Planted Forest Thinning and Soil Retention Measures

This Sanctuary is located upstream of the Otaki waterfall, but no viable route has been found to extend a vehicle-accessible logging road into this area. In other words, it is a forest where even fully-grown cedar and cypress trees cannot be removed for timber.

Nonetheless, this sizeable area was once planted with Japanese cedar, cypress, and larch.

Why were so many conifers planted in a location where, even when they matured to timber size, they could not be removed? In fact, forests like this exist all across Japan.

Though the trees cannot be harvested for lumber, when left unmanaged, the space between trees becomes overcrowded, the forest floor darkens, and not a single blade of grass can grow. This leads to severe soil erosion, and in the worst cases, the entire slope can collapse.

That is why we conduct thinning operations every few years, laying the harvested trees along slope contour lines to serve as soil-retaining barriers. Though it feels like a waste to use such good-quality wood this way, a bit of extravagance is necessary to keep the forest healthy. What is more, in several decades, these trees will be broken down by fungi and enrich the soil as they decompose. They protect the soil when harvested, and eventually return to it.

Soil retention measure using harvested trees from thinning