Cindy Q. Tang

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.

Man-made Versus Natural Forests in Mid-Yunnan, Southwestern China Plant Diversity and Initial Data on Water and Soil Conservation

Abstract Plant diversity, water, and soil conservation of man-made versus natural forests in Mouding (25°24′09″ N, 101°28′18″ E), mid-Yunnan, were investigated and analyzed. Various plant communities exist in this mountainous region: 4-year-old shrubland, a 10- to 14-year-old plantation of Eucalyptus smithii, a 35- to 45-year-old plantation of Pinus yunnanensis, a 35- to 45-year-old semi-natural forest of Keteleeria evelyniana and Pinus yunnanensis, a 35- to 55-year-old natural secondary forest of Keteleeria evelyniana and Cyclobalanopsis glaucoides, and a climax forest of Cyclobalanopsis glaucoides, Castanopsis orthacantha and Castanopsis delavayi as the original mid-subtropical, semi-moist, evergreen broad-leaved trees in the region. The species diversity and the regenerative quality were poorest under the Eucalyptus forest. The Pinus forest had the lowest interception and stemflow (26.4%) of rainfall, followed by the Eucalyptus forest (29.5%). The leaching loss of nutrients was greater in the two planted forests than in the natural ones. The soil under the Eucalyptus forest was impoverished and showed deterioration of its chemical characteristics, as compared to the shrubland, semi-natural, natural, secondary, and climax forests in the same area.

Potential effects of climate change on geographic distribution of the Tertiary relict tree species Davidia involucrata in China

This study, using species distribution modeling (involving a new approach that allows for uncertainty), predicts the distribution of climatically suitable areas prevailing during the mid-Holocene, the Last Glacial Maximum (LGM), and at present, and estimates the potential formation of new habitats in 2070 of the endangered and rare Tertiary relict tree Davidia involucrata Baill. The results regarding the mid-Holocene and the LGM demonstrate that south-central and southwestern China have been long-term stable refugia, and that the current distribution is limited to the prehistoric refugia. Given future distribution under six possible climate scenarios, only some parts of the current range of D. involucrata in the mid-high mountains of south-central and southwestern China would be maintained, while some shift west into higher mountains would occur. Our results show that the predicted suitable area offering high probability (0.5‒1) accounts for an average of only 29.2% among the models predicted for the future (2070), making D. involucrata highly vulnerable. We assess and propose priority protected areas in light of climate change. The information provided will also be relevant in planning conservation of other paleoendemic species having ecological traits and distribution ranges comparable to those of D. involucrata.

Species Diversity Patterns in Natural Secondary Plant Communities and Man-made Forests in a Subtropical Mountainous Karst Area, Yunnan, SW China

Abstract We quantified plant diversity patterns according to changes in species composition, floristic richness, and species diversity in various plant communities in the Shilin karst area (24°38′–24°58′N, 103°11′–103°29′E, altitude 1600–2203 m) of central Yunnan, China, in which the previous land use had been documented. Cluster analysis of floristic similarity of all the stands showed that plant species composition and diversity were primarily influenced by the legacies of land use (as coppices, pastures, and plantations). The DCA (detrended correspondence analysis) grouped 14 sampling transects into 3 plant communities, including a shrubland, a mixed deciduous and evergreen broad-leaved stand (secondary forest), and a premature semihumid evergreen broad-leaved stand (natural premature forest), along a disturbance gradient. We also analyzed Pinus plantations. While plant species diversity was particularly low in the Pinus plantation, stands developing (secondary forest) on former coppice sites were becoming increasingly similar to the natural premature forest. The results would indicate that vegetation and plant species diversity is more efficiently restored by letting degraded vegetation regrow rather than establishing plantations.

Nutrient relocation, hydrological functions, and soil chemistry in plantations as compared to natural forests in central Yunnan, China

The relocation of nutrients among dominant plant species, along with hydrological functions and soil chemistry in five plant communities, including Eucalyptus plantation, Pinus plantation, shrubland, semi-natural, and natural secondary forests were investigated in central Yunnan, China. The nutrient P, N, and K accumulation in above-ground biomass of Eucalyptus smithii (stems, barks, branches, and leaves) were the highest, followed by Pinus yunnanensis of both the Pinus plantation and the semi-natural forest. The nutrient retranslocation efficiency (NRE) of E. smithii was the highest for nutrient P, N, and K with values of 56, 66, and 67%, respectively, among the dominant plant species of the five plant communities, while the NRE of P. yunnanensis in Pinus plantation had the second highest value of NRE for nutrient N. The nutrient content (available P, N, and soil organic matter) in the upper two soil layers under Eucalyptus and Pinus plantations was correspondingly found to be lower than that of the other forests. Moreover, under the Eucalyptus and Pinus plantations, surface runoff, soil erosion, and nutrient loss were more serious, and the water storage of litterfall and canopy interception were significantly lower than that in the other plant communities. Accordingly, we suggest that single-species plantations cannot present the same ecological benefits as natural forests, because of their simple, uniform structures, and the characteristics of the dominant plant species.

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.

Population persistence of a Tertiary relict tree Tetracentron sinense on the Ailao Mountains, Yunnan, China

The persistence of the Tertiary relict tree Tetracentron sinense Oliv. on the eastern slope of the Ailao Mountains, Yunnan, SW China, was here studied in terms of population structure (size, age) and regeneration patterns. T. sinense occurred in unstable habitats by stream banks, on steep slopes, on scree slopes, or on roadsides near streams in narrow valleys, all places subject to frequent natural disturbances, whereas none were found on stable gentle slopes free of major disturbances at similar altitudes. Further, no established saplings of T. sinense were found in forests having high bamboo (Yushania crassicollis Yi) coverage in their understory. The size and age structure of T. sinense were multimodal. The reproduction of the tree was either by means of abundant minute wind-dispersed seeds or by resprouts in unstable habitats. These populations depended on disturbance or gap regeneration to survive. T. sinense, along with other tree life-forms including evergreen broad-leaved species and conifers, dominated in the forest canopy layer, even reaching the emergent layer in places. Results of the study provide insight into the ecological characteristics and survival mechanisms of this East Asian paleoendemic tree species. The study will provide a scientific basis for recommendations for the conservation of this species and for other Tertiary relict plants having similar regeneration dynamics.

Endemism in Mainland Regions – Case Studies

Vascular plant endemism of different mainland regions in relation to ecological conditions and habitats is analysed in detail. The regions belong to different biogeographical zones, climates and are of different sizes. Because of their species richness, level of endemism, and a long history of human occupation affecting the biota, some of the regions are partly or completely located in Biodiversity Hotspots.

Effects of management on vegetation dynamics and associated nutrient cycling in a karst area, Yunnan, SW China

The legacies of land use (such as plantations, pastures and coppices) in the Shilin karst area of central Yunnan, SW China have strongly influenced the plant communities’ structure, dynamics, species diversity, litter nutrients inputs, and soil chemical properties. To evaluate the effects of various restoration approaches on ecosystem recovery in the area, we analyzed vegetation characteristics of a Pinus plantation, natural successional plant communities (the shrubland, the secondary forest and the natural premature forest), and their leaf litter nutrients and soil chemical properties. The natural successional plant communities had better regeneration, higher species diversity, higher litter nutrient input, and higher soil fertility as compared with the Pinus plantation. The results indicate that the natural secondary succession facilitates regeneration to young and old secondary forests, promotes recovery of plant diversity and cycling of litter-soil-nutrients, yielding greater ecological benefits. The study will provide guidance for restoration of the vegetation and for forest management planning in this fragile mountainous ecosystem.

Effects of climate change on potential habitats of the cold temperate coniferous forest in Yunnan province, southwestern China

We built a classification tree (CT) model to estimate climatic factors controlling the cold temperate coniferous forest (CTCF) distributions in Yunnan province and to predict its potential habitats under the current and future climates, using seven climate change scenarios, projected over the years of 2070-2099. The accurate CT model on CTCFs showed that minimum temperature of coldest month (TMW) was the overwhelmingly potent factor among the six climate variables. The areas of TMW<-4.05 were suitable habitats of CTCF, and the areas of -1.35 < TMW were non-habitats, where temperate conifer and broad-leaved mixed forests (TCBLFs) were distribute in lower elevation, bordering on the CTCF. Dominant species of Abies, Picea, and Larix in the CTCFs, are more tolerant to winter coldness than Tsuga and broad-leaved trees including deciduous broad-leaved Acer and Betula, evergreen broad-leaved Cyclobalanopsis and Lithocarpus in TCBLFs. Winter coldness may actually limit the cool-side distributions of TCBLFs in the areas between -1.35°C and -4.05°C, and the warm-side distributions of CTCFs may be controlled by competition to the species of TCBLFs. Under future climate scenarios, the vulnerable area, where current potential (suitable + marginal) habitats (80,749 km2) shift to non-habitats, was predicted to decrease to 55.91% (45,053 km2) of the current area. Inferring from the current vegetation distribution pattern, TCBLFs will replace declining CTCFs. Vulnerable areas predicted by models are important in determining priority of ecosystem conservation.