In the grasslands, trees do not replace the grasses as a part of an ecological succession because of

In grassland ecosystems, trees do not replace grasses during ecological succession primarily due to water limits and fire. Grasslands are often maintained by periodic disturbances that prevent the establishment of woody vegetation. Fire plays a critical role by favoring grasses over trees, especially in moist conditions, and preventing the invasion of shrubs in dry conditions [1]. Additionally, grasslands are defined and maintained by a combination of fire, grazing, and drought. Without these ecological processes, many prairies would naturally transition into woodlands. While secondary succession typically moves toward a forest climax community, frequent disturbances like annual fires in savannahs or severe weather events like droughts act as limiting factors that reset or stall the successional process. These factors ensure that grasses remain the dominant vegetation by creating an environment where tree seedlings struggle to survive or reach maturity.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 3: Terrestrial Ecosystems > 3.3.4. Role of fire > p. 27