UC Irvine

Historically, over 4,000 acres of the Orange County Central & Coastal Sub region NCCP/HCP Reserve System have been invaded by a number of exotic plant species including several annual grasses, artichoke thistle (Cynara cardunculus, CYCA), mustards and other exotic forbs. Invasion has resulted in displacement of many desirable plant species and overall degradation of the reserve’s target plant community, coastal sage scrub. To control the spread of CYCA, the Nature Reserve of Orange County (NROC) established a management program involving spot application of herbicide (Fusillade and Round-up) to individual plants. Since 1994, thousands of acres have been treated annually. Additionally, NROC has chemically and mechanically managed other exotic, invasive species such as Ricinus communis (castor bean) and Nicotiana glauca (tree tobacco). While these weed control efforts reduce target invasive species, whether the native plant community is recovering is not necessarily clear, nor is the long-term sustainability of control efforts.

Following degradation, recovery of a native system rarely follows the reverse path of degradation (Fig. 1). Instead alternative paths that may or may not have a trajectory towards the original or goal state can occur (Bradshaw; Cramer et al 2008). In highly degraded areas, sites may become stuck in an alternative or novel state. These novel or alternative trajectories and states play a key role in recovery and restoration and may be dependent on management action. A common example of this is the replacement of a targeted exotic species by a new exotic following control of the original target exotic (Denslow & D’Anonio 2005; Flory & Clay 2009). Within the NROC community, there has been concern that such a replacement occurred following the long-term CYCA removal program such that Brassica nigra (black mustard, BRNI) replaced CYCA. Assessing recovery after control measures is a powerful tool to aid in restoration decision-making and ultimately guiding future management actions for the reserve system.

Goals and Objectives:

Our objectives were to address a number of critical issues relevant to restoration planning at NROC, including:

 Task 1: Provide an updated description of the vegetation community at 109 sites within the Reserve System previously sampled in 1998, 2007 and 2008.

 Task 2: Teasing apart trends due to management efforts from other trends due to environment or land use change (e.g., grazing cessation in the early 1990s).

 Task 3: Determining thresholds in both native and weed species abundance that will allow for further unassisted recovery.

 Task 4: Identifying areas where sites are “stuck” (i.e., not recovering) and need additional intervention (e.g., seeding, mowing, soil amendments).

By capitalizing on past vegetation monitoring and additional analysis of monitoring data, we hoped to reveal the mechanisms underlying the complex dynamics of vegetation recovery over time and inform restoration decision-making within the NCCP/HCP Reserve System.

 Project Start Date: April 1, 2013

Project Completion Date: December 31, 2014

Contracted Organization: University of California, Berkeley