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Photos & text

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Photos & texts by Sabina Burrascano is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 2.5 Italy License.
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Are we valuing what is really unique in temperate forest?

Besides hosting most terrestrial plants and animals, forests provide a wide range of services to human societies, ranging from the provision of timber and other forest products, protection from landslides and avalanches in mountain areas, clean water and clean air. Forest also sink and store large amounts of carbon, mostly in wood and soils, contributing to climate change mitigation.

Currently, climate change has a greater relevance in the scientific and political agenda as compared to the ongoing dramatic biodiversity decline. Therefore, global and regional environmental policies often prioritize forest carbon stocks and assume that a forest with a high amount of woody biomass also has a high value for the conservation of biodiversity.

One the one hand, this assumption is particularly convenient when it comes to monitoring, since quantifying the amount of carbon in woody biomass is much less difficult and costly than measuring forest biodiversity. On the other hand, looking at carbon without directly assessing the patterns of forest biodiversity can be dangerous. As a matter of fact, carbon is just the same across pools and ecosystems, whereas forest biodiversity represents a unique and irreplaceable value that differs across forest types and regions.

Recent studies confirm the correlation between carbon stocks and biodiversity at the global scale with regards to vertebrates’ species richness. Still, it is unclear whether the same happens at the fine scales relevant for management and for multiple taxonomic groups.

When managing forests, we should preserve both carbon stocks and biodiversity and, in case not both of them can be jointly maximised, make choices and set priorities. In our paper ‘Trade‐offs between carbon stocks and biodiversity in European temperate forests’, recently published in Global Change Biology, we try to assess whether we can we manage forests to both support biodiversity and maximize the amount of carbon they store.

Such a complex research question should account for information on multiple ecosystem components and requires the joint effort of several research groups bringing together data and expertise. A huge field work, carried out under different research projects, provided information on forest carbon, vascular plants, lichens, bryophytes, saproxylic beetles, wood-inhabiting fungi and birds in more than 352 plots in 22 beech and deciduous oak forest sites across Hungary, France and Italy.

 

fieldwork

Insect, lichen and plant taxonomists during field sampling. Credits: F. Parisi, S. Ravera, S. Burrascano.

These data were used by Francesco Maria Sabatini to model the relationships between forest biodiversity and carbon considering both an aggregated measures of biodiversity (i.e., species richness) and the individual response of individual species.

We found little evidence that above‐ground live carbon and species richness in temperate forests are congruent at the extent of individual forest stands.

brt

Relationship between species richness of different taxonomic groups and above‐ground live carbon modelled through Boosted Regression Trees. Scaled richness equals the fraction of the species pool for a given plot. Ticks on the x‐axis represent above‐ground live carbon data distribution. Values in parenthesis represent the relative importance of aboveground live carbon. Credits: freedownloads.com; openclipart.org.

Considering species richness does not return the whole picture. Our analyses on species composition indicate that, for increasing carbon levels there is a turnover between species adapted to carbon-dense forests ( ‘win-win’ species), which slowly replace open-habitat species (‘trade-off’ species).

We checked whether a specific threshold in forest carbon exists at which most of this turnover occurs. Such a threshold would provide an indication for forest managers on how forest carbon can be manipulated without negative repercussions on biodiversity. However, we found that species and community‐level change points differed between win‐win and trade‐off species, and across taxa and forest types.

 

change-points
Community-level change-points and 90% quantiles along the aboveground live carbon gradient for different taxonomic groups in oak and beech forests. Tick marks on the x-axis represent aboveground live carbon data distribution.

Overall, our results suggest that, at the extent of an individual forest stand, biodiversity and carbon cannot be jointly maximized. Rather, forest planners and managers should carefully evaluate whether to give priority to biodiversity conservation or carbon‐related goals, since maximizing forest carbon stock (e.g., by altering the number and arrangement of trees via thinning or planting) may only benefit some species, while being detrimental to others.

Reconciling biodiversity and carbon objectives requires planning across multiple scales, so to find the optimal arrangement of management types which delivers highest co‐benefits by integrating stand‐level structural and compositional features.

 

Full Reference

Sabatini FM, de Andrade RB, Paillet Y, Ódor P, Bouget C, Campagnaro T, Gosselin F, Janssen P, Mattioli W, Nascimbene J, Sitzia T, Kuemmerle T, Burrascano S, 2018. Trade‐offs between carbon stocks and biodiversity in European temperate forests. GLOBAL CHANGE BIOLOGY. n\a, 1-13. DOI: 10.1111/gcb.14503

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