Vegetation History Characteristics of Planted Forests in Japan: Analysis of the 1960 World Census of Agriculture and Forestry

There have been significant changes in the forest landscape during the Anthropocene. There was a sudden change in Asia. For instance, with the large amount of forest loss occurring in Cambodia, forest area is decreasing at approximately 166,000 ha per year [1]. Malaysia lost 8.12 ha of forest between 2000 and 2019 (28% for the year 2000) [2]. Following World War II, the Japanese archipelago underwent major changes. Since 1955, the Japanese government has promoted afforestation by converting existing natural forests into planted forests as part of a “long-term comprehensive economic plan” [3]. As a result of these policies, planted forests made up of cedar and cypress are found in the temperate zone in west Japan. Planted forest made up of larch are mainly found in the boreal zone in north Japan. Now, Japan’s forests cover about 25 million hectares, which accounts for two-thirds of the national land area. About 40% of them are planted forests [4].

Nowadays, wood production is increasing [5] as the accumulation of Japan’s planted forest is increasing [4]. Additionally, climate change is expected to cause an average temperature increase of 2.5–3.5 °C and a 5% increase in annual rainfall by the end of the 21st century (2076–2095) compared with the end of the 20th century (1980–1999), as well as an increase in the frequency of short-term intense rainfall and heavy rain [6]. In Japan, forests play an important role in the preservation of land by protecting soil and water sources. They help prevent and mitigate mountain disasters such as landslides and floods [4]. Therefore, it is crucial to carefully consider land use decisions for deforested areas, taking into account future changes in climate. Natural regeneration is gaining popularity as a land use option for deforested areas; however it is influenced by the amount of buried seed, which is determined by the planted forest’s vegetation history (referred to as “vegetation history” hereafter) [7]. Moreover, in Japan, the increasing population of Sika deer (Cervus nippon) has become a major social problem, as deer cause the most forest damage [8]. Japanese Sika deer have a major impact on vegetation and can inhibit forest regeneration because they eat a wide variety of foods and congregate in groups [9]. Therefore, understanding the vegetation history of planted forests is necessary when selecting natural regeneration as a land use option following felling. It is suggested that the expansion of afforestation has provided a suitable environment for Shika deer and that their numbers have increased [10]. Thus, understanding the vegetation history of planted forests can help clarify forest landscapes and reveal the source of current wildlife damage, which is important for ecological conservation. Global ecosystem modification has occurred rapidly since the end of the 20th century, resulting in the degradation of many ecosystem services [11]. These ecosystem changes can be recognized as changes in land cover and landscape at the regional level [12]. Therefore, understanding changes in forest landscapes as a result of land use change is critical when evaluating changes in ecosystem services at a regional level [13].

When considering ecosystem conservation, having an understanding of the vegetation history of each region’s planted forests can be helpful in recognizing how the changes in land use in various areas have affected the forest landscape. Prior research on landscape ecology, geography, and rural planning has documented cases of changes in the landscape and land use of mountainous areas (for example, the Sendai River basin in Tottori Prefecture [14], Moroga Village in Tottori Prefecture [15], the Hitotsugawa upstream area in Kyushu Mountains [13], Oguni Town in Kumamoto Prefecture [16], Kuroiwa Village in Ashikita Town, Kumamoto Prefecture [17], Higashisefuri Village in Saga Prefecture [18], Omogo Village in Ehime Prefecture [19], Hiwa Town in Hiroshima Prefecture [20], Kukino in Minamata City [21], and the mid-stream area of the Aritagawa River in Wakayama Prefecture [22]). According to these studies, abandoned grasslands, forests left after fuelwood harvesting during the energy revolution, logging areas for wood processing plants, slash-and-burn areas, and poorly conditioned terraces have all been used to develop planted forests. However, these studies did not quantitatively analyze the vegetation history of planted forests. A regional study [23] examined the progress of afforestation on a prefecture-by-prefecture basis. Although it clarified the characteristics of human-induced changes in terrestrial ecosystems by defining disturbed biomes as anthropogenic and analyzing land use change globally using the HYDE data model, which is a comprehensive database that compiles past global environmental data with an emphasis on demographic and land use changes [24], it did not analyze vegetation history. Land use and land cover changes in Japan from 1900 to 1985 were investigated using the Geographic Information System (GIS) based on the Land Use Information System (LUIS) dataset [25], but no systematic vegetation history analysis was performed. The vegetation history on a prefecture-by-prefecture basis [23] was considered coarse because of the influence of natural environmental factors, such as altitude and slope [26]. In addition, mixed broadleaf forests and planted cedar and cypress forests were allocated as mixed forests [25]. This makes accurate analysis of the vegetation history of planted forests difficult.

Based on previous studies, this study aims to capture vegetation history at the macro level, rather than focusing on a single region as a case study. This study examines the vegetation history of land use on a municipal unit basis used in 1950 to determine the differences in vegetation history between regions. A previous study classified Kyushu’s vegetation history in 1960 into municipalities with afforestation rates greater than 50% as natural forest conversion, reforestation, and non-forestry conversion types and municipalities with afforestation rates less than 50% as mixed type [27]. Despite comparisons with other regions, mainly Hokkaido and Kinki, the vegetation history analysis remained an approximation. We compare the vegetation histories of Hokkaido and Kyushu, which currently produce a substantial volume of raw materials, with that of Kinki, an area where raw material production is now low, despite being considered a forestry region from pre-modern times.

In this study, we identify the patterns of land use change in 1960 in more detail by categorizing them into ten groups and comparing the vegetation history of the three regions using classifications based on afforestation rates as a reference [27]. By clarifying the vegetation history of planted forests in the three regions established after World War II, this study provides useful information for determining the land use of clear-cut areas.

Using data from the 60-year census, we attempted to quantify the vegetation history of planted forests in Hokkaido, Kyushu, and Kinki. The analysis showed that the proportion of natural forest conversion was high, and the proportion of afforestation in artificially harvested forest areas was relatively low compared with other regions in Hokkaido’s vegetation history. In addition, afforestation outside mountain forests was noticeable, and it is believed that it reflected afforestation in unused grasslands based on the value of unused grassland rates. The analysis showed that the proportion of afforestation outside mountain forests in Kinki was extremely low compared with that in other regions, as shown in Table 2.