Forests with dead wood have 23% more biodiversity

Trees fallen in the forest and in full decomposition are not very popular among society. We tend to think that they are a source of pests, that they indicate neglect or that they will cause a fire. The reality is more complex than that and we can be surprised. Research led by CREAF and the Autonomous University of Barcelona (UAB) has analyzed among 10 years the pine forests of Catalonia affected by episodes of tree mortality and reveals that the dead wood generated is more varied and therefore also harbors greater biodiversity. Specifically, stand forests affected by mortality have 83% more dead wood, with more fallen or standing dead trees, and have 23% more different types of dead wood. The key point is in the diversity of habitats offered by these trees which are the food, den or hiding place for many species of fauna and flora. Examples are woodpeckers, the mushroom Phenillus robustus or the threatened beetle Rosalia alpina at common beech forests. In addition, forests with dead wood also have a more complex structure and this makes the forest more resistant to disturbances.

“When trees die due to drought, the deadwood they leave behind can become a lifesaver for diverse biodiversity. To understand this, we visited 20 Scots pine forests that had suffered from drought-related tree deaths around a decade ago. What we found was truly interesting: several biodiversity proxies (e.g., deadwood and microhabitats) now dominating in these forests. Over time, nature had begun to nurture life in these seemingly lifeless places. A quiet remarkable transformation indeed. It’s a gentle reminder to us that, if given enough time, nature can find its way to heal and renew”, explains Faqrul Islam, CREAF’s researcher and first author of the research. 

Where can we find this valuable dead wood? The study, published in Forest Ecology and Management, points out that the most humid localities, such as Pyrenees regions, are the ones that have the higher dead wood and it is more diverse, but this situation is short-lived, since the humidity favors that it decomposes very quickly. And this is a complicated situation: if it is not generated anew at the same speed, the generated microhabitats will disappear.

On the other hand, the decomposition is slower in cold places, or drier places such as most Mediterranean locations, where, despite having less amount of dead wood, it decomposes little by little and offers its benefits for a longer time. So, the fauna and flora that depend on it, and that often cannot live in other places, will remain active for even more months or years. 

"When we talk about disturbances in ecosystems, we tend to bring a basically anthropocentric view. We think about how our economy or our well-being is affected, or how the emotional bond we have with these ecosystems is damaged. On the other hand, for ecosystems these "disasters" are often part of their dynamics and are an opportunity to create new habitats. The problem arises when humans increase the intensity or frequency of these disturbances", explains Francisco Lloret, CREAF and UAB researcher. This is demonstrated by this research, which has analyzed the dead wood that was generated, precisely, as a result of the great drought of 2012 in Catalonia and highlights that it has been an opportunity for many of the affected forests, because thanks to the forest death it has appeared to them more dead wood (and biodiversity). 

"Obviously, this does not mean that the recurrence of drought episodes is positive. What our results show is that in some cases it can be interesting to keep the dead wood and retain some weakened trees to promote this heterogeneity in the structure of the forest and its biodiversity, bearing in mind that this process will have different speeds depending on the local climate", adds Josep Maria Espelta, also CREAF researcher and author of the article.