Demographic monitoring of Arabis fecunda in the Pioneer Range, Beaverhead National Forest, Montana : 1990 progress report (Volume 1990) online

583.123



Lesica* Peter
Denographxc

nonitorine of
Arabxs fecunda in
the Pioneer Raneet
Beaverhead
National Forest*



DEMOGRAPHIC MONITORING OF ARABIS FECUNDA
IN THE PIONEER RANGE, BEAVERHEAD NATIONAL FOREST, MONTANA



1990 PROGRESS REPORT



Prepared by:

Peter Lesica

P.O. Box 8944

Missoula, MT 59807

and



STATE DOCUMENTS COLLKTION

JAN -8 1307

MONTANA STATE LIBRARY

1515 E. 6th AVE.
HELENA, MONTANA 59620



J. Stephen Shelly

USDA Forest Service, Region One

Range, Air, Watershed and Ecology

P.O. Box 7669

Missoula. MT 59807



Prepared for:

Montana Natural Heritage Program

State Library Building

1515 E. 6th Avenue

Helena, MT 59620



January 1991






lit






S Lesica* Peter
583*123 Demographic
Nlldmaf reonitorina of
1991 Arabis fecunda in
the Pioneer Rancet
Beaverhead
National Fore«t«



DEMOGRAPHIC MONITORING OF ARABIS FECUNDA
IN THE PIONEER RANGE, BEAVERHEAD NATIONAL FOREST, MONTANA



1990 PROGRESS REPORT



STATE DOCUMCNTS COLLECT!

JAN -8 1397

MONTANA STATE LIBRARY

Prepared by: ur. i?,^^ ^- ^^^ ^v^-

^ ^ HELENA, MONTANA 59620

Peter Lesica

P.O. Box 8944

Missoula, MT 59807

and

J. Stephen Shelly

USDA Forest Service, Region One

Range, Air, Watershed and Ecology

P.O. Box 7669

Missoula, MT 59807



Prepared for:

Montana Natural Heritage Program

State Library Building

1515 E. 6th Avenue

Helena, MT 59620



ON



January 1991



c">, f



rLi;/v7.: nvnim



1

INTRODUCTION

In order to adequately protect populations of an organism,
it is necessary to understand its life history and population
dynamics (Massey and Whitson 1980, Sutter 1986, Palmer 1987) ,
Sapphire rockcress ( Arabis fecunda Rollins) is a rosette-forming
perennial in the Mustard Family (Brassicaceae) . This recently
described species (Rollins 1984) is endemic to highly calcareous,
azonal soils in the foothills of the Sapphire Range in Ravalli
County and in the Pioneer Range in Beaverhead and Silver Bow
counties, Montana (Lesica 1985, Schassberger 1988). Arabis
fecunda occurs on eroding slopes with low vascular plant density
but often a relatively high cover of cryptogamic soil crust. In
Ravalli County, populations of Arabis fecunda are thought to be
threatened by livestock grazing and encroachment by an aggressive
exotic weed, spotted knapweed ( Centaurea maculosa ) (Lesica 1985) .
Arabis fecunda is a candidate for listing as a threatened or
endangered species by the U.S. Fish and Wildlife Service (USDI,
FWS 1990) and is considered threatened in Montana (Lesica and
Shelly 1991) .

This paper is a progress report on a long-term demographic
monitoring study of A^ fecunda populations, established in order
to determine important life history attributes and determine
trends in overall recruitment and mortality.



2

METHODS

Study Areas

We conducted our studies at two sites in Ravalli County,
Montana: Charley's Gulch and Birch Creek. The Charley's Gulch
site is on a steep, eroding, southwest-facing slope along the
gulch at an elevation of ca. 5,000 ft. (T6N R19W S29,NWl/4). The
Birch Creek site is on a steep, eroding, southeast-facing slope
above the creek at an elevation of ca. 4,700 ft. (T7N R19W
S16,NWl/4). More complete descriptions of the study sites can be
found in Lesica (1985) and Schassberger (1988) .

In May, 1987, we established permanent belt transects of 12
adjacent 1-m^ plots at both sites following the methods outlined
in Lesica (1987) . Individual A^ fecunda plants were mapped and
recorded using the following system:

S = Seedling (rosette less than 15 mm diameter)

R - indicates the number of rosettes (> 15 mm diameter) per

plant
I - indicates the total number of inflorescences (stems)

per plant
F - indicates the total number of fruits produced by the

plant



3
Thus, a plant with two rosettes, three stems and a total of nine
fruits would be recorded as R1-I3-F9. In cases where plants had
not finished blooming, two flowers or flower buds were recorded
as one fruit. Since a first year plant can bloom and set fruit
(Lesica and Shelly, personal observation) , the above system
describes size rather than age classes.

We also noted the presence of recently disturbed soil and
evidence of livestock trampling. We did not record seedling-size
plants at the Birch Creek site in 1987. We collected 25 randomly
selected fruits at each site starting in 1989. Each fruit was
hand-dissected and the number of seeds in each was recorded. We
read the transects on May 19-20, 1987; May 19-20, 1988; May 24-
25, 1989 and May 29-30, 1990. In 1987 we recorded data from 12
quadrats at Birch Creek. In 1988 this number was increased to
14.

Population growth rate was calculated by taking the change
in number of individuals over one year, and dividing this by the
number of individuals present in the plot at the beginning of
that year. Negative growth rates reflect a decreasing population
size.



4
RESULTS AND DISCUSSION

A summary of the data from four years of long-term
monitoring is presented in Table 1. Fecundity, as measured by
percentage of plants fruiting, fruits/plant, fruits/inflorescence
and seeds/fruit increased or was stable at Charley's Gulch in
1990 compared to 1989; however, these same parameters were all
noticeably lower at Birch Creek. Population growth was positive
at Charley's Gulch but negative at Birch Creek,

In 1989 most of Montana received above-normal precipitation
in late summer and early autumn, and although snowpack v/as light
in southwestern Montana during the following winter, late spring
precipitation was also above average. Since germination of
Arabis fecunda seed occurs readily without any cold treatment,
the wet period in late summer and early autumn should have
resulted in high levels of recruitment and strong seedling
growth. Both higher than average levels of autumn and spring
precipitation should have resulted in an increase in fecundity.
Arabis fecunda populations at Charley's Gulch did experience an
increase in both recruitment and fecundity. The negative
response at Birch Creek, only five miles distant, is difficult to
explain. Negative growth may be the result of mortality due to
disturbance of the habitat by livestock or ungulate grazers, but
we did not observe recent slumping of the soil as in 1988.
Future observations may help explain this dilemma.



^ Table 1. Population density and fecundity statistics for Arabis
P fecunda in long-term monitoring transects in the Pioneer Mountains,
1989-1990.



1989
1990

# plants fruiting 1989

1990

% plants fruiting 1989

1990

Mean # fruits per 1989

fruiting plant 1990

Mean # fruits per 1989

inflorescence 1990

% plants with more 1989

than one rosette 1990

% one-rosette plants 1989

with fruit 1990

% multi-rosette plants 1989
with fruit 1990

Population growth 1989

1990 36.7% 21.9%

Mean # seeds per 1989 34.2±10.5 31.1±5.6

fruit (± SD, n=25) 1990 26.0+10.3 34.3+7.6



Vipond
Park


15.


8


21.


6


95


208


25,


,1%


41.


.9%


10,


.8


19,


.1


5,


.5


9


.8


20


.3%


22


.1%


23


.8%


39


.5


29


.9%


50


. 0%



Lime


Gulch


15.


4


18.


5




6


158


1.


,6%


35,


.6%


3,


.2


9,


.3


1,


.7


3,


.3


12


.2%


14


.0%





.9%


35


.1%


6


.7%


38


.7%



5
The percentage of plants with more than one rosette has
remained constant at both sites for the entire period of our
study. The Charley's Gulch population has consistently had 3-4
times as many multi-rosette plants as Birch Creek. We do not
know if this difference is a result of a plastic response to
environmental differences or genetic differences between the two
populations.

To date we have observed the two populations for a period of
three years. During this time fecundity and recruitment have
fluctuated in both populations. Nonetheless, no definite trends
are discernable, and both populations appear to be stable.



6

LITERATURE CITED

Lesica, P. 1985. Report on the conservation status of Arabis
fecunda, a potential candidate species. Submitted to the U.S.
Fish and Wildlife Service, Office of Endangered Species, Denver,
CO.

Lesica, P. 1987. A technique for monitoring nonrhizomatous ,
perennial plant species in permanent belt transects. Natural
Areas Journal 7: 65-68.

Lesica, P. and J. S. Shelly. 1991. Sensitive, threatened and
endangered vascular plants of Montana. In preparation.

Massey, J. R. and P. D. Whitson. 1980. Species biology, the key
to plant preservation. Rhodora 82: 97-103.

Palmer, M. E. 1987. A critical look at rare plant monitoring in
the United State. Biological Conservation 39: 113-127.

Rollins, R. C. 1984. Studies in the Cruciferae of v/estern North
America II. Contributions to the Gray Herbarium 214: 1-18.

Schassberger, L. A. 1988. An update of the report on the
conservation status of Arabis fecunda , a candidate threatened
species. Report to the U.S. Fish and Wildlife Service, Office of
Endangered Species, Denver, CO.

Sutter, R. D. 1986. Monitoring rare plant species and natural
areas - ensuring the protection of our investment. Natural Areas
Journal 6: 3-5.

U.S. Department of Interior, Fish and Wildlife Service. 1990.
Endangered and threatened wildlife and plants; review of plant
taxa for listing as endangered or threatened species; notice of
review. Federal Register 55 (35): 6184-6229.



Appendix A. Performance of individual Arabis fecunda plants in
permanent monitoring transects in Ravalli County in 1987, 1988
and 1989. Seedlings were not recorded at Birch Creek in 1987.
An asterisk (*) indicates a plant lost due to slumping soil. A
"b" indicates a plant that has "bolted," produced an
inflorescence from the terminal bud.



Charley's Gulch

1988 1989 1990



1.



s


Rl


R1-I3-F10


R1-I5-F19


R1-I1-F2


R1-I1-F3


R3


R3-I3-F9


S


R2


R2-I3-F9


R2-I4-F27b


S


Rl


-


—


R1-I4-F15


R1-I5-F23


-


—



2.


s






Rl-


-11-


-F6


R1-I6-


•F31


Rl


3.




NO PLANTS














4.


Rl-


-13-


-F5


Rl






R1-I6-


â– F33


R1-I1-F3




R2-


-14-


-Fll


R2-


-11-


-F5


R2-I13


1-F58


R2-I6-F19


5.


S






__






__




_-




Rl-


-15-


-F15


Rl-


-12-


-F5


Rl




R1-I3-F14




—






-






-




S


6.


S













__




-_


b


Rl-


-11-


-F4


Rl-


-11-


-F5


-




-


c


Rl-


-I5-


-F13


Rl-


-12-


-F12


Rl




R1-I4-F15


d


—






R2






—




—


e


—






S






-




-


f


—






S






—




-


g


—






S










-


h


S






Rl






Rl




R1-I1-F4


i


—






—






S




-


j


—






-






S




Rl


k









—






—




S


1


—






-






—




S


m


—






-






—




s


n


—






—






—




Rl


o


—






-






—




s


P


—






-






—




S


q


—






-






—




S


r


—






—






—




S


s


—






__






—




Rl


t


—






—






—




Rl


u


—






—






—




S



7.


Rl-


-15-


-Fll


R1-I13-F17


-


R1-I5-F17


b


Rl-


-11-


-F2


R2


R2-I4-F9


R2


c


Rl-


-12-


-F3


— *


—


-


d


S






S


-


—


e


S






R2


R3-I5-F21


R2-I5-F18


f


Rl-


-13-


-Fl


R1-I4-F17


R1-I5-F17


R1-I7-F27


g


—






-


Rl


Rl


h


—






—


Rl


Rl


i

J
k


~






—


Rl


Rl

s
s


~






—


~


8.


S






Rl


R1-I6-F29


Rl


b


s






—


-


-


c


s






—


-


-


d


s






Rl


R1-I6-F42


R1-I1-F8


e


s






Rl


R1-I2-F12


R1-I4-F1


f


R2-


-11-


-Fl


R2


R2


Rl


g


S






Rl


-


-


h


Rl-


-13-


-F2


R1-I1-F2


Rl


Rl


i


R2






R2


-


-


J


Rl-


-14-


-F9


R2


R2-I7-F33


R1-I2-F6


k

1
m


S
S
S






- -


~


-






S








o


R3






R3


R3-I1-F5


R3-I3-F0


P


R4






R3


—


-


q


Rl-


-11-


-F2


Rl


Rl


-


r


Rl






Rl


Rl


R1-I3-F15


s


S






—


—


-


t


—






Rl


R1-I2-F3


-


u


—






Rl


R1-I4-F3


R1-I3-F9


w


—






Rl


—


—


X


—






—


s


-


y


—






—


s


—


z


—






—


s


-


aa


—






—


—


S


bb


—






~


—


Rl


9.


S















b


Rl-


-11-


-F7


R2


R2-I1-F6


R2-I9-F32


c


R3-


-13-


-F5


R3


R3-I3-F8


R3-I8-F27


d


S






Rl


—


-


e


R2-


-11-


-F2


R2


—


-


f


s






-


-_


__


g


R2-


-12-


-F6


—


—


-


h


s






Rl


R1-I5-F22


R1-I6-F31


i


S






R2


R3


-


j


R2






R2


R2


R2


k


Rl






Rl


Rl


Rl


1


Rl






Rl


Rl


R1-I8-F55


m


R3






R3


—


—



R2

R2-I1-F2

R3-I2-F4

R2-I2-F4

R1-I3-F8

Rl



R2
R2
R2

Rl

Rl

S

R2

R2



R2
R2
R2

R1-I4-F11
R1-I2-F5



R2
Rl
S
S



R2-I3-F18
R2-I5-F14
R2-I5-F22

R1-I5-F14
R1-I3-F9



RlSl

Rl
Rl
S



10.
b

c
d

e
f

g

h
i

J
k

1
m



11,



g

h
i

J
k

1

12.
b
c
d



R2

R1-I3-F6

Rl

Rl

R2-I2-F5

S

S

R1-I6-F0



R3-I4-F8

R1-I1-F2

Rl-Il-Fl

R3

Rl

Rl

Rl

R2

R3-I3-F5



R2-I1-F4
R1-I1-F2
R1-I1-F2
R2



R2

Rl

R1-I1-F2

Rl

R2



R3

Rl
Rl

Rl
Rl
Rl
R2
R3



Rl
Rl
R2
S



R1-I5-F12

Rl-Il-Fl

R2-I2-F8



R1-I4-F13
R1-I4-F21
R2-I3-F9



—






Rl


—






R1-I3-F9


—






S


—






Rl


—






s


R3-


â– 11-


-F4


R3-I11-F43


Rl






RlSl


Rl






R1-I4-F5


Rl






Rl


Rl






Rl


Rl






Rl


R2






R2


R3






R3-I6-F7


S






Rl


—






S


—






Rl


Rl-


•11-


-F4


R1-I3-F13


Rl









R2






R2


Rl






Rl


S






Rl


S






R1-I2-F6


—






S3


—






S5



10



Plot f


1987


1.


Rl


b


Rl


c


R3


d


R2-I3-F6


2.


Rl


b


Rl


c


Rl


d


Rl


e


Rl


f


Rl


g


R1-I1-F3


h


Rl


i


Rl


J


Rl


k


R1-I2-F3


1


—



Birch Creek

1988

Rl
Rl
R4
R2



— *



Rl
Rl

Rl



1989



R1-I1-F7

Rl



R2-I1-F5



1990



Rl

Rl



R1-I8-F56


-


Rl

R1-I7-F36
Rl


Rl


R1-I1-F5


Rl
R1-I3-F6



3.


Rl-


•11-


-Fl


— *






—






-


b


Rl-


â– 12-


-F4


- *






—






-


c


Rl






— *






—






-


4.


Rl






Rl






Rl






Rl


b


Rl






Rl






Rl






R1-I2-F0


c


—






R2






—






-


d


—






Rl






—






-


e


—






Rl












—


5.


Rl




















_-


b


Rl






Rl






Rl






Rl


c


Rl






Rl






Rl






-


d


Rl






-






—






-


e


Rl






Rl






Rl






Rl


f


R2-


•11-


-F6


Rl






—






-


g


Rl






Rl






Rl






Rl


h


—






—






Rl






Rl


i


—






~






—






Rl


6.


Rl




















__


b


Rl






Rl






Rl






Rl


c


Rl-


â– 11-


-F3


Rl






Rl






Rl


d


Rl-


â– 12-


-F6


Rl-


13-


-F9


Rl-


â– 12-


-F3


Rl


e


R2-


-12-


-F5


-






-






-


f


Rl






-






—






-


g


Rl






Rl-


12-


-F12


Rl-


â– 11-


-F5


R1-I2-F6


h


Rl






Rl






Rl






RlSl



11



i

J

k

1

7.
b
c
d

e
f

g



Rl-Il-Fl
Rl

R1-I2-F2
Rl



R1-I1-F3

Rl

R1-I2-F4

Rl

Rl



R2
Rl
Rl
Rl



R3
Rl
Rl
Rl
Rl



Rl


Rl






R3-I1-F3


R4-


-13-


-F9


Rl


-






R1-I4-F18


Rl






R1-I3-F13


Rl-


-11-


-F2


R1-I5-F39


Rl-


-11-


-F5


R2


__






R1-I2-F12


-






S


Rl






R3-I3-F17


R3-


-11-


-F5


Rl


Rl-


-11-


-F6


R1-I1-F3


-







9.

b
c
d

e



R2-I2-F5

R1-I3-F6

R1-I1-F5

Rl

R2-I1-F2



10.
b
c
d

e



Rl

Rl
Rl
Rl



11.
b
c
d

e
f

g

h
i

J

1



12,



Rl
Rl
Rl
Rl
Rl



R1-I3-F7

Rl

Rl

Rl

Rl-Il-Fl

Rl

R1-I2-F3

Rl

Rl



Rl


R1-I2-F10


Rl-Il-FO


R1-I1-F3


R1-I5-F38


Rl


Rl


R1-I2-F10


Rl


Rl


Rl


R1-I1-F2


Rl


Rl


Rl


-


R1-I1-F8


Rl


-


Rl


R1-I3-F19


—


~


Rl


Rl


R1-I4-F21


Rl


Rl


R1-I1-F5


R1-I2-F1



Rl
Rl



Rl
R1-I6-F22



R1-I2-F10



Rl



12



j


—


Rl






R1-I5-F28


R1-I1-F2


k


—


Rl






R1-I3-F11


R2


1


—


S






Rl


S


m


—


S






S


S


n


—


S






S


s


o


—


Rl






Rl


R1-I1-F2


p





Rl






Rl


Rl


q


—


—






Rl


Rl


r


—


—






Rl


S


s


—


—






Rl


Rl


t


~


~






S


S


13.


NOT


Rl






R1-I3-F7


Rl-Il-F5b


b


RECORDED


Rl






R1-I1-F5


Rl-I2-Flb


c




Rl-


â– 11-


-F5


R1-I11-F78


-


d




Rl






R1-I6-F35


-


e




Rl






R2


R2


f




Rl-


â– 15-


-F22


Rl-I3-F65^


-


g




-






-


Rl


h




—






—


Rl


i




—






—


Rl


14.


NOT


Rl-


â– 15-


-F34


R1-I4-F35


__


b


RECORDED


Rl






Rl


-


c




Rl






Rl


R1-I5-F4


d




Rl






R1-I2-F83''


-


e




Rl-


â– 12-


-F13


-


-


f




-






R2-I2-F12


Rl


g




-






Rl


-


h




—






Rl


Rl


i




—






—


Rl


J




—






—


S


k




—






—


S



DEMOGRAPHIC MONITORING OF ARABIS FECUNDA
IN THE SAPPHIRE RANGE, RAVALLI COUNTY, MONTANA

1990 PROGRESS REPORT



Prepared by:

Peter Lesica

P.O. Box 8944

Missoula, MT 59807

and

J. Stephen Shelly

USDA Forest Service, Region One

Range, Air, Watershed and Ecology

P.O. Box 7669

Missoula, MT 59807



Prepared for:

Montana Natural Heritage Program

State Library Building

1515 E. 6th Avenue

Helena, MT 59620



January 1991



Table 1. Population density and fecundity data for Arabis
fecunda in long-term monitoring transects, 1987-



Density (plants/m^)



Population growth



plants fruiting



# fruits per
fruiting plant



fruits per
inflorescence



% plants with more
than one rosette



% one-rosette plants
with fruit



multi-rosette plants
with fruit



Mean # seeds per
fruit (±SD, n=25)



Birch Creek Charley's Gulch



1987


4.8


6.5


1988


4.6


6.0


1989


4.9


5.5


1990


4.6


7.0


1988


-0. 14


-0. 08


1989


0.05


-0.08


1990


-0. 07


0.18


1987


35%


42%


1988


11%


15%


1989


47%


36%


1990


27%


42%


1987


3.8


5.1


1988


14.0


8.8


1989


22.0


15.8


1990


4.4


16.0


1987


2.2


2.1


1988


5.2


3.0


1989


6.8


3.9


1990


2.4


3.7


1987


9%


27%


1988


8%


38%


1989


9%


30%


1990


8%


25%


1987


29%


37%


1988


12%


22%


1989


45%


35%


1990


25%


34%


1987


83%


57%


1988


0%


4%


1989


67%


40%


1990


40%


62%


1989


38.6+5.6


32.3±4.7


1990


30.4+5.6


31.2±5.2



1

INTRODUCTION

In order to adequately protect populations of an organism, it
is necessary to understand its life history and population dynamics
(Massey and Whitson 1980, Sutter 1986, Palmer 1987) .

Sapphire rockcress ( Arabis fecunda Rollins) is a rosette-
forming perennial in the Mustard Family (Brassicaceae) . This
recently described species (Rollins 1984) is endemic to highly
calcareous, azonal soils in the foothills of the Sapphire Range in
Ravalli County and in the Pioneer Range in Beaverhead and Silver
Bow counties, Montana (Lesica 1985, Schassberger 1988). Arabis
fecunda generally occurs on steep, often eroding slopes with low
vascular plant density. In Ravalli County, populations of A.
fecunda are thought to be threatened by livestock grazing and
encroachment by an aggressive exotic weed, spotted knapweed
( Centaurea maculosa ) (Lesica 1985, Schassberger 1988) . In Silver
Bow and Beaverhead counties, populations may be threatened by
mining activity and livestock grazing. Arabis fecunda is a
candidate for listing as a threatened or endangered species by the
U.S. Fish and Wildlife Service (USDI, FWS 1990) and is considered
threatened in Montana (Lesica and Shelly 1991) .

Here we report the results of the first two years of a long-
term demographic monitoring study at two sites in the Pioneer Range
on Beaverhead National Forest.



2

STUDY SITES



Lime Gulch



Location: Five miles west of Interstate Highway 15 on the
north side of Birch Creek Road, approximately 1/4
mile up Lime Gulch from the road; T5S RlOW Secl4 ;
approximately 6,200 ft elevation.

Vipond Park

Location: Approximately 12.5 miles west of Melrose on the
Canyon Creek Road, at the corner of the road
overlooking the kilns; T2S RlOW Sec 8; 7,200 ft
elevation.

Further information on the study sites and location of the
transects can be found in Lesica (1989).



3

METHODS

In 1989 we established two permanent belt transects of 12
adjacent m^ plots at each site following the methods outlined in
Lesica (1987). Lime Gulch transects were read on June 15, 1989 and
June 15, 1990. Vipond Park transects were read on June 16, 1989
and June 29, 1990. Individual A^ fecunda plants were mapped and
recorded using the following system:

S = Seedling (rosette less than 15 mm diameter)

R - indicates the number of rosettes (> 15 mm diameter) per

plant
I - indicates the total number of inflorescences (stems) per

plant
F - indicates the total number of fruits produced by the

plant

Thus, a plant with two rosettes, three stems and a total of nine
fruits would be recorded as R1-I3-F9. In cases where plants had
not finished blooming, two flowers or flower buds were recorded as
one fruit. Since a first year plant can bloom and set fruit
(Lesica and Shelly, personal observation) , the above system
describes size rather than age classes.



4
At each site we collected 25 randomly-chosen fruits. We
dissected each fruit and recorded the number of viable-appearing
seeds in each.

Population growth rate was calculated by dividing the increase
in individuals over the previous year divided by the number of
individuals present in the plot the previous year. Negative growth
rates reflect a decreasing population size.

Many of the plants at Vipond Park were still flowering when we
read the transects in 1989, thus we read these transects in late
June in 1990.

In 1990 the No. 10 quadrat of the Vipond Park East transect
was so crowded that interpretation was impossible, thus this
quadrat was dropped from the analyses.



RESULTS AND DISCUSSION

A summary of the data collected in 1989 and 1990 is presented
in Table 1. At both sites plant density increased substantially,
and this increase is reflected in the high positive growth rates.
The percentage of plants producing fruit and the mean number of
fruits per fruiting plant were also substantially higher at both
sites. This change was particularly dramatic at the Lime Gulch



5

site where fecundity was very low in 1989. Nonetheless, fecundity,
as measured by both of these statistics, was higher at the Vipond
Park site, and population growth was also higher at this site. The
percentage of plants with more than one rosette remained constant
at both sites. The mean number of seeds per fruit was constant at
Lime Gulch but decreased at Vipond Park.

In 1989 most of Montana received above-normal precipitation in
late summer and early autumn, and although snowpack was light in
southwestern Montana during the following winter, late spring
precipitation was also above average. Previous to this period,
southwestern Montana had experienced two years of serious drought
conditions. Since germination of Arabis fecunda seed occurs
readily without any cold treatment (Lesica, unpublished data) , the
wet period in late summer and early autumn probably resulted in
high levels of recruitment and strong seedling growth. Both higher
than average levels of autumn and spring precipitation may have
contributed to the dramatic increase in fecundity.

Generally Arabis fecunda plants do not produce fruit during