Data from: Water regime and nitrogen enrichment facilitate the encroachment of woody plants at various developmental stages in freshwater marshes

It is often presumed that the establishment of woody plants into
grass-dominated freshwater marshes is influenced by environmental changes
such as alterations in water regimes and nutrient availability. However,
it has not been rigorously tested through empirical studies. We conducted
a three-year common garden experiment in a freshwater marsh to investigate
the separate and combined effects of water (flooded vs. drained) and
nitrogen levels (ambient vs. added) on germination, seedling survival,
growth of seven woody plant species, and their potential competitive
interactions with the resident vegetation. Drainage in the first year
significantly improved both seed germination and seedling survival of
woody plants, and these survival benefits persisted over the following two
years. The structural equation model revealed that drainage indirectly
facilitated seedling survival by reducing light asymmetry. In contrast,
continuous flooding over three years resulted in complete seedling
mortality. However, after three years of drainage, the addition of
nitrogen significantly increased the leaf count, maximum height, and stem
diameter of the surviving woody plants. Our study demonstrates that water
regime is the primary factor driving the establishment of woody plant
seedlings in freshwater marshes. As seedlings mature, nutrient
supplementation can accelerate their development, potentially accelerating
their encroachment into freshwater marshes.