species that depend on mast crops for food. Poor mast years have resulted in lowered reproductive success in wildlife species, which can reduce the size of wildlife populations.
“Conversely, good mast years can improve individual fitness and overwinter survival rates of wildlife species,” she added. “This, in turn, can increase wildlife population size.” In addition to affecting population dynamics, that poor mast production will cause some wildlife species to travel greater distances in search of food and, in some cases, they’re more apt to feed on crop fields.
MDC personnel conduct mast surveys each September in 56 counties in the central and southern portions of the state. In the survey counties, the tree crowns of mature oak, hickory and walnut trees are examined. Several factors are utilized to produce an MPI – Mast Production Index – for white oaks, red oaks, hickories and walnuts. Determining a tree species’ MPI for a given year may follow a set formula, but trying to predict what a tree’s nut production will be from one year to the next is a process fraught with variability.
To sum it up in a phrase: It’s complicated.
“Many environmental and genetic factors can impact hard mast production,” Buchanan said. “Influential environmental factors include weather, insects and pathogens that affect trees during flower bud development, flowering and fertilization, and nut maturation.” She said that studies have shown that, in oak trees, warm spring temperatures during the year of acorn maturation have a positive correlation with acorn production. Factors that can negatively impact acorn production include late spring frosts, summer droughts and insect damage to leaves and developing acorns.
For black walnuts, a lack of soil moisture – especially during July and August when nuts are rapidly emerging and filling – can drastically reduce nut production. A spring frost can also be harmful.
Then there’s location – trees that are in open areas tend to produce more mast than those growing in a closed-canopy forest. Size is also a factor – large trees tend to produce more mast than small ones.
There’s also the matter of periodicity – in other words, if there is any type of recurring, multi-year pattern to mast crops. Also included in this topic is theories on the periodic occurrence of “bumper crops” of acorns; events that are referred to as “masting years.” However, Buchanan said patterns of acorn production over a multi-year period are hard to predict because environmental factors that reduce acorn production occur randomly and can muddle any pattern.
While determining what a tree’s nut production will be from one year to the next is difficult, ordering trees through the Missouri Department of Conservation’s annual tree seedling sales program is easy. The ordering period for this program, which is currently underway, runs through will run through May 1. Tree seedling order forms are currently available at the Department of Conservation’s Southwest Regional Office in Springfield, the Springfield Conservation Nature Center and at most other Department of Conservation offices. Seedlings can also be ordered on-line at mdc.mo.gov/seedlings. Information about the oaks, walnuts and other types of Missouri trees can be found at www.missouriconservation.org
Francis Skalicky is the media specialist for the Missouri Department of Conservation’s Southwest Region. For more information about conservation issues, call 417-895-6880