The　rapid　spread　of　Spartina　alterniflora　poses　a　critical　threat　to　coastal　wetland　ecosystems　in　China,　requiring　accurate　monitoring　of　its　spatiotemporal　dynamics　for　sustainable　management.　Earth　observation　data　are　valuable　for　tracking　vegetation　dynamics,　but　frequent　cloud　cover,　tidal　flooding,　and　spectral　confusion　challenge　the　accuracy　of　satellite-derived　coastal　vegetation　maps.　To　address　these　limitations,　we　developed　a　method　using　phenological　traits　derived　from　Landsat　time　series　to　distinguish　Spartina　alterniflora　from　intertidal　vegetation　communities　in　Fujian　Province.　Accuracy　assessment　of　the　Spartina　alterniflora　maps　showed　an　Overall　Accuracy(OA)　of　more　than　93%,　with　a　kappa　coefficient　of　more　than　0.92　over　the　study　period.　The　resulting　accurate　maps　showed　a　significant　increase　in　Spartina　alterniflora　coverage　from　21.41　km2　to　107.14　km2　from　1990　to　2020.　Bare　flats,　which　accounted　for　60%　of　the　total　increase　in　area,　were　the　primary　coastal　habitats　lost　to　Spartina　alterniflora.　An　increasing　trend　of　the　intertidal　ecosystem　occurred　during　the　same　period　due　to　the　rapid　invasion　of　Spartina　alterniflora　into　native　habitats.　It　is　also　found　that　there　are　three　types　of　Spartina　alterniflora　expansion　in　spatial　pattern,　driven　by　morphology,　hydrodynamic　environment,　and　biological　stress.　Notably,　human　activities　emerged　as　the　dominant　factors　influencing　the　expansion　of　Spartina　alterniflora,　surpassing　natural　factors.　This　suggests　that　Spartina　alterniflora,　driven　by　its　remarkable　reproductive　capacity,　will　continue　to　encroach　on　available　habitat.　Therefore,　strategic　management　of　the　coastal　zone　is　crucial　to　maintain　the　ecological　balance.　©　2025　Wuhan　University.　Published　by　Informa　UK　Limited,　trading　as　Taylor　&　Francis　Group.