66 Science & technology The EconomistAugust 10th 2019
2E
cology is acomplicated thing. Given
the facts that elephant damage often
kills trees and bush fires often kill trees it
would be reasonable to deduce that a
combination of the two would make
things worse. Counter-intuitively,
though, as research just published in
Biotropica, by Benjamin Wigley of Nelson
Mandela University in South Africa
shows, if a tree has already been dam-
aged, fire can actually help to make
things better.
One common way in which elephants
harm trees is by stripping them of their
bark. Dr Wigley, who did indeed start
from the obvious assumption, set off to
find out how much worse bush fires
would make the effects of this bark-
stripping. To this end he set up a study in
the Kruger National Park, a reserve on
South Africa’s border with Mozambique.
Since 1954, the Kruger has been the
site of experiments in which plots of
land have been burned at intervals, to
discern the effects of fire on savannah
ecology. Dr Wigley tapped into these
experiments by looking at trees in threedifferent zones. In one of these the vege-
tation was burned every year. In the
second it was burned every other year.
The third zone, by contrast, was actively
shielded from fire.
To keep things consistent, he looked
at the fate of a single tree species, the
marula (pictured), in all three zones. He
picked marulas because they are partic-
ular victims of elephant activity. Their
fruit are delicious, and prized by ele-
phants and people alike. But elephants
also seem to enjoy eating their bark.
In July 2016 he and his colleagues
identified 20 marulas in every zone and
used a hammer and a soil corer to re-
move from each of them a circular sec-
tion of bark 5cm in diameter. Having
inflicted this damage, they monitored
the wounds over the course of the follow-
ing two years, to see what would happen.
To their surprise, they discovered that
the wounds of trees in fire zones recov-
ered far better than those of trees that
had seen no fires at all. Wounded trees in
the annual burn zone regrew 98% of their
lost bark during the two years of the
study. Those living in the biennial burn
zone regrew 92% of it. But those in the
zone where fires were suppressed regrew
only 72%.
The researchers also found some-
thing else when they were measuring the
trees’ wounds: ants. Ten of the 20 trees in
the fire-suppression zone developed ant
colonies in their wounds. The ants in
question were a species that is known to
damage trees and is presumed to impair
tissue healing. By contrast, only five trees
in the biennial burn zone and three in
the annual zone developed ants’ nests in
their wounds.
It looks, therefore, as if bush fires are
cauterising trees’ wounds by killing ants
that might otherwise infest them.
Though such fires are surely harmful to
healthy trees, it seems, in an example of
two negatives making a positive, as if
they are actually helpful to sick ones.Burning questions
EcologyNature is complex. And unpredictableA quick snackconserving some ecosystems and destroy-
ing others to make way for pastures and
fields, or chopping down trees for timber,
human activities on the land add an extra
layer of complexity to already complex nat-
ural cycles.
The report found that between 2007 and
2016 such activities produced emissions
equivalent to 9bn-15bn tonnes of carbon di-
oxide each year, or roughly 23% of all man-
made greenhouse-gas emissions. During
that time, land surfaces soaked up
8.6bn-13.8bn tonnes of carbon dioxide.
At the moment, then, these sinks and
sources are roughly in balance. But climate
change, deforestation and agriculture
mean the CO 2 -soaking-up ability of the
continents is being depleted. The acceler-
ating destruction of the Amazon forest,
which researchers fear may be approach-
ing a point of no return, is of particular
concern. And across the world, depending
on the type of husbandry practised, farm-
ing is eroding soil at a rate between ten
times and more than 100 times faster than
new soil forms.
Climate change, moreover, creates a vi-
cious feedback loop. Higher temperatures
promote the degradation of land through
drought, desertification and rising seas,
and the promotion of wildfires like the
ones currently blazing in Alaska, Siberia
and Greenland. This, in turn, increases the
amount of greenhouse gases being re-
leased by landmasses, which further accel-
erates global warming.
A swelling human population also
needs more land to feed itself. Balancing
these needs—for space to grow food on the
one hand, and natural carbon sinks to keep
temperatures low on the other—is a huge
challenge. There are, however, solutions.
Recently, a report by the World Resources
Institute, a multinational think-tank, list-
ed 22 actions that could be taken to feed,
sustainably, close to 10bn people by 2050.
Number one on that list is stopping de-
forestation, along with efforts to regener-
ate degraded ecosystems. Reducing food
waste is also important. More than a quar-
ter of what the world grows to eat is never
actually consumed. That creates a huge
carbon footprint to no benefit. And diets
themselves need to change. In particular,
raising livestock contributes dispropor-
tionately to the problem. That means eat-
ing less meat, an admonition directed
mainly at rich countries, whose people, of-
ten overweight, might in any case benefit
from going on a diet.
This last point presented one bone of
contention between the 195 government
delegations charged with approving the
panel’s report. The role of bioenergy (grow-
ing crops for fuel) and beccs(bioenergy
with carbon capture and storage) was an-
other. A previous ipcc report, published in
2018, on the feasibility of limiting globalwarming to 1.5°C, made it abundantly clear
that this would require large amounts of
greenhouse gases be removed from the at-
mosphere and somehow stored away.
beccs, in which power stations capture
and store the CO 2 from burning biofuel, has
been touted as a way to do that on a large
scale, but the area of land required to grow
the biofuel needed to absorb billions of
tonnes of CO 2 would be enormous—severaltimes the size of India.
Optimistically, the report’s authors con-
clude that there should be enough room to
provide a growing population with suffi-
cient food, without rushing towards a dan-
gerously warm climate. There is, though, a
caveat. That outcome would require what
one commentator called a “global intelli-
gent response”. But the world, like the dele-
gates, seems to be asleep. 7