Under the background of global climate change, accurately estimating forest carbon stocks is crucial for assessing the carbon sequestration capacity of coastal protection forests and formulating adaptive management strategies. This study focused on the implementation areas of the coastal protection forest system construction program in Fujian Province. Utilizing forest resource inventory sample plots, second-class survey patches, and remote sensing data, we estimated the forest vegetation carbon density and carbon stocks in 2014 and 2022, as well as their changes, by employing biomass model methods combined with average carbon coefficient methods. The differences in estimation results from different data sources were systematically analyzed. Our results show that: (1) differences were observed in the estimation results from different data sources. Carbon density showed a trend of patch data (31.29 Mg/hm2) < sample plot data (33.34 Mg/hm2) < remote sensing data (50.48 Mg/hm2). Using sample plot data as the reference value, patch data underestimated carbon density by 6.64%, while remote sensing overestimated it by 51.41%, likely due to measurement errors in patch-based volume estimation and uncertainties in remote sensing biomass data, Carbon stocks estimated from patch data (35.33–44.93 Tg) were lower than those from remote sensing data (60.53-65.84 Tg). However, the carbon sequestration from patch data (9.60 Tg) was higher than that of remote sensing data (5.31 Tg), primarily influenced by forest area recognition biases. (2) Among different forest types, evergreen broadleaf forests and evergreen coniferous forests had the highest area, carbon density, and carbon stocks, making them the primary contributors to forest carbon sequestration in Fujian Province. Remote sensing estimates of carbon density were generally higher than those from patch data across most forest types, further reflecting potential biases in remote sensing biomass data. In addition, significant differences in carbon stocks among different forest types were observed between patch and remote sensing data, which not only result from the higher carbon density estimates from remote sensing, but also highlight the impact of area recognition discrepancies among different forest types. We recommend to establish a multi-source data fusion mechanism in the future, optimize the carbon sequestration monitoring system, and enhance carbon sequestration capacity by increasing the proportion of closed forests through differentiated forest management. |