Spatial Variation of Piiion-Juniper
Woodlands in New Mexico
Rex D. pieper'
-
Abstract
PiAon-juniper woodlands occupy foothills and areas of
intermediate elevations on a variety of soils in New Mexico. Since these
woodlands occur in nearly every part of the state, considerable variation in
density, species composition and other characteristics is to be expected.
Extensive habitat type classification in the Lincoln and Gila National Forests
has provided comparative information on coarse levels of spatial variation
within these two important areas. Seven habitat types were identified in the
Lincoln National Forest and twelve in the Gila. The Pinus edulis-Juniperus
monosperma/Muhlenbergia pauciflora habitat type occupied the greatest
area in the Lincoln National Forest while the Pinus edulis-Juniperus
deppeans/Bouteloua gracilis habitat type occupied the greatest area in the
Gila National Forest. Fine scale variation is also expressed at the stand
level where understory species are influenced by the tree overstory canopy.
Species composition of these woodlands appear to be related to climate,
soils, elevation, past disturbance, geographical location, and other
topographic variables.
INTRODUCTION
Piilon-juniper woodlands and savannas occur in nearly all
parts of New Mexico except for the extreme southeastern portion
(Dick-Peddie 1993). While these woodlands and savannas
appear similar in overall appeatame, closer inspection reveals
considerable variation at both coarse and fine scale levels of
resolution. Knowledge of these patterns of variation are
important for multiple-use management of these woodlands. The
U.S. Forest Service has developed a system of classification for
vegetation in the Southwest which offers considerable flexibility
and a framework for adding detail as it becomes available
(Ferguson 1987). Johnston (1987) has reviewed previous
classification systems for piiion-juniper woodlands in the
southwest. He includes these woodlands in the Coniferous
Woodland Formation and 10 series in the Juniper-Piiion
woodland. In the southwest he included the Pinus edulis series,
the Pinus edulis-Juniperus deppeana series and the Pinus
edulisJuniperus monosperma series. In addition he listed the
Pinus cembroides-Juniperus series in the Juniper-Piilon
'~rofessor,Department of Animal and Range Saences, New
Mexico State University, Las Cmces, NM.
Woodland of the Southwest. Dick-Peddie (1993) included these
woodlands in the coniferous and mixed woodlands and juniper
savanna where the woodland grades into grassland.
These ways of considering piiion-juniper distribution
indicates considerable spatial variation at rather coarse scales of
pattern. Since the initial study of Arnold in 1964, smaller scales
of patterns have been recognized in relation to areas under crown
canopies of the trees and the interspaces. These patterns illustrate
small-scale variations within piiion-juniper stands (Armentrout
and Pieper 1988, C l q and Morrison 1973, Everett et al. 1983,
Jameson 1966, and Schott and Pieper 1985). The objective of
this paper is to evaluate these patterns of spatial variation within
piiion-juniper stands in New Mexico.
METHODS
Two detailed studies have analyzed habitat types within the
piiion-juniper woodlands in New Mexico. These areas are in the
Lincoln and Gila National Forests (Hdl and Pieper 1992 and
Kennedy 1982). Both these studies utilized cluster analysis on
data collected from individual, relatively undistuI'bed stands in
both forests to class@ similar stands. Principal components
analysis was used to help idenw important controlling factors.
The studies on the Gila were more detailed with 92 stands
sampled than those on the Lincoln with 39 stands sampled.
Small-scale variation was determined by analysis of
understory vegetation under canopies on both Pinus edulis and
Juniperus monosperma in the Lincoln National Forest
RESULTS
CoarseScale Variation
Pifion-juniper vegetation occurs on foothill situations and
on level terrain in some locations of New Mexico. The maps
presented by Dick-Peddie (1993) show the distribution of the
pifion-juniper woodlands and the juniper savanna in the state.
At upper elevations these woodlands form ecotones with
coniferous forests such as ponderosa pine and mixed conifer
forests. At lower elevations, they form ecotones with desert
shrubland and grasslands. Nearly all sections of the state are
represented by some piiion-juniper vegetation with the
exception of the east-central and extreme southeastern
portion. The greatest concentration of the type is in the
western section, the north-central and the area around the
Sacramento Mountains (Dick-Peddie 1993). While most
piiion-juniper woodlands appear similar in outward
appearance, they vary considerably in species composition of
the understory and overstory.
Kennedy (1982) identified elevation, soil texture and the soil
water regime as the main factors controlling distribution of
pifion-juniper habitats in the Lincoln National Forest. The Pinus
edulisJuniperus deppeana habitat type occurred at the highest
elevation (average 2400 m) while the Pinus edulisJuniperus
rnonospemta/Cercocarpus montanus habitat occurred at the
lowest elevation (average 2000 m) (table 1). Several habitat
types were bunched at about 2300 m elevation Nearly a third
of the habitat types sampled in the Lincoln National Forest were
in
the Pinus edulis-Juniperus monosperma/Rhus
tri1obatdMuhlenbergia pauczjlora habitat type followed by the
P. edulis-J. monosperma/Bouteloua gracilis, P. edulis-J.
Table 1.
MonospemtaLAndropogon gerardii, and the P. edulisJuniperus
deppeana habitat types (table 1). The P. edulis-J.
monosperma-Bouteloua gracilis habitat type is apparently
widespread and was reported for areas in northwestern New
Mexico (Francis and Aldon 1983).
Elevation and soil water pdients were apparently not closely
related in the Lincoln National Forest since the two habitat types
classified at the most xeric o c c m d at the lowest and highest
elevation (table 1).
Habitat types classified as intermediate on a soil water
gmbent included both Juniperus monosperma and J. deppeana
(table 1, Kennedy 1982) in the overstory. Habitat types listed
by Hill and Pieper (1992) for the Gila National Forest show that
only one, the Pinus edulis-Juniperus deppeandVuhlenbergia
dubia habitat type occurred in both forests (table 2). However,
Pinus edulis was at least codominant on all habitat types in
both forests except for several lower elevation areas on the Gila
National Forest where Pinus discolor occurs. In addition, two
juniper species, J. monosperma and J. deppeana, were the main
other co-dominants with Pinus edulis. However, Juniperus
monosperma was restricted to the Lincoln National Forest.
Controlling factors in the Gila National Forest appeared to
be somewhat more complex than those for the Lincoln. The
habitat types in the Gila National Forest appeared to sort first
along a soil water gradient, while aspect, rock and litter cover
and latitude appeared to be important factors. While elevation
was not identified as an important variable in the PCA analysis,
the habitat types could be w e d on their mean elevation with
the Pinus edulis/Cercocarpus montanus/Brornus anomalus
habitat at the highest elevation (2400 m) and the Pinus
edulis-juniperus erythrocarpd3outeloua curtipendula phase
Ceanothusfindleri at the lowest elevation (1663 m) (table 2).
Several habitat types occurred at elevations between 2100 and
2300 m. Thus, the habitat types in the Gila National Forest
occurred at the upper elevations comparable to those on the
Lincoln, but at much lower elevations. The Pinus discolor series
also occm at relatively low elevations in the Gila National
Forest (table 2).
The Pinus edulisJuniperus depeannaBouteloua gracijis
habitat type occurred on nearly 18% of the stands sampled on
the Gila National Forest. Several other habitat types occuned
on between 10 and 14% of the stands sampled (table 2).
- Characteristics of piiionjuniper habitat types in the Lincoln National Forest (from Kennedy 1982).
Avg.
Elevation (m)
Soil Water
Regime
Tree Density
(No.1100 Sq. m)
Pinus edulis-Juniperus monosperma/Cercocarp us montana/Adropogon geradii
2059
Xeric
9.6
Pinus edulis-Juniperus deppeana
2381
Xeric
Pinus edulis-Juniperus monosperma/Rhus trilobata/Muhlenbergia pauciflora
2157
Intermediate
Pinus edulis-JuniperuslBouteloua gracilus
2126
Intermediate
Pinus edulis-Juniperus monosperma/Bouteloua gracilis
2226
Mesic
Pinus edulis-Juniperus monospenna/Stipa columbiana
2225
Mesic
Pinus edulis-Juniperus deppeanaAUuhlenbergia dubia
2307
Mesic
Habitat Types
Table 2.
- Characteristics of piiion-juniper habitat types in the Lincoln National Forest (from Hill and Pieper 1992).
Avg. Elevation
(m)
Habitat Types
Tree Density
(No.1100 Sq m)
Percent
of Area
Pinus edulis-cercocarpus montanus43romus anomalusPh Quercus ganbellii
Pinus edulis-Juniperus deppeanaA3outeloua gracilis
Pinus edulis-Juniperus deppeandQuercus griseaLycurus phleoides
Pinus edulis-Juniperus deppeanaAMuhlenberga montana
Pin us edulis-Juniperus deppeana/Cercocarpus montanus-Quercus
griseaA4uhlenbergia montana
Pinus edulis-Juniperus deppeana/Quercus grisea/Muhlenbergia dubia
Pinus edulis-Juniperus deppeana/Cercocarpus montanus-Quercus
griseaA4uhlenbergia emersleyi/Ph Agave parryi
Pinus edulis-Juniperus deppeanaFallugia paradoxalLycurus phleoides-Elymus
elymoides
Pinus edulis-Juniperus depeana/Bouteloua curtipendulal
Pinus discolor Quercus grisea/bouteloua curtipendula-B. Hirsuta
Pinus discolor-Pinus cembroides/Piptochaefiu m fimbriatumph Quercus arizonica
Pinus edulis-Juniperus erythrocarpus~QuercusturbinellaAiouteloua
curtipendula~hCeanothus fendleri
Composition of oak (Quercus) species also differs between
the two locations. The only important oak species in the Lincoln
National Forest was Quercus undulata (wavyleaf oak) while
several oak species were important in the Gila National Forest
(Pieper 1992). These included Quercus gambelii, Q. arizonica,
Q. grisea, Q. turbinella, and Q. emoryi.
FINE-SCALE VARIATION
Piiion-juniper vegetation is characterized by mosaic patterns
including the larger trees and their associated understory plants
and vegetation in the open interspace areas. These patterns were
described by Arnold (1964) for a single one-seed juniper in
northern Arizona He recognized 4 zones around the tree. Claq
and Morrison (1973) found that Juniperus deppeana trees
favored cool-season species beneath their canopies in contrast
to areas where the trees were absent. Armentrout and Pieper
(1988) described three zones around Pinus edulis and Juniperus
monsperma. Most shrubs were confined to the zone next to tree
bole while species under the crown and in the interspaces varied
between the two trees species. For example, blue grama
(Bouteloua gracilis) had the highest basal cover under the
canopy of Pinus edulis but had the highest basal cover in the
interspaces rather than under any canopy position of Juniperus
monosperma in the Sacmento Mountains.
Some species such as Piptochaetium jimbriatum,
Muhlenbergia emerslcyi, Muhlenbergia paucrfIora and Lyrmrus
phleoides often occur mainly under tree canopy. Others may
occur more often in the interspaces between trees. Consequently
the density and cmwn closure of the overstory species has a
profound influence on understory species. Dense stands may
support mostly those species tolerant of canopy position while
those species requiring conditions in the interspaces may be
limited.
LITERATURE CITED
Armentrout, S.M. and Pieper, R.D. 1988. Plant distribution
surrounding Rocky Mountain pinyon pine and one-seed
juniper in southcentral New Mexico. Journal of Range
Management. 4 1:139-143.
Arnold, J.F. 1964. Zonation of vegetation around a juniper tree.
Journal of Range Management. 17:41-42.
Clary, W9.and Morrison, D.C. 1973.Large alligatorjunipen benefit
eady-spring forage. Journal of Range Management. 26:70-71.
Dick-Peddie, W.A. 1993. New Mexico vegetation, past, p~sent,
and future. University of New Mexico h s s , Albuquerque, NM.
Everett, R.L., S h w , S.H., and Meeuwig, R.O., 1983. 1983.
Pinyon-juniper woodland understory Qstribution patterns and
species associations. Bulletin Torrey Botanical Club
110:454-464.
Francis, R.E. and Aldon, E.F. 1983. Preliminary habitat types
of a semiarid grassland. In: Moir, W.H. and Hendzel, L.
(Tech. Coords). Proceedings of the Workshop on
southwestern Habitat Types. U.S. Department of Agriculture,
Forest Service. Albuquerque, NM.
Jameson, D.A. 1966. Pmyon-juniper litter reduces growth of
blue g m . Journal of Range Management. l9:2 14-217.
Johnston, B.C. 1989. Woodland classification: The
pinyon-juniper formation. In: (Ferguson, D .E., Morgan, P.,
Johnson, F.D., Compilers). Proceedings - Land Classifications
Based on Vegetation: Applications for Resource
Management. U. S. Department of Agriculture. Forest.
Service. General Technical Report INT-257. Intermountain
Research Station, Ogden, UT.
Kennedy, K.L. 1982. A habitat type classification for the
pinyon-juniper woodlands of the Lincoln National Forest.
M.S. Thesis. New Mexico State University, Las Cruces,
NM.
Hill, A. and Pieper, R.D. 1992. Habitat-type classification of the
piiion-juniper woodlands in Western New Mexico. New
Mexico State University Agricultural Experiment Station
Bulletin 766.
Schott, M.R. and Pieper, R.D. 1985. Influence of canopy
characteristics of one-seed juniper on understory grasses.
Journal of Range Management. 38:328-330.