The way that water flows through forests is complicated, but so dang important!
Different soil types have different carrying capacities of water based on the levels and types of organic and mineral content they contain, and when they become saturated, that water creates space between those soil particles and reduces friction between them, which leads to increased erosion, sedimentation of streams, and more frequent and larger landslides. Plant and tree diversity are able to increase carrying capacity by slowing the flow of water into soils through infiltration, uptake by their roots to photosynthesize, as well as their roots acting like rebar within the soil to hold particles together.
When forests are logged, the lack of plants available for uptake and roots in the soil leads to an increase of soil saturation and thus more frequent and severe landslides, and the lack of soil holding capacity that would normally store excess water leads to more frequent and larger flood events.
A new study from UBC looked at two neighbouring watersheds that were clearcut logged and found that the north facing watershed had more than 50% more frequent flooding events that were much larger than in the south facing one as a result of less sunlight that evaporated less water and kept soils saturated more often. For the past 40 years, over-simplified clearcut management practices have been shown to dramatically increase the size and frequency of landslides by as much as double, and this study reaffirms these impacts by showing an 18 fold increase in severe flood events in watersheds that have been industrially logged.
Clearcut, shelterwood, seed-tree or any other rebranded form of myopic industrial logging are not viable management practices, and it’s time we move to a closed-canopy selective harvest system that maintains this ecological and hydrological complexity for all of those who depend on these forest ecosystems.
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