Shedding light on the murky need to “let in light” to promote forest biodiversity

“Letting in light” to promote biodiversity was one of the first excuses put forward by the forestry lobby and one that continues to be used and abused today.

The canton of Bern’s GürbeForst AG, for example, claims that: “As forests with a closed canopy tend to be too dark on average for species that require light, the aim is often to bring more light and therefore warmth to the forest floor and add small structures such as piles of branches or stones.”

Let’s be quite clear. The main goal of the professional forestry industry is to produce timber. The industry is much less interested in biodiversity, rarely keeps species inventories and usually fails to actually identify the famous light-loving species it wishes to promote. 

Take the Belpau nature reserve which abuts the capital, Bern. According to the canton’s website, its forests are “flooded with light” and provide “new habitats” for a vague assortments of “amphibians, wild bees and butterflies.”

The Belpau’s forests are light-flooded because they are being intensively logged, largely for biomass. The same thing is happening in nature reserves across Switzerland and indeed Europe.

It comes as little surprise to learn that clearcutting does not benefit biodiversity, as a court in Holland recently ruled.

Swiss forests represent some of the country’s most biodiverse habitats, sheltering over 20,000 animal species and some 130 species of trees and shrubs. While certain woodland species, particularly insects do benefit from more light reaching the forest floor, silvicultural interventions designed to boost “light-loving” species should be targeted, minimal and replicate conditions found in clearings. They should not involve clearcutting several hectares as is increasingly the case, including in nature reserves and on the central Plateau whose deciduous forests are being decimated.

It is also true that piles of stones and branches can help shelter a variety of small mammals, amphibians and insects, but these are just token gestures to provide cover when all cover has been removed. In fact, the piles of branches left behind usually consist of valueless slash and lack the large diameter assortments needed by endangered wood beetles, for example.

Moreover, interventions to let in light also let in heat and wind, resulting in increased stress, disease, windthrow and windsnap. The beech (Fagus sylvatica) is the most common deciduous tree in Switzerland and beech forests are particularly susceptible to drought and sunburn. 

While professional forestry purports to act responsibly in its dealings with other forms of life, the forests which it modifies to varying degrees through logging represent brittle, artificial systems whose internal functioning and networks have been disrupted. Needless to say, radical logging is antithetical to both ecosystem health and biodiversity.

Claiming that forests, especially those in nature reserves, require “intensive management” to boost biodiversity is not just false, it is downright dishonest.

February 2025