For my Ph.D. dissertation, I studied a unique plant community aptly named the “pygmy forest” that occurs in patches along the coast of Northern California. Plants of the pygmy forest are severely stunted, due to acidic, shallow soil that is extremely low in vital nutrients. In places, these trees remain only head-height, despite being several decades old. When transplanted onto richer soils, however, these trees can grow to full height (to the dismay of gardeners who want ready-made, cute bonsai trees).
For the first chapter of my thesis, I examined how the leaves of pygmy plants function, and I compared them to leaves of same-species plants growing nearby, outside of the pygmy forest. I had hypothesized that the growth of the pygmy plants was so stunted because their leaves weren’t able to photosynthesize quickly. The process of photosynthesis requires enzymes and pigments that take a lot of nutrients to build, so it makes sense that plants on low-nutrient soils would have some difficulty with photosynthesis. However, I found that most pygmy forest plants have similar rates of photosynthesis as non-pygmy forest plants. Instead, pygmy plants often grow fewer leaves: instead of producing many leaves that they don’t have enough nutrients for, they grow a few leaves that they can invest more of their nutrients into. They also grow thicker/tougher leaves, so that their few, high-quality leaves are less likely to be eaten by deer, damaged by fungi, broken by passing animals, or otherwise lost.
For my second chapter, I examined how the pygmy plants deal with water. I knew from prior research that the pygmy forest plants don’t experience much water stress throughout the year (Sholars 1982), and I confirmed this during the 2014 drought. I hypothesized that the pygmy forest plants would be more vulnerable to damage from water stress, because they are already so nutrient stressed. However, I found that different species of plants respond very differently. In two species, Bolander pine and Mendocino cypress, the pygmy plants were just as resistant to water stress as non-pygmy plants of the same species growing within a few miles. In one species, Labrador tea, the pygmy plants were more vulnerable to water stress. Finally, in a fourth species, redwood, the pygmy plants were more resistant to water stress. Thus, it is clear that nutrient limitation and stunted growth can affect how plants resist water stress, but we’re not sure exactly why the species differ in their response. However, you may want to avoid fertilizing redwood trees if you want them to survive drought!
For the third chapter of my thesis, I examined different patches of pygmy forest. Some patches are more stunted, remaining only waist-height, while other patches grow taller and reach over head-height. I hypothesized that fewer plant species would be able to survive in the pygmy forest compared to nearby tall forests, because it is difficult for plants to grow in the pygmy forest. However, I discovered that the patches with the most species were the intermediate sites! The most stunted pygmy forest patches typically had only 3-6 species, and the tall conifer forest patches had 5-8 species, while the pygmy forest patches that were only somewhat stunted (12-20 ft trees) had 6-12 species. In other words, there were some plants that could not survive in the tall forest, and some plants that could not survive in the most stunted patches of pygmy forest, but almost all of the plants I saw in either location could survive in the transition zone between the pygmy forest and the tall forest, where trees are only somewhat stunted. I also saw some interesting patterns in how related plants were to each other: the most stunted sites had the most closely related plants. So, I think it is great that our State Park system preserves both the extremely stunted pygmy forest patches, which are stunning to see in person, as well as the areas where plants are less stunted and the most species can survive.
Overall, Mendocino’s pygmy forest is a great place to study how plants grow and survive while nutrient-limited. If you are passing by the town of Mendocino, I definitely recommend stopping by the pygmy forest! There’s a great place to park and walk on a short boardwalk to see the pygmy forest down Little River Airport Road. There’s also a longer hike in Jug Handle State Natural Reserve where you can walk from the beach and see the transition from beach, to tall conifer forest, to pygmy forest. (As of 2019, parking in both locations was free.)