Soil Ecology Restoration Group

last update December 13,1999

Ambrosia pumila- monitoring, outplanting, and salvage

Jessica Johnson, David Bainbridge, Julie Janssen, Dave Truesdale

On April 13, 1999, the U.S. Fish and Wildlife Service made a 90 day finding on a a petition to list Ambrosia pumila as endangered. They determine that the petition presented "... substantial scientific or commercial information indicating that listing A. pumila as endangered may be warranted." Therefore, a 12-month status review under the Endangered Species Act has been initiated to determine if listing is warranted (Federal Register, 1999). We are continuing our salvage and transplant efforts since there are currently no other means of protection in place. We appreciate the opportunity to have started work experiments before it was under review. This includes continued monitoring of the transplanted salvaged plants in Penasquitos Canyon and Pilgrim Creek, and the small population at Tecolote Canyon Park.

A. Los Penasquitos Canyon Preserve Planting

On May 13 and 14, 1999, we planted approximately half of the plants we had salvaged from the Sweetwater area in the summer of 1006 to six locations along the Los Penasquitos Canyon Preserve. This is an area which historically supported at least one population of A. pumila, but this was extirpated during the construction of a bridge for Black Mountain Road.

Sites were chosen according to vegetative cover, proximity to a water source and soil characteristics. A. pumila appears to require full sunlight and is well suited for areas with and open canopy and few weedy grass species. Historically it appears most commonly on flood terraces and we chose sites that are either on the apparent floodplain or are in runoff areas from the adjacent mesas. Site soils chosen were sandy loam texture since the majority of soils from which this plant has been salvaged are sandy loam. We also attempted to match outplanting and salvage site soil levels of organic matter content, pH, nitrogen, phosphorus, potassium and various micronutrients.

Into each of the six fenced sites running the length of the Canyon, one 2.5' by 2' tub, two 1.5' square tubs and eight approximately nine inch square "plugs" were transplanted, figure 1

The GPS coordinates of each site are as follows:

Site 1: UTM zone 11, 0488055, 3644696

Site 2: UTM zone 11, 0485631, 3644445

Site 3: UTM zone 11, 0484560, 3644038

Site 4: UTM zone 11, 0484092, 3643849

Site 5: UTM zone 11, 0484010, 3643705

Site 6: UTM zone 11, 0484020, 3643671

Figure 1. Typical A. pumila planting and fencing at Penasquitos Canyon


Plant holes were dug using an auger and shovels and were prewatered to a depth of about 4 inches. The various sized sections of A. pumila were placed into the holes intact, dirt was backfilled and tamped in, and they were watered again. Each planting was surrounded by its own shelter made of chicken wire and bubble wrap or a simple treepee, depending on its size. The purpose of the shelters was to reduce the risk of herbivory, and reduce wind and sun exposure and moisture loss while the plants were still vulnerable and becoming established. Each of the six sites was surrounded by a chicken wire fence and in three cases, where the site was close to a busy hiker trail, by a split rail fence. In addition, as an experimental treatment, two of the sites received a layer of bark mulch, two received cocoa mulch and two received no mulch as a control. Sites were watered every two weeks for the first three months and are now being watered once each month until winter rains begin.

Results and Discussion

in September 1999, three of these sites were vandalized and the fencing and tree shelters were stomped into oblivion, but fortunately, the plants themselves were unharmed. So, as of the last week of September, all plantings appeared alive and healthy with the exception of four of the smallest sized plantings in plot number four in area with the riches soil and some native grasses. These were completely removed by gophers. This may be one reason. A. pumila is found on compacted soils in exposed sites.

The healthiest appear to be the medium and large sized plantings. These have withstood herbirvory and dry conditions much better than the small plantings and after just four months have begun to produce new shoots beyond the boundaries of the original planting. The largest (2.5' by 2') plantings however, were very heavy and awkward to work with, so overall, the medium sized plantings seem to be most appropriate. It is too early yet to determine if mulch type will affect plant health, but we hope to have some answers by Spring 2000.

B. Pilgrim Creek Monitoring

In June 1997, forty individual plants were transplanted at Pilgrim Creek just south of Camp Pendleton. Now, over two years later, 82.5% of these plants remain. More impressively, however, a total of 373 new shoots that stretch up to 70 inches away from the original plant been counted.

At this site, experiments were established to compare three irrigation treatments: conventional basins (in which a mound of soil is formed around the plant in order to temporarily trap water and direct it toward the plant), deep pipe (in which a three inch diameter piece is inserted into the ground so that water can be added to the deep root zone) and porous clay capsules (a method for gradual dispersal of water to plant roots). Using a count of total number of new shoots, we compared these three treatments and found that, overall porous clay capsules were most effective, figure 2.

Figure 2.A. pumila by irrigation treatment at Pilgrim Creek

We also examined two types of plant shelters at this site. We compared chicken wire enclosures to tree shelters and found that, again using a count of total number of new shoots, tree shelters were superior, figure 3. The tree shelters probably helped by reducing moisture stress while the vulnerable new plants were first becoming established. Tree shelters reduce temperatures, wind exposure, and sun exposure to transplants.

Figure 3. A. pumila sprouts by protection at Pilgrim Creek

C. Tecolote Canyon Park

The first small planting was done at Tecolote Canyon Park with three plants in the native garden and three in the open park. The three planted in cleared spots in thick annual grassland were eaten by slugs and snails despite tree shelters The plants in the garden have fared much better. They have continued to grow and spread.

D. Ambrosia pumila Genetics

Our transplanting efforts have taught us that A. pumila is a vigorous and very low maintenance plant when it comes to vegetative reproduction. Its rhizome-like root system enables it to spread rapidly even in locations that might be considered sub- optimal, such as the heavily compacted soil outside our greenhouse which it has colonized. However, for a plant that has been reduced to such extremely small numbers, vegetative reproduction is not enough. Restoration efforts must also focus on sexual reproduction since it is the key to maintaining a species' genetic diversity and since it is obviously much easier to spread the seeds of a plant than to dig it up and transport it piece by piece. So far, all attempts to germinate A. pumila seeds have failed, and some people have suggested that is doesn't produce viable seed. This could be related to loss of a critical pollinator, the need for genetic diversity for pollination to occur (i.e. not self fertile), or inappropriate conditions for pollination. We are beginning some preliminary tests which will hopefully determine the reason for this.

We will examine:

1) Genetic Viability- Preliminary genetic analysis has been conducted on two populations of A. pumila, one from El Cajon and one form the Sweetwater area. Electrophoretic gels have shown that although two populations are indeed identifiably distinct, there are surprisingly few genetic differences within each population. This might explain why viable seeds have not yet been found from within a single population. Different tests on a greater number of individuals from a greater number of populations are underway, but if these trends persist, then the next logical step would be to try some pollination studies.

2)Pollination Studies- We will attempt to create viable seed by crossing individuals from between two different populations. The theory is that individuals within remaining populations are too genetically similar to be able to successfully reproduce.

3) Means of Pollination (wind, insects)

4)Pollination Viability- We will be running a test called a "pollen goodness test" which observes pollen tube growth and will determine if A. pumila pollen has simply lost the ability to germinate.

5)Conditions Required for Germination (temperature, scarification)


Although some previous reports have suggested that salvage and transplant attempts for A. pumila will result in 100% mortality, our efforts have so far proven to be quite successful. We have found that vegetative reproduction for this species is relatively easy, but to ensure long term survival and maintenance of this species further research is need to determine if this plant is capable of sexual reproduction. Transplanting, will probably continue to play an important role in the management of this species since remaining populations are so small and fragmented that they may be considered nonviable. Any future transplant projects that might involve combining individual plants from different populations should be carried out only after genetic analyses have been conducted on all populations and genetic viability is considered.


Federal Register Online via GPO Access

(4/19/99. Ambrosia pumila [DOCID:fr19ap99-22]