Shrub-Steppe Plant Ecology

The Sage Hills environment -- shrub-steppe habitat -- is one of limited water, hot summers, cold winters, and gusty winds. Most of the precipitation comes during the winter as snow. Although local plants don't benefit while the snow is falling, in spring when the snow melts, the water saturates the ground, making it easier for perennial plants to break their winter dormancy and for seeds of annuals and perennials to germinate. Spring is the best time for wildflower viewing, as most plants grow, flower, and set seed before the heat and dryness of summer begin.

Plants of the Sage Hills have developed amazing adaptations to survive in the shrub-steppe habitat. Survival strategies involve methods of escaping drought, conserving water, avoiding predation, and spreading their seed. Some feast off a host plant to survive.

Escaping Drought

Some plants escape drought by carrying out their entire life cycle during the moist time of year. Many flowering plants are annuals (bulbous prairie-star) and lay dormant in the earth encased in tough seed coats to protect the seeds until the rains come. Following rain, the seeds germinate and mature quickly so a new seed crop can be dispersed before summer heat dries up the plant. Other plants are perennials, such as woolly-pod locoweed and Geyer's biscuitroot, and their roots lie dormant for a period of years, if necessary, before sending out shoots with new leaves above ground.

Plants in an arid habitat must act quickly when temperatures, moisture, and light inform them it is time to bloom. The variety of plants in bloom can change daily. Early bloomers, like sagebrush buttercup, are triggered by soil temperature if moisture is plentiful. Late spring bloomers, like upland larkspur, have deeper roots and are triggered by the length of daylight and availability of moisture. This timing is also be coordinated with the appearance of the plant's insect pollinators. Our Sage Hills bloom season is very spread out, starting with the blooming of Geyer's biscuitroot in February and ending with rabbitbrush bursting forth in yellow flowers in October.

Conserving Water

The ability to conserve water is of supreme importance to plants (and humans) in the Sage Hills.

Shrub-steppe plants have structures and growing habits adapted to survival with little moisture throughout the year.

Sagebrush and tall buckwheat have hairy leaves that reflect sunlight and protect the plant from drying out in the wind. Rabbitbrush has very small leaves that minimize surface-area evaporation. Arrow-leaf balsamroot has leaves with a waxy coating to retain moisture. Big sagebrush grows two sets of leaves: the principal leaves grow throughout the year, while a secondary set appear along the branch tips in early winter and drop during drought conditions in summer. This allows more rapid growth during the relatively moist conditions of early spring but conserves moisture during the hot, dry summer.

All plants lose water through transpiration, the process of water evaporation through tiny pores in the plant called stomata. Many plants have leaves with minimal surface area from which water can be lost. Other plants reduce water loss by having fewer stomata or opening the stomata only at night when it is cooler.

Many of the plants have water conservation adaptations in their root systems. Grasses have extremely large and complex root systems that enable them to collect water over a wide area. The biomass underground can be more than twice what is visible above ground. Bluebunch wheatgrass has two sets of roots: one set of small, widely dispersed, shallow roots to absorb water rapidly before it evaporates after rain storms; a second set of coarse, penetrating roots draws water from the water table deep underground. The roots of bluebunch wheatgrass also have a heavy endodermis, a waxy layer that prevents desiccation in dry soil conditions.

Plants also protect their stems from water loss. Rabbitbrush and bugloss fiddleneck have woolly hairs that densely cover the stems as well as the leaves. Some plants, such as biscuitroot, have a waxy coating on their stems.

Plants may feed off a host plant to help them obtain water. Thompson's Indian paintbrush has adapted to draw water and organic materials from the roots of certain plants, such as sagebrush. In this way the paintbrush survive much drier conditions than they would normally survive.

Perennial plants in an arid habitat can have twenty times the amount of biomass below ground as above ground, providing the ability to survive the summer. Members of the Lily family, such as sagebrush mariposa lily and yellow bells, store energy within their roots. This stored energy allows the plant to survive for most of the year in a dormant state. By early summer, after flowering and setting seed, the upper parts of the plant and leaves dry out above the ground, leaving none of the plant's soft tissues exposed to the summer heat. By the middle of summer, many plants in our environment are dormant, and show few signs of life above ground.

Avoiding Predation

Plants have evolved varying methods of avoiding predation in order to assure their survival. Predation may include defoliation by grazing animals, or consumption of the seeds and fruits. Yarrow has toxins in its tissues that deter animals from feeding on it. Russian knapweed is toxic to horses if they eat sufficient quantities. It also releases allelochemicals into the soil which inhibit the growth of neighboring plants.

Spreading Seed

To survive in a dry harsh climate, plants must take advantage of every opportunity to spread their seed. When Russian thistle plants die in the fall, they break off from their roots. Their circular shape allows them to tumble freely. With our frequent wind and fairly wide-open spaces, the plants can tumble for many miles, scattering seeds as they go and finding suitable places to grow.

Other plants have bristles (sagebrush stickseed), or sharp tips (cheatgrass), or sticky coatings (large-flowered collomia) on their seeds so that they can latch onto fur or clothing for a ride to another place to grow. Some seeds have parachutes (bearded hawksbeard) or wings (Dalmation toadflax), allowing them to float more easily in the wind. Another strategy is to produce a huge quantity of seeds (Russian thistle - 100,000 seeds per plant) to increase the odds in their favor. Finally, other plants have seeds that can last in the soil for many years (50 years for field bindweed), waiting for the right opportunity to sprout.

Excerpted from:
Latin for Gardeners: a Brief Pronunciation Guide
Phil Peters, Adams County Pennsylvania Master Gardener