During some restoration work here, we had three largish Douglas firs limbed and topped for wildlife snags. We didn’t kill them, because the thinking at the time was that live damaged trees remain standing longer to provide wildlife habitat. Ten years on, these guys do, in fact, still have a lot of life left in them. One study1 found that 23% of non-fatally topped Douglas fir (Pseudotsuga menziesii) were still alive 16-18 years later. Raptors can use them for perching, and the thick growth stimulated by cutting the leader makes a wide nesting area. The height and breadth of a tree provides the structural diversity of vertical space and occasionally cavities, but see below.
Dead trees equal higher biological diversity
I would argue that dead trees might be more useful than live snags. Once dead, biological resources in a live tree’s wood, sequestered during its lifetime, become available to microbes, fungi and arthropods. That is a gateway to creating living space for cavity nesting birds, mammals, bees, and other wildlife.
At first, even a dead tree is still hard and intact. Woodpeckers have to wait awhile before they can really tuck in and excavate nest cavities. Also their prey may not be able to get past a live tree’s defenses, which are many.
After defensive chemicals leach from the dead tree, wood-rotting fungi (ubiquitous in Pacific Northwest forests) move in to soften up the wood and begin the recycling process. One of these pioneers is a mushroom called veiled polypore (Cryptoporus volvatus). Fruiting bodies (mushrooms) appeared on the snag above, soon after it died, indicating that the mycelium had already invaded the sap wood.
This fungus is called a veiled polypore because it forms a pouch or envelope over the pore layer where spores are produced. The Latin name is more descriptive: hidden pores, covered by a sac-like membrane. At first look, one might mistake it for a puffball type mushroom (I did).
Bark beetles and many other insects take up residence inside the moist and nutritious interior. They may be eating or parasitizing each other, or just taking advantage of the warm, moist, and protected space and available mushroom food. Beetles carry spores into the bark when they bore into the sap wood of this or other dead and dying trees. Billions more spores are shed and dispersed via air currents.
This fungus colonizes recently dead or almost dead trees, causing sap rot that softens the wood under the bark. That’s the beginning of an explosion of diversity and nutrient recycling: microorganisms, invertebrates, birds, mammals, and others use the resources built by the tree over its lifetime. Some, like molluscs, newts, frogs, and reptiles, take advantage of the spongy, water-retentive rotting wood and physical shade during the dry season. Others forage for insects, eat algae, or feast on abundant carbon in the wood itself. A large log on the ground even attracts nitrogen, an essential plant nutrient in short supply in the soil.
When the wood is soft enough, primary cavity nesters2 begin to chip off bark and make holes. Secondary cavity nesters follow: squirrels, owls, and others that don’t excavate but need the holes for nesting and protection. Cavities are in short supply in modern landscapes and birdhouses do not replace the complexity and richness of large dead trees.
Whether as a standing snag or a log on the ground, dead and partially dead trees provide long lasting ecosystem benefits. Snags and large downed logs rule, obviously! Let’s keep more of them (looking at you Oregon Dept of Forestry).
Monarchs are probably the best ambassadors for conservation. They are popular, great looking, and they need habitat from their wintering forests in Mexico all the way to Canada. Here on the west coast we have our own population that winters in California. Because the midwestern migration route can be as long as 3000 miles, if farmers can be convinced to use farming practices that help monarchs, it helps a ton of other species, over a huge area. This means no Roundup Ready crops, because that means no weeds on the margins of agricultural fields, and that is where the monarchs are. Even better is organic farming with hedgerows, beetle banks, conservation cover, and windbreaks with some evergreen trees. By advocating for uncultivated margins, Aldo Leopold had the formula in the twentieth century.
Monarchs are dependent on milkweed (Asclepias sp.) because their caterpillars only eat milkweed. Adults lay their eggs on milkweed as they make a multi-generational journey from Mexico each year.
As Monarchs head north, they feed on nectar, stopping at night in protective tree canopies. The first and second generations from Mexico will die before the population gets where it’s going. After newly transformed butterflies emerge from chrysalises they continue on their leg of the migration relay. There may be three or four generations of butterflies by the time the population reaches the farthest point in their travels. In the fall, the last generation will travel all the way back south, looking for sustenance along the way. After overwintering as adults, they will head north again. It’s amazing that this works at all!
If you’d like to have a look at some nice milkweed and possibly an egg, caterpillar or monarch, check out the gardens at Winter’s Hill Winery and Vineyard. (That is some butterfly-friendly wine, and so delicious!!)
I recently found these clumps of milkweed on the side of the road:
If no one sprays it before it goes to seed I will collect seed and grow out plants next year. Having planted a few this year, I can say they are a bit slow to get going but once established they thrive on neglect. A seasonally wet ditch in the sun is best. A wet prairie is ideal. That way the monarchs can find them.
While I was photographing these clumps, a honeybee and a western tiger swallowtail butterfly came by.
I have to post this excellent synopsis of what ecosystem services are, and how we affect their functioning – including the definition of “externalities”. The article is from the Vancouver Sun, but applies to anyone.
Next time a flood occurs, think of the cost of prevention as an investment, the disaster costs as a penalty for using our natural capital unwisely…. Not unlike that of the recent bank failures.
Here’s a snippet:
People often talk about “nature’s bounty,” especially during this harvest month. But how much is it really worth?
Well, humanity’s failure to figure out and charge a fair price for Earth’s natural assets costs trillions in the long run, according to a new UN report released today. And Canada’s share of that loss is substantial.
It’s much more than just the obvious forest products, fish catches and that sort of thing. In addition to these — the report calls them provisioning services — it identifies:
– Regulating services such as filtration of pollutants by wetlands, climate regulation through carbon storage, water cycling, pollination and protection from disasters.
– Cultural services such as recreation areas and spiritual and esthetic retreats.
– Supporting services such as soil formation, photosynthesis and nutrient cycling.
A number of factors make it difficult to put a value on these things, let along to collect an appropriate payment from those who use up such resources or who monopolize the benefits. But the numbers at stake are huge.
The report estimates, for example, that 3,000 large companies in the world are responsible for “externalities” — that is, net costs foisted onto the public — of $2 trillion.
These companies got this astounding benefit — seven per cent of their combined revenues, or as much as a third of their profits — by not paying for greenhouse-gas emissions, overuse or pollution of water, air emissions, waste and unsustainable use of fish or timber.
How do they get away with it, year after year and in jurisdiction after jurisdiction? more…