The Wood Wide Web is often described as a subterranean communication and support system in forests. But how much exchange do the trees really have? Three experts come to a surprising conclusion.
In recent years, the so-called Wood Wide Web has repeatedly made headlines: The idea behind it is that trees in the forest communicate with each other via a network of fine underground fungal threads, supply their seedlings with nutrients and even protect them. In fact, however, the scientific evidence for such claims is poor or they are misrepresented in public, three experts now write in the journal "Nature Ecology
Whispering foliage, groaning branches, whispering leaves: trees have long been able to speak in poetry. But for some time now there has been a lot to be read about the astonishing communication skills of the forest dwellers beyond the realm of poetry. The so-called "Common Mycorrhiza Networks" (CMNs) are said to play a central role in this.
Mycorrhiza is the symbiosis between extremely fine fungal threads and the root tips of almost all land plants: while the plants give their fungal partners easily digestible sugars obtained through photosynthesis, they receive water and salts such as phosphate and nitrate from the fungi in return. In addition to this symbiosis, the networks are also attributed other abilities: Trees could communicate with each other via CMNs, for example by sending warning signals to other, younger trees when they are damaged by insect infestation or other hazards. In addition, they would use the fungal pathways to provide resources to their still weak seedlings.
A team led by mushroom expert Justine Karst from the Canadian University of Alberta has now examined these popular claims. After analyzing hundreds of professional articles and influential studies, the trio came to a sobering conclusion: It still has to be scientifically proven that such networks are widespread in forests or ecologically important. In their evaluation of the most common claims, the biologists find that the results of such field studies vary, also allow other explanations or are too limited to support generalizations. The fact that the networks exist is scientifically proven. However, not enough is known about their structure and functions, the researchers conclude.
For example, they question the claim that adult trees use the networks to pass on nutrients to their offspring and thus promote their growth: A review of 26 studies found that resources from trees can be transferred underground, but that CMNs can use this process not necessarily have an effect and that seedlings usually do not benefit from access to these networks. In fact, most studies reported neutral - i.e. neither positive nor negative - effects.
But where do the claims about the Wood Wide Web come from? On the one hand, Karst and her co-authors observe a bias in the research community when it comes to naming positive effects, although the functional role of CMNs in ecosystems has been disputed for decades. In addition, there is a wave of popular scientific representations that ignore such uncertainties in favor of a spectacular narrative, overinterpret individual research results or quote inaccurately.
"As mycorrhizal researchers who have studied the function of CMNs, we are thrilled that the public is as excited as we are about the many roles fungi play in forests," they write. However, it is important for the public and the scientific community to understand the nature and extent of the evidence supporting the role of mycorrhizal networks in forests.
In addition, the biologists observe a trend towards humanization in scientific reports on the functions of CMNs. In order to study those functions and structures scientifically, they propose a series of different experiments. They conclude: "Let's design new experiments, demand better evidence, think critically about alternative explanations for the results, and be more selective about the claims we make. Otherwise, we risk the Wood Wide Web becoming a fantasy beneath our feet ."
