The impact of Scotch Broom on the North Cowichan Forest clear-cuts

December 12, 2018
Research

Source: BC Forest Practices Branch

Broom has become increasingly noticeable in newly logged areas. There is concern that it may be spreading and could pose a threat to forests and other resources.

For years broom was regarded as a beneficial plant. During pioneering times, the seeds of broom were roasted and used as coffee substitute, while new shoots were used as a replacement for hops in beer production. However, it is now known that the leaves, buds and pods of broom contain toxic chemicals or substances that can affect the nervous system and the heart.

Broom was intentionally planted to stabilize road cuts and as an ornamental in private gardens and some parks. These practices have resulted in wide distribution of broom throughout the south coastal area of B.C. There are indications that broom is spreading rapidly into forested areas of southern Vancouver Island and western Oregon and Washington where it is interfering with forest establishment.

Like many introduced species, broom does not have any of the natural enemies of its land of origin in B.C. For this reason broom has spread indiscriminately. It has readily established on many droughty and disturbed sites, growing to heights of 2.5 metres in only two years. Excessive seed production and longevity have ensured that broom can dominate a site for long periods. As many of our native species cannot effectively compete with broom, they are being replaced.

Each broom plant produces approximately 18,000 seeds per year, beginning at age two or three. Seed can remain dormant in soil for up to 30 years waiting for suitable conditions to germinate

Fire Risk

Dense thickets of Broom can: increase wildfire fuel loads, thereby escalating wildfire intensity;
Invasive Species Council of BC

Scotch broom burns readily and carries fire to the tree canopy, increasing both the frequency and intensity of fires
Parsons 1992

Be aware that the volatile oils in broom can produce intense heat and large flames.
City of Portland Department of Parks and Recreation Natural Resources Division, The Society for Ecological Restoration Northwest Chapter and The Nature Conservancy

Brooms grow rapidly and form dense stands that are inaccessable to wildlife. The dense stands make regeneration of most species difficult or impossible, they also create a dangerous fire hazard. As plants grow, the inner stems die back, providing a highly flammable fuel.
University of California - Agriculture and Natural Resources

As Scotch broom stands age, the ratio of woody to green material also increases, and dead wood accumulates .  Older broom stands as "a mosaic of dead, partly dead and living plants." The ratio of dead to live fuel is critical in determining combustion  and several authors suggest that dense broom stands create a serious fire hazard‍
USDA Fire Effects Information System (FEIS)

Stoney Hill Clear-cut

Is Scotch Broom interfering with clear-cut reforestation?

Broom has become increasingly noticeable in newly logged areas. There is concern that it may be spreading and could pose a threat to forests and other resources. There are indications that broom is spreading rapidly into forested areas of southern Vancouver Island and western Oregon and Washington where it is interfering with forest establishment.
BC Forest Practices Branch

Scotch broom is a major forestry problem in the U.S., Canada, and New Zealand, particularly in reforestation after logging, as it can quickly overtop commercial crop trees . Scotch broom establishment after logging interferes with conifer establishment in the Douglas-fir region. Scotch broom may occupy 90% canopy cover and intercept 65% of the intermittent light in Douglas-fir plantations. In Oregon and Washington, there have been complete stand failures of Douglas-fir regeneration because of Scotch broom infestations
Fire Effects Information System (FEIS) - USDA

Due to its affinity for light-dominated, disturbed areas, any disturbance activity, such as road or home construction near infested areas, can enhance spread. Scotch broom invades rangelands, replacing forage plants, and is a serious competitor to conifer seedlings; Douglas fir plantation failures in Oregon and Washington have been credited to infestations of this plant.
Invasive Species Council of BC

According to the Oregon Department of Agriculture, SB costs the state of Oregon more than $40,000,000 per year, mostly in lost forest production due to delays in reestablishing trees in clear-cuts. Broom is also effective at displacing native vegetation in meadows, riparian areas and floodplains. The damage caused by SB is perhaps worst in meadows and other open areas where it not only displaces native species, reduces biodiversity and forage, but also alters the fundamental nature of the habitat by converting it from open systems to dense shrub lands
https://www.invasive.org/gist/moredocs/cytsco01.pdf

How many of the existing clear-cuts are infested with broom?

Based on our observations to date - many of the existing clear-cuts on Stoney Hill and Maple Mountain are severely affected by Scotch Broom.

The latest clear-cut on Mt Tzouhalem is also showing signs that it will be infested soon.

The areas marked in red are severe, orange is moderate to high > and will likely go to red unless treated.

The Broom spreads along the logging roads and follows the logging operations into the forest.

The light green areas are older clear-cuts - in more remote areas - with less traffic.

The more remote the area - the less broom there is in the patches

QUESTION: it is cost efficient to log these infested areas - what will it cost to make sure that the reforestation is successful?

QUESTION: are the infested cuts fire hazards?

This map will be updated as we visit more of the clear-cuts.

red= extreme broom infestation | orange = medium to high | green = low

This article is designed to pose questions and spark debate, not to provide answers. This article is based on online research, talking with experts and visual observation. Please use the online form below if you believe there is more to this story than we are aware of.

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Location

District of North Cowichan, Vancouver Island BC