Peninsula Open Space Trust protects more than 80,000 acres in the Bay Area. This is their current email signup page:
The POST Hiking Guide is their most popular communication piece.
People care about the outdoors because they want to get exercise, go on picnics, see wildlife or find spectular vistas.
I propose they change the format to focus more on activities people want to do.
I believe this benefits focused approach would increase their email signups.