A few Thoughts About Snags Part I

Biological richness of snags and logs

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.

Recent heat waves and droughts have hastened death for some trees.

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).

Up Next: Part II – Structural Diversity

Notes

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Truffle, Spider, Lizard

It’s hard to get a lot of “work” done because I find so many things that necessitate a trip to the bookshelf to look at one field guide or another. One day earlier this spring I was raking leaves to mulch some plants we put in for butterflies, and I found three interesting things:

Truffle of one of many species of fungi associated with Oregon white oak

1. A truffle. Raking is one method to find truffles. I uncovered this one under an oak as I raked up leaves.

Truffles are the fruiting bodies of fungi, found in the layer of duff on the forest floor, or just below the surface. They are related to mushrooms, but have evolved a different strategy for dispersal. They form underground. When their spores are ripe, truffles give off an enticing aroma which signals to squirrels and rodents that they are ready to eat and the animals dig them up. The spores pass through their digestive tracts intact and are spread around in their feces.

All truffle-producing fungi participate in a mutually beneficial mycorrhizal (literally fungus-root, from Greek) relationship with plants. This is essential for plants’ survival. The fungus is composed of threads, or hyphae that form a sheath around, and in some cases penetrate, the cells of tree roots. The hyphal threads provide a large surface area and extensive system for gathering nutrients and water which are exchanged with the plant for carbon. They also protect plants from pathogens.

One study found 40 species of fungi associated with Oregon white oak roots, 18 of which are truffles. Researchers hypothesize that truffle spores spread by rodents make it possible for oak seedlings to stay alive after they germinated far from its source of fungi around the parent plant (more info here http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=eng&journal=cjb&volume=87&year=0&issue=9&msno=b09-044)

In Oregon, there is a buzz about truffles because there are two or three native species that some consider to be as good as the expensive European delicacies. Unfortunately the one I found is not one of these. The glamorous three species naturally associate with younger Doug firs – in Christmas tree plantations and tree farms. The catch is that unless you harvest them when they are ripe, their culinary value is low (people without specialized knowledge dig up the resource and disturb the fungal threads, thus potentially destroying the resource). The solution to finding ripe ones and leaving the rest to mature is to use an animal with a better nose than you have. Training dogs to hunt truffles is of interest currently, and you can see one in action here: http://www.oregonblacktruffles.com/zoe_trufflehound.html

The truffle info above is contained in either a great new Field Guide to North American Truffles, by Matt Trappe, Frank Evans and James Trappe, or the North American Truffling Society website http://www.natruffling.org/ where mycologists have provided a rich trove of information and links.

Wolf spider with egg sac

2. This wolf spider got scooped up in the oak leaves and it stood out because of the blue egg sac it was carrying around. These spiders don’t have webs. The babies climb on the mother’s back after hatching and stay there until they molt. The spider is quite small – less than 1/2 inch, and the egg sac is almost as large. Notice the long legs to get around in the grass more easily. I was able to locate a wonderfully helpful website, http://www.spideridentification.org where anyone can send photos of spiders for i.d. and get great information from generous and friendly experts. Boy, I love the internet. Even if spiders give you the creeps, this is really an entertaining site! My submission got a quick response with the following information:

“I actually believe this to be of the Pardosa genus, rather. Although the two genera, Pardosa and Pirata, are very similar, the carapace design of Pirata is pretty unique and I don’t think it matches this mama’s. There are nearly 100 species of Pardosa in North America and they are all very similar to one another so, as Eric said, one really needs a microscope to tell the species apart.

Some life history: Spiders of the genus Pardosa are small to medium-sized. Because of their relatively long, slender legs, they are sometimes called “thin-legged wolf spiders”. The body is carried high, and this helps them to pursue prey in open, often grassy or stony ground. Many are characteristic of marshes and fields, tundra and talus, and open conifer forests. The egg sacs of these spiders are distinctively pill-shaped and often bluish or greenish. The total body length (without legs) of these spiders ranges from 3.8-10.7mm. Pardosa is one of the largest of spider genera, comprising an estimated 450 species around the world. None of those species have medically significant venom.

P.S. Great images, Gopher!

->Lady Arachnophile”

Northern alligator lizard in oak savanna

3. A Northern Alligator Lizard. Along with a more colorful Oregon alligator lizard, these are one of our reptile residents.