Drivers of shrub primary production and associated landscape impacts of encroachment are well known in drylands but have not been thoroughly studied in mesic and coastal habitats. The native, nitrogen-fixing shrub, Morella cerifera, has expanded into coastal grassland along the US Atlantic coast due to warming temperatures, but impacts on ecosystem function are not well known. Annual net primary production (ANPP) of Morella cerifera and key environmental drivers were measured long-term (1990 – 2007) across a chronosequence of shrub age on a mid-Atlantic barrier island. Soil and groundwater nutrients were compared with un-encroached grassland soil to evaluate impacts of vegetation on nutrient dynamics. Shrub ANPP declined with age at the same rate among all thickets, but there was variability from year to year. When climate variables were included in models, shrub age, precipitation, and freshwater table depth were consistent predictors of ANPP. Water table depth decreased over time, reducing ANPP. This may be due to rising sea-level, as well as to feedbacks with shrub age and evapotranspiration. Soil N and C increased with shrub age and were higher than adjacent grassland sites; however, there was a significant loss of N and C to groundwater. Our results demonstrate that drivers influencing the encroachment of shrubs in this coastal system (i.e., warming temperature) are not as important in predicting shrub primary production. Rather, interactions between shrub age and hydrological properties impact ANPP, contributing to coastal carbon storage.

灌木初级生产的驱动因素和侵占的相关景观影响在旱地是众所周知的，但在中等和沿海生境中尚未得到彻底研究。由于气温变暖，本土固氮灌木莫雷拉（Morella cerifera）已扩展到美国大西洋沿岸的沿海草原，但对生态系统功能的影响尚不清楚。对大西洋中部障壁岛上的一个灌木年龄序列进行了长期（1990-2007 年）羊肚菌的年净初级生产（ANPP）和关键环境驱动因素的测量。将土壤和地下水养分与未侵占的草地土壤进行比较，以评估植被对养分动态的影响。所有灌丛中灌木丛的 ANPP 随年龄的增长而下降，但各年份之间存在差异。当模型中包含气候变量时，灌木年龄、降水量和淡水位深度是 ANPP 的一致预测因子。地下水位深度随着时间的推移而降低，从而降低了 ANPP。这可能是由于海平面上升以及灌木年龄和蒸散量的反馈所致。土壤N和C随着灌木年龄的增长而增加，并且高于邻近的草地；然而，地下水中的氮和碳大量流失。我们的结果表明，影响沿海系统中灌木侵占的驱动因素（即气温升高）对于预测灌木初级生产并不那么重要。相反，灌木年龄和水文特性之间的相互作用会影响 ANPP，从而促进沿海碳储存。