Questions: List the top two biological/ecological characteristics of this plant that allow it to successfully invade the Los Angeles River Watershed. For each characteristic, explain why

Questions:
List the top two biological/ecological characteristics of this plant that allow it to successfully invade the Los Angeles River Watershed. For each characteristic, explain why this makes this plant a cause for concern. Be sure to support your argument with specific evidence from the plant profile you read and what you know about the ecological and environmental characteristics of the Los Angeles River Watershed from the Biomes lesson.
What is the most important reason that your species should be eradicated? Explain your answer, considering both the environmental and economic impacts described in the plant profile.
Which method of eradication would you be most likely to recommend and why? Which method of eradication would you be least likely to recommend and why? Do you think any of these methods are likely to be effective in eliminating your species? Support your argument with specifics from the plant profile.
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Background:
(Maltese star-thistle – Centaurea melitensis)
Geographic origin: Spain and Portugal
Method of introduction to CA: Most likely in the 1700s during the period of Spanish colonialization
Identifying characteristics: Small plant with gray-green leaves covered in tiny hairs. Young leaves are covered entirely in gray smooth hairs. Bases of flowers covered in spines, and petals are yellow.
Biology and Ecology
Physiology and Phenology
Most seeds germinate after the first autumn rains. Young plants remain as tightly clustered leaves while growing deep tap roots throughout the winter and early spring. Flowering occurs from April through July (Keil and Ochsmann, 2006).
Since C. melitensis, has shallower roots than many other species it has a shorter growing season.
Reproductive Biology
C. melitensis reproduces solely by seed. Flowers develop in early spring. Seed production is highly variable, ranging from one to 60 seeds per flower head and one to more than 100 heads per plant, for an average of 1500 seeds per plant depending on the availability of resources (DiTomaso and Healy, 2007).
Seeds are dispersed through short-distance wind dispersal. Animals can occasionally move seed longer distances in hair or birds after ingestion. Seeds only blow short distances. Most seeds fall to the ground just below the parent plant.
Longer distance dispersal is usually mediated by human or other animal activities such as being carried on vehicles, transported in mud or soil, on hooves or equipment, clinging to fur or hair, or passing through a digestive tract of an animal. Researchers found C. melitensis seeds distributed in rabbit feces (poop) (Fernandez and Saiz, 2007), indicating that European rabbits were vectors. The presence of C. melitensis seeds in fleeces cleaned at woolen mills indicates that sheep transport the seeds (Nesom, 2004).
Environmental Requirements
C. melitensis invades open, disturbed sites (including waste areas and roadsides), open (oak) woodlands, rangelands, and natural grasslands (both annual and perennial), non-irrigated pastures, and cultivated fields (Roché et al., 1986; DiTomaso and Healy, 2007).
During monitoring of the response of C. melitensis populations after a wildfire in California, its population expanded beyond pre-fire levels from 2004-2005, but declined in frequency during 2006, probably because of reduced rainfall during the third year (Hubbert, 2007).
Environmental Impact
The Forest Service included C. melitensis in the list of the invasive, non-native species posing the greatest threat to the successful restoration of native vegetation in chaparral types following the 2003 Grand Prix/Old Fire in the San Bernardino Mountains of southern California (Hubbert, 2007).
After the fires, surveys for infestations of the target weed species found that C. melitensis covered large acreages. Fire disturbance aided the spread of weed infestations that were already present before the fire, either in the seed bank or in close proximity to the burn, including infestations of C. melitensis which expanded beyond the pre-fire levels, especially on fire roads. It was probably already established along roadsides before the fire but was able to spread into new areas because of a lack of competition after the fire. Dozer lines, safety zones, and hand lines were the second most infested areas and, in most cases, C. melitensis grew faster than the native species (Hubbert, 2007).
Methods of Control
Biological control
A small beetle (Lasioderma haemorrhoidale) that feeds in the capitula of C. melitensis was unintentionally introduced in California from the Mediterranean region but has had little impact on controlling C. melitensis populations (DiTomaso and Healy, 2007).
Chemical control
Many herbicides are effective against C. melitensis including glyphosate (RoundUp).
Cultural Control
Cattle may graze C. melitensis, but only when other grasses are unavailable
Sheep and goats would probably be effective but have not been studied.
Grazing by animals could also contribute to spreading of the weed
Frequent fires increase the numbers of C. melitensis plants, fire is therefore not recommended for control
Sources
Text modified from: CABI, 2021. Centaurea melitensis. In: Invasive Species Compendium. Wallingford, UK: CAB International.
Joe DiTomaso. 2003. Plant Assessment Form Centaurea melitensis. From Cal IPC.
Image Credits
Kevin Thiele from Perth, Australia, CC BY 2.0 , via Wikimedia Commons
Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0 , via Wikimedia Commons
Philmarin, CC BY-SA 3.0 , via Wikimedia Commons
All maps are from iNaturalist
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(Los Angeles River Watershed) BIOMES LESSON:
Chaparral
Much of southern California, including the Los Angeles River Watershed and the region containing Pasadena City College, can be classified as a chaparral biome. Chaparral is found throughout California, southern Oregon, and northern Baja California, both near the coast and inland. Chapparal plant communities are incredibly biodiverse; in fact, chapparal contains 20% of the plant species in California, despite making up only 9% of the wild vegetation. Chaparral is considered a biodiversity hotspot — with high species diversity that is under threat by human activity. Without all of the roads, freeways, and buildings, the landscape across the Los Angeles basin would be covered with evergreen shrubs, annual flowers, oak trees, and sagebrush.
So, what is the climate like in a chaparral biome? Winters are mild and rainy, with typically 10-20 inches of annual rainfall. The summers are hot and dry, with little to no rain typically occurring between the months of March and October. After many months of heat and no rain, chaparral is most vulnerable to fire in the late summer and fall.
Chaparral characteristically is found in areas with steep topography and shallow stony soils, and the plant community is dominated by drought-tolerant woody shrubs. Most plants that live in chaparral have small leaves. This adaptation prevents the plant from losing too much water through its leaves during the hot summer months. Chaparral plants are often deciduous, meaning that they lose their leaves seasonally (typically in autumn).
(Youtube Name: Valuing Chaparral)

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