Arata Momohara

Evidence for the persistence of wild Ginkgo biloba (Ginkgoaceae) populations in the Dalou Mountains, southwestern China

PREMISE OF THE STUDY The possible persistence of wild Ginkgo biloba populations in China has long been debated but never scientifically confirmed. We test our hypothesis that the extant Ginkgo populations in the Dalou Mountains (SW China) represent fragments of the original natural Ginkgo range and offer a range of pertinent perspectives on the living fossil Ginkgos history, prehistory, ecology, and place in human culture-all important aspects of this highly valued species. METHODS We analyzed the vegetation of the study area, determined the population age structure of Ginkgo, and compared it to existing fossil records. For supporting material, we also examined records of the lack of human presence before the mid-17th century in the area, the local peoples beliefs regarding preservation of the forests and existing genetic studies. KEY RESULTS Current species composition of Ginkgo forests in the Dalou Mountains agrees closely with floristic assemblages from fossil records bearing G. biloba. Current populations are found in habitats similar to those of fossil Ginkgo, which, as today, favored rock crevices. Female to male ratios are 3:2. Estimated ages for many of the trees show that Ginkgo was present in this area prior to human settlement and indigenous peoples of this area are unlikely to have planted Ginkgo because of traditional beliefs. Our results agree with existing genetic studies that show that these mountains were glacial refugia for G. biloba. CONCLUSIONS The corroborative evidence confirms the finding that these populations represent fragments of the original natural Ginkgo in the valley and lower mountain slopes of the Dalou Mountains.

The Fossil History of Quercus

The evolution of plant ecosystems during the Cenophytic was complex and influenced by both abiotic and biotic factors. Among abiotic forces were tectonics, the distribution of continents and seas, climate, and fires; of biotic factors were herbivores, pests, and intra- and interspecific competition. The genus Quercus L. (Quercoideae, Fagaceae) evolved in this context to become an established member of the plant communities of the Northern Hemisphere, commencing in the Paleogene and spreading to a diverse range of environments in the later Cenozoic. Its palaeontological record, dominated by leaves and pollen, but also including wood, fruits and flowers, is widespread in Eurasia and North America. Consequently, a great number of species have been described, from the 19th century to the present day. Although Quercus is currently an ecologically and economically important component of the forests in many places of the Northern Hemisphere and Southeastern Asia, no comprehensive summary of its fossil record exists. The present work, written by an international team of palaeobotanists, provides the first synthesis of the fossil history of the oaks from their appearance in the early Paleogene to the Quaternary.

Paleoecology and History of Metasequoia in Japan, with Reference to its Extinction and Survival in East Asia

The occurrence of fossil Metasequoia Miki in and around Japan was reviewed based on recent stratigraphic and paleoenvironmental data to reconstruct the regional ecology and discuss the processes that led to the extinction of Metasequoia in Japan during the late Miocene and its survival in eastern Asia. The frequent and abundant occurrence of Metasequoia fossils with wetland plants during the Eocene indicates that Metasequoia was one of the dominant components of the flood plain wetland forests of Japan. In the Paleogene, Metasequoia was widely distributed in the vegetation zones located between the Paratropical Rain Forest and polar Mixed Coniferous Forest zones. Metasequoia populations in East Asia were limited by a mild maritime climate and were absent from the subtropical regions where fossil assemblages were represented by semi-arid sclerophyllous forests. Climatic cooling may have exterminated Metasequoia populations in northeastern China and the Russian Far East during the late Miocene. However, Metasequoia survived up until the latest early Pleistocene in central and southwestern Japan. Metasequoia was less common in the small subsiding basins than in the wide sedimentary basins that were associated with contiguous fluvial flood plain ecosystems. Thus, orogenic and volcanic induced changes in topography in the flood plains were also assumed to have influenced the distribution of Metasequoia since the late Miocene. These topographic changes culminated during the late early Pleistocene and were accompanied with eustatic events and likely exterminated Metasequoia populations in the alluvial lowlands in southwestern Japan and hindered the post-glacial migration of the genus.

Phylogeography of the genus Cardiandra based on genetic variation in cpDNA sequences

We investigated the phylogenetic relationships within the genus Cardiandra based on plastid DNA sequences. The phylogenetic tree showed that Cardiandra populations from the Ryukyu Islands (Japan) and Taiwan were monophyletic (Ryukyu–Taiwan clade), whereas taxa from China and mainland Japan were sisters to this clade. The divergence time between the Ryukyu–Taiwan clade and the other species was estimated to be 0.082 MYA, i.e., the late Pleistocene. The infrageneric and/or infraspecific differentiation of Cardiandra is estimated to have depended largely on allopatric differentiation caused by the presence or division of the past landbridge of the Ryukyu Islands, which connected mainland Japan to the Asian Continent during the Quaternary.

Paleovegetation reconstruction of fossil forests dominated by Metasequoia and Glyptostrobus from the late Pliocene Kobiwako Group, central Japan

ABSTRACT A late Pliocene (1.8–1.9 Ma) wetland fossil forest community that was dominated by Metasequoia and Glyptostrobus was reconstructed based on the species composition of the stumps and other plant macrofossil assemblages. The plant fossils were recovered from a fossil forest preserved in deposits of the Kobiwako Group that are exposed in the Echi River, Shiga Prefecture, central Japan. Fossil wood of Metasequoia and Glyptostrobus was distinguished based on anatomical characteristics. Apportionment of the wood from different horizons in the fossil forest indicates Metasequoia grew over a long period of time in a stable environment, while Glyptostrobus and Alnus grew in unstable environments characterized by shortinterval floods. The fossil forest as a whole represents a fluvial back-marsh environment. The upland forest was composed of mixed evergreen conifers and deciduous broad-leaved trees including Chamaecyparis pisifera, Tsuga, Magnolia, and Acer. Aquatic and wetland herbs such as Cyperus, Carex, Scirpus, Polygonum, and Menyanthes grew in and around the wetland forest. The assemblage of fossil plants recovered from the fossil forest consists of plants that are currently distributed in the cool temperate climate zone, such as Picea, Thuja, Betula maximowicziana, Pterocarya rhoifolia, and Menyanthes trifoliata. Glyptostrobus is distributed only in subtropical areas at present, but it also grew under a cool temperate climate zone in Japan during the latest Pliocene.

Middle to late-Holocene decreased fluvial aggradation and widespread peat initiation in the Ishikari lowland (northern Japan)

This study investigated the influence of sea-level and climate changes on the decreased fluvial aggradation and subsequent widespread peat initiation in the middle to late-Holocene in the Ishikari lowland, which is a coastal floodplain formed in response to the postglacial sea-level change. By introducing a new approach to separately evaluate the rates of organic and clastic sediment input, we demonstrated that the peat began to form when the fluvial sedimentation rate was significantly decreased (less than 0.6 mm/yr), while plant macrofossil analysis suggested that lowering of water level is also important to the peat initiation. Such changes in sedimentary environment may be associated with the abrupt abandonment of crevasse splays. The concentrated ages of the peat initiation around 5600–5000, 4600–4300, and 4100–3600 cal. BP suggest that an allogenic control promoted the abandonment of crevasse splays, and different onset ages can be explained by different fluvial responses of the Ishikari River and its tributaries. The abandonment of crevasse splays could result from sea-level fall or decreased precipitation. While submillennial sea-level fluctuations coincident with the peat initiation have not been reported in coastal lowlands of Japan, the close comparison of the onset ages and decreased precipitation recorded in a stalagmite from China, which represents the strength of the East Asian summer monsoon (EASM), suggests that decrease in precipitation led to the abandonment of crevasse splays. Our results may indicate that similar fluvial responses might be common in other coastal floodplains affected by the EASM.

Community Structure and Survival of Tertiary Relict Thuja sutchuenensis (Cupressaceae) in the Subtropical Daba Mountains, Southwestern China.

A rare coniferous Tertiary relict tree species, Thuja sutchuenensis Franch, has survived in the Daba Mountains of southwestern China. It was almost eliminated by logging during the past century. We measured size and age structures and interpreted regeneration dynamics of stands of the species in a variety of topographic contexts and community associations. Forest communities containing T. sutchuenensis were of three types: (1) the Thuja community dominated by T. sutchuenensis, growing on cliffs; (2) the Thuja-Quercus-Cyclobalanopsis community dominated by T. sutchuenensis, Quercus engleriana and Cyclobalanopsis oxyodon, along with Fagus engleriana and Carpinus fargesiana, on steep slopes; (3) the Thuja-Tsuga-Quercus community dominated by T. sutchuenensis, Tsuga chinensis, and Quercus spinosa, on crest ridges. The established seedlings/saplings were found in limestone crevices, on scarred cliff-faces, cliff-edges, fallen logs, canopy gaps and forest margins. The radial growth rate was 0.5-1.1 mm per year. Its growth forms were distorted. It had strong sprouting ability after disturbances. The T. sutchuenensis population thrives on cliffs where there is little competition from other species because of harsh conditions and rockslide disturbances. It is shade-intolerant but stress-tolerant. Its regeneration has depended on natural disturbances.

Evolutionary History of Atmospheric CO2 during the Late Cenozoic from Fossilized Metasequoia Needles

The change in ancient atmospheric CO2 concentrations provides important clues for understanding the relationship between the atmospheric CO2 concentration and global temperature. However, the lack of CO2 evolution curves estimated from a single terrestrial proxy prevents the understanding of climatic and environmental impacts due to variations in data. Thus, based on the stomatal index of fossilized Metasequoia needles, we reconstructed a history of atmospheric CO2 concentrations from middle Miocene to late Early Pleistocene when the climate changed dramatically. According to this research, atmospheric CO2 concentration was stabile around 330–350 ppmv in the middle and late Miocene, then it decreased to 278–284 ppmv during the Late Pliocene and to 277–279 ppmv during the Early Pleistocene, which was almost the same range as in preindustrial time. According to former research, this is a time when global temperature decreased sharply. Our results also indicated that from middle Miocene to Pleistocene, global CO2 level decreased by more than 50 ppmv, which may suggest that CO2 decrease and temperature decrease are coupled.

The effects of bryophyte communities on the establishment and survival of an epiphytic fern

Ferns typically grow in soil that has sufficient moisture to enable the germination, fertilization and growth of gametophytes. However, the epiphytic fern, Lepisorus thunbergianus grows on tree trunks often in urban areas, where its gametophytes are susceptible to desiccation and its spores are easily washed off by rainwater. To understand how these ferns become established and survive in such challenging conditions, we conducted a quadrat survey on trunks of Prunus mume (which has cracked bark) and Ilex integra (which has smooth bark), focusing on the presence of bryophyte communities, which are known to facilitate seed establishment. Regardless of bark roughness, fern gametophytes occurred more frequently in the communities of small-leaved and short-bodied liverworts, and young fern sporophytes occurred more frequently in the communities of tall-bodied mosses. As the gametophytes of L. thunbergianus are taller than the liverworts, they are able to grow in the presence of liverworts without experiencing shading effects. However, sites with liverworts were unsuitable for fertilization of fern gametophytes because they were more desiccative environments than the sites where tall mosses grew. In habitats where tall mosses grow, fern gametophytes tended to be affected by competition from the bryophytes, whereas once fern gametophytes had established and matured, it was easy for them to generate young sporophytes because tall mosses retain sufficient moisture for the ferns’ fertilization. In summary, the presence of a moss community is an important factor aiding the establishment of this epiphytic fern in desiccated urban areas.

Past and future global transformation of terrestrial ecosystems under climate change

Future predictions from paleoecology Terrestrial ecosystems will be transformed by current anthropogenic change, but the extent of this change remains a challenge to predict. Nolan et al. looked at documented vegetational and climatic changes at almost 600 sites worldwide since the last glacial maximum 21,000 years ago. From this, they determined vegetation responses to temperature changes of 4° to 7°C. They went on to estimate the extent of ecosystem changes under current similar (albeit more rapid) scenarios of warming. Without substantial mitigation efforts, terrestrial ecosystems are at risk of major transformation in composition and structure. Science, this issue p. 920 Global vegetation change since the Last Glacial Maximum is used as an indicator of transformation under warming scenarios. Impacts of global climate change on terrestrial ecosystems are imperfectly constrained by ecosystem models and direct observations. Pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was comparable in magnitude to warming projected for the next century under high-emission scenarios. We reviewed 594 published paleoecological records to examine compositional and structural changes in terrestrial vegetation since the last glacial period and to project the magnitudes of ecosystem transformations under alternative future emission scenarios. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change and suggest that, without major reductions in greenhouse gas emissions to the atmosphere, terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.