FORMATH
Online ISSN : 2188-5729
ISSN-L : 2188-5729
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Showing 1-5 articles out of 5 articles from the selected issue
Original Article
Scientific Category
  • Tetsuji Tonda, Ken-ichi Kamo, Masayoshi Takahashi
    Type: research-article
    2021 Volume 20 20.001
    Published: September 07, 2021
    Released: September 07, 2021
    JOURNAL FREE ACCESS

    In regression model for longitudinal data such as forest growth, it is important to model the growth behavior and to evaluate the effects of covariates such as the impact of environmental factors on growth behavior. In this paper, we consider a situation where the primary interest is centered on the effects of covariates. Though the time trend of the baseline is non-negligible, it is out of scope for this study. Considering age dependent growth behavior as baseline, we can reconstruct the models to include a nuisance baseline. Then it is possible only to estimate the regression coefficients of covariates without modeling the shape for the baseline growth behavior. The linear regression model assumes normality and homoscedasticity for error terms. However, forest growth data sometimes fail to meet the above assumptions because of data non-negativity. In this paper, we develop a regression model for longitudinal non-negative continuous data, using gamma distribution. We apply the proposed method to a forest growth data on Sugi (Cryptomeria japonica) at Hoshino village in Japan.

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  • Ken-ichi Kamo, Hirokazu Yanagihara
    Type: research-article
    2021 Volume 20 20.002
    Published: September 07, 2021
    Released: September 07, 2021
    JOURNAL FREE ACCESS

    Growth functions are often used to describe longitudinal growth processes. In growth analysis, it is first necessary to estimate the parameters included in the growth function based on real life data. During the numerical estimation process, this is often accomplished using iterative algorithm. The initial value setting is the key to this iterative algorithm process. An improper setting of the initial value is risky, because it may lead to non-convergence. Another element of risk is the “convergence of an improper solution” without an error message. Under such a scenario, because the estimation process is correctly completed, it is difficult to identify the source of the error. To resolve this problem, we focus our attention to ridge estimation and how it applies to growth analysis. Ridge estimation method can be used to stabilize the estimation process by imposing the ℓ2 -norm condition as a constraint. In this paper we evaluated the performance of the ridge estimation technique using two cases of numerical experiments. Under several settings of the initial value, we were able to evaluate the behavior of the estimate, especially for dispersion. We concluded that the estimate from the ridge estimation process is more stable compared to the residual sum of square approach. Actually the mean squared error value in ridge estimate is smaller than the residual sum of square. Although ridge estimation method is not universal, this paper has shown us that it is possible to extend the range of setting initial values that converge to a proper estimate.

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  • Masashi Konoshima, Tetsuji Tonda, Ken-ichi Kamo, Bam H.N. Razafindrabe
    Type: research-article
    2021 Volume 20 20.003
    Published: September 07, 2021
    Released: September 07, 2021
    JOURNAL FREE ACCESS

    Unplanned land use conversion driven by increasing food demand has threatened rich forest resources and freshwater fishery resources in Madagascar as a result of increasing sedimentation. For sustainable use of freshwater fishery resources, it is important to examine the impact of land use changes on sedimentation. Severe sedimentation often fills-in and shrinks lakes. Also, sedimentation causes lakebeds to rise, which can lead to flooding and therefore affect the position of the lake’s boundary, over time. Recently available historical satellite images can be useful in assessing the changes in the position of lake boundaries over time. In this study, we propose a modeling approach for evaluating the impact of surrounding land uses on the extents of Lake Itasy, in Madagascar. In order to demonstrate our approach, we utilized satellite imagery available via Google earth to obtain a historical snapshot of the lake boundary. We delineated it and combined the results with a land use map. We then conducted a simple spatial statistics analysis using a logistic regression model with time varying coefficients. Our approach quantifies the impact of surrounding land uses on varying positions of lake boundaries over time.

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  • Eri Takahashi, Diana Surová, Masashi Konoshima
    Type: research-article
    2021 Volume 20 20.004
    Published: September 07, 2021
    Released: September 07, 2021
    JOURNAL FREE ACCESS

    An increasing number of tourists from both within and outside of Japan are attracted to the rich natural resources in Okinawa, as result recreation has become potentially an important source of income to the local economy. Previous survey show that tourists are particularly interested in outdoor recreation in the context of natural surroundings of Okinawa. However, few studies have analyzed the relationships between landscapes preferences for vegetation types on different landscapes and recreation activities. We conducted interview survey to explore public preferences toward various landscapes for various recreational uses in Okinawa. We designed a photo-questionnaire in order to identify desirable surrounding vegetation for each recreation use. A total of 93 survey responses were collected and a non-parametric analyzes (chi-square test, gamma coefficient) was applied to examine the effect of socio-demographic characteristics (age, gender, marital status, employment status, income, education level, birthplace, current residential address, the number of family members) on their preferences. Our results show that Pasture landscape, Coastal forest and Mangrove forest were the most appreciated for recreational activities in this study. Forest landscapes were ranked the highest for nature observation and marine sports. For the other recreational activities, the three top ranked landscapes included a mixture of an open landscape such as pasture and forests. Our results also show that preference for a particular landscape depends on the socio-demographic characteristics of the respondent. In summary, it can be concluded that both the type of recreational activity and the socio-demographic characteristics of recreationists, significantly influence their landscape preferences.

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Discussion Category
  • Phongxiong Wanneng, Barbara Ozarska, Somvang Phimmavong, Atsushi Yos ...
    Type: research-article
    2021 Volume 20 20.005
    Published: September 07, 2021
    Released: September 07, 2021
    JOURNAL FREE ACCESS

    In this study, we assessed the relationship between the price of teak timber and wood characteristics and properties. We interviewed one hundred teak buyers from wood sawmilling and manufacturing companies in Vientiane Capital, in Luang Prabang Province, Northern Laos. Our statistical analysis for manufacturing companies, revealed that 1) the price of timber from teak plantation is statistically correlated with wood characteristics and property such as heartwood, log diameter, log length, wood colour, and wood defect, 2) for non-wood defect, wood properties are not considered important by buyers since they do not consider wood properties when deciding on what timber to purchase, and, 3) buyers reject decay and pipe in timber. On the other hand, the analysis for wood sawmilling companies further revealed that 1) large heartwood proportion, large diameter size and long logs are most preferred by buyers, 2) decay, pipe, insect hole, bend, and knot hole are classified as worse wood defects and negatively impact the decision to purchase timber, 3) wood properties are not considered important for the buyers, and 4) there is significant relationship between price and wood features such as long dimensions (log length and diameter) and heartwood proportion. Our study suggests that while meeting timber market demands, wood processers and manufacturers need to have a clear understanding of the value of timber using tools such as communication on the specific qualities and quantities in order to seek the market efficiency for teak timber.

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