| Juglans cathayensis, a tree species of the family Juglandaceaein in Tianshan valley Xinjiang, China, is a relic species in tertiary period in central Asian. It is ranked as a second-class national endangered plant species. It mainly distributes along Western Tianshan and Pamir Alai mountains of former Soviet Union, but in Asia it is only found some small areas in Gongliu County in Xinjiang, China. J. cathayensis has important scientific value for the study of cultivation walnut origin, evolution, changes of paleobotany flora,palaeogeography, and climate changes of tertiary and quanternary. Due to the narrow distribution and the surrounding vast desert, J. cathayensis population is now threatened with extinction. Coupling with climate change, human disturbance, habitat fragmentation and other factors, it is urgent to carry out conservation biology research.Using flora and plant ecology methods of community and population, we researched on the flora composition of J. cathayensis community in Xinjiang Nature Reserve, the structures of plant ecological type, characteristics of phytoclimate and soil moisture, population age structures, fluctuation cycle and evolutionary trend of age composition, population growth characteristics, morphological plasticity and biomass allocation of seeds and compound leaves, et al. We give a comprehensive analysis of the endangered mechanism of this species,and also we try to put forward scientific protection measures. Our main results are as follows:(1)There were 329 species in the Reserve belonging to 182 genera and 56 families,with average of 27.88/km2 species. The number of dominant family was 14 and typical family is 8. There were 17 dominant genera and 4 typical genera. There was not any monotypic family, but 6 monotypic genera, 1 Chinese endemic genus, which included 14 Chinese endemic species and 9 Xinjiang endemic species.(2) Temperate distribution type of floristic geographical elements belonging to 14 families, 140 genera and 299 species in the Reserve, they accounted for 60.87% of total families, 94.5% of total genera and 96.78% of total species(not including the widely distributed type). The flora had more communication with Central Asia and Mediterranean,but relatively few communication with tropical and East Asia, and showed strong temperate characteristic.(3)The angiosperm in the Reserve included 6 shoot growth types, 4 root growth types,6 Raunkiaer life forms, 5 water ecological types and 6 forage value types. The most species of shoot growth type was erect, and cluster type was the second. The most species of root growth type was taproot, and rhizome was second. Hemicryptophyte was the most and annual plantwas following in life forms. Mesophyte was the most in aquatic classification, and hygromorphism was the second. Most species had high feeding value. The plant species compositions showed characteristics of shoot and root in temperate community, and traits of typical hemicryptophytes climate in temperate and soil moisture conditions of mesophytic.(4)The diameter at breast height(DBH) of J. cathayensis populations decreased with elevation increase, the maximum DBH of three plots were 91.7 cm, 82.8 cm and 58.9 cm,respectively. There were three death peaks, the highest mortality of the low elevation site(H1)and the high elevation site(H3) was in the 9th age, and the highest of the middle elevation site(H2) was in the 12 th age. Plant development from juvenile to adult was not continuous.Population survival curve tended to Deevey-Ⅱ, which was an expanding age structure.(5)Life expectancy of 1-6 age J. cathayensis seedlings on sunny slope was higher than that of shade slope. Its survival curve tended to Deevey-Ⅱ,and seedlings number of 1-3 age was absolutely dominant, so it was an expending age structure. Seedling mortality on sunny slope was less than that of shade slope and the 3th age was a peak, and the average mortality rate was 80.4%. Only 1.9% 1 age seedlings can survive to the 7th age, therefore seedlings took r-strategy in its life history.(6)Growth relationships between tree height and age, DBH and age, tree height and DBH of J. cathayensis adult plants were all allometric models of power function. Growth relationships between seedling height and age, basal diameter and age, tree height and basal diameter were all allometric models of exponential function. These models showed that height and basal diameter of seedling showed a shift from slowness to acceleration.(7)There were 14 variant fruits and significant differences among the quantitative traits of their modules(P<0.05), and had bigger fruits after transplanting. Most relationships between quantitative characters were logarithmic and exponential functions.(8)J. cathayensis has odd-pinnately compound leaves, with 5-9 leaflets. The length,width, biomass of compound leaves, and rachis biomass all increased with the number of leaflets increase, but the rachis length decreased. Leaflets biomass increased with the increase of phyllotaxy of compound leaves. Biomass of opposite leaflets was symmetrical. Most growth of compound leaves were powerly and exponentially allometric.(9)According to our comprehensive analysis, although the few fruit yields, slow growth of seedlings, and the lower survival rate of seedling and sapling, the seedlings and whole populations were all expanding age structures. The population will not be endangered in intrinsic factors at present, but this species may be endangered owing to the external factors,such as changes of geology and climate, human effects of picking fruit and community environment. Our proposals are: taking the management of Ex-situ conservation, increasing the financial investment and strengthening scientific management methods. Regularlythinning the mixed broadleaf trees to reduce canopy density, these approaches can increase the survival rate of seedlings and improve fruiting percentage of adult trees, and also can expanding the number of population. These managements can protect the origin of seedling propagation and its habitat to promote the natural regeneration of population. |
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