Once established, soils remain dynamic systems that are always at risk of some form of erosion. This may occur naturally, but erosion is often associated with anthropogenic activities. The initiation of erosion may be related to some form of disturbance, with the removal of the vegetation cover being by far the most significant. Erosion is greatest where there is the greatest amount of energy, which in the context of soil erosion is on slopes.
In this module, we will first look at some of the processes occurring on slopes and how these interact with anthropogenic activities. The movement of rock materials and soil downslope is known as mass wasting, and is very important for forestry. The material may accumulate at the base of the slope, or may enter the fluvial system and be removed by streams and rivers. In some cases, the slope system and the fluvial system are coupled – material may be eroded from a gully wall on the upper part of a steep slope, directly entering the fluvial system, or a landslide or debris flow may transport debris directly into a stream channel.
We will also examine the processes that lead to soil degradation. These vary from one forest area to another, but in some parts of the world are very important. Forestry activities may be particularly important, and can actually lead to some of the erosion processes found in the slope and fluvial systems. On the other hand, forestry activities can also help conserve soil and can help stabilize areas that are unstable for a number of different reasons (such as eroding slopes or moving sand dunes).
Innes, J., & Tikina, A. (Eds.). (2014).Sustainable forest management: From principles to practice.London: Earthscan Publications. ISBN: 1844077241. Chapter 6.
Further Readings
Bonn Perspectives. (2013, April 16).The value of soil[Video file]. Retrieved fromhttps://www.youtube.com/watch?v=403sT9CGRl0 Links to an external site.Soil is of course essential not only for forests but also for agriculture. The two are closely related as the degradation of agricultural land can result in pressure to remove forests to make way for more agricultural land. A useful video that links these ideas can be found at the above link.
Soil-Net.com, an Educational Resource for Information on Soil Science. (n.d.).Soils: Advanced. Retrieved fromhttps://www.soil-net.com/legacy/advanced/index.htm Links to an external site.Soils are a complex subject, and there is a wealth of information available on-line. A useful starting point is at the above link.
The self-test quiz is designed to check your understanding of important learning concepts for this topic. The quiz contains ten multiple choice questions. There is no time limit for you to take the quiz and you may attempt to take it as many times as you like. After you click the Submit button, you will see your Grade, number of Correct Answers, your answers, and the Answer Key for each question.
Quiz Instructions:
While you are taking the quiz, we advise you not referring to any course materials. After you Submit your answers, you may self-reflect the missing points, review relevant contents as necessary, and retake the quiz again until you get the full points.
When you are ready, click the link Topic Quiz 3.2or go to left menu > Quizzes > Topic Quiz 3.2 to start taking the quiz.
Activities & Assignments
Online Discussion Module 3
If you have not already done so, once you have read Chapters 6 and 7 of Innes, J.L. and Tikina, A. 2017. Sustainable Forest Management: From Concept to Practice, post one thought provoking question related to the maintenance of soil and water resources, and remember to answer/respond to at least one other student’s question on the discussion board Online Discussion Module 3. While you are only required to post one question and answer per module, we encourage you do so for each topic, and you will receive a higher grade if you do.
Assignment #5: Six Sentence Answer #5
Clayoquot Sound is famous for the beauty of its landscape. Its coastal location, with the steep, snow-covered mountains towards the interior of Vancouver Island, is particularly attractive. However, the combination of high rainfall and steep slopes means that slope stability is a major issue. Rainfall in the region is high, and averages about 4000 mm annually. Some sites may have as much as 6000 mm annually. Rainfall can also be very intense, and a number of British Columbian rainfall intensity records have been set in the region: 2 hours (70.9 mm), 6 hours (139.4 mm), and 24 hours (489 mm).
Flying over the area, you can see much evidence of past landslides. Many of these are associated with forest roads installed on steep slopes. These roads are largely inactive, dating back to the time when logging was much more widespread. Some of the roads have been deliberately "deactivated", which means that they have been closed to access by vehicles, and a certain amount of restoration may have been done. Other roads remain active, including some on slopes that have the potential to be unstable. Looking into the future, there is a strong possibility that the slope stability calculations for particular areas may have to change as a result of changes in the magnitude and frequency of rainfall events associated with climate change.
