Fire has been present in the Earth Planet for 400 million years and was a key tool for hunter-gatherers and farmers. However, fire also risks properties and causes casualties when out of control. It is necessary to determine the fire hazards to achieve sustainable management. Three novel models consisting of XGBoost, CatBoost, and LightBoost were implemented to prepare a probability distribution map showing fire susceptibility in Astara City, northern Iran. The case study (42,600 ha) is part of the Hyrcanian temperate forests and is one of the most sensitive cities to wildfire in this region. A SHapley Additive exPlanations (SHAP) model was used to investigate the contribution of different factors to the fire simulation in the applied algorithms. To assess the performance of the applied algorithms, the accuracy indexes consist of sensitivity, specificity, PPV, NPV, and AUC. Among the algorithms, the LightGBM model has the highest performance with accuracy indexes of 0.9712, 0.963, 0.9765, 0.966, and 0.98, respectively. The SHAP degree chart showed that between the contributed factors, the distance from road factor has the highest effect on wildfire, with a negative contribution to the simulation up to -0.25. According to the LightGBM model, very low, low, moderate, high, and very high susceptibility classes cover 51 %, 13 %, 8 %, 14 %, and 15% of the study area, respectively. The findings of this research can be used to develop strategic and operational plans for controlling and managing wildfires effectively in the temperate region of Iran and other forest areas of the world.
Teak (Tectona grandis) is a highly valued tropical timber species widely cultivated across the tropics. In Tanzania, it is an important industrial timber, with the Kilombero Valley Teak Company (KVTC) being a major producer. Despite standardized silvicultural practices, substantial growth variation occurs within KVTC plantations, yet quantification of intra-block soil and topographic heterogeneity is limited. This study assessed the contribution of environmental factors to teak growth by integrating diameter at breast height (DBH), total height, and dominant height measurements from 48 permanent sample plots (PSPs) with fine-scale soil (pH, organic carbon, bulk density, texture) and topographic (slope, elevation) attributes across four plantation blocks of varying site qualities and stand ages. ANOVA revealed significant effects of site class (DBH: F = 167.8, p < 0.0001; height: F = 182.0, p < 0.0001; dominant height: F = 40.1, p < 0.001), age (p < 0.0001), and a strong site & times; age interaction (p < 0.0001). Regression analysis indicated that a 1 unit increase in soil organic carbon and silt content corresponded to dominant height increases of 15.5% (beta = 0.155, p = 0.011) and 0.86% (beta = 0.0086, p = 0.003), respectively (adjusted R-2 = 0.255). These findings highlight dynamic site growth interactions mostly driven by intra-block edaphic variability. Although models explained moderate variance at the plantation scale, the results demonstrate how localized gradients underlie microsite productivity variation. The findings support precision silviculture through site-specific management strategies such as soil amendments and resource allocation to optimize teak productivity in Tanzania and similar regions.
Population dynamics of four co-occurring bamboo species (Gigantchloa albociliata (Ga), Gigantchloa hasskariana (Gh), Bambusa tulda (Bt), Cephalostacyum pergracile (Cp)) were monitored for 13 years to investigate the culm and clump dynamics, flowering and inter-specific interaction in a 4 ha permanent plot in a mixed deciduous forest in Mae Klong Watershed Research Station, Thailand. In nine sub-quadrats (20 m & times; 20 m), all the culms > 1 m height in each clump were tagged and their demographic dynamics were monitored annually. Gh flowered in 1989 before the establishment of the plot. Ga and Cp flowered and died in 1998 and 2001, respectively, while Bt did not flower. Distributional pattern of Ga, Gh and Cp strongly associated with topographical niche differentiation. Ga was the most dominant occupying the middle and upper slope and partially overlapping with Bt and Cp. In contrast, Cp and Gh was occupying ridge and vally, respectively. After death of Ga and Cp, suppressed clumps of Bt started to grow, producing large culms and forming the mature clumps. The spatial distribution and relative dominance of four bamboo species were found to be not stable. They are regulated not only by the self-replacement through seedling establshment after the gregarious flowering and simultaneous death of the parent population, but also by release and expansion of the suppressed saplings of competing bamboo species. The presence of clumps of other bamboo underneath mature individuals partly inhibits the regeneration of the dead species and reduces the adaptive significance of simultaneous death after flowering.
The variability of throughfall in forests has an important effect on the hydrology and biogeochemistry of forest ecosystems. On hillslopes, the canopy structure is expected to vary with slope location, leading to spatial and temporal variations in throughfall. To clarify the characteristics of spatial and temporal variation of throughfall generation on the slope scale, canopy structure, throughfall, and stemflow were investigated along a 90-m forest hillslope covered by deciduous trees. There were no significant differences in LAI, canopy cover ratio, or tree height between the upper and lower slopes, but the trunk inclination was significantly greater at the lower slope than at the upper slope. A significantly higher throughfall ratio to precipitation was found for the lower slope area compared with the ridge slope area during the leafed period. In contrast, no significant difference was observed in the throughfall ratio during the leafless period. Stemflow was clearly smaller at the lower slope area than at the ridge slope area throughout the year. In the lower part of slopes with large stem inclination, stemflow was considered to drip as throughfall from branches and trunks before reaching the ground, thereby increasing the proportion of throughfall. This study suggests that spatially different canopy structures may influence the spatial distribution of canopy partitioning and throughfall generation on the slope scale, even within the same tree species.
To estimate litter and soil organic matter decomposition by using soil temperature at 5 cm in depth, litterbag and soil incubation experiments were conducted. Litterbags, filled with leaf litter obtained from oak and Japanese cedar forests in Rokkasho village, were placed on the soil surface of each forest, and each soil temperature were measured. In another experiment, soil from each forest was incubated at temperatures of 10 degrees C, 20 degrees C, or 30 degrees C for approximately 700 days, and the atmospheric carbon dioxide concentrations in the incubation bottles were analyzed to estimate the amount of carbon dioxide released from the soil at each temperature. The remaining amount of SOM was calculated from the estimated cumulative carbon dioxide release. SOM decomposition rates and their temperature sensitivity were analyzed using a known model with two decomposable compartments with different decomposition rates (an active and an intermediate compartment) and one recalcitrant SOM compartment. The Arrhenius equation was applied with the field soil temperature or incubation temperature as the temperature parameter, and then Q10 and the activation energy of decomposition rate of leaf litter and two SOM compartments were calculated to examine the temperature sensitivity of each decomposition rates. The cedar leaf decomposition rate was estimated to be more sensitive to temperature than oak leaf. The estimated decomposition rate of the active compartment of SOM was more sensitive to temperature than that of the intermediate compartment. These experimental methods make it possible to use the same soil temperature within a forest to predict litter and SOM decomposition rates.
This study investigated the effects of large-scale forestry disturbance on litter decomposition and forest-dwelling organisms. Specifically, we focused on changes in Sasa kurilensis litter following soil scarification and assessed whether such modifications affect litter decomposition dynamics over a 50-year period in Japan. Additionally, we reared larvae of Hynobius retardatus, a forest-dwelling salamander endemic to Hokkaido, in Sasa kurilensis leachate to evaluate the effects of plant trait changes on the salamander. Our results showed that, following soil scarification, the concentration of phenolic compounds in young dwarf bamboo leaves and leaf litter was higher in scarified areas than in untreated control areas. As phenolic compounds function in plant defense, their elevated production likely reflects a defensive response to disturbance. This effect persisted for several decades but mostly disappeared after 50 years. Decomposition experiments using dwarf bamboo litter collected from soil sites that had undergone scarification 10 and 50 years previously revealed that litter from the 10-year scarified site decomposed more slowly than that from the control site, whereas no significant difference in decomposition rates was observed between treatments at the 50-year site. These findings indicate that large-scale forestry disturbances can influence litter decomposition for decades via increases in litter phenolic levels. Additionally, the growth rate of H. retardatus larvae reared in litter leachate was slower at the 10-year scarified site than at the control site. While the specific constituents affecting larval growth were not identified, changes in litter traits likely played a role.
Using allometric equations to predict biomass is a reliable approach for estimating biomass in bamboo forests. This approach has been widely applied in various bamboo forests worldwide. However, the independent variables used in allometric models are inconsistent across bamboo species. Therefore, selecting the appropriate independent variables for a specific species is essential for predicting biomass. The present study addressed a Makino bamboo (Phyllostachys makinoi) plantation. A total of 81 samples were employed in this study to develop aboveground biomass (AGB) models. The datasets contained diameter at breast height (DBH), culm height (H), age (A), foliage biomass, branch biomass, and culm biomass for each sample. We used AGB as a dependent variable and DBH, H, and A as independent variables to develop four models. Each model contained one to three independent variables. Four indicators, R2adj, the residual sum of squares, root mean square error, and Akaike information criterion, were employed to examine the models. The findings demonstrated that only using DBH had an excellent performance for AGB prediction, as AGB = 0.435 & times; DBH1.621. It indicated that adding other variables did not significantly promote the predictive effects for the models. This study further adopted DBH to predict the biomass of foliage, branches, and culms. The results showed that the model used in culms had the best performance due to the highest R2adj. Therefore, our study suggested that using only DBH as a predictor for AGB prediction was adequate and recommended it for Makino bamboo.
In order to clarify the effects of litter-layer removal treatment in 2013 on the ecosystem cycling of radiocesium in a Quercus-Pinus forest, soil Cs-137 inventory and Cs-137 concentration in litterfall were measured from 2014 until 2023. Due to the litter-layer removal treatment, the soil Cs-137 inventory decreased to 67% of the control plot in 2014. During the measurement period, the Cs-137 migration from the organic (O) horizon to the mineral soil horizon progressed. The effects of litter-layer removal on the Cs-137 activity in litterfall varied depending on the litterfall type. Both the initial Cs-137 concentration and the reduction coefficient (lambda) derived from an exponential decrease in non-foliage litterfall Cs-137 concentration were similar between the control and the litter-layer removal plots. For broadleaf litterfall, the initial Cs-137 concentration after the litter-layer removal was lower than that in the control, while the lambda remained similar between the litter-layer removal and control plots. In needleleaf litterfall, the initial Cs-137 concentration in the litter-layer removal plot was lower than the control, but the lambda was numerically higher in the litter-layer removal plot than in the control. Litter-layer removal treatment two years after the radionuclide fallout reduced the Cs-137 concentrations in leaf litterfall from the year after treatment but did not significantly affect the subsequent reduction rate.
Japanese oak wilt is a tree disease caused by the pathogenic fungus Dryadomyces quercivorus, which is transmitted by the ambrosia beetle Platypus quercivorus acting as a vector, and it continues to threaten broadleaf forests across Japan. Among the various control strategies adopted, chemical control remains limited due to insufficient data on insecticide efficacy, particularly via contact exposure. This study evaluated the contact toxicity of three insecticides, i.e. dinotefuran, emamectin benzoate, and permethrin, against P. quercivorus larvae and adults under controlled laboratory conditions. Using a standardized application method, we quantified survival duration across multiple concentrations and estimated 7-day LD50 (median lethal dose) values. Treatments with all three compounds resulted in significant dose-dependent reductions in survival time in both adults and larvae compared with the control groups. The estimated LD50 values indicated interspecific variation in sensitivity across insecticides. These findings provide baseline toxicity profiles that may inform future assessments of chemical control strategies against P. quercivorus.
It is known that a high height-to-diameter ratio (H/D ratio) of saplings at planting suppresses subsequent height growth. However, few studies have compared the duration of this effect across different competition conditions, and essential knowledge for the "omitting weeding" practice for low-cost reforestation remains limited. This study aimed to clarify how initial H/D ratio affects height and diameter growth in Cryptomeria japonica D. Don container-grown large saplings, and whether its impact differs by competitive status, using analyses other than relative growth rate. Using four years of growth data from five cultivars planted in January 2019, growth was standardized by initial size (standardized growth rate), and its relationship with the initial H/D ratio was analyzed across growing periods and competitive status. Results showed that the initially high H/D ratio declined gradually over time; individuals with higher H/D ratios tended to show suppressed height growth, while those with lower H/D ratios showed suppressed diameter growth. Analysis of standardized growth revealed that, regardless of competition, height growth was consistently influenced by the H/D ratio, whereas diameter growth was more strongly suppressed under severe competition (strong suppression). This suggests that under severe competition, limited photosynthetic production and physical support from surrounding vegetation reduce the risk of lodging, allowing for preferential allocation to height growth.
Monitoring bird communities is essential for evaluating ecological recovery in restoration efforts, yet point counts, a commonly used bird census method, have limitations in detecting inconspicuous species. This study compared bird diversity detected by two survey methods: point counts and continuous video monitoring using closed-circuit television (CCTV), in early-stage Dipterocarpus alatus restoration plots supplemented with artificial perches and puddles. Overall, a total of 64 bird species were recorded, representing a wide range of functional guilds, with 30 species detected by both methods. Point counts effectively detected 57 species across the ground to canopy strata. In contrast, 34 species were detected through continuous video monitoring, specifically 19 species at artificial perches and 31 species at artificial puddles, including 7 species that were otherwise undetected by point counts. Multivariate analyses revealed distinct differences in community composition across camera-based methods, highlighting their complementary value. Additionally, 86% of the birds detected using CCTV at artificial puddles displayed drinking and bathing behaviors, particularly during hot and dry periods. The results suggested that CCTV, particularly in combination with artificial structures, could be used to complement point counts and other active techniques in monitoring and managing wildlife in restoration areas.
Reforestation areas undergo rapid and continuous changes in vegetation structure, posing challenges for accurate and cost-effective monitoring. Here, we evaluate the accuracy of the geometric registration of orthomosaic images and digital elevation models using co-alignment, which does not rely on Ground Control Points or the Global Navigation Satellite System, to facilitate time-series analysis of the reforestation area. Three alignment methods - individual alignment (Ind), co-alignment among all epochs together (CA_All), and co-alignment between two epochs (CA_1on1) - were compared. The results show that both co-alignment methods significantly reduce horizontal and vertical relative errors compared to individually aligned images. This approach achieves geometric registration with horizontal accuracy within 0.05 m, whereas the vertical accuracy reaches approximately 0.1 m. When flight conditions and intervals differ markedly, the number of inter-epoch tie points decreases, occasionally leading to meter-scale misalignments. However, connecting more than two epochs reduces these errors and maintains accuracy sufficient for continuous monitoring. These findings suggest that co-alignment, combined with only one accurately georeferenced reference epoch, is highly effective for frequent and detailed forest monitoring. By leveraging a minimal subset of stable features (e.g. logging residues), multi-epoch unmanned aerial vehicle imagery can be seamlessly integrated, providing substantial cost and labor savings over traditional ground-control approaches. This paper presents an easy method for applying time-series analysis to early-stage forest management, with the potential to enable fine-scale detection of growth and changes in spatially complex and rapidly transforming landscapes in the future.
Medium- to low-density airborne LiDAR enables cost-efficient, wide-area forest management inventories; however, conventional approaches to evaluating individual tree crowns often fail to identify overcrowded stands in closed-canopy conifer plantations. This study proposes a stand-density-independent framework to assess canopy crowding using two plot-level indicators derived from LiDAR height distributions: mean live crown ratio (CR) and vertical canopy cover (CC). The core of the method is a dynamically defined height threshold that isolates canopy returns while accounting for spatial variability in understory vegetation height. A two-parameter zero-shift Weibull probability density function is then fitted to the extracted canopy points. The resulting Weibull parameters provide robust mean crown base height (CBH) and mean tree height (H), which underpin CR calculation. CC is estimated from the proportion of dynamically defined canopy returns, improving robustness to understory effects relative to fixed-threshold approaches. Field validation in monoculture conifer plantations in Ibaraki and Fukuoka, Japan, yielded CBH biases of 0.17 m and 0.25 m with RMSEs of 1.64 m and 1.94 m (11.2% and 12.3% of field means, respectively), and H biases of 0.10 m and 0.22 m with RMSEs of 1.47 m and 1.56 m (6.7% and 7.8%). CR estimation errors showed no systematic dependence on stand density across a wide density range (250-2800 trees/ha), enabling reliable identification of stands requiring thinning. By combining CR and CC, 20-m resolution canopy crowding condition maps were generated, supporting prioritization of thinning operations. The proposed framework is computationally efficient and potentially applicable to monoculture conifer plantations in different countries.
This study proposes a two-source mixing model based on a Cs isotopic approach for the source apportionment of 137Cs; it is applicable to the 137Cs/133Cs ratios of two distinct sources and enables delineation of their mixtures. This approach was applied to identify the main pathway contributing to 137Cs accumulation in the buds of Eleutherococcus sciadophylloides (Koshiabura), an edible wild plant known for high 137Cs concentrations. 137Cs in current-year buds was partitioned into internal translocation and root uptake fractions based on two assumptions: (1) all 137Cs and 133Cs in buds originate exclusively from internal translocation or root uptake, with each source maintaining a constant 137Cs/133Cs ratio, and (2) the 137Cs/133Cs ratios in previous-year leaves and soil exchangeable fractions serve as proxies of internal translocation and root uptake, respectively. The 137Cs/133Cs ratios were obtained from the authors' previous study on three small E. sciadophylloides trees. The representative ratio in the soil exchangeable fraction was calculated considering the vertical root distribution. The results showed that internal translocation accounted for 89%-99% of 137Cs in buds, indicating that it was the dominant pathway. Moreover, the 137Cs concentration in current-year buds attributed to internal translocation was higher than that in previous-year leaves. This internal redistribution during the spring growth enhances localized 137Cs accumulation and contributes to the consistently high concentrations observed in E. sciadophylloides buds. This study highlights the importance of internal translocation in 137Cs cycling within forest ecosystems.
It is well established that radiation effects on wild organisms from nuclear power plant accidents primarily depend on the dose received at the accident; however, impacts of prolonged low-dose exposure remain poorly understood. In this study, oxidative DNA damage in Pinus densiflora, assessed via 8-OHdG levels, was compared between inside (0.87-7.74 mu Sv/h) and outside (0.094-0.16 mu Sv/h) the difficult-to-return zone 10 years after the Fukushima accident. Leaf 8-OHdG levels varied among the sites but were unrelated to the absorbed dose. In buds, 8-OHdG levels were very low. An irradiation experiment on 2-year seedlings using Cs-137 at three dose rates (44.8, 461, 1738 mGy/h) also found no association between dose rate and 8-OHdG levels; only sampling points correlated with 8-OHdG levels. In contrast, both dose rate and 8-OHdG levels negatively affected seedling survival after the irradiation experiment. Even without irradiation, samples with >0.04% 8-OHdG did not survive. These results suggest 8-OHdG status indicates seedling health and that environmental stress induces oxidative stress via photosynthesis disruption. Additionally, microsatellite mutation rate in megagametophytes was assessed in 1136 seeds using nine markers, detecting only one mutation in contaminated areas, not statistically significant. This mutation rate was too low for sufficient statistical power. In this study, no evidence was found that low-dose chronic exposure affects oxidative DNA damage or mutation rate in P. densiflora. To understand the impact of low-dose chronic radiation exposure on wild plants, further studies incorporating environmental stress and using endpoints other than mutations, such as genome methylation levels and/or responses to oxidative stress, are necessary. [GRAPHICS]
