Dynamic Changes And Population Viability Analysis Of Populus Cathayana Populations With Different Altitude

Since the industrial revolution, with the increase of the emissions of greenhouse gases, the warming trend is becoming evidently. Mountains have complex geological structure and uneven underlying surface. These conditions make the impact of the climatic factors to the region become strong. Populus cathayana is distributed in the valley areas. The cheuchs are the regions where the interactions of Geographical factor and climate factor are very evident and these areas are good regions for the observation of the impact of the climate change. Therefore, the study of the population dynamics and viability of P.cathayana population in valley of the mountain are important for predicting the development of plants and animals under the background of global change. We investigated the P.cathayana population in West Valley in Xiaowutai Mountain Nature Reserve, apply quantitative ecology theory and set two sample plots which was in 1400 m above sea-level and 1700 m respectively. A study of P.cathayana population based on static life table and a study based on Matrix Projection models were made.A static life table of P.cathayana population was obtained by using the age class structure based on DBH class and the smoothing out technique. we made survival analysis and spectral analysis for analyzing the population quantitative dynamics of P.cathayana. At the low site, There were abundant seedlings, young individuals(added up to 90.0% of the total) and maturing individuals(9.4% of the total) but few old individuals; At the high site, abundant seedlings, young individuals were added up to 62.3% of the total and maturing individuals are 26.2% of the total. the number of the first age class of low elevation was 6.04 times of the high-altitude. The survival curve of the population of low elevation was like Deevey type Ⅱ and the high elevation was Deevey type Ⅱ. Peaks of mortality rate and killing power existed in the lifespan of low elevation: the 8s,and the high elevation is 10 s. The survival functional curves showed that both of the P.cathayana populations decreased sharply at young stage, grew stably at mature stage and declined at old stage. The spectral analysis of the population dynamics of P.cathayana suggested that the process of regeneration of P.cathayana of low elevation exhibits some periodic variations. The amplitude Ak of the population of P.cathayana of low elevation had the largest values at A2=9.579 and it’s A1 was 5.285. for the population of P.cathayana of high elevation, it’s A1 was 0.169.Results which Based on Matrix Projection models suggested that the number of P.cathayana population at low altitude increased, and the growth rate was significant, and the number at high altitude was in decreasing trend but it was not obvious. The progressive growth rates at low altitude was 1.109 and at high altitude was 0.980. The results of Resampling statistical test show that the average of λ at low altitude was 1.070, 95% CI was 0.929~1.212, confidence interval length was 0.283; the average of λ at low altitude was 0.990, 95% CI was 0.941~1.016, confidence interval length was 0.075. λ-value was greater than 1 at low altitude and the viability of the population is high. The Population Viability of the high-altitude population was stability. We compared the matrix parameters of population of P.cathayana at low altitude to population at high altitude. It was found that reproduction rate of low-elevation population was significantly higher than the high-altitude population,and they were 0.608 and 0.042. The survival rate for all stages suggested that the value of the first class and the second class at low altitude was greater than the value at the high altitude, while the third and fourth class level was lower than the value at high altitude. We used ULM software for Sensitivity analysis and Elasticity analysis. The results of the sensitivity matrix showed that, in low elevation the value of the turnover rate from a1 to a2 and the survival rate of a2 were 1.888 and 0.567;in high elevation the value of the turnover rate from a3 to a4 and the survival rate of a4 were 1.330 and 0.593. The results of the elasticity matrix showed that, in low elevation the value of the the survival rate of a1 and the survival rate of a2 were 0.280 and 0.494; in high elevation the value of the the survival rate of a3 and the survival rate of a4 were 0.336 and 0.586.This study showed that the population of P.cathayana at low altitude was developing, had a strong survivability and the number of individuals would increase; the population at high altitude was steady, had a stable survivability and the number of individuals would remain stable within a certain limits. The population of P.cathayana at low altitude was younger than at high altitude. Two populations adopted a different strategy respectively for survival. The population at low altitude maintained population growth through high reproduction rate and the high ensured the stability of the population by low mortality of the old individuals.