My father was a bushman before the war.
My father burnt many hectares of ancient native forest.
He burnt the trees down to a hilly grey ashscape. An ashscape
littered with black, smouldering stumps and half burnt logs.
In the years before world war 2, my father and his brother worked on
their block of native forest in the 'King Country' (as he called
it). Day after day they left their homemade 'whare' with their axes
and two-man crosscut saws on a mission to "clear the bush". The
forest rang to the thud of the axe as they bit notches ('scarfs')
into the base of selected forest giants. These scarfs directed where
the trees would fall. The two man push-pull crosscut saws severed
the trees connection to the earth, and wedges hammered into the cut
levered the limb-heavy top over, until, earth-fibres snapping, it
tipped, crashing to it's death.
A pit was dug under the fallen tree, and sawing commenced, with my
father below (receiving a face full of sawdust on the down-pull
stroke - but he was the younger of the two...) and his brother
standing atop the trunk. The sawn lumber was dragged out and sold
for "3 pence a super foot". Totara is ground durable and splits
well, so it was sectioned and split for posts and battens. The fate
of the rest of the 'worthless' native forest was to be burned in
place. Smaller trees that happened to be more or less in line with
the hoped-for direction of fall of the big tree (the 'drive tree')
were pre-notched to weaken them and direct their fall, so that the
first to be knocked down by the drive tree would in turn knock down
the next in line, and so on, like dominos.
The fallen forest would be left for a year or two to dry. Then the
fire was set. Once the fierce blaze had died out and the acrid smoke
had finally drifted away there was "a five inch layer of ash", my
father told me. Whatever native animals survived the destruction of
their home became refugees, pushed into remnant forested "gullies",
or perhaps a narrow strip of forest left as a windbreak.
Five inches of ash was also five inches of fertility. Five inches of
'free' fertility gave about 5 years before bagged fertiliser had to
be applied. Grass seed spread into the warm ash grew lush and strong
(and so did the Californian thistles - a common contaminant in the
seed in those days). The bigger of the blacked stumps were blown up
with a mixture of black gunpowder and sugar. Playing with fire...
Fire destroyed ancient forests; and created pasture. A once-ever
natural subsidy. And ryegrass-clover pasture created New Zealand's
economic success. With the end of forest ash, our pastoral
agriculture took subsidy from phosphate deposits on Christmas Island
(mined to extinction), Nauru (mined to extinction), and now is
subsidised by phosphate deposits in West Sahara (containing 75% of
the world's phosphate reserves, and still being mined - illegally -
by Morocco, but not yet extinct).
'Slash and burn' agriculture is practiced today, all around the
world. Forests in Malaysia, Borneo, Indonesia are still being
burned, mainly to plant palm oil trees. The smoke and pollution is
so dense in the 'burning season' that peoples health is affected.
Tourists switch to northern Thailand to escape the pollution. In
contrast, New Zealand has conserved very large areas of native
forest. Other countries are not doing so well.
In a recent paper titled ' Forests, atmospheric water and an
uncertain future: the new biology of the global water cycle',
Douglas Sheil notes that "over one third of the Earth’s ice-free
land comprises agriculture, pasture and urbanisation", and
this 'forest-denuded' area is expanding. He notes that "one
and a half million square kilometres of dense tree-cover were lost
between 2000 and 2012".
That statistic - one and a half million square kilometres of dense
tree-cover - is very hard to visualise. Imagine the entire of the South
Island of New Zealand was covered in dense forest (no cities farms
etc). Coast to coast. Now chop it all down, Bluff to Nelson. That is the picture.
And all in 12 years. But that is not a one-off event. It is a
This graphic of forest loss in the Amazon is more powerful than
images conjured up by words alone:
Forests and climate are an intimately linked system.
and climate are linked in both directions: when climate changes,
so will vegetation, and when vegetation changes, so will the
climate. These links are more important, more complex, and more
poorly characterised than most people realise." - Douglas Sheil
Well, vegetation in New Zealand and around the world has certainly
changed. According to Douglas Sheil this must lead to changes in
climate, although the nature of the changes are uncertain. He notes
that the global water-cycle is still one of the least understood
natural cycles. The interaction of water on the land - water bodies,
water in soil, transpired by plants etc - and the interaction with
atmospheric water is complex and poorly understood.
Changing climate has the effect of melting frozen water stores in
permafrost, glaciers, ice caps and sea ice. What effect these
changes have on atmospheric moisture, the formation of clouds,
precipitation (rain or snow) and the water cycle are full of
uncertainty. But the effects of atmospheric moisture patterns and
reliability, from a human perspective, are of intense concern.
Snowpack supplies water to cities. Monsoons are the guarantors of
harvests, the givers of life. Winter rains recharge underground
artesian water stores. Summer rains can ruin grains that were dry
and ready for harvest. Half a billion people endure scarce water
supplies all year long, and two-thirds of the worlds people have
insufficient water for more than a month in a year. Recent tree ring
data that show that periods of severe drought in parts of western
Mediterranean are within the range of natural variability occurring
over the last 900 years, but the drought in Syria, and in some other
parts of the eastern Mediterranean, is the worst in 500 years. The
Syrian drought falls outside the range of expected variation for the
900 year period studied - suggesting a shift in the local
hydrological cycle. Examples of such vulnerabilities and
uncertainties are endless - and endlessly important.
Perhaps most important is change in atmospheric water vapour,
because water vapour is the dominant greenhouse gas, trapping heat,
warming air, allowing more water vapour to be held, and therefore
heavier rain to fall. This can be an amplifying feedback loop in
areas surrounded by large bodies of water. Models predict water in
the atmosphere will increase by 7% for each degree Celsius of
surface warming, and experience so far shows precipitation increases
at roughly the same rate.
Almost 40% of the rain and snow that falls on land comes from water,
but 60% of rain and snow is water recycled from land. Water vapor
from large scale forests, such as the Amazon, East African forests,
the temperate forests of Western North America, and the massive
forests of Central Eurasia can travel downwind in the atmosphere for
up to 500 kilometers (typically) to 5,000 kilometers (less
frequently) before falling as rain. So global warming means more
water vapour can be held by air over water, but in some areas,
de-forestation might mean less water vapor being pumped into the
atmosphere over land.
flows and uncertainty
of a system is its interlocking stocks, flows, and feedback
loops...Systems fool us by presenting themselves - or we fool
ourselves by seeing the world - as a series of events. Much of
our ordinary conversation is about specific happenings at
specific times and places. A team wins. A river floods...A
forest is cut. Events are the outputs, moment by moment,
from the black box of the system...Its
endlessly engrossing to take in the world as a series of
events, and constantly suprising, because that way of seeing
the world has almost no predictive or explanatory value
...long-term behaviour [of the system] provides clues to the
underlying systems structure. And structure is the key to
understand not just what
is happening, but why."
Systems Analyst Donella Meadows
Donella Meadows observes that most
attempts to explain what is happenng in the world is simply a
superficial opinion on events. A slightly deeper analysis looks at
the motives for the behaviours of the actors. Deeper analysis
looks at the current flows of stocks (she gives the example of
flow of goods and services at any point in time) rather than the
stock (physical capacity of factories and farms, physical supply
and limits of capital stock of raw materials etc). This simplistic
superficial linear thinking - 'well, this will lead to that, and
then probably to that' - assumes no complexity, let alone accounts
for rare but 'game-changing'events. Linear thinking cannot even
conceive of feedbacks coming from other ignored parts of a complex
dynamic system. A system might tend to be self-balancing, with a
bad effect tending to be cancelled by a good effect, or it could
be at some point in developing a 'runaway' self-reinforcing
feedback loop. It is easy to understand a runaway self-amplifying
feedback loop when it is an immediate event - Fukushima nuclear
power plant disaster is a good example - but much harder when it
is a slow and constantly micro-varying trend - like human 'forced'
climate change. The main root cause of climate shift is
carbon dioxide increase.
Let there be no doubt about it - there
are two 'stocks' of carbon that are being burned to form
carbon dioxide, one harmless, the other deadly.
Put simplistically, one stock is the 'body' of all the plants on
earth. Carbon dioxide 'flows' from this stock when forests are
burnt, or the trees fall and rot. But under a 'natural' system, any
time a tree falls another seedling takes it's place in the sunny gap
in the dense forest canopy. Soon the gap closes again, and the tree
that grows to close the gap takes carbon dioxide out of the
atmosphere to build its body. Death and new life balance to nett no
gain or loss of atmospheric carbon dioxide. Man-made or natural, the
'flow' of growth, removal, and replanting of forests are more or
less carbon nett neutral in the 'natural system' stock.
The other stock is the buried ancient geological stock, primarily
the coal, crystalline carbon. It should never ever be drawn on. It
should remain buried forever. This stock should never have been
allowed to 'flow' into the atmosphere. Unlike the 'natural' stock,
the ancient carbon dioxide released from burning coal cannot
Planting more trees does not help.
First, the trees will be cut and eventually rot, releasing carbon
dioxide. Storage, in other words, is only temporary.
Second, extra tree planting is not even compensating for the South
Island's worth of trees being destroyed every ten years or so, let
alone re-sequestering ancient carbon dioxide that should never have
been released from its deep underground tombs.
This bad situation continues to be made worse. For example, forests
continue to be cut in Pakistan even while coal production from the
Thar coalfields in eastern Sindh is due to start next year (2019).
The Thar coalfield contains about 175 billion metric tons of coal. A
metric tonne of coal creates 3 - 5 tonnes of carbon dioxide
(depending on carbon content).
The only way to pull this ancient carbon dioxide back out of
circulation is to re-create coal. That is, wait for a warm and wet
global hydrological condition, don't drain the resultant
ever-expanding swamps, let vegetation fall into the waters and rot,
let heavy rain wash silt onto the layers of carbon-containing
vegetation, let earthquakes drop some of these swamps under the
earth, compress for millions of years until heat and pressure form
crystalline carbon (coal), and bingo! Success!
My Take Home Message
Of course, if the human footprint is reduced; if there
is a massive global effort to abandon coal; if there is
massive re-forestation; and if we do a million small things
to use renewable energy and re-green, well, there might be a
Agreement on Climate Change, the United Nations is pursuing
efforts to limit global warming to 1.5°C, whereas earlier
aspirations focused on a 2°C limit.
With current pledges, corresponding to [about] 3.2°C warming,
climatically determined geographic range losses of >50% are
projected in ~49% of insects, 44% of plants, and 26% of
At 2°C, this falls to 18% of insects, 16% of plants, and 8% of
vertebrates and at 1.5°C, to 6% of insects, 8% of plants, and 4%
When warming is limited to 1.5°C as compared with 2°C, numbers
of species projected to lose >50% of their range are reduced
by ~66% in insects and by ~50% in plants and vertebrates."
- Warren et al, 2018. 'The projected effect on insects,
vertebrates, and plants of limiting global warming to 1.5°C rather
than 2°C' Science, Vol. 360, Issue 6390, pp. 791-795
There is no chance average global warming will be
limited to 1.5oC.
Putting money on at least 3oC warming is a pretty safe bet.
Either we choose to stop releasing stocks of ancient carbon dioxide
now, or the remnant population living in the still habitable parts
of the planet will have so few energy requirements it won't matter.
Douglas Sheil Take Home Message
"Among the most profound and disturbing insights offered by
this review is the potential for non-linear behaviours: the
indication that a continent or region that passes some threshold of
forest loss might tip from a wet to a dry climate. While various
details remain poorly characterised, and some are debated, the
overall linkages appear uncontroversial. We know that large
scale forest loss or die-back
will generally reduce atmospheric moisture, rainfall and cloud
cover, and increase the likelihood of drought and further loss or
die-back. Add in human activities, increasing temperatures and
fires, and changes could be rapid, making whole regions near
uninhabitable and releasing vast amounts of carbon stored in
vegetation and soils into the atmosphere over only a few years.
There is also a positive side: rainfall can be stabilised and
regained by maintaining and restoring tree cover. Characterising
these threats and opportunities is a priority."
Read much, much more at:
Douglas Sheil, 'Forests, atmospheric water and an uncertain future:
the new biology of the global water cycle'.