Agate Fossil Beds National Monument

Agate Fossil Beds National Monument


Trees and Shrubs


The prairie is not known for its abundance of trees, but with over 200 acres of wetlands, cottonwoods grow well at Agate. There are also several shrubs at Agate including buffalo berry, willows, and sumac. Trees and shrubs grow mostly in the wetland areas but sumac is found in the prairie. Shrubs can be distinguished by size, though some shrubs grow very tall, and by the number of branches. Trees generally have one main stem or trunk, while shrubs have several stems growing upwards with shoots coming off.
The riparian area supports many large cottonwoods and smaller willows. The cottonwoods provide vital habitat for wildlife such as red-tailed hawks, Swearinger’s hawks, great horned owls, and some species of bats. The trees also shade the waters of the Niobrara River, keeping them cool, allowing more oxygen in the water for fish. The willows serve a similar purpose, providing cover and food for rodents and shading the river.
Sumac is found on the hillsides throughout the park and is most common in disturbed areas. Buffalo berry bushes are also found in the park, but are most common near the Visitor’s Center and Museum. Both are used by rabbits and rodents as shelter from the wind and to hide from predators. Deer do occasionally browse on the shrubs but the plants are adapted to survive and recover quickly.

Environmental Factors of Plant Life in Agate

Environmental factors, such as weather, and other natural cycles play an important part in shaping the park landscape, dictating the plant and animal species that survive in this area. Agate is located in rural northwest Nebraska surrounded by ranches that produce beef, alfalfa and hay. In this setting, the park is concerned with water quality due to ongoing irrigation upstream and fertilizer application. At this time this has not been a problem. For more discussion on this topic, read about Rivers and Streams in the Natural Features of this web site. Other park concerns are noxious weeds that include cheatgrass and Canada thistle. Canada thistle is discussed under the topic Other in the Plant section of this web site. The park also monitors weather and observes air quality.


Wildflowers are as much a part of the prairie as the grasses. There is a diverse variety of flowers that bloom at Agate from April to November with colors including shades of yellow, white, blue and pink. The flowers provide food for insects who also pollinate the flowers by moving from place to place.
Flowers have several adaptations for living in the semiarid environment at Agate. The prickly poppy, Platte and Flodman thistle all display wonderful flowers but are prickly to deter deer, rodents and other browsers from chewing on them. Some plants such as the yucca and cacti have waxy coatings over the stem and leaves to limit the amount of water loss in the heat of the day. The evening primrose and the yucca both avoid the heat of the day by flowering in the evening. Species also survive dry times as seeds that germinate after light rains or as bulbs that grow up quickly after moisture.

The best time to see the wildflowers at Agate is in the early spring, from April to May, but there is almost always a flower blooming. One of the most spectacular bloomers is the Siberian yellow iris that fills the wetlands in June with large, yellow flowers. These irises are not native to the United States, but were introduced by James Cook in the late 1800’s when he established the ranch house near the west border of the monument. Prickly pear cacti have medium sized yellow flowers in June and July. One of the first flowers to appear in early April is the western wall flower with a big ball of yellow flowers. In August, the sunflowers dot the landscape with medium sized yellow flowers while the rocky mountain bee plant has a ball of small purple flowers. Agate is a great place to look at wildflowers anytime of year.


Agate supports several species of grasses, which are mostly found on the slopes and buttes throughout the park, but a few species are found in the wetter, riparian areas. As a mixed grass prairie, Agate’s grasses are generally less than four feet tall. All grasses are of the family Poaceae, also called Gramineae, which is considered the third largest family of flowering plants in the world. The grass family includes many production crop species such as corn, rice, wheat, and sugarcane. Grasses can be distinguished from other plants by their hollow, herbaceous stem, narrow leaves with parallel veins, and small flowers. 
The leaves of grasses are specialized to cope with the arid environments they inhabit. As wind blows across plant leaves, it takes valuable moisture from the plant. Grasses have vertical leaves to minimize this loss while maximizing surface area for photosynthesis. Another adaptation grasses have made due to environment is their rooting system. Roots are extensive, which allows the plants to absorb moisture from different layers of the ground and to limit competition. Based on rooting types, grasses can be divided into two groups, bunch grasses and sod forming grasses.
Sod is created by grasses growing close together with an abundance of small roots and shoots that reproduce into new plants. These shoots are called rhizomes when below ground and stolons when above ground. Extensive roots serve two purposes, to anchor the plant against the wind and to block out competition from other species. Sod forming grasses are usually dominant in the wetter years and in wetter areas. Bunch grasses tend to thrive in drier years and drier areas due to their spacing. Bunch grasses grow in scattered clumps with more space in between plants to limit competition for soil nutrients and water. Sod houses were built by early homesteaders in this area as shelters due to the lack of trees and other building materials. Sod is the upper stratum of soil held together by grass roots. It was cut out of the ground into long brick-shaped sections and piled to construct homes.
Cheat grass or downy brome grass is a sod forming grass that was introduced from Europe in the 1800s and often takes over areas disturbed by grazing and fire. Cheat grass is present in a few disturbed sites of earlier homesteaders. Crested wheat grass is an introduced bunch grass from Russia but is found in scattered locations throughout the park. The threadleaf sedge, a grass-like species that is not a true grass is prominent at Agate and serves as part of the prairie grassland system.

Cacti / Desert Succulents

Cactus might not be what visitors expect to find in the prairie, but Agate has at least three species of cacti. The average rainfall at Agate is about 15 inches with intense winds that increase evaporation and reduce available water. Cacti are a succulent plant with special adaptation for the dry environment.

Succulent plants are those plants capable of storing water in roots, stems, or leaves during wet times in order to survive times of drought. Cacti are stem succulents, meaning they store the water in their stem. These are called pads or branches and they have a waxy coating to prevent loss of stored water. Cacti are unique in the succulent group because they contain areoles, the structure that bears spines, buds, flowers and then fruit. When spines or branches of other plants are broken off, the tissue is damaged leaving a weakness and a means of water loss. If a spine on a cactus is broken from the areoles, the plant is not damaged. The sharp spines are leaves adapted to break up wind to reduce evaporation and shade the pad. These spines also condense mists and dew at night, which then drip on the soil and can be absorbed by roots. Roots are broad and shallow to quickly soak up rainwater. Soon after a rain, small roots grow to absorb the water and then dry up.
Due to the environments cacti live in, they use CAM (Crassulacean acid metabolism) photosynthesis, unique to succulent plants. Photosynthesis is the method by which plants collect carbon dioxide through holes in their leaves called “stomata” and convert it into sugar and oxygen with the use of sunlight. In CAM photosynthesis, the stomata open only at night when the plant is relatively cool, so less moisture is lost through transpiration. The carbon dioxide collected at night is then chemically stored until the sun comes out and the process can be completed. The sunlight is also absorbed through the stomata, even when they are closed.
Cacti at Agate bloom during the day in a variety of colors. The brittle cactus and prickly pears have beautiful yellow flowers that are hardy and last several days. The ball cactus has a wonderful hot pink bloom that appears in July but only lasts a couple of days. Due to their pretty flowers, cacti are also grouped with wildflowers. Cacti grow in the prairie grasses and along the rocky bluffs and can be seen on both the Fossil Hills and the Daemonelix Trails at the park. 



Agate was created to preserve the fossils of Miocene era mammals, but has preserved the prairie as well. The wetland and riparian areas offer a look at water-loving plants that are not always seen in the prairie. Vegetation plays a vital role in the ecosystem. Plants capture particulate dust in the air, filter gaseous pollutants, convert carbon dioxide to oxygen, provide animal habitat and food, and possess many raw materials useful to humans.
The semiarid climate of the Great Plains area has led to the evolution of the grasslands. Agate is a mixed grass prairie, meaning it is a mixture of tall and short grasses growing together. The mixed grass prairie extends from North Dakota through South Dakota, Nebraska, Kansas, central Oklahoma and the north-central part of Texas. Prairies have semiarid climates with high seasonal fluctuation and yearly fluctuations. Most precipitation is received during the growing season; at Agate this is from April to June. Agate averages 15 inches of precipitation a year but during droughts this can be as low as 9 inches or less. Another characteristic of prairies is their flat to rolling terrain and fertile soil rich in organic matter. The climate and soils promote the growth of grasses, not trees which require more water.
Agate displays the rich diversity of the prairie grassland that includes more than just grasses in three distinct areas of the park. The broad floodplain of the Niobrara River has created a riparian area for water-loving plants like cottonwoods, fox tail barley, cattails, reeds, sedges, yellow Siberian irises and blue flag irises. The buttes and hilltops are inhabited by plants that tolerate the drier, rocky conditions such as little blue stem grass, threadleaf sedge, sandhills muley and tufted milk vetch. In between the riparian area and the buttes is the area that most people think of as prairie. This area is inhabited by western, slender, and crested wheat grasses, Blue grama grass, threadleaf sedge and needle and thread grass.


The dry, rocky bluffs at Agate provide an ideal habitat for lichens. Lichen are a composite plant, consisting of fungi and algae with a symbiotic relationship. In a symbiotic relationship both plants benefit and are capable of living in places where neither one could live alone. The body of the lichen, called a thallus, has no outer covering like a leaf so air is freely exchanged across the entire surface of the plant.
Lichen are extremely slow growing, only a few millimeters per year, but live for many years if undisturbed. Lichens are a good indicator of air quality due to their method of air exchange. Some lichen are sensitive to carbon dioxide, nitrogen oxides, fluorides or ozone, alone or in combination. The sensitivity of the lichens also varies with atmospheric conditions. When the plant is wet and active, it absorbs more air and pollutants and is affected faster than when it is dry and dormant. When damaged, lichen becomes discolored because of death of the algae causing bleached lobes followed by death of the algae. The lichen decomposes into the soil within a few months after its death. Because of the longevity of lichen, they indicate environmental factors over a long period of time. Chemical analysis of the plants can give indications of levels of toxic substances which accumulate in the plants.
The lichens at Agate are generally healthy with a total of 64 species documented. Lichen grow on more than just rocks and at Agate, species of lichen are found on trees, rocks and soil. The wetland areas are densely covered with vascular plants with limited space available for lichen growth, but the thin soil on ridges provides habitat for soil lichens. The trees have several species of rare lichen that would not otherwise be found in a grassland. The most abundant locations for lichen are the rocks and rock outcroppings.

Other Plants

Canada thistle (Cirsium arvense) is a problem weed for many areas. Originating from Eurasia and North Africa, it was brought to Canada in contaminated crop seed in the mid to late eighteenth century. From Canada the thistle spread south into the northern United States and onto the Great Plains. It is found in Wyoming, Nebraska, Oregon, Washington, Idaho, Colorado and many other states today. Canada thistle has been designated a noxious weed in Nebraska since 1873. It competes with natural prairie species and planted cropland species. Wheat yields can be decreased 65% and corn yields 35% by severe thistle infestations. Cattle avoid areas with prickly thistles, causing a loss in carrying capacity of infested pastures.

Canada thistle is most likely to occur in moist environments with previous disturbances, such as in pastures, range land, crop land, ditch banks, road sides, mud flats, lake shores and stream banks. Approximately 450,000 such areas are infested with Canada thistle across Nebraska, with the majority being in the panhandle region.�We have implemented an intensive thistle control program at Agate.

Canada thistle can reproduce in two ways, which makes it very difficult to control and is the reason it has become so wide spread. This perennial forb spreads through seed production as well as by creeping roots known as rhizomes. Canada thistle is dioecious, meaning each plant contains all male or all female flowers. However, a population of all males or all females can sustain itself and spread through the extensive lateral root system. Cultivation (tilling, ploughing) only causes the thistle population to increase due to the plants ability to reproduce from as little as 1/2" of root.

Plants appear at Agate in early to mid-May as small rosettes of spiney-tipped, wavy leaves. The plant grows vigorously until flowering in July or August. At this time stems are one to four feet tall and rigid with several branches. Plants remain green until the first frost, when the above ground portion dies, but the roots remain until the following spring.

Agate Fossil Beds National Monument has about 3,000 acres within its boundaries but only 2,270 acres are federally managed. The Niobrara River winds eleven miles through the parks' four-mile width, creating extensive riparian and wetland habitats. These areas provide excellent growing conditions for many plants, including the Canada thistle that thrives in the moist environment. Canada thistle is competitive with native plants, making it difficult for them to reproduce and survive. The thistle disturbs the natural, scenic qualities of the park and spreads to neighboring pastures. Canada thistle is believed to have entered Agate around 1970. It spread through out the wetland and lower terraces of the monument. In 1996 it was estimated that approximately 100 acres where infested with thistle. This signaled the need for action.�

Agates' first biological thistle control agents were released in May 1997. One hundred and forty-eight stem mining weevils (Ceutorhynchus litura) were released near the Bone Cabin, west of the Visitors Center and Museum. In early spring the weevils inject eggs into the young thistle shoots, and the eggs hatch into larvae by mid-May. The larvae mine the thistle stem, root crown, and roots, weakening the plant by using nutrients. This inhibits the thistles' ability to produce seeds and grow roots. The larvae then chew an exit hole near the base of the plant and move into the soil to pupate. The exit hole leaves the plant susceptible to secondary infestation of ants, fungi and other insects. The weevil overwinters as an adult in the soil near the base of the plant. It emerges in March and April to again lay eggs in the thistle until mid-May when the plants are too large to be easily penetrated by the weevil. A female can lay 120 eggs in young shoots. Six to seven larvae are needed in the shoots to effectively weaken the plant.

In 1998, Agate located a second release site near the boardwalk on the south side of the river. At each the new site and the original site 125 stem mining weevils were released. A new species, the stem and shoot gall fly (Urophora cardui), was also released at both sites. These were still in the larval stage, contained in galls. A gall is a round growth or tumor on a stem caused by irritation from larvae. Galls can contain zero to ten living gall fly larvae. The larvae begin to pupate in warm, spring temperatures and emerge from the galls as adults in late spring or early summer. The flies then lay one to 30 eggs in young shoots. After the egg hatches, larvae tunnel into the stem, creating the gall. The fly over winters in the gall as a larvae. In 2000, five additional insect release were created in the wetland areas between the Bone Cabin and the west park boundary with 2,000 gall flies and 440 stem mining weevils released at those sites.

In addition to biological control of Canada thistle, Agate uses mowing and herbicides. Areas of dense infestations are mowed from late July to mid-August to prevent the plant from seeding. Herbicides are then applied mid-September after the first hard frost. The park is currently using Telar �, containing chlorosulfuron, which is approved for non-cropland use, and is used in small amounts. It does not leach deep into the soil, is practically nontoxic to most fish and aquatic invertebrates, and does not bioaccumulate (build up) in fish. Telar is also shown to be nontoxic to birds and mammals. Agate has had a contract with the Sioux County Weed Superintendent to spray the Telar � annually since 1999. Telar is applied after the first frost, when the thistle begins to go dormant for the winter and draws moisture and nutrients into the roots which brings the herbicide with it, reducing the roots ability to spread the following spring. Approximately 40 acres are mowed and have herbicides applied annually.

Agate Fossil Beds National Monument has experienced success in its efforts to control its exotic Canada Thistle populations. Staff estimates that from 1996 though 2002 there was a 70% reduction in Canada Thistle population across the park. The project is documented in the parks Geographic Information System (GIS) and in reports on file. New methods of control are being evaluated including new biological control agents, prescribed burns, and different herbicides.