Forest Carbon Coalition – Science Synthesis

Why restoration of native forest ecosystems is critical for making the land more resilient to climate change.

The conversion of native forest ecosystems to timber plantations, agricultural lands, and urban development has left rural landscapes more vulnerable to the effects of climate change. Loss of forest cover is a direct cause of increased flooding during wet periods and diminished water supplies during dry months. Clearcuts and deforested areas along streams boost water temperatures and, coupled with applications of fertilizers and herbicides, increase the risk of harmful algae blooms. Tree plantations are far more susceptible to wildfires than the natural forests they’ve replaced because they lack heterogeneity and big trees that help keep wildfires in check. Monoculture tree plantations are also more susceptible to pests and disease that will become more abundant as the climate warms. Restoring native forests will help reverse these trends and make our rural landscapes more resilient to climate change.

Key research on restoration of native forests and climate resiliency:

Zald, H.S., Dunn, C.J., 2018. Severe fire weather and intensive forest management increase fire severity in a multi-ownership landscape. Ecological Applications 28(4): 1068-1080.

Link: https://doi.org/10.1002/eap.1710

Summary: The authors completed an intensive study of the 2013 Douglas Complex fire in southwestern Oregon and concluded that high biomass loads characteristic of native, old growth forests were not a major contributor to fire severity. In contrast, the authors found that intensively managed timber plantations were a significant driver because of their lack of diversity and structure.

Key excerpts:

“Our findings suggest intensive plantation forestry characterized by young forests and spatially homogenized fuels, rather than pre‐fire biomass, were significant drivers of wildfire severity.”
“…mean predicted RdNBR [normalized burn ratio] was higher on private industrial forests (RdNBR 521.85 ± 18.67 [mean ± SE]) vs. BLM forests (398.87 ± 18.23) with a much greater proportion of older forests.”

Lutz, J.A., Furniss, T.J., Johnson, D.J., 2018. Global importance of large diameter trees. Global Ecol Biogeogr. 2018: 1-16.

Link: http://www.columbia.edu/~mu2126/publications_files/Lutz_et_al-2018-Global_Ecology_and_Biogeography.pdf

Summary: Because large-diameter trees constitute roughly half of the mature forest bio-mass worldwide, their dynamics and sensitivities to environmental change represent potentially large controls on global forest carbon cycling. We recommend managing forests for conservation of existing large-diameter trees or those that can soon reach large diameters as a simple way to conserve and potentially enhance ecosystem services.

Key excerpts:

“The relationship between the large-diameter threshold and overall bio- mass (Figure 2a) suggests that forests cannot sequester large amounts of aboveground carbon without large trees…”.
“Large- diameter tree richness in tropical forests suggests more resilience to projected climate warming in two ways. First, absolute large-diameter tree richness was highest in tropical forests, suggesting that the large- diameter tree guild may have different adaptations that will allow at least some species to persist (Musavi et al., 2017). Secondly, the pool of species that can reach large diameters may have been undersampled in the plots used here, implying an even higher level of richness may exist in some forests than captured in these analyses.

Perry, T.D., Jones, J.A., 2016. Summer streamflow deficits from regenerating Douglas-fir forest in the Pacific Northwest, USA. Ecohydrology 10:e1790.

Link: https://andrewsforest.oregonstate.edu/sites/default/files/lter/pubs/pdf/pub4981.pdf

Summary: Using 60-year records of daily streamflow from eight paired basins in the H.J. Andrews and South Umpqua experimental forests the authors found that average daily streamflow in summer in basins with 34-43 year old plantations of Douglas fir was 50% lower than streamflow from reference basins with 150-500 year old forests.

Key excerpts:

“Together, the paired basin and experimental gap results indicate that even‐aged plantations in 8 ha or larger clearcuts are likely to develop summer streamflow deficits…”.
“Long‐term paired‐basin studies extending over six decades revealed that the conversion of mature and old‐growth conifer forests to plantations of native Douglas‐fir produced persistent summer streamflow deficits of 50% relative to reference basins, in plantations aged 25 to 45 years.”
“Widespread transformation of mature and old‐growth forests may contribute to summer water yield declines over large basins and regions around the world, reducing stream habitats and sharpening conflict over uses of water.”