Gold Ray Dam Invasive Vegetation Survey
Introduction
For any major landscape project to stand a chance of being successful and realistic, it
requires adequate inventory of resources, and consideration of probable outcomes based
on planned actions.
Rogue Valley Council of Governments, overseeing the removal of Gold Ray Dam has,
through this contract, requested the inventory, mapping, and photographing of vegetation,
specifically alien invasive weeds, within six mapping areas (Appendix A), as well as
making prioritized recommendations for treatment of the weeds and management of the
vegetation. Recommendations for practical alternatives will also be offered in this
document.
This contract required all streamside vegetation to be identified, as well as the vegetation
along six 100 ft. linear transects, one in each of the six designated areas (Appendix B).
Narratives, illustrations, and photographs will be presented by area, while
recommendations will be based on the project area as a whole.
In a situation like this, with the alien invasive weed species intermingled within a diverse
native environment, it is critical that we keep an open mind to management options
possibly not considered before.
METHODS
Shorelines of the entire project area were viewed from a drift boat. The project area was
divided into six survey areas. Dominant vegetation visible along the shoreline was
recorded, including noxious weeds. Each vegetation type was photographed, and
recorded a GPS waypoint for each of the photo-points. Within each survey area,
dominant vegetative cover was recorded along a 100-foot-long. In most cases this
required cutting a swath into dense vegetation using a machete. Photographs were taken
at various points along each transect. Another photo was taken from the boat showing the
entrance to each transect, which was marked with red and yellow flagging, tied
conspicuously to a branch at the shore. The GPS waypoint can be considered the
permanent marker for the beginning of each transect, because it is likely that this flagging
will not be discernable in a year’s time. The flagging bears the transect number, latitude
and longitude, and the transect azimuth from that point.
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Section I. List of observed and potential noxious weeds for the GRD survey area.
Species observed are in bold type.
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Garlic mustard (Alliaria petiolata)
Yellow flag iris (Iris pseudacorus)
Purple loosestrife (Lythrum salicaria)
Himalayan blackberry (Rubus armeniacus)
Poison hemlock (Conium maculatum)
Yellow nutsedge (Cyperus esculentus)
St. Johnswort (Hypericum perforatum)
Canada thistle (Cirsium arvense)
Bull thistle (Cirsium vulgare)
Diffuse knapweed (Centaurea diffusa) [along Upper River Road near Gold Hill]
Yellow starthistle (Centaurea solstitialis)
Spotted knapweed (Centaurea stoebe) [along Kirtland Road near Bear Creek]
Meadow knapweed (Centaurea moncktonii) [downstream on Rogue River]
Rush skeletonweed (Chondrilla juncea) [present along I-5 in Jackson County]
False brome (Brachypodium sylvaticum)
Johnsongrass (Sorghum halepense)
Pampas grass (Cortaderia jubata)
Flatpea (Lathyrus latifolius)
Puncturevine (Tribulus terrestris)
Spiny cocklebur (Xanthium spinosum)
Dyers woad (Isatis tinctoria)
Leafy spurge (Euphorbia esula)
Scotch broom (Cytisus scoparius)
Spanish broom (Spartium junceum)
French broom (Genista monspessulana)
Japanese knotweed (Fallopia japonica)
Other Invasive Species Found
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Reed canarygrass (Phalaris arundinacea)
Cultivated grape (Vitis vinifera)
Common teasel (Dipsacus fullonum)
Dog rose (Rosa canina)
Jimsonweed (Datura stramonium)
Tree of Heaven (Ailanthus altissima)
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Section II. Vegetation survey
Area #1 Rogue River
Right bank: Dominant vegetation includes Himalayan blackberry (Rubus armeniacus),
Oregon ash (Fraxinus latifolia), willows (Salix exigua, S. lucida, S. lasiolepis, S.
sessilifolia), chokecherry (Prunus virginiana), red-osier dogwood (Cornus sericea),
brown dogwood (Cornus glabrata) and syringa (Philadelphus lewisii). Climbing over the
top of this vegetation were assorted vines: escaped cultivated (feral) grapes (Vitis
vinifera), native grape (Vitis californica), California greenbriar (Smilax californica),
orange honeysuckle (Lonicera ciliosa) and woodbine (Parthenocissus vitacea). The
dominant grass was reed canarygrass (Phalaris arundinacea), which occurred mostly in
dense patches along the shoreline, sometimes intermingled with cat-tails (Typha
latifolia). Broad-leaved forbs included poison hemlock (Conium maculatum), deadly
nightshade (Solanum dulcamara), St. Johnswort (Hypericum perforatum), black mustard
(Brassica nigra), bull thistle (Cirsium vulgare), sweet clover (Melilotus) and bladder
campion (Silene latifolia ssp. alba).
Photo 8a (waypoint 19): Blackberry
bushes with California greenbriar vines
overtopping them.
Photo 9a (waypoint 19): Red-osier
dogwood at water’s edge.
Common vegetative combinations were blackberries or red-osier dogwood overtopped
with feral grapes or smilax. The most common trees were Oregon ash, and shining and
narrow-leaf willows. The shoreline along this reach of the river was a dense, almost
impenetrable mass of various native trees, and exotic and native shrubs and vines.
Narrow-leaf and sandbar willow (Salix sessilifolia) dominate the island.
Near the entrance to Kelly Slough is a small inlet. Here we found several invasives,
purple loosestrife (Lythrum salicaria), yellow flag iris (Iris pseudacorus), and Canada
thistle (Cirsium arvense) in small patches along the shoreline, growing among reed
canarygrass and cattails. The primary trees and shrubs here are native willows, red-osier
dogwood, Oregon ash.
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Photo 15a (waypoint 20): purple loosestrife
in the inlet, growing with reed canarygrass
and cattails.
Left Bank:
This area has somewhat less blackberry along the shore and more willow, Oregon ash,
red-osier dogwood, and hardhack (Spirea douglasii). Along the shoreline are patches of
cattails, reed canarygrass, and torrent sedge (Carex nudata). The vines are primarily
woodbine and feral grapes.
Transect for Area #1 at waypoint 26. Azimuth of 210º.
Vegetation in Transect #1: reed canarygrass, purple loosestrife, water smartweed, cluster
dock, deadly nightshade; blackberries, woodbine, Oregon ash, native and feral
grapevines, California greenbriar, native willows, poison hemlock, gooseberry (Ribes
sp.), creeping jenny (Lysimachia nummularia), Douglas sagewort (Artemisia
douglasiana), awl-fruit sedge (Carex stipitata), whiteroot sedge (Carex barbarae). The
most important invasive species in this transect is garlic mustard (Alliaria petiolata).
Photo 34a
Photo 39a
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Kelly Slough Area #2
Invasive species found along the shoreline in Kelly Slough were yellow flag iris, purple
loosestrife and Canada thistle. The iris and the loosestrife were also present on the small
island, which was dominated by willows.
Photo 17a (waypoint 21): entering Kelly Slough.
Photo 21a (waypoint 23): purple
loosestrife and yellow flag iris.
Photo 22a (waypoint 24): banks of Kelly
Slough showing willows, cattails, reed
canarygrass, yellow flag iris and
loosestrife
Transect #2 in open area, vegetation
(species in order of descending
abundance)
cattails
reed canarygrass
purple loosestrife
yellow flag iris
red-osier dogwood
willows
broadfruit bur-reed (Sparganium
eurycarpum)
clustered dock (Rumex conglomeratus)
water smartweed (Polygonum
amphibium)
water speedwell (Veronica anagallisaquatica)
rush (Juncus sp.)
annual rabbitsfoot grass (Polypogon
monspeliensis)
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Photo 28a (waypoint 25): transect
vegetation.
Photo 30a (waypoint 25): seed capsules
of yellow flag iris (Iris pseudacorus).
Photo 31a (waypoint 25): purple loosestrife.
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Tolo Slough Area #3
Entering the slough, the banks are a nearly solid wall of blackberries, with overhanging
Hinds walnut (Juglans hindsii), then it opens up into more willows and Oregon ash, and
red-osier dogwood. The native and feral grapes have climbed up over the willows and
blackberries, in particular.
Photo 43a (waypoint 28): Tolo Slough.
Photo 46a (waypoint 28): Yellow flag
iris along shore in Tolo Slough.
Photo 51a (waypoint 29): Yellow flag
iris along shore in Tolo Slough.
Transect #3:
At water’s edge, yellow flag iris, purple loosestrife, cattails, reed canarygrass; small
amounts of water speedwell, bur-reed, dock. Inland more reed canarygrass, then willow,
red-osier dogwood, and Oregon ash creating dense shade, without understory forbs.
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Photo 55a (waypoint 30): Transect for Tolo Slough (Area #3).
All of Tolo Slough has intermittent yellow flag iris and loosestrife along the shoreline.
Rogue River Area #4
Right bank: Hinds walnut and Oregon ash and white alder (Alnus rhombifolia) form the
tree overstory closest to the water with an understory of blackberries, narrow-leaf and
shining willow, red-osier dogwood, brown dogwood, chokecherry, syringa, hawthorn
(Crataegus suksdorfii), spirea and ninebark. Climbing over the shrub and tree canopies
are California greenbriar, native and feral grapevines, Western white clematis (Clematis
ligusticifolia), and orange honeysuckle. Graminoids include reed canarygrass and
whiteroot sedge. Forbs present were moth and common mullein (Verbascum blattaria, V.
thapsus), poison hemlock, sweetclover, soapwort (Saponaria officinalis), Douglas
mugwort, nettles (Urtica dioica), St. Johnswort, deadly nightshade, purple loosestrife,
common teasel (Dipsacus fullonum), bladder campion, and bull thistle.
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Photo 4a (waypoint 16): Ninebark along
the river.
Photo 15b (waypoint 36): Reed
canarygrass along water edge with
blackberries and red-osier dogwood
forming a wall on the bank.
Photo 5a Red-osier dogwood with
California greenbriar along the river
(waypoint 17)
Photo 18b (waypoint 36): Dog rose
(Rosa caninum) is the dominant shrub
for a short distance. This rose is the
aggressive weedy shrub near Immigrant
Lake; this was the only location were it
was observed in the survey area.
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Photo 21b (waypoint 36): Red-osier
dogwood is the dominant shrub.
Photo 27b (between waypoints 37 and
38): native grapevine over red-osier
dogwood.
Photo 24b (waypoint 37): Native
grapevines over the trees.
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Photo 28b (between waypoints 37 and
38): native grape and smilax over
blackberry.
Photo 29b (between waypoints 37 and
38): native grape over red-osier
dogwood.
Transect #4: Waypoint 32. Azimuth 220º.
A white alder overhangs the shoreline here, with syringa an important understory shrub,
but not as abundant as the Himalayan blackberries. California greenbriar, grapevines,
honeysuckle and clematis climb over all the woody vegetation. Poison hemlock and reed
canarygrass are major non-natives here. Native plants include nettles, snowberry
(Symphoricarpos), gooseberry, chokecherry and blue wildrye. In the understory were
copious amounts of garlic mustard, scattering seeds everywhere at the slightest touch.
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Photos 73a-74a (waypoint 32): transect
#4 vegetation described above.
Left bank: A solid wall of Himalayan blackberries is overlain with California greenbriar,
and grapevines. Interspersed with the blackberries are large clumps of red-osier
dogwood, also overlain with vines. Oregon ash, bigleaf maple (Acer macrophyllum) and
Hinds walnut occur here, and farther from the water’s edge are black cottonwood trees
(Populus trichocarpa). Non-woody species include birdsfoot trefoil (Lotus corniculatus),
soapwort, and bladder campion.
Photo 1b (waypoint 33): solid patches of
reed canarygrass between the shrubs and
the water.
Photo 3b (waypoint 34): native
grapevines trailing over blackberry and
red-osier dogwood.
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Photos 7b-8b (waypoint 35): examples
of escaped cultivated grape climbing
over the tops of native trees (probably
Oregon ash), and completely covering
them. Other native trees in photo include
Hinds walnut, white alder and black
cottonwood.
Photo 11b (waypoint 36): feral grape covering Himalayan
blackberry bushes with poison hemlock protruding through.
Rogue River Area #5
Right bank: Cattails, sedges, reed canarygrass, willows, blackberries, and grapevines;
occasional poison hemlock, deadly nightshade, Canada thistle.
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Photo 41b (between waypoints 39 and 40): reed canarygrass with
thistle and clumps of cattails are interspersed with blackberries and
grapevines; black cottonwoods are the tall trees back from the
river.
Photo 105b (below waypoint 44): Canada thistle with reed
canarygrass and poison hemlock.
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Photo 109b (waypoint 45): cattails and willows, then blackberries
with reed canarygrass along river bank.
Transect #5 Waypoint 44. Azimuth 300º.
The first 50 feet is reed canarygrass with a few narrow-leaf willow, all overtopped with
feral grapevines; a few plants of nightshade and poison hemlock. The second 50 feet of
transect is a solid stand of Himalayan blackberry, overtopped with feral grapevines.
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Photos 99b & 97b (waypoint 44): transect vegetation, as described above.
Left bank: Most of this stretch of the river borders tall fescue pastureland, where the
vegetation is either pasture weeds (poison hemlock, teasel, Canada thistle) or a narrow
line of Himalayan blackberry and reed canarygrass. At the mouth of Bear Creek there is
more purple loosestrife, some horsetail (Equisetum), yellow nutsedge (Cyperus
esculentus), native willows, and a variety of grasses, sedges, and rushes (Scirpus
microcarpus, Eleocharis palustris, Juncus effusus var. pacificus, Juncus acuminatus,
Agrostis stolonifera).
Photo 35b (waypoint 38): snowberry
grows between the field and the edge of
the river.
Photo 38b (waypoint 39): St. Johnswort
between the field and the edge of the
river.
Photo 42b (waypoint 40): mouth of Bear Creek. Willows and St. Johnswort where the
bank is sloughing.
Photos 43b-44b (waypoint 40): the left bank of Bear Creek is steep and sloughing off
with teasel and other weedy vegetation as well as Equisetum along the water edge; the
right bank is gentle with wetland vegetation, including sedges, rushes, bulrushes and
willows.
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Photo 48b (waypoint 40): the wetland vegetation at the island at the
mouth of Bear Creek included vigorous stands of purple loosestrife.
Rogue River Area #6
Right bank: A solid wall of Himalayan blackberry lines the river, interspersed with tree
and shrub willows, and red-osier dogwood. A native rose (Rosa) is present in this area.
Nettles, reed canarygrass and poison hemlock are also common.
Photo 50b (just north of waypoint 40): wall of blackberries with vines.
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Photo 77b (waypoint 43): St. Johnswort
and bladder campion in blackberries and
dense vegetation on banks.
Photo 80b (waypoint 43): looking
downstream; dense wall of impenetrable
shrubs.
Photos 84b, 90b (between waypoints 43 and 44, looking downstream): blackberry bushes
and vines.
Transect #6 Waypoint 41. Azimuth for transect is 160º.
The transect starts under a large native hazelnut (Corylus cornuta) tree overhanging the
shore. The understory shrubs include snowberry, syringe, red-osier dogwood, ninebark,
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and gooseberry. Adjacent trees are Oregon ash. Vines are primarily western white
clematis and California greenbriar. Abundant garlic mustard grew under this multilayered canopy and was spreading copious amounts of seed when disturbed.
Photo 58b (waypoint 41): transect vegetation as described above.
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Garlic mustard in flower; most plants had ripe seed.
Island: This was dominated by native willows and reed canarygrass, but we noted a
single young catalpa (Catalpa speciosa) tree that had become established and was several
feet tall.
Photo 69 (waypoint 42): view of the
island.
Photo 72b (waypoint 43): catalpa tree on
island.
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Left bank: Native trees included black cottonwood, Oregon ash, and native willows. Parts
of the bank was a wall of Himalayan blackberry with intermittent red-osier dogwood,
with grapevines and sometimes greenbriar, but there were also areas were black mustard,
poison hemlock, mugwort, bladder campion, great hedgenettle (Stachys cooleyae), St.
Johnswort, deadly nightshade and birdsfoot trefoil found some sun to thrive.
Summary
The Rogue River upstream from Gold Ray Dam was, by design, an area of slow-moving
water (particularly Tolo and Kelly Sloughs). Materials carried downstream with the
current tended to settle out and remain there until floods carry them further downstream.
Included in the sediments are seeds and other fragments of plants such as roots, branches,
leaves, fruits. The survey area shown on a map on page 3 contains a mixture of native
and introduced species, some which were part of the existing landscape (before the dam),
while others arrived later via water (downstream flow or clinging to boats), air (wind or
waterfowl), or were transported by wild or domestic animals or humans.
The reasons why certain plants are currently found in association with others may not be
obvious by casual observation, but are likely related to several factors, including biology
of the species, availability of key resources (light, water) and to timing of introduction
(i.e., when a particular plant or propagule found its way to the pond). Once introduced to
favorable habitats, they intermingled with existing resident plants, and became part of the
vegetative community as their populations expanded.
Plant associations in the survey area are complex, but there are some patterns based on
relative availability of water and sunlight, and frequency of disturbance. For example,
some species such as purple loosestrife, yellow flag iris and reed canarygrass were seen
primarily in full sun along the wet shoreline or in shallow standing water. Others,
including the native willows are well adapted to rapid colonization following flood
scouring and deposition, so were often seen along shorelines exposed to these events,
including islands. Vines, both native (honeysuckle, smilax, native grape) and non-native
(woodbine and cultivated grape) ascend through existing canopies to access the sunlight
they require. Others species are more shade-tolerant, including garlic mustard, which was
found even under dense canopies of Himalayan blackberry. The native tree community is
segregated primarily by the water table; e.g., Hinds walnut grows with Oregon ash in
openings on depositional floodplains with a consistently high water table, while black
cottonwood, as the tallest tree, forms the dominant canopy of the floodplain woodland,
even a considerable distance from the current shoreline. Because introduced and native
species are so intermingled, treatment and/or control of the invasive species without
harming desirable vegetation would be difficult.
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Conclusions
Treatment and management of the former impoundment area behind Gold Ray Dam will
not be easy, nor will it be quick. There are now, and will be, different forces at work than
prior to removal of the dam (e.g., rapidly moving water, through traffic by boats, higher
level of human interface).
The open, newly exposed mudflats are especially vulnerable to invasion by a host of
candidates; not least of which are those located on immediately adjacent lands. Areas
farther back from previously standing water (the periphery of the green zone) may lose
subsurface water, changing from a subirrigated to a well-drained, dryland environment.
Both Kelly and Tolo Sloughs drained in August 2010, a time at which many annual and
perennial plants were producing seed. Daily afternoon winds, typical in southwestern
Oregon, can be expected to carry seeds from these ruderal species onto the newly
exposed mudflats, where many will germinate and become established. This situation
should not come as a surprise, nor should it cause much alarm. If prompt action is taken
to establish competitive, desirable species, the presence of annual weeds is likely to be
relatively short-lived (in the absence of further disturbance).
In addition to immediately adjacent plants colonizing this newly exposed setting, noxious
weeds upstream of the ponded area (species not currently observed in the contract area)
may be moved downstream. Thus, the area should be monitored for new invaders, which
should be treated when found. Some of those species are listed on pages 3 and 4 (in
regular, not bold type).
Recommendations
Little or no action should be taken without a clear idea and understanding of what future
vegetative cover of the project area is desired. Short-term and long-term vegetation
management goals should be established within a landscape plan. Widespread and
uncoordinated treatments in the project area prior to the creation of a landscape plan may
result in irreversible damage, or at the very least, expensive, redundant projects.
Recommended short-term goals might include:
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Consult with landowners with regard to desired outcome in landscape vegetation;
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Prevent garlic mustard, yellow flag iris, and purple loosestrife from occupying the
newly exposed mudflats;
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Collect seeds and/or cuttings or ‘slips’ of desired native trees (e.g., willow, white
alder, hawthorn, hazelnut, black cottonwood Hinds walnut, Oregon ash) in
preparation for planting; [Frank Callahan, local seedsman and president of the
Siskiyou Chapter of the Native Plant Society of Oregon, is exceptionally
knowledgeable on the ecology of riparian woodlands in Jackson County, and
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would be a good individual to consult when developing a landscape vegetation
plan.]
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Collect seeds of native shrubs (ninebark, red-osier dogwood, smooth dogwood,
snowberry, gooseberry, chokecherry) for out-planting in preparation for
establishment with the tree species;
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Submit grant proposals for rehabilitation funds of newly exposed areas;
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If photo-points were not previously established for key treatment areas, this
should be done soon. They will help monitor success/failure, as well as establish
historical references.
Recommended long-term goals might include:
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Contracts for survey and treatment of undesirable plant species, focusing on new
invaders;
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Contracts for planting tree and shrub ‘slips,’ plugs, or seedlings;
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Armoring of ‘at-risk’ banks and exposed slopes;
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Agreements with landowners for long-term management, including weed
treatment, on adjacent lands;
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Strong consideration should be given to reed canarygrass as a temporary
dominant species in the newly exposed mudflats. Although this grass is not native,
it is already widespread and is a highly competitive dominant in the area,
excluding annual weeds and many invasive perennials. It is also a superb bank
stabilizer, and is not on Oregon’s A, B, or T list of noxious weeds.
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Where grape plants are climbing large, desirable trees, the grape vines should be
severed close to the ground. Heavy masses of grapevines in the upper canopy of
desirable trees makes them more vulnerable to windshear of branches, or may
result in the entire tree falling in the event of high winds.
In terms of treatment of undesirable plant species, certainly a prioritization for time and
money is important. For these reasons, as well as the likelihood for success, the
following is recommended:
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Focus the majority of resources on garlic mustard, yellow flag iris, and purple
loosestrife. Populations of yellow flag iris and purple loosestrife are relatively
small at present, and although there are other populations upstream, which could
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re-populate the project area, they would establish along the newly created
riverbank, not the prior high water line.
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Garlic mustard is widespread throughout the project site, but the fact that it is a
biennial gives control a good chance. Every effort should be made to treat this
species prior to seed production. Ultimate success in controlling this species is
more likely under this prescription.
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Because only one Catalpa was seen on the furthest upstream island, that should be
removed.
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If and when Japanese knotweed or spiny cocklebur appear, they should become
priority weeds, and targeted for removal.
Other species, such as Himalayan blackberry, grape, and yellow nutsedge are so
widespread and numerous that the chances for success are minimal. That doesn’t mean
they couldn’t or shouldn’t be targeted in the future as part of an overall vegetation
management plan, but first efforts should be targeted as stated above. The recent change
in environment may be detrimental to existing non-target weeds, and they may be less
competitive as a consequence of the drop in water level.
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