San Francisco, California

June 2, 2023

We visited the Tennessee Hollow Watershed from 10:00 am to 1:00 pm.

We explored Chrissy Field and the beach from 1:30 pm to 4:30 pm.

We enjoyed a beautiful day! It was partly cloudy with light winds and a high of 66° F.

Urban development includes paving over natural ecosystems to create concrete buildings, parking lots, sidewalks, and roads. Cities are often built near the coast, rivers, creeks, or estuaries because these are useful areas for trade and to set up agriculture. The impact is the displacement of what previously existed in those spaces and a rich ecology that is subsequently homologized. Because the soil and plants are replaced by concrete, the habitat necessary to support mammals, birds, reptiles, insects, amphibians, worms, and more lifeforms is destroyed. Cover to protect from predators, places to lay eggs or reproduce, sufficient nutrients and resources at each trophic level are all harder to find in the concrete jungle. For “last chance” species that can only exist in that ecosystem, they must survive on the islands of remaining habitat.

Before colonization, the rich diversity of the Presidio included at least 18 different habitat types. Some of the more unique habitats included sprawling mobile dunes, dune scrub and grasslands, serpentine grasslands and chaparral, tidal and freshwater lagoons, and tidal marshes. For 150 years, the major presence in the Presidio was a military base. In 1994, the base was decommissioned, and the area became part of the Golden Gate National Recreation Area. There are around 500 buildings on site that are considered historic landmarks. Various income streams from the park fund improvements and maintenance. There has been a large and concerted effort to restore historical habitats to the Presidio, which has resulted in an increase in heterogeneity of the landscape and at least 300 bird species that are supported by those habitats. One of the more recent and profound transformations was the removal of a concrete parking lot to reintroduce an area of tidal marshland. While walking by, we witnessed many shore birds eating the abundance provided by the marsh.

Among the many beautiful flowers, I had the pleasure of seeing my first Ocean Spray bloom of the season. The cloud-like inflorescence floated daintily in the air. A highlight of spotting this checkerspot butterfly was the bright yellow ends of its antennae and red face. I was also very impressed with the size of the flowering and fruiting stock of the soap plant. Having only observed single or double shoots that had not yet bloomed, I had no idea that the soap plant could create such large branches full of seed.

Because of the heterogeneity of the restored urban landscape, we observed a variety of bird species utilizing resources in a relatively small area in comparison to non-urban landscapes. Around 300 species of bird, many migrants, utilize the tidal marshes and nearby resources of the Presidio. The area includes ecosystems such as woodland, grassland, marshes, dunes, and ocean. Part of the reason for this heterogeneity is the history of a rich and varied landscape that existed pre-development. Part of the reason for the heterogeneity is the restoration efforts added in with the varying taste of humans for plants within their built environment. In the woodland environment, we observed abundant fruit from plants such as the above currant, ceanothus, and red berried elder is one of several valuable food sources for the birds.

We observed Brown Pelicans hunting for food. They spot fish from flight, determine the movement of both fish and wave, dive beak-first into the water, and use their gular pouch to scoop up the fish and anything immediately around it. They then push out the water from their gular pouch and eat the fish. Brown Pelicans breed at sea whereas White Pelicans breed inland. Another difference is that White Pelicans swim and eat rather than diving for their food.

In an almost comical fashion, a gull was quickly pestered by competing gulls after obtaining a nicely sized fish. The other gulls were out of luck, as the whole fish went quickly from beak to stomach while being swallowed whole.

One way to spot serpentine grassland is to look where nothing is growing. In the first picture, it looks quite barren. This is because of the chemical profile of serpentine soils, including a low level of calcium coupled with a higher level of magnesium. However, there are native California plants that have adaptations that allow them to grow within a serpentine grassland habitat. The second photo above includes exposed serpentine with the wildflowers: coastal red onion, presidio clarkia, poppies, and buckwheat. The last photo shows the bluish tint of serpentine and also shows some Ithuriel’s Spear, the purple flowers, going among previously mentioned flowers.

Sedges, rushes, and grasses can look pretty similar and it is helpful to know some defining characteristics.

Identification basics:

Sedge: has edges, triangular stems

Rush: has round stem

Grasses: has flat leaves and round stems

The colors of yellow, purple and grey from a showy bloom on the coastal dune habitat. The foredune community consists of low growing perennials and small shrubs that can withstand salt, low levels of soil nutrients, and frequent disturbances. We observed this community in the sand adjascent to the beach. Plants in the coastal dune community include beach primrose, dune sagewort, and Chamisso’s lupine.

We came upon these isopods mating. If you look closely, you can see that there is a large male isopod on top of the smaller female isopod. As they moved away from us to return to the ocean, they moved as one.

I have been incredibly surprised this spring to see so many stands of California Bee Plant, each taking a slightly different form to best survive in a variety of conditions. This stand was on a small hill, with the ocean across a rocky beach and single-lane road. With the incredible winds and salty air, these plants were still thriving and showing off a magnificent bloom.

Scientific Name Glossary:

Red Berried Elder: Sambucus racemosa

Ocean Spray: Holodiscus discolor

Soap Plant: Chlorogalum pomeridianum

Coast Red Onion: Allium dichlamydeum

Presidio Clarkia: Clarkia franciscana

Ithuriel’s Spear: Triteleia laxa

Beach Primrose: Camissonia cheiranthifolia

Dune Sagewort: Artemesia pycnocephela

Chamisso’s Lupine: Lupinus chamissonis