A study has shown that hungry caterpillars can eat so many leaves in temperate forests that it can dramatically shift the local nutrient cycle, and increase greenhouse emissions.
Outbreaks of invasive gypsy moths and forest tent caterpillar moths occur at least every five years in temperate forests, experts from the University of Cambridge said.
The bugs eat leaves that would otherwise cycle carbon to the surrounding trees. However, their droppings (or frass’), also release large amounts of nitrogen.
When this washes into local lakes, it fertilises bacteria which go on to emit carbon dioxide (CO2) as they metabolise — all at the expense of CO2-absorbing algae.
This effect will only get worse as climate change causes more little insects to move northward and increases their numbers.
This is worrying because there tends to be more lakes further north and climate shifts that will promote deciduous forests favoured by the insects.
The image shows how hungry caterpillars in temperate forest can eat so many leaves that their net impact can dramatically shift the local nutrient cycle, and increase greenhouse emissions.
Andrew Tanentzap, a University of Cambridge paper author and plant scientist, said that these insects are basically tiny machines that convert carbon-rich leaves to nitrogen-rich soil.
He said, “The poo is dropped into lakes instead than the leaves, and this significantly alters the water chemistry.”
“We believe it will increase the extent lakes are sources for greenhouse gases.”
In their study, Professor Tanentzap and colleagues analysed 32 years’ worth of monthly lake water chemistry data and governmental records of caterpillar outbreaks for 12 lakes and their catchments in the Ontario province of Canada.
This was in addition to the analysis of remote sensing data that satellites collected on the area’s monthly leaf coverage and forest type.
The team found that years with outbreaks of the insects tended to see a reduction in forest leaf cover of around 22 per cent — while nearby lakes exhibited an average of 27 per cent less dissolved carbon but 112 per cent more nitrogen than usual.
These effects were at their greatest, the experts explained, when the lake catchment areas were populated by a higher proportion of deciduous, broadleaved trees like oaks and maples, which the caterpillar species prefer over conifers like pines.
In non-outbreak years, the carbon and nitrogen that enters lakes usually comes from decaying leaves and needle litter — with the greatest influx in the autumn.
Experts from the University of Cambridge stated that invasive gypsy and forest tent caterpillars (pictured), occur at least once every five years in temperate rainforests.
The bugs eat leaves that would otherwise cycle carbon to the surrounding trees. However, their droppings (or “frass”) also release large amounts of nitrogen. When this washes into local lakes, it fertilises bacteria which go on to emit carbon dioxide (CO₂) as they metabolise — all at the expense of CO₂-absorbing algae
Sam Woodman, a paper author and plant scientist, stated that leaf-eating insects can increase the carbon dissolved within lake water by almost a quarter of a percent when the trees around the lake surround them are mainly deciduous.
He said, “It’s amazing that these insects could have such an pronounced effect on the water quality,” he continued.
‘From a water quality perspective they’re a good thing, but from a climate perspective they’re pretty bad — yet they’ve been completely overlooked in climate models,’ the researcher concluded.
The journal Nature Communications published the full results of the study.