The highest margin of an undisturbed tidal marsh is a vital transition zone linking marshland with the habitats immediately inland—shrubland, grassland, low dunes. Around San Francisco Bay, this upland ecotone has largely been obliterated by human changes to the landscape. Yet a functioning tidal marsh needs this upland boundary in order to thrive. Marshlands naturally expand and decrease, due to fluctuating sea level and sedimentation rates, and this can only happen if there’s a flexible landward edge. This is even more critical with rising sea level with climate change.
At Point Blue, our cooperative restoration efforts recognize the importance of the wetland-upland boundary zone. Our STRAW Project carries out restoration in this habitat type at several sites along the northern edge of San Francisco Bay. One such example is in the San Pablo Bay National Wildlife Refuge. In the past, people built levees there to limit the extent of tidal marshlands. Today the Refuge is removing and revegetating former levees, using native plant seedlings that we help cultivate and that we teach students to place in the ground.
As sea levels rise with climate change in this century, the value of a natural buffer zone above the tidal marsh will increase. Great challenges exist throughout San Francisco Bay, so restoring the upland boundary where possible is our priority.
By restoring the wetland-upland ecotone on a portion of San Pablo Bay, Point Blue and our partners aim to enhance habitat for marsh birds and small mammals, including the highly vulnerable salt marsh harvest mouse and California Clapper Rail. During extreme high tides these species need to take refuge in higher ground transition habitat.
Restoring the upland ecotone with a suite of native plants will also build a supply of seeds in the ground—so that the tidal marshland can ebb and flow in the future with its flexible upper transition zone.