The largest Douglas Fir in Forest Park has a circumference of over 20’ and is estimated to be 176’ tall. It surprised me to learn that it is probably growing faster than any other Douglas Fir in the park.
In 2014, Nature published the results of an amazing study showing that contrary to widely held assumptions, large trees actually grow faster than small trees. In the study, 38 scientists took repeated measurements over time to estimate the mass of over 670,000 individual trees belonging to 403 species in forests all over the world.
This massive data set was then analyzed statistically to show that for almost all species of trees, their rate of growth increases continuously for their entire lives. The study found this to be true for 87% of tree species of all sizes and for 97% of large trees. I emphasize the word “rate” because not only do trees continue to add mass, but the amount of mass they add each year continues to increase. If instead a tree added only the same amount of mass each year, then the rate would be flat. If at some point, a tree began to add less mass each year then the rate of growth would be declining. But the rate is actually increasing, because throughout their lives almost all trees add more mass each year than they did the year before.
We’re all aware of the importance of trees in addressing climate change by sequestering carbon. In my mind, learning that large trees grow faster than smaller trees reinforced the importance of removing invasive plants to help protect the health of the forest. I also began to wonder, especially in terms of carbon capture, if it makes sense to plant new trees under the canopy of the forest. Even if the new trees thrive, we now know that their rate of growth is far less than the existing trees. Why go to all of the effort and expense of planting trees in the forest where they can take resources away from the trees that are growing the fastest? Well, as it turns out there is not a simple answer to that question, and planting new trees does make sense. Why? The rather complicated answer will be the subject of my next blog.