The growth of teak (Tectona grandis L. f.) seedlings in sandy soil in northeast Thailand is suppressed by infertility and drought stress. In a preliminary field pot experiment, we confirmed that bentonite was useful for increasing soil water availability. To monitor early growth characteristics of teak seedlings in sandy soil, we curried out an experiment of teak seedlings using bentonite and fertilizer in the field from July 2014 to November 2015. We then compared the growth, biomass, photosynthetic rate, leaf water potential, and concentration of elements in the plant organs among the four treatments. Bentonite increased both soil pH and Ca during the experimental period, and retained P in fertilizer. The dry mass of teak seedlings was markedly increased by concurrent use of bentonite and fertilizer. However, the use of bentonite alone showed little increase of dry mass of teak seedlings. Moreover, application of bentonite was mitigated drought stress in dry season, and photosynthetic rate showed high value by high concentration of chlorophyll. The concentration of K in root of teak seedlings was increased by application of bentonite, and its value showed positive correlation with the relative growth rate of teak seedlings. We concluded that bentonite was useful for the uptake of K and retention of P in fertilizer, as a result, growth of teak seedlings was accelerated.

When teak (Tectona grandis L. f.) is planted on acrisols in Northeast Thailand, its growth is suppressed by low pH, infertility, and low water holding capacity. To examine materials capable of increasing water holding capacity in soil and improving teak growth, we conducted an experiment with teak seedlings. We selected bentonite, charcoal, and corncob and added these materials at a rate of 4% to sandy soil from northeast Thailand. Teak seedlings were potted on these soils and raised from July 2013 to July 2014. We compared growth, photosynthetic rates, leaf water potential, and concentrations of elements in plant organs among bentonite, charcoal, corncob, and no addition (control) treatments. Water content in the soils was increased for the bentonite and charcoal treatments. Teak seedlings potted in these two conditions did not suffer from drought stress. Comparing the growth traits of the teak seedlings, the charcoal treatment produced larger root growth and promoted the uptake of phosphorus and potassium, whereas the bentonite treatment did not show positive effects on growth or nutrient acquisition. In contrast, the corncob treatment decreased water content in the soil, and teak seedling growth was suppressed. We concluded that charcoal was a useful material to improve teak growth in sandy soils.

Sprouting ability is highly variable among different tree species. In many cases, there are trade‐offs in carbon allocations between growth and storage in seedlings. However, this trade‐off is likely to change with growth stages from seedling to mature plant because carbon investments in reproductive activities and/or risk of disturbance also change by species and growth stage. To examine how sprouting ability and carbohydrate storage change with growth stage, we compared two tropical secondary‐forest trees, Macaranga bancana and M. gigantea, which have different ecological traits. Maximum tree size and growth rate are higher in M. gigantea. We monitored sprout growth and stored resources, including total non‐structural carbohydrate (TNC) and nitrogen in the root, among different tree sizes for 12 months following stem‐cutting treatment. Sprouting ability (total sprout mass) and TNC concentrations were significantly higher in small individuals than in larger specimens in both species. TNC concentration decreased in all size classes after stem cutting. Macaranga bancana had greater sprout survivorship than M. gigantea, which had higher sprouting ability in larger tree‐size classes. Thus, sprouting ability likely depends on root TNC concentration and tree‐size class in both Macaranga species. Higher TNC concentration and sprout survival rates in M. bancana may be related to greater carbon allocation in survival than in growth. This hypothesis is consistent with the ecological traits of M. bancana, such as its growth rate, which was lower than that of M. gigantea.

We developed simple practical methods to estimate deer appearance frequency and damage risk for cedar saplings protected by tree shelters, by using field signs such as browsed understory plants, debarked trees, and animal trails. The appearance frequency of the sika deer was recorded using camera traps at 29 clear-logged and young plantation sites in the Shikoku Island of western Japan. Field signs such as fecal pellets, footprints, animal trails, and browsed plants were recorded in three transects that were 2 m × 50 m each, located at the margins of the sites. Cubic regression analysis showed that the frequency of deer appearance could be predicted from the number of browsed plant species categorized into three ranks, that is, 0, 1, and ≥2 species. To use this method, plant species are not required for identification, as the user can simply judge whether browsed plants found in 5-m sections are all the same species or not. The damage of sheltered cedar saplings was assessed at 36 sites in the Kyushu and Shikoku Islands of western Japan, and surveys of deer field signs were also conducted. The proportion of heavily damaged saplings could be determined from the indices of binary summarized data of bark stripping and animal trails using a logistic regression model. The indices derived from the field signs will help forest managers to detect relatively low frequency of deer appearances and high risk of cedar sapling damage at a sheltered plantation in the western Japan.

Tree shelters are used in forestry to prevent large herbivores from browsing on young trees. Although tree shelters can generally prevent browsing damage while the young trees are within the tree shelters, they have been observed to fail in some cases. In this study, to clarify the protective capacity of tree shelters against damage due to deer browsing, the condition of tree shelters on planted Japanese cedar (Cryptomeria japonica) seedlings 2 to 7 years after installation was investigated at 42 sites in southwestern Japan where the density of sika deer (Cervus nippon) is high. The results showed that tree shelters failed for three reasons. Firstly, the shelter had collapsed or incline and could no longer protect the saplings within. Secondly, the saplings in the shelters died relatively shortly after they were planted. Thirdly, and possibly most importantly, the saplings are browsed upon by deer after they extended beyond the top of the shelter. Since there was no correlation between the damage rate and the number of years after planting, it is likely that the damage occurred immediately after the young trees protruded form the shelter. Shelters with a height of only 140 cm, which are widely used in Japan, may be too short to completely prevent herbivory damage by deer.

We studied the microclimate inside treeshelters to examine how they affected growth of Japanese cedar (Cryptomeria japonica) seedlings in western Japan. Air temperature (T), relative humidity (RH), and photosynthetic active radiation (PAR) were measured inside and outside of commonly used design of tubular treeshelters made of translucent polypropylene at a nursery throughout a year. Vapor pressure deficit (VPD) was calculated from T and RH data. Results indicated that the inside T and VPD above the seedling foliage were extremely higher than ambient air. However, T within the seedling foliage showed 2.7°C higher than ambient T even though 10.3°C higher above the foliage in August. The VPD within seedling foliage was lower than ambient VPD in summer, and increased with decreasing RH when the precipitation was low. Microclimate in an empty treeshelter showed higher T and VPD than those in treeshelter with seedling. These results indicated that high T and VPD were mitigated by transpiration from needle leaves of seedling, and Japanese cedar seedlings could grow in treeshelters at sufficient water supply.