Soil, Geomorphology and Pre-European Settlement Vegetation Associations of Southwest Louisiana

Defining the pre-European range of vegetation communities can enhance our understanding of the role soil, hydrology, and climate had on climax plant communities within southwest Louisiana. Coastal prairie grasslands were in a perpetual state of succession due to two primary disturbances; grazing, primarily by bison and other ungulates, and fires ignited by lightning and Native Americans. Along its borders, prairie vegetation blended into adjacent plant communities forming biologically diverse ecotones that may have fluctuated between a prairie, marsh, or forest dominated community as a result of variable conditions including climate cycles, disturbance and soil characteristics. Since European settlement, this landscape has undergone dramatic change with less than 1% of intact coastal prairie remaining. Conservation entities across the Western Gulf Coastal Plain are taking a collaborative, strategic, landscape scale approach to pollinator conservation. This effort encourages communication and implementation of restoration and habitat enhancement actions within water sheds. We have produced a spatial dataset which considers landscape position and soil type, based on Soil Survey Geographic Database (SSURGO) data, to predict appropriate vegetation associations for plantings across southwest Louisiana based on expert elicitation, and historic references. Methods to produce this product begin with soil boundaries and identification information using Map Unit Keys (MUKEY) which were gathered from SSURGO data (Soil Survey Staff, NRCS 2017). Each mukey number was reviewed on the SOIL WEB to obtain information about components. Components include the proportion and general geomorphic features associated with soil series. Natural vegetation associations were examined and documented for each soil series individually using multiple references, including USDA Soil Series descriptions, expert elicitation, and historical spatial references. Professional reference maps contributed to this spatial dataset and include an 1863 work by Henry L. Abbot and numerous General Land Office surveyor maps and surveyor descriptions from the early 1800s drawn at the scale of a township. General vegetation categories associated with Soil Types (Mukey) were derived from reviewing the vegetation associations of the dominant components, or soil series. These general categories include: anthropogenic, prairie, transition, forest, marsh, swamp, uncertain, and water. Anthropogenic categories were generally due to significant dredging, or other industrial activities. Transitional areas included savannas and areas which may have significantly changed from prairie to forest dominated communities due to rainfall and/or fire frequency and intensity. Forest and swamp includes a range of forest types from which the distinction between these two categories primarily depend upon relative elevation and hydrology. There were a few soil series in which we are uncertain of their pre-settlement vegetation. These areas are anomalies on the landscape and include salt domes and old, disjunct river meanders which are largely comprised of Pleistocene soils and were most likely marais, yet currently much of it is heavily forested as bottomlands, and we are therefore uncertain if this result is solely due to absence of fire. Attribute data include MUKEYs within the parishes which are included in the Louisiana portion of the Gulf Coastal Plain Ecoregion. Information in the table includes symbols, common names, and components which were compiled from SSURGO dataset and Soil Web online resources (Soil Survey Staff, NRCS, accessed 2/2017). For more detailed vegetation associations for individual soil series, please refer to 'VegSoilAssoc_SWLA.pdf' or 'VegSoilAssoc_SWLA.csv'.

确定欧洲殖民前的植被群落分布范围，有助于深化我们对路易斯安那州西南部土壤、水文与气候如何作用于顶级植物群落的认知。沿海草原本因两类主要干扰而处于持续演替状态：一是以野牛及其他有蹄类动物为主的放牧活动，二是由闪电与原住民点燃的野火。沿海草原的边界会与相邻植被群落相互融合，形成生物多样性丰富的生态交错带；这类交错带会因气候周期、干扰强度与土壤特性的变化，在草原、沼泽或森林占主导的群落之间动态波动。自欧洲定居者到来后，这片景观发生了剧烈变化，现存完整的沿海草原已不足1%。西墨西哥湾沿海平原的各类保护机构正采用协作式、战略性的景观尺度方法推进传粉者保护工作，该工作鼓励在流域范围内开展沟通协调，并实施修复与栖息地提升行动。
我们基于土壤调查地理数据库（Soil Survey Geographic Database, SSURGO）的景观位置与土壤类型数据，结合专家咨询与历史文献记录，构建了一套空间数据集，用于预测路易斯安那州西南部适宜种植的植被组合。该数据集的制作流程始于从SSURGO数据（美国农业部自然资源保护局土壤调查团队，2017）中提取的土壤单元编号（Map Unit Keys, MUKEY）及其边界与标识信息。我们通过土壤网络（SOIL WEB）逐一审查每个MUKEY，获取其对应的土壤组分信息，包括各土壤系列的占比与典型地貌特征。我们依托多类参考资料——包括美国农业部土壤系列描述、专家咨询结果与历史空间参考资料——逐一检视并记录每个土壤系列对应的自然植被组合。专业参考地图为本数据集提供了支撑，其中包括亨利·L·阿博特1863年的测绘作品，以及大量19世纪早期以乡为比例尺绘制的美国土地总署测绘地图与测绘描述。
与土壤类型（MUKEY）相关的通用植被类别，源自对优势组分或土壤系列的植被组合的梳理归纳，涵盖人为干扰类、草原类、过渡类、森林类、沼泽类、湿地类、不确定类与水体类。其中人为干扰类通常源于大规模疏浚或其他工业活动；过渡区域包括稀树草原，以及因降水、火灾频率与强度变化而从草原显著转向森林主导的区域。森林与湿地类涵盖多种森林类型，二者的区分主要取决于相对海拔与水文条件。有部分土壤系列的殖民前植被类型难以确定，这类区域属于景观中的异常地块，包括盐丘与古老孤立的河曲地带：此类区域大多由更新世土壤构成，原本大概率为沼泽，但当前多数区域已演变为河漫滩森林，因此我们无法确定该变化是否仅由缺乏野火干扰导致。
本数据集的属性数据包含墨西哥湾沿海平原生态区路易斯安那州段所辖各堂区内的MUKEY。表格中的信息包括从SSURGO数据集与土壤网络在线资源（美国农业部自然资源保护局土壤调查团队，2017年2月访问）中汇编得到的代码、通用名称与土壤组分。若需查询单个土壤系列的详细植被组合，请参阅《VegSoilAssoc_SWLA.pdf》或《VegSoilAssoc_SWLA.csv》。