Ecological Characteristics Of The Loess Plateau Of Seeds Of Quercus Studied

Seed size and number are two important biological characteristics of seeds.Seed size represents the seeds of nutrients,whose variation had great influence on seed to germinate and to disperse,and on seedling to settle,thereby affecting population regeneration.Sufficient seed can ensure tree seed spreading through the soil seed bank to avoid the adverse environment,reaching the completion under appropriate conditions for seedlings,and supplementing to reach stability and development of the population.The oak(Quercus wutaishanica) is the main dominant species of the Loess Plateau,and constitutes a natural advantage of a relatively stable community which have very important function and meaning on spring conservation,water soil conservation and the likes in the Loess Plateau.Due to the influence of human activity,many wild oak forests had disappeared.Present secondary oak forests exist mostly in form with fragmented patches and regenerated infrequently.The natural secondary oak forests existing distributively in Malan forest region on the Loess Plateau is the climax community in natural succession.The seeds producted by oak trees played an important role on recovery and stability of the forest.In this paper we studied seed size and number variation of natural secondary oak forest after the implementation of natural forest protection project in Malan forest region on the Loess Plateau,and compared impact of the tree size and stand characteristics on seed size and number,and tested the above.Results showed as follows.(1) The oak forest in the area was at stable stage with high frequency of trees with abundant developped seeds;(2) The oak seed mass was normally distributed(Kolmogorov -Smirnov Test Z = 0.926,P = 0.357) with a fivefold range in magnitude.Average seed mass in sample trees was also normally distributed(Kolmogorov-Smirnov Test Z = 0.988,P = 0.283) with variance about 1.8 times. Seed mass varied significantly among stands(as average seed mass within stands),among sample trees(as average seed mass within trees),and among individual seeds in a tree(as every seed mass within a tree)(all P＜0.05),indicating that seed mass was affected by both maternal and environmental effect.Seed mass variance occured among stands(16.02%),among trees(58.23%) and within trees(25.75%),indicating that seed mass was most pronouced within trees.Distribution of seed mass varied significantly between in sunny slope and in shady slope(Kolmogorov-Smirnov Test Z = 4.271,P＜0.001),average seed mass in sunny slope was lower significantly than in shady slope(Mann-Whitney Test Z =-10.130,P＜0.001);(3) The oak trees with seeds reduced as density-dependence namely,the density of trees with seeds was significantly negative correlated with average tree size(r = -0.874,F = 19.34,P = 0.004) while frequency of oak trees with seeds was significantly negative correlated with stand density (r = -0.916,F = 31.21,P = 0.001).Within tree level developped seeds was significantly positive correlated with fertilizated ovules(r = 0.969,F = 78.05,P＜0.001),indicating that more fertilizated ovules produced more viable seeds.The theoretical seed production in trees increase linearly significantly with DBH of trees(R~2 = 0.6465,P＜0.001),indicating that larger tree had more seeds.For different branches,its height were significantly linearly correlated with fertilized ovules,abored seeds and developped seeds,respectively(all P＜0.001),indicating that light,pollination or both may play an important role on fructification of oaks.Moreover, frequency of oak trees with seeds in sunny slope was lower significantly than in shady slope(χ~2 =60.00,d_f=35,P= 0.005 ),indicating that aspect of slopes have certain effect on fructification of oaks;(4) Average seed mass was significantly positively correlated with number of seed within sample trees(r = 0.774,F = 8.965,P = 0.024),indicating that the tree with more seeds had larger seed. variation coefficient of seed mass was significantly negatively correlated with number of seed within sample trees(r = -0.768,F =8.647,P = 0.026),indicating that variation of seed mass minished within sample trees with the number of seeds increaseing.The theoretical seed production in trees increased linearly significantly with DBH of trees while average seed mass wae insignificant with DBH of trees,indicating that this study did not detect a trade-off between seed size and seed number.