The Importance of Old-Growth Forests

Mature, old-growth forests are a bastion of biodiversity.

“Protecting forest ecosystems from further degradation is of critical importance owl for a fully functioning biosphere and our own survival. Forests and other natural ecosystems are central to the global crisis of biodiversity loss. Forests are the terrestrial equivalent of coral reefs in terms of the biodiversity they support. A few examples are sufficient to show the critical importance of forests as bastions of biodiversity. Some 5,000 amphibian species (80% of  known amphibian species), 7,500 bird species (75%), and 3,700 mammal species (68%), all depend on forest habitat around the globe (Vié, Hilton-Taylor, and Stuart 2009). The UN panel on biodiversity and ecosystem services (IPBES 2019) reported that a million species are at risk of Imminent extinction.”  

—Bill Stubblefield  

Figure 1. Hawk. Bird populations across North America have fallen by 29%, almost 3 billion birds, since 1970. Over the past decade, continent-wide radar systems have recorded steep declines in migrating birds, Decline of the North American avifauna.  Photo: Bart Bouricious


“The fact is that no species has ever had such wholesale control over everything on earth, living or dead, as we now have. That lays upon us, whether we like it or not, an awesome responsibility.  In our hands now lies not only our own future, but that of all other living creatures with whom we share the earth.”

– David Attenborough, Life On Earth

As much as fifty percent of forest species live on the ground or in the soil. Scientists are gradually unraveling the mysteries of the complex underground community of organisms that cycle carbon, water, and nutrients through mycorrhizal fungal networks and roots. An intricate system has evolved that enables trees to communicate with each other and exchange sugar and minerals between trees of different species and different ages, increasing their chances of survival. The roots of wildflowers, such as this Lady Slipper growing at the base of a hemlock, may tap into the fungal network.


Figure 2: The roots of wildflowers, such as this Lady Slipper growing at the base of a hemlock, may tap into the fungal network. Photo: Nancy Polan

Logging is the largest immediate threat to forests and wildlife in Massachusetts.

Figure 3. Drone view of a clear cut in Muddy Brook Wildlife Conservation Forest managed by the MA Division of Fish and Wildlife. This clear cut is located in the Quabbin watershed, which is the source of drinking water for Boston. Quabbin Reservoir is pictured in the back of the photo. Photo: Christopher Matera



Figure 4. Solar array in Wareham, MA. One million trees will be cut for additional solar installation on 500 acres. A solar farm in Wareham, which has built 300 acres of solar farms in forests, with plans for an additional 500 acres of solar farms.


The IPCC Report, Climate Change 2022: Impacts, Adaptation and Vulnerability states that preserving and restoring forests and other natural systems will increase their resilience to a changing climate and safeguard against biodiversity loss. Logging reduces the climate resiliency of forest ecosystems and reduces biodiversity. Logging removes mature trees, which slows and inhibits natural succession to old-growth habitat

A major Canadian forest study, “Forest degradation drives widespread avian habitat and population declines,” examined the effects of forest loss on many species of migratory birds with breeding grounds in eastern Canada. The Canadian government is restoring thousands of acres of forests that were logged in southeastern Canada. Clear cuts have been replanted, creating vast tree plantations holding younger and less diverse stands than the original primary forests they replaced. Researchers found that bird breeding habitat in the tree plantations was much lower than habitat in neighboring unlogged, unmanaged forests, and that “the amount of area clear-cut was strongly associated with habitat loss for old forest-associated bird species.”

Researchers documented avian breeding habitat loss from 1985 - 2020 and found a high correlation between forest degradation and shrinking population size for 94% of bird species studied.

This study, which examined forests with diverse management histories, showed a direct relationship between: all types of forest management; forest degradation; species loss; and reduced ecosystem integrity. Managed forests that are logged, regardless of reason—sustainability, thinning, habitat restoration, fire suppression, insect control, invasive species—are degraded forests. The greatest decline was among species dependent on mature and old-growth forests. Though the study took place in eastern Canada, many of the birds in the study are common in Massachusetts: American goldfinch, gray catbird, rose-breasted grosbeak, dark-eyed junco, cedar waxwing, ruby-throated hummingbird, red-breasted nuthatch, blue jay, black-capped chickadee, hermit thrush, pileated woodpecker, Northern flicker, and many warblers, birds we see on our forest walks and at our backyard feeders.

Figure 5 Declining populations of species—such as the rose-breasted grosbeak, goldfinch,and house finch—correlates with degraded forest breeding habitat. Photo: Nancy Polan


The Canadian bird study provides strong evidence for radical policy changes.

This study, along with a growing body of research, provides evidence that current forest management practices add to the climate and biodiversity crises. It is critically important to reverse course. Conservation practices that support the logging industry must be replaced with policies that preserve mature and old forests. Globally, we need to develop forest management practices that reduce warming and decrease biodiversity loss.

Over the past century, forest conservation goals have centered on preventing forest conversion–conversion to shopping malls and subdivisions, in order to provide adequate timber resources for future generations. Conservation for the purpose of maintaining timber harvests. For many, the definition of a good working forest is one that is managed “sustainably,” where “sustainability” is measured by maintaining continuous tree cover. The Canadian study found that working forests and replanted forest plantations are degraded forests, with lower biodiversity and increased carbon emissions. Simply maintaining tree cover is not a climate solution. The Canadian study, see Figure 6, found that even when tree cover was maintained, replanting forests was accompanied by massive declines in breeding habitat for the vast majority of songbirds. In other words, forest trees are irreplaceable.