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Scientists announce importance of the world’s primary forests and large, old trees in climate regulation and biodiversity conservation

primary forestPrimary (unlogged) forests and large, old trees provide high biodiversity and carbon value benefits

Dominick A. DellaSala and William R. Moomaw

Summary: Primary (unlogged) forests and large old, trees (live and dead) provide multiple benefits that forestall biodiversity and climate emergencies. They have high conservation value if allowed to achieve their ecological potential to support superior biodiversity, carbon storage and ecosystem benefits.


  • Protection of intact forests of older and middle-aged trees that have the potential to become older forests, host a wider range of biological diversity from plants and animals to ferns, fungi, lichens, invertebrates and habitat for diverse wildlife. They also store more carbon than do logged forests (1, 2) contributing disproportionately to cost-effective CO2 mitigation required to avoid a climate catastrophe (3).
  • The replacement of older diverse forests with younger less diverse production forests has significantly reduced biodiversity. These forests provide more ecosystem services than managed forests including productive soils, nutrient cycling, pollination, pollution mitigation, water purification, oxygen production, climate regulation, recreation, and hunting/fishing opportunities.
  • Primary forests store 30-60% more carbon than logged forests and up to half of the carbon stored in an older multiage forest is represented by the largest (oldest) 1% of trees (4, 5).


  • Size and age of a tree increase over time accumulating unique features that provide habitats such as large internal cavities and canopy structures not present in younger trees.
  • Large old trees are among the most massive organisms on Earth. They are keystone and bio-cultural elements of our natural inheritance, and are declining worldwide due to deforestation and forest degradation (6).
  • Large, old trees provide nutrients and increased soil carbon; are associated with more plant varieties; play critical roles in hydrological cycles, and are “blueprints” for restoration (5,6).
  • Large, old trees store a disproportionate amount of carbon over centuries with larger leaf surface area for CO2 absorption, and massive carbon storing tree trunks and roots (4,7).
  • Large trees provide stable microclimates; less soil desiccation and lower temperatures (8).
  • Large trees are nature’s “water towers” and the planets “lungs” (4,5,6)
  • Mycorrhiza soil fungal networks become more connected and carbon rich as forests mature.


  1. Brandt, P et al 2014. Multifunctionality and biodiversity: ecosystem services in temperate rainforests of the Pacific Northwest. Biol Conserv. 169:362-371.
  2. Mackey B, et al 2014. Policy options for the world’s primary forests in multilateral environmental agreements. Conservation Letters 8:139-147.
  3. Griscom, B W et al 2017. Natural climate solutions. PNAS 114:11645-11650.
  4. Mackey, B 2014. Counting trees, carbon, and climate change. The Royal Statistical Society:19-23.
  5. Lutz, J A et al 2018. Global importance of large diameter trees. Global Ecol Biogeogr:1-16.
  6. Lindenmayer, D L et al 2012. Global decline in large trees. Science 338:1305-1306. doi 10.1126/science.1231070
  7. Keith, H et al 2009. Reevaluation of forest biomass carbon stocks and lessons from the world’s most carbon-dense forests. PNAS:pnas.org_cgi_doi_10.1073_pnas.0901970106.
  8. Frey, S J K et al 2016. Spatial models reveal the microclimatic buffering capacity of old-growth forests. Sci Adv 2016:e1501392. 9 pp. doi: 10.1126/sciadv.1501392

About the authors

Dominick Della Sala is President and Chief Scientist of the Geos Institute in Ashland Oregon. He is Editor and prime author of “Temperate and Boreal Rainforests of the World: Ecology & Conservation”, Co-editor “The World’s Biomes” (Elsevier, in press) and has produced over 200 additional books and research articles on forests, biodiversity and climate change.

William R. Moomaw is Professor Emeritus at Tufts University, a climate scientist and five-time IPCC lead author, and was coordinating lead author of the Special Report on Renewable Energy for Climate Mitigation (including biological systems). He has published research articles on Proforestation management to increase forest carbon storage and additional papers on the role of forests and wetlands in the carbon cycle. He is a co-author of the World Scientists’ Warning of a Climate Emergency that was signed by over 11,000 scientists in 2019. He also chairs the board of directors of the Woods Hole Research Center, a leading climate, land and carbon research institute.

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