[permaculture] casuarina/ironwood

John Schinnerer eco_living at yahoo.com
Wed Mar 13 01:36:43 EST 2002


> I've heard by word of mouth that the ironwood needles contain an
> allelopathic substance which supresses potentially competitive growth
> around
> the tree - and, indeed, there are stretches of forest on the Big
> Island

I haven't heard this rumor, though I can't rule it out either...  
I suspect that the growth and leaf (needle) fall rate is high enough
that they can shade and mulch out everything else without any
allelopathics in places where initial conditions are right.

The PFAF database returns six varieties for a search on casuarina; none
mention allelopathy that I could find.  Several do say they fix N via
microbes in the roots.  The only one with a picture link shows a
close-up of those familiar needle-leaves in flower, though, and several
mention that it tolerates maritime/salt spray climates.
> However, I've also seen reference (in "Agroforestry in the Pacific
> Islands:
> Systems for Sustainability") reference to how in Papua New Ginuea (or
> somewhere down there... ;) the native people preferred to plant
> gardens where ironwoods had been because it was better soil.

Someone mentioned phosphorus-rich mulch...and perhaps they planted
there partly because they created 'enough' soil where there wasn't
enough before?  At places like MacKenzie park in Puna, there's not much
under those needles except more fully decomposed needles, and then
lava... ;-)

> maybe the needles
> are actively allelopathic only for a short time after they fall, and
> then lose that quality in older soil?

Hmmm - coconut palms grow in the midst of some coastal ironwood groves
I know of on the Big Island - some might be older than the ironwoods,
true, but they drop nuts that sprout on top of the ironwood leaf mulch
and put their roots right down into and through it.  But then, coconuts
will wash up on a beach and sprout and grow right in sand, too, so
they're probably not that great an indicator of allelopathy (or not) in
ironwood leaves... ;-)

John Schinnerer, MA
- Eco-Living -
Cultural & Ecological Designing
Food - Shelter - Community
john at eco-living.net

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