By João M. Cordeiro Pereira
Imagine walking through a primeval forest – towering trees with gnarled branches, thick undergrowth, and chaotic piles of fallen branches and logs. It would also be bursting with life, from the mats of moss and lichens covering logs, to the birdsong echoing across the canopy, or the insects of all sizes buzzing around on a hot day.
Primeval forests like this are a rare sight in today’s Europe. But this is changing as ever more forests are set aside from active management, allowing nature to take the reins. We would expect to see an increase in biodiversity within these “rewilded” forests, but is that really true? This is one of the key questions the WILDCARD project is asking, and answering it will be the main goal of my research for the next couple of years. What I can already tell you is that the answer will not be as straightforward as it may seem.
Forests change over time – and so does their wildlife
Following a large disturbance or a clearing, forests will go through a series of development stages, which vary in many aspects: most obviously tree height, but also the tree species present, the vegetation layers or the deadwood volume. Many forest organisms rely on a specific combination of those features, and thus thrive only in forests at specific development stages. For example, butterfly species (such as the silver-washed fritillary, Argynnis paphia, pictured below) need sunny clearings with young vegetation for their larvae and flowers for nectar. The three-toed woodpecker (Picoides tridactylus, pictured below) and the white-backed woodpecker (Dendrocopos leucotos) instead prefer old forests with decaying trees, which they can use for nesting and foraging.
This means letting forests develop into old age will probably not help all species – rather those adapted to older, undisturbed forests. Since traditional forestry often removes deadwood and harvests trees before they reach full maturity, these old-forest specialists are often the most threatened – and the ones most likely to benefit when we as humans step back. This is why these species will be in the center of my analyses.
Counting species is not enough
And how should biodiversity be measured? At the scale of individual forest reserves or research plots, simply measuring the number of species (the species richness) can be misleading. Within some species-rich groups, such as plants or ground beetles, most species are either generalists (using various habitat types) or depend on open habitats. Thus, over time, unmanaged forests may witness no change in species richness or even a decline, as the canopy closes up. However, this can obscure that, in fact, old-forest species of high conservation value may be recovering. That is why, in my analyses I will focus on which species appear (the community composition), rather than how many, as time goes on after management has stopped.
The hidden role of legacies and the landscape
Some species struggle to return even after a forest recovers. Why? Let us take the example of the blue ground beetle (Carabus intricatus, pictured below). This a large-bodied, flightless species, that relies on a stable forest habitat. If its environment changes, it has a limited ability to disperse in search of new habitat. If this species’ habitat in a forest patch was degraded in the past, and if this patch was too isolated from other areas with good habitat, this may have led to a local extinction of the beetle. The species would then have trouble returning, even if conditions improved. This means today’s biodiversity is not just the result of current management or the absence of it – it is also shaped by past events and how well-connected forest habitats are.
What is next?
My aim is to identify more clearly which components of forest biodiversity profit from non-intervention – and which elements may be the “blind spots” of this approach. To do this, I am working with a large amount of biodiversity data, contributed both by WILDCARD partners and external institutions (mostly in the EuFoRIa network). This data spans across multiple countries, forest types and taxonomic groups, and offers a unique opportunity to answer these questions. However, it also poses unique challenges – the data is very heterogeneous and often collected using different methodological approaches. Right now, I am working on bringing all datasets together, documenting and harmonizing them (a big job in itself!), before embarking on statistical analyses. Despite the challenges, I cannot help but feel excited to discover the stories hiding in these forests and share what I learn along the way.