• Journal of Broadcast Engineering
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• v.20 no.1
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• pp.92-109
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• 2015

Broadcast encryption is a cryptographic primitive that allows a sender to securely broadcast a message to a set of receivers. The most influential broadcast encryption system was proposed in 2001 by Naor, Naor, Lotspiech, based on a pseudo-random generator and the Subset Difference (SD) method. In this paper, we suggest a new broadcast encryption system that is based on secret sharing and SD methods. On an efficiency aspect, our system achieves O(r) transmission cost, O($log^2n$) storage cost, and O(1) computational cost for the number n of users and the number r of revoked users. Compared to O(log n) computational cost in the previous SD method, our system has the advantage that it needs only constant-sized computational cost for decryption, regardless of the number n or r. On a security aspect, our system can achieve tighter security reduction than the previous SD method and the gap of security loss is about O(n log n). Moreover, our result shows that it is possible to give the effect of the SD method while using an information-theoretically secure key distribution technique as in the Complete Subtree method.

• Korean Journal of Agricultural and Forest Meteorology
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• v.4 no.2
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• pp.86-94
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• 2002

This study was carried out to identify the relationship between naturally introduced vegetation on the abandoned coal mine lands and the surrounding forest, and to select the indigenous tree species for the revegetation of the real mine lands in Taeback, Kangwon Province, Korea. The apparent species in the surrounding forest of Sododong were 9 species of tree layer, 13 species of subtree layer, 23 species of shrub layer and 23 species of herb layer, respectively. The dominant species in Sarijae were 6 species of tree layer, 15 species of subtree layer, 31 species of shrub layer and 25 species of herb layer, respectively. The plant species in the abandoned real mine land were 31 species in Sododong and 30 species in Sarijae, respectively. The number of plant species in the abandoned coal mine land was smaller than the surrounding forest. The common species of the coal mine lands and the surrounding forest were 6 species(Betula schimidtii etc.) in Sododong and 4 species(B. costata etc.) in Sarijae. It was considered that the species in the coal mine lands introduced from the species of top layer in the surrounding forest. Especially, B. costata in Sarijae showed the edge effect which regenerates the vegetative community from the boundary area of coal mine land and surrounding forest. Natural revegetation in Sododong was also progressing by the invasion of tree species in surrounding forest, such as B. schmidtii. Consequently, natural revegetation in the disturbed coal mine lands may be related to the species composition of the surrounding forest.

• Korean Journal of Agricultural and Forest Meteorology
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• v.8 no.4
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• pp.260-269
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• 2006

This study was conducted to provide basic information for effective management strategies on nature trails in Mt. Jiri national park. Vegetation structure of nature trails in Yupyeong, Jungsanri, Hadong and Baekmudong districts was researched to accomplish the purpose of study. The tree and subtree layer consisted of 16 and 11 species for Yupyeong, 14 and 16 species for Jungsanri, 10 and 13 species for Hadong, and 19 and 10 species for Baekmudong district, respectively. The importance value of Quercu variabilis in the tree layer was highest for Yupyeong, Jungsanri and Baekmudong districts, and that of Pinus densiflora was highest for Hadong district. The herbaceous layer was composed of 70 species for Yupyeong, 53 species for Jungsanri, 65 species for Hadong, 57 species for Baekmudong districts, respectively. The value of species diversity ranged from 0.752 to 1.162, 0.957 to 1.085 and 1.283 to 1.506 at tree, subtree and shrub layer, respectively. Evenness ranged 0.752 to 0.983 at all layers for four nature trails in Mt. Jiri national park.

• Korean Journal of Environment and Ecology
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• v.22 no.3
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• pp.320-324
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• 2008

This study was conducted to investigate abundance of breeding birds in relation to forest environment, to figure out the influential factors in abundance of breeding birds and to get the basic data for effective management of the bird community in Jirisan National Park. For this purpose, this research selected 4 main hiking trails as survey points and conducted a survey on breeding bird species and forest environment from April to August in 2007. The study results are as follows: The number of the birds observed during the breeding season was 33 species at the elevation of 300 meters to 1,900 meters. This research made a regression analysis of 13 bird species appearing at more than 30% of all surveyed points, species richness, and richness in the number of individuals. As a result of making a simple and multiple regression analysis of the factors, among the forest environment factors, that have an effect on richness in bird species, each species was found to be less influenced by an elevation. In addition, this analysis revealed that among the forest environment factors, coverage of tree-1 layer(>12m), tree height, coverage of shrub layer(2${\sim}$0.5m), slope, coverage of subtree-2 layer(4${\sim}$2m) appeared as more influential ones on the variation of abundance in more species than an elevation itself. That explains why it is necessary to continuously maintain and manage the coverage of tree-1 layer(>12m), tree height, coverage of shrub layer(2${\sim}$0.5m), slope, and coverage of subtree-2 layer$(4{\sim}2m)$, etc. for the preservation and management of bird species in a breeding season at Jirisan National Park.

• Journal of Environmental Impact Assessment
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• v.20 no.2
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• pp.187-198
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• 2011

The objective of this study is to analyze the flora and forest vegetation of trails with high visitor density at Molundae. Nine quadrats of $20{\times}20m$ were selected for the survey. The survey was conducted from April to October 2010. The obtained results are summarized as follows. Plot1, plot2, plot3, plot4, plot6, and plot7 were located at slopes of $5{\sim}20^{\circ}$, 17~40m above sea level, and were formed with the colony of Japanese black pine(Pinus thunbergii Parl) and Japanese black pine(Pinus thunbergii Parl)-white oak(Quercus aliena Blume). Tree layer had the height of 8~20m, and the coverage of 50~70%, while subtree layer had the height of 3-8m, and the coverage 30~80%. On the other hand, shrub layer had the height of 2~4m, and the coverage of 10~30%, and herb had the height of 0.2~1m and coverage 5~20%. Plot5, plot8, and plot9 were located at the summit areas of 57~78m above sea level, and $0^{\circ}$ slope. Japanese black pine(Pinus thunbergii Parl) formed a community there. Tree layer was 8~20m high, and covered 60~70%, of the area, and subtree layer was 6~8m high, and coverage 30~40%. Shrub layer had the height of 2~6m, and the coverage of 30%, while herb layer had the height 0.2~2m, and the coverage 20-80%. Succession does not occur in the surveyed areas which have high visitor density. Artificially planted sawtooth oak(Quercus acutissima) trees were found to disturb succession and formation of multi-layer vegetation, resulting in the ecologically unstable forest. Therefore, the researcher suggested the strategy of managing the vegetation in the conclusion. This study has the limit in that the plots selected for the survey reflected only part of various trails in the Molundae area. It is necessary to suggest the vegetation management plans by selecting more diverse trail areas in consideration of the visitor density and behaviors, and analyzing the changes in vegetation quantitatively in order to manage the vegetation in urban areas damaged by visitors more effectively.

• Korean Journal of Agricultural and Forest Meteorology
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• v.7 no.4
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• pp.303-310
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• 2005

Vegetation composition and structure of forest community around Mt. Kumbong, Uiseong-Gun, Korea, were studied using a qualitative and a quantitative approach. Vegetation types and various ecological characteristics including constancy classes, relative coverage, species diversity and interspecific similarity of the major component species were analyzed. Seventy relatives were sampled in $100 m^2$ plots. Forest communities were grouped into mountain vegetation and lower-valley vegetation. The former were divided into 3 communities (Quercus mongolica, Quercus variabilis and Quercus dentata communities). The latter was an Acer mono community. Vegetation units were classified into ten groups. Woody vegetation coverage was $50\~65\%$. The lower-valley vegetation type showed from $2.06\pm0.25\;to\;2.31\pm0.26$ in the species diversity. The species showing interspecific similarity over 0.5 with Quercus mongolica appeared to be Pinus densiflora, Quercus dentata and Tilia amurensis in the tree and subtree layer, and Lindera obtusiloba, Fraxinus sieboldiana, Carex humilis and Carex siderostica in the shrub and herb layer, The species showing higher interspecific similarity with Acer mono were Cornus controversa and Ulmus davidiana in the tree and subtree layer, and Philadelphus schrenchkii and Aristolochia manshuriensis in the shrub and herb layer.

• Journal of Korean Society of Forest Science
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• v.85 no.2
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• pp.260-270
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• 1996

Structure and dynamics of Pinus densiflora community in Mt. Kaya were studied to provide the information needed for management of Pinus densiflora forest in the southern inland of Korea. Stratification structure of Pinus densiflora community in the lower and middle slope consisted of tree layer(10~15m), subtree layer(4~10m), shrub layer(1~4m), and herb layer(below 1m), while in the rock zone of ridge and top area consisted of tree layer(7~10m), subtree layer(2~7m), shrub layer(1~2m), and herb layer(below 1m). According to the diameter distribution of tree species in Pinus densiflora community, secondary Pinus densiflora forest will gradually decline. Its forest may be replaced by Quercus mongolica, Quercus serrata, Carpinus laxiflora, C. cordata, and Fraxinus rhychophylla in the lower slope, and by Quercus mongolica in the middle slope. Pinus densiflora forest has its seedlings and saplings in ridge and top area, so it may be sustained. By taking cores from Pinus densiflora trees in research area, it could be obtained that in the lower and middle slope, age of Pinus densiflora forest was about 80~90 years old. When the age of its trees was about 72~80 years old, withering trees of standing dead occurred. Disturbance regime of Pinus densiflora community in Mt. Kaya consisted of standing dead, uprooting and limbfall, these were 70.6%, 17.6% and 11.8% respectively. It takes about 100~110 years for advance growth of Pinus densiflora in ridge and top area to reach tree layer. During the period, it has twice chances of disturbance in standing dead. Annual diameter growth of Pinus densiflora was 2.45~2.9mm in the lower and middle slope, while it was 1.75mm in ridge and top region, by measuring cores.

• Journal of the Korean Institute of Landscape Architecture
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• v.38 no.3
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• pp.107-114
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• 2010

This study was undertaken to suggest a Pinus densiflora community planting model in the central cool temperate zone of Korea and nearby areas. For the purpose of this study, we surveyed various DBH classes of the P. densiflora community in Dangjin-gun, Choongchungnam-do. We surveyed the size of entire individuals in the 92 plots as well as surveyed the location of individuals in each tree layer and sub-tree layer(1/100 scale) of 44 plots using a quadrant method from young to old communities. As a result of analysis, the tree layer was growing well but the basal areas of the subtree layer were less than 10% compared with the tree-layer. This indicates the subtree layer is not in general growing well in the P. densiflora community. There were no significant patterns in the shrub layer. A P. densiflora community planting would consist of a tree layer and a shrub layer and the finding of growth patterns of the tree layer is significant. In order to make a model of the shrub layer, an additionally survey of another shrub layer is needed in a nearby planting area. Both regression models, 1) between tree layer DBHs and individuals per unit area, and 2) between individuals per unit area and shortest distances of individuals, can yield much information through study.

• Korean Journal of Environment and Ecology
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• v.16 no.4
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• pp.449-456
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• 2003

The valley forests at Baraebong area, Jirisan National Park were studied to investigate forest structure of tree, subtree and shrub layers in relation to aspect and altitude of the slope. Density and basal area of the tree layer in the north-facing slope were greater than those in the south-facing slope. As elevation increased, basal area of the tree layer decreased in north-facing slope. The impotance percentage of Quercus mongolica increased with increasing elevation while those of Quercus serrata and Pinus densiflora decreased. Species diversity of the north-facing slope was 1.307 and that of the south-facing slope was 1.114. There was a tendency that number of species, species diversity and evenness decreased with increasing elevation. The result of cluster analysis for the tree and subtree layer indicated that the studied forests were classified into Quercus senrraa-broad-leaved tree species community at the low and middle elevation belts of the south-facing slope, Quercus mongolika-broad-leaved tree species community at the high elevation belt of the south-facing slope, the middle and high elevation belts of the north-facing slope and top area, and Pinus densiflora-Quercus mangolica community at the low elevation belt of the north-facing slope. There were significantly positive correlations in the importance percentages among Carpinus laxiflora, Quercus serrata, Styrax obassica and Linden obtuiloba, and among Castanea crenata, Rhodndendron schippen-bachii and Vibntnum erosum.

• Journal of Environmental Science International
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• v.12 no.11
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• pp.1181-1187
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• 2003

Hibiscus hamabo, called "Hwang-geun", growing about 3m in height is a deciduous shrub or subtree of Malvaceae. Because the number of these species is very limited in the world, the Ministry of Environment has designated H. hamabo as a preserved plant. The Korea Forest Service also protects it strictly by law since H. hamabo is an out-of-the-way plant and possibly may be exterminated soon in Korea. Investigation for distribution and ecological characteristics of the habitat for H. hamabo was carried out on Soan Island. Two wild H. hamabo were found at the forest edge (equation omitted) along the sea coast located in the southern part of Soan Island and this was the first report in the Korean academic world. These two wild H. hamabos were growing in a naturally inhibited area. The diameters at the base were 12cm and 15cm. The Tree heights were 150cm and 210cm and the number of branches of each wild H. hamabo was 4 and 7. However, the present condition of these plants was not good. Environmental conditions of the naturally inhibited area of H. hamabo were very mild because it is located at the edge of the forest and is always sunny during the daytime since the slope of the inhibited area is facing South. The ground drained very well since the soil was made of gravels and sand. Because the percent of vegetation of the subtree layer where H. hamabo was growing was 40%, the cover degree and sociability of flex crenata trees and Eurya japonica were found to be high. In the naturally inhibited area of H. hamabo, a dominant value of Rubus parvifolius in the lower part of the herb layer was very high and many plants in Compositae, such as Artemisia princeps var. orientalis and Erigeron annuus, were also present. A dominant value of liana, such as Vitis thunbergii var. sinuata, Rosa multiflora, Clematis terniflora and Hedera rhombea, and Gramineae plants that rhizomes were well developed and aggressively propagated, such as Miscanthus sinensis var. purpurascens, Phragmites communis, Spodiopogon cotulifer and Oplismenus undulatifolius which were surveyed as high, too. These results imply that H. hamabo might be exterminated soon through a natural selection if the proper management of the naturally inhibited area of H. hamabo is not conducted continually.