Talus

Photo of cliff face, talus, Jacks Fork River, and leafless injured sycamore trees

Talus slopes often occur at the bases of cliffs and consist of loose rock fragments or slabs covering more than half the surface area. Because the rocks are prone to movement, trees have trouble getting established in these areas.

We most often hear about talus (pronounced TAY-luss) when people talk about alpine habitats and glaciers, but talus occurs in Missouri, too. It’s a naturally occurring slope made of a jumble of loose rocks that have fallen from a rocky cliff or other rock face above.

A talus natural community, by definition, must have more than 50 percent of its area covered by coarse rocky debris. The slopes range from 15 to 60 percent.

In general, talus habitats are rocky places with little soil and rather sparse vegetation.

Rock type has a strong influence on the character of talus communities, as different types of rocks respond differently to the processes of freezing and thawing, differ in how quickly they break down and form soils, and vary in their effects on soil pH.

In talus slopes, the mass of rock actively moves downward with gravity and with the arrival of newly broken-off rocks from above. This downward shifting topples and damages trees.

Talus Plants

Vegetation can be patchy or barren on talus, or it can be dense and covered with trees. The amounts and types of vegetation depend on how much organic matter accumulates amid the pile of rocks. Over time, branches and leaf litter falls or slumps from nearby cliffs or slopes. As these materials decompose, soils develop, supporting plant growth.

In sun-exposed areas, talus communities tend to be hot and dry, but in sheltered, north-facing areas, they can be cool and damp.

In dry talus communities, the most prominent plant types are vines and lichens. In moist, shaded talus communities, mosses, ferns, algae, fungi, and cyanobacteria (blue-green algae) are prominent. Trees typically struggle to survive in talus, often sustaining root damage or falling over, as the unstable rocks shift around. Trees in talus often have missing limbs or bear scars caused by falling rocks. These injured trees are more likely to succumb to root fungus and to be blown over by strong winds.

As soils build up in a talus community and vegetation increases, trees may become established that can eventually stabilize the rock mass, allowing the development of deeper soils and increased vegetation. Eventually, the talus community can be transformed into another type of natural community — a mesic limestone/dolomite forest, for example.

Talus Animals

Although talus is an unstable, generally inhospitable place for large animals, it offers an excellent habitat for small, agile animals. Many talus communities occur along rivers and streams, allowing animals to take shelter in the cool, moist pockets created by the jumble of boulders.

  • Amphibians. Cave salamander, southern redback salamander, and pickerel frog. In north-facing, cool, moist talus, Ozark zigzag salamander and four-toed salamander are notable.
  • Reptiles. These especially use the talus for overwintering sites: timber rattlesnake, cottonmouth, and northern watersnake.
  • Birds and small mammals (such as rodents). Species living in nearby woodlands or forests often visit talus communities.
  • Invertebrates. Spiders, beetles, snails, and slugs are commonly present.

Types of Talus Communities

In Missouri, two types of talus communities have been identified.

Limestone/dolomite talus 

Limestone/dolomite talus is created by fragments of rock that have broken off cliff faces. Shrubs, wildflowers, vines, mosses, liverworts, and lichens cover up to 40 percent of the area. Trees are absent or rare. Soils are slightly acidic to moderately alkaline. This community occurs statewide along large streams and rivers, especially in the Ozarks and along the Mississippi River in northeast Missouri.

Representative Limestone and Dolomite Talus Sites

  • Ha Ha Tonka Oak Woodland Natural Area
  • Big Spring Natural Area
  • Grand Bluffs Natural Area
  • Vilander Bluff Natural Area
  • Jam Up Bluff and Angel Bluff in Jacks Fork Natural Area
  • Cardareva Bluff Natural Area

Igneous talus

Igneous talus is created by long-term weathering and erosion of cliff faces or mountain domes, which causes large rock fragments and boulders to accumulate below. Shrubs, annual wildflowers, vines, mosses, liverworts, and lichens are sparse. Trees are sparse to absent. Soils are very strongly acidic to moderately acidic. This community occurs in the St. Francois knobs and basin and Current River hills region of southeastern Missouri.

Representative Igneous Talus Sites

  • Mudlick Mountain Natural Area
  • Johnson’s Shut-Ins Natural Area
  • Bell Mountain Wilderness (Iron County)
  • St. Francois Mountains Natural Area

Statewide, but talus communities are best developed in the southern half of the state and along major stream drainages, including along the Mississippi River.

Photo of wolf spider with young
Wolf Spiders
Nearly 250 species in North America north of Mexico
A wolf spider doesn't spin webs to catch its prey — it runs it down like a wolf! Spiders in this family have long legs and are usually gray, brown, black, or tan with dark brown or black body markings (especially stripes).
image of Six-Spotted Tiger Beetle crawling on dead leaves
Tiger Beetles
Subfamily Cicindelinae (about 100 species in North America)
Dizzyingly fast runners and fliers, tiger beetles are remarkable, and often very colorful, insect predators.
Image of a cave salamander
Cave Salamander
Eurycea lucifuga
The cave salamander is a common amphibian of the Ozark Plateau. It lives in caves, springs, and rocky streams. Recognize it by its normally bright orange skin dotted with dark brown or black spots.
Photo of a four-toed salamander on a mossy rock.
Four-Toed Salamander
Hemidactylium scutatum
A glacial relict in Missouri’s eastern Ozarks, the four-toed salamander lives among mosses in heavily forested streams and creeks and sinkhole ponds. It has a thick, round tail that is constricted at its base. There are four toes on each limb.
Photo of a southern red-backed salamander on an oak leaf.
Southern Red-Backed Salamander
Plethodon serratus
The southern red-backed salamander is small and slender, with a distinct, narrow, red or orange stripe along the back that has saw-toothed edges. It hides under rocks, mosses, and rotten logs in Ozark forests.
A reddish-brown salamander with an orange stripe down its back is curled on a moss-covered rock.
Ozark Zigzag Salamander
Plethodon angusticlavius
The Ozark zigzag salamander is small and slender, with a narrow, somewhat lobed back stripe that can be yellow, orange, or red. This woodland species lives in Missouri’s southwestern counties along the Arkansas border.
Image of a pickerel frog
Pickerel Frog
Lithobates palustris (formerly Rana palustris)
The pickerel frog is medium-sized, with square or rectangular spots in two parallel rows down the back. There is a distinct ridge of skin along each side of the back. It is absent from the northwestern third of Missouri.
Photo of a northern watersnake rearing back in grass on land.
Northern Watersnake and Midland Watersnake
Nerodia sipedon sipedon (northern watersnake) and N. s. pleuralis (midland watersnake)
The northern watersnake and midland watersnake are Missouri's two subspecies of common watersnake. Together they occur statewide. Color is variable: gray, tan, or reddish brown with dark crossbands or blotches. The belly is cream-colored with red, brown, or black spots or half-moon markings.
Image of a northern cottonmouth
Northern Cottonmouth
Agkistrodon piscivorus
The cottonmouth is named for the cotton-white lining of its mouth, which it opens widely when alarmed. This dangerously venomous, semiaquatic snake occurs in the southeastern corner of Missouri, with a spotty distribution in the Ozark Region.
Image of a timber rattlesnake
Timber Rattlesnake
Crotalus horridus
Missouri’s largest venomous snake, the timber rattlesnake, is dangerously venomous, but there are few cases of rattlesnake bites in our state. It frequents rough country, is mostly nocturnal in summer, and few Missourians ever encounter it.
Illustration of chinkapin oak leaf.
Chinkapin Oak (Chinquapin Oak)
Quercus muehlenbergii
Chinkapin oak is fairly easy to identify because of its distinctively toothed leaves. Look for it growing in rocky soils derived from limestone or dolomite on bluffs and in upland woods, and in floodplain forests and lower slopes along streams.
Illustration of black walnut compound leaf and nuts.
Black Walnut
Juglans nigra
Easily Missouri’s most valuable tree, the black walnut provides the finest wood in the world, as well as delicious nuts. Both are in high demand and thus form an important part of Missouri’s economy.
Illustration of sugar maple leaves, twigs, fruits
Sugar Maple
Acer saccharum
Sugar maple is a tree that inspires much “oohing and aahing” during fall color season. Its sap is famous as a source for maple syrup, but its use in landscaping and for furniture is also widespread.
Illustration of virginia creeper leaves, stem, flowers, fruit.
Virginia Creeper
Parthenocissus quinquefolia
Occasionally confused with poison ivy, Virginia creeper is easily identified by simply noticing that most of its leaflets are in fives, instead of threes. This common native vine is useful in landscaping.
Illustration of raccoon grape leaves, flowers, fruit
Raccoon Grape
Ampelopsis cordata
Raccoon grape is a woody vine climbing by tendrils to a length of 60 feet. The most aggressive native vine in the state, it can smother small- to medium-sized trees.
Illustration of summer grape leaves, flowers, fruit
Summer Grape
Vitis aestivalis
Summer grape is a vigorous, woody, wild grapevine climbing to a height of 35 feet. It grows mostly in the southern two-thirds of Missouri, often in drier situations than many other grape species.
Illustration of catbrier leaves, flowers, fruits
Catbrier
Smilax bona-nox
Catbrier is a green-stalked perennial vine with stout spines. It climbs up to 25 feet using tendrils that arise in pairs from the bases of the triangular, heart, or fiddle-shaped leaves.
Illustration of greenbrier leaves, flowers, fruits
Greenbrier
Smilax glauca
Greenbrier is a slender, spiny, woody vine climbing by coiled tendrils. Its leaves can be broadly heart-shaped, oval, or lance-shaped. The leaf undersurface is smooth and notably whitened, silvery, or blue-gray with a waxy coating.
Illustration of poison ivy leaves, flowers, fruits.
Poison Ivy
Toxicodendron radicans
Poison ivy is a toxic plant that contains an oil in all its parts that, if you come into contact with it, can cause an intense skin reaction. Learn to recognize it, and sidestep it on your outings.
Photo of leaf cup flower
Pale-Flowered Leaf Cup
Polymnia canadensis
Leaf cup is named for the leafy appendages that wrap around the stem at the bases of the opposite leaves. Part of the sunflower family, leaf cup has about 8 white ray florets surrounding yellow disk florets.
Photo of spotted touch-me-not or jewelweed flower.
Spotted Touch-Me-Not (Jewelweed)
Impatiens capensis
Many Missouri children learn about this orange-flowered native plant by playing with the juicy green seedpods, which, when ripe, "explode" upon the slightest touch. This is jewelweed's mechanism for seed dispersal, and it's the reason for the name "touch-me-not."
Photo of woollen breeches flower cluster
Woollen Breeches (Great Waterleaf)
Hydrophyllum appendiculatum
Woollen breeches bears clusters of light blue, bell-shaped flowers. The lower leaves of this hairy plant are shaped something like maple leaves and often have grayish or light green marks that look like water stains.

Cliffs

Photo of cliffs overlooking Ha Ha Tonka Spring
Cliffs

Cliffs are steep to vertical exposures of bedrock (or loess) 10 feet or more in height. Nine distinct cliff natural communities have been identified in Missouri, distinguished by rock type and by amount of moisture.

Stream Edges

Photo of Silver Fork Creek and its banks, viewed from atop the Pinnacles rock formation.
Stream Edges

Streams and rivers, of course, are aquatic habitats. But there are also distinct land habitats that occur along streams and rivers. Stream edge habitats include sandbars, gravel washes, and the banks of streams and rivers.

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