Overview

          Cape ivy (Delairea odorata) has been recognized for many years as a potentially destructive invader of riparian woodlands of northern California (Eliott 1994, Dudley and Collins 1995, Bossard 2000, Alvarez and Cushman 2002), but only recently has it come to dominate some ecosystems of coastal southern California. Both the stipulate and non-stipulate forms are now common in the region, and surprisingly it is well established not only in the typical mesic sites where it forms dense understory mats and Kudzu-like tangles in riparian trees, but Cape ivy has also extended its habitat range into highly exposed sites such as coastal bluffs, treeless streambanks and chaparral woodlands well away from riparian corridors. This explosive range expansion may be associated both with unusually wet years such as 2005 and with the discovery that viable seed is now present and common in California (Robison 2004). Once established, it appears to be quite tolerant of normal drought conditions, as we are now seeing during the current La Nina conditions of early 2006. In such open sites managers are concerned that establishment by desirable vegetation will be inhibited, as many plants in this Mediterranean system depend upon relatively open substrates for germination, so its competitive potential may be expressed during both wet and dry years and implying that it may become a major element in the vegetation in the near future.

Left: Cape ivy (light green creeping vine) invading chaparral woodlands in Ventura County. Right: Cape ivy climing vegetation along San Antonio Creek, Santa Barbara.
          
          Southern California riparian ecosystems are already heavily altered by anthropogenic disturbances which have facilitated the invasion of numerous other invasive species such as Arundo donax, Tamarix spp., Ricinus vulgare, Oxalis pes-caprae, Nicotiana glauca and other woody or semi-woody weeds, but the incorporation of invasive vines like Cape ivy brings an entirely new guild into these systems that are critical habitats for many sensitive wildlife species. Furthermore, expansion into relatively undisturbed chaparral ecosystems is a disturbing new phenomenon since these systems were previously considered quite resistant to non-native species invasions (Mooney and Drake 1986). Because Cape ivy growth appears to be rapid and very dense, the potential for negative impacts to native plants and wildlife species is potentially extremely high.
          A biological control program is being developed for management of Cape ivy infestations, with two agents proposed for experimental field testing to determine its capacity for development and target impact under field conditions (Balciunas et al. 2004). However, no field trials are planned for southern ecosystems, despite increasing evidence that Cape ivy impacts may be very significant in this region. Thus, there is a need to expand the biocontrol program to determine suitability of candidate agents in this region. But before such research testing can take place it is important to justify the potential introduction of specialist herbivores for Cape ivy control by establishing information on the ecological associations of Cape ivy in southern California, its growth dynamics, and its interactions with native plant species. Such information is critical for establishing a baseline for comparison when and if biocontrol agents can eventually be released in the region.

Immediate Research Objectives
A. Determine Cape ivy associations with habitat types and ‘host’ native species at risk to infestation in the south coast bioregion (primarily Santa Barbara and Ventura counties with secondary targeting of Los Angeles, Orange and San Diego counties);
B. Identify representative infestations where plant growth dynamics, reproductive behavior, and impacts to ‘host’ plant species will be quantified;
C. Determine if biocontrol agents proposed for testing in northern California can establish populations and cause target impacts in southern California ecosystems

Long-Term Research Objectives
A. Characterize the current and potential impacts of Cape ivy invasion to native plants, habitat types and wildlife species in California, including economic costs, in order to provide quantitative justification for the introduction of specialist herbivores for biological control;
B. Provide a comprehensive evaluation of the distribution, abundance and growth dynamics of Cape ivy as a baseline dataset for assessing efficacy of biocontrol agents when and if open releases are ultimately approved;
C. Determine whether active restoration is required to achieve desired thresholds of Cape ivy control and to ameliorate ecosystem damage caused by Cape ivy invasion, or whether natural recovery of native vegetation and associated species will occur.


Collaborators

Nicole Molinari, UCSB - EEMB
David Chang, Santa Barbara Co. Agricultural Commission


References

Alvarez, M.E. and J.H. Cushman. 2002. Community-level consequences of a plant invasion: effects on three habitats in coastal           California. Ecological Applications12:1434–1444.
Balciunas, J., C. Mehelis and M. Chow. 2004. Biological control of Cape ivy project. Annual Report, USDA-ARS.           http://www.cal-ipc.org/file_library/20035.pdf
Bossard, C. 2000. Delairea odorata. In: Invasive Plants of California’s Wildlands. Bossard, C., J. Randall and M. Hoshofsky           (eds.). U.C. Press.
Grobbelaar, E., J. K. Balciunas, O. Neser, and S. Neser. 2003. South African insects for biological control of Delairea odorata.           pp. 16-28 in: Proceedings, Cal-IPC Symposiums, 2000, 2001, 2002. M. Kelly (ed.), Concord, CA.
Dudley, T. and B. Collins. 1995. Biological invasions in California wetlands: the impacts and control of non-indigenous species in           natural areas. Pacific Institute for Studies in Development, Environment & Security, Oakland. 62 p.
Eliot, W. 1994. German ivy engulfing riparian forests and heading for the uplands. CalEPPC News 2:9.
Holland, V. L. and D. J. Kell, 1995. California Vegetation. Kendall/Hunt Publishing, Dubuque, Iowa.
Mooney, H.A. and J.A. Drake. 1986. Ecology of biological invasions of No. America and Hawaii. Springer-Verlag, New York.
Robison, R. 2004. Reproductive biology of Cape ivy (Delairea odorata) in California. Proceedings, Cal-IPC, Ventura, CA.

© 2006 Tom Dudley