I have not observed any impact on ecosystem processes. I have not observed any impact on ecosystem processes. However, my observations are limited to land managed fairly intensively. Therefore, for example, the fire regime is already drastically altered (there are no fires) and it is difficult to say whether cotoneaster in a different setting would an impact on fire occurrence.
Cotoneaster may influences natural erosion processes, such as reducing erosion in old sand dunes and coastal bluffs, this erosion creates opening in coastal scrub for rare and endangered dune and serpentine annual plants. It is not clear whether the extensive root system of the cotoneaster impeded erosion more than the larger scrub plants such as Lupins chamissonis, Bacharis pilularis, Ceanothus thyrsiflorus, etc.
From the horticultural literature it seems that Cotoneasters do not impact the nutrient and mineral dynamics of the soil, as they are considered a possible candidate for planting in any well-drained soil and not noted to effect plants around them. However, the impact of one or two cotoneasters may be negligible though greater numbers are not.

C. Christman, Observation,
Sigg, J., 2000. Cotoneaster spp. in Bossard, C., J. Randall, and M. Hochovsky. Invasive Plants of California Wildlands. University of California Press. Berkeley, Ca.
The Sunset Western Garden Book.ed. Brenzel, Kathleen. Sunset Publishing Corporation, Menlo Park, CA. 2001

Reduces habitat for burrowing rodents such as voles and shrews, reduces habitat for bird species such as quail that require open grassy areas for seed foraging, reduces space in which raptors can hunt. Reducing habitat for rodents and some birds will in turn reduce food source for raptors, foxes, coyotes and other carnivores. Coastal areas of california are defined by areas of scrub and oak interspered with open areas in which grasses and annual forbs persist, this pattern is constantly changing depending on erosion, rainfall, and natural progression from open sand into scrub and eventually oak woodland. However, Cotoneaster grows and spreads much more quickly than native plants and fills in open areas in scrub and covers grasslands when not rigorously controlled. It's dense roots and branches can effectively close off the area under its canopy making it inhospitable to rodents and difficult for larger birds to penetrate.

C. Christman, Observation

Cotoneaster can invade wildlands without any dramatic anthropogenic or natural disturbance. I have observed Cotoneaster growing in undisturbed scrubland, grassland and forested areas. Because birds eat the berries and drop the seed in scat, disturbance is not necessary for the spread of the seed. Additionally, Cotoneaster are well-adapted to many soil types and can do well in full sun or aprt shade conditions. It is likely that the fragmentation of wildlands has been at least partly responsible for this spread, Cotoneasters are a popular horticultural plant (in part because they attract birds!) and they are often cultivated close to wild areas. It has been noted by Jake Sigg that the oldest Cotoneasters seen in the wild are only 15 to 20 years old and that a change in genotype mighy have allowed Cotoneasters to spread more rapidly in the recent past as they have been cultivated in California since 1854.

C. Christman, Observation.
Sigg 2000

Increasing steadily, unable to quantify Cotoneaster has only recenly been noted as a wildland invader, but so far has spread significantly along the coast, esp. near urban areas where it has been in cultivation for many years. It seems likely that as the population of California grows and housing along the coast becomes denser, the Cotoneaster will be brought into local gardens and will spread from them into wild areas. It does not seem likely to spread inland as it prefers the cooler, moister climate of the coast.

Sigg 2000

Used in public and private ornamental cultivation. First, I worked in the nursery industry in the past and have sold Cotoneasters (believe me, I have been chastened). Second, there are hundreds of websites advertising many species and varieties of Cotoneaster for sale by mail order or at local nurseries, all over the USA and in many other countries. All of these websites give information on planting and caring for your Cotoneaster.

C. Christman, Observation
Sigg 2000

Noted as invading Australian bushland (different websites say there are 6 or 9 species that have invaded Australia: C. pannosa, C. franchettii, C. lacteus and C. gluacophylla are esp. problematic there, Cotoneaster pannosa and C. franchettii, very similar species, are noted in Hawaii and South Africa.

Iziko, Museums of Cape Town: http://www.museums.org.za/bio/plants/rosaceae/
Ecoaction Australia: http://www.ecoaction.net.au/ccserac/docs/weeds/cotoneaster.htm

Cotoneaster can be found in all coastal ecosystems except foredunes, as I know from observation, and it is found mainly in an area around Los Angeles, an area around the San Francisco Bay, along the central coast near Big Sur, and in far Northern California near the border with Oregon. It was introduced to the state in 1854 for ornamental purposes. I have no information on where else it may be or what percentage of total ecosystem in California it has invaded. I would guess around 5%-10% for riparian woodland, and more like 20% for coastal scrub and prarie, considering how reduced in size and number these ecosystms are. However, I have no information to prove this. Per Worksheet C, invades 5 major types, on enter text here

C. Christman, Observation
Invasive Plants of California Wildlands. Sigg, Jake, on www. cal-ipc.org