Pennings Steven C, Moore Darrin J
University of Georgia Marine Institute, 31327, Sapelo Island, GA, USA.
Oecologia. 2001 Feb;126(4):587-594. doi: 10.1007/s004420000548. Epub 2001 Feb 1.
We explored the generality of the processes mediating shrub zonation in western Atlantic salt marshes by comparing the results of our experiments in Georgia, USA with previous studies from Rhode Island, USA. The shrub Borrichia frutescens dominates the terrestrial border of many Georgia salt marshes. Within the shrub zone, physical stress increased at lower elevations, shrubs at lower elevations were stunted, and experimentally reducing physical stress reduced shrub stunting. Below the shrub zone, physical stress increased further, and the grass Spartina alterniflora dominated. Transplant and neighbor-removal experiments indicated that the lower border of the shrub zone was set more by physical stress than by competition, but that the upper border of the grass zone was set primarily by competition with shrubs. Laboratory experiments indicated that S. alterniflora seedlings survived best and shrub seedlings worst in the flooded, salty treatment that mimicked low-marsh conditions. These processes are similar to those maintaining zonation patterns between the shrub Iva frutescens and the rush Juncus gerardi in Rhode Island salt marshes. However, markedly different processes appear to occur further to the north, where woody shrubs are absent from coastal marshes, and further to the south, where woody plants (mangroves) dominate coastal wetlands.
我们通过比较在美国佐治亚州的实验结果与美国罗德岛州先前的研究，探讨了西大西洋盐沼中灌木分带现象背后过程的普遍性。灌木Borrichia frutescens在佐治亚州许多盐沼的陆地边界占主导地位。在灌木区内，较低海拔处的物理胁迫增加，较低海拔处的灌木发育不良，通过实验降低物理胁迫可减少灌木发育不良的情况。在灌木区以下，物理胁迫进一步增加，互花米草占主导地位。移植和去除邻体实验表明，灌木区的下限更多是由物理胁迫而非竞争决定的，但草区的上限主要是由与灌木的竞争决定的。实验室实验表明，在模拟低地盐沼条件的水淹、含盐处理中，互花米草幼苗存活得最好，灌木幼苗存活得最差。这些过程与罗德岛州盐沼中维持灌木Iva frutescens和灯心草Juncus gerardi之间分带模式的过程相似。然而，在更北部沿海盐沼中没有木本灌木的地方，以及更南部木本植物（红树林）主导沿海湿地的地方，似乎发生了明显不同的过程。
