I will never forget my first encounter with the Big Trees.
It was early afternoon of November 5, 2011. The forest was quiet and peaceful, covered in an ankle-deep blanket of fresh snow. We were at 1,800 metres altitude and it was freezing. We were slowly making our way through the forest – there were nearly 20 of us, snow was deeper in some places, with some icy logs laying across the path here and there. Snow, however, made it very easy to spot the fiery orange trunk – it would have been very hard to miss it though, even under non-snowy circumstances. After 3-hour drive and an hour hike, there it was: incredibly thick, fire-scarred stem with snow powdered crown so tall that you can get light-headed just from looking at it. My first Giant sequoia. Further along the path we saw a gigantic trunk of a tree that fell during a storm some 150 years ago, and despite losing the reddishness of the bark, it didn’t seem to be affected by decomposition at all. Finally, we came across three (relatively) smaller sequoias growing very close to each other, in a neat row, tall and slender. The ground around the first tree was littered with tiny sequoia cones; I picked one up and brought it home. It still smells like that forest on a snowy day. And vanilla!
OK, so, ahem, ecology! This emotional meeting with the largest trees in the world (not the tallest though – see next post) occurred at the Placer County Big Trees Grove during the field trip with my Plant Ecology class. It is the northernmost sequoia grove in California harbouring only six giant trees within old-growth forest of various conifers such as Ponderosa and Sugar pines, Incense cedar, Douglas and White firs – the usual companions of Giant sequoias.
Giant sequoia Sequoiadendron giganteum, sometimes also known as Sierra redwood, are the biggest trees by volume and are among some of the oldest, as some specimens are about 3,000 and up to 3,500 years old. Sequoias are endemic to California and are not found anywhere else in the world. They grow in groves with moist swales or streams high up in Sierra Nevada mountains and are part of lower montane mixed-conifer forest communities. Moisture is highly seasonal, however, as most of the precipitation falls in winter months. Trees also have to withstand temperature extremes: hot summers and cold winters are common in these areas.
As summers tend to be dry and hot in the western Sierra Nevada, forest fires are a common disturbance in sequoia groves – on the bases of many adult trees there are large fire scars known as “cat faces” (honestly don’t know why they are called that, couldn’t see any similarity!) While adult trees are robust enough with extremely thick bark (insulation up to a 1 m thick) to withstand even large forest burning, fires predominantly are surface and low-intensity, killing the understory but not affecting the canopies of the mature trees. Sequoias are highly-adapted to fire as they have lived with it for tens and hundreds of thousands of years. They require fire for natural regeneration as only post-fire conditions are suitable for seedling establishment: 1) sequoia cones are serotinous – the trigger for seed release is the death of the branch (and fire can be one of the causes of this); 2) fire clears the understory and prepares mineral soil bed required by seedlings; 3) it also reduces competition from other species. Later on I will write a separate post on fire ecology in Sierra Nevada because it’s very interesting, right, so I’m not going to give too many spoilers now. Let’s just say that sequoia regeneration has been severely impeded throughout the most of the 20th century due to very effective fire suppression programmes run by US Forest Service. However, since 1960’s when ecologists started to realize the role of fire in seedling establishment, prescribed burning has been carefully carried out in national and state parks, where most sequoia groves are located.
Surprisingly, about 65 percent of remaining sequoias are old-growth trees, meaning that only a third of the trees have been cut down since the arrival of Euro-Americans to California. The reason for this is the fact that the wood of sequoia turned out to be very brittle and the tree wouldn’t simply stay in one piece as coastal redwoods do. For loggers such wood was too much work and simply economically unviable. The groves, however, are scarred by the activities of ignorant 19th century people: from passage ways cut through the trees to debarking of entire trunks to making dance floors on the stumps. While logging is no longer an issue, uncontrolled fires and atmospheric pollution (ozone!) are among the greatest threats to these ancient giants, something that needs to be addressed seriously and with urgency in order to preserve these great natural monuments for future generations.
Next up, Coastal redwoods!
- Forest Giant by David Quammen from ‘National Geographic’ December, 2012 — beautiful pictures and interesting text about sequoias.