All over the internet you can read about how willows cause increased flooding. For a sample, just try here:
“…..the trees are a menace and cause flooding….”
“They form thickets which divert water outside the main watercourse or channel, causing flooding…..”
“…..willows form thickets which can cause floods and erode vulnerable banks, especially on flood plain areas.” (my emphasis)
Although some of us hold to the peculiar idea that climate extremes (especially high rainfall periods) have something to do with it, according to anti-willow literature, it is willows that cause flooding.
Furthermore, as far as I can tell, flooding is a BAD thing.
But have you ever heard the phrase: ‘…of droughts and flooding rains.’? It’s from Dorothea Mackellar’s well-loved poem ‘My Country’.
If you’re someone who occasionally get’s the chance to step outside the office, you’d have noticed that southeast Australia is full of floodplains–they’re all over the place! These are natural landscape features which occur regularly in proximity to flow-lines. They are periodically inundated by flooding and have, over time, developed a generally flattish geomorphology composed of alluvial deposits. Often they are populated by species and ecological communities that are adapted to occasional flooding.
So, floodplains are a sure indication of the natural process of flooding. In fact, not much could be more natural in southeast Australia, because flooding on floodplains has long been an essential life-giving driver of many major ecosystems in this part of the world.
But what happens when an Australian floodplain floods? Well, lots of things really: wetlands are replenished with water and nutrient, many fish and birds spawn and breed, forests are inundated with life-giving waters causing spikes in seeding and seedling recruitment.
The Barmah-Millewa forest (links above) is just one very large example of how floodplain ecosystems rely on flooding to function properly, but these same principles can operate at any scale down to even the smallest surface flow. Flooding boosts nutrient and hydration levels in soils adjacent to flow-lines. Within native and non-nativist ecosystems, even within agricultural ecosystems, the productivity of floodplains is boosted by periodic flooding.
So what’s the story with the story about how willows are bad because they increase flooding? Surely more flooding is a major ecological benefit (and an agricultural-productivity benefit too); especially within Australia’s widely incised stream systems which now flood less-often than they once did–or even not at all. Surely, under these circumstances, flooding caused by willows should be widely welcomed.
But no; this natural process of nutrient and water replenishment on floodplains, which apparently willows are increasing (actually, just helping to reinstate), is often presented as a terrible problem.
Obviously, increased flooding wouldn’t be welcomed as a good thing where human settlements and infrastructure have developed upon historic floodplains. But does this mean willows are considered as bad for causing floods when they might damage human infrastructure, but good for causing floods when ecological and agricultural productivity are boosted?
…..Well no, apparently not; because you don’t see anything written about the ecological benefits of riparian willows that cause floods, even though we know flooding is essential to the health of Australian floodplain ecology.
Basically, it seems the take home message from all of this is perfectly clear:
Floods in Australia can be both good AND bad…..
……except if they are caused by willows when they must be unquestionably bad under all circumstances.
Is that a fair assessment of the situation?