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Project description

Control and restoration of riparian communities invaded by giant reed. (06CC013)
Program UC IPM competitive research grants program
Principal
investigator
J.S. Holt, Botany and Plant Sciences, UC Riverside
Host/habitat Riparian Area
Pest Giant Reed Arundo donax
Discipline Weed Science
Review
panel
Cultural Controls
Start year (duration)  2006 (Three Years)
Objectives Evaluate differential timing and levels of giant reed removal in riparian habitats.

Quantify phenology and growth rate of native riparian species used in restoration.

Use the best combinations of results from Objectives 1 (giant reed control) and 2 (native species success) to evaluate control and restoration treatments in riparian field sites.

Project
Summary
Riparian field sites containing mixed communities of native species and giant reed have been located in Los Angeles County. Permits to conduct control and restoration experiments (Objective 1) are pending. Once permits are secured, experimental plots and giant reed clumps will be marked and prepared for field control experiments to be initiated in spring 2007. Phenology and growth of the common native riparian species mulefat (Baccharis salicifolia) and willow (Salix gooddingii) were studied in an experiment initiated in fall 2006.

Several protocols were tested in a greenhouse experiment to determine the most rapid and effective method of sprouting stem cuttings for subsequent planting in field restoration plots. Cuttings were harvested from live plants in August 2006. For mulefat, pretreatment by removing the leaves and by soaking the cuttings in water significantly increased the number of sprouts on the cuttings. However, very little sprouting occurred from willow stem cuttings harvested in late summer. This experiment will be repeated in January 2007 and seasonally thereafter to examine the effect of season on sprouting success. Using the eventual results from these sets of experiments, the most effective giant reed control treatments will be combined with the most effective native species propagation method in field control/restoration experiments.

The outcome of this research will provide new approaches for management of giant reed in riparian communities where other more destructive methods are not feasible due to the presence of rare species or sensitive habitats.

Third-year
progress
Two experiments were conducted to determine the best method for controlling giant reed and propagating native riparian species for restoration. Field control experiments are under way at riparian sites containing mixtures of native species and giant reed. Treatments include season (spring, fall), percent giant reed removal (0, 33%, 67%, 100%), herbicide (glyphosate, imazapyr), and follow-up treatment (none, repeat herbicide application) with four replications. Experiments were initiated in spring 2007; duplicate treatments were applied in spring and fall 2007 to 50 clumps each season. Data are taken monthly to evaluate giant reed response to treatments. All control treatments reduced giant reed growth, and regrowth consists of abnormal "tufted" shoots so follow-up treatments were not applied. The only difference between the two herbicides is greater soil moisture in imazapyr plots. No differences were found between 33%, 66%, and 100% stem treatment, suggesting that effective control can be achieved by treating only 33% of the stems in a clump. Greenhouse experiments were conducted to evaluate method and timing of propagation of mulefat (Baccharis salicifolia) and willow (Salix gooddingii). Treatments include planting time (four seasons), cutting size (four weight classes), soaking treatment (none, 7 days, 14 days), soil type (sand, UC mix, peat/perlite mix), and gender (cuttings from male or female plants). Preliminary analyses show that cutting size, soaking, and gender affect establishment and survival of cuttings. Results of the most effective giant reed control treatments and native species propagation methods will be tested in field control/restoration experiments in spring 2009.

Second-year
progress
Two experiments are under way to determine the best method of controlling giant reed (Objective 1) and propagating native riparian species for restoration (Objective 2). Field control experiments are under way at Los Angeles County riparian sites containing mixtures of native species and giant reed. Treatments include season (spring, fall), percent giant reed removal (0, 33%, 67%, 100%), herbicide (glyphosate, imazapyr), follow-up treatment (none, repeat herbicide application), with four replications. Experiments were initiated in spring 2007 by locating and marking 100 clumps of giant reed and taking background data on native species and environmental conditions. Duplicate treatments were applied in spring and fall 2007 to 50 clumps each season. Data are taken monthly to evaluate giant reed response to treatments. All control treatments have reduced giant reed growth, but it is too early to detect significant differences among various treatments.

Greenhouse experiments are under way to evaluate method and timing of propagation of mulefat (Baccharis salicifolia) and willow (Salix gooddingii). Treatments include planting time (four seasons), cutting size (four weight classes), soaking treatment (none, 7 days, 14 days), soil type (sand, UC mix, peat/perlite mix), and gender (cuttings from male or female plants). Duplicate experiments were conducted in fall 2006 (both species), summer 2007 (willow), and winter and fall 2007 (mulefat). Preliminary results show that cutting size, soaking, and gender significantly affect establishment and survival of cuttings. Results of the most effective giant reed control treatments and native species propagation methods will be tested in field control/restoration experiments (Objective 3).

First-year
progress
Riparian field sites containing mixed communities of native species and giant reed have been located in Los Angeles County. Permits to conduct control and restoration experiments (Objective 1) are pending. Once permits are secured, experimental plots and giant reed clumps will be marked and prepared for field control experiments to be initiated in spring 2007. Phenology and growth of the common native riparian species mulefat (Baccharis salicifolia) and willow (Salix gooddingii) were studied in an experiment initiated in fall 2006 (Objective 2). Several protocols were tested in a greenhouse experiment to determine the most rapid and effective method of sprouting stem cuttings for subsequent planting in field restoration plots. Cuttings were harvested from live plants in August 2006. For mulefat, pretreatment by removing the leaves and by soaking the cuttings in water significantly increased the number of sprouts on the cuttings. However, very little sprouting occurred from willow stem cuttings harvested in late summer. This experiment will be repeated in January 2007 and seasonally thereafter to examine the effect of season on sprouting success. Using the eventual results from these sets of experiments, the most effective giant reed control treatments will be combined with the most effective native species propagation method in field control/restoration experiments (Objective 3). The outcome of this research will provide new approaches for management of giant reed in riparian communities where other more destructive methods are not feasible due to the presence of rare species or sensitive habitats.

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