Many Wisconsin oak stands are aging, potentially losing value from stem decay
A history of oak regeneration problems in Wisconsin means that maples are slowly replacing oaks as the dominant genus in many stands
SEATTLE -- Oak trees, which are common in the canopy of many Wisconsin woodland properties, have been regenerating poorly in many areas for 50 years or more, leading ecologists and foresters to worry that the oak supply will run low in upcoming decades.
“Because of a lack of disturbance, many sites are more heavily shaded than they would have been historically,” said Brad Hutnik, a silviculturist with the Wisconsin Department of Natural Resources. “More shade-tolerant trees like red maple, sugar maple, and invasive shrubs can take advantage of that.”
Most oak species are adapted to regenerate and survive in stands that burn frequently. Oak savannas and woodlands were the dominant ecosystem of southern Wisconsin before settlement, and were maintained by frequent surface fires, often set by Native Americans living in the region. Oaks found in more-heavily wooded areas throughout the rest of the state also benefitted from fire.
Oak saplings store large amounts of energy in their roots, so they re-sprout and grow quickly after the stem is killed. Fire was likely more beneficial to oaks than other common disturbances like wind, tree diseases, and flooding, because it killed competitors at higher rates than oaks. Oak seedling and sapling re-sprouts have an advantage over non-oaks that store less energy in their roots. Additionally, most species of oak have thick bark when mature, which gives greater insulation from heat than most other tree species have.
Oak versus maple price trends in Wisconsin
Red maple and sugar maple are the two most common species replacing oaks in Wisconsin. According to Forest Data Network statewide pricing reports, the two species’ monetary value is significantly different. Red maple lumber had about 60 percent of the value of sugar maple lumber in 2016 to 2018. Whether red or sugar maple is more common on any given property depends on many ecological factors, but sugar maple tends to thrive on rich and well-drained sites while red maple tends to do better on dry or very wet sites.
Depending on which species are compared, maple prices can be similar to oak prices. Sugar maple prices during the 2016-2018 period were similar to red oak prices, and red maple prices were slightly lower than white oak prices. However, many landowners with stands undergoing transition away from oak forests are likely to have smaller maples and larger oaks, and thus the oaks are likely to hold more monetary value if they are free of rot. Additionally, it is possible that over the next few decades, oak prices will rise as they become less common on the landscape, while maple prices will fall as they become more common. This is, however, contingent on many market and ecological factors, both of which are subject to rapid changes and difficult to predict.
Fires continued to be common after early settlement by European descendants until the 1920s, when fire suppression techniques became mostly effective, according to the Wisconsin Historical Society. Hutnik said that many ecologists and foresters believe that oaks began having regeneration problems in the decades following fire suppression. Maples and other tree species became more common during this time and began competing with oaks. Deer populations have also skyrocketed in the past few decades, and deer prefer browsing oak seedlings over many other tree species.
Thus, oaks on any given property are likely to be relatively old. Many oak species have long lifespans, but it’s common for older oaks to have rot that can drastically reduce their merchantable volume. Oak stands in southwest Wisconsin may begin to lose value by the age of 80 to 120, depending on site quality and stand history, said Glen Stanosz, a professor of tree and forest health at the University of Wisconsin – Madison. Stanosz cautioned, however, that this information comes from only one study, and the optimal age of harvest can vary widely by site, history, and dominant species. A forester can more accurately determine the decay status and value of a specific stand.
The key takeaway for landowners is that oak stands often decline in value after a certain age. This is a natural process independent of oak wilt, a disease that kills oaks in small pockets. Oak wilt is caused by an invading fungal pathogen now found across much of Wisconsin.
Landowners interested in keeping oak stands in the long term often need to take active measures to regenerate them. Forestry experts recommend frequent heavy cutting and sometimes burning, especially on sites with richer soil. Oaks are quite valuable both for wildlife and timber, so the heavy forest disturbance required for oak regeneration may well be worthwhile for many landowners, particularly on properties with many healthy and valuable trees.
Don Radcliffe is a PhD student studying forest ecology at the University of Washington, and a native of central Wisconsin. He holds a master’s degree in forest ecology from The Ohio State University, and a bachelor’s degree from the University of Wisconsin-Madison, with majors in forest science and life sciences communication. You may contact him through FDN at firstname.lastname@example.org