Iowa’s forest health report released
—by Steve Lekwa
Yet another cloudy, misty day has dawned as I write this week’s column. We could all use some sunshine to brighten our moods as we go through the holiday season. Seasonal Affective Disorder (SAD) is made worse when sunlight is blocked by clouds, compounding the affect of reduced light from shorter days. Try to spend some time each day in a well-lit area until the sun again makes its pleasant presence available. At least the day length will begin increasing again from here on.
I recently read an interesting report on Iowa’s forest health that’s released by the Iowa Department of Natural Resources each year. 2014 saw the continued march of emerald ash borer (EAB) across Iowa. Story, Boone, and Polk counties were added to the list of counties across southern and eastern Iowa where the lethal pest has been found. It’s likely that many other counties already have infestations that haven’t been identified yet since it takes several years for obvious symptoms to develop after initial infestation. EAB is lethal to all native ash species, but individual trees can be treated with systemic insecticides to hold off the beetles. It remains likely that most Iowa ash trees will succumb to the pest in the years to come, just as the state’s elms died in the mid 1900s. While treatment will keep some ash trees alive for the time being, the only long-term plan is to begin planting a diverse community of other trees to replace ash trees as they are lost.
The bur oak is Iowa’s state tree. Oaks, in general, are very important trees in Iowa’s forests. Their wood is valuable for lumber and fire wood and their acorns are a preferred food for many native birds and animals. Unfortunately, oaks have been in decline for many years in Iowa. It is estimated that Iowa still has about a million acres of oak forest, but is losing about 7500 acres each year. Oaks are being replaced by more shade tolerant species like maple and basswood in many areas. Natural reproduction isn’t keeping up with losses as mature trees die or are harvested. The future of oak forest in Iowa may depend on humans planting new stands.
Oaks can only grow in good sunlight, and thus can’t grow under their parent trees. Openings where new oaks can grow are few in Iowa woods. A variety of diseases and pests threaten our remaining oaks. They include oak wilt, a fungal disease that spreads from tree to tree through root grafts underground. Though present statewide, oak wilt does not appear to be increasing and its presence is spotty. Diseased trees should be removed to slow the disease’s spread. Bur oak blight is another fungal disease that has increased due, at least in part, to more frequent spells of wet, cool spring and early summer weather that favors fungal diseases.
Iowa has been monitoring gypsy moths for years. These pests eat many species of tree leaves and can totally defoliate entire forests when infestations are bad. Trees are not killed outright by gypsy moths, but years of moth attacks can significantly weaken trees and leave them vulnerable to other diseases and insects that can kill them. Female gypsy moths can’t fly, but the presence of males can be monitored when they are captured in traps baited with pheromones that attract them. Although some males have been captured around the state every year for quite awhile, no defoliating populations have developed so far. Pheromone laced flakes are spread around areas where males have been captured. These distract the male moths and disrupt their breeding activity. That, and natural weather conditions, have prevented this forest pest from becoming well established in Iowa so far.
Iowa continues to monitor for thousand cankers disease in black walnuts. Once limited to another walnut species in the southwestern U.S., the disease jumped to black walnuts and began moving east several years ago. There is no defense yet known for this lethal fungal disease that can wipe out walnuts, but, thankfully, it hasn’t become established here yet.
The key to insuring future forest health in Iowa is to maintain diversity in our forest stands through management and planting, continuing the fight against invasive species, and limiting practices like grazing in forest areas that compacts soil and blocks reproduction. Many of our most serious forest pests don’t move very far or fast naturally, but can jump across whole states when infested forest products and nursery stock are moved around. People who haul firewood around the state can unwittingly spread diseases and pests. Plan to buy and burn only local wood.