When people talked of removing logs, slash, etc from the watershed during the tour of projects, my gut reaction was that's not right: biomass is biological wealth, removing it deprives the watershed of nutrients, already deprived from past logging, and at some point we must stop taking away & start putting back, or we'll impoverish it. I figured I better have more than a gut feeling before raising the issue, so I did some research and found it's considerably more significant than I had imagined.
Here is a smattering of quotes.
Dead trees (snags) are the life of the forest because they house many more creatures than live ones.
The Forest Service acknowledges that "Wildlife and fish need dead, hollow, or fallen trees for food and family homes. Nationwide over 149 species of birds, 73 species of mammals, 93 species of amphibians and reptiles, and nearly all fish use downed trees for food, nesting, or shelter. Only 31 bird species can make their own nest cavities in trees. Another 54 species of birds and other animals also use these holes."
Rotting logs are critical to the survival of Salamanders.
The total biomass of the Red Backed Salamander may equal or exceed that of birds and mammals in hardwood forests[!]. Decreased leaf litter, removal of coarse woody debris, exposure to full sunlight, and the resulting decrease in ground level humidity can be detrimental to these important vertebrates.
Juvenile salmonid abundance is often directly related to the amount of large woody debris in a stream. Woody debris in upstream reaches routes sediment and organic debris; the loss of large woody debris in these upstream reaches may result in excessive sediment transport into salmonid habitat.
Overland sediment movement is inversely proportional to obstructions (downed vegetation) on the hillside.
Coarse woody debris (snags, fallen logs, large branches) plays a key role in soil stability, nutrient cycling, moisture retention, and habitat. Coarse woody debris that falls across the hill slope acts as a barrier and traps soil along the uphill side. Plants in turn take root and act to further stabilize this new soil. Logs on the forest floor act like a slow release vitamin supplement, making nutrients available for new plant growth. Leaves and plant material falling from the canopy, along with nutrients captured in rain, accumulate on the fallen logs and are held until another living organism captures them. Bacteria work to decompose a fallen log while producing nitrogen. The decaying log is also an important source of moisture. Even when the surrounding soil and duff are dry, the sponge-like decaying log will be moist and can support seedlings.
Accumulations of debris in a stream creates gradual steps, gravel bars and pools. These are important structural elements which both disperse stream energy and create fish habitat. They also provide a key nutrient source by allowing up to 70% of the litterfall to be retained and decomposed by stream organisms.
One of the best sources is the book The Hidden Forest: biography of an ecosystem, by Jon Luoma, which describes the results of research at Andrews Experimental Forest and the Long-Term Ecological Research Program (US Forest Service). Here are some excerpts.
Virtually everybody believed rotting logs were trash - wood fiber that had gone to waste. In retrospect, it's incredible that we could have been that stupid. The tree that's green and standing up is the one they should have called 'dead'. The tree down on the ground is the one that's _really_ alive. Only about 5% of a live tree might be living cells, but as much as 20% of the weight of a rotting log can be living tissue. Termite guts are filled with nitrogen-fixing bacteria.
Logs play an especially significant role when the forest must rebound from disturbances. We came to believe that logs were the focus of recovery in the forest. Old-growth forests are resilient in ways that younger forests are not. Logs are supersponges. They can accumulate enormous volumes of water and can retain it even after an intense fire at the peak of a summer drought. In one acre they measured 219 tons of down logs plus 47 tons of standing snags. [more rotting matter could help buffer the surges Sausal has been experiencing]
A lot of people have assumed that there's always enough nutrients in the deep layers of the soil to take care of trees forever. But now we're coming around to the general conclusion that the vast percentage of nutrients that exist in the forest ecosystem are in fact recycled - that the roots that go down deeply are mainly going down to tap water sources. But it's the soils at the top, those that are almost entirely biological in origin, that contain most of the nutrients used by the system.
Researchers determined that virtually all of the nutrients that entered the forest remained bound up in the ecosystem, continually recycled and retained by living plants and animals. After the researchers had one of the valleys clear-cut, nutrients promptly began to surge out of the stream that drained the valley: nitrate loss alone increased sixtyfold. [I wonder if our watershed is still deficient from losses of past logging.]
Logs in the stream played far more important ecological roles than anyone previously imagined. In a stream where woody debris has been neatly cleared away, banks and bottoms tend to be uniform and well graded. Log-choked waters offer far more complex structure with pools and riffles. Currents are slowed dramatically, dropping their sediments to the stream floor and dissipating their energy, thus reducing their ability to erode stream banks. Logs slow down the flow of nutrients so they can be consumed by small invertebrates that form the animal base of stream food-webs.
Using time-lapse cameras and watching the stream as it breathed with the cycles of rainfall and snowmelt, they were able to figure out why artificial logjams broke up no matter how strongly anchored. It was because logs are very buoyant and must be able to float up and down with fluctuations in water levels. [anyone planning trout habitat restoration take note.]
In the moist soils of old-growth forests, Andrews entomologists discovered an astonishing diversity that now appears to rival that of tropical ecosystems. Andrews researchers counted some 3500 species of arthropods in the forest soil but believe that is less than half of the estimated 8,000 species that inhabit Andrews, most of them in the soil. In contrast, they have counted a grand total of 143 species of mammals, birds, reptiles, and amphibians at the site.
Insect communities of the forest are so finely tuned to their environment that they serve as a sort of precision barometer: a knowledgeable entomologist might, simply by analyzing the species of tiny organisms in a handful of soil, describe in astonishing detail the ecosystem above.
There are "keystone bugs" in the soil so critical to survival of the forest ecosystem that if they vanish the ecosystem might collapse.
Mycologists believe that mycorrhizal fungi effectively connect trees with as much as 1,000 times more soil area than the roots themselves. A single gram of forest soil may contain several miles of fungal hyphae. As they pump water and mineral nutrients to the roots, the fungi form a sort of protective armor against disease bacteria around the roots, and sometimes actually innoculate the soil with antibiotics that kill disease bacteria. Some trees can thrive on acidic mine slag heaps if they have enough fungi-mediated defenses against the acids in the soil. Mycorrhizal fungi are keys to how a damaged ecosystem heals.
40% of photosynthate made by leaves of trees does not feed the plant at all but rather seeps out of the roots to feed mycorrhizal fungi and the rest of the ecosystem surrounding the roots.
Some mycorrhizal fungi can dissolve stones and pump the minerals into the ecosystem. Their density plummets after a clearcut, and the missing mineralization of rock and freeing nutrients in humic matter may explain why some replanted forests are unable to thrive. A forty-acre site was leveled by loggers in 1968. It has been replanted with new seedlings four times, but most of the new seedlings died each time they were planted. 3 years after replanting some seedlings the usual way and some seedlings innoculated with soil from healthy forest, only the inoculated ones had survived.
Root zone fungi and bacteria exude glues (polysaccharides) that bind soil particles together, resulting in better retention and movement of air and water. Mycorrhizal fungi break down nitrogen into forms that can be used by plants, and chelate iron which is needed by trees. Mats of fungi in the soil store nutrients that otherwise would be likely to dissolve and leach away. Mycorrhizal fungi provide a bridge connecting trees, allowing shaded ones to borrow photosynthate from overstory trees, even of different species.
In Japan and Europe some forests are in profound decline. The problems have been blamed on pollution, but Trappe wonders if it is more because these soils have not had their input of woody debris, and associated development of the right fungal balance.
= = =
I'm used to thinking that the purpose of soil is to feed plants, but who knows, maybe as far as Nature is concerned the soil is where it's at, and plants are appendages whose purpose is to feed the soil.
By remarkable coincidence, a couple days after finishing Hidden Forest, I bumped into someone walking in the watershed who does soil microbiology for a living. It's fascinating stuff. Here are notes from our conversation.
They make a tea in a large brewer (costing thousands of dollars) from compost inoculated with soil microorganisms & enzymes & sugars (& maybe heat) to culture them. They grow billions in as little as a day, then they spray the tea on the soil that is deficient. For example if there's a landslide they'll put sterile soil on it and spray it with tea made from local microorganisms to inoculate it and have an instant medium for growing natives, otherwise exotics are liable to colonize it while nature slowly moves microorganisms in. Their services are also used to jumpstart the transition from Chemlawn to non-chemical management or even organic, and for remediation of other toxics.
Air pollution does dramatic damage to soil microorganisms that do nitrogen fixing, resulting in a need for more nitrogen-fixing plants to make it up. Eucalyptus oil probably has a substantial impact on soil microorganisms, other nonnatives probably also have an impact.
When I asked how to tell the quality & character of the soil microbiology when we don't have fancy equipment and aren't microbiologists, he said good soil smells different & has a different texture, it hangs together even when dry, if missing microorganisms it turns to dust. When I asked about fungal filaments he said they're too small to see, they're best seen with an electron microscope and may not be easy to see with a regular microscope, but with a simple microscope you should be able to see protozoa etc, and the unaided eye should be able to see some arthropods higher up on food chain, and that earthworms are a good indicator, they're at the top of the soil food chain. Bacteria keep fungi in check/balance. He suggested you wouldn't necessarily have to analyze it, you could just take samples from healthy places where natives are doing well, incubate it, and spread it on areas that are impaired.
Unfortunately he isn't local but he offered to send more info when he gets back from vacation and I'll be checking their websites later. He said one was under construction and another was being reorganized.
Here are some tidbits on other subjects from Hidden Forest:
There was a dramatic difference between watersheds logged & not. Within 5 years peak flows increased 50%, as long as 25 years later flows were 25-40% higher, logging as little as 5% of some watersheds could increase peak flows by 10-55%. They think the mechanism is the roads transmitting the water, not simply the cutting. [this could be significant for us with the density of footpaths we have.]
Geomorphic change is decades of boredom punctuated by hours of chaos when a really big storm hits. During those hours, more sediment and other changes occured to the landscape than occurred in the previous 3 decades. These major events are rare enough that a researcher may not witness one in his entire career.
We think of defoliator insects as pests, but we're learning that they can play extremely critical roles in the health of the forest. Even when they defoliate part of a tree and kill a branch, or when they kill whole trees, they often do it for a good ecological reason. We're learning that they're better managers of the forest than we are. Defoliators that successfully devour needles on the lowest most shaded branches of a growing Douglas-fir actually serve to prune branch and needle systems that are draining more resources from the tree than their weak photosynthetic capacity is returning. The fact that defoliators strip away the lower branches that could serve as fuel ladders for fire to move into the high canopy is one of the reasons old-growth Douglas-firs are so fire-tolerant. The apparent scourge of defoliating spruce budworms that raged through the driest, low-lying forests on the east side of the Cascade Range between 1987 and 1992 could be seen not as a disaster but as an ecosystem trying to tell us something. Fire had been suppressed in this naturally fire-prone ecosystem for years. By the late 1980s, trees that had been replanted after logging, many of them Douglas-firs poorly suited to these drier soils, were competing fiercely for limited water. The budworms were merely killing the least hardy trees. The budworms were seen as the problem. But if you really look at it, they were the solution to the problem.
If anyone is interested in pursuing these subjects, the Long-Term Ecological Research Program has lots of publications and a website at www.fsl.orst.edu/lterhome.html which I haven't had time to look at.
-- Walter Epp for7gen àt idiom døt com