The term steward refers to "holding something in trust for another" (Hendry 54).
A stewardship model of environmentalism suggests that humans have a responsibility to oversee and manage natural resources wisely. On one hand, such a view can sometimes privilege anthropocentric worldviews in which humans "dominate" or hold dominion over land (and therefore have a responsibility to care for it). On the other hand, ethicists such as Aldo Leopold argue that humans must be stewards of the land because they are part of the land or ecosystem (i.e., the "land ethic").
Creating and maintaining protected areas (National Recreation and Parks Association)
the Pesticide Environmental Stewardship Program (PESP), which is overseen by the EPA
Hands-on activities, such as environmental clean-up
Reducing harmful activities that pollute environment (eating locally sourced produce to cut back on transportation of goods).
Often the "framework" or motivations behind activities determine whether someone is adopting a stewardship model, more so than the activity itself. For example, someone who suggests humans should act as "stewards" in national parks is adopting this point of view. But not everyone who attends or advocates for parks is necessarily a proponent of the stewardship model.