[permaculture] Priority One Buzz
erda at nor.com.au
Sat Feb 3 02:23:34 EST 2007
On 3/2/07 1:24 PM, "Darren Doherty" <darren at permaculture.biz> wrote:
> There are some other things in P1 that I do have a hard time with though as
> I do know just a little about tropical forest systems: Allan makes some
> sweeping statements that some of these systems are not as rich as they are
> proported and that their "conversion" into organic biofuel production
> systems would be quite reasonable. I find this very hard to swallow and
> accept as I know that this is simply not the case. Their is some evidence
> now that climax wet tropical forests are net greenhouse emitters, as all of
> us are! That doesn't mean that we should be rid of simply on that basis,
> should we ban paddy rice and wetlands while we are at it and certainly don't
> forget the belching cow!....
This really piqued my interest and have just been reading his assumptions re
tropical rainforests. The point he misses is the constant rapid rate of
biological activity and nutrient cycling in these systems due to constant
high temperatures and moisture (humidity & condensation as well as
rainfall). It's a somewhat disparaging statement to claim these systems
support nothing more than a few woody plants and low-nutrient sugary fruits.
The sheer volume of biodiversity (plant and animal: micro, meso, macro) they
support knocks this on the head for starters.
Anyway the key thing he misses is the nutrient cycling - that these woody
plants are bringing up nutrients from the subsoil constantly depositing them
via detritus through leaf litter etc as well via the excrement of the
prolific herbivorous animal life in the system, which in turn are rapidly
broken down and taken up by the living woody plants. Most sustainable
traditional perennial production systems in the tropics emulate the
rainforest structure as multi stacked diverse and complex assemblies of
predominantly fruit-producing plants together with legumes - tall tree
legumes as emergent spp (most of these tend to be tropical deciduous) and in
the understorey more densely interspersed shrub or small tree legumes which
are regularly coppiced or pollarded (some in cycles as short as every 6-8
weeks) to supply nutrients from leaf litter as mulch and through the release
of Ammonia in their associated rhyzobium nodules.
The nutrients in tropics soils are in constant dynamic motion throughout the
living system as opposed to the predominantly in-soil storage of fertile
An in-depth study of the Pekarangan (traditional home garden food forests of
Java and Bali) determined yields as calories per square meter per year for
the different levels of vertical strata:
0-1m (sweet potato, taro, chili, eggplant etc) 15 c/m2/yr
1-2m (cassava, yams, galangal etc) 45 c/m2/yr
2-5m (banana, papaya, small fruit trees, coffee, legumes etc) 300 c/m2/yr
5-10m (fruit trees: Jakfruit, breadfruit, avocado, mango etc) 500 c/m2/yr
Over 10m (coconut palm & albizia) 450 c/m2/yr
i.e.over 1300 calories per m2 per year with minimal human input post
planting apart from hacking back some legumes and harvesting the produce.
Re the other point raised...
> now that climax wet tropical forests are net greenhouse emitters
There was an interesting article in one of the science journals last year
(don't have time to track it down right now, either New Scientist or
Scientific American) about greenhouse positive feedback loops and it
referred to research showing that as temperatures rise due to greenhouse
induced temperature increases that rainforests are giving off increasing
amounts of CO2 on an exponential scale. The same article noted that
destroying these forests would release massive amounts of CO2 difficult to
sequester and presented a sound scientific case for conservation.
I did enjoy reading Allan's stuff on soil apart from the unfortunate
assumptions on tropical rainforests...
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