Turns out it might be bugs that can answer whether a tree falling in the forest makes a sound.
As much of Western Canada faces worsening drought, the region's forests are drying out – and as the trees dehydrate, they make sounds that attract the kinds of insects that can then kill them off, says a scientist who has studied the phenomenon.
"Insects know that [the trees] are under stress. They can hear that popping," said Sandy Smith, an entomologist at the University of Toronto.
"Especially those that are tuned into feeding on trees."
The hot and dry conditions that have plagued British Columbia and parts of Alberta since May are improving insect survival while impeding the forest's ability to defend itself, leading to what researchers say could be a perfect storm for widespread tree mortality and wildfires across the Rockies into Alberta's boreal forest.
"The mountain pine beetle is just one of a whole suite of possible issues to hit our forests, and it already has happened," said Allan Carroll, a forest scientist at the University of British Columbia.
Usually, trees protect themselves from insect attacks by producing chemicals that repel invasive species.
But during drought it's more difficult for a tree to pull water through its roots from the soil, hindering its ability to generate the nutrients it needs to make and circulate those defence chemicals.
And the risks are twofold: While the tree is weaker and more vulnerable during dryness, tree-eating insects develop faster in the heat.
"It very quickly escalates," Prof. Smith said. "One tree can produce a million beetles in a drought year that in a regular year, maybe, that tree can only produce 1,000 beetles."
Much of the province is considered dangerously dry and the proportion of the province facing drought conditions is increasing.
On the Sunshine Coast, the drought level is so high that residents have been barred from using hoses to water even vegetable patches and flower gardens – only greywater (water already used in the household such as in sinks and showers) may be used.
If drought conditions persist, the lasting impact on forests could mean even worse wildfire seasons in the future, Prof. Smith added. "You've got a whole bunch of dead trees sitting there – a huge bonfire just waiting to go for lightning to strike."
And pest problems are expected to grow with climate change.
"This is all pointing in the same direction, which means losing your forests," Prof. Smith said.
Drought-induced beetlemania is exactly how the mountain pine beetle came to destroy about 730 million cubic metres of the province's pine forest.
"We had a couple of years of drought [that] impaired trees' capacity to defend themselves over massive areas, which allowed the [mountain pine beetle] population to thrive and build up and spread," Prof. Carroll said.
In 2014, the invasive beetle – which prefers to eat old, dying trees – wiped out a total of 18.8 million hectares of pine forest, according to the province. Much of the pine beetle-killed wood was harvested in salvage efforts and sent to market.
Although the mountain pine beetle population is fading in B.C. – largely because there's no more pine for it to feast on – the insect lives on in the province's Peace Region, and has expanded its range across the Rockies into Alberta, feeding on jack pine, which grows all the way across to the eastern seaboard.
"The problem has changed; it's no less serious," Prof. Carroll said.
Alberta and Saskatchewan have invested money and resources into efforts to slow the spread, he noted, such as harvesting older pine trees to minimize an excess of the beetle's preferred food. "But those efforts are all conducted with the knowledge that it's slowing the spread, not stopping the spread."
In B.C., other voracious insects are already hitting forests. Prof. Carroll noted outbreaks of the mountain pine beetle's close relative, the Douglas-fir beetle, as well as a species called the western spruce budworm – both of which have been causing defoliation, growth loss and mortality in Douglas-fir trees across the southern half of the province.
The spruce beetle is another bug, he said, that's threatening to come down from the Yukon and Alaska – where it's already caused mass tree deaths – and attack British Columbian spruce.
"The mountain pine beetle is just a canary in a coal mine in terms of suggestions and indications that more insects have the potential to become a big issue that weren't big issues in the past," Prof. Carroll said.