The influences of regional atmospheric precipitation characteristics and its element inputs on the existence and development of Dinghushan forest ecosystems
The influences of regional atmospheric precipitation characteristics and its element inputs on the existence and development of Dinghushan forest ecosystems
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作者：
Zhou Guo
北回归线附近地区以半荒漠或荒漠为主。鼎湖山位于北纬23°10′，112°34′，虽然位于该地区，但却被区域性季风常绿阔叶植被所覆盖。这无疑是季风气候带来的大量降雨的结果，但其他事实可能使这一解释变得复杂。鼎湖山附近的一些地区，沙漠化程度很高。 退化的生态系统如果不及时恢复是不可避免的。对于这类退化的生态系统来说，高降雨量会加速退化。本研究将考察降雨、矿物质输入的特征及其对森林生态系统生存和发展的影响，找出其典型植被形成的主要原因。以高要市和肇庆市气象台数据为参考，利用双累积降雨曲线对1959—1965年和1973—1999年34年的降雨数据进行了检验，并采用回归分析法估算了鼎湖沙1956—1958年和1966—1972年缺失的降雨数据。在林冠范围内采集了2个降雨样本。每月之间 1998年和1999年。氨氮和硝酸盐浓度分别采用小型凯氏定氮法和酚二磺酸法测定，磷含量采用钼蓝法测定，钾、钠、镁含量采用原子吸收法（型号Zee man 180-80）测定。年降水量的80%以上集中在雨季（4-9月），雨季气温较高，植物生长活跃。水热输入的结合对生态系统的发育和恢复产生影响：（1）雨季大雨常造成水土流失和养分流失。旱季热量输入充足，表层土壤被冲刷松动，下一个雨季容易被冲刷； (2)由于旱季太阳辐射输入适度，植物生长潜力仍保持较高水平，对水分的需求量适中，但季节降雨量较少，无法满足需要，不利于植被恢复。 1993-1997年平均降雨强度为8.3mm·h -1 ，中、强降雨占年降雨量的30%以上，小强度降雨较多，但仅占15.3%。与同属亚热带的鹤山相比，鼎湖山的暴雨降雨量及其频次要少得多。鼎湖山多年降雨量变化率为 9.3%，远低于江南地区的20%。这些结果支持了这样的论点：降雨及其分布使鼎湖山的植被比同纬度其他地区更容易恢复。 1956年至1999年期间,鼎湖山共发生暴风雨事件228次,平均每年5.3次。约86.4%的暴雨降雨发生在雨季,旱季(10月至3月)仅占13.6%。80年代以来,11月、12月和1月偶有暴雨,这可能与全球气候变化有关,值得进一步研究。 1956年至1999年期间,共发生台风132次,台风多发生在5月至11月之间。通过年代际统计发现,1950年代9月、1960年代和1970年代8月、1980年代7月、1990年代8、9月飓风发生次数最多。自相关分析公式如下：C D=1N-DΣN-Di=1(x\-i-)(xi+d-) 上式中，C D 为降雨时间序列的协方差，x\-i 为时间点的降雨量，i，N 为时间序列的长度；D 的值为 0,1,2,…,m(mN)；x 为 x i 的均值。 系数等于C D 与C 0 之比。对于鼎湖山降雨时间序列，自协方差函数的第一个峰值为7a，第二个峰值为11a。全球气候振荡也有一个峰值周期为7a，以及11a至13a
The region near tropic of cancer is dominated by semi-desert or desert.Dinhushan,being at 23°10′N,112°34′,is located in the region,but is covered by regional monsoon evergreen broad-leaved vegetation.This is undoubtedly resulted from the large rainfall due to monsoon climate,but other facts may complicate this explanation.Some regions near Dinghushan,desertification is unavoidable if the degraded ecosystem is not restored timely.For those kinds of degraded ecosystems,high rainfall will accelerate degradation.This study will examine the characteristics of rainfall,mineral input and their influences on the existence and development of forest ecosystems,and identify the major causes for formation of its typical vegetation. 34 years'rainfall data for the periods 1959 to 1965 and 1973 to 1999 were checked for accuracy using double cumulative rainfall curves with data from Gaoyao and Zhaoqing meteorological observatories as reference.The regression analysis was used to estimate the missing rainfall data of Dinghusha for the periods of 1956 to 1958 and 1966 to 1972. Two rainfall samples over the canopy of forest were taken monthly between 1998 and 1999.Concentrations of ammonia and nitrate were measured using Miniatnvized Kjeldahl and Phenoldisulphonic Acid methods respectively,content of phosphorus was measured using Molybdenum Blue method,and these of potassium,sodium and magnesium were measured using atomic absorption(model Zee man 180-80). More than 80% of annual rainfall falls in wet season(April to September),over which the air temperature is high,and that period coincides with active plant growth.The combination of water and heat inputs influences the development and restoration of ecosystems in this way:(1)Heavy rain in wet season often results in soil erosion and nutrient loss.Sufficient heat input in dry season will loose the washed surface soil,which makes it easy to be flushed in next wet season;and (2)Because of moderate solar radiation input in dry season,the plant growth potential still keeps high and demands for moderate water,but less rainfall in the season can not meet the need,which are detrimental to the recovery of vegetation. The mean rainfall intensity was 8.3mm·h -1 during 1993 to 1997.The medium and heavy rainfall accounts for over 30% of annual rainfall.Low intensity rainfall is much more frequent,but only accounts for 15.3% of the total.As compared with that in Heshan located in the same subtropical zone,the Dinghushan rainfall from the heavy rain and its frequency are much less.Yearly rainfall variability in Dinghushan over many years is 9.3%,much lower than 20% for the regions in the south of Yangtze River.Those results support the assertion that the rainfall and its distribution here have made the vegetation in Dinghushan to recover more easily than that in other regions of the similar latitudinal zones. Over the period of 1956 to 1999,there were 228 storm events with a mean of 5.3 times per year in Dinghushan.About 86.4% of storm rainfall occurred in the wet season,and only 13.6% in the dry season (October to March).There were occasional storms in November,December and January since 80's,which may relate to global climate change,and is worth further study. Over the period of 1956 to 1999,there were 132 typhoons.Typhoon usually occurred between May and November.Using the decadal statistics,we found that the highest number of hurricanes occurred in September in 1950's,August in the 1960's and 1970's,July in 1980's and August and September in 1990's. Following formulae is for autocorrelation analysis:C D=1N-D∑N-Di=1(x\-i-)(x i+d-)In the above equation,C D is he covariance of the rainfall-time series,x\-i is the rainfall at time,i,N is the length of the time series;D has a value of 0,1,2,…,m(mN);x is the mean of x i.The autocorrelation coefficient is equal to the ratio of C D and C 0. The first peak in the auto-covariance function was 7a and the second one was 11a for the rainfall time series in Dinghushan.Global climate oscillation also has a peak period of 7a,and 11a to 13a