Healthy Soils Build Healthy Ecosystems


[ Music ]>>Healthy soils are a foundation
of healthy ecosystems. Soil, along with sunlight and
climate, are basic building blocks. Soils provide food and habitat for organisms, as
well as a medium for catching and storing water. What is a healthy ecosystem? What is a healthy soil? How does management affect
ecosystems and soil health? This presentation will address these questions. First, let’s look at a definition of soil. First, soil is a mixture of minerals, organic
matter, and voids through which water, gases, and organisms move and interact. The development, makeup, fertility, and
condition of soil is strongly dependent on the breakdown of organic
matter on the soil’s surface. Let’s look at a few examples
of ecosystems and their soils. Is this a healthy ecosystem? Does it have a healthy soil? Is this a healthy ecosystem? Is its soil healthy? What do you think about this
ecosystem and its soil? How about this ecosystem? Is the soil healthy? Let’s take a close look at the life of the soil. The healthy soil is reflected by its biology. Healthy soils support an abundant
and diverse population of organisms, including those that cause disease and
insects that we often consider harmful. This stylized ecosystem depicts by proportion
the number of described species on earth or, stated differently, the relative size
represents the number of species. Note that the elephant represents all mammals. Eighty percent of terrestrial species get
part or all of their life cycle in the soil. Let’s take a quick look at some of
the organisms that live in the soil. Birds, rodents, reptiles and amphibians; small
mammals, such as moles, shrews, and voles; the grubs of many insects, many spend part
or all of their life cycle in the soil; the ubiquitous ant plus wasps and bees;
centipedes, the timberwolf of the soil world; millipede, primary shredders of raw material;
arachnids, or spiders, there are small ones, large ones, pseudo-scorpions;
earthworms; the larvae of many insects, such as this click beetle larva; the
lowly cell bug or isopod; dipluran; mites, such as this turtle mite; another
turtle mite, or oribatid mite — they are microscopic and not
visible to the naked eye; nematodes, which are microscopic worms; algae and protozoa;
many, many species of fungi; actinomycetes; bacteria and viruses; and plants. The list goes on and on. These organisms interact and many
depend on each other in some way. Many also exist in large
numbers and multiply rapidly. So the soil is a very busy place. Soil is the foundation of terrestrial ecosystems
and provides habitat for many organisms. Let’s begin with an investigation of
the organic matter portion of soil. Soil organisms cannot survive
without organic matter. We will look at three types of organic
matter: large woody material; duff and litter; and soil organic residues
in the soil or soil humus. The first is large woody material or
downed logs, which are the largest and most obvious source of organic matter
and habitat on top of the soil surface. As these logs decay, they provide a habitat
for a succession of many organisms that add, conserve, or convert nutrients
within the ecosystem. There are a number of ways
to classify decaying logs. We will use a system that has five classes. Class I are the recently fallen logs. Class V logs are in the final
stages of decaying. Class II through IV logs are intermediate
stages between I and V. As the logs decay, they lose branches and bark, getting better
contact with the soil, gain moisture, lose carbon, and eventually lose volume. We’ll look at each class in a minute. First let’s look at the cross-section of a log. Logs are composed of outer bark, inner
bark or cambium, sapwood, and heartwood. Sapwood decomposes rapidly. Heartwood decomposes slowly and
this provides persistent habitat. Large logs are good habitat for organisms,
since the heartwood to sapwood ratio is high. Let’s talk about a few things that
happen at each stage of decomposition. First, when a tree falls and
loses its leaves or needles, water is no longer pumped out of the trunk. This graph, based on data from
Oregon, shows that water content in the log increases as the log decays. In addition, because Oregon has
wet winters and dry summers, the winter moisture is generally
greater than summer moisture. The difference between winter and summer moisture is most pronounced
in Class IV and Class V logs. As the log decays it acts more and more
like a sponge, taking in more water. The presence of moisture
speeds the decay process. But if the log becomes saturated, an overabundance of water restricts the
amount of oxygen and decay slows down. Temperature also has an effect
on the rate of decay. Biological activity is greatest
during the summer months, provided adequate moisture is available. At the Class I stage, not
much is happening for soils. The limbs and bark are intact. There is little contact with the soil. The log is drying out and cracking, which
exposes new woody surfaces to attack by organisms, and moisture
content is decreasing. The log remains in Class I stage
for about three to five years. This is a stage of feverish
activity by a multitude of organisms, such as burrowing insects. The insects penetrate the outer bark and
mine the cambium and the outer sapwood, along with their symbiotic fungal partners. At the Class II stage there is
still not much happening for soils. The log has lost its limbs,
but the bark is still intact. Moisture is still low; however, the log is
beginning to make contact with the soil. The log is in Class II stage for
approximately five to fifteen years. At this stage the log is
increasing in biological activity. The outer bark is fully penetrated
by organisms and activity in the inner sapwood area is increasing greatly. Organisms in the log, such as grubs, provide a
good food source for wildlife, including birds. At the Class III stage things are
really beginning to pick up for soils. The log is partially buried in the soil. It has a high moisture content and is
becoming spongy, allowing it to take in water from rain, dew, and fog. The outer and inner bark is gone and the
sapwood is fully penetrated by organisms. The log may stay in Class
III stage for 50 to 80 years. At this stage species diversity and
biological activity are rising rapidly. We’ll look at just one species, the Pacific
dampwood termite, one of the many species that converts large organic matter
or cycles nutrients in the ecosystem. This is actually a symbiotic relationship
of three organisms in one insect body. The protozoa secretes an enzyme which
allows the termite to digest cellulose, which is an extremely difficult
food source to break down. The bacteria living in the
intestine are nitrogen fixers, which means that they have the unusual ability
to use atmospheric nitrogen to make protein. When the termite dies, this protein
is recycled for use by other organisms in the soil ecosystem, including
roots of plants. These nitrogen-fixing bacteria slow down
or speed up the process depending on needs. Although the amount of nitrogen fixed
in termite colonies is not high, it is important in sustaining
this part of the ecosystem. At the Class IV stage the log is down to
40 percent of its original solid volume. It is just cubical heartwood. One-half to three-fourths of
the log is buried in the soil. It is very wet. Even after a very dry summer you can actually
wring water out of the log in the fall. The log may persist for over 100 years in
this stage and is occupied by many roots. Species diversity is near its maximum at
the Class IV stage, but much is microscopic and sub-microscopic fungi and small
arthropods, such as this oribatid mite. [ Music ] It is the log structure that is important
at this stage, since it provides habitat for these smaller species,
especially fungi and small arthropods. There are many predator-prey relationships. Everyone is chowing down on everyone
else and having a grand old time. [ Music ] And finally at the Class V
stage the log is so much a part of the soil it is not readily observed. It is little more than a low
mound on the forest floor, often missed without digging, even by experts. The log is all cubical heartwood. Fully buried in the soil, it can have high
moisture content and can be fully occupied by roots and especially by mycorrhizal fungi. The mycorrhizae is a symbiotic relationship
between the plant root rhizome and fungus. This compound structure greater increases
the effective rooting area of the plant. The tree supplies the mycorrhizae with
sugar made by photosynthesis in the canopy and the mycorrhizae supply
the tree with nutrients. As much as 50 percent of the carbon fixed
by trees can go into the mycorrhizae. Mycorrhizae offer several benefits to
the host plant, including faster growth, improved nutrition, greater drought
resistance, and protection from pathogens. Benefits to the plant community,
especially important in re-vegetation, are higher plant species diversity
and improved soil structure. Most plants are mycorrhizal;
that is, the roots are capable of developing a mutually beneficial
relationship with certain fungi. In poor soils it seems that
mycorrhizae are absolutely essential for the survival and growth of the host plant. In Western conifer forests, they can extend the
root surface area for more than a million times and they can occupy two and a half tons per acre
dry weight or 11 percent of the total root mass. Soilwood, both in the soil
and on the soil surface, is important habitat for the mycorrhizal fungi. Al Harvey from the Rocky Mountain
Research Station in Moscow, Idaho looked at root colonization
by mycorrhizal fungi in four soil components the roots occurred
in: humus, litter, soilwood, and mineral soil. Mineral soil comprises more than 90
percent of the total soil volume, but he found that mycorrhizal fungi occurred
predominantly in the soilwood and humus, indicating that Class V heartwood is
important habitat for mycorrhizal fungi which, in turn, are important for healthy trees. Now that we have seen that as logs progressively
decay they provide habitat for a succession of organisms that carry out processes
essential to the functions of ecosystems, let’s look at residence time by decay class. Note that large woody material stays much
longer in decay Classes III through V, the ones most important to soil
organisms, than in Classes I and II. Therefore you would expect a greater
number of Class III through V logs on the floor of a healthy forest. In summary, large, woody material is vital
habitat for a whole host of organisms that contribute to cycling
nutrients in the forest ecosystem. The logs persist for a long time if undisturbed. This adds to the importance
of not disturbing them. Our management should focus on protecting
some of the Class III and IV logs and recruiting large logs
that are mostly heartwood. Now let’s look at the second type
of organic matter, duff and litter. If you were a small critter trying
to make a living in the soil, would you want to live here or here? Most would agree this is more suitable
habitat for most soil critters. Let’s take a look at why this
is more desirable habitat. This desirable habitat comes in three types, each with slightly different
properties and dynamics of cycling. The ground cover of dead branches, which
is often seen under coniferous forests; the forest floor of decomposing
leaves and needles; and grass litter, in which nutrients cycle quite differently. Most organic matter is added directly to
the soil from dieback of fine grass roots, in contrast to being deposited
on top of the soil. Next we are going to cover several
basic concepts about forest litter. Forest litter represents an
equilibrium between the rate of litter fall and the rate of decomposition. When decomposition is slower than
litter fall, litter depth increases. When it is faster, litter depth decreases. When trees are removed, both the
processes of litter accumulation and litter decomposition are affected. Removing logs, as in timber harvest,
greatly decreases litter fall and may increase the decomposition
rate because there is not as much to decompose due to increased weathering. If harvesting is done properly, the nutrients
remaining are rapidly cycled and not lost from the ecosystem, but if the job is done
without regard to preserving the habitat of the organisms responsible for recycling
nutrients, environmental degradation can occur. By leaving some fine woody litter on
the soil surface and mixed conifer, we can slow down the decomposition process
and provide habitat for soil organisms. Another important concept about forest
litter is that it provides mulch. This mulch modulates extremes in temperature
and moisture to create desirable habitat. [ Music ] Most of these little guys, just like us, need
air, water, a food source, and an environment that is not too cold or not too hot. This physical effect of duff and litter is
fully as important as the nutrients it contains. Millipedes are the primary
shredders of duff and litter, the teeth and molars of the soil organisms. They break down larger plant
material, which enables other organisms to process the nutrients efficiently. As the organic matter goes through
various stages of decomposition, some steps can be carried out by a large number
of species, but other steps by only a few. These are called keystone species. Some ecologists call millipedes
a keystone species. The soil, especially at the soil litter
interface, is very rich with many organisms. Soil can have up to 250,000
mites in a square yard, including 75 to 100 different arthropod
species with specialized functions. Some feed on fungi, some on dead
material, and some feed on each other. These little guys are barely
visible to the naked eye. A half dozen of the larger ones could site
on the head of a pin, like this turtlemite, without being too crowded,
but many are much smaller. Mites are everywhere, not just in the soil. An ounce of house dust in your
home can hold up to 40,000. Other mites live on your skin and
some even keep your eyelashes clean. Finally, as organic material is broken down
to finer particles, we have the sow bug or wood louse, another keystone species that
transforms organic matter down to a size that microorganisms can utilize
or make available for plants. The soil is home for billions
and billions of little critters, and when you walk through the
woods, I want you to remember that each time you put your foot
down, it is being held up on thousands of little backs supported by
several hundred thousand legs. Another important concept
about forest duff and litter is that it is extremely important
to hydrologic function. How can four to six inches of water from
a big storm move through saturated soils to streams without causing erosion? Mostly because forest litter has
a high hydrologic conductivity or a tremendous capacity to
move large amounts of water. Also, forest duff and litter provides good
structure at the soil litter interface and this soil zone also has a huge
capacity to move water without erosion. Without duff and litter, [inaudible]
gully erosion is likely to occur. So how can we reduce excess
woody debris in the forest and still maintain the function
of this forest floor? We can use equipment that does not move
the surface soil and organic matter around, does not exert excessive pressure that reduces
soil pore size, equipment with capabilities to reach out and grab logs and branches,
rather than driving over every inch of soil, equipment that allows us
to be selective as to what and how much organic material is taken
off the site, and we can use fire. In summary, some of the major effects of
duff and litter: they modulate temperature and moisture, they are important in
developing soil structure, they are important for hydrologic function, they are
important in nutrient cycling, and they are habitat for
soil micro and macro fauna. The third type of critter habitat
is the well-decomposed humus, the end product of the decomposition process. The humus, mixed with mineral
soil, makes fertile topsoil. The importance of this habitat
component cannot be over-emphasized. Humus has tremendous effects on
physical and chemical soil properties, as well as providing biological habitat. Let’s look at what some of
this magical stuff does. Soil organic matter is an important
source of nutrient reserves. It has a high cation exchange capacity. This is one measure of the soil’s ability to
hold plant nutrients and resist chemical change. It is important in the formation of
soil structure, creates soil porosity, causes aggregate stability, and enhances
water infiltration and retention. It provides habitat for soil organisms and it is
key to the sustainability of forest ecosystems. This soil is not providing all these benefits. This soil is alive. It is providing all the benefits
we just mentioned. Much of the activity that takes place in
the soil humus is microbial and carried out by microbes, such as these bacteria. There can be six to eight million
bacteria in a gram of soil. A gram of soil is about the
size of a pencil eraser. This gram might contain 16,000 different species
of bacteria, all with specialized functions. There are many larger specialized soil
organisms, as well, such as this springtail. This organism gets its name from
an appendage on its rear end, which is held under hydrostatic pressure until
released, which causes it to spring away. The springtail is only one-eighth
to one-quarter inch long, but it can catapult over a yard when in danger. A square meter of soil may contain as many as 50,000 springtails, representing
20 to 30 species. There are also many other
species and many other critters that have adapted to the soil environment. Throughout the world there are
many species of earthworms. They eat dead plant material and
move tremendous volumes of soil. They were once thought to be
limited to grassland soils. Now we know there are species adapted
to chaparral and forest ecosystems. Bioturbation is very important
to ecosystem function. Bioturbation is the process of
moving large volumes of soil as an indirect effect of burrowing. For example, in chaparral ecosystems
bioturbation mixes persistent seeds more deeply in the soil, assuring that whenever the
moisture and temperature conditions or soil loss after a fire, there will be
seedbank of native plant species. Structure developed by soil
organisms creates macropores. Pores are important for water movement
and the balance of water and air. It is common to have as much as 50 percent
of the soil volume occupied by empty space. Soil pores can be filled with water. Plant roots and soil critters
need oxygen, just as you and I do. In wetlands, the soil biota have
evolved ways to still obtain oxygen. In western forests, prolonged saturated soils
will kill the trees, critters, and fungi. Let’s look at the typical nitrogen distribution
in the soil of a mixed conifer forest. Many other nutrients have similar patterns. Large dead woody material has only
a trace of the nitrogen; however, it is still important for
the habitat it provides. The crown and the bowl of living
trees have about five percent each, which means that removing some of this
material will not have a major effect on the total soil nitrogen. Litter contains about 10 percent, but
note that the vast majority of nitrogen and other nutrients is in the soil,
the major reserve, or the capital. This material must be mineralized or released
by the soil biota before plants can use it. Let’s take a closer look at the
soil organic matter component. About 15 percent of the soil organic
matter pool is called labile. This is organic matter that is readily
available or usable by soil organisms. This material breaks down rapidly matter
such as roots, decaying organisms, and feces, and turns over in 0 to 10 years. The bulk of soil organic
matter, however, is recalcitrant. It is very resistant to decomposition. It is material that turns over very
slowly, say 1,500 to 3,000 years. Looking at organic matter this
way offers a new way to look at sustainability of forest ecosystems. The labile fraction can be used up
and replaced frequently or maintained at some level below climax forest
levels and still be sustainable. But if the management system causes a
recalcitrant pool to be dipped into, this uses up capital and is
not a sustainable system. What are some ways we can manage
the forest without dipping into the recalcitrant pool and
still retain sustainability? We can prepare sites for reforestation in ways
that do not compact soils and leave ground cover on the soil surface, leave some large woody
material on the site, and avoid disturbing some of the Class III through V logs; use light
prescribed fire, leaving some organic material on the soil surface; and when piling
slash we can select the material to pile. We can use thinning, shelter wood and patch
cut logging methods and we can reduce chances for large, hot fires by maintaining
lower fuel levels. The information I presented here
shows that ecosystems are complex and Mother Nature makes tradeoffs. So people should also make trade-offs
for the good of the ecosystem. Many points on forest management
are controversial, but let’s not lock horns pulling off our own
special interests, but work together and learn from each other, preferably in the field to
provide solutions as interdisciplinary teams. In summary, soil habitat comes in
three forms: large woody material, duff and litter, and soil organic matter. Organic matter can affect physical
and chemical soil properties. Soil biota affects structure. Structure developed by critters
affects soil hydrologic function. And soil organisms carry out biological
processes critical to ecosystem function. Now let’s revisit the questions
I raised earlier. This is a healthy ecosystem. Although there is evidence of erosion at
this disturbed site, general conditions in the ecosystem are such that organisms
can become established and thrive. This is obviously not a healthy ecosystem. Much of the organic matter in
the topsoil has been displaced or removed by both equipment and erosion. There is not sufficient ground
cover to protect soil from erosion, nor provide for nutrient replenishment. This ecosystem appears to be in poor condition, but on close examination
its vital signs are good. Soils are not compacted,
soil organisms are thriving, and there is sufficient organic matter left for
nutrient replenishment and organism habitat. This ecosystem appears healthy, but upon
further examination the vital signs are poor. Soils have been severely compacted. Topsoil was removed and little organic
matter remains on the soil surface. Soil organisms and evidence of
their activity are very limited. This site is using up organic
matter and nutrients faster than they are being replenished
for long-term soil productivity. In conclusion, remember that soils
are the basis of a healthy ecosystem. Soil is a living system and fertile topsoils
are made up predominantly of all the organisms that live and die in the
soil and their byproducts. These organisms depend on organic
material for their livelihood. [ Music ]

12 Replies to “Healthy Soils Build Healthy Ecosystems”

  1. Thanks a lot it was really helpful.
    I think the music was annoying and distracting in some parts of the video.
    Thanks again.

  2. Some interesting information, in particular, log decomposition. However, the production quality is from the early 80's.

  3. The video is great and informative. Forestry has come a long way in the past few years and has stopped clearing whole areas and burning what they can not sell. They now realise that what they used to consider waste when replanting is a required natural resource that keeps the soil alive and helps the whole system recover a lot faster when replanted. As with all harvests from nature giving back what the system requires to sustain its self is as important as the crop harvested. Dead soil is not a viable option any where on this planet of abundant life.

  4. Your work and research provide tremendous hope for better stewardship of our planet and subsequent generations. Thank you for your service.

  5. Great content, but the background music is annoying. A lecture does not need background music. Imagine going to a university lecture while music is playing in the background. Please stop!

  6. Very interesting presentation but the completely unnecessary music is annoying – for crying out load stop adding the noise pollution .

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