Section 8 – Invasive Vegetation and Noxious Weeds

 

Introduction

This section of the Millerton area watershed assessment addresses the challenges associated with invasive vegetation and noxious weeds and the impact to the watershed, working landscapes and our communities economically and environmentally.  The information within this section was developed as a collaborative effort with the Sierra-San Joaquin Noxious Weeds Alliance.  This three county organization (Mariposa, Madera and Fresno Counties) has been in existence for over five years and is located in North Fork, Madera County working out of the US Forest Service’s Bass Lake District Office.  The group has been the primary source for information related to weed types and their location within the Millerton watershed.  Information regarding noxious weeds with a presence within the watershed and the resultant economic and environmental impacts was also part of a public presentation conducted in January, 2003 by Joanna Clines, botanist for the U.S. Forest Service, Sierra National Forest and chairperson for the Alliance.  The Alliance worked collaboratively to develop the first GIS-based weed map for the Millerton area watershed.[1] 

There are over 18 weed types that have been identified within or adjoining the Millerton watershed in 62 locations.  Easily recognizable, Yellow Star Thistle seems to be the most prevalent of all weeds – followed by Tocalote within the watershed.  There has been the recent identification of Spotted Knapweed within the Bass Lake area.  This is part of the Willow Creek watershed which flows into the Upper San Joaquin River just above Kerchoff Reservoir.  A number of weed types can choke out native plants and create a monoculture which can be economically devastating to landowners – and impact wildlife.  Some  species such as Arundo (False Bamboo)  can choke waterways and use excessive amounts of water.  Then when dry, Arundo as well as Broom can become a significant fire hazard.  Erosion can be created along stream banks impacted by invasive species.  Bermuda grass is prevalent along the “flux zone” of Millerton Lake.  This vertical zone of  approximately 110 feet is the fluctuating shoreline along Millerton Lake in which Bermuda grass can flourish.

In 2001, The Sierra-San Joaquin Noxious Weeds Alliance published educational materials for landowners called the Top 10 Noxious Weeds and Invasive Non-native Plants of Mariposa, Madera and Fresno Counties.  In December 2003, a new publication Field Guide to Invasive Non-Native Weeds of Mariposa, Madera, and Fresno Counties identifying the 25 most invasive plants and noxious weeds was published by the group.  Both publications have been provided as part of the Appendices.  Additional information on weeds can be obtained through the California Invasive Plant Council (Cal-IPC) and the California Department of Food and Agriculture (CDFA).[2]

 

Figure 30 – Weed Type and Location map for the Millerton Watershed

 

 

Table 12 – Noxious Weeds / Invasive Species Location Table within the Millerton area watershed

 

Summary of Findings

 

1.      Noxious weeds can create significant economic impacts – as well as adverse environmental impacts in watersheds such as the Millerton area watershed.  Within California this is a multi-million dollar problem.

 

2.      Based on the Weed Management Alliance’s top 25 weed species – 18 have been discovered as being within the watershed or adjoining areas in 62 locations.

 

3.      Based on initial information collected, Yellow Star Thistle followed by Tocalote appears to be the two most prevalent noxious weeds within the watershed or adjoining area.

 

4.      Weed species such as Arundo can consume large quantities of water and then can dry out, creating an un-necessarily high danger of fire.  Weed species can alter the course of a stream and impact riparian habitat.

 

5.      Noxious invasive weeds are generally a monoculture excluding other plant species.

Conclusions

 

1.      Noxious weeds must be addressed and action taken to eradicate or control if we are to maintain a healthy watershed.

 

2.      New invasive plant species can be controlled easily in the early stages of introduction – if identified and control measures deployed.  Training and identification of local interested people to keep watch is necessary.  Community education efforts are crucial for the control of noxious weeds.

 

3.      Leading edge population control of invasive species in areas not inundated with weeds is worthwhile – and eradication is possible.

 

4.      Control of populations is worthwhile – even if eradication is not feasible in some cases (i.e. Arundo donax).

 

5.      Increase of human population is a contributing factor of noxious weed spread and introduction within the watershed.

 

6.      Noxious weeds will always be a problem in this watershed.  Education of landowners and funding for control are critical to an effective weed abatement program.

 

7.      There is a probable reduction of forage production due to noxious weeds in grazing areas – which can lead to increased herbicide use in rangelands, increased soil erosion and degradation of wildlife habitat. Non-native species are a multiple threat to the Millerton watershed and California in general.

 

8.      While many plant communities within the watershed are no longer comprised of all native plants (and haven’t been for many years), non-native naturalized plants may have some economic benefit and may possibly improve environmental condition of the plant community.

 

9.      Noxious invasive plants are of little value and usually devastating to the diversity of vegetation necessary for a healthy watershed’s environment.