Michio Oguro

Context‐dependent changes in the functional composition of tree communities along successional gradients after land‐use change

Summary Land-use change can modify the functional composition of tree communities, which is an essential determinant of the ecosystem functions. The lack of consensus about the functional responses of tree communities to land-use change is a major uncertainty in the assessments of human impacts on terrestrial ecosystem functions. In this study, we applied a machine-learning method to a large data set consisting of 2574 tree communities across Japan to examine changes in the functional composition of tree communities after land-use change while considering contexts including successional trajectories, forest types and the presence of gymnosperms. Specifically, we hypothesized that functional changes along successional gradients after land-use change can be different in different contexts. Effects of two successional variables (stand age and basal area) on functional composition were highly significant throughout the study region. Changes in functional composition with changes in the two successional variables differed greatly, and the effects of basal area often outweighed those of stand age. Tree communities with small basal area were generally characterized by functional traits related to the resource-acquisitive strategy, that is short adult stature, low leaf mass per unit area, small seeds, low wood density and large leaves, especially when gymnosperms were excluded from the analysis. Decreasing basal area but not decreasing stand age often led to a considerable loss in functional diversity. Despite these general trends, functional changes along successional gradients after land-use change were not necessarily parallel and the opposite patterns were sometimes observed among forest types, traits and taxonomic groups. Synthesis. As a whole, our analyses demonstrate that the functional changes in tree communities after land-use change are highly evident in a given context but can be different under different contexts. These changes in functional composition can trigger variable changes in ecosystem functions such as carbon and nutrient cycling that depend on the context.

Detecting latitudinal and altitudinal expansion of invasive bamboo Phyllostachys edulis and Phyllostachys bambusoides (Poaceae) in Japan to project potential habitats under 1.5°C–4.0°C global warming

Abstract Rapid expansion of exotic bamboos has lowered species diversity in Japans ecosystems by hampering native plant growth. The invasive potential of bamboo, facilitated by global warming, may also affect other countries with developing bamboo industries. We examined past (1975–1980) and recent (2012) distributions of major exotic bamboos (Phyllostachys edulis and P. bambusoides) in areas adjacent to 145 weather stations in central and northern Japan. Bamboo stands have been established at 17 sites along the latitudinal and altitudinal distributional limit during the last three decades. Ecological niche modeling indicated that temperature had a strong influence on bamboo distribution. Using mean annual temperature and sun radiation data, we reproduced bamboo distribution (accuracy = 0.93 and AUC (area under the receiver operating characteristic curve) = 0.92). These results infer that exotic bamboo distribution has shifted northward and upslope, in association with recent climate warming. Then, we simulated future climate data and projected the climate change impact on the potential habitat distribution of invasive bamboos under different temperature increases (i.e., 1.5°C, 2.0°C, 3.0°C, and 4.0°C) relative to the preindustrial period. Potential habitats in central and northern Japan were estimated to increase from 35% under the current climate (1980–2000) to 46%–48%, 51%–54%, 61%–67%, and 77%–83% under 1.5°C, 2.0°C, 3.0°C, and 4.0°C warming levels, respectively. These infer that the risk areas can increase by 1.3 times even under a 1.5°C scenario and expand by 2.3 times under a 4.0°C scenario. For sustainable ecosystem management, both mitigation and adaptation are necessary: bamboo planting must be carefully monitored in predicted potential habitats, which covers most of Japan.

Effects of nutrient contents and defense compounds on herbivory in reproductive organs and leaves of Iris gracilipes

Optimal defense theory (ODT) states that the plant tissue with the highest value to fitness will receive the most protection compared with other plant parts. ODT can be applied to the differences in defenses among floral organs, although most studies have concentrated on the comparison between leaves and flowers. Using Iris gracilipes, we investigated whether ODT is supported when primary and accessory floral organs and leaves are distinguished. We found that anthers and perianths tended to be attacked more severely than ovaries and leaves in the bud and flower stages and that anthers contained the highest nitrogen and phosphorus concentrations. Although ovaries were also found to contain high nitrogen and phosphorus concentrations, they were less severely attacked by herbivores than anthers, perhaps because ovaries contained the highest condensed tannins concentrations among the floral organs except for perianths in the flower stage. Thus, noting that the number of ovules is very much smaller than that of pollen grains, we concluded that ovaries are the most intensively protected, consistent with the prediction of ODT as applied to floral organs. ODT is applicable to the difference in defense allocation among floral organs.

Difference in defense strategy in flower heads and leaves of Asteraceae: multiple‑species approach

Although a vast number of studies have investigated defenses against herbivores in leaves, relatively little is known about defenses in flowers. Using wild individuals of 34 species of Asteraceae, we investigated differences in five traits that are thought to affect the intensity of herbivory (C, N, P, water, and total phenolic contents). Combinations of these traits between flower heads and leaves were studied as well. We also evaluated phylogenetic patterns of flower head and leaf traits. Flower heads had higher P and lower total phenolics than leaves. Water and C contents were negatively correlated both in the flower heads and leaves. N, P, and water contents were positively correlated in the flower heads, whereas this pattern was not found in the leaves. Thus, the traits we measured were more tightly inter-correlated in flower heads than in leaves. Because the flower heads had a lower total phenolic content, the relative allocation of defensive compounds could not be explained solely by fitness values of the organs. Perhaps plants employ an escape strategy rather than a defense strategy to cope with floral herbivores and higher allocation in P may enhance their escape from herbivores by improving the growth rate of flower heads, though our result might be affected in part by the plasticity of plants growing at different sites. Moreover, we found weak phylogenetic signals in the defensive traits. Because we found significant differences in the flower head traits, these weak signals may imply that the traits we measured evolved frequently.

Relation between flower head traits and florivory in Asteraceae: A phylogenetically controlled approach

UNLABELLED • PREMISE OF THE STUDY While much research has examined the relation between leaf traits and herbivory, very little is known about the interaction between floral traits, particularly biochemical traits, and florivory. We investigated patterns between floral traits and florivory across multiple species using phylogenetic comparative approaches to enhance our understanding of the evolution of plant-florivore interactions.• METHODS The relation between the intensity of florivory and five biochemical traits (concentrations of carbon, nitrogen, phosphorus, water, and total phenolics) and two morphological traits (diameter and number of flower heads) were investigated in wild individuals of 18 native species of Asteraceae. The phylogenetic signals in the morphological traits and intensity of florivory were also tested.• KEY RESULTS We found that species with higher nitrogen, water, and total phenolics and lower phosphorus concentrations in the flower heads and species with a large number and diameter of flower heads tended to be attacked by florivores. In addition, we found significant phylogenetic signals in florivory and morphological traits.• CONCLUSIONS Our results clearly show that biochemical traits also play important roles in plant-florivore interactions, as previously shown in plant-leaf herbivore interactions. The positive relationship between florivory and total phenolics implies that phenolic compounds in flower heads may not act as a defense in the species. In addition, the observed pattern of signals in florivory might not be solely explained by the signals of the measured traits and other plant traits may also play significant roles in plant-florivore interaction in these species.

Mortality due to Japanese oak wilt disease and surrounding forest compositions

Japanese oak wilt (Raffaelea quercivora) is a vector-borne disease transmitted by the flying ambrosia beetle, Platypus quercivorus, and causes mass mortality in the fagaceous species of Japan. The data described in this article are available in Mendeley Data, DOI: 10.17632/xwj98nb39r.1 [1] and include the mortality status of 1089 Quercus crispula and 846 Quercus serrata trees and surrounding forest conditions. The findings using this dataset were published in M. Oguro, S. Imahiro, S. Saito, T. Nakashizuka, Relative importance of multiple scale factors to oak tree mortality due to Japanese oak wilt disease, For. Ecol. Manag. (2015) doi:10.1016/j.foreco.2015.07.016 [2].

Importance of national or regional specificity in the relationship between pollinator dependence and production stability

Stable production of crops depends on pollination services provided by animals. Although crop production is more stable in pollinator-independent crops than in pollinator-dependent crops at the global scale, the situation at the local scale is unknown. Here, we investigated the relationship between pollinator dependence and production stability of 40 crops in Japan and show that the global relationship does not apply at the local scale, i.e., most pollinator-dependent crops showed stable production and most pollinator-independent showed instable production possibly because of local policies and agricultural practices. Examining relationships at the local scale will help establish effective local management of pollination services and crop production.

Floral-induced and constitutive defense against florivory: a comparison of chemical traits in 12 herb species

Little is known about how plants protect flowers—their reproductive organs—against florivory. Additionally, the induced floral defense system has been examined in only a few species. We tested the inducibility of putative floral defenses and investigated the relationship between natural florivory and the floral defenses of 12 naturally growing plant species. The relationships between florivory and four chemical traits (nitrogen, phosphorus, total phenolics, and condensed tannins) were investigated in 12 plant species. We also studied whether flowers induce changes in chemical defenses in response to artificial damage in 10 plant species. A higher concentration of floral nitrogen was associated with a decreasing frequency of florivore attacks. Among the four traits of the 10 plant species studied, no trait changed in response to the artificial damage. We suggest that induced defense systems may not be advantageous for flowers, although it is also possible that these species simply do not use induced defense in any of their plant parts.

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.