Age-related variations of needles and twigs in nutrient,nonstructural carbon and isotope composition along altitudinal gradients

The biochemical and physiological properties of alpine woody plants responding to elevation are associated with needles and twigs age.However,the interactions with elevation were not well studied.In this study,we investigated age-related(current,one-year and two-year old)functional traits of Abies faxoniana in needles and twigs with elevation(2500 m,2750 m,3000 m,3250 m,and 3500 m a.s.l)at the eastern edge of the Tibetan Plateau.The macro-elements(C,N,P,K,Ca,and Mg),nonstructural carbons(soluble sugar,sucrose,and starch)and isotope composition(δ13C)were measured in needles and twigs of adult A.faxoniana trees(breast height diameter about 30 cm).There were significant age,elevation and their interaction effects on these traits(except forδ13C).Compared with twoyear-old needles and twigs,the current and one-yearold tissues possessed higher concentrations of P and K,lower Ca concentrations,as well as a lowerδ13C values and C:P and N:P ratios in needles.The current-year twigs generally had higher sucrose concentration and sucrose:starch ratio than the old ones.This study suggested that more nutrients were invested to young needles and twigs to cope with elevation for A.faxoniana than the old ones.

Species Diversity Based on Vertical Structure as Indicators of Artificial Restoration for Coniferous Forests in Southwest China

Five indices of species richness, species diversity and species evenness were used to assess a diversity of four types of coniferous forests undergone different artificial regeneration time. The study was based on the vertical structure of forests, involving growth-forms of total plants as well as vertical layers of woody plants. The results showed that, except for the fourth layer of woody plants, the vertical structure of the four forests exhibited significant difference in terms of their species richness, species diversity and species evenness, suggesting that a species diversity index provided more detailed information and was a better index reflecting the regeneration processes in this region. It was recommended that silvicultural management of artificially regenerated forests should be strengthened to conserve the biodiversity of the forests, optimize forest structure and, in the long run, promote sustainable development of forest ecosystems.

Alterations of the Nitrogen Mineralization Rates in Soils of Forest Community Depending on the Ski Run Construction (Mount Uludag,Bursa,Turkey)

Since 194os, Mount Uludag （Bithynian Olympus） has been considered famous with winter sports center in Turkey. In addition, it is one of the rare places because of its plant diversity and is also one of the important plant areas of Turkey. The ski run constructions are rapidly increased in the past decades in the alpine and subalpine belts of the mountain. Rate of nitrogen mineralization and some properties of soft were investigated in the soils of the three ski runs and undisturbed neighborhood forest sites. These ski runs are at the upper part of the forest belt in the mountain. Abies bornmuelleriana forest community is the postclimax and very sensitive to destruetion. The rates of the nitrogen mineralization in the soils were determined in controlled conditions （60% water-holding capacity, 20℃）. Nitrification and nitrogen mineralization were in the ski run inside where the natural recovery started, increased compared with the outside of the ski runs. Waterholding capacity, organic carbon, and total nitrogen were decreased in the massive damaged ski run, and due to these changes, the rates of mineralization and nitrification were also decreased.

STATISTICAL ANALYSIS OF TEMPERATURES ON BOTH THE UPPER AND LOWER BOUNDARIES OF SUB－ALPINE DARK CONIFER FORESTS IN CHINA

Temperature of every month on both the upper and lower boundaries of sub-alpine dark conifer forests at various sites in China are estimated in terms of their distributions and temperature records. Based on these estimated data, the heat factors to influence and control the distribution and growth of subalpine dark conifer forests in China are discussed. It is found that the most important heat index to influence and control the distribution and growth of subalpine dark conifer forests is neither the mean temperature in the warmest month, nor the maximum or minimum temperatures, but monthly accumulated temperature of>0℃ or monthly effective accumulated temperature of>5℃.When monthly accumulated temperature of>0℃ is more than 40℃, or monthly effective accumulated temperature of>5℃ is over 50℃, sub-alpine dark conifer forests cannot grow well. When monthly accumulated temperature of>5℃ is less than 60℃, sub-alpine dark conifer forests can not grow at all. When monthly effective accumulated temperature of>5℃ is in the range 15℃-45℃, subalpine dark conifer forests in China can grow well. The ecological significance of temperature in May and September, and in summer half year are discussed.

Convergence of community composition during secondary succession on Zokor rodent mounds on the Tibetan Plateau

Aims The community succession theory is much debated in ecology.We studied succession on Zokor rodent mounds on the Tibetan Plateau to address several fundamental questions,among them:(i)During secondary succession,does the community composition converge towards one community state or multiple states depending on the initial colonization?(ii)Do mound communities located in different background communities exhibit different assembly trajectories?Methods In a sub-alpine meadow,we investigated a total of 80 mound com-munities at several successional stages in three different background communities resulting from different management histories and compared their changes in species composition.The distribution of plant communities over time was analyzed with quantitative clas-sification and ordination methods.The co-occurrence patterns of species were evaluated at each successional stage,and the degree of convergence/divergence among communities was obtained by calculating two beta-diversity indices.Important Findings During secondary succession,species richness of mound com-munities changed over time,and this change was dependent on the background community.Five life-form groups exhibited different dynamic patterns in species richness and plant cover.Community composition and the degree of species co-occur-rence between communities increased over time since disturb-ance.There was much variation in species composition at earlier stages of succession,but communities on older mounds became more similar to each other and to their surrounding vegetation over the course of secondary succession.Post-disturbance suc-cession of Zokor mound communities transitioned from‘multiple alternative states’to‘background-based deterministic commu-nity assembly’over time.Tradeoffs between competition and colonization,as well as the characteristics of different life-forms and mass effects within a limited species pool are the mecha-nisms responsible for convergence of mound communities.