Wandering through UBC Botanical Garden’s British Columbia Rainforest Garden on a foggy morning, I was struck by this western hemlock rising out of the mist. Tsuga heterophylla is one of the most common and economically important trees in my “neck of the woods”, and I am pleasantly surprised to be the first to write a Botany Photo of the Day entry for this beautiful species.
Western hemlock is one of my favourite trees, and I am perpetually amazed at the roots that I see in the forests nearby; growing sometimes above my head, barely touching the soil, or growing horizontally for many meters before morphing into their vertical trunks. Sometimes I imagine that I will find a massive Tsuga heterophylla, growing over what once was an old growth Douglas fir (Pseudotsuga menziesii) stump that has long since decayed, leaving a vaulted room that I can hide in, daydreaming away the afternoon. I have yet to find the hemlock room of my dreams, though many have come close; perhaps the three saplings in this photo will form a magical space that my great, great, great grandchildren will one day explore and marvel at.
West Coast forests are peppered with western hemlocks growing out of stumps, and it is next to impossible to see these without being deeply moved by thoughts of decay, rebirth, and the inter-connectedness of all life. Intellectually, I know that my survival depends on the life around me–the plants, insects, animals, and other people–but this interdependence is made tangible by the western hemlock, which relies on decaying coniferous wood for the establishment of 97% of its seedlings. Tsuga heterophylla seeds are tiny and light, and they cannot penetrate the dense carpets of moss that line the soil in the shady and wet environments that Tsuga heterophylla calls home. Rotting tree stumps and downed wood, however, create the perfect environment for the tender western hemlock seedling, remaining moist even during the driest summer months. These stumps and logs are so important to the survival and regeneration of many temperate rainforest plant species that they are often called nurse logs, and contain rich communities of detritivores, mycorrhizal fungi and nitrogen-fixing bacteria that supply nutrients to many types of plants. The Kind of Curious blog (link removed pending a check for security) has a wonderful post showing nurse logs moving through the cycle of falling, decaying, being colonized by moss and seedlings, hosting growing trees, and finally falling to become the next generation of “nurses”.
Tsuga heterophylla is one of the most common trees in North American western rainforests. It can be quickly identified by its drooping leader and feathery foliage. A closer look will reveal needles of two different sizes (hetero = “different”, phylla = “leaved”) alternating along the twig. The round-tipped needles are arranged in flat sprays and are yellow-green above with two white bands below. Tsuga mertensiana, or mountain hemlock, is very similar, but has its needles arranged radially around the twig. Tsuga heterophylla is one of the most shade-tolerant tree species in its range. It also has a very dense canopy, generating so much shade that few plants are able to grow on the forest floor below it. Below the bare ground, however, a dense network of mycorrhizal fungi link the roots of western hemlock to other trees and plants growing nearby. The UBC Fungi from Mycorrhizal Western Hemlock database (now offline) listed 30 different species of fungi that form mycorrhizal associations with Tsuga heterophylla. Above-ground and below-ground, western hemlock teaches us that our forests are intricately connected, through both time and space.