Old Growth Forest on Mt Sutro

Some months ago, we got into a discussion with “Jimbo” about old-growth forests, in the comments section of the front page of this website. (Scroll down to see the discussions.) At the time we said: “As for old-growth, I don’t know who said that (except you). We said 100-year-old cloud forest, which is demonstrably true.”

Well, today we want to revisit that statement. Jimbo was on to something. Mt Sutro Cloud Forest certainly does appear to have the characteristics of an old-growth forest. Where this is coming from is an interesting article on the Muir Woods National Monument website about old-growth forests, which we quote in detail below.

Some of the trees are 200 feet tall...

It starts with, “There are four characteristics that slowly develop through time, and together define an old-growth forest.”  It lists the characteristics as: (1) Large live trees; (2) Multi-layered structure; (3) Dead trees; (4) Interdependent communities.

Anyone walking through Sutro Cloud Forest with an open mind and heart will see all these things.

“An old-growth forest is not only a product of a vast amount of time, it is also a result of several other factors, such as adaptation and luck. Even the most highly adapted forest could not withstand repeated disturbances. This makes old-growth very rare in the cycles of nature, but even rarer when humans are included in the picture… These forests provide habitat for hundreds of birds, mammals, amphibians, reptiles, insects and plants. They minimize soil erosion, produce clean water and air and maintain high biological diversity, which is crucial for this planet.”

The eucalyptus that dominates this forest – as redwood does Muir Woods – is clearly beautifully adapted to the location. If it’s chopped down, or the forest gutted as planned, it will completely alter its ecological characteristics. This would seem to put an extra responsibility on UCSF and the Mt Sutro Stewards to protect this treasure from disturbance.

(For more detail, keep reading.)


To go into more detail (the italicized material quotes from the Muir Woods website):

  • “Large Live Trees. The large live trees of an old-growth forest not only stand testimony to the amount of time required to develop into old-growth but also largely determine the structure of the forest… The tallest coastal redwood at Muir Woods is about 258 feet, approximately the height of a six-foot person stacked head to toe 45 times…”

[The tallest trees in Sutro Forest are 200 feet high.]

  • “Multi-layered StructureBesides being a collection of immense trees, Muir Woods is a rich community of other interesting plants. An old-growth forest commonly has three distinct layers: Herbaceous; Understory; Canopy… the herbaceous layer is similar to the carpet, the understory like the furniture, and the leafy canopy similar to the roof. Each of these three layers support a different community of plants…”

[This describes Mt Sutro Cloud Forest precisely. The canopy is eucalyptus; the understory is dominated by ivy and blackberry – both native and Himalayan – providing cover, flowers, fruit and insect-life; and the herbaceous layer is very diverse. All told, there are 93 plant species in the forest.]

Snags are habitat

  • “Dead Trees. The National Park Service used to remove all dead material from this forest to keep it clean and reduce fire threat. However, dead trees are vital for the forest and take many different forms…[ The article explains that fallen trees keep the soil moist by soaking up rainwater, shelter insects, amphibians, and mammals,  replenish the soil by slowly releasing nutrients, and serve as a nursery for young seedlings.] The standing dead  “snags,” are habitat for insects, birds and mammals: “Insects feed on these trees, which in turn give woodpeckers plenty of food to prey on… bats roost under the loose bark and hollows of snags. Hawks, owls and eagles use snags as a perching platforms. “The importance of a tree does not diminish after it has stopped living. It is a common saying here at Muir Woods that only half the life a tree is spent standing, while the other half is spent on the ground.”

[Mt Sutro Forest has a certain percentage of dead trees – like the one in the picture here – in areas where they have not been cleared out.]

  • Interdependent Communities. All the different components of an old-growth forest are dependent on one another. The large live trees depend on the downed logs for water and much of their nutrients… An old-growth forest is also itself very interconnected and through time, many of the plants and animals become reliant on one another… An old-growth forest is more than just large trees, it is an interconnected and diverse community of plants and animals.”

[The forest is full of insects, birds, and animals. The interconnectedness has not been studied since those who manage the forest do not apparently value it.  But it’s obvious:  The birds feed on the berries, and disperse the seeds; the mosses grow on the trees and ground and form a substrate for insects; the trees grab moisture from the fog and maintain a cool damp environment in which ferns and moss can grow. This eco-system has been coming together for a century.]

Note: [Our comments are in square brackets.] Elisions (three dots) indicate material cut for conciseness.

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