This study tested the Miyawaki method of rapid natural forest regeneration (which has been shown to work in Japan and elsewhere) in the arid Mediterranean. In this area, millennia of human civilization have resulted in degraded soils and reduced and changed forest cover, traditional reforestation efforts have often failed, and desertification is a looming threat. The Miyawaki method speeds up the process of ecological succession by densely planting a multilayer forest made up of a wide diversity of indigenous species.
In a natural forest cycle, as Clements (1916) described, annual plants on barren land are succeeded by perennial grass, sun-tolerant shrubs, light-demanding, fast-growing trees, and ﬁnally natural forests; each step may require decades, and the climax vegetation could be formed after two centuries or more. Currently, most forest reforestation programs adopt a scheme of planting one or more early successional species; after successful establishment, they are gradually replaced by intermediate species (either naturally or by planting), until late successional species arise. This pattern tries to simulate natural processes of ecological succession, from pioneer species to climax vegetation. However, it requires several silvicultural practices and normally takes a long time [Shirone 2011: 82].
In the Miyawaki method, by contrast, one plants all at once the many plant species normally present in a native forest community, thus bypassing the earliest stages of ecological succession. Other tree-planting methods favor fast-growing non-native tree species, while omitting understory species – in other words, creating a simple plantation rather than a forest community that functions ecologically and can evolve and sustain itself.
Multilayer forests, and natural biocoenosis [ecological community] is possible, and well-developed ecosystems can be quickly established because of the simultaneous use of intermediate and late successional species in plantations. The Miyawaki method involves surveying the potential natural vegetation of the area to be reforested and recovering topsoil to a depth of 20– 30 cm by mixing the soil and a compost from organic materials, such as fallen leaves, mowed grass, etc. In this way, the time of the natural process of soil evolution, established by the vegetational succession itself, is reduced [Shirone 2011: 82].
The authors of this study found that compared to traditional reforestation, there was “a more rapid development of trees on the Miyawaki plots, in particular, early-successional species [especially maritime pine]. The beneﬁts over previous methods are remarkable and comparable with those obtained by Miyawaki in Asia and South America.” The Miyawaki method favoring denser plantings works even in arid climates, in spite of traditional views favoring sparse plantings in arid places, although the optimal density for the Mediterranean still needs testing, according to the authors.
In fact, low plant density has been traditionally retained as appropriate in arid and semiarid environments in order to avoid competition for water resources between plants, but it is now evident that cooperative processes, e.g., mutual shading, prevail over competitive processes. High plant density also reduces the impact of acorn predators, thus encouraging oak regeneration, i.e., the main late-successional forest species in Mediterranean environments. In addition, excellent plant stock remains fundamental for planting success in harsh environments [Shirone 2011: 91].