Are pests needed to control climate change?

November 2013

CC photo by William Warby on Flickr

A recent study by American ecologists has cast an interesting new light on our intuitive concept of the carbon cycle, especially on the realities of carbon storage, carbon release as CO₂, and the resulting threat of climate change.

We've never before doubted that plants left undisturbed will grow maximally, and store maximum carbon from their photosynthetic endeavours. Nor have we ever doubted that the destruction of plants by herbivorous animals will reduce carbon storage, while the action of carnivorous animals will keep the herbivores in check and thus offset the carbon lost to them.

We've never questioned the role of liberal applications of insecticidal chemicals, and more recently 'Bt' GM plants which suffuse themselves with insecticidal proteins, in enabling maximal carbon storage and growth of our crops.

But, interestingly, no one's ever scientifically verified these 'intuitions'.

Model ecosystems designed to compare the carbon storage of plants grown alone with plants grown in the presence of herbivores, or, with a more 'natural' situation in which both herbivores and carnivores are present produced some surprising results.

As expected, when carnivores were present to control the herbivores, the plants stored a massive 40% more carbon compared to the ecosystem destroyed by unchecked plant-eating. However, the ecosystem with carnivores also packed away a very significant 20% more carbon than the plants living in isolation.

Related research has shown that the very presence of the carnivores causes plant physiology to change: respiration slows and biomass increases, especially below-ground.

The scientists who made these findings speculated that a light nibble here and there actually boosts plant growth.

Important implications of this include the possibility that conventional agriculture's blanket destruction of crop pests (herbivores) along with the inevitable collateral damage to the wider environment (including carnivores), could be having significant and unforeseen impacts on carbon storage and therefore on our climate.

One of the authors commented:

“Right now, there is a crisis in terms of predator diversity loss. And that may mean we are losing the potential to help regulate the carbon cycle in ways that go far beyond just growing more trees.”

Other lines of scientific inquiry have revealed that minor pest damage is also important for boosting the plants' immune responses (see HOW PESTS CONTROL PESTS - April 2013).

In light of all this, organic agriculture appears a top priority for dealing with climate change. An organically-managed system will always have the benefits of combined herbivores and carnivores amongst the crops. Importantly, the chemicals which lead to a loss of carbon from the soil are replaced with carbon-creating manures. Moreover, as Nabhan notes, since “Increasing organic matter in soils from 1% to 5% boosts water storage in the root zones from 33 pounds to 195 pounds per cubic meter”, plants in an organic system have less water stress to cope with in our warming, and increasingly dry, world.

OUR COMMENT

Our food is being produced in simplified, sterile environments. The situation is being made worse by the GM extremes of herbicide-tolerance and insect-resistance layered on top of routine agri-chemical use. This is not, it seems, the way to produce healthy plants nor a healthy world. What hope has our health under these circumstances?

The benefits of organic agriculture are becoming clearer especially in the interest of dealing with climate change.
 
If you're not already a member, check out the Soil Association.

SOURCES:

• Arielle Duhaime-Ross, The Spider in the Grass, Scientific American, September 2013
• Gary Paul Nabhan quoted by Mae-Wan Ho, Towards 100% Renewables - Surviving Global Warming, Instutute of Science in Society Report 25.09.13
• Michael S. Strickland, et al., 2013, Trophic cascade alters ecosystem carbon exchange, PNAS 110:27