Have you seen the film Jaws? I have seen it more than once, and I’ve regretted that for years now, because it ruined swimming in the ocean for me. I know that sharks are rarely dangerous – a study done in California showed that 1 in 738 million people who go to the beach and swim in the ocean are attacked.

And even though there are fewer and fewer of these endangered creatures in the ocean, fear always swims alongside me. When there are a lot of other people in the water, it’s sort of okay, but if I’m alone, I don’t dare venture any deeper than a few feet. My intellect can run through as many facts as it wants, but my emotions refuse to listen.

The key here is to familiarise yourself with local conditions and know what you are dealing with. Most wild animals, even fearsome predators, prefer to give people a wide berth and do not attack unless threatened. They do not want to risk injuries, which could end up being life- threatening for them, because that could affect their ability to hunt.

They also simply don’t recognise us as food. And if they recognise us as enemies, their instinct is to flee rather than to approach us. The more time you spend out in the forests, the more you will get a feel for the animals that live there, how to act appropriately around them, and when you should – and should not – be concerned.

There are striking parallels between fears and allergies. Allergies arise because we have removed most of the threats that normally attack our immune systems. Medications such as antibiotics and, even more importantly, extreme hygiene mean that in many cases our bodies don’t have to deal with tiny attackers such as viruses, bacteria, or worms, and don’t have to break down the proteins they contain.

But our immune systems must remain constantly on the alert – just in case. And because they mostly have nothing to do, they begin to turn their attention to less dangerous alien entities. This is the reason the pollen of grasses and trees brings on such severe allergic reactions – after all, they are mostly made up of protein.

In Germany, the concentration of pollen from birch trees, a species that is particularly likely to trigger an allergic reaction, is increasing year by year. There are a couple of reasons for this: not only do cities continue to plant birches despite warnings from medical professionals, but these trees also spread easily on their own.

The birch is a pioneer species, which means it is one of the first trees to grow on surplus land. And there is no shortage of this: railroad embankments, the margins of industrial areas, green islands where high- ways intersect, or the roofs of abandoned buildings where birches eke out an existence despite the lack of soil. The wind is their ally, distributing their dust-fine pollen for many miles.

Ragweed is a good example of how far wind-borne pollen can travel. As many as 23 million Americans suffer allergic reactions to ragweed pollen, making it one of the most common plant allergies in the country. Unfortunately, the plant grows in every state but Alaska, and its pollen has been found up to 400 miles (650 kilometers) offshore and up to 2 miles (3.25 kilometers) in the air.

Tree pollen can travel even farther. One study in the southern United States found that pollen from loblolly pines can travel up to 1,800 miles (2,900 kilometers). In years when a particularly large number of trees from any species bloom, there is so much pollen coming from forests that the landscape looks as though it is shrouded in fog. The long airborne journeys their pollen makes help trees avoid inbreeding. Pollen in spring air, therefore, is something completely normal. Pollen allergies, however, are something new.

Are our bodies, now that they don’t have to defend themselves against other dangers, gradually turning against the place we once called home?

And what about our state of mind? Something similar, it appears, is happening in our heads.

From prehistory to the nineteenth century, a walk in the woods really could be a dangerous undertaking. Not so much because of predatory animals, but more because of our fellow human beings.

According to historical reports, as late as the 1870s, robber bands lurked along forest roads in the Eifel, where I live, waiting to attack wagons filled with food being sent from the rich city of Cologne to the starving people in the country. Of course, there were also wolves. They were mainly a threat to livestock and were therefore seen as a deadly danger, for who could survive without milk cows and oxen to pull plows?

Even back then, however, there were not many reports of wolves attacking people. Nevertheless, fairy tales fixed the idea of the big bad wolf in the public imagination, and Europeans took their fears with them when they immigrated to North America.

And today? Forests have become – for the most part – extremely safe places to be. There are no longer any robber bands, and animal attacks (with the exception of domestic dogs and the odd cow or two when you have to cross a pasture) are almost unheard of. Most poisonous snakes and insects or large predators are either in short supply or prefer to avoid people if they can. And yet, many people are afraid when they are out alone in the woods.

Try it for yourself. If you don’t feel a frisson of fear during the day, test yourself with a night hike. Our instincts kick in particularly strongly in the dark and shoot down any attempt reason makes to reassure us that everything is just fine. I admit, even I occasionally feel a touch of fear lurking in the back of my mind (just a touch). Luckily, I have spent enough time in the forest over the years that it never succeeds in gaining the upper hand.

So, I suggest you embark on the same kind of desensitisation programme you might undertake with allergies: nighttime hikes, carefully measured out in small doses, will break down fears while at the same time giving all those senses that are underused during the day a welcome workout.

The Heartbeat of Trees: Embracing our Ancient Bond with Forest and Nature

Excerpted with permission from The Heartbeat of Trees: Embracing our Ancient Bond with Forest and Nature, Peter Wohlleben, translated from the German by Jane Billinghurst, Penguin Viking.