by Alex Gugel , all rights reserved
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Plants Living on the Edge
Rim Environment
The arid environment of the South Rim
poses a number of challenges for the
plants living here. The rim averages only 16
inches/41 cm of rain a year, which varies
widely from year to year. Periods of drought
are common. Half of the precipitation
falls as winter snow, when many plants are
dormant and cannot use the moisture. The
other half arrives with summer monsoon
storms starting in July. Huge thunderclouds
build as the day heats up, often producing
violent torrents of rain. Since much of the
ground surface is rock, only a portion of
the rainwater penetrates the soil while the
rest rushes away. Fractures within the rocks
draw water deep into the ground, below the
roots of the plants.
Grand Canyon National Park
Walk the Hermit Road portion
of the Greenway Trail to learn
about the South Rim’s plant
communities and how they thrive
in this challenging environment.
entire trail or only a portion of it, picking up
the free shuttle bus at Pima Point along the
way. Enjoy the quiet overlooks and rest on
benches along the trail. Water, snacks, and
restrooms are available only at Hermits Rest.
Carry water and snacks and wear clothing
appropriate for the weather. The exposed
rim becomes hot in the summer and quite
cold with sharp winds in the winter. Be
prepared and enjoy your learning adventure
against the backdrop of Grand Canyon.
This section of the Greenway Trail starts at
Monument Creek Vista and ends at Hermits
Rest, a distance of 2.8 miles/4.5 km. The
paved trail is relatively level with some slight
up and downhill sections. Walk along the
The rim effect influences local environments.
Warm, dry, summer air rising from the
depths of the abyss spills over the rim,
stunting trees that grow tall and stately just
a few hundred feet back from the edge.
Winter storms laden with snow and ice
sweep across the canyon, blasting the plants
close to the rim and exacting a toll on foliage
and the next season’s leaf and stem buds.
Rim Trail 7.8mi / 12.6km Hermits Rest to Grand Canyon Village
N
Greenway Trail 2.8mi /4.5km
Hopi Point
Hermits Rest to Monument Creek Vista
Powell Point
Mohave Point
Pima Point
oad
/ 2.
7km
Trailview
Overlook
rm
mi
it R
1.7
He
1.
1m
i/
1.
8k
m
Maricopa Point
Pinyon - Juniper Community
Pinyon pine (left), Utah juniper (right)
Woodlands dominated by pinyon pine and
various species of juniper grow throughout
the Southwest and dominate the vegetation
along the edge of Grand Canyon’s South
Rim.
Pinyon pine is easily recognized by its dark
bark, short, curved needles in groups of
two, and small cones. The Utah juniper has
shaggy bark, small scale-like needles, and
light blue-green cones that look like, and
are called, berries. A rich variety of shrubs,
flowers, and grasses grow beneath these
trees, comprising a complex, fascinating
community.
Hermits Rest
Monument
Creek Vista
or
Greenway Trail
Greenway Trail - pedestrians only
Rim Trail - dirt
Rim Trail - paved
Road
0
Shuttle bus stop
1/2
Village/Hermits Rest
Route Transfer
The Abyss
1 km
0
1/2
1 mile
Grand
Canyon Village
Pinyon cones (left) and juniper berries (right)
Microhabitats
Both pinyons
and junipers
illustrate
adaptations
to this dry
environment.
Short, stout
trees better
withstand the
strong winds
battering the
rim. Small,
wax-coated
needles use
less water.
Evergreen
trees retain
their needles
Ponderosa pines
for years and do not expend precious water
and energy replacing all their foliage each
year. These long-lived trees grow very
slowly. Even the smaller trees are decades
old and can survive more than 600 years.
Temperature increases and rainfall becomes
more scarce as you descend into the canyon.
Desert plants replace pinyons and junipers.
Biologist C. Hart Merriam documented
this pattern of changing plant and animal
communities with changes in elevation
more that 100 years ago. He introduced the
concept of life zones—broad bands of plant
and animal species that could be associated
with certain latitudes, elevations, and
exposures.
At elevations higher than those found on
most of the South Rim, ponderosa pines
replace the pinyon-juniper community. At
even higher elevations on the North Rim,
Engelmann spruce, subalpine fir, and aspen
replace the ponderosa pine community.
Within each landscape are microhabitats,
areas with conditions ideal for a plant or
community that otherwise would not be able
to flourish.
As you walk along the Greenway Trail
west of Monument Creek Vista and
leave the canyon’s rim, notice several
ponderosa pines towering along the trail.
Ponderosas have tall, straight trunks and
long needles. Generally found at higher
elevations than pinyons and junipers, here
they grow together. Why would that be?
First, by leaving the rim, you are leaving
the rim effect, the strong winds and hotter
air temperatures that would prevent a
ponderosa from living right along the rim.
Also, the trail traverses a drainage that holds
more moisture below the ground surface
than other areas, providing ponderosas
sufficient moisture to live. You have
encountered a microhabitat suitable for
ponderosas.
Microhabitats can be much smaller in scale,
such as a crack in the rock. While at first
glance a crack seems like an impossible
habitat, it is
actually quite
favorable.
Cracks trap
and hold soil
and moisture,
giving plants
growing
within them a
better habitat
than available
nearby.
Adaptations to the Environment
Interactions with other Plants and Animals
Like pinyons and junipers, many plants have adapted to
this challenging environment in a variety of ways.
Plants often develop symbiotic relationships
with animals, benefitting both the plant and
the animal. You may be surprised by the
complexity of these interrelationships and
the dependency of the participants on each
other.
Prickly pear cactus roots extend well beyond the plant and spread close to the surface, poised to
rapidly absorb as much moisture as possible during short-lived monsoon storms. Cacti store large
amounts of water for use during droughts.
Yucca (left) and agave
(right) grow thick,
waxy leaves that store
moisture. Although
they have very
different leaf edges,
both plants form as
a rosette of tough,
spine-tipped leaves.
Many plants—cliffrose (left above), Mormon
tea (middle), and sagebrush (right)—have
small leaves to minimize water loss. The
green stems of Mormon tea take on the
food-producing function of leaves. Silvery
sagebrush leaves reflect the sun’s rays,
keeping them cooler.
Claret-cup cacti have
fluted, accordion-like
stems that expand
for maximum water
storage.
Watch for
scrub jays
collecting
pinyon
nuts
ripening
in the fall.
Jays cache
the seeds in
the ground away
from the tree.
In the spring they
remember where they
left the nuts and return to
eat them. Seeds the birds do
not retrieve are left to sprout as
future trees.
Fungi form an
elaborate transfer
system with pinyon
pine roots. The
fungi grow thin,
root-like hyphae
that transfer water
and minerals from
the soil to the tree.
The tree, in turn,
contributes sugars
to the fungi. With
this association, tree roots need to grow less
extensively, while fungal hyphae (the thin
lines) extend to areas far beyond the roots.
National Park Service
U.S. Department of the Interior
Past, Present, and Future
Today the pinyon-juniper community
prospers along the South Rim and partway
down the canyon, but its range has changed
through the millennia. During the most
recent ice age (35,000 – 11,000 years ago),
when the region was cooler and moister,
pinyon-juniper communities spread
to the bottom of the canyon. Scientists
determined this from plant evidence left
in caves and alcoves by packrats. As global
climate continues to warm, the pinyonjuniper habitat type may become established
at higher elevations. Plants within this
community may find the South Rim
uninhabitable.
A healthy pinyon-juniper community
consists of a large variety of plants that
provide rich wildlife habitat. This important
community needs to be protected and
nurtured at Grand Canyon National Park
and throughout the Southwest. Tree cutting,
introduction of non-native plants, and
overgrazing have degraded the community.
The combination of recent droughts and
insect infestations has killed many trees.
We must work to preserve this vibrant
collection of plants and animals so that it
continues to be a widespread component of
the Southwestern landscape.
Yucca plants and yucca moths cannot
survive without each other. Adult moths
lay eggs in a flower, then pollinate the same
flower. The larvae eat only the mature seeds,
which developed because the moth
fertilized the flower. Larvae do not
eat all the seeds, leaving the
yucca sufficient to
reproduce.
Tiny hairs cover the stems and foliage of
Navajo fleabane (left) and cheatgrass (right)
contributing to the plants’ light color and
helping to reduce moisture loss.
Coyotes and birds eat juniper berries and leave the seeds in their droppings. The
undigested seeds may germinate at some distance from the parent tree.
Photographs and illustrations © Lisa Kearsley
0711
Grand Canyon National Park
Arizona
Plants Living
on the Edge
Along the
Hermit Road
Greenway Trail