Tsuga heterophylla growing on a stump
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.
Wonderful photo and explanation. I will daydream about the network of mycorrhizal fungi.
Does the western hemlock become infested with the wooly adelgid as the Eastern Hemlocks are???
A stunning photo and wonderful text. Thank you.
I love your write-up
Delightful entry and very interesting and will encourage seeking out these trees. Thanks so much
Lovely writeup. Also one of my favourite trees. When I used to do natural history programs in provincial parks, I would tell young children the tree’s “official” name, and then tell them they could remember heterophylla by substituting the word “higglety-pigglety.” It worked!
What a lovely and personal writeup on this ubiquitous Northwest tree.
Is the western species also a vigorous root-grafter like the eastern species, T. canadensis? Here in Vermont, I’ve seen the cut stumps of young hemlocks healing over, no foliage involved – at least, not from that particular stem.
Loved your photo and very descriptive write-up – not to mention your imagery of a secret vaulted room , I will keep an eye out you when I am in the woods on Vancouver Island. I am a huge fan of stumps and despite the loss of the tree – stumps must have a place in our forest history – although mostly they are ignored.
Nice job…I moved from there to here (Nova Scotia) miss the big trees, and today, the milder weather. Got to go shovel freezing slush now…
careful of the ‘kind of curious’ link, it took me to a browser hijack site and started to download malware.
Tried it twice and got the same result
Beautiful essay; thank you.
Fascinating picture and story told so beautifully!
R Rich, it didn’t flag on my antivirus when I was checking the links yesterday, but I’ve removed the link and accompanying sentence to be sure.
While most western hemlocks may come up on rotted wood inside the canopies of stands that have specific forest floor conditions that cause the species to be restricted in this manner elsewhere within its range it certainly has no problem coming up in quantity throughout a site.
I’ve been told the northernmost natural grove of coast redwoods is effectively not reproducing because its seedlings are being excluded by the faster growing western hemlock seedlings carpeting the forest floor beneath the redwoods. I’ve seen then same thing in my own back yard, where the native hemlocks and the neighbor’s planted coast redwood both generate seedlings that come up in the mulched areas there. Where the two meet the hemlocks push the slower-growing, more delicate baby redwoods aside.
Hemlock adelgids thin out and may perhaps sometimes wear down the western hemlocks here but do not kill them outright as they do the eastern species in their native areas.
“Does the western hemlock become infested with the wooly adelgid as the Eastern Hemlocks are???”
It does, but not so severely – the trees usually survive.
@ Brian Tremback: at a former home of mine there was a row of seven Douglas firs on the property line (the neighbor lady in her nineties remembered when they were planted when she was seventeen). Several had been removed over the years, but their stumps had healed over and were still alive, though without any way to photosynthesize. I asked a forester about the phenomenon and he said they were root grafted to their neighbors.
Brian and Michael,
Thanks for pointing out the way that hemlock stumps (and other trees) will sometimes heal over and continue to grow. I while ago I went on a tour of Merv Wilkinson’s sustainable woodlot on Vancouver Island, BC. My guide pointed out a number of such stumps, and told me that the network of Mycorrhizae was connecting these cut trees to the other trees of the forest, and that the standing trees were essentially sharing their sugars with the cut ones, allowing them to survive.
This method of seedling establishment on dead trunks and stumps is common all around the northern world. It is all about the stable water realtions of the rotted wood as you say, and some avoidance of competition. I detailed this in my masters thesis at University of New Brunswick Biology Dept., but I did field work in Newfoundland (boreal forest).
Tamara- Thank you for this excellent entry. As a botanist that lived in Ketchikan AK for some years I have a special place in my heart and mind for the western hemlock. I’ve since moved back to the lower 48 and miss those magnificent trees… their root systems, and their fungi. Thanks for reminding me of their magnificence. Our eastern Hemlock is suffering the effects of the adelgids, very big trees are starting to crash to the forest floor. Laura