The Flora
at Lake Merced

Juan Ochoa, Christopher Campbell, and Paul Pribor, Graduate Students, Geography
San Francisco State University

Historic Vegetation        Present Vegetation

The  Historic Vegetation of Lake Merced
in the Pre-Hispanic and Early Spanish Period

Introduction
   The following information about the vegetation cover of Lake Merced was compiled from previous works describing the flora of the San Francisco Bay area during the Pre-Hispanic and early Spanish periods. Very little information specific to the flora of Lake Merced during these two periods was found in the literature. Therefore, in this section we attempt to describe the plant composition that may have existed before the 1800s at Lake Merced in San Francisco, California.

History of the Vegetation of Lake Merced
    The San Francisco Bay was unknown to Europeans until 1769, when the Portola expedition, marching northward from Baja California, discovered the Bay area (Clarke 1952). After this, the process of European and American colonization started to alter the appearance of the lands of the bay (Clarke 1952). Before the coming of the Spanish, human utilization of the area consisted of the exploitation by the Indians of the spontaneously occurring flora (Clarke 1952).

Clarke (1952) reviewed the archives of different expeditions describing the landscape of the "Laguna de la Merced":

South of Laguna de la Merced (Palou, 1926, vol. III, p. 278). Marching north toward Laguna de la Merced, Palou passed "...over low hills, crossing some valleys, in which we encountered three arroyos of running water with no trees in them but some small willow and little tule."

Near Laguna de la Merced (Rivera y Moncada, 1774, Dec. 4). Rivera remarked of the area that there was no firewood and no timber for building.

Laguna de la Merced (Palou, 1926, vol.III, p. 279). Palou reported encountering sand dunes about a mile south of Point Lobos.

In western San Francisco, the grass-covered area near Laguna de la Merced merged on the north with low, barren sand-hills, which reached almost to Point Lobos; it was an extensive treeless area (Clarke 1952). There were vast areas largely covered with grass and other herbs, although there was some chaparral and oak on the sandy soil between Yerba Buena and the mission.

It can not be assumed that the vegetation remained unchanged throughout the Spanish and Mexican periods. Nevertheless, during the first fifty years of occupation, the direct activities of the inhabitants affected only small areas: agriculture was limited to the immediate vicinity of the mission (Clarke 1952). But the most widespread change in the flora during this period was a decrease in grass and a probable increase in brush --the result of years of constant grazing by Spanish livestock.

It was not until 1949 that it became apparent that the flora of San Francisco was disappearing rapidly. Up to 1940, the natural wild areas in San Francisco seemed secure enough. Yet, during and after the war, vast industrial developments and housing projects took place, changing the landscape (Howell, Raven, and Rubtzoff 1958). At Lake Merced, surface soils have been altered, removed or covered over, primarily on the upland terrace surface (Trihey & Associates, Inc. 1998).

Lake Merced: Sand Dunes and Vegetation
   Lake Merced, located in the western part of the city of San Francisco, is part of the formerly common and widespread sand dunes, which extended inland through low places between the hills almost to the bay (Howell, Raven, and Rubtzoff 1958). In the west the drifting sands blocked drainage channels and created a series of dune ponds and lakes, the most important being Lake Merced (Howell, Raven, and Rubtzoff 1958). Therefore, the vegetation present at Lake Merced in the pre-Hispanic and early Spanish period may have been typical of sand dunes. However, although most of the local soils at Lake Merced have similar sand-textured geologic parent materials, there are some slightly more resistant --terrace soils on the north, east, and south--, but still poorly consolidated bedrock (Trihey & Associates, Inc. 1998).

Wagstaff (1962) carried out a study about the flora of the San Francisco sand-dunes from 1938 to 1962. He noted that the sand-dunes were located on the ocean side of the peninsula, between Golden Gate Park and Ocean Boulevard, and extended inland from the beach to the base of Mt. Sutro and Twin Peaks. Golden Gate Park was part of the large dune area that once covered much of the peninsula north of Lake Merced (Wagstaff 1962). Wagstaff also mentioned that beneath the sand-dunes are embedded sands of the Terrance formation of Pleistocene and later ages, and this above the Franciscan Series of Mesozoic period. The shore from the Lake Merced outlet to Point Lobos has been filled with the drift sand from the cliffs toward the south (Wagstaff 1962).

Vegetation also plays an important role in the growth and establishment of dunes.  Formation of dunes is often dependent upon plants and other objects that decrease the velocity of the wind and, therefore, its carrying power (Wagstaff 1962). If the plant growth continues rapidly enough to prevent sand coverage, the vegetation serves the double purpose of holding the soil already deposited and aiding in further deposition of soil (Wagstaff 1962). One of the main characteristics of this dune flora is that it can withstand the xerophytic conditions of sand-dune life, covering by sand, and periodic uncovering and exposure of the roots (Wagstaff 1962).

Plant Composition at Lake Merced
   Although there is no list of the flora of Lake Merced during the pre-Hispanic and early Spanish periods, the information provided below includes the plant species recorded in one of the first studies (Wagstaff 1962) describing the flora of the San Francisco sand dunes. It is likely that some of the species listed are not present in Lake Merced anymore or that they have probably never existed there. However, it is important to have a baseline of the San Francisco flora in the sand dunes so that it can provide an idea how the vegetation may look like in these two time periods.

Lake Merced is part of the western sand dunes of the San Francisco marine shore. However, there is a specific dune classification that may help to determine more accurately the type of flora that may have been present during the pre-Hispanic and early Spanish periods. The flora of sand dunes along marine shores encompasses the beach, littoral dune, active dune, and the protected dune associations (Wagstaff 1962). Inland from the beach flora, is the littoral association of the shore dunes; farther inland from the shore are the associations on the active dunes, and scattered throughout the dunes are the associations of protected areas (Wagstaff 1962).

Dunes at Lake Merced could be classified as belonging to the active and protected associations, however, flora of the beach and littoral associations may be present as well. Plant communities of dunes are composed principally of low-growing annual or perennial herbs (Clarke 1952). The woody plants that occur are also low growing or prostrate and blend indistinctly with the herbaceous and suffrutescent plants (Clarke 1952).

Wagstaff (1962) provided a list of the most common plants found in the active and protected dunes in San Francisco. For the active dunes he recorded Franseria chamissonis, Franseria bipinnatifida, Abronia latifolia, Oenothera spiralis, and Lupinus chissonis. These plants are practically the only ones that can survive the rigid environment of the most exposed areas of the sand-dunes and are continually subject to covering and uncovering roots, the mechanical injury caused by the wind and, and to high transpiratory conditions (Wagstaff 1962). Scattered throughout the sand field, Wagstaff (1962) also listed the genera Tenacetum, Ammophila, Salix, Franseria, and Abronia. Plants belonging to these groups are considered pioneers of the dunes. 

When compared to the active dunes, the protected dune associations have a more diverse plant composition. The most common and conspicuous member is Lupinus chamissonis, however other common species found are: Lupinus arboreus, Tanacetum camphoratum, Artemisia pycnocephala, Bromus rigidus, and Anaphalis margaritacea (Wagstaff 1962). In some places of the protected dunes and for short periods of time there may be found large patches of the annuals Brassica, Bromus, and Raphanus, and the perennials Agrophyron junceum and Frageria chilensis (Wagstaff 1962).  Other plant species are also found: Juncus lescurii, Juncus falcatus, Cotula coronopifolia, Mimulus guttatus, Tanacetum camphoratum, Salix lasiolepis, Baccharis piluralis, Artemisia pycnocephala, Ericameria ericoides, Diplacus aurantiacus, Anaphalis marguaritacea, Achillea millefolia, Bromus sterilis, and Castilleia latifolia (Wagstaff 1962).

Howell, Raven, and Rubtzoff (1958) noted that the dune vegetation of San Francisco, related in its shrubby members to the coastal brush and in its herbaceous members to the grassland, is rich and varied, whether it is found on the beaches, dunes, or sandy slopes and flats. Among the characteristic woody plants the authors reported are Lupinus arboreus, Lupinus chamissonis, Artemisa pycnocephala, and Baccharis piluralis. Salix lasiolepis forms thickets in wet places. There are numerous herbaceous plants associated with these shrubs: Bromus maritimus, Poa douglasii, Chorizanthe cuspidata, Abronia latifolia, Lotus stigosus, Croton californicus, Oenothera cheiranthifolia, Phacelia distans, Amsinckia spectabilis, Franseria chamissonis, and Tanacetum camphoratum.

Conclusion
   The flora of Lake Merced during the pre-Hispanic and early Spanish periods may have been composed predominantly by sand-dune type of vegetation. Appendix 1 presents a complete list of the San Francisco sand dune flora found between 1938 and 1962. Some of these species may still be found at Lake Merced. However, many other species are currently present in the area due to human or natural disturbances. Although the information provided in this section was not specific to Lake Merced, a correlation can be made between what has been reported for the San Francisco sand dunes and the lake under study.

 

The Present Vegetation at Lake Merced

The Data
   The data in this report were obtained from the 1998 Lake Merced Natural Resources Inventory prepared by the San Francisco Public Utilities Commission (PUC) that includes surveying by Pete Holloran and Lisa Wayne from 1997 and the Biology and Geography Departments of San Francisco State University (SFSU), which sampled in concert with the Natural Areas Program (NAP) of the San Francisco Recreation and Park Department.

Although the later collection by SFSU and NAP is the most up-to-date, it is still a work in progress. The classification of the types and series of vegetation communities is reflective of the data gathered by the PUC. The PUC prepared a natural resources inventory of Lake Merced assessing the natural resources around the lake. This inventory documents the native plant communities and dominant species found within them. This has also proved useful in assessing the current condition, monitoring, and identifying changes in the composition of the native plant communities. Finally it identified the locations of remnant communities, while determining the most important priority sites for future restoration.

The presented data in the PUC report was gathered in May and June of 1998. Vegetation types were marked as polygons on a large scale photograph. Species were documented if found during field observations. A Geographic Point System (GPS) was used to accurately identify the location of plant communities. A GPS unit is a hand held device that displays the geographic coordinates correlating to geographic latitude and longitude. This was then noted and indicated on the map, creating a useful base for continued monitoring and documentation of the sites.

Vegetation types were based on the designations of the California Native Plant Society (CNPS). The PUC made additional categories of vegetation to help aid in the management of the lake. Dominant species determine the vegetation series and types. On a macro-scale, these include tree, scrub and herb dominated series.

 

General Description
    Vegetation around Lake Merced is a mosaic of upland and wetland types that occur generally as a series of linear bands (GeoResource 1993). Within the wetland areas, California bulrush (Scirpus californicus) (also known as tule) rings almost the entire lake, and extends out to 150’ from the shore. Water smartweed (Polygonum amphibium var. emersum) occurs beyond the bulrush, and willows (Salix ssp.) predominate beyond this. Above the wetland areas, the vegetation is composed of shrubs and herbaceous species, both native and exotic. Trees form the outermost ring in the upland areas. It is important to note that, although some of the vegetation types do occur in distinct bands, most of the shrubs and especially the trees occur in clusters, rather than as distinct bands.

Exotics dominate the majority of uplands surrounding the lake, while the mesa overlooking the north bank of East Lake supports a native coastal scrub community. The California bulrush that surrounds most of the Lake is a native. Significant areas of native vegetation also exist along the lake bank adjacent to the Harding Park Golf Course.

Vegetation Types
         The Lake Merced 1998 Baseline Natural Resources Inventory lists three types of general vegetation types at Lake Merced. These are tree-dominated, shrub-dominated, and herb-dominated (Trihey & Associates, Inc. 1998).

There are a number of tree dominated vegetation communities in Lake Merced. Monterey pine (Pinus radiata) and Monterey cypress (Cupressus macrocarpa) were planted mostly along the mesas around Lake Merced and along the margins of Harding Park Golf Course. The understory of these tree stands consists mostly of annual grasses and invasive iceplant. Trihey and Associates, Inc. (1998) note the presence of Fumaria parviflora, a non-native herb that covered extensive areas under the pines and cypresses along the golf course, and extended past the conifers into the scrub vegetation on the south shore of East Lake. Also noted as present in denser understory were poison oak (Toxicodendron diversilobum), California blackberry (Rubus ursinus), bush monkeyflower (Mimulus aurantiacus), toyon (Heteromeles arbutifolia), and red elderberry (Sambucus racemosa).

Blue gum eucalyptus (Eucalyptus globulus) is found scattered around the Lake, with extensive stands along the west shore of South Lake and along the west and north shores of North Lake (Trihey & Associates, Inc. 1998). As with the conifers above, the understory of these eucalyptus groves is often composed of annual grasses. Several eucalyptus groves have understories of the invasive cape ivy (Senecio mikanioides), which is encroaching on adjacent areas of native scrub or wetland species.

Trihey and Associates, Inc. (1998) mention a small cluster of coast live oak (Quercus agrifolia) on the north slope of East Lake, which is surrounded by acacias and annual grassland.

As mentioned in the general vegetation description, willows predominate between the wetland vegetation species and the upland vegetation, forming a fairly distinct band between these two communities. The largest stands occur on the east shore of South Lake and the north shore of East Lake (Trihey & Associates, Inc. 1998). Arroyo willow (Salix lasiolepis) dominates the willow stands, but other species of willow are present as well.

The final type of tree community is the acacia, which generally have a dense canopy with little or no understory. Blackwood acacia (Acacia melanoxylon), star acacia (Acacia verticillata), and plume acacia (Albizia lophantha) dominate most of the acacia groves, but myoporum (Myoporum laetum) is occasionally found among or adjacent to the acacia species. Trihey and Associates, Inc. (1998) did not specify locations of acacias around Lake Merced.

It is important to note here some incorrect findings by the inventory. According to Christopher Campbell, with San Francisco Recreation and Parks Department Natural Areas Program (2000), there is low diversity of natives found under the canopy of non-native trees, since there is high competition from non-natives. Only a few natives are able to compete with the non-natives within the canopy. These are: bee plant (Scrophularia californica), poison oak, some bracken (Pteridium aquilinum), and native blackberry. More diversity is found on the periphery of the canopy, where there is less competition from non-natives.

The second type of vegetation community mentioned by Trihey and Associates, Inc. (1998) is the shrub-dominated community, which is dominated by the native coyote brush (Baccharis pilularis). Coyote brush occurs primarily on steep slopes along the north and south shores of East Lake, the northeast shore of North Lake, and the east shore of South Lake. Coyote brush occurs with toyon, and patches of California figwort (Scrophularia californica), and intermingles with iceplant and exotic grasses and forbs. Other plants found in the coyote brush community include seaside woolly sunflower (Eriophyllum staechadifolium), California sagebrush (Artemisia californica), mock heather (Ericameria ericoides), yellow monkeyflower, poison oak, yellow bush lupine (Lupinus arboreus), California blackberry, wax myrtle (Myrica californica), powdery dudleya (Dudleya farinosa), and wallflower (Erysimum franciscanum).

California blackberry forms dense stands on certain slopes of Lake Merced, particularly on the west shore of South Lake, and southwest shore of North Lake, and the south shore of East Lake. Many of these areas are overgrown with wild cucumber (Marah fabaceus). Trihey and Associates note that during their inventory in spring 1998, these slopes were wet and inaccessible due to slippage, so a close inventory was impossible.

The herb-dominated species include the California bulrush and its associated species, California annual grassland, and iceplant (Carpobrotus edulis). As mentioned above, California bulrush borders almost the entire lake, with only a few gaps in its coverage on the bars between the lakes and around the pumphouse at the southeastern end of South Lake (Trihey and Associates, Inc. 1998). Cattails are present in some locations with the bulrush. An interesting note is that GeoResource (1993) reported that the changes in the width of the bulrush band between 1987 and 1992 did not obviously correlate with the change in lake levels.

Polygonum has formed extensive stands inland of the bulrush in locations around the lake, and rush (Juncus sp.) dominates the landing on the northeast shore of North Lake and an area on the southeast side of the viaduct.

California annual grassland species dominate disturbed or maintained areas at various locations around the lake, and, as previously mentioned, often are the only vegetation in the understory of tree canopies. California annual grasses are frequently intermingled with iceplant, which is also found in many disturbed areas around the lake.

The Native Flora of the Franciscan Bioregion
    Currently Found at Lake Merced
The following is a discussion and overview of the native flora found at Lake Merced. This area is a unique feature on the San Francisco Peninsula because it is the area's largest fresh water body. Although permanent and seasonal lakes were once common throughout San Francisco, there are currently only two other permanent bodies of fresh water within the city that retain native vegetation. These are Mountain Lake, located in the Presidio, and Pine Lake, located in Stern Grove. In addition to lakes there are three creeks that support riparian vegetation: Los Lobos Creek, located in the Presidio, Islais Creek in Glen Canyon and Yosemite Creek located in McLaren Park. Yosemite Creek feeds an open marsh, Yosemite Marsh. There are additional bodies of water in Golden Gate Park, but these waters are distinctly different, in that the flora surrounding them has been extensively altered with only minimal native flora remaining.

Lake Merced supports diverse native flora. What makes a species native versus non- native? Native plant species have evolved over geologic time, adapting to local environmental conditions, providing unique food and habitat resources to local wildlife. Some species evolved under local climatic and topographic conditions. These species are known as endemics. Quammen (1996) defines an endemic species as a relict, indigenous to a given region having evolved in and remaining in a restricted place. California is known world wide to have numerous endemic plant species. Within California, the San Francisco Bay Area is known for a high degree of plant endemism.

Why are endemic species important? Endemic species make an important contribution to the biodiversity of a particular region. Biodiversity is defined as a variety of many living organisms contributing genetic variability and richness of species which in turn makes up a complex working ecosystem. Individual species within this ecosystem may express variations in size, color, and ability to adapt and tolerate numerous habitats. These types of variation are important for species survival in our changing climate. Greater biodiversity means more habitat for more animals.

The habitat of Lake Merced is unique because it supports riparian communities, dune scrub communities and woodland forests on one of the few remaining natural bodies of water remaining on the peninsula. Although the topography around the lake has been altered, it still supports endemic species, an assortment of plant communities and a variety of plant species within these communities infrequently found elsewhere in the city. In addition to supplying food and habitat, these species have evolved to aid in the stabilization of the slopes, thereby helping to prevent erosion. Many of these plants were once found throughout San Francisco. However, there has been a significant loss of habitat due to a complexity of factors: urbanization, competition from introduced non-native species, disturbance of soils, alteration of soil nutrients, changes in the watershed and an overall fragmentation of a once continuous cohesive working community.

There are several locally rare species and uncommon species found around the lake. These plants have been displaced in all but a few isolated patches within the city. At Lake Merced they are found growing in the sandy, nutrient poor, xerophytic dune soils in the upland areas around the lake.

Locally Rare Species Found in Remnant Dunes at Lake Merced
      Lake Merced has seven species that are locally rare. The canyon oak (Quercus chrysolepis) is found nowhere else in city. This oak is characteristically found in the Central Valley and Foothill Woodlands. It is uncommon for them to be present in areas with high fog and cool summer temperatures. The Mount Diablo and Hamilton Ranges in the east San Francisco Bay regions are typically where you would expect to see this species. The canyon oak is similar to the coast live oak (Quercus agrifolia) which is also found at Lake Merced. They differ in the appearance of the underside of their leaves. The underside of young leaves on the canyon oak are golden with hairs, the older leaves are grayish. The golden feature is uncommon and much different from other oaks. The leaf of the coast live oak is convex, lacks the golden hairs and often has tufts of hair on the veins on the underside of the leaves.

The San Francisco wallflower (Erysimum franciscanum) is a biennial or perennial coastal species, sometimes found growing on serpentine soils, but most commonly found growing in sandy soils. It is found in sandy dune type regions of the city, however due to a loss of its natural habitat it is infrequently seen. The wallflower found within the City of San Francisco has cream colored petals, whereas the more common and widespread taxon found just south of the city on San Bruno Mountain has either yellow or cream colored petals. This may signify a very local genetic variation in this species. An interesting characteristic is its night fragrance which indicates that pollination is by moths. This species is in the mustard family (Brassicaceae). Other plants in the same family include radishes, cabbage, cauliflower, broccoli, bok choy, kohlrabi, watercress and mustard. As Kozloff and Beidleman point out, "this family's flowers are easily recognized: 4 sepals, 4 petals, 6 stamens (4 long, 2 short), and a pistil that is partitioned lengthwise into 2 divisions, each with its own row of seeds". In nursery conditions this plant is very successful at germinating.

Tower mustard (Arabis glabra) also of the mustard family is an annual that grows up to 8 inches tall. The petals of the flower are cream colored or slightly yellowish. There is only one population of tower mustard found on the south lake. Dutchman's pipe (Aristolochia californica) is in the same family as wild ginger (Asarum caudatum), the pipevine family (Aristolochiaceae). Dutchman's pipe is a very unusual woody deciduous vine with heart-shaped alternate leaves and an unusual yet wonderful flowering body that is greenish with purple veins. The plant gets its name from its flower because it resembles the bowl of a smokers pipe. This vine requires the support of other shrubs to grow. Although it resembles a carnivorous plant, Nepenthe, they are not related, nor is the Dutchman's pipe carnivorous.

Indian paintbrush (Castilleja spp.) belongs to the snapdragon family (Scrophulariaceae). These species are hemiparasitic. They are able to produce some sugars from their green leaves but they attach their roots with a host plant, which supplies them with other required nutrients. Although Indian paintbrush is frequently seen throughout the state and adjoining states, it is more common in chaparral environments and, therefore, locally rare within the city limits.

Coast manroot (Marah oreganus) is similar to the widespread California manroot (Marah fabaceus) but locally rare. These manroots belong to the gourd family (Cucurbitaceae) which also give us cucumbers, watermelons, cantaloupes squashes and pumpkins. Manroot is also commonly known as wild cucumber.

Pink flowering currant (Ribes sanguineum ssp. glutinosum) is a substantial woody shrub with alternate palmately lobed (hand shaped) leaves. In spring the Ribes shrub flowers in racemes (grape-like clusters) in white or pink with a musky fragrance. The leaves that later develop are musky, often filling the air with a pleasant earthy fragrance. As the common name suggests, Ribes produce currants that are sought after by birds and other wildlife. The current that we consume is a hybrid variety of this species, that has considerably less seeds and more fleshy fruit.

Cobwebby thistle (Cirsium occidentale) is found growing in sandy soils along the coast. It belongs to the sunflower family (Asteraceae) and is discernible by its large purple or magenta, bristly and spiky flower head. It is commonly known as cobwebby thistle because its leaves are covered with thick white hairs which resemble a spiders web.

The Location of Diverse Native Plant Communities
   The most species diverse native plant communities are found on the steep, sandy   highly erodable banks of two of the four lakes at Lake Merced. Due to the sensitivity of the soils and rarity of plant species, we request you remain off these areas. The following information is included only for purposes of reference. The most diverse community is found on the east shore of the south lake. This area supports willow, smartweed, wallflower, Indian paintbrush, Dutchman's pipe, Lotus, Dudleya, cobwebby thistle, coyote brush, seaside daisy, Artemisia, mock heather, lizardtail, lupine, manroot, California brome, wild blackberry, Phacelia, wild strawberry, coyote mint, California poppy, sticky monkey flower, soap plant and Juncus.

The east lake has several areas which in concert support a rich diversity of natives. Near and across from the mesa there are oaks, lizardtail, beeplant, sticky monkey flower, Elymus, Artemisia, evening primrose, bracken fern, poison oak, manroot, beeplant, mock heather, coyote bush, coffeeberry and toyon.

To view a diversity of native plants you can visit the restoration site located on the mesa north of east lake. Volunteers from The Friends of Lake Merced, CNPS and a number of school and volunteer groups have been diligently removing ice plant for many year in this area. You will see large forfeit areas of ice plant piles dehydrating for future removal. In addition to iceplant removal volunteers and the NAP have been increasing the local plant diversity on the mesa by planting locally collected and propagated species that likely once occurred on these sandy soils. Some of the species that have been added to the coyote brush remnants include: June grass, coffeeberry, California sage, sea pink, strawberry, sticky monkey flower, knotweed, wallflower, mock heather, California brome, cow parsnip, Indian paint brush, and cobwebby thistle. Ongoing planting restoration is can also be viewed at impound lake at the east side of the viaduct.

Exotic and Invasive Species Found on Lake Merced
   Due to a confluence of factors the San Francisco region is host to a unique array of species, some found nowhere else. This region is referred to as the Franciscan biological region or Franciscan landscape. One of the few existing remnants of that region is Lake Merced. Although there are many different exotic species found in and around the lake not all of them constitute a serious threat to the native biodiversity. A recent survey of the North Lake turned up at least thirty-seven exotic plant species and only a fraction of these are adaptive enough to pose a significant threat to the native biota. The invasive non-natives found in Lake Merced are all native to Mediterranean climates which means they are adapted to summer drought and all of these plants were introduced without their natural predators, diseases, or competitors. These factors all contribute to their rapid proliferation. If not actively managed the native vegetation can be quickly out-competed and replaced by monocultures of invasives. As the native plant communities decrease in diversity so do the various faunal communities dependent on them.

Many of these non-natives have been introduced for benign reasons. Some were prized as ornamentals, others were planted as windbreaks or erosion control, and others were brought here for agricultural reasons. Once these plants escaped cultivation they found a landscape that did not present the checks and balances present in their land of origin and many spread rapidly. As destructive as these plants can be many are still valued for aesthetic and utilitarian reasons and can be found for sale in commercial nurseries. Part of the challenge of effective eradication and control of these species lies in educating the public about the dangers posed by invasive exotics. Control efforts can be futile if well intentioned but clueless gardeners continue to foster their spread. The role of education becomes more apparent as the ecological consequences of their spread, however inadvertent, impacts other communities.

Successful eradication of these pernicious invaders cannot be achieved with a single effort. Restoration and enhancement efforts at Lake Merced focus on reestablishing the structure, function, diversity, and dynamics of native plant communities. The dynamic nature of ecosystems precludes a "species only" approach to restoration so every restoration effort must take into account a variety of factors including slope, aspect, soil type, species interactions, and natural and human caused disturbances. Of the many exotics currently found around Lake Merced a handful warrant special attention. These invasives all have the potential to adversely impact large areas of the native flora.

Cape Ivy (Delairea odorata) formerly known as German Ivy (Senecio mikanioides) is not a true ivy but a member of the Sunflower (Asteraceae) Family. It is native to South Africa and was first introduced as a container plant and for landscaping. It is especially prevalent throughout riparian ecosystems in California. This plant is considered very invasive. It has the ability to root at every leaf node and along the stem. Pieces can break off and get transported in running water or by wind and resprout. Tiny portions of the stem can survive for long periods before resprouting. Plants can live for an extended period of time without light or water. This plant needs to be manually removed and great care must be taken not to drop any fragments of the plant for they will resprout. Plants should be allowed to desiccate and dry completely before removal from site and these areas need to be monitored regularly for resprouting.

English Ivy (Hedera helix) is a member of the Ginseng (Araliaceae) Fanily. It is native to Europe and was originally introduced as a popular landscaping plant. This ivy tends to form thick carpets on forest floors and chokes out native vegetation. It creeps up trees into the canopy where it flowers and forms berries. These berries are then eaten by birds and further dispersed. The vines can become so extensive that they weigh down branches causing them to break. It is one of the few exotics that can invade and survive in a redwood forest. Cutting vines from trees will kill all the ivy growing on the trees. Stems and rots on the ground must be pulled and the area watched for resprouts.

Eucalyptus (Eucalyptus globules) also known as Tasmanian Blue Gum is in the Myrtle (Myrtaceae) Family and it is native to Australia and New Zealand. Blue refers to the appearance of the juvenile leaves which are glaucous, or blue-colored and waxy. It was originally introduced in 1853 as a windbreak and ornamental. Although it is an extremely fast growing tree its spiral grain renders it useless for lumber. Most of the stands are devoid of understory vegetation except for a few hardy grasses or English Ivy. The leaves of Eucalyptus trees produce water-soluble phytotoxins that can prevent radicle growth of many herbaceous plants. The first step for control is to prevent the stands from spreading. This involves hand-pulling or sawing saplings from the immediate perimeter of existing stands. Control of the larger more established trees is a bit more involved. Because of their size they need to be removed with heavy equipment and then resprouts monitored and recut as needed. The phytotoxins in the soil will eventually leach out with the rains before native vegetation can be reestablished.

Andean Pampas Grass (Cortaderia jubata) or True Pampas Grass (C. selloana) are members of the Grass (Poaceae) Family and are native to South America but not the Pampas Region of Argentina. It was originally used as an ornamental in landscaping. It was likely highly prized for its feathery plumes. It is highly invasive throughout coastal California and tends to colonize bare or disturbed ground such as roadbanks, cutbanks, dunes, coastal bluffs, rock outcrops, landslides, and logged areas. It does not easily colonize native grasslands. It is a prolific seed producer; one plant can produce million of viable seeds without pollination and these are easily dispersed by wind. It is an aggressive colonizer that competes with native vegetation and can replace native dune and shrub communities. Eradication entails fostering an environment conducive to the rapid growth of native trees which will soon provide enough shade to inhibit its growth. Ideally plants should be removed when small; the plumes should be removed and bagged to prevent further seed dispersal. Larger plants are more difficult to remove. They can be trimmed off just above ground-level and hands-prayed with glyophosate (a short-lived herbicide). Spray is applied directly to the leaves of the plant. After treatment native trees grow much more quickly without Pampas Grass to compete with them .

Wild Radish (Raphanus sativa) is in the Mustard (Brassicaceae) Family. It is native to Europe and was originally brought over for culinary reasons. It hybridized with native radish but has since reverted to its more woody, fibrous state which is not as edible as the hybrid. This plant is a prolific seed producer that favors disturbed soils. Like the Eucalyptus it has an alleopathic mechanism that prevents the germination and growth of other plants. Eradication and control is best done in the winter or early spring before the plant goes to seed. The plants can be simply pulled up but they must be removed because of the phytotoxins in the plant tissue.

French Broom (Genista monspessulana) is member of the nitrogen-fixing Legume (Fabaceae) Family. It is native to the Canary Islands. This is a very aggressive invader often found in disturbed areas where it quickly creates monocultures and crowds out native plants by shading them out. Pea-like pods often form while the flowers are still in bloom. Seedlings may be pulled by hand but as it grows it develops a taproot that is as deep as the plant is tall. All roots must be removed or they will resprout. Because of the vast amount of viable seeds produced it tends to have a seed bank that persists for years. This necessitates vigilant monitoring and removal of sprouts.

Iceplant (Carpobrotus edulis) also known as Sea Fig or the Hottentot Fig is a member of the Fig-Marigold (Aizoaeceae) Family. It is native to South Africa and was brought here for bank stabilization. It stabilizes sand preventing its natural movement which most native dune species need to survive. Has the capacity of quickly becoming a monoculture. It is easy to pull out of the sand but roots must be removed and all parts taken from area to prevent resprouting. It has the capacity to invade natural habitats far away from where it was planted because rabbits and deer eat the fruits and disperse the seeds. After removal the decline in soil fertility is slow to reverse because it tends to decrease the pH of the soil beneath it.

Poison Hemlock (Conium maculatum) is a member of the Parsnip (Apiaceae) Family and is native to Eurasia. Famed for its role in the death of Socrates this plant has moderate to high toxicity. All parts are dangerous and must be kept away from children and pets. It was probably introduced accidentally and tends to favor disturbed areas. It can be easily handpulled provided the soil is moist enough. Spring is the best time for removal while the soil is moist and before it has gone to seed.

Sheep Sorrel (Rumex acetosella) is in the Buckwheat (Polygonaceae) Family and is native to Eurasia. It is a perennial with edible arrow shaped leaves that have a slight lemon flavor however because of the relatively high quantity of oxalic acid present care must be taken to ingest only in small amounts. It is relatively easy to remove; it can be pulled by hand as long as care is taken to remove the entire rhizome (underground stem) to prevent reprouting. It is best removed in early spring when the soil is moist and before it has had a chance to seed.

 

Management of Native and Non-native Vegetation at Lake Merced
   Lake Merced was designated a Significant Natural Area by the San Francisco Recreation and Parks Department Commission in 1995, and in April 1998, a draft version of the Lake Merced Comprehensive Management Plan (LMCMP) was developed in cooperation with city agencies, private citizens and community groups. The report was prepared by the San Francisco Public Utilities Commission (SFPUC) and the San Francisco Recreation and Parks Department (SFRPD), and identified one of the three beneficial uses of Lake Merced as habitat for native plant and animal species. The report called for a natural resources survey and assessment report, particularly in regard to the impact of the changing lake level on the natural resources of the lake. In response to this, the SFPUC contracted with Trihey and Associates, Inc. to prepare the Lake Merced Baseline Natural Resources Inventory. The draft report was published in December 1998, and identified the use of Lake Merced as a source of emergency water as the 1st priority of management. This ranking of priorities is bound to create conflict between advocates of other uses of the lake.

The Natural Resources Inventory listed three goals as part of its suggested Natural Resources and Education Program for Lake Merced. These three goals are: