Upland Invasive Species
Control and Restoration

About Starr Ranch

Starr Ranch is a 4000 acre Audubon preserve in southeast Orange County, California. Our activities at the Ranch focus on four major areas: conservation activism, education, habitat preservation, and research. We take an adaptive management approach to land management, using carefully controlled experiments to test most of the techniques we employ to remove weeds and restore native habitat. Artichoke thistle has invaded approximately 700 acres of grassland-dominated habitat. It was first on our list of invasive plant species prioritized for immediate research and control.

Land Management Brief

2010 Land Manager of the Year



 

About Artichoke Thistle (Cynara cardunculus)

Artichoke thistle is a robust, spiny member of the Composite Family. It is on the California Department of Food and Agriculture "B" list of noxious weeds, which contains some of California's most invasive and wide-spread wildland pest plants. Artichoke thistle originated in the Mediterranean Basin but has invaded grasslands in South America, Australia, and California. Two cultivated forms, globe artichoke and cardoon, were brought to California from southern Europe in the 19th century and escaped and spread. Artichoke thistle is a perennial with a taproot that can grow down to six feet. Our research at Starr Ranch has shown that flower heads have an average of 180 - 800 seeds and each plant may have 3 heads but in some years as many as 12.

Biology and Ecology of Artichoke Thistle

In 1997, we began investigations on biology and ecology of artichoke thistle. We asked many questions: how many seeds are plants capable of producing per year, how far can seeds disperse, what conditions do seedlings require to survive? Our research is ongoing, but we have already learned many things about this formidable weed. Seed production is strongly influenced by rainfall and is much higher in years of higher precipitation. Despite their long, bristly dandelion-like appendage, most seeds do not travel much farther than 6 feet from the parent plant. Seeds germinate and establish under a wide range of conditions: on gopher mounds, under annual and perennial grasses, under mature artichoke thistle, and in artichoke thistle litter.

Small animals such as rodents and birds eat artichoke thistle seeds, but no animals ate seedlings in our experiments. A study in 48 of our grassland stands determined some factors associated with high artichoke thistle cover and density. We found that there is an association with gopher mounds. We know that gophers dont eat seedlings from our experiments, but we have watched pocket gophers eat the stalks of mature plants (spines and all!). We also discovered the first Orange County record of Terellia fusicornis, a fly that lays its eggs in artichoke thistle flower heads. The eggs hatch and the larvae eat the ripening seeds.

Seed production data

Seed dispersal data

Seedling microsite data

Results from a test of the effects of vertebrates on seedlings

 

Artichoke Thistle Control

In 1997, research on non-chemical control of artichoke thistle commenced. The research director reviewed the literature on the most prevalent herbicides used against artichoke thistle, and found - "red flags" - for both environmental and human safety. So, in spring 1997 a Starr Ranch intern did our first experiment on non-chemical control. We tested several methods including soil solarization and regular mechanical removal (using a brush cutter) of leafy rosettes. The effects of rosette removal after only one season were dramatic, so we began two larger experiments. One experiment was set up in a site in which natives were present - here, brush cutters were used to cut back rosettes. We initiated a second experiment in a site of nearly 100% artichoke thistle cover where we could use a tractor with a flail mower attachment to remove leaves. Again, results were dramatic, with artichoke thistle reduced to 0 - 5% cover in treatment plots after a single season.

We were convinced. In 1999, we began removal treatments in twelve native bunchgrass stands (240 acres), invaded to varying degrees by artichoke thistle. Crews of 2 - 4 went out with brush cutters every three weeks from December - March then every four weeks until plants died back during the summer drought. We began surface tilling in more heavily invaded areas with a new tractor with MeriCrusher attachment in winter, 2000. So far, we have reduced artichoke thistle to < 5% cover after 1-2 years per stand in 340 acres of grassland habitat. However, we continue to monitor and treat seedlings that germinate from seed banks. After one year of repeated brush cutter or surface till treatments, our crews switch to hoes and cutting intervals become four, six, or eight week depending on monitoring data.

Artichoke thistle removal experiment #1 results

Surface till results

Seed bank data

 

Coastal Sage Scrub & Native Grassland Restoration

Removal of artichoke thistle results in large patches of bare ground that are prime invasion sites for annual exotic species, both grasses and forbs. We are currently testing timing and effectiveness of non-chemical approaches to control of annual weeds that include use of a propane flamer during the rainiest part of the year, brush cutting, surface tilling, and hand weeding. In year two of artichoke thistle treatment, we begin restoration to native habitat. In some sites, shrub species of the endangered shrubland, coastal sage scrub, have already begun to invade. In these sites, work involves enhancement of the scrub stand that had already begun to form. Ongoing experiments on planting techniques guide decisions on plug and seed rates and timing of direct seeding. By spring, 2005 we will be working on coastal sage restoration in 45 acres. All seeds are collected on Starr Ranch. Standards for coastal sage scrub restoration (i.e. which shrub species to plant and at what densities) come from intensive sampling in 54 stands of beautiful mature coastal sage scrub at Starr Ranch. In spring, 2004 we commenced a long term study that examines effects of scrub restoration on songbirds and small mammals.

In minimally invaded native grassland sites where the native bunchgrass, purple needlegrass (Nassella pulchra), is dominant, we plant seeds and plugs of the bunchgrass. We are also testing the effects of different timings and intensities of mowing treatments on stimulation of declining needlegrass grassland stands. Starr Ranch protects some of the last native needlegrass grasslands in California. We are currently sampling in six of our best native grassland stands to establish standards for bunchgrass density and cover as well as forb species expected in a prime native grassland.

Results from experiment on effects of soil tamping and different seed rates

Shrub height data

Coastal sage scrub restoration monitoring

Effects of precipitation on shrub heights

Evidence from monitoring data of needlegrass grassland decline

Early results from test of effectiveness of mowing treatments to enhance needlegrass grasslands

The Future

We plan to add 20 - 50 new acres of thistle-invaded sites for treatment each year. At this rate, our goal is to have artichoke thistle under control at Starr Ranch by 2015. We begin work on control of other upland exotics as we initiate restoration, year two of artichoke thistle control. During summer 2002, in our new native plant nursery, we started our first shrub and bunchgrass plugs for restoration. All seeds are collected at Starr Ranch.

All control treatment, restoration, and research is done by a field crew leader and four field assistants who live at the Ranch for seven months - one year. Field crews closely track their work hours. Estimated costs for artichoke thistle and exotic annual control as well as restoration for the 2004-05 season was approximately $395/acre, based on a $20/hour/person rate.

Thanks to the following:

Sandy DeSimone, Ph.D
Director, Research and Education
Starr Ranch Sanctuary
June, 2006