Dung Dealer

Fox poop has a surprising impact on tree growth

A gift that keeps on giving.

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Fox dens are a lot more than holes in the ground.

These hidden burrows provide unmatched shelter from the elements — especially for mothers and their young pups.

And while foxes reap the benefits of their underground hideaways, plants growing above get a boost, too.

A new study uncovered just how much foxes shape the forests around them.

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This week, researchers detailed a clear link between tree growth and the presence of fox dens in the journal Ecosphere.

For the study, they collected slices of spruce tree cores in the Hudson Bay Lowlands in northern Canada to get a better look at their rings.

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Some tree samples came from parts of the forest with no fox dens present.

Others came from areas directly around fox dens.

The researchers found that spruces collected near the animal’s burrows grew 55 percent more over their lifetimes than the ones from the regions without dens.

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The effect was similar year-to-year.

Trees near fox dens grew 90 percent more annually compared to their den-less counterparts.

The top plot shows average tree ring growth from 1808 to 2017. Red represents the den trees, while blue is the non-den trees.

Lang et al, Ecosphere 2022

So why are fox dens so good for trees?

It’s likely due to the activities foxes do in and around their dens: They leave behind trails of droppings and scraps from meals, which enrich the soil over time.

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Foxes are known to burrow in the same dens for generations, providing a steady stream of nutrients for decades.

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“On a couple of dens, a cool thing we noticed is that if you go far enough back in time, there are no differences in tree ring growth. Then, all of a sudden, the trees start growing much better. That’s a pretty clear indication that that’s when the foxes arrived.”

-John Markham, study author, in a press release.

Previous research on arctic foxes found that even when dens are abandoned for years at a time, nutrient concentrations in the soil still remain higher than in places with no fox dens.

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So the new study verifies something the ecosystem already knew: Fox poop and scraps are gifts that keep on giving.