Invasive plants: like pouring oil on water – and setting it on fire.

August 29, 2009 § 9 Comments

My heart goes out to all of you dwelling on the edge of the San Gabriel Mountains, who are either in the evacuation zones or in the smoke zone.  This is a difficult time for all.

These fires are pounding the canyons above some of my favorite waterway haunts.  Up Azusa Canyon, the Morris fire burns around the Morris Dam, which sits on the upper San Gabriel River.  My friends and I shook our heads in disbelief years ago when we saw the Mountain Cove development go in, right in the floodway of of the SGR; now I shake my ahead again, this must be one of LA’s most miserable places to be right now.  To the west, the Station Fire burns above the Arroyo Seco, heading now up Millard Canyon, having run through Brown’s Canyon – as well as over the ridge to the west and into the heights above Tujunga (and thank you, Meredith McKenzie, for the FB updates on its movement).

We all know what this means – come winter, there will be debris flows.  But that’s not what I’m writing about today.

You’ve probably noticed, these fires seem to be occurring with an ominous, greater frequency than in the past.  They also are tending to burn with greater intensity.  I read we are fortunate this time around, it sounds like it is a lower temperature fire.

We all know Southern California rains and burns in cycles.  We will often go 8-10 years pretty dry, then get a good soaking.  Within that, every 15-20 years, it will be more than a soaking – it will be a thunderous wet El Niño hell for about three weeks.  Usually right after several hot, dry years.  But it has seemed that in the last five, ten years or so, the dry has been drier.

So more drier weather, less moisture in those plants up in the forest.  Things tend to burn hotter.  And those hotter temperatures of recent wildfires make recovery of our native habitats more difficult (even the ones that regenerate with fire are adapted to lower temperature, slower fires, believe it or not!), and the non-native material (that pretty fountain grass you see everywhere, mustard, castor bean, etc) that moves in pretty quickly is prone to be drier and burn hotter than even our native chaparral, keeping a downward habitat spiral alive.

Even in streams.  Streams are generally less fire-prone than the uplands, although they too will burn (just less).  I’ve heard some ecologists refer to steams as something like natural fire breaks.  Riparian (stream-side) plants aren’t generally adapted for fires – which means, they don’t generally get exposed to them.  Their higher water content in their leaves and branches generally protects them as well.  But consider that today:

“Riparian and wetland lowland habitats are at high risk from the fires, due to opportunistic exotic plants, including Giant reed (Arundo donax) and other non-native grasses and forbs”. (San Diego Wildfire Education Project)

So if you love hiking in streams but don’t know what all us creekfreaks get worked up about when we start ranting at the Arundo or Cape Ivy or Sticky Eupatorium or LA’s iconic Washingtonia palm tree (aka riparian Roman Candle) or that g@%$& fountain grass in the stream please understand:  this is a big part of why.  For example, on the Rio Grande in New Mexico, the increasing dominance of Russian Olive and Tamarisk (in part facilitated by decrease in natural flood cycles, due to levees – ok, it’s a long story) has resulted in devastating bosque fires, from which the native cottonwood trees aren’t generally regenerating.  You get habitat loss and nasty fires.

We can’t control the lightning strikes that start fires.  We could – but it would be a major political undertaking – control the potential risks caused by electrical utility lines.  And I don’t know if anyone can control kids playing with fire, workers with equipment that accidentally sparks or the myriad other “accidental” things that start fires(remember the heartbroken ranger who was burning letters? I’d hate to have to explain that to the boss).  We could (again p-o-l-i-t-i-c-al) stop building in wildlands, but I don’t know that we will (and in fairness – I totally fantasize about living in Topanga or a cabin up Baldy-way, so this is a conversation between pots and kettles).

But we can be responsible in our landscaping choices, we don’t have to recklessly landscape without knowing whether or not the latest thing at Home Depot is going to turn into the next high-tinder invasive weed nightmare.  We can choose to use native plants, or the non-natives that are demonstrated not to escape.  This is not obvious information, when it comes to landscapes, we generally only know what we are marketed.  It sounds counter-intuitive, but supporting our native habitats generally supports lower-intensity fires.  The San Gabriel Mountains on those steep slopes may not have a lot of the non-native material. It will be interesting to get ahold of the post-mortem of this fire, and see if any further correlations between fire intensity and vegetation type shows up.

In the meantime, stay safe.


Lotsa good reading on this topic:

The Fires This Time, Los Angeles and San Gabriel Rivers Watershed Council (LASGRWC)

Watershed-Wise:  Brush Clearance, Fuel Reduction, and Fire-safe Landscaping, LASGRWC

Watershed Council Symposia on these topics.

And because I’ve really, really got an axe to grind with fountain grass, an article about its evil cousin, the buffelgrass:

Bonfire of the Superweeds, High Country News

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