Tradeoffs among carbon storage, sequestration, and plant species richness in managed forests of western Oregon, USA

Background/Question/Methods

Concerns about climate change have stirred worldwide interest in managing forests for the uptake and storage of carbon (C). Simultaneously, preserving and enhancing structural, functional, and species diversity in forests remains important. Linkages between carbon and plant diversity arise from a variety of processes and mechanisms operating over different temporal and spatial scales. Thus, forest management aimed to increase carbon storage by maintaining high density forests may negatively affect aspects of conservation and maintenance of biodiversity within stands. Understanding tradeoffs and synergies among C storage and sequestration, and diversity in managed forests is key to achieving these management objectives. We examined the relationships among a suite of thinning treatments (i.e., stands of high, moderate and variable residual densities relative to untreated controls), above-ground C stocks, and understory plant species richness using field experiments replicated seven times along the Coast and western Cascade mountain ranges in Oregon, USA.

Results/Conclusions

Six years following treatments, above-ground C storage declined with residual density. Carbon storage in the high-density (HD) treatment (300 trees per ha) did not differ from the untreated control treatment, and stands in these two treatments stored 33% and 61% more C, respectively, than the moderate density (MD) and variable density (VD) treatments. Differences among treatments were related to reductions in live overstory stocks. For all treatments, C stored in the live overstory > large down wood > snags > stumps > small down wood although over 30% of the total C was stored as large downed wood. Between years 6 and 11 post treatment, overstory C increment tended to decline with residual density although this trend was not statistically significant. In contrast, understory plant species richness was greater in all thinning treatments than in untreated controls. Within stands, relationships between above-ground C and richness varied among stands and were generally weak (R² = 0.04 - 0.26). However, most relationships were negative, suggesting a trade-off between plant species richness and above ground C storage.