BIODIVERSITY

VERTEBRATES
The Blue Oak Ranch supports around 130 species of birds, approximately forty-one species of mammals, at least seven species of amphibians, more than fourteen species of reptiles, around seven species of fish, and hundreds of species of invertebrates.

Rare Species
In their report to the California Department of Fish and Game, Jennings and Hayes (1994) reviewed the status of 80 taxa of amphibians and reptiles native to California. Of the 80 species, they determined that 48 warranted listing. Five of those species are known to occur on the Blue Oak Ranch: California tiger salamander; Foothill yellow-legged frog; California red-legged frog; Western pond turtle, and California horned lizard. The latter species has only been seen occasionally (Eric Remington, pers. comm.). Habitat exists for the Alameda whipsnake along the Arroyo Hondo, but so far all specimens found on BORR have been of the chaparral whipsnake subspecies.

California tiger salamander (Ambystoma californiense)
California tiger salamanders are a state species of special concern. They have been found to breed in seven of the ranch ponds; South Pond, Steep Road Pond, Center Road Junction Pond, Barn Pond, High Pond, Lower Center Road Pond, and Windmill Pond (Larry Serpa, pers. comm.). No information exists on their population numbers or health. The adults spend most of their time in rodent burrows. They return to the ponds to breed when the breeding sites fill with the first heavy rains of the season, and are more vulnerable to predators while on the surface. Soon after the eggs are attached to submerged vegetation or twigs, the adults return to the safety of their burrows. The resulting larvae have to complete their metamorphosis to the terrestrial salamander form before the breeding sites dry up. If the ponds are permanent, introduced predators such as largemouth bass, other sunfish, trout, mosquitofish and bullfrogs can make survival difficult. On the ranch, these salamanders have not been found in any of the ponds with fish.

Foothill yellow-legged frog (Rana boylii)
This frog is a state species of special concern. Foothill yellow-legged frogs inhabit streams with relatively natural hydrological regimes. They are numerous in North Creek and Smith Creek at the bottom of the Arroyo Hondo, but have not been seen in any other streams on the ranch. The eggs are laid in the early spring after the water has begun to warm slightly, and after hatching, the tadpoles feed on diatoms that they scrape from underwater rocks. As with the California red-legged frogs, the tadpoles can complete their metamorphosis in most areas even if the water dries up later in the season.

California red-legged frog (Rana aurora draytonii)
The California red-legged frog is Federally listed as threatened. The species is most common in the Mt. Hamilton area in perennial ponds that have abundant amounts of aquatic buttercup, a plant which provides the frogs with cover and a feeding area for the tadpoles as they graze on algae. Buttercup does grow in most of the ranch ponds, but no frogs have been found on the ranch in this type of habitat. These frogs are also found in stream pools with relatively slow moving water. One was spotted in High Pond in spring, 1999, but it didn’t stay long. Another was seen in a pool just downstream of the road in Deer Creek on August 7, 2000. Red-legged frogs usually can’t persist in ponds with non-native bullfrogs, bass, or other introduced fish predators. They can be successful in ponds that dry up periodically, or even dry up every year, as long as the water stays long enough for the tadpoles to complete metamorphosis.

Western pond turtle (Clemmys marmorata)
The pond turtle is a state species of special concern. It is noted as “Threatened” in “Amphibian and Reptile Species of Special Concern in California. “ Western pond turtles are found in six of the ranch ponds; Gramps Pond, Cabin Pond, Big Lake, Lower Center Road Pond, Upper Center Road Pond, Rope Swing Pond. Their population appears to be on the increase; over the last three years I have seen most age classes, from approximately three to eight inches in size. Young turtles are eaten by both bass and bullfrogs. Ponds and lakes that have these exotic predators usually have no turtles or only adult turtles. They only seem to reach high density where there are a lot of basking sites. In fall, 1999 I constructed anchored, floating rafts made of wood from the old barn and fences, and installed them in nine ponds; Gramps Pond, Cabin Pond, Big Lake, Lower Center Road Pond, Upper Center Road Pond, North Pond, South Pond, High Pond, and Rope Swing Pond. These rafts have successfully provided turtles basking sites out of the reach of terrestrial predators—specifically wild pigs. Ducks, snakes, and frogs also use the rafts. The females also need to be able to reach adjacent terrestrial habitats to construct nests for their eggs. Western pond turtles are omnivores, and feed on plants, insects, crustaceans, and carrion.

Fish
Farther downstream, the Arroyo Aguague is the focus of a Department of Fish and Game project to enhance steelhead populations. According to the The Nature Conservancy Project Ecologist, Larry Serpa (pers. comm.), a natural fish barrier exists downstream of the ranch, within the boundaries of Alum Rock Park, blocking the steelheads’ passage to ranch property. Rainbow trout do well above the waterfall barrier, though, and occasionally a few make it onto the ranch itself. Although Smith Creek at the bottom of the Arroyo Hondo is blocked by Calaveras Reservoir, it is home to at least three species of fish: rainbow trout (Oncorhynchus mykiss), California roach (Lavinia symmetricus), and Sacramento sucker (Catostomys occidentalis). There are 17 ponds and lakes on the ranch; three of them—Big Lake, Rope Swing Pond, and Cabin Pond—have been stocked with large–mouth bass (Micropterus salmoides) and another sunfish species, while West Pond has been stocked with mosquito fish (Gambusia affinis),

Mammals and Birds
Black-tailed deer are common on the ranch year-round, in all communities. They frequent meadows and ridge tops in the crepuscular hours. Coyotes are abundant. Bobcat sightings are not uncommon, particularly in winter and spring. Badger sightings are more rare. River otter tracks and scat were found along Smith Creek in the Arroyo Hondo in June 1999. The most conspicuous rodent is the California ground squirrel, especially during warm months. Several bat species, including pallid bats (Antrozus pallidus), frequent the ranch and use the roosting boxes erected for them on the south side of the White cabin.

Up to a year ago, the introduced wild boar (crossed with feral pigs) was abundant. With the construction of a perimeter hog fence and increased hunting pressure, the population has dropped dramatically. In 1997 sounders of 40 to 60 pigs were not uncommon; today, a sighting of more than two individuals together is unusual. The fox squirrel (Sciurus niger) has also invaded the ranch area, spreading from the Stanford University campus and urban San Jose parks, where it was introduced early in the 20th century (Sam Blankenship, pers. comm.).

Golden eagles, turkey vultures, and red-tailed hawks are present year–round. Cooper’s hawks, sharp-shinned hawks, and kestrels are year-round residents, and the ranch is occasionally visited by merlins and prairie falcons. The ranch is also home to band-tailed pigeons, wood ducks, an abundance of California quail, and five species of owl. Migrants include phainopepla, Lewis’ woodpecker, chipping sparrow, and grasshopper sparrow.

The three nonnative species are the ubiquitous European starling, the rock dove, and the introduced game bird, the wild turkey.

Reptiles and Amphibians
Pacific rattlesnakes abound on the Blue Oak Ranch, and I have discovered several dens. Gopher snakes are common in the meadows, and garter snakes frequent streams and ponds, particularly when prey is concentrated in shrinking summer pools. Racers and California kingsnakes are resident, but infrequent. Sharp-tailed snakes can be found under logs and planks in the winter months. California horned lizards are said to have been seen infrequently on Poverty Ridge (Eric Remington, pers. comm.). Pacific treefrogs are abundant, and numbers may burgeon it the introduced bullfrog can be diminished or eliminated from West Pond and Big Lake. Western toads are frequently seen crossing roads at night.

Plants and Plant Communities

There are 73 vascular plant families at BORR. Of the 462 taxa of vascular plants on the ranch, almost 80% are native (Bainbridge and Kan, 1977). Four species of concern by the California Native Plant Society are :

Santa Clara thorn mint (Acanthomintha lanceolata)
Chaparral harebell (Campanula exigua)
Santa Clara red ribbons (Clarkia concinna, ssp. automixa)
Serpentine linanthus (Linanthus ambiguus)

Only the chaparral harebell is not endemic to the Diablo Range and the eastern slope of the Santa Cruz Mountains.

Plant communities of the Blue Oak Ranch include blue oak woodland, valley oak woodland, black oak woodland, coast live oak woodland, riparian forest, chamise chaparral, Diablan sage scrub, nonnative annual grassland, wildflower field, and native perennial grassland (Bainbridge and Kan, 1997). Four of these are threatened plant communities; valley oak woodlands, blue oak woodlands, wildflower field, and native perennial grasslands. Streams on the ranch support healthy stands of riparian vegetation in addition to aquatic species. They are important habitat for migratory birds, and may be migratory corridors for numerous aquatic and terrestrial animal species. The steep slopes of the Arroyo Hondo canyon provide an excellent contrast of vegetation, with the north and east-facing slopes supporting vegetation adapted to relatively cool, moist environments, and the west and south-facing slope vegetation (including chamise chaparral) adapted to hot, dry conditions.

Grasses
Patches of native grasses still occur in many places on the ranch. They are dominated by purple needle grass (Nasella pulchra), but perennial species of barley (Hordeum), bluegrass (Poa spp.), three-awn (Aristida ssp.), melic (Melica ssp.), and wildrye (Elymus and Leymus ssp.) are sometimes dominant or codominant (Bainbridge and Kan, 1997). The native grasses are most abundant on mesic north-facing slopes, in the understory of mixed evergreen woodland (Arroyo Hondo), under trees in oak savannas, and in open areas on ridge tops and slopes.

Oak Woodland
Blue and valley oak woodlands have become quite rare in California, and few are protected from grazing and the encroachment of suburban development. Oak woodland covers a large extent of BOR, much of this is composed of blue and valley oaks. Compounding the possibly bleak future for oak woodlands is the lack of recruitment of young oaks. In the Mt. Hamilton area, valley oaks seem to be suffering most from this problem. The exact mechanism or mechanisms preventing oak regeneration is not known, but protection from pigs, cattle, and ground squirrels has been shown to increase survivorship of existing seedlings. Prescribed fire may also help by opening canopies and reducing competition between grasses and seedlings. However, fires must be carefully controlled for low heat, and conducted at frequency intervals that allow seedlings to become established. Physiological research suggests that ozone may extend stomata opening in blue oak, forcing nighttime transpiration during periods of drought and influencing shorter leaf retention. Oaks, as the most widespread and representative forest and woodland species in California, offer excellent research opportunities for climate change and pollution-effects research.

Non-native Plant Infestations
Among introduced species, yellow starthistle (Centauria solstitialis) and medusahead grass (Taeniatherum caput-medusae) are highly invasive. At present, C. solstitialis occupies only about 30 acres of the ranch, but it is spreading quickly. Taeniatherum, probably introduced from bales of hay, covers most of the flat areas of the ranch.

Other introduced species of concern are Italian thistle (Carduus pycnocephalus), tocalote (Centauria melitensis), Canada thistle (Cirsium arvense), and bull thistle (Cirsium vulgare). Italian thistle in particular has become widespread in dense stands, and is a spring and summer feature under the drip lines of many oaks on the ranch.

Posted on March 7, 2014 06:38 AM by infomgr