神农架北坡麻花杜鹃灌丛群落特征

Dynamic Characteristics of Rhododendron maculiferum Community on North Slope of Shennongjia

摘要: 以3个400 m²样方对神农架亚高山麻花杜鹃(Rhododendron maculiferum)灌丛群落进行研究。群落中有植物84种，58属，32科。木本植物中蔷薇科(Rosaceae)种类最多，有19种。灌木层箭竹(Fargesia)的重要值最大。草本层常见的有东方草莓(Fragaria orientalis)、凉山悬钩子(Rubus fockeanus)、星果草(Asteropyrum peltatum)等。3个样方物种数平均为38种，乔木层、灌木层、草本层的平均物种数分别为6种、15种、20种。杜鹃高度主要分布在在4~7 m之间，占总株数的80.9%。径级构成以5~8 cm最多，占61.3%。枯立木数量与活立木株数的比值为7.0%，杜鹃枯立木占枯立木总株数的86.5%。枯死的杜鹃在高度3~5.9 m及胸径3~5.9 cm为最多，分别占枯立木的75%与81.3%。体现了群落在高度郁闭下的自疏作用。随着海拔的升高，群落层次趋向简单，种群密度降低，高度也趋于变小。矮高位芽植物占31%，地面芽植物占27.4%，是群落的主要成分。这种生活型结构与较长寒冬季节与湿润气候相适应。样地属级水平区系温带成分为76.4%，植物区系温带属性明显，尤其北温带属是主要成分，东亚植物区系占较大比重。人为干扰后上层的巴山冷杉消失，下层杜鹃层发展形成单优麻花杜鹃群落，乔、灌、草三层的物种多样性降低，平均树高变小。随着海拔的升高，杜鹃灌丛的生物多样性降低，高度与直径也变小。盛年期的单纯杜鹃群落相对稳定，但冷杉、糙皮桦(Betula utilis)等乔木在群落中或林缘的侵入推动了杜鹃群落的演替。造成林窗的成因有自然死亡、大风、虫害、兽害等。枯立木与倒木造成的林窗是促进更新作用并推动演替的主要原因，杜鹃群落有被巴山冷杉取代的演化趋势。

Abstract: The Rhododendron maculiferum community in the Abies fargesii forest belt in Shennongjia was studied via three 400 m² quadrats. There were 84 plant species of 58 genura and 32 families in three quadrats. Rosaceae is the most in the wood layer with 19 species. The importance value of Fargesia spp. was the highest. Fragaria orientalis, Polygonum pinetorum, Saussurea populifolia were commonly seen in the herb layer. On average, there were 6 species in the tree layer, 15 species in the shrub layer, and 20 species in the herb layer, and the total was 38 species. The most individuals were in 5 -8 cm diameter class with a percentage of 61.3%, and the height of Rhododendron is mainly distributed between 4 - 7 m accounting for 80.9% of the total. Because of the high density, some young individuals died before they can grow up. The ratio of the dead to living standing trees is 7.0%. Most of the dead standing trees of Rhododendron were between the height of 3 - 5.9 m and between the diameter of 3 - 5.9 cm, respectively accounting for 75% and 81.3% of the total number of dead standing trees. With the increase of altitude, population density and tree height of Rhododendron community have decreased and the community levels tend to be simpler. The nanophanerophyte accounted for 31% and hemicryptophyte for 27.4% as the main elements of the community. This kind of life form structure adapted to the local conditions of long cold winter and humid climate. The north temperate type is the most at genus level, accounting for 76.4%. The main plant distribution type is temperate distribution. East Asia type also accounted for an important proportion. Upper Abies fargesii layer disappeared after disafforestation decades ago, so the Rhododendron maculiferum at under layer developed into single-storied stand, and then the species diversity of the tree layer, shrub tree and grass layer decreased, and the average tree height was smaller. As the elevation increased, the biodiversity of Rhododendron shrubs decreased, and the height and diameter also decreased. Rhododendron community at prime period is relatively stable, while the invasion of Fir, Betula utilis in forest or at the edge promotes the succession. The main cause of the forest gap is natural death, high wind, insect pest and animal damage. Gap caused by the dead wood or windthrow is the main reason promoting the regeneration. In general, the evolution tendency is that fir forest would displace rhododendron shrubs.