Naoko Yamashita

Acclimation to sudden increase in light favoring an invasive over native trees in subtropical islands, Japan

Abstract Bischofia javanica Blume, an exotic tree, dominates many forest areas of the Bonin Islands in the western Pacific of Japan. The aim of this study was to test the hypothesis that the success of B. javanica (a mid-successional plant species) is related to its high acclimation capacity to sudden light increase due to canopy gap formation. We compared its ecophysiological response to simulated canopy opening with those of native species of different successional status: Trema orientalis Blume, Schima mertensiana (Sieb, et Zucc.) Koidz, Elaeocarpus photiniaefolius Hook.Et Arn. and Ardisia sieboldii Miquel. In all species, transfer of leaves developed in shade (5.3% of full sun) to full sun resulted in a substantial initial reduction in the dark-adapted quantum yield of photosystem II (Fv/Fm). T. orientalis, a pioneer plant species, showed the least reduction (38%), whereas E. photiniaefolius and A. sieboldii, both late-successional plant species, demonstrated large reductions (about 80%). In all four native species, Fv/Fm in shade leaves gradually recovered following transfer, but B. javanica recovered more fully and rapidly than the other species. Unlike Fv/Fm, the chlorophyll content in all species did not recover following the initial decline. This indicates that the recovery of quantum yield (Fv/Fm) was independent of the reduction in chlorophyll. Among all the species, B. javanica showed the highest (1) increase in maximum photosynthetic rate of shade leaves after transfer, (2) production of newly formed sun leaves, and (3) increase in relative growth rate. Ecophysiological characters of B. javanica in simulated canopy openings indicated rapid photosynthetic acclimation in existing shade leaves by minimizing photoinhibition and a rapid deployment of new sun leaves with high photosynthetic capacity. Because its habitats on these Pacific Islands are prone to typhoon disturbance, the successful invasion of B. javanica may lie in the congruence of its acclimation potential and the frequent gap events.

Coordination between leaf and stem traits related to leaf carbon gain and hydraulics across 32 drought-tolerant angiosperms

We examined 15 traits in leaves and stems related to leaf C economy and water use for 32 co-existing angiosperms at ridge sites with shallow soil in the Bonin Islands. Across species, stem density was positively correlated to leaf mass per area (LMA), leaf lifespan (LLS), and total phenolics and condensed tannins per unit leaf N (N-based), and negatively correlated to leaf osmotic potential and saturated water content in leaves. LMA and LLS were negatively correlated to photosynthetic parameters, such as area-, mass-, and N-based assimilation rates. Although stem density and leaf osmotic potential were not associated with photosynthetic parameters, they were associated with some parameters of the leaf C economy, such as LMA and LLS. In the principal component (PCA) analysis, the first three axes accounted for 74.4% of total variation. Axis 1, which explained 41.8% of the total variation, was well associated with parameters for leaf C and N economy. Similarly, axis 2, which explained 22.3% of the total variation, was associated with parameters for water use. Axis 3, which explained 10.3% of the total variation, was associated with chemical defense within leaves. Axes 1 and 2 separated functional types relatively well, i.e., creeping trees, ruderal trees, other woody plants, C3 shrubs and forbs, palms, and CAM plants, indicating that plant functional types were characterized by similar attributes of traits related to leaf C and N economy and water use. In addition, when the plot was extended by two unrelated traits, leaf mass-based assimilation rates and stem density, it also separated these functional types. These data indicate that differences in the functional types with contrasting plant strategies can be attributed to functional integration among leaf C economy, hydraulics, and leaf longevity, and that both leaf mass-based assimilation rates and stem density are key factors reflecting the different functions of plant species.

Defense characteristics of seral deciduous broad-leaved tree seedlings grown under differing levels of CO2 and nitrogen

Mixed broad-leaved forests are abundantly populated by several kinds of herbivore species in northern Japan. The life of herbivores depends strongly on the quality of food leaves. Leaf quality is changing with increasing atmospheric CO2 and nitrogen deposition. Four seral species of deciduous broad-leaved tree seedlings (alder, birch, oak and maple) were raised in all four combinations of two levels of CO2 and two levels of nutrient, to examine foliar defense traits. To evaluate the relative defense capacity of the four tree species, we used wild silkworms (Erisan; a generalist herbivore) as a bioassay material. Except with alder, the survival rate and longevity (ML50) of the silkworms were least when they were fed with leaves of seedlings raised under high CO2 and infertile soil conditions, and longest on a diet of leaves grown in ambient CO2 and fertile soil, especially in birch and maple. The longevity of Erisan decreased in the order birch, oak, and maple. The longevity of Erisan fed with alder leaves was independent of CO2 levels and was longer on alder seedlings grown in infertile soil conditions. Alder is an actinorhizal plant that can fix atmospheric nitrogen in root nodules formed by the actinomycetes Frankia sp. The activity of symbiotic microbes would have been enhanced by the greater amount of photosynthates received from the host plants at high CO2, improving the food quality for the silkworms. It was concluded that in all but alder, leaf chemical traits, especially C/N ratio, affect the ML50 of Erisan larvae.

Reforestation following harvesting of conifer plantations in Japan: Current issues from silvicultural and ecological perspectives

Following the Second World War, the number of Cupressaceae plantations in Japan increased, in accordance with government policy for the restoration of timber resources and conservation of soil and water. Currently, these even-aged plantations occupy approximately 44% of the forested area and 24% of the national land area of Japan. Although many of these plantations have become available as timber resources, there are several silviculture-related problems associated with reforestation following clear-cutting of these plantations. The abundant annual precipitation in Japan allows for dominance by competitive vegetation, which makes natural regeneration difficult and increases the cost of silvicultural operations during and after the planting of seedlings. Because the number of seedling producers has decreased, there has been little incentive to keep seedling production techniques up to date. Additionally, damage to planted seedlings by the overabundant sika deer (Cervus nippon) population has increased dramatically in the last dozen years or so. To determine how to overcome these difficulties, various studies are underway in Japan. For example, seedling studies have examined the relationship between seedling size and competitive ability with other species in reforested areas, and have led to the development of lower-cost systems to produce customized Cupressaceae seedlings, as well as measures to minimize transplanting damage to seedlings. Previous studies have shown that no-weeding operations might lower the risk of sika deer browsing seedlings, although this silvicultural countermeasure may potentially reduce seedling growth. Studies have also examined the types of physical protection against sika deer browsing that are most efficient. We must combine these findings into a unified silvicultural system for successful restoration via lower-cost plantations.

Park pruning prompts a competitive reversal of an exotic tree, Ligustrum lucidum, in urban forests of Japan

Ligustrum lucidum, a tree native to China has naturalized in Japan where it is often planted in parks and along roads. Naturalized individuals in urban woodlands have uncertain competitiveness against native species, particular in light of the frequent pruning undertaken in these woodlands. We compared fitness-related traits of Ligustrum against two co-occurring native species: a pioneer tree (Mallotus japonicus) and an understory tree (Eurya japonica) under pruned and un-pruned settings. A growth experiments where we assessed the leaf and whole plant characteristics of the 3 species under two environments simulating forest edge and forest interior, and two pruning treatments (with or without) was conducted. Under simulated forest edge without pruning, Ligustrum had lower stem growth and Amax (maximum photosynthetic rate) than Mallotus, suggesting that native species can competitively suppress invasive expansion. With pruning, however, Ligustrum resprouted vigorously in both spring and summer with significantly higher apical growth and total shoots than Mallotus and Eurya in forest edge and interior, respectively. Also, with similar Amax between resprouts of Ligustrum and Mallotus, we see a reversal of competitive advantage in favor of Ligustrum in forest edge. In the forest interior, Ligustrum exhibited shade tolerant properties (i.e., Amax, chlorophyll a/b, and leaf density) similar to Eurya but had more resprout shoots, suggesting that the invader also maintains an advantage under low light. The competitiveness of Ligustrum clearly increased with human disturbance in the form of park pruning. Such management practice can inadvertently enhance the invasiveness of exotic species in urban settings.

Leaf Physiological Adjustments to Changing Lights: Partitioning the Heterogeneous Resources across Tree Species

Rain forest trees with various light requirements exhibit a high variation in their physiology and morphology as they encounter contrasting light environments, contributing to higher leaf carbon gain in each environment. A desire to understand the species-specific variations of capturing and using of light resources in terms of photosynthetic processes provides the setting for this chapter. Both niche partitioning and chance effects in the distribution of tropical trees are widely recognized. The objective of this chapter is to clarify tree responses at the single leaf and whole plant levels for the spatial and temporal changes of lights, providing an improved background of ideas on rain forest dynamics and coexistence and an improved plan for the sustainable forest management and conservation. Recent evidences that the ecophysiological adjustments of plant to changing lights influence replacement success under the changing environments and tropical forest dynamics, are reviewed briefly.

Sex Ratio Variation of Bischofia javanica Bl. (Euphorbiaceae) between Native Habitat, Okinawa (Ryukyu Islands), and Invaded Habitat, Ogasawara (Bonin Islands)

The sex ratios of Bischofia javanica, a dioecious tree species, were studied in populations native to the island of Okinawa and in populations that invaded the island of Ogasawara. The sex ratios of all (six) populations in Okinawa were not significantly different from 1:1, but all (five) populations in Ogasawara were significantly biased ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Developing a pre-entry weed risk assessment system for use in Japan

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