Mangrove forest growth in the Fly River delta, Papua New Guinea

During September 1991 and January 1993, permanent plots were established in the three major mangrove forest types in the Fly River delta to follow the growth rates of marked trees. A total of 13 plots were established in Nypa forests on Puruta, Aibinio and Wabuda Islands in September 1991. In January 1993, 5 plots were established in Rhizophora-Bruguiera forests on Umuda Island and 5 plots in Sonneratia-Avicennia forests on small islets east of Sumagi Island.The size of plots varied with tree densities in each forest type and ranged from 50 to 500 m². The diameter of each tree in the plot was measured at breast height (DBH = 1.5 m above the sediment). In the Nypa plots all emergent tree species other than Nypa were similarly measured and tagged. For Nypa, the plot was surveyed using an angle-count cruising method to obtain size frequency distribution of Nypa fronds (the palm has a creeping trunk with upright fronds) and their density per hectare. All fronds of at least four trees in each of 12 plots were measured (DBH) and tagged (13-19 fronds per plot).Size-frequencies and densities of trees and Nypa fronds in plots were converted to biomass per hectare using known allometric relationships between DBH and weight for trees or a measured relationship for Nypa based on harvesting and weighing fronds in the Fly Delta.All Nypa plots were remeasured 12 months after establishment in September 1992. Significant turnover and growth of Nypa fronds was observed. For the two canopy emergent tree species in the Nypa forests, Heritiera littoralis and Xylocarpus granatum, only Xylocarpus granatum showed significant trunk growth within this period. The plots in the other forest types were not remeasured at this time. However, these plots were revisited in February/March 1995.Trunk mass increments for individual Xylocarpus granatum trees were calculated by subtracting mass at time zero (calculated from DBH measurements and allometric relationships between DBH and weight) from mass at t = 1 yr. For Nypa, the same procedure was followed for fronds present at t= 0 and also for fronds that were produced during the year. For Xylocarpus granatum, mass increments were summed for all trees in a plot to obtain annual trunk and branch wood production per unit area. For Nypa, annual mass increments per tree were multiplied by tree densities to obtain production on an areal basis. Permanent plots were established to check the validity of previous estimates of mangrove forest production in the Fly River delta. Earlier estimates were based on a rapid survey technique, which is thought to underestimate productivity. Determining the growth rates of marked trees in these plots allows for a more accurate estimation of the production of trunk and branch wood in the major forest types. A larger number of Nypa plots were chosen to examine the potential for aging stem sections of Nypa for investigations of recent metal histories. This research project was a component of a larger project "The influence of fluvial discharge on the pelagic and benthic ecology and biogeochemistry of the Fly Delta and Gulf of Papua". It follows on from an earlier project "The influence of freshwater and detrital export from the Fly River system on adjacent pelagic and benthic systems".Rhizophora-Bruguiera forests dominate the seaward end of the Fly Delta and Nypa palm forms extensive forests in the mid intertidal zone in the mid- to low-salinity regions. Sonneratia-Avicennia forests occurr on accreting mud banks throughout the delta, but Sonneratia lanceolata is most abundant in the near-freshwater regions of the upper delta and extended some 240 km upstream from the sea.The rapid survey techniques used in the 1989/90 surveys are described in:Robertson AI, Daniel PA, Dixon P (1991) Mangrove forest structure and productivity in the Fly River estuary, Papua New Guinea, Marine Biology 111: 147-155. This publication is also referred to in the metadata record:Mangrove forest structure and productivity in the Fly River estuary, Papua New Guinea

1991年9月至1993年1月期间，研究人员在弗莱河三角洲的三种主要红树林类型中设立永久样地，以追踪标记树木的生长速率。

1991年9月，在普鲁塔岛（Puruta）、艾比尼奥岛（Aibinio）和瓦布达岛（Wabuda）的水椰（Nypa）林中共设立13个样地。1993年1月，在乌穆达岛（Umuda）的红树-木榄（Rhizophora-Bruguiera）林中设立5个样地，在苏马吉岛（Sumagi）东侧小岛的海桑-白骨壤（Sonneratia-Avicennia）林中设立5个样地。

样地面积随各林型的树木密度有所差异，介于50至500平方米之间。对样地内每株树木均测量其胸高直径（DBH，即距沉积物表面1.5米处的树干直径）。在水椰样地中，除水椰外的所有其他上层乔木物种均按相同标准测量并标记。对于水椰，研究采用角规测树法（angle-count cruising method）开展调查，以获取水椰叶丛（该棕榈植物具匍匐茎与直立叶丛）的大小频率分布及其每公顷密度。

在12个样地中，至少选取4株水椰的所有叶丛测量其DBH并进行标记（每个样地对应13至19个叶丛）。利用已发表的树木DBH与生物量间的异速生长关系（allometric relationships），或基于弗莱河三角洲叶丛采收称重得到的水椰实测关系，将样地内树木与水椰叶丛的大小频率与密度转换为每公顷生物量。

所有水椰样地均于1992年9月，即样地设立12个月后进行了重测，观测到水椰叶丛存在显著的周转与生长。在水椰林中的两种上层乔木树种银叶树（Heritiera littoralis）与木果楝（Xylocarpus granatum）中，仅木果楝在此期间出现了显著的树干生长。其余林型的样地当时未进行重测，但于1995年2月/3月进行了回访。

单株木果楝的树干生物量增量通过将t=1年时的生物量减去初始时刻（t=0）的生物量计算得到，初始生物量由DBH测量值与DBH-生物量异速关系推导得出。对于水椰，针对t=0时刻存在的叶丛以及当年新生的叶丛均采用相同流程计算增量。对于木果楝，将样地内所有树木的生物量增量求和，即可得到单位面积的年树干与枝条木材生产量。对于水椰，将单株年生物量增量乘以树木密度，即可得到单位面积的生产量。

设立该永久样地旨在验证此前弗莱河三角洲红树林生产量估算结果的可靠性。早期估算基于快速调查技术，该方法被认为会低估生产力。通过对这些样地内标记树木的生长速率进行测定，可更准确地估算主要林型的树干与枝条木材生产量。

选取更多的水椰样地，旨在探究利用水椰茎段进行年代分析以研究近期金属历史的潜力。本研究项目是大型项目"The influence of fluvial discharge on the pelagic and benthic ecology and biogeochemistry of the Fly Delta and Gulf of Papua"的组成部分，该项目承接自早期项目"The influence of freshwater and detrital export from the Fly River system on adjacent pelagic and benthic systems"。

红树-木榄林分布于弗莱三角洲的向海端，水椰棕榈在中低盐度区域的潮间带中下部形成大面积森林。海桑-白骨壤林分布于三角洲各处的淤积泥滩，但披针叶海桑（Sonneratia lanceolata）在三角洲上游的近淡水区域最为丰富，其分布范围距海向上延伸约240公里。

1989/1990年调查中使用的快速调查技术详见文献：Robertson AI, Daniel PA, Dixon P (1991) Mangrove forest structure and productivity in the Fly River estuary, Papua New Guinea, Marine Biology 111: 147-155。该文献也见于元数据记录：Mangrove forest structure and productivity in the Fly River estuary, Papua New Guinea