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.
