Prescribed Burns a Restoration Tool

Nature Notes for April 28, 2017

When I arrived at the Alderville Black Oak Savanna on Monday (April 24), I was greeted by several trucks and ATVs and men in orange jump suits. Orange signs along the bordering roads indicated that this was the day of a prescribed burn.

Prescribed burns are an important tool for habitat restoration. Burns are a necessary part of grassland ecology. Native prairies frequently burned. The plants that grow in this habitat have evolved with fire and are adapted to survive it. The herbaceous plants have very deep roots. Big bluestem, a native prairie grass, will grow to a height of six to seven feet, but the roots go down twice that deep. Most of the mass of the plant is underground so it readily survives fire.

The mature black oaks that grow in the prairie/savannah habitats in this area have thick bark that protects them from the fire. They may lose a few lower branches, but the main tree is not harmed.

The fire does kill younger woody vegetation that encroaches on the site. This is necessary in order to maintain the grassland. Native prairies would have been a shifting mosaic of open grassland area and regenerating woody vegetation. When a site has been set aside as a grassland reserve, it is necessary to have regular prescribed burns to mimic what nature would have done in the past.

Prescribed burns are not just a wild fire. Lots of planning goes into each one. Permits are required. The burn must be managed by a trained “Burn Boss”. There is a relatively small window of time in which burns can be done. Usually, in this area, the date is some time in April before there is much new growth. The humidity, temperature and wind must be just right for the burn to proceed.

The fire burns very close to the ground, burning hot and fast. The burn at Alderville was ignited at 12:40 and was out by 3 p.m.

The burn underway at Alderville Black Oak Savanna. 

photo by Radek Odolczyk

The fire leaves behind a black field that warms in the sun more quickly than the unburned areas surrounding the burn. The warmth helps seeds in the soil germinate. The ash acts to fertilize the plants. Within about 10 days, the black area will be showing green shoots.

Only about 1% of the native prairie that existed in Ontario prior to European settlement still exists. Much of the remainder is degraded due to overgrazing, disturbance from agriculture, introduction of non-native invasive species and regeneration of woody vegetation.

Many invertebrates overwinter in the litter that is burned. It is necessary not to burn the entire site every year so as not to kill off their entire populations. Some of these invertebrates are prairie/savannah specialists and thus just as rare as the habitat.

Bobolink, Eastern Meadowlark, Grasshopper Sparrow, all now listed as species at risk breed only in open grasslands. Another species at risk, Barn Swallow, doesn’t nest on the grassland, but prefers to feed over it.

Although my area of expertise in not botany, I know that several provincially rare plants grow on Northumberland County’s prairies and savannahs. Among them are prairie buttercup, wild blue lupine, cylindrical blazing star, fragrant sumac and New Jersey tea.

The Northumberland Land Trust and the Nature Conservancy of Canada have performed burns on some of their properties this spring.