Why noxious weeds matter | Guest column

by County Noxious Weed Control STAFF MEMBERS

While invasive weed populations are expanding at an almost exponential rate across North America, annually costing the US economy billions of dollars, we in the San Juans have been more fortunate.

Weeds have been slower to establish here and relatively fewer species have become problems.  Several varieties have become so widespread that they  threaten our forests, meadows, agricultural traditions and public health and safety.

Plants such as Scotch broom, gorse, English ivy, oldman’s beard (wild clematis) and spurge laurel will, over time, proliferate into widespread monocultures, gradually suppressing and replacing the native flora of our forests and meadows. Gorse and broom change the soil chemistry making it difficult to restore the native flora long after the invasive species have been removed.  The proliferation of berries, spread primarily by birds, has caused infestations of ivy, spurge laurel and holly on county parks and outer islands.

Many of the invasive weeds are unpalatable or toxic to livestock, thus degrading valuable and limited pasture and hay fields. Ingestion of tansy ragwort and groundsel causes liver damage and has been implicated in the deaths of horses and cattle.  Humans, as well are not exempt from the toxic effects of some of our invasive weeds.

Giant hogweed exudes an irritating clear sun-activated sap which has caused permanently disfiguring scars on hundreds of children and adults in the Pacific Northwest over the past several years. After having ingested a tiny piece of a spurge laurel leaf, an Orcas preschooler became ill.

One of the greatest threats posed by noxious weeds is that of fire. It has been more than a half a century since there has been a major wildland conflagration in this county and it is no longer a question of “if” we have another major fire but rather “when.”  Gorse and dry stands of Scotch broom are highly flammable, developing hot, fast moving low crown fires.  While gorse is primarily a threat on Orcas, broom is wide spread, forming dense patches in both wild areas and residential settlements. Both species add to the already heavy natural forest fuel loads.

We have been fortunate that the islands have remained isolated, forested, and the soil floor comparatively undisturbed. However, as our population increases, forests are being cut and soils disturbed. Invasive plants are brought in inadvertently with off-island hay, contaminated topsoil, or on purpose, as exotic ornamentals.

Help control the spread of invasive weeds by requesting weed-free hay and topsoil, revegetating bare land and planting non-invasive ornamental plants.

For info, call the Master Gardeners at 378-4414 or the Noxious Weed Control Program at 376-3499.