Brooks Island
Map SatelliteLocated in the northeastern part of San Francisco Bay, 1.2 km. (0.75 mile ) south of Point Richmond to which it is related geologically, this low-lying island has several unique botanical and zoological attractions.
Brooks Island represents one of the few, if not the only, remnants of the pre-civilization grasslands of the Berkeley Hills and surrounding area. Among the biotic communities present are Baccharis grassland, open perennial grasslands, a small Salicornia-Distichlis marsh, freshwater ponds and, along the shore, sand, mud and rocky beaches.
At least 50 species of grasses are present, many of which are perennial. A number of the perennial grasses and the associated herbs are rare or uncommon. In the overstory the major plants are Baccharis, Rubus, and a few buckeyes, Aesculus californica.
Mammals present include the California meadow mouse (vole), Microtus californicus. This Microtus population contains a rare pelage color mutant.
The island is an important stop for migrating shorebirds and there is a resident population of varied chaparral, grassland and marsh birds. Canada goose, Branta canadensis, nest here occasionally.
Populations of reptiles and amphibians are found on the island.
Quarrying operations created three small, freshwater ponds on the island. These ponds are permanent, being fed by freshwater springs. The total area of the three is less than an acre and the maximum depth of the largest is 3 meters (10 feet).
The Costanoan Indians used the island as a hunting and fishing ground. Several Indian shell mounds are still present.
Integrity: Earlier in the century the island was lightly grazed and, at the south end, was the scene of extensive quarrying. Recurrent fires and, in the past 2 to 3 years, extensive use of herbicides to control poison oak have affected the vegetative cover. Present development is limited to a house and garage for the caretaker and a jeep road around the island and to the summit. Proposals have been made to develop the island for heavy recreational use.
Use: Research, educational; the Microtus population has been the subject of a detailed ecological study since 1959.
Ref: Lidicker, W. Z., 1963. The Genetics of a Naturally Occurring Coat-Color Mutation in the California Vole. Evolution. Vol. 17, No. 3, p.340-346.
Anderson, P. N. , 1960. Ecology and Evolution in Island Populations of Salamanders in the San Francisco Bay Region. Ecological Monographs, Vol. 30, p. 359-385.
January 1975
Inventory of California Natural Areas
Revision © 2009 Steven Louis Hartman
