Re-Analysing Forest Biodiversity

The Gribskov Forest in Denmarkj, where this study took place (Image Credit: Malene Thyssen, CC BY-SA 3.0)

Biodiversity response to forest structure and management: Comparing species richness, conservation relevant species and functional diversity as metrics in forest conservation (2019) Lelli et al., Forest Ecology and Management, https://doi.org/10.1016/j.foreco.2018.09.057

The Crux

The classification of biodiversity is something that has become more and more relevant as the term ‘biodiversity’ has worked its way into the public’s vernacular. How we measure biodiversity can vastly influence our perception of it, and whilst we’ve previously looked at spatial interpretations¬†of biodiversity on EcoMass, today I’m examining a paper that looks at interpretations of biodiversity by species groups.

Species richness (how many species are present in a given place) is often the go-to measurement for biodiversity. But it doesn’t always help when trying to conserve an ecosystem. For instance, we may wish to focus on certain types of species which are rare, or that preserve certain ecosystem functions. This paper looks at the differences in the effect of management on biodiversity, depending on which approach to biodiversity you take.

What They Did

The researchers isolated plots in four different types of forest in a large beech forest in Denmark. They looked at 1) forest which had remained unmanaged for over 50 years, 2) forest which had remained unmanaged for less than 50 years, and forests which are still extensively managed, with 3) reasonable levels of structural complexity and 4) very little structural complexity.

The habitats were then measured based on a number of factors, some which accounted for levels of management (presence of older trees or stumps), others which related to more biological factors (soil pH, topography, soil productivity). Their biodiversity was measured among five species groups, vascular plants, lichens, bryophytes, fungi and birds.

To quantify functional diversity among the groups, several functional traits of the species were used. For instance, reproductive strategy among vascular plants, host preference for fungi, or body mass for birds. Alongside species richness and richness of rare species, these were measured against the environmental factors.

Did You Know: Promoting Biodiversity in Agriculture

Silvilculture, or the cultivation of wood, is not stopping anytime soon. Yet forests which are primarily used for silviculture generally show lower biodiversity. As such, there have been movements in different parts of the globe to enable higher levels of heterogeneity among forests. “Near-natural” forestry involves practices like leaving retention trees and deadwood behind to provide valuable habitat to other species. On the agricultural side, agroforestry is on the rise. This occurs when food crops are grown in forests, decreasing the extent of monocultures and the subsequent loss in biodiversity.

What They Found

The species richness of vascular plants actually increased with increasing levels of management, whilst there were no clear trends among the other groups. However, functional divergence for vascular plants actually decreased for many of the traits as management increased, with many habitats becoming more homogenous. There were also certain types of species among the larger groups which showed positive associations with levels of management.

Tinder Mushroom Sponge Tree Fungus

A saproxylic fungal species, here suggested as a potential indicator species for the extent of forest management (Image Credit: Max Pixel, CC0 1.0)

Problems

I always have issues when the take-home message is “it’s complicated”. It’s not the fault of the researchers, especially when they’ve completed such a comprehensive look at what ‘functional diversity’ entails. But I often find it hard to get through a paper that presents so many different possible explanations for so many different scenarios.

So What?

Richness of vascular plants is an easily measured variable often used to calculate biodiversity in forests, but this study indicates it can be a poor indicator of functional diversity, and a poor indicator of the impact of management in general. However uncovering species which show definite associations with levels of management is a powerful tool, as it gives us new indicator species.

Building on this work would yield fantastic results, with tangible applications for forest management groups. It also gives a variety of indicators to build on, and reminds us that the easiest group to monitor is often far from the most useful as an indicator of ecosystem health.

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