Dr. Sue Grayston and her team are leading a study of soil ecology in Gwaii Haanas and Laskeek Bay that seeks to uncover the effects invasive deer are having on everything from plant roots to nutrient cycles, fungi, worms, bacteria, and even carbon storage. (Gwaii Haanas photo)

Scientists go underground to see how Haida Gwaii deer impact the soil

Holding a spoon heaped with rich black Haida Gwaii soil, Dr. Sue Grayston asked the Ḵay Centre crowd: about how many things live inside?

“More than three,” said the first person.

“A thousand?” said the next.

The room went quiet. Counting soil microbes is no jar of jelly beans.

“There are more organisms in this tablespoon than there are people on the Earth,” Dr. Grayston said.

“Without them, we wouldn’t exist — plants wouldn’t be able to grow. But they would quite happily exist without us.”

A UBC professor who holds a Canada Research Chair in microbial soil ecology, Grayston is leading a study of Haida Gwaii soils that is the flip-side, underground version of a 20-year project by Dr. Jean-Louis Martin.

The key question for both is, what are invasive deer doing to Haida Gwaii forests?

Aboveground, Martin’s team used plant enclosures and sweep-net surveys to track what most islanders can see from walking Haida Gwaii’s many open, moss-carpeted woods. Uncontrolled deer will eventually mow down most western red cedar, shrubs, and wildflowers.

For many creatures, that causes a cascade of problems.

Most insects lose the plants they need. Songbirds lose insects to eat, as well as shrubs to hide in. Raptors, in turn, lose the songbirds as prey.

A few species make good on deer-ridden forests, such hemlock and spruce trees, or crows, ravens, and squirrels. People get plenty of meat, too.

Underground, Grayston is uncovering a similar domino effect.

Deer-trampled soils get more and more compacted, making plants work harder to grow their roots.

Between that and the many munching deer, eventually there are far fewer plants in the forest understory, meaning fewer leaves fall to the ground ground. Eventually there is much less organic matter for soil organisms to feed on.

Over time, the soil’s dark organic layer gets thinner and thinner.

Like the crows and squirrels aboveground, a few species actually benefit from the change. Grayston’s work shows some worms and beetles do better on Haida Gwaii islands that have deer, while millipedes do better on those without.

“But the key decomposers in forests are the soil microorganisms,” Grayston said.

Besides removing plants and trampling the ground, deer also add things to the forest, namely urine and feces.

One question Grayston hopes to shed light on is how deer urine and feces may be speeding up the rate of decomposition in soil, and altering the nutrient cycle.

It may be that all that waste provides trees with easy-access nutrients, meaning they no longer need lots of helpful fungi to break down organic matter for them.

Already, one of Grayston’s students has found some islands with heavy deer populations have significantly less fungal biomass.

Fortunately for Grayston and her team, the Gwaii Haanas Restoring Balance project that recently removed 407 deer from Ramsay Island (researchers are hoping to confirm it as a complete eradication) offers an ideal scenario to do a wide-ranging study on the effects deer have on soil ecology.

Such work usually involves finding islands with varying levels of deer, as Grayston and Martin have done around Laskeek Bay.

On Ramsay, the evidence will likely be of better quality, because Grayston’s team has been able able to test the soil on a single island before and after deer.

Grayston hopes the work begins to answer an even bigger-picture question — what effect might the deer have on how much carbon is stored in Haida Gwaii forests?

While people tend to think of tropical rainforests storing lots of carbon, Grayston said those forests tend to have quick growth and quick decomposition. On the other hand, temperate rainforests like Haida Gwaii’s tend to grow quickly, but decompose much more slowly.

“Really, you have a lot of carbon storage in these forests,” she said.

But if deer are indeed speeding up the decomposition rate, that carbon-storage function could change.

“Soil is not just dirt,” she said. “It’s a very dynamic medium.”

Gwaii Haanas

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