崇明东滩南部盐沼植被空间分布及影响因素分析

Spatial distribution of species and influencing factors across salt marsh in southern Chongming Dongtan

崇明东滩南部滩面高程、土壤盐度在空间上呈明显的梯度变化规律。高程整体西高东低、北高南低,盐度东北高、西南低,两者共同限制着盐沼植物在空间上的分布。该文围绕崇明东滩南部主要植被类群及其空间分布,探讨了土壤盐度、潮滩高程两大环境因子与植物种群分布的对应关系。基于2013年夏、秋季植被空间网格采样和空间插值,分析了东滩南部植物的空间分布现状,发现不同植物类群在高程和土壤盐度上存在极显著的差异(p<0.01)。高程差异:莎草科类群主要分布于高程区间2.93–4.07 m的低潮滩,禾本科主要集中分布在高程3.13–4.31 m的中、高潮滩;盐度差异:海三棱藨草(Scirpus mariqueter)和互花米草(Spartina alterniflora)优势种群植被覆盖区表层30 cm的平均土壤盐度为(3.2±0.6)g·kg–1,显著高于其他类群植物分布区的平均土壤盐度(2.0±0.3)g·kg–1(p<0.01)。崇明东滩湿地生态系统的关键种兼先锋种——海三棱藨草,分布高程介于2.53–3.97 m,而互花米草能适应海三棱藨草80%的高程区间,两者在高程上存在竞争关系。统计数据显示,研究区域中近90%的海三棱藨草分布在研究区东北部,土壤盐度范围为1.6–4.5 g·kg–1,海三棱藨草、互花米草能较好地适应该空间内的盐度胁迫,两种植物在此交替出现。但是在高程和土壤盐度的综合作用下,互花米草的生长状况更好,因此该区的海三棱藨草很可能会被互花米草逐步取代。对各类群植被分布和优势面积的研究发现,海三棱藨草总分布面积为294 hm2,优势群落面积120 hm2,海三棱藨草仅占莎草科植物总优势面积的15.7%,占研究区总面积的6.9%,在6种主要植物(芦苇(Phragmites australis)、白茅(Imperata cylindrica)、互花米草、糙叶薹草(Carex scabrifolia)、藨草(Scirpus triqueter)、海三棱藨草)中比重最小,这给保护区内海三棱藨草种群的恢复和保护带来极大的挑战。

Aims The relationship between vegetation structure and environment factors is an important subject in plant ecology. The elevation and soil salinity of the tidal fiat are the important factors affecting the vegetation commu- nity. Both the elevation and salinity at our sites showed clear gradients. The aims of this study were to： （1） inves- tigate the major species and their distributions in southern Chongming Dongtan; and （2） quantify the two factors that influence the vegetation distribution： elevation and soil salinity. Methods Based on the spatial grid sampling and the spatial interpolation in 2013, we analyzed the distribution of key species as well as their empirical relationships with the environmental factors. Important findings We found that both elevation and soil salinity were significantly different among the vegeta- tion cohorts （p 〈 0.01）. Along the elevation gradient, sedges distributed mainly in the low tidal zone of 2.93-4.07 m, while Gramineae species were found in the middle and high tidal flat （3.13-4.31 m）. Soil salinity of the 30 cm surface in Scirpus mariqueter and Spartina alterniflora zone was around （3.2 ＋ 0.6） g·kg^-1, which was signifi- cantly higher than that of other groups （2.0 ± 0.3） g·kg^-1 （p 〈 0.01）. Scirpus mariqueter, a key and pioneer species at our sites, was mainly found at elevation of 2.53-3.97 m, with 80% of the area overlapping with the habitats of Spartina alterniflora. More than 90% of the Scirpus mariqueter located in the northeast of the study area. The soil salinity of the study site was 1.6-4.5 g.kg^-1, with Scirpus mariqueter and Spartina alterniflora showed positive adaptations. Spartina alterniflora replaces Scirpus mariqueter with increasing elevation due to its high competi- tive ability. The total area of Scirpus mariqueter was 294 hmz, with a dominant area of only 120 hm2. Scirpus mariqueter occupied 15.7% of the sedge dominated area and 6.9% of the total study area, which is the least among six species （Phragmites australis, Imperata cylindrica, Spartina alterniflora, Carex scabrifolia, Scirpus triqueter and Scirpus mariqueter）. It is of great challenge to restore and protect this important endemic species.