Online Articles
about nature - by Boyd
Shaffer,
artist /naturalist
Observations
of a Naturalist
This Article: If Everything in Nature Has a Purpose ...
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(*Notes:
This article was first presented at the regular
meeting of the Botanical Society on January 6,
1996. A related article, written by Ed Berg,
appeared in the Peninsula Clarion in October 13,
2000 and can be viewed on
this page in their on-line
archives.
Also see additional plant nutrition
information in the nitrogen
article,
in the observations listings. Below is and illustration showing the stages of forest development. You can simply scroll down and read about each step in forest growth, or you can click on the letters under the illustration (A - J) to link to corresponding description in the article. To return here, click on any of the red letters in the article (A -J) .
A
-
In Alaska, the beginning of forest growth is when
glaciers recede leaving sterile scarred lands
consisting of sand, gravel and boulders. Few plant
species can live and colonize such nutritionally
poor environments. A few small hardy species can
colonize and they try; some seeds blown into
crevices and covered with wind-blown dust and fine
sand is enough for a start. Their life expectancy
is very short. As the plant grows, its demands for
more nutrition are not met, and these first
pioneers usually die, decompose, and create new and
richer soil for the next individual to grow in.
This continues throughout the glaciated area, some
places are more conducive to plant growth, with
more water holding qualities and perhaps on the
south side of a raised area. Other places might
remain barren for a thousand years. The first
plants are sure to die of starvation, leaving
behind composting material for the next generation
to live in. Each time a plant community thrives,
runs out of nutrients and dies, it adds to the
buildup of soil consisting of rich, composted
materials for a larger variety of diverse plant
species. But these too will ultimately succumb to
lack of nutrition and as they weaken, insects will
invade the colony hastening its demise.
Pictured
at right is a small plant with the amount
of root necessary to allow it to live, but
not enough to allow much more growth or
reproduction. If there are a number of
plants near each other, each one will
attempt to put out roots equal to the
shoot, and the end result is they quickly
use up all of the nutrients, and those
that live will not be able to sustain a
normal growth rate unless there is deep
soils and plenty of water to help compost
the dead plants. If the soil is shallow
the trees will never reach their optimal
height and width. B
-
As the soil is built up from dead plants, compost
is added, from the dead roots as well as the dead
upper plant parts. Willows and populus are often
the first larger woody plants to grow, and in some
areas, alders and many herbaceous species too
numerous to name here. As with the preceding growth
in A, these kill most of them, a few days of
drought will weaken them and they will succumb to
insect attack and surely die out. At this stage in
the forest's development the first spruce appear,
they can withstand more shade than deciduous
species and will live much longer, although stunted
and gnarled. Black spruce will persist for over one
hundred years in areas where white or Sitka spruce
cannot. But even these will add to the soil depth
as they are reduced by bacteria, fungi, insects,
and other natural composters. C - Within this stand there will be a greater number of species of deciduous plants, mosses and broad leafed evergreens, such as lingonberry, club mosses horsetails, cornus and many more. These add compost as they die as do the leaves of aspen, cottonwood, birch and alder. The alders are very beneficial because they have nitrogen fixing bacteria, and add greatly to nitrogen poor soils. The spruce, being protected by the faster growing deciduous species, thrives and within time their numbers increase and they grow into a dense shaded umbrella which kills any species that must have abundant sunlight. In fact the lower limbs of spruce, growing in dense groves, will lose all of their lower limbs from lack of sunlight. D - What has happened is, through natural forest succession, a very small and weak climax spruce forest has been born. This has been a long time building, perhaps as much as a five hundred years. But alas, the reason it is filled with odd shaped spruce trees is simply that there is not enough soil depth yet, and they have used up all of the nutrients provided by the other dead plants. They weaken and once again they are vulnerable to attack by insects, usually bark beetles, psyllids, and a host of others, including fungi in the form of molds and rusts. This creates the next die off. E - The die off pictured is from bark beetles, a fire is not pictured because it robs the forest of the natural compost and nitrogen which is needed to grow a better forest than the one just devastated. Fires leave a great deal of carbon and other chemicals needed for plant growth but, to grow in what? The same shallow soil, and the forest is literally "set back" about one hundred and fifty years. If however, spruce trees do not grow too soon and in great numbers, the forest can through natural succession, once again build good composted soil, and the next time the forest becomes climaxed with spruce, they will be larger and stronger. F - Is about where most of the Alaskan forests, currently being devastated by the bark beetles are at this time. Some are older and have gone through an additional stage, and perhaps have had more moisture. They are still a long way from being capable of sustaining themselves against much drought or any of a great number of conditions and enemies. G - Natural succession occurs, and as the dead tree roots decay and the trees fall to the ground, new composting takes place and soil depth is again added to the forest floor. The next forest is very strong but still vulnerable but to a lesser degree. H - I - These too will be struck by beetles or other natural composters, but their die off numbers will be less and the recovery more swift. J - Represents a very old but strong forest, healthy, but always with some bark beetles present. If general weakness occurs within the forest the beetles will return in force, causing another major die off. The beetles will be there when the last spruce tree fades into memory.
The
bark beetle is without a doubt the most important
insect in the growth of strong forests. As with
wolves and other predators, they prey upon the weak
and guarantee stronger generations to come. But all
of their work will be for nothing, if the dead
material is hauled away and not allowed to
decompose. All it will do is guarantee another weak
forest that beetles will be waiting for. --End *See
Related story in the Peninsula
Clarion
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