How the forest ecosystem shapes its abiotic conditions and thereby itself

In a 2020 publication, Pierre Liancourt and Jiri Dolezal (Czech Academy of Sciences Trebon and University of Tübingen) address the topic of „abiotic facilitation“ at the community level (i.e . biocoenosis). In ecology, facilitation refers either to a positive biotic or abiotic interaction between different species that is beneficial for at least one of the species or to a benefit that occurs due to improved environmental conditions (nutrients or microclimate) experienced by a species.

The vast majority of studies on this topic focuses on positive interactions between species, i. e. where both species benefit from each other. This kind of „+/+“ interaction usually generates noticeable patterns, such as biomass accumulation, higher plant density or higher species diversity. These noticeable patterns lead research on ecological facilitation to focus primarily on environments where such enhancement is most likely and most apparent – for example, areas with sparse plant cover, such as high-montane or arctic areas, or early successional stages. However, this focus impedes to notice the large-scale potential of ecological support and its general importance in nature.

Ecological facilitation through the improvement of abiotic factors plays a significant role in shaping entire biotic communities. An example for this can be found in forests, where the biotic community generally has positive effects on the biophysical properties of its habitat. Largely, these effects occur due to the plant cover and its structure, which makes the abiotic environmental factors, such as microclimate and soil properties, more favourable for some species, i. e. closer to their ecological optimum. Such vegetation-related effects are, for example, reduced light incidence and soil drying rate, increased relative humidity, buffered temperature fluctuations or wind protection. Vegetation properties such as biomass, plant density, species richness and functional diversity are likely to play a decisive role. The interacting elements of the biotic community thus create certain conditions, patterns and structures, which in turn influence the community (feedback effect).

Abiotic support is most noticeable where vegetation is sparse. Inconspicuous and therefore often overlooked, on the other hand, are the facilitation effects in vegetation-rich communities where abiotic conditions are improved over a large area. The extent of such inconspicuous facilitation effects within a closed vegetation becomes most visible when compared to a corresponding, cleared, vegetation-free area. The effects of community-level nurturing effects can be significant: they can partially mitigate the effects of climate change on plant communities or, in the case of abrupt vegetation „collapse“, they can amplify them.

Further and more intensive research on ecological support that goes beyond positive 1:1 interactions (species A favours species B) and striking patterns could greatly improve our understanding of the role of ecological support at large scales. An important step is to understand how ecological support can mitigate the effects of climate change on biodiversity, how it influences species distribution, species community composition, species coexistence and ecosystem function, and interdependencies in species communities. This is because the consequences and context dependence of the interplay between community-wide effects, pairwise and indirect interactions in ecosystems are still largely unknown.

Comment

The review article by Liancourt and Dolezal makes clear how easily widespread but little noticeable ecological effects can be overlooked, although they play an essential role for ecosystems and also for their resilience, for example in climate change. Among other things, this affects our understanding and treatment of forests, whose polydimensionality is still poorly understood and often underestimated. The tree species composition, age and dimensional structure, canopy architecture, tree density, herbaceous layer, soil, (management) history, and overall species inventory of a forest or stand create a unique physiological environment that in turn affects all of the above. The forest as an ecosystem should be understood as a dynamic network of feedback loops and self-regulation. Any intervention in this system has effects; direct, apparent effects that we can see and easily track, but also indirect effects hidden from our eyes and knowledge, the magnitude of which cannot (yet) be readily appreciated. An appeal is therefore also derived from this study to keep interventions in ecosystems as minimal as possible and not to equate the obvious with the whole reality.