Functional diversity and management mediate carbon storage in small forest fragments

Background/Question/Methods

We currently face increased demand for ecosystem services (ES), yet ES provision is decreasing. This is occurring concurrently with accelerating rates of biodiversity loss, driving ecologists to seek “win-win” solutions for conservation of biodiversity and ES. Improved landscape connectivity - via habitat networks - is increasingly considered a viable way to maintain both biodiversity and ES. The links between connectivity, biodiversity, and ES, however, are uncertain, especially with respect to regulating services such as climate regulation, commonly quantified via landscape level carbon (C) storage. The effects of forest fragmentation on C storage remain largely unknown. This is further complicated by disagreement regarding both the direction and magnitude of the relationship between C storage and biodiversity. We investigated the effects of forest fragmentation (fragment size/connectivity), and local forest management on C storage and biodiversity in the Monteregie, QC. We quantified aboveground C stocks (live/dead trees, woody debris) in 24 small forest fragments of two sizes, and two connectivity levels, using a combination of satellite data, field-based methods, and allometry. We correlated this data with biodiversity, measured as woody plant species richness and functional dispersion (FDis), to determine whether synergies or tradeoffs occur between biodiversity and C stocks.

Results/Conclusions

Functional dispersion was a significant predictor of aboveground carbon stocks, interacting with forest management and connectivity in this fragmented forest system. Both synergies and tradeoffs between biodiversity and C stocks were observed. Unmanaged forest stands stored less C on average than managed, but demonstrated a significant positive relationship between FDis and aboveground C stocks,  corroborating the results of biodiversity-ecosystem function experiments. The slope of this relationship was significantly increased in connected fragments, implying that increasing connectivity may strengthen the relationship between biodiversity and C storage in this region. We found an ~8.9% increase in C for each 0.01 unit increase in FDis (~7% of the total range of FDis across the study system) in unmanaged, connected fragments, compared to ~3.4% in isolated fragments. Managed fragments exhibited a significant negative relationship of similar magnitude, with an ~5.0% decrease in C for each 0.01 unit increase in FDis, demonstrating that anthropogenic influence can alter the link between biodiversity and C in natural systems. Our results emphasize that in a fragmented landscape, all forest fragments are not equal regarding C storage, and by failing to take into account management, connectivity and heterogeneity in functional diversity, we risk over or under-estimation of C stocks at the landscape scale.