Abstract The quantification of kelp forest distribution across space and time is critical to support decision-makers responsible for habitat management and conservation. Spatial data such as aerial photos and satellite imagery are key for deriving kelp distribution; however, they have only become available at an adequate quality within the 20th and 21st centuries. In this study, British Admiralty (BA) charts created between 1858 and 1956 covering the British Columbia coast and portions of the adjacent Washington and Alaska coast were used to create a digital historical baseline map of kelp presence. A total of 137 BA charts were scanned at 200 DPI, georeferenced, and kelp features were manually digitized following a rigorous method considering the scale and quality of the data. An accuracy assessment of the digitized kelp features concluded that 99% of the kelp features occurred in expected areas within a depth of less than 40 m, and only about 1% of the features occurred entirely outside of this depth. Recently mapped kelp forests in similar areas reaffirmed the results of the produced baseline map. Potential sources of uncertainty should be considered when working with the historic BA charts such as the surveyor's method for defining floating kelp features, the artistic ability of the cartographer when transcribing the information from the surveys to the BA charts, and the regional seasonality of kelp cover. The outcome of this research shows that the historical BA charts are an unconventional but extremely rich source of baseline coastal habitat data from the 19th century. The methods conducted are simple and robust and could be applied to other regions where historical charts with sufficient quality exist.

中文翻译：

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不列颠哥伦比亚省海岸海藻林的历史分布：1858-1956

摘要 海带森林跨时空分布的量化对于支持负责栖息地管理和保护的决策者至关重要。航空照片和卫星图像等空间数据是推导海带分布的关键；然而，它们只有在 20 和 21 世纪才能以足够的质量获得。在这项研究中，英国海军部 (BA) 海图在 1858 年至 1956 年之间创建，涵盖不列颠哥伦比亚省海岸以及邻近的华盛顿和阿拉斯加海岸的部分地区，用于创建海带存在的数字历史基线图。总共以 200 DPI 扫描了 137 个 BA 图表，进行了地理参考，并考虑到数据的规模和质量，按照严格的方法手动数字化海带特征。对数字化海带特征的准确性评估得出结论，99% 的海带特征出现在小于 40 m 深度的预期区域内，只有大约 1% 的特征完全出现在该深度之外。最近绘制的类似地区的海藻森林再次证实了所制作的基线图的结果。在使用历史 BA 图表时，应考虑潜在的不确定性来源，例如测量员定义浮动海带特征的方法、制图员将调查信息转录到 BA 图表时的艺术能力以及海带覆盖的区域季节性. 这项研究的结果表明，历史 BA 图表是 19 世纪基线沿海栖息地数据的非常规但极其丰富的来源。