In order to verify the appropriate conservation of urban forests, we used continuous survey data to analyze the secular change of stand structure and plant diversity of urban forests that are being conserved and managed by citizens. The survey was conducted every year for about 10 years by setting up three quadrats in different parts with different origins and management conditions. In the minimal management stand of middle-aged secondary forest, the number of evergreen trees in the lower layers gradually increased. There were few non-forest type species in this stand, and there were many evergreen trees originating from garden trees. In the brightly maintained stand of middle-aged secondary forest, many summer green trees invaded the lower layer, and the current stand structure was maintained in a dynamic equilibrium state by continuous management. Many non-forest type species were also found here. In the young artificial forests, the canopy height was low and not closed in the fourth-grade stands, but in the final year of the survey, a closed tall tree layer was formed. Initially, there were few forest type species and many alien species, but the species composition of the young artificial forests approached the species composition of middle-aged secondary forest year by year. Young plantations have the same diversity as conserved forests due to natural invasion from adjacent sources of forest-type species. In this forests, stands with high diversity and which have many non-forest type species, and stands which are dark but require minimal management, are maintained according to the needs of each location.
We examined the effects of understory clearing at thinning operation on the long-term development of forest floor vegetation. We investigated responses of vegetation cover, species richness, and Shannon-Wiener diversity index (H ') of forest floor vegetation to four different experimental treatments, testing thinning (treatment T), weeding (including shrub clearing) (W), their combination (TW) and control (C) in a hinoki plantation. In the treatment TW, where both thinning and weeding were conducted as ordinary thinning, vegetation cover, species richness, and H' were highest among the four treatments. The treatment W also showed significant development of forest floor vegetation during the measurement period, showing significantly higher vegetation cover and species richness than those in the treatment T at 8th year after the treatments. In contrast, the treatment T where shrubs were retained showed no significant change in vegetation cover and H' during the measurement period. In addition, vegetation cover was not different between treatments T and C throughout the measurement period. These results suggested that thinning of canopy trees without clearing of dense shrub cannot successfully promote the development of forest floor vegetation, and that understory clearing at thinning operation is effective for the purpose of long-term development and diversification of forest floor vegetation.
To evaluate the browsing damage caused by sika deer (Cervus nippon), we surveyed damage to planted trees in young coniferous plantations where deer exclosure fences had been installed. We recorded the number, height and damage status of planted trees in 100 m2 study plots (width 2 m, length 50 m) in 18 Cryptomeria japonica stands and 27 Chamaecyparis obtusa stands in Shikoku Island, Japan. Damage was observed in 23.3% of the surveyed C. japonica trees and 44.6% of C. obtusa trees: damage to C. obtusa was characterized by bark stripping. The percentage of study plot in which the number of healthy tree was < 15 per 100 m2 was 22.2% (4 of 18) for C. japonica and 55.6 (15 of 27) for C. obtusa. It is assumed that such stands might not grow economically due to low tree density and low tree height. We found a tendency that the number of healthy trees decreased as slope inclination increased and as estimated deer density increased. Caution should be paid when we install and maintain deer fences in such a place.
Dark-storage at room temperature can stop the elongation growth of containerized sugi seedlings during the growth period. The inability of photosynthetic production in the dark has a negative impact on seedling vigor such as fine root growth ability. In this study, we aimed to determine the growth period under full sun necessary for the recovery of fine root growth ability of containerized sugi seedlings after 4 weeks of dark-storage. In the summer of 2021, after 4 weeks of dark-storage, there were 0, 1, 2, or 4 weeks of growth under full sun, and all the seedlings including the seedlings that were not stored in the dark (control) were planted on the same date in early August. One week after planting, all the seedlings were dug up and the dry weights of elongated fine roots that had grown into the soil was measured. The seedlings without the growth under full sun after the dark-storage showed the smaller dry weight of elongated fine roots for one week after planting compared to the control seedlings without the dark-storage. The dry weight of elongated fine roots of the seedlings grown under full sun for more than one week after the dark-storage was not significantly different from that of the control. It was suggested that the reduction in fine root growth ability caused by the dark-storage could be restored by growing the seedlings under full sun for more than one week after the dark-storage.