The burning of wood is a technique accomplished by artisans, adapting an ancient Japanese method of Shou Sugi Ban to give beauty and endurance to a fence. It is purposely burnt to achieve a deep black finish that contrasts with the wood grain, while also increasing resistance to weather, insects, and rot. Not much else is required in terms of maintenance, making it an even rarer and more textured feel.
https://www.inflamed.eu/shou-sugi-ban-fencing