Ojibwe Lifeway: Maple Sugaring and Birch Bark Harvesting (“ziigwan”-spring)

Overall, Wisconsin is expected to warm by 3°F, with more warming in the winter projected to be + 5°F statewide by the middle of this century. What is the potential impact of these changes on sugar maple and paper birch?

CLUE:

Shorter, warmer winters can negatively affect the flow of maple sap, which is boiled down to make syrup. Sap flow is controlled by alternating freezing and thawing cycles in the late winter. The best conditions for sugaring are cool nights, just below freezing, and fairly warm days, in the upper 40s °F. This temperature change causes shifts in pressure outside the tree that send sap flowing throughout the tree. When a small hole is tapped into the tree, some of that sap will flow out and can be collected to make maple syrup.

Paper birch is a northern species adapted to cold climates. It is seldom found growing naturally where average July temperatures exceed 70° F.  Paper birch is predicted decline and may even disappear from Wisconsin forests by the end of the century. 

Plant scientists have documented a northward shift in Wisconsin’s growing zones. The growing season has become between 1-3 weeks longer in the central and northern portions of Wisconsin. What is the potential impact of these changes on sugar maple and paper birch?

CLUE:

Longer growing periods could mean greater growth and productivity—as long as there is enough moisture and nutrients. As trees will need more moisture from the soil, over a longer growing period caused by warmer temperatures, the amount of water they use through evapotranspiration will increase. This will reduce the amount of moisture available in the soil which would limit growth or possibly cause plant die off if there is not enough rain. A longer growing season will benefit some tree species and encourage new tree establish themselves here. Other trees not adapted to higher temperatures and less soil moisture will decline or may be lost. Boreal species, like paper birch, may not be able to sustainable in Wisconsin under these conditions.

Most climate models project that for most of Wisconsin, the average annual precipitation will increase by 5% by mid-century. Wisconsin is projected to experience increases in winter and spring precipitation, but a trend toward less rain in summer. What is the potential impact of these changes on sugar maple and paper birch?

CLUE:

The decrease in summer rain, combined with the added amount of evapotranspiration by plant caused by increased temperatures, will decrease soil moisture later in the growing season. Sugar maple, which prefers mesic sites, may be stressed. The loss of soil moisture in late summer could stress paper birch growing on drier sites, making them more susceptible to insect infestations from pests such as the bronze birch borer and die back.

While winter precipitation is expected to increase, warming winter temperatures above 32-degrees F, can cause precipitation to fall as freezing rain rather than snow.  What is the potential impact of these changes on sugar maple and paper birch?

CLUE:

Longer periods of warmer winter weather, either due to early spring warm-up or warmer late falls, would mean less snow cover. Winter temperatures are expected to warm causing more precipitation to fall as rain. Maple trees rely on snowpack during this time to protect their roots from freezing. Sugar maple needs nights below freezing to produce good sap flow. Paper birch thrives in cool to cold habitats.

Compare the change in 2-inch rainfall events recorded in Wisconsin from 1991-2020 to what is projected by mid-century.  By the mid-21st century, Wisconsin is projected to see a 30% increase in 2 inch extreme rainfall flooding events per decade. What is the potential impact of these changes on sugar maple and paper birch?

CLUE:

Trees like sugar maples are less flexible and tend to be affected more by storm and wind damage because their limbs are more susceptible to breakage than more flexible species like birches and pines. In a forest, the loss of trees due to storm damage can open the canopy area and allow more in sunlight. This can provide openings for sun loving species such as paper birch to get established.

Ice storms are expected to increase due to more winter precipitation falling as rain, rather than snow due to warming winter temperatures. Paper birch has low to average resistance to its crown being damaged by ice storms, while sugar maple has average to strong resistance to ice-caused crown damage.

By the 2060, the frequency of very hot 90-degree days in Wisconsin is expected to triple from from a statewide average of 9 to 26 days per year   What is the potential impact of these changes on sugar maple and paper birch?

CLUE:

Increases in the length and severity of very hot temperatures can mean drought conditions that can affect the sustainability of tree species and increase risk for wildfire. Drought is closely linked to temperature and rainfall amounts. While northern Wisconsin is expected to have more heavy rainfall events, little change in the total amount of summer rain is predicted, but temperatures will be much warmer. Climate models suggest more frequent, localized periods of extreme drought which will dry up forest soils. Trees on dry sites, such as paper birch, could decline or become extinct in Wisconsin. As susceptible trees die, greater amounts of deadwood will increase the chances of forest fires.