Newly-Introduced Non-Native Species at the Santa Rosa Plateau Ecological Reserve, and the Rate of Introduction of New Species With Time
UNFINISHED DRAFT; ADD WATERLINE ROAD effect; mention of other species such as african daisy, yellow star thistle, artichoke thistle; species extirpated at the srp (aloe, nicotiana glauca)
Introduction and Summary
The Newly-Introduced Non-Native Species
Rate of Introduction of New Species With Time
Introduction and Summary
Non-native species are a huge problem nearly everywhere in the world, and the Santa Rosa Plateau Ecological Reserve is no exception. This page lists the 34 non-native species found from my 2005 survey of the trails of the Santa Rosa Plateau Ecological Reserve that were not found here in previous surveys by Lathrop and Thorne in 1985 and earlier. (There are additional newly-introduced species at the Reserve not found on trails that are not included in this list.)
The total of 34 species in 20 years gives a raw average introduction rate of 1.7 species per year. Analysis of this list shows that it is unlikely that most of these species were missed in the Lathrop and Thorne surveys, and hence there has indeed been an explosion in the rate of introduction of new species since approximately 1995.
This huge increase in the rate of introduction of new species is probably due to the following factors:
- a rate of ~1 new species per year introduced into Riverside County as a whole and present at the Santa Rosa Plateau Ecological Reserve;
- development of properties surrounding the Santa Rosa Plateau Ecological Reserve; and
- increased visitor traffic at the Santa Rosa Plateau Ecological Reserve due to scientists, hikers, bicyclists, horse-riders, and vehicles.
Note that the introduction rate for new non-native species for Riverside County as a whole will be larger than the number quoted above, which only includes new non-native species found at the Reserve.
The Newly-Introduced Non-Native Species
The following non-native species were not found in the area of the Santa Rosa Plateau Ecological Reserve in the Lathrop and Thorne 1985 Flora of the Santa Rosa Plateau, Southern California. A few of these species are listed in that flora, but were only found in restricted localities in a small portion of the 82% of the area in that Flora outside the Reserve itself. See Flora of the Greater Santa Rosa Plateau Region for more information about the difference in areas.
For each species, information about their spread in Southern California was deduced from the following sources:
Date Source Abbreviation 1959 Munz, A California Flora Munz 1959 1968 Lathrop and Thorne, Aliso 6:17-40 LT 1968 1974 Munz, A Flora of Southern California Munz 1974 1978 Lathrop and Thorne, Flora of the Santa Ana Mountains, California Aliso 9:197-278 LT 1978 1985 Lathrop and Thorne, Flora of the Santa Rosa Plateau, Southern California, Southern California Botanists Special Publication No. 1 LT 1985 1986 Beauchamp, Flora of the San Diego County, Southern California Beauchamp 1986 2004 Fred M. Roberts, Jr., Scott D. White, Andrew C. Sanders, David E. Bramlet, and Steve Boyd, The Vascular Plants of Western Riverside County, California: An Annotated Checklist, F.M. Roberts Publications WRC 2004 2005 Rebman et al, San Diego County Plant Atlas SDCPA 2005
San Diego County is only 2.2 miles south-southwest of the Mesa de Colorado, and hence is as important a source of information about nearby taxa as Riverside County. Orange County is 13 miles west, and largely on the other side of the Santa Ana Mountains from the Santa Rosa Plateau, but still is an important source of information about nearby taxa. Unfortunately, there is no flora of Orange County with locations and abundance that can easily be checked for this study.
Information about the spread at the Santa Rosa Plateau Ecological Reserve is from my observations from 2001-2005, augmented by those of Zach Principe, the Reserve Biologist from 1990 to 2005.
The species are given in order of their current abundance on the trails of the Santa Rosa Plateau Ecological Reserve. For each taxon, I give my estimate of the introduction date to the Santa Rosa Plateau Ecological Reserve and the earliest voucher in the SMASCH database for Riverside County. The SMASCH database includes the vouchers from UC Riverside, but does not yet include vouchers from Rancho Santa Ana Herbarium. I will attempt to get any earlier dates from RSA in the future. Vouchers I collected in 2005 have not yet been given to UCR, but I treat those vouchers as if they were in SMASCH and report that date if it is the only voucher.
Discussion of each species follows the list, and is linked to the name for each species in the table.
List of New Non-Native Species
Family Name Scientific Name Common Name Widespread and abundant Taxa 2003 1967 Asteraceae Carduus pycnocephalus Italian thistle 1985 1961 Asteraceae Hedypnois cretica Crete weed 1985 1980 Asteraceae Cirsium vulgare bull thistle 1990 1971 Fabaceae Vicia villosa ssp. varia winter vetch 1985 2005 Poaceae Aegilops cylindrica jointed goatgrass Common Taxa or Taxa Rapidly Expanding Their Range 2003 1999 Apiaceae Torilis arvensis field hedge-parsley 2000 1966 Asteraceae Tragopogon dubius yellow salsify 2003 1986 Fabaceae Trifolium hirtum rose clover 2000 1992 Fabaceae Vicia sativa ssp. sativa spring vetch 1985 1908 Plantaginaceae Plantago lanceolata English plantain Locally-Abundant Taxa 2000 1954 Asteraceae Picris echioides bristly ox-tongue 1995 1994 Geraniaceae Erodium botrys long-beaked filaree 1985 1941 Malvaceae Malva parviflora cheeseweed 2000 2001 Rubiaceae Galium murale tiny bedstraw 1995 1956 Poaceae Phalaris aquatica Harding grass Infrequent Taxa 2000 1904 Asteraceae Silybum marianum milk thistle 2000 1999 Crassulaceae Crassula tillaea Mediterranean pygmy-weed 2000 2001 Rubiaceae Galium parisiense wall bedstraw 2000 1915 Poaceae Dactylis glomerata orchard-grass 2000 2006 Poaceae Brachypodium distachyon purple false-brome 1995 1995 Poaceae Hainardia cylindrica barbgrass Scarce Taxa 2000 2005 Asteraceae Acroptilon repens Russian knapweed 2000 1934 Asteraceae Anthemis cotula dog-fennel 2005 1919 Asteraceae Cotula australis Australian brass-buttons 2005 1965 Brassicaceae Lobularia maritima sweet alyssum 2000 2004 Brassicaceae Sinapis arvensis charlock 2000 1895 Convolvulaceae Convolvulus arvensis field bindweed 2000 1962 Lamiaceae Lamium amplexicaule henbit 2000 1996 Liliaceae Aloe saponaria soap aloe 2000 1897 Poaceae Digitaria sanguinalis crabgrass 2005 1952 Poaceae Eleusine indica goose grass 2000 2005 Poaceae Elytrigia repens quackgrass 2000 1950 Poaceae Festuca arundinacea tall fescue 2005 1965 Poaceae Piptatherum miliaceum smilo grass
Discussion of Each New Non-Native Species
Widespread and Abundant Taxa
- Carduus pycnocephalus, Italian thistle. This species was noted as a weed along roadsides, waste places, etc.; Sonoma Co. to Santa Barbara Co., San Diego Co. in Munz 1959; Munz 1974 noted that it was mostly to the north of [Southern California]. It was not given in LT 1978 for any part of the Santa Ana Mountains, and not given in LT 1985 for the Santa Rosa Plateau. Beauchamp 1986 says it was Rare, and cites only two locations in San Diego County. WRC 2004 said Uncommon weed in disturbed areas mostly in the north; locally common in the southern Santa Ana Mountains.
The first plants I saw at the Santa Rosa Plateau were two plants in the uppermost drainage of Cole Creek in May 2003. There must have been a handful of other plants I didn't notice in 2003, since thousands of plants appeared in 2005 in many places on the Reserve. See Noxious Weeds at the Santa Rosa Plateau: Italian Thistle, Carduus pycnocephalus for a map of its current extensive distribution.
An individual plant is capable of producing hundreds to thousands of seeds, so it only takes a few years for a small number of individuals to produce the thousands of plants observed in 2005.
From a virtually zero population in 2001, Italian thistle now seems to be widely distributed and abundant in Southern California. I observed huge populations of them in the Santa Monica Mountains and the Santa Ynez Mountains in 2005. Italian thistle is now in 19 grid squares in SDCPA 2005, so it has spread widely in San Diego County as well.
- Hedypnois cretica, Crete weed. This taxon, along with Cirsium vulgare, surprise me the most that they were not found previously at the Reserve. In the first year I surveyed the Santa Rosa Plateau, this was an abundant and widespread taxon. It lines Waterline Road, Fault Road, and the eastern portion of Monument Hill Road, with tens of thousands of plants, along with scattered populations elsewhere. Furthermore, its range has been essentially constant since my first observation in 2001.
Yet is seems likely that this taxon has spread north from San Diego County, perhaps sometime near the end of the LT 1985 fieldwork. LT 1978 notes that this species is a rare introduced weed in disturbed soil along a roadside through chaparral in Coal Canyon, which is the northernmost point of the Santa Ana Mountains. WRC 2004 state scarce weed in cultivated ground, but much more common toward the coast. Beauchamp 1986 gave it as frequent, weed in disturbed areas; coastal, below 200 m, and cites locations south of northernmost San Diego County. By 2005, this species appears in 28 grid squares in SDCPA 2005, so it has spread widely in San Diego County as well.
Furthermore, it is difficult to miss this taxon. It not only blooms over a long period during prime time, when botanists are out doing surveys, but it remains noticeable to a trained eye even when long dead, due to its distinctive hardened phyllaries.
From the above, it seems unlikely that Lathrop and Thorne missed this species at the Santa Rosa Plateau. Instead, this species probably expanded into northern San Diego County and the Santa Rosa Plateau area sometime in the late 1980s.
- Cirsium vulgare, bull thistle. Given its present coverage of the Santa Rosa Plateau Ecological Reserve, this is another species for which it is hard to believe that it was not found by Lathrop and Thorne. This species has taken over many of the drainages and moist flattish areas at the Reserve. There are thousands of these plants in the Reserve, some of them several meters tall and one meter wide.
Yet there seems no doubt that this taxon was absent in a large area of Southern California in 1980. This species was not given in any part of the Santa Ana Mountains in LT 1978. LT 1985 found it only in disturbed areas along De Luz Road. The first Riverside County voucher was only in 1980. Beauchamp 1986 says it was uncommon in San Diego County, and gives only three widely scattered locations.
This taxon apparently appeared in the 1980s, and quickly spread throughout the Reserve and other locations in Riverside and San Diego Counties. Tom Griggs, a botanist who was the Reserve Manager from 1984 to 1990, says that it was present but restricted to places that were heavily disturbed by cattle ( as near corrals and water troughs) and just a few individuals. It certainly was not common.
Cirsium vulgare is definitely common today. It is present on 14 out of the 16 plant trail guide routes at the Reserve. It is present in 6 plant trail guides I've done outside the SRP, and in 25 of the 49 floras from throughout Southern California I've digitized, being absent mostly from the higher-elevation floras. WRC 2004 says it is a common weed in urban areas and at the edges of springs and wetlands, primarily in the lowlands. It already appears in 13 grids in the SDCPA 2005 scattered over a large area.
The speed of spread of this taxon is abundantly clear to anyone who hikes during the late summer seed dispersal time of this taxon. The abundant seed is easily carried in great quantities for distances of ~km (~mile). If this species could grow outside of wetlands, it would already have been essentially the only species present anyplace in Southern California, displacing nearly every single other plant.
- Vicia villosa ssp. varia, winter vetch. I've watched this species spread literally before my eyes at the Reserve. In ~2000, it was present on the Reserve as a single patch in one location near the Main Vernal Pool. It then began to grow along Via Volcano / Tenaja Roads. Every year the patches would extend farther along the road, and more into the Reserve perpendicular to the road. Last year I began photographing areas not yet invaded by this taxon so I could document its spread into those areas.
This taxon wasn't found by LT 1968 at the Plateau. It was not found in the Santa Ana Mountains by LT 1978 from their own survey, but they noted a voucher from 1965 in Trabuco Canyon. LT 1985 found a single occurrence along De Luz Creek south of the Plateau. Beauchamp 1986 found it to be infrequent; coastal and foothill, below 900 m at De Luz Creek and a three other locations in San Diego County.
It is now common in Riverside and San Diego Counties. WRC 2005 says Common in disturbed areas; it is now in 9 grids in the SDCPA 2005 scattered over a large area.
- Aegilops cylindrica, jointed goatgrass. Zach Principe found about 300 plants of this species in two different areas of the Reserve in 2001, at Clay Hill and Hidden Valley. No plants were seen on any trail route until 2005, when thousands of plants were observed along the entire ~1.5 mile length of Hidden Valley Road. It is possible that the plants were there in previous years, but their bloom time of June cuts down the number of botanists available to observe them, and the plants are impossible to see once the seeds have dispersed, since there is no inflorescence left. The spread along Hidden Valley Road was possibly aided by bulldozing of that road.
This taxon doesn't appear in LT 1985 or LT 1978; and is absent from the Riverside County, Orange County or San Diego County Floras, despite the SW distribution given in the Jepson Manual. The only SMASCH vouchers in Southern California are in Santa Barbara and San Bernardino Counties.
This species is spread by contaminated wheat straw or unprocessed grain, and by livestock. The seeds retain viability of up to 75% after passing through ruminants. Hidden Valley was grazed as late as 1991, and livestock are the likely source of introduction to the Reserve.
- Torilis arvensis, field hedge-parsley. This taxon entered the Reserve by sneaking up the Sandia Creek / De Luz Creek from San Diego County. One advance contingent, probably a single plant, made it to the Adobe Loop Trail, presumably in 2003, and produced ~50 plants in 2005. The main body of the invasion has just made it to the lowest southwest portion of the Reserve in 2005, on the Punta Mesa Trail at the De Luz Creek tributary.
This taxon is not in LT 1978, LT 1985, and is given in only one location (Dyche Valley, Palomar Mountain) in Beauchamp 1986. It is not given for any part of Southern California in Munz 1974. The WRC 2004 reports it as scarce weed of cultivated ground, possibly expanding northward from San Diego County. (This taxon also loves to appear under trees, so the De Luz tributary was ideal for it.) The first and only SMASCH voucher in Riverside County was in 1999, as a weed in a planter bed at the UCR campus.
However, this species is widespread in northern San Diego County as of 2005, and the Jepson Manual says CA-FP (esp NW, CW, n SNF); rapidly spreading. I'm pretty sure this will in fact be a widespread taxon in Southern California within a decade or so.
- Tragopogon dubius, yellow salsify. This taxon appeared in roughly the year 2000 or 2001; my first observation of it was in 2001. It spread rapidly; by 2003, there was an extensive patch of it in one location at the Reserve. By 2005, there were outliers in many places in the Reserve, with several extensive patches, despite considerable work in trying to control it.
This taxon does not appear in LT 1978, LT 1985, or Beauchamp 1986, nor in Munz 1974, who says to be watched for in Southern California.
The WRC 2004 says scarce weed in the lowlands; locally common at Morrel Portrero, Santa Ana Mountains (just northeast of Elsinore Peak). The SDCPA 2005 reports it in 4 grid squares in the Laguna Mountains.
- Trifolium hirtum, rose clover. This taxon was first seen as a few plants in one location at the Reserve in 2003. However, judging from its distribution in 2005, it must have been present at several other locations in 2003. It is rapidly expanding its range; the several plants in the first location became several patches in 2005, and there are a widespread dozen or so extensive patches in 2005.
This species does not appear in LT 1978, LT 1985, or Beauchamp 1986. Munz 1974 has it just entering Southern California in the Santa Ynez Mountains. WRC 2004 says widely scattered, mostly on disturbed soils; used in soil stabilization mixes and so often appearing on roadsides, but increasingly showing up in wildlands.
Rate of Introduction of New Species With Time
A histogram of the estimated introduction dates to the Santa Rosa Plateau Ecological Reserve for all observed non-native species (not just the new ones listed above) shows that new introductions exploded after 1995:
The above plot includes additional non-native species over the list of 34 presented above, with their introduction dates estimated primarily from Munz 1959, LT 1968, LT 1978, and LT1985. No dates were obtained prior to 1960 since I had no earlier sources to pin down earlier dates.
The number of introduced species per decade was 26 new species in the decade from 1995 to 2005, after being between 0 and 5 new species per decade in the previous four decades.
This dramatic increase is not due to omissions in the Lathrop and Thorne surveys. The detailed discussion for each of the species above shows that many of the species have clear support from many sources that they are recently introduced in this area. Analysis given below will also show that many of these species are recent introductions.
Instead, the increase is most likely the result of three factors, which will be explored in turn below.
Rate of Introduction of New Non-Native Species to Riverside County As a Whole
Part of the increase is due to introductions in Riverside County (and often Southern California) as a whole. To estimate how much of the increase is part of this area-wide trend, I histogrammed the dates for the first voucher for these species in Riverside County. The following histogram shows that there has been a significant increase in the number of introduced non-native species to Riverside County as a whole.
The number of introductions to Riverside County increased from 1-2 species per decade in 1895 to 1945 to an average of 3 per decade in 1945 to 1985 to 4 in 1985 to 1995 and 9 in 1995 to 2005. Purely statistically, the average of 9 in 1995 to 2005 is a two-sigma increase over the average of 3 per decade and thus is formally significant at the 95% confidence level.
However, voucher collections vary tremendously with time, geographic location, and with the abundance of a given taxon. It is possible that the dramatic increase in the number of first collections in the last decade is due to one or more of the following effects:
- this area being vouchered for the first time at UC Riverside (one of the biggest sources for the SMASCH vouchers in Riverside County), or
- the number of vouchers increasing dramatically in the last decade.
- non-native species being under-collected in earlier years.
To understand these factors, I created a control population within the Santa Rosa Plateau Trail Flora that has similar characteristics to the new non-native species. Analysis of the control population, given below, verifies that the number of introductions to Riverside County as a whole has indeed increased significantly, and that it is not due to any effect of the Riverside County vouchering.
To obtain the control population, I sorted the Trail Flora first by the number of trails on which I observed each taxon in my 2005 survey and then by family. I then selected the taxon immediately following each one of the new non-native taxa at the Santa Rosa Plateau, irrespective of whether it was native or non-native, and histogrammed their first Riverside County voucher.
This procedure ensured the selection of plants with very similar characteristics to the new non-native species in terms of the above factors which might compromise deductions from the date of the first voucher. The species in the control population are from the same geographic area, and have the same abundance distribution. If the new non-native species I have found at the Santa Rosa Plateau Ecological Reserve had actually been present earlier, but missed by previous surveys of the Santa Rosa Plateau, one would expect them to have similar dates for their first voucher collection in Riverside County.
The histogram for the control population, shown on the above plot, is dramatically different from that of the new non-native species, with a huge peak in the 1895 - 1905 decade that is completely absent from the histogram of the new non-native species. Except for that peak, the numbers are essentially constant with time, varying from 0-4 taxa per decade.
One variable that couldn't be controlled as well in the above selection was native vs. non-native, due to the smaller numbers of other non-native taxa. I explored whether there was any difference in collecting non-native taxa vs. native taxa in two ways.
First, albeit with less statistical significance, I can break down my control population into native and non-native species. There were 25 native species in the control population, and 8 non-native species. The separate histogram for the non-native species is similar to the separate histogram for the native species, with a huge peak in the 1895 - 1905 decade (three of the eight taxa were collected in 1901, 1902 and 1906). Clearly, non-natives were being well-collected as far as 100 years ago.
Second, I can histogram the first SMASCH voucher in Riverside County for every non-native species in the Santa Rosa Plateau Ecological Reserve Trail Flora. The following histogram shows that plenty of non-natives were vouchered one hundred years ago, with a peak in 1895-1905 that is very similar to the peak seen in the control population as a whole.
Furthermore, this plot shows that the number of species introduced to Riverside County, and found on trails at the Santa Rosa Plateau, has apparently increased from an average of 0.5 species per year in the 1905-1945 period to an average of 0.9 species per year in the 1945-2005 period. This is very different from the decline seen in recent decades in the control sample plotted above, especially when compared against just the native population in that control sample. There is a slight tendency toward more recent collections for the non-natives species in my control sample: the latest voucher for a native species is 1980, whereas two of the non-native control sample were collected first in 1985 and 1993.
I therefore conclude that the observed recent increase in the introduction rate of non-native species into Riverside County is not due to under-collection of non-native species in previous decades. This increase is a real effect that has been going on for perhaps a half century.
One should note that a newly-introduced non-native species will appear much earlier in a large area such as Riverside County than for any smaller specific area within that larger area. It takes time for a newly-introduced species to spread from the introduction point to another location. Hence it is not surprising at all that the rate of introductions to Riverside County is a smoother function than the rate of introductions to a specific area, especially in light of the factors considered next.
Introduction of Non-Native Species By Development Around the Santa Rosa Plateau
As late as 1995, the environs of the Santa Rosa Plateau Ecological Reserve remained largely undeveloped. However, beginning around 1995 the Temecula - Murrieta area experienced explosive growth. The north and east sides of the Santa Rosa Plateau Ecological Reserve became essentially fully-developed by 2005, and significant development occurred on the western side as well.
Developments on the west side, at the origins of several branches of Cole Creek, have likely been the source for four species: Lobularia maritima, sweet alyssum; Lamium amplexicaule, henbit; Aloe saponaria, soap aloe; and Elytrigia repens, quackgrass. Aloe saponaria appeared about a half mile inside the Reserve, directly downstream and along Stevenson Canyon Creek, and probably resulted from someone either dumping a plant outside the Reserve at the head of the Creek. Lamium amplexicaule appeared just across Clinton Keith Road along the stream from Sylvan Meadows homes. Lobularia maritima appeared much deeper in the Reserve along Cole Creek in the heavy flooding of 2005. This is a common garden plant, and there were probably numerous sources in the headwaters of Cole Creek. Elytrigia repens is a common lawn, garden or crop weed, which has never before been recorded in Riverside County. New developments, which often bring in nursery plants from outside the County, are by far the most likely suspect for this record.
All of these four species are garden plants or garden or lawn weeds, rarely found in natural settings.
Nearby developments may also be a factor in the introduction of two other taxa: Silybum marianum, milk thistle; and Dactylis glomerata, orchard-grass (at least in Sylvan Meadows). All of these species appeared in drainages below developments outside the Reserve.
These two species are not ones new to the Riverside County Flora. Their first vouchers are 1904 (Silybum marianum) and 1915 (Dactylis glomerata). Silybum marianum is sometimes planted as an ornamental, and Dactylis glomerata is usually a cultivated species, primarily for hay and / or forage for horses.
In summary, new developments near the Santa Rosa Plateau Ecological Reserve are likely the source for 4-6 species of the 34 listed here.
Introduction of Non-Native Species By Visitors to the Santa Rosa Plateau
Copyright © 2005 by Tom Chester.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Tom Chester
Updated 12 October 2005.