What are soil horizons?
Soil horizons are different layers within a section of soil. These layers are parallel to the surface, and each layer has distinct characteristics produced by the soil forming process. Various types of soil horizons include O horizon (organic), A horizon (topsoil), B horizon (subsoil), and C horizon (substratum).
What is podzolization?
Podzolization is soil formation. It refers to the process in which spoils are depleted of metallic cations and become acidic and have developed separate soils layers (or horizons). Organic debris are relatively low in metallic cation concentration and give rise to acid products. As acids are moved downwards by water, the acids dissolve alkaline earth carbonates and salts. Once carbonates are no longer in the upper soil part, the hydrogen ions of acid waters replace many of the cations. Metallic cations move downward and the upper part becomes acid. This makes an unstable environment for iron and aluminum oxides. Eventually, four distinct layers develop: Organic layer (O horizon), acidic and siliceous layer (A horizon), zone of accumulation (B horizon),and the unweathered portion of soil body (C horizon).
How much of the winter has soil temperatures less than 2°C? If Douglas-fir has a known temperature threshold of 7°C (below this temperature roots do not grow or easily take up water), then how many months would Douglas-fir do well? If the temperature threshold is 1°C for Pacific silver fir, how many months would it have? What is the known elevational distribution for these two species?
January through May has soil temperatures less than 2°C. There would be only 1-2 months that a Douglas-for would do well if the temperature threshold was 7°C. There would be 7-8 months were a Pacific silver fir would do well if its temperature threshold was 1°C. The Douglas-fir is a lower elevation species and the Pacific silver fir is a higher elevation species.
Why is the minimum temperature so late in the spring and the maximum temperature in August for the Oa and September for the C horizons?
The temperatures warm so late in spring because there may be existing snow pack and frozen layers of soil. It takes time for the snow to melt and for freezing grounds to warm up enough to become productive again. However once water starts to flow through the ground efficiently again, then the temperatures are buffered and then slowly taper off again in the early fall.
To answer the next question, use the table below (these data were collected by the 2002 class in the Asahel Curtis Picnic Area). What is the relationship between height and diameter of old Douglas-fir trees?
The relationship is a positive correlation. As the diameter increases, so does the height of the tree.
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