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Persistence of Uncommon Cryopedic Plants in
the Chiricahua Mountains Spruce Forest Island
W.H. Moir1
Abstract.-There are small populations of boreal plants persisting in
spruce forests. Twenty years after they were first noted by the author,
plants such as Vaccinium myrtillus, Lonicera utahensis, L. involucrata,
Sorbus scopulina, and Rubus parviflorus survived the warm decade of
the 1980s. The spruce forests are not well structured into herb and shrub
layers as they are elsewhere in Arizona and New Mexico. Instead these
understory plants of cryic soil temperature regimes are found where
there is little competition from other plants and where compensatory
microsite factors exist. In 1993 most populations were at about their
levels in 1974 or increasing. Climate change in these mountains does
not seem to be a threat of population decline.
INTRODUCTION
'.'~---.----r-------."""-----,---,
~
Plants growing near the extreme of their
physiological tolerances can be sensitive to small
changes in climate (WoQdward 1987, Colhoun
1979). If a climatic change, when expressed locally, exceeds an ecophysiological threshold,
plants with short response times can become locally extinct. Plants of insular environments are
vulnerable if their genetic variability is small and
favorable microenvironments for surviving adverse climates are not available.
The northern hemispheric climate of the 1980s
has been exceptionally warm, and a similar warm
period during the 1980s, though less pronounced,
occurred in the southern Rocky Mountains (Karl
et al. 1990; fig. 1). This warm period was reflected
in weather records of some of the mountains
along the U.S./Mexico border. In March, 1993, I
and and several plant pathologists visited the
Chisos Mountains, Texas, to examine a forest
monitoring plot established in 1978 where
Douglas-fir (Pseudotsuga menziesii) was growing
very near its environmental limit of moisture and
temperature (Moir et al. 1993). In addition to unusually high temperatures, a severe drought had
occurred here in the 198Os. We speculated that because of adverse climate the Douglas-fir
population might reveal high mortality or other
a
I
1901-1987, 5-year averages
.
Ii
i_
; --Ef---j ...."".. . "'-" ~~-=r~
...
E
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i'·.
...:.
5 .e.J ..'-"-"r"
01:
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t::
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m
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•.,.. '.,i·
i!o
:
t····-·-·
.......... '" I
--------t--------:
I
'
~1i_t~~~1~-.-~-1+M---.--l~~~--I~_-~
Year
Figure 1.-Running 5-year averages of departures from Northarn
Hemisphere mea!,! annual temperatures (from Karl et al. 1990).
symptoms of stress. We remeasured the monitoring plot and found that all the Douglas-fir
seedlings and saplings were of extremely low
vigor and had suffered near-lethal defoliation(s)
from unknown cause(s). It was tempting to conclude that under climatic extremes of that decade
the heat and drought stressed trees became vulnerable to insect predation or disease (Colhoun
1979, Franklin et al. 1987), events which in fact
took place although the exact causes remain unresolved.
Could similar happenings have taken place in
other mountains of the U.s.-Mexico border?
Could plants of Engelmann spruce forests in the
Chiricahua Mountains, adapted to cold environments mostly above 2680 m (8800 ft) elevation, be
1Research Ec%gist, USDA Forest Service Rocky Mountain Forest
and Range Experiment Station, Ft Col/ins, Colorado.
214
harbingers through mortality or loss of vigor of a
warming climate? The forests belong to the Corkbark-fir-Engelmann spruce-White fir series whose
average soil temperatures are at the warm end of
the cryic soil temperature regime (around 3-6 °C
mean annual soil temperature at 50 em depth;
Moir 1993, Carleton et al. 1991).
In 1974 I observed some uncommon or rare
plant populations in the spruce (Picea engelmannil) forests as part of a habitat type study (Moir
and Ludwig 1979), but most of the plants were not
in the sample plots (Table 1). The understory
plants in the plots were mostly those that were
common in mixed conifer forests where frigid
rather than cryic soil temperature regimes exist
(Carleton et al. 1991, appendix B in Muldavin et
al. 1990). Why were we not finding the usual
cryopedic plants in the sample plots, which were
chosen to represent typical characteristics of the
spruce forests here (Moir and Ludwig 1979)? To
try to answer this question, I explored the spruce
forests to find just where these plants occurred.
Apparently, one reason we did not sample them
more frequently was that the plants were at low
popUlation levels, in extreme cases less than 10
individuals and in many cases less than 3-4 subpopulations were located. Another reason was
that the plants grew in special microsites, rather
than the more typical and extensive sites where
the spruce forests occurred.
In September 1993 I returned to most of these
locations to see if any of the populations had declined. I was especially interested to see if the
events observed in the Chisos Mountains, namely
climatically induced stress followed by low vigor
or heightened mortality, had also taken placed
among vulnerable plants in the Chiricahua Mountains.
HYPOTHESIS
Table 1.-Spruce forest plots, Chlricahua Mountains, Arizona,
sampled for habitat type classification (Muldavln et al. 1990).
Plot
yea
elev
TREES and SIZE
Plcea engelmannll
dbh<!5cm
dbh 5-22.!5cm
dbh>22.5cm
P8eudot8uga menzle.1I
dbh<5cm
dbh 6-22.5cm
dbh>22.5cm
Ables concolor
dbh<5cm
dbh 5-22.6cm
dbh> 22.5cm
Pinus stroblformls
dbh<5Cm
dbh 5-22.5cm
dbh>22.5cm
Populus tremuloldes
dbh 6-22.6cm
dbh>22.5Cm
Clma
Cabin
1974
2773
Bromu8 ell latus
B. porterl
Festuca sororla
Chlmaphlla umbellata
Erigeron exlmlus
Goodyera oblongl1olla
Llgustrlcum porterl
Lonicera arlzonie&
Pterldium aquilinum
Pyrola ehlorantha
SeneCio blgelovli
Smllaclna spp.
Vlcla americana
Viola canadensis
HERBACEOUS understory
Round Raspberry
Ridge
Park
1982
1983
2880
2804
METHODS
s.ems/ha
1709
187
107
10i~
ge1
294
134
27
27
53
80
63
0
107
2068
107
214
347
53
134
27
'134
63
187
347
o
27
80
27
27
1202
0
80
o
134
0
o
o
Plants censused in 1974 and 1993 were
Goodyera oblongifolia, Sorbus dumosus, Vaccinium myrtillus, ChimllphiJa umbelJata, Lonicera
utahensis, Pyrola chlorantha, Rubus parviflorus,
Veratrum caJifornicum, Erigeron scopulin us, and
Lonicera involucrata.
The 1974 census was conducted in September
by searching for the above plants along the Crest
Trail and at other trailside locations where Picea
engelmannii forests occurred. When found, notes
were made of location, abundance, and vigor. A
population consisted of individuals at a particular
location. Abundance was measured by counting
individuals or ramets. I made no attempt to discern between genetically distinct individuals and
ramets. Vigor was a subjective assessment of
shoot robustness, growth rates, and symptoms of
disease, herbivory, or parasitism.
In addition I examined aspects of weather records from two Chiricahua Mountain stations.
The Portal 4SW station is in Cave Creek canyon,
subject to cold night airflow, and the Chiricahua
National Monument station is in Madrean oak
woodland. Neither reflects an Englemann spruce
climate, although they might reveal significant
trends. I graphed yearly precipitation from 1967
o
o
o
o
o
a
0
721
107
27
27
464
o
214
187
27
o
o
UNDERSTORY
Acer glabrum
Physocarpus monogynus
Holodlacu8 dumosus
Vacclnlum myrtlllus
Fly
Peak
1982
2880
Cryopedic plant populations of spruce forests
in the Chiricahua Mountains declined during an
adverse warming period in the 1980s.
'" canopy coverage
10
0.01
36
0.01
0.1
0.1
2
0.01
0.01
4
0.01
0.01
0.01
0.01
0.01
0.01
0.1
0.01
0.1
3
0.1
0.01
0.01
0.01
0.01
0.1
0.01
0.1
0.01
0.01
0.1
5.2
0.01
3.8
0.1
0.01
0.3
215
to 1992 and maximum monthly temperatures during the growing season from April through
September from 1967-1993 inclusive. Running 5year averages were computed to visually reveal
possible trends of temperature Of- precipitation
during this 26 year period.
•
RESULTS
Here are the reports for the two surveys:
• Goodyera oblongifolia -1974: Found at 2 locations
along Crest Trail and in one plot, with a few
(4-7) shoots at each site. No flowering shoots.
1993: no change. An additional clone (4 shoots)
was found near Goobber Spring in 1994 (see
postscript below).
• Sorbus dumosus - 1974: one tree above Cima
Cabin; in 1993 that individual not relocated,
but 3 additional small trees were found along
the Crest Trail near Raspberry Peak.
• Vaccinium myrtillus - 1974: occasional small
populations grew in extremely cobbly soils
along the Crest Trail and on similar soil on
north-facing slopes along the Greenhouse and
Monte Vista Lookout trails; in 1993thesepopulations remained intact. The populations were
segregated from Holodiscus dumosus and Physocarpus monogynus which also occurred on these
cobbly soils. The Vaccinium shoots were
sparse, had few leaves (about 4-6 per shoot),
and were not filling in the site with 'high canopy cover as usually occurs in spruce-fir /vaccinium environments (fig. 2, Muldavin et al.
1990).
• Chimaphila umbellata - 1974: one individual
with about 20 ramets was found along the
•
•
•
•
•
Crest Trail. In 1993 this individual had increased to about 80 ramets and occupied a
larger area; 9 additional populations varying
from 3-30 ramets were found along the Crest
Trail, which were probably missed in the 1974
census. No flowers or fruiting stalks in either
census.
Lonicera utahensis -1974: nine individuals were
scattered and uncommon along the Crest Trail;
1993 - only three individuals were relocated,
however a population of between 10-20 individuals was found near the junction with the
Monte Vista LO trail. This population was
clearly overlooked in 1974. No flowers or fruits
were seen in either census.
Pyrola chlorantha - 1974: one location with a few
shoots; in 1993 I found four shoots (possibly
ramets of 1 individual) at the same site. I am
unsure if the exact location was the same as it
was in 1973.
Rubus parviflorus - 1974: rare along the Crest
Trail but frequent along the Greenhouse Trail.
1993: one population of 8 shoots grew along
the Crest Trail near the 1974 location; 3 extensive populations (30 shoots) were growing
along the Greenhouse Trail. There were no
flowers or fruits in either census.
Veratrum californicum - common along Cave
Creek in vicinity of Cima Cabin in both 1974
and 1993, some individuals flowering. Also at
Goobber and Anita Springs. Shoots in both
censuses were robust and preempted wet sites
to the exclusion of other species.
Erigeron scopulinus, a plant of particular interest because of its rarity (Nesom and Roth 1981)
- 1974: 3 individuals on rhyolite rock near
Raspberry Peak; 1993: no change, and no additional individuals upon further search. No
flowering stalks at either date. Identificatuon
was based upon distinctive vegetative characters of this compactly matted plant and where
the plants were growing.
Lonicera involucrata - 1974: 4 individuals grew
streamside along the Greenhouse Trail above
Wynn Falls; 1993: 7 individuals were tallied
along the same reach.
DISCUSSION
There was no evident diminution in populations of any of the species during the 20 years.
Some plants increased. Although the sampling
methods precluded statistical comparisons between survey dates, the generally similar
Figure 2.-Vacclnlum myrtlllus on cobbly soils In spruce forests,
Chlrlcahua Mountains, Arizona, September 1984.
216
responses by all species are suggestive. If a period
of climate warming had taken place, why would
plants arguably of cold soils be increasing? A climatic lag (Davis 1989) is possible for long-lived
perennials, but would not account for population
increases. I suggest some possibilities, and perhaps there are others.
It is possible that sample biases account for
the apparent increases in plant populations; in the
second census I was more efficient in finding additional populations and individuals. However,
the hypothesis may be true for some species, untrue of others, and again the sampling was too
subjective to distinguish.
The assumption of climate warming may be
untrue in the Chiricahua Mountains. Examination
of weather data indicates that the Chiricahua
Mountains were not subject to adverse climates
during the 27-year interval from 1967 to 1993. The
Chiricahua Mountains have sufficient geomass to
modify a regional climate. Figures 3-4 show patterns of temperature and precipitation from the
'if
c
-~
~
c:
o
~
30
Q.
.~
~
Q.
::J
C
C
<
~
~
:::::iE
1970
1975
1980
1985
1990
1995
two weather stations. There is no evidence of a
1980s warm interval during the growing season.
There was a trend of increasing precipitation during the 1980s which ~ould have favored
population growth of plants in the spruce forests
(Stephenson 1990).
The hypothesis may be false and makes no
sense if the premise is untrue. In this "island" environment it is not necessarily true that plants
maintain the same genetics as they do on "continents" (i.e., more contiguous forest locations
throughout the Southwest). Some ecotypes may
be adapted to warmer soils (i.e., a frigid soil temperature regime). Others, like Veratrum and
Lonicera involucrata may simply need wet soils,
and temperature fluctuations are immaterial. Another, Erigeron scopulinus, is a plant of rhyolite
cracks and crevices, not necessarily a cryic soil
temperature regime. In the aggregate, therefore,
the various species corroborate nothing, since
each responds to different microsite conditions.
Vaccinium myrtillus inhabits extremely cobbly
soils that may buffer it against adverse soil moisture or temperature extremes. Its greatest threat
appears to be competitive displacement by Physocarpus and Holodiscus dumosus of similar soils.
Seldom were vacciniums found on sites occupied
by these taller shrubs. These shrubs are generally
of warmer mixed conifer forests and clearly seem
able to displace Vaccinium if stress from any cause
further lowered its vigor. This may in fact be occurring, not because of any short climate trend,
but possibly driven by a more general warming
since the end of the Little Ice Age about 100 years
ago.
c
~
/X
0)
c
e
~
~
5+----4----~---~---+----4----+10
1965
Figure 4.-Mean annual precipitation at two weather stations
In the Chiricahua Mountains, Arizona. The period, 19811988, was wetter than average, with yearly precipitation
totals mostly above the trend line.
25 ~
~ro
15
"ffi
'i
E
25
~
Portal 4SW, 539011 alav.
.----.-----r----~--~r---~----~35
•
Portal S-yr average
;t:
~
65
15 :::::iE
1980 1981 1982 1983 1984 1985 1986 1987 1988 1989
'-~--~----~--~90
c.-
c
:::::iE
*
Portal 4SW. 5390 ft
o
CJ
--I--..III!\-'~I---+-~-+-~I0---++--i-20·~
~
"'"
c:
a
~
35
.c
Chiricahua Natl Monument, 5300 ft
a
•
Chlrl Nat Monument
~
E
~
~
60-f---..!--.--....- -.........---i1-----l---+15 ~
1965
1970
1975
1980
1985
1990
1995
Figure 3.-Growlng season temperature variations at two weather
stations In the Chiricahua Mountains, Arizona. The graphs
reveal that there was no warm decade of the 1980s. Other
measures of temperature from these stations lead to the same
conclusion.
217
ter the fire their tenure is more precarious. Further
search in remaining, unburned forests of this island summits will doubtless turn up plants that I
missed.
CONCLUSION
I found little sign that climatic variability during the last 30 years adversely affected rare or
uncommon plants of the spruce forests in the
Chiricahua Mountains. Would these plants - Vaccinium especially - provide an adverse climate
signal, using a more rigorous monitoring technique, if climate warming intensified? I am
unsure that even if a population decline is measured, it can be interpreted without additional
information. Many of the species discussed here
can persist vegetatively, expanding or contracting
in response to a complexity of microsite variables.
Small, insular populations are vulnerable to a
wide possibility of events leading to local extinction. Environmental or demoqraphic stochasticity
might be hard to distinguish, Research Ecologist,
USDA Forest Service Rocky Mountain Forest and
Range Experiment Station, Ft Collins, Coloradoand . correlative observations would need
experimental treatments to test for causative factors of population changes.
Nevertheless, these plants have persisted in
the Chiricahuas from the time boreal forests were
extensive in the Southwest (Betancourt et aI1990).
Their future may not be so certain.
LITERATURE CITED
Betancourt,Julio L., Thomas R. Van Devender, and Paul S.
Martin [editors]. 1990 Packrat middens, the last 40,000
years of biotic change. Univ. Arizona Press, Tucson,
Ariz., vii,467p.
Carleton,J.O., D. Shaw,J. Gass, H. G. Brown III, C. Spann,
G. Robertson, W. Robbie, T. Robison, W. H. Moir, D.
Potter, R. Fletcher, and R. M. Galeano-Popp.1991. General Ecosystem Survey, 4th printing. USDA Forest
Service Southwestern Region, Albuquerque, New Mexico,188p.
Colhoun, J. 1979. Predisposition by the environment.
Pages 75-96 (chap. 4) in: Plant disease, an advanced
treatise. Vol.lV, how pathogens induce disease, Academic Press, Inc.,New York.
Davis, M. B. 1989. Lags in vegetation response to greenhouse warming. Climatic Change 15:75-82.
Franklin, J .F., H.H. Shugart, and M.E. Harmon. 1987. Tree
death as an ecological process. Bioscience 37: 550-556.
Karl, T.R., C.N. Williams and F.T. Quinlan. 1990. United
States Historical Climatology (HCN) serial temperature and precipitation data. NDP-019/R1, Carbon
Dioxide Information Analysis Center, Environ. Sci.
Div., OakRidge Natl. Lab, Oak Ridge, Tenn.
Moir, W. H. 1993. Alpine tundra and coniferous forests.
Pages 47-84 in: W. A. Dick-Peddie, New Mexico vegetation past present and future. University of New Mexico
Press, Albuquerque, New Mexico, xxxii, 244 p,map.
Moir, W. H., D. N. Appel, D. B. Drummond, and H. V. Toko.
1993. A peek at forest health monitoring, Chisos Mountains, Texas, March 1993. USDI National Park Service,
Big Bend National Park, Texas, 1993 Annual Report, 3 p.
Moir, W. H., and J. A. Ludwig. 1979. A classification of
spruce-fir and mixed conifer habitat types of Arizona
and New Mexico. USDA Forest Service Research Paper
RM-207:1-47.
Muldavin, E., F.J. Ronco, Jr., and E.F.Aldon.1990.Consolidated stand tables and biodiversity data base for
Southwestern Forest habitat types. USDA Forest Service General Technical Report RM-190:51 p + computer
diskettes.
Nesom, G.L. and Vincent D. Roth .1981. Erigeron scopulinus
(Compositae), an endemic from southwestern United
States.J.Arizona-Nevada Acad.ofScience 16: 39-42.
Stephenson, N. L. 1990. Climatic control of vegetation
distribution: the role of the water balance. American
Naturalist 135(5):649-670.
Woodward, F.1. 1987. Climate and plant distribution. Cambridge,xi, 174p.Cambridge University Press.
POSTSCRIPT AFTER THE 1994 FIRES
The Rattlesnake burn took its toll of these
plant populations. On September 17, 1994 I revisited their locations along the Crest Trail with side
trips to Boogger and Anita Springs and along a
short portion of the Monte Vista Lookout Trail.
Erigeron scopulinus was gone, along with lichens,
mosses, and other saxicolous plants of rhyolite
cliffs and ledges that got roasted. The fire was so
hot at sites where Chimaphila umbellata grew that I
doubt any survived. The same holds for Rubus
parviflorus. The Sorbus dumosus trees that I knew
are gone. Two populations of Vaccinium myrtillus
survived where scorching ground fires missed,
and I saw Lonicera utahensis in similar places. The
site where Pyrola chlorantha occurred had burned
hot enough to doubtless kill the plant and/or its
fungal symbionts. Goodyera oblongifolia was alive
and well in the Goobber Springs area, but nowhere else in its former sites did I find it.
The Rattlesnake burn is an example of how
vegetation changes are not gradual but sudden.
The spruce forests of the Chiricahua Mountains
continue to harbor relictual boreal plants, but af-
218