The soil structure has particles and spaces that are occupied by air. These spaces are important for the root growth and soil drainage. Soil compaction occurs when the particles are compressed together reducing the pores between them. The soil looks like a caked block with little air in it.
Heavily compacted soils have a reduced rate of water filtration and poor drainage due to the compacted layer of soil. Moreover, the soil has aeration problems. Small organisms that live in the soil such as earthworms do not have enough air to continue with their soil activities.
What causes soil compaction?
Soil can be compacted by both natural and man-induced activities. The heavier the force applied on the soil surface, the higher the rate of soil compaction. Some common causes include:
Continuous paving of a similar depth each time creates a very hard tillage pan that is about an inch to two inches.
The weight of tractors and four-wheel driving units travelling around existing trees is a major cause of soil compaction.
What is the effect of soil compaction on the trees?
The roots survive in the aerobic region of the soil. However as this layer is taken over by an anaerobic layer due to compression, the available space for the tree roots declines, which affects the root growth.
Reduced elongation and radial growth
Trees begin generating short and thick roots as well as many more lateral roots. Moreover, the roots are physically unable to pass the compaction layer and therefore very short and very weak.
Poor root formation often results in less access to soil resources. Allocation of the diminishing resources reduces dramatically thereby resulting in stunted growth. Moreover, there is reduced uptake of phosphorus and nitrogen due to declining protein and carbohydrate synthesis.
Root crushing and shearing
Mechanical soil compression can crush roots that are already formed. Large roots are at a risk of higher damage and death especially with large forces compressing the soil. In some cases, the young trees may die from shearing and crushing.
Greengrid’s root bridge system allows for a shallow, unobtrusive support structure to carry the loads generated by surrounding traffic, paving and other threats to tree life that can be found on development projects.
With a structure height of only 75mm it is a simple, cost effective engineering solution that can be retrofitted into most design projects, both large and small where there are existing trees that need protecting. Please look at our case studies for examples of projects we have worked on.