Spatial database of canopy plant densities created from satellite images over Galapagos in 2011, with intent to manage invasive species

Mapping is an important tool for the management of plant invasions. If landscapes are mapped in an appropriate way, results can help managers decide when and where to prioritize their efforts. We mapped vegetation with the aim of providing key information for managers on the extent, density and rates of spread of multiple invasive species across the landscape. Our case study focused on an area of Galapagos National Park that is faced with the challenge of managing multiple plant invasions. We used satellite imagery to produce a spatially-explicit database of plant species densities in the canopy, finding that 92% of the humid highlands had some degree of invasion and 41% of the canopy was comprised of invasive plants. We also calculated the rate of spread of eight invasive species using known introduction dates, finding that species with the most limited dispersal ability had the slowest spread rates while those able to disperse long distances had a range of spread rates. Our results on spread rate fall at the lower end of the range of published spread rates of invasive plants. This is probably because most studies are based on the entire geographic extent, whereas our estimates took plant density into account. A spatial database of plant species densities, such as the one developed in our case study, can be used by managers to decide where to apply management actions and thereby help curtail the spread of current plant invasions. For example, it can be used to identify sites containing several invasive plant species, to find the density of a particular species across the landscape or to locate where native species make up the majority of the canopy. Similar databases could be developed elsewhere to help inform the management of multiple plant invasions over the landscape.

植物入侵管理领域中，制图是一项重要手段。若能以恰当方式对景观开展制图，所得结果可辅助管理者确定何时、何地优先开展治理工作。本研究针对植被开展制图，旨在为管理者提供多入侵物种在景观中的分布范围、种群密度及扩散速率等关键信息。本次案例研究的对象为加拉帕戈斯国家公园（Galapagos National Park）一片面临多植物入侵治理难题的区域。本研究借助卫星影像构建了冠层植物物种密度的空间显式数据库，研究发现92%的湿润高海拔区域存在不同程度的植物入侵现象，且冠层中有41%的植被为入侵植物。本研究同时依据已知的物种引入时间，计算了8种入侵植物的扩散速率，结果显示扩散能力受限最显著的物种扩散速率最慢，而具备长距离扩散能力的物种则呈现出各异的扩散速率。本研究得到的扩散速率结果，处于已发表的入侵植物扩散速率区间的下限范围。这一现象的成因可能是：多数相关研究以物种的整个地理分布范围为研究基础，而本研究的估算纳入了植物种群密度这一因素。诸如本案例研究构建的这类植物物种密度空间数据库，可供管理者确定治理措施的实施地点，从而助力遏制当前植物入侵的扩散态势。举例而言，该数据库可用于识别同时存在多种入侵植物的区域，查询特定物种在整个景观中的种群密度，或是定位本土植物占据冠层多数的区域。其他区域亦可构建类似的空间数据库，为区域内多植物入侵的景观管理提供决策依据。