Bark beetle makes positive contribution to forest development

Šumava, photo: Miloš Turek

The tiny pest known as the bark beetle, which has repeatedly infested coniferous forests at the country’s Šumava National Park, has sparked a number of controversies over the past decades, on whether to chop the infested trees down or let the forest deal with the outbreak without human intervention. A recent survey carried out by Czech scientists, published in the prestigious Journal of Applied Ecology strongly suggests that the forest is able to deal with the situation on its own.

Tree infested by bark beetle,  photo: L. Shyamal,  CC 3.0
I spoke to Martin Starý, the deputy head of the Šumava National Park, who is one of the authors of the study:

“The main focus of the survey was to evaluate regeneration dynamics in the upper zones of the national parks at the Czech-Bavarian border between the Šumava national park and the Bavarian Forest national park. The main focus was to evaluate the dynamics of regeneration of the upper tree canopy and to evaluate the reaction of the regeneration and its structure.

“The assessment combines the data from both sides with the data collected during the inventories over the past fifteen years. We have evaluated the forest regeneration in three steps – four years, ten year and fifteen years after the canopy die-out.”

So what are the main outcomes of your assessment?

“We found out that after 15 years the density of natural regeneration is surprisingly very high. Already four years after the die-out of the canopy the density is almost twice as high. So the regeneration is surprisingly very fast, even in areas over 1,100 metres above the sea-level.

“We can say that once it occurs, the bark beetle promotes better structure and higher biodiversity of the forest.”

Did the composition of trees in the forest change after the bark beetle calamity?

“Surprisingly we found out that the so-called pioneer tree species such as mountain ash, willow or birch, are in fact not that powerful and not that important for the forest regeneration. It is quite surprising for us that at this elevation these species don’t influence the structure of the forest these as they do in lower elevations.

“The other thing is the proportion of the original regeneration, which has been here already before the tree-tops started to die. Even when we look at the forest and we have the impression that we are looking at a new generation of a forest, in fact the continuity of the regeneration hasn’t stopped. Around thirty percent of the regenerated forest has already been here, so the process of the forest growth has actually never stopped.”

So while you see the dead canopy, there are live trees underneath...

“They are already there. We are speaking about something we call a seed bank which is in the soil. These seeds are able to start to grow after several years but we have found out that the growth dynamics of the Norway spruce is slightly different. What this three needs is a base which survives under the canopy and which makes a fundament for the regeneration of the adult trees.

Photo: Martina Schneibergová
Would you say that the results of your study are proof that a natural regeneration is the most effective way of managing a forest in the national park?

“Definitely. This study confirmed our previous findings. We have focused on sites with no management but previous studies have shown that areas managed by people have a completely different scenario of regeneration. Once you transport dead wood, once you tread on the soil - you have to keep in mind that the soils are very thin and very sensitive to erosion and movement of heavy vehicles – the pioneer species have much more influence, their growth is denser and it takes much longer to reach the natural structure of a forest.”

“So I would say passive management brings us better results concerning structure of the forest and it happens much faster.”

And I guess that the method of leaving the forest without human intervention is also cheaper than planting a new one…

“The forest regeneration is surprisingly very fast, even in areas over 1,100 metres above the sea-level.”

“Of course management is expensive. If we want to plant the trees we also have to look after them for some time, and this is of course very expensive. So not only the planting of the trees is expensive but also the management of these planted trees.”

Would you say that a bark beetle calamity is actually useful to a forest in any way? Does it perhaps serve as an accelerator of changes in a forest?

“When we speak about the results of our study we can say that the bark beetle supports the natural dynamics of the Norway spruce. If we take into account other studies dealing with biodiversity and other species, such as beetles, fungi or flowers, it is clear that the bark beetle promotes biodiversity.

“It is not a pest, it is not a calamity, in fact we call the bark beetles the biodiversity engineers because the number of species that profit from the bark beetle outbreak is much higher than the number species that don’t. So the number of the winners is higher than the number of the losers. So yes, we can say that once it occurs, the bark beetle promotes better structure of the forest and higher biodiversity.”

Šumava,  photo: Miloš Turek
And finally, will the new findings change your approach to the management of the Sumava national park?

“Not really. We have already started to promote the natural processes. But we as the national park administration are also responsible for the planting of the trees, and the study confirmed that it doesn’t make sense to plant the trees at high elevations, even if we worry about the next generation and its composition. So yes, we are trying to reduce planting under our management.”