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In the present study, the distribution, population size and structure, habitat and stand disturbance of a critically endangered plant Euryodendron excelsum H. T. Chang were examined using field investigations. A total of 179 individual plants, including 23 adult trees, were found. The population was distributed in 10 highly isolated and fragmented patches. Half of the 10 patches had less than 10 individual plants and two patches had only one remnant adult; there were no adult plants in two of the patches. Although the overall population structure trends to a reversed 'J' shape, two fragile stages of E. excelsum limit its natural recruitment and regeneration: seed germination and seedling growth toward adulthood. The major threats for the survival of this species are its specific small population size and the high frequency of anthropogenic destruction. Based on the results, some strategies were put forward for the conservation of E. excelsum populations.

Abstract. In this paper, the stability of a Timoshenko beam with time delays in the boundary input is studied. The system is fixed at the left end, and at the other end there are feedback controllers, in which time delays exist. We prove that this closed loop system is well-posed. By the complete spectral analysis, we show that there is a sequence of eigenvectors and generalized eigenvectors of the system operator that forms a Riesz basis for the state Hilbert space. Hence the system satisfies the spectrum determined growth condition. Then we conclude the exponential stability of the system under certain conditions. Finally, we give some simulations to support our results.Mathematics Subject Classification. 93D15, 93C20, 49K25, 34H05.

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