TNC Invasive Species Listserve Digest #076


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Global Invasive Species Team listserve digest #076
Tue Jan 23 2001 - 09:50:49 PST

--CONTENTS--
1. Regarding burning Vinca (Michigan)
2. Herbicide timing with knapweed (Wyoming)
3. Regarding burning Microstegium (Maryland)
4. More on burning Microstegium (Maryland)
5. Giant Salvinia meeting (Texas)
6. Recent weed articles (Nationwide)

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1. Regarding burning Vinca (Michigan)
From: Jack McGowan-Stinski (jmcgowan-st(at)tnc.org)

I have used spot-burning with propane torches on Vinca minor, followed by
wiping of herbicide with resprouts. Propane torches were used since there
was no fuel for Rx fire. Treatment of herbicide alone did not work since
the waxy outer cell layer of adult leaves did not allow penetration of
herbicide (even with a "penetrating" agent mixed in). However, the
resprouts after burning had not yet developed the waxy cell layer and were
susceptible to glyphosate. I used 5% active glyphosate (Roundup) in mix
that was wiped on with a sponge-tipped PVC applicator. Application was
three weeks after spot-burning; burning took place in June, although it
may be possible to burn in winter, since Vinca often remains green through
"dormant" season.

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2. Herbicide timing with knapweed (Wyoming)
From: Suzanne Halvorson (suzanne_halvorson%fws(at)fws.gov)

My question relates to the timing of herbicide application on Acroptilon
repens (Centaurea repens), Russian knapweed. At Seedskadee NWR in Wyoming
we have applied clopyralid (Curtail, Transline) after the first hard
frost. Is this too late to control seed production and/or hit the best
time when the plants are sending nutrients back into the roots?

I have reviewed the TNC Element Stewardship Abstract on chemical control.
It states that "...applications to the late bud and fall growth stage is
critical with most herbicides...". Does fall growth stage mean vegetative
only with no seed heads or does this statement assume that seed has set?

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3. Regarding burning Microstegium (Maryland)
From: Donnelle Keech (dkeech(at)tnc.org)

Here in Maryland, we had the following experience with Microstegium and
fire in the early 1990s: at Pilot Serpentine Barren, Microstegium was well
established along the banks of a creek and several intermittent streams
which run adjacent to/between several serpentine barren openings in
various stages of openness. We are working on restoring what we believe
to be historic openings which have been closing in with woody species
(Virginia pine and red cedar) through mechanical removal of woodies, and
prescribed fire. In one of the historic openings, girdling of woodies and
a prescribed burn was *immediately* followed by almost complete invasion
of the restoration area by Microstegium. Fire (admittedly along with
other possible or unknown factors) seemed to facilitate invasion in this
case -- not a good indication for its potential as a control method.

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4. More on burning Microstegium (Maryland)
From: Doug Samson (dsamson(at)tnc.org)

Just a quick clarification - The prescribed burn that Donnelle refers to
(above) was a spring burn (April 22, 1996) and it presumably pre-dated the
germination flush of Microstegium that year. We had hoped to test the
effects of a "late" growing season (Sept.) burn this past year, but didn't
fit it into the burn window. If/when you burn this beast, we'd be very
interested in hearing about your results!

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5. Giant Salvinia meeting (Texas)
From: Jil Swearingen (jil_swearingen(at)nps.gov)

A conference on Salvinia molesta will be in Texas on March 13-15, 2001.

The conference will provide the platform to develop a National Control
Plan and define the partnerships for implementation. Service Eco-teams,
Field Stations, and programs such as Partners for Fish and Wildlife and
the Coastal Program could play crucial roles assisting in local control
actions while stepping forward to show leadership with commitment in a
true ecosystem approach to management.

More information is on line at http://www.giantsalvinia.org

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6. Recent weed articles (Nationwide)
From: John Randall (jarandall(at)ucdavis.edu)

TWO STUDIES ON SPATIALLY EXPLICIT MODELS OF WEED SPREAD AND CONTROL
PROGRAMS FOCUS ON DIFFERENT SITUATIONS AND ARRIVE AT DIFFERENT CONCLUSIONS
FOR BEST CONTROL STRATEGIES.

Simulating the spread and management of alien riparian weeds: are they out
of control? R.A. Wadsworth, Y.C. Collingham, S.G. Willis, B. Huntley and
P.E. Hulme. 2000. Journal of Applied Ecology 37 (Suppl 1): 28-38.

The authors modeled the spread of two non-native invaders of riparian
areas in Britain (Impatiens glandulifera and Heracleum mantegazzanium) and
the impacts of several strategies and intensities of management of these
two species at the scales of a county (Durham) and a watershed within that
county (roughly 50,000 and 16,000 ha). The model successfully mimicked
the observed patterns of spread of these species. It also indicated that
management strategies that targeted upstream populations and the largest
infestations were the most successful and that high intensity and highly
efficient (nearly 100% kill) efforts would be required to contain or
eradicate these species at these scales. Strategies that targeted small,
new populations (outliers) were not effective, which is contrary to the
findings of Moody and Mack (1988) who emphasized the importance of
attacking outlier populations much as firefighters attack spotfires.
This also contradicts similar advice on setting control priorities
frequently given by TNC's weed program. The authors suggest that this
difference results from the fact that long-distance dispersal is important
in the spread of the two species they modelled but was unimportant in
Moody and Mack's model. Important food for thought as we seek better ways
to prioritize weed control on our sites.

Using a dynamic landscape model for planning the management of alien plant
invasions. S. I. Higgins, D.M. Richardson and R.M. Cowling. 2000.
Ecological Applications. 10(6): 1833-1848.

The authors modeled the spread of two non-native invaders (Acacia cyclops
and Pinus pinaster) of fynbos vegetation and the impacts of several
strategies and intensities of management of these two species on South
Africa's Cape Peninsula (roughly 88,300 ha). They found that scaling up
from individual-based to stand based models did not lead to a change in
the behavior of the model. Using slow, medium and rapid spread scenarios
the models predicted that these species would cover 75%, 85% or 95% of
available habitat within 50 years without controls. Annual clearing
budget had a stronger influence on the total overall cost and time that
would be required to control these species than did rate of spread of the
invaders or the control strategy used. Strategies that targeted juvenile
stands of these tree invaders were, however, more cost-effective than
those that did not and that clearing low density stands first was better
than clearing high density stands first. This is similar to the findings
of Moody and Mack (1988) who emphasized the importance of attacking
outlier populations much as firefighters attack spotfires but contrary to
those of Wadsworth et al. (2000; see above). Delays in beginning clearing
operations increased the overall cost and time to completion of clearing
operations. Prioritizing stands in areas with highly valued native species
mitigated the threats to native plant biodiversity best and that even if
funds are limited, strategic efforts can reduce threats to and loss of
plant diversity. The model indicated that it will cost a total of at
least US$ 4,000,000 and take from 12 to 50 years to clear the Cape
Peninsula of woody alien plants. More important food for thought.

A GENERAL THEORY OF INVASIBILITY

Fluctuating resources in plant communities: a general theory of
invasibility. M.A. Davis, J.P. Grime and K. Thompson. 2000. Journal of
Ecology 88: 528-534.

The authors propose a new theory identifying fluctuations in resource
availability as the key factor controlling "invasibility", the
susceptibility of an environment to invasion by non-native species.
Specifically, they theorize that an environment becomes more susceptible
to invasion whenever there is an increase in the amount of unused
resources, which may occur if resource use by the resident vegetation
decreases or if an increase in gross resource supply occurs for any reason
ranging from abnormally wet weather (more available water) to atmospheric
fallout of nitrogen from volcanic eruptions or pollution. Increases of
this sort are likely to occur periodically and be temporary so that a
given environment's invasibility will vary with time. This theory leads
to a number of predictions that can be experimentally tested:

a)Environments subject to pronounced fluctuations in resource supply, for
example due to periodic disturbances, will be more susceptible to invasion
in the long run than will environments with more stable resource supply
rates;

b)Susceptibility to invasion will be high immediately following a
disturbance or other abrupt increase in resource supply or decline in
resource use by resident vegetation;

c)Long intervals between an increase in resource supply and capture or
recapture of those resources by resident vegetation leave an environment
more susceptible to invasion;

d)Grazing will increase an environment's susceptibility to invasion,
particularly in nutrient rich communities; The authors also predict that
there will not necessarily be a relationship between plant species
diversity and invasibility or between community productivity and
invasibility.

The authors also emphasize that availability of invading species
propagules, characteristics of the invading species, and the invasibility
of a particular environment combine to determine whether an invasion will
occur or not. They note that most of the ideas embodied in this theory
have been voiced by other researchers but that these ideas had not been
unified as a single, coherent theory. The theory can be strengthened by
the addition of a prediction that harsh environments (skree, tundra, salt
marshes) may prevent invasion even when resources are otherwise abundant
simply because few species can survive prevailing conditions to capture
those resources. Tests of this theory will be most helpful to
conservation if invasibility is measured as the abundance (cover, density,
biomass) of all non-native plants in a given environment rather than as
the number of species of non-native plants. Invader abundance serves as a
far better (though still indirect) measure of the impact of the invaders
on the natives species, the ultimate measure of concern for conservation
interests, than simple numbers of invading species.

ARTICLES ON GARLIC MUSTARD, LEAFY SPURGE

Responses of the biennial forest herb Alliaria petiolata to variation in
population density, nutrient addition and light availability. J. F.
Meekins and B.C. McCarthy. 2000. Journal of Ecology 88: 447-463.

Garlic mustard was grown in an experimental garden under two different
population densities, three nutrient levels and three light levels.
Overall, results indicated that density and site fertility may play
important roles in garlic mustard invasion, light availability may be the
most important factor for subsequent growth and spread.

Biological control of leafy spurge (Euphorbia esula) with Aphthona spp.
along railroad right-of-ways. R.G. Lym and J. A. Nelson. 2000. Weed
Technology. 14: 642-646.

This is the first peer-reviewed paper I have seen with quantitative data
on the population-level impacts of any of the biocontrol agents released
against leafy spurge in North America. Both Aphthona lacertosa and A.
czwallinae reduced leafy spurge stem densities by about 65% up to 16 m
from initial release sites within 3 to 5 years. A mixed population of
both Aphthona species reduced stem densities by over 95% within 4 years
after release. Establishment and rate of spread of the insects was
similar regardless of the number of insects released initially (from 500
to 2000 per release).