Vegetation and Elevation Surveys of the Gulf of Carpentaria Mangrove Dieback 2017 - 2019 (NESP TWQ 4.13, JCU)

Vegetation and Elevation surveys were conducted at four sites in the Gulf of Carpenteria to provided crucial validation of observations made from aerial surveys and provided further significant insights of the impacts and subsequent changes that occurred across the Gulf coastline up to late 2019.

Field studies primarily focused on shoreline fringing stands dominated by the Grey Mangrove Avicennia marina var. eucalyptifolia. A total of eight transects, perpendicular to the shoreline were established at four shoreline sites across the Gulf of Carpentaria. These included matched pairs for each of two severity levels of 90%–100% and 60%–80% dieback of mangrove fringes.

A series of profile transects were established and measured from the landward edge to the sea edge of mangroves. Transects were run from a highwater point at the head, directly towards the sea edge. This method captured common reference elevation levels for all sites while maximising coverage of the entire elevation range of the tidal wetland (mangroves plus tidal saltpan and saltmarsh vegetation), from approximately highest astronomical tide levels (~HAT) at the head, to approximately mean sea level (~MSL) at the seaward edge of living mangrove trees.

On ground surveys consisted of two components: a) elevation measures from HAT (highest astronomical height – defined by the highwater mark) to MSL (mean sea level – defined by the seaward mangrove edge); and b) vegetation species, structure and density for mangrove and saltmarsh species present along with observations of condition and being likely 2015 dieback. The latter condition was determined from vegetative degradation states of mangrove trees, and as seen in satellite imagery mapping.

Methods:
Locations:
The field studies started with the two locations in Queensland during 4–10 August 2018 and
then moved onto those in the Northern Territory during 11–17 October 2018. A total of eight transects, perpendicular to the shoreline were established at the four shoreline sites across the Gulf of Carpentaria.

Limmen – Roper region (NT)
- 1A with 90% - 100 % dieback
- 1B with 60% - 80% dieback

Mule - Roper region (NT)
- 2B with 90% - 100 % dieback
- 2A with 60% - 80% dieback

Karumba - SE Gulf (QLD)
- 4A with 90% - 100 % dieback
- 4B with 60% - 80% dieback

Mitchell north - W Cape (QLD)
- 5A with 90% - 100 % dieback
- 5D with 60% - 80% dieback

Transect Set Up Summary:
Each transect was based or anchored at the observed nominal Highest Astronomical Tide (~HAT) level of the highwater benchmark at each transect ‘head’, via the beach wash zones indicative of the highest reach of tidal waters. A second reference position at the sea edge of mangroves was taken as a proxy relative to mean sea level (~MSL). The location of the head position was chosen so that a straight line transect could be taken to the fringing mangrove stand, and to the sea edge at the proxy position of mean sea level (~MSL).

Three additional ‘internal’ ecotone position markers between ~HAT and ~MSL of the tidal wetland zone were recorded for each transect, including the landward fringing mangrove to the saltpan–saltmarsh position (M1-lower); the lower elevation limit of saltpan–saltmarsh bordering the upper dieback mangrove
edge (M2-upper); and the lower elevation limit of mangrove dieback (M2-dead/live). Further details about the transect set up can be found in the final report volume 2 (Duke et al, 2020).

Surveys:
Long plots were used to describe and quantify mangrove and saltmarsh vegetation along
each transect. The long plot method allowed the plot width to be adjusted during the survey
depending on stem density of particular sections along the transect - where there were closely spaced trees, plots were narrower (2 m wide).

Elevation levels were recorded at 20–30 m intervals or more frequently where there were
otable changes in topography or there were notable changes in vegetation type and condition. Levels were made using a Topcon construction surveyors rotating laser and staff. Where it was necessary to relocate the laser instrument, additional reference points were taken for each
transition point providing offset measures to link each series of measurements. Elevation levels were recorded all the way from the head marker to the sea edge amongst or just beyond the last trees.

Vegetation was scored for species, stem diameter, height, condition as well as distance along the transect and distance left or right of the measuring tape. Trees were scored in 30 m sections within a fixed distance from the measuring tape depending on stand density. The width was mostly set at two metres, but on occasion, this was reduced to one metre or up to four metres wide as necessary.

Along each transect, at each 30-metre interval or at ecotone points, photographs were taken at four square directions to the transect line – towards the sea, 90 degrees to the right, back towards the ‘head’ and 90 degrees to the left. At these same points, canopy photos were taken using a camera with a fisheye lens.

The survey data contains wood sampling and tree coring investigations which could not be completed during the project's reporting time frame. Future project work will include high-level analytical work required, including elemental scans and carbon dating. Evidence of tree cores collected during the field surveys can be found within each vegetation survey sheet and the tree cores tab of the workbooks.

Limitations of the data:
While terrestrial forestry practice recommended that stem diameter be measured at 1.3 m above the ground – as diameter measured at breast height (DBH) – this was found to be impractical in these and other mangrove forests. The difficulties encountered included the common occurrence of multiple stems, short height mature trees and shrubs (

针对卡奔塔利亚湾（Gulf of Carpentaria）的4处点位开展了植被与高程调查，旨在为航空调查获取的观测结果提供关键验证，并深入揭示截至2019年末卡奔塔利亚湾海岸线所经历的干扰与后续变化。

本野外研究以灰红树林（Grey Mangrove，*Avicennia marina* var. *eucalyptifolia*）占优的岸线带状林为核心研究对象。在卡奔塔利亚湾的4处岸线点位共布设8条垂直于岸线的样带，涵盖2个衰退等级的匹配样对：90%~100%衰退与60%~80%衰退的红树林岸带。

本研究布设了一系列从红树林陆缘延伸至海缘的剖面样带，以每个样带起点的高潮点位为起始点，直接向海缘布设。该方法可统一所有点位的高程参考基准，同时最大化覆盖潮汐湿地（含红树林、潮间带盐沼与盐生草本植被）的完整高程区间：从样带起点的天文最高潮位（Highest Astronomical Tide, ~HAT），直至存活红树林海缘的平均海平面（Mean Sea Level, ~MSL）。

地面调查包含两项核心内容：(a) 从天文最高潮位（以高潮线为界定）至平均海平面（以红树林海缘为界定）的高程测量；(b) 红树林与盐沼物种的种类、结构与密度调查，同时记录植被健康状况及疑似2015年衰退的特征。后者通过红树林的植被退化状态结合卫星影像解译结果进行判定。

## 研究方法与点位布设
野外调查于2018年8月4日至10日率先在昆士兰州（QLD）的2处点位开展，随后于2018年10月11日至17日转战北领地（NT）的点位。卡奔塔利亚湾的4处岸线点位共布设8条垂直于岸线的样带，各点位的样对设置如下：
1. 利门-罗珀地区（NT）：
- 1A：衰退等级90%~100%
- 1B：衰退等级60%~80%
2. 缪尔-罗珀地区（NT）：
- 2B：衰退等级90%~100%
- 2A：衰退等级60%~80%
3. 卡鲁姆巴-湾东南部（QLD）：
- 4A：衰退等级90%~100%
- 4B：衰退等级60%~80%
4. 米切尔北部-西角（QLD）：
- 5A：衰退等级90%~100%
- 5D：衰退等级60%~80%

### 样带布设概要
每个样带以该样带起点处观测到的名义天文最高潮位（~HAT）为基准锚点，该基准点位于代表潮汐水最高漫溢范围的滩涂冲蚀带内。以红树林海缘作为平均海平面（~MSL）的替代参考点位。样带起点的选址需确保可沿直线布设至岸带红树林，并延伸至代表平均海平面的海缘替代点位。

在每个样带的~HAT与~MSL之间的潮汐湿地带内，额外布设3处内部生态过渡带（ecotone）定位标记，分别为：陆缘红树林向盐沼-盐生草本带的过渡位置（M1-下限）；盐沼-盐生草本带的下限边界（紧邻衰退红树林上缘，M2-上限）；红树林衰退区的下限边界（M2-存活/衰退分界）。样带布设的更多细节可参见最终报告第二卷（Duke等，2020）。

### 野外调查实施
采用长条样方法对每条样带沿线的红树林与盐沼植被进行描述与量化。长条样方的宽度可根据样带沿线特定区段的茎秆密度灵活调整：在树木分布密集的区段，样方宽度设为2米。

高程测量以20~30米为间隔进行记录，当地形或植被类型、健康状况出现显著变化时，则加密采样频次。高程测量采用拓普康（Topcon）工程测绘旋转激光水准仪与标尺完成。若需移动激光仪器，需在每个过渡点位增设参考点，通过偏移量计算衔接各段测量数据。高程测量覆盖从样带起点标记直至最后一棵红树林附近或外侧海缘的全部区域。

植被调查记录内容包括物种、茎秆直径、株高、健康状况，以及沿样带的距离和相对于测绳的左右偏移距离。依据林分密度，以测绳为基准，在30米区段内固定距离范围内开展树木打分统计。样方宽度通常设为2米，必要时可调整为1米或最大4米。

沿每条样带，在每30米间隔或生态过渡带点位处，需从四个垂直于样带的方向拍摄照片：朝向海方、向右转90度、朝向样带起点、向左转90度。同时在相同点位使用鱼眼镜头相机拍摄冠层照片。

本次调查数据包含木质部采样与树木取芯分析内容，但受项目报告时限限制，该部分工作尚未完成。后续项目将开展相关高阶分析，包括元素扫描与碳定年。野外调查采集的树木取芯样品信息可查阅每份植被调查表及工作簿的“树木取芯”工作表。

## 数据局限性
陆地林业实践通常建议在距地面1.3米处测量茎秆直径（即胸径DBH），但在该研究及其他红树林群落中，该方法并不具备可操作性。所遇到的困难包括：普遍存在多茎干现象、成熟树木与灌木株高偏矮（原文未完整收尾）