Invasive Plants of the Gila

Invasive Species of the Gila Wilderness

The Gila Wilderness, known for its rich biodiversity, faces significant challenges from invasive plant species. These non-native species can rapidly spread, outcompeting native flora and disrupting the delicate ecological balance. Below is an overview of some of the most concerning invasive species currently found within the Gila Wilderness.

Bull Thistle (Cirsium vulgare)

Bull Thistle is a robust biennial plant that is highly invasive in disturbed areas such as grasslands, pastures, and along roadsides. This plant is easily recognized by its distinctive physical characteristics and its ability to form dense stands that outcompete native vegetation.

Physical Characteristics:

• Height: Bull Thistle typically grows between 2 to 6 feet tall, with a stout, erect stem that is covered in sharp, needle-like spines.
• Leaves: The leaves of Bull Thistle are dark green and deeply lobed, with a rough, hairy surface. Each lobe ends in a sharp spine, making the plant unwelcoming to herbivores.
• Flowers: The flower heads are large, typically 1 to 2 inches in diameter, and are composed of numerous small, purple florets. These florets are surrounded by spiny bracts, adding to the plant's overall prickly appearance.
• Stem: The stem is rigid, often branching near the top, and is covered with spines and fine hairs. The spines on the stems and leaves give Bull Thistle a very formidable look, deterring grazing by animals.
• Roots: Bull Thistle has a deep taproot that anchors the plant firmly in the ground, allowing it to access water and nutrients from deep within the soil.

Growth and Spread:

Bull Thistle is a biennial, meaning it has a two-year life cycle. In its first year, it forms a low-growing rosette of leaves. In the second year, the plant bolts, sending up a tall, flowering stalk. After flowering and producing seeds, the plant dies. However, Bull Thistle produces a large number of seeds that are easily dispersed by the wind, allowing the plant to spread rapidly across open areas.

This plant's ability to thrive in disturbed soils, combined with its spiny defenses, makes it a formidable invader. Once established, Bull Thistle can dominate an area, reducing the availability of resources for native plants and wildlife. Its dense growth can also interfere with the movement of animals and people through infested areas.

Horehound (Marrubium vulgare)

Horehound is an invasive perennial herb that belongs to the mint family (Lamiaceae). Originally from Europe, this plant has spread widely across many parts of the world, including North America, where it often invades disturbed areas such as roadsides, pastures, and open fields.

Physical Characteristics:

• Height: Horehound typically grows between 1 to 3 feet tall, forming a bushy, branched plant.
• Leaves: The leaves of Horehound are grayish-green, oval-shaped, and deeply wrinkled. They have a soft, hairy texture, giving the leaves a slightly fuzzy appearance. The edges of the leaves are coarsely toothed, adding to the plant's distinctive look.
• Flowers: Horehound produces small, white flowers that grow in dense clusters along the upper parts of the stems. Each flower is tubular and has a characteristic two-lipped structure typical of the mint family. The flowers are often found in the leaf axils and are arranged in whorls around the stem.
• Stem: The stems of Horehound are square-shaped, which is a common trait among plants in the mint family. The stems are also covered in fine hairs, giving them a slightly rough texture.
• Roots: Horehound has a fibrous root system that allows it to establish quickly in disturbed soils. The plant can spread both by seed and vegetatively through its roots.

Growth and Spread:

Horehound is a hardy plant that thrives in dry, well-drained soils, particularly in sunny locations. It often invades areas that have been disturbed by human activity, such as overgrazed pastures, roadsides, and construction sites. Once established, Horehound can form dense patches that outcompete native vegetation, reducing biodiversity and altering the habitat.

The plant produces a large number of seeds, which are dispersed by wind, water, and animals. Horehound’s seeds can remain viable in the soil for several years, making it challenging to eradicate once it has become established. The plant’s unpalatable, bitter taste also makes it undesirable to livestock, which contributes to its spread as animals avoid grazing on it.

Due to its invasive nature, controlling Horehound is important to protect native plant communities and maintain the ecological balance in affected areas. Effective management often involves a combination of mechanical removal, herbicide application, and restoration of native vegetation.

Horseweed (Conyza canadensis)

Horseweed is a highly adaptable and invasive annual plant that is native to North America. While it naturally occurs in many habitats, it has become problematic in disturbed areas such as agricultural fields, roadsides, and urban environments due to its rapid growth and ability to outcompete native species.

Physical Characteristics:

• Height: Horseweed typically grows between 1 to 6 feet tall, depending on environmental conditions. It has a slender, erect stem that is usually unbranched until it reaches the flowering stage.
• Leaves: The leaves of Horseweed are narrow, lance-shaped, and arranged alternately along the stem. They are dark green with a slightly toothed margin and may have a rough, hairy texture. The lower leaves are often larger and may have a more noticeable toothed edge, while the upper leaves are smaller and more linear.
• Flowers: Horseweed produces small, inconspicuous flowers that are greenish-white or yellowish in color. These flowers are clustered densely at the top of the plant in a branched, spike-like formation called a panicle. Each tiny flower consists of a central disk surrounded by small ray florets, similar to those found in other members of the aster family (Asteraceae).
• Stem: The stem of Horseweed is stiff and hairy, often with a reddish tint near the base. It is generally unbranched until it begins to flower, at which point it produces numerous small branches topped with clusters of flowers.
• Roots: Horseweed has a shallow, fibrous root system that allows it to establish quickly in disturbed soils. It can be difficult to remove once established because it often produces a large number of seeds that contribute to its persistence in the environment.

Growth and Spread:

Horseweed is a fast-growing annual that completes its life cycle within a single growing season. It germinates in the spring or fall, with seeds that can remain viable in the soil for several years. The plant rapidly develops a rosette of leaves at the base before sending up a flowering stalk. Once it flowers and sets seed, the plant dies, but not before producing thousands of tiny seeds that are easily dispersed by the wind.

Due to its adaptability, Horseweed can quickly dominate disturbed areas, particularly those that have been recently cleared or affected by agricultural activities. It is particularly problematic in agricultural settings, where it can reduce crop yields and complicate weed management due to its resistance to certain herbicides.

Effective control of Horseweed often requires a combination of mechanical removal, herbicide application, and cultural practices that promote the growth of competitive native or desirable plants. Early detection and management are crucial to preventing the spread of this invasive plant in sensitive areas.

Mullein (Verbascum thapsus)

Mullein, scientifically known as Verbascum thapsus, is a biennial plant that has become invasive in many parts of the world, particularly in North America. Originally native to Europe, Asia, and northern Africa, this plant has spread widely, often invading disturbed soils such as roadsides, fields, and open areas where it can quickly establish itself and outcompete native vegetation.

Physical Characteristics:

• Height: Mullein is a tall plant that can grow up to 6 to 8 feet in height during its second year. In its first year, it forms a low-lying rosette of leaves at the base.
• Leaves: The leaves of Mullein are large, oblong, and covered with a dense layer of woolly, silvery-gray hairs, giving them a velvety texture. The basal leaves can grow up to 12 inches long and 5 inches wide, while the leaves along the flowering stem become progressively smaller as they ascend the stalk. The leaves are arranged alternately along the stem.
• Flowers: Mullein produces a tall, unbranched flowering spike in its second year, which is densely packed with small, yellow flowers. Each flower is about 1 inch across, with five petals arranged in a slightly asymmetrical pattern. The flowers bloom sequentially from the bottom to the top of the spike, often from late spring through summer.
• Stem: The stem is thick, sturdy, and covered in fine hairs, contributing to the plant’s overall woolly appearance. The stem supports the tall flowering spike and is typically unbranched.

Growth and Spread:

Mullein is a biennial plant, meaning it has a two-year life cycle. In its first year, it forms a rosette of large, woolly leaves close to the ground. In its second year, the plant sends up a tall flowering spike that can reach several feet in height. After flowering and producing seeds, the plant dies. However, before it dies, Mullein produces a large number of tiny seeds—often up to 100,000 per plant—that can remain viable in the soil for many years.

This prolific seed production, combined with the plant’s ability to thrive in poor, disturbed soils, makes Mullein a highly successful invader. It can quickly dominate an area, crowding out native plants and altering the local ecosystem.

Mullein’s invasive nature, combined with its ability to produce large quantities of seed, makes it a challenging plant to control. Management often requires mechanical removal of the entire plant, including its deep taproot, before it has a chance to set seed. Herbicide treatments may also be effective, particularly for large infestations.

Mullein’s tall, flowering spikes and woolly leaves make it a distinctive and easily recognizable plant, but its invasive potential means it poses a significant threat to native ecosystems.

Prickly Lettuce (Lactuca serriola)

Prickly Lettuce, scientifically known as Lactuca serriola, is a highly adaptable and invasive annual or biennial plant that belongs to the Asteraceae family, the same family as sunflowers and dandelions. Native to Europe and parts of Asia, Prickly Lettuce has spread widely across North America, where it thrives in disturbed areas such as roadsides, fields, gardens, and vacant lots.

Physical Characteristics:

• Height: Prickly Lettuce can grow between 1 to 5 feet tall, with some plants reaching up to 8 feet under optimal conditions. The plant typically has a single, upright stem that may branch near the top.
• Leaves: The leaves of Prickly Lettuce are deeply lobed and have a distinctive midrib lined with small, sharp prickles on the underside. The leaves are bluish-green and may have a rough, slightly hairy texture. The lower leaves are larger and can grow up to 12 inches long, while the upper leaves are smaller and more linear. As the plant matures, the lower leaves may wither and drop off, leaving the upper portion of the plant with smaller, clasping leaves.
• Flowers: The plant produces small, yellow flowers that resemble those of dandelions. The flowers are about 1/2 inch wide and are arranged in loose clusters at the ends of the stems. Each flower head is composed of multiple ray florets and no disk florets. The flowers typically bloom from midsummer to early fall and are followed by the production of small, wind-dispersed seeds.
• Stem: The stem of Prickly Lettuce is rigid, hollow, and often covered with fine hairs. It may have a slightly purplish or reddish hue, especially near the base, and is usually covered with short prickles, particularly at the lower portion.
• Roots: Prickly Lettuce has a taproot that allows it to access water and nutrients deep in the soil, making it particularly resilient in dry conditions. The taproot also makes the plant difficult to remove once established.

Growth and Spread:

Prickly Lettuce is a prolific seed producer, with each plant capable of producing thousands of seeds that are easily dispersed by the wind. These seeds can remain viable in the soil for several years, leading to the rapid spread of the plant across disturbed areas. Prickly Lettuce is most commonly found in sunny, open locations where the soil has been disturbed, but it can also invade gardens, agricultural fields, and other managed landscapes.

As a highly competitive plant, Prickly Lettuce can outcompete native vegetation, reducing biodiversity and altering the structure of the ecosystem. Its sharp prickles make it unpalatable to livestock and wildlife, allowing it to thrive even in grazed areas.

Controlling Prickly Lettuce requires a combination of mechanical, cultural, and chemical methods. Mechanical removal should be done before the plant sets seed, and the entire taproot must be removed to prevent regrowth. Herbicides can be effective, particularly for large infestations, but timing is crucial to prevent seed production.

Prickly Lettuce’s ability to thrive in a variety of conditions and its aggressive spread make it a significant invasive species that poses challenges to land managers and gardeners alike.

White Sweet Clover (Melilotus alba) and Yellow Sweet Clover (Melilotus officinalis)

White Sweet Clover (Melilotus alba) and Yellow Sweet Clover (Melilotus officinalis) are invasive biennial plants belonging to the legume family (Fabaceae). Originally introduced from Europe and Asia as forage crops and for soil improvement, both species have spread widely across North America. They are commonly found in disturbed areas such as roadsides, fields, and prairies, where they can rapidly colonize and outcompete native vegetation.

Physical Characteristics:

• Height: Both White and Yellow Sweet Clover can grow between 2 to 6 feet tall, with some plants reaching up to 8 feet in favorable conditions. They have tall, branching stems that support a dense canopy of leaves and flowers.

• Leaves: The leaves of both species are compound and trifoliate, meaning each leaf is composed of three smaller leaflets. The leaflets are oblong to lance-shaped, with serrated edges. The leaves are arranged alternately along the stem, giving the plant a lush, bushy appearance.

• Flowers:

  • White Sweet Clover (Melilotus alba): The flowers of White Sweet Clover are small, white, and densely clustered in elongated, spike-like racemes that grow from the upper parts of the stem. Each flower is about 1/8 inch long and has a characteristic sweet fragrance.
  • Yellow Sweet Clover (Melilotus officinalis): The flowers of Yellow Sweet Clover are similar in size and structure to those of White Sweet Clover but are bright yellow. They also grow in spike-like racemes and emit a sweet, honey-like scent.

• Stem: The stems of both plants are slender, branching, and slightly ridged. They are often green but may take on a reddish tint, particularly near the base. The stems are usually hairless or have only a few fine hairs.

• Roots: Both species have a deep taproot system that allows them to access water and nutrients from deep within the soil. The taproot also contributes to the plant’s ability to survive in poor, dry soils and makes it difficult to remove once established.

Growth and Spread:

White and Yellow Sweet Clover are biennial plants, meaning they have a two-year life cycle. In the first year, they form a low-growing rosette of leaves. In the second year, the plants rapidly grow tall stems that produce flowers, followed by seed production. After setting seed, the plants die, but not before producing large quantities of seeds that can remain viable in the soil for several years.

These plants are prolific seed producers, and their seeds are easily dispersed by wind, water, and animals. Once established, White and Yellow Sweet Clover can quickly dominate an area, forming dense stands that crowd out native plants. Their ability to fix nitrogen in the soil can also alter soil chemistry, making conditions less favorable for native species that are adapted to low-nutrient environments.

Ecological Impact:

The invasive nature of White and Yellow Sweet Clover poses significant threats to native ecosystems. They can outcompete native grasses and wildflowers, leading to reduced biodiversity. Their dense growth can also alter fire regimes by providing additional fuel that increases the intensity and frequency of wildfires.

Control Methods:

Controlling White and Yellow Sweet Clover typically involves a combination of mechanical, chemical, and cultural methods. Mechanical removal, such as mowing or cutting, should be done before the plants flower and set seed. Herbicides can be effective, especially when applied in the early stages of growth or to young rosettes. In areas where Sweet Clover has become established, restoration efforts may involve reseeding with native plants to outcompete the clover and restore the natural ecosystem balance.

In summary, White Sweet Clover (Melilotus alba) and Yellow Sweet Clover (Melilotus officinalis) are aggressive invaders that can significantly disrupt native plant communities. Effective management and control are essential to protect the integrity of natural ecosystems where these plants have become established.

Cheatgrass, scientifically known as Bromus tectorum, is an aggressive, invasive annual grass native to Eurasia. It has spread extensively throughout North America, particularly in the western United States, where it has become a major ecological threat. Cheatgrass is notorious for its ability to dominate landscapes, especially in disturbed areas such as overgrazed rangelands, roadsides, and abandoned fields.

Physical Characteristics:

• Height: Cheatgrass typically grows between 6 inches and 2 feet tall, depending on environmental conditions. The plant forms dense, tufted stands that can cover large areas.

• Leaves: The leaves of Cheatgrass are narrow, flat, and slightly hairy, measuring about 2 to 12 inches in length. They are green in color during the early stages of growth but quickly turn a reddish-brown as the plant matures and dries out. The leaves have a rough texture due to the presence of small hairs.

• Flowers: Cheatgrass produces small, slender flower spikes that emerge from the top of the stems. These spikes are composed of multiple spikelets, each containing several florets. The flower spikes are initially green but turn purplish, and eventually brown as the plant matures. The awns, or bristle-like appendages attached to the spikelets, are one of the plant's most distinctive features, giving the inflorescence a feathery appearance.

• Stem: The stems of Cheatgrass are thin, erect, and slightly hairy. They are typically green in the early stages but turn brown and brittle as the plant dries out.

• Roots: Cheatgrass has a shallow root system that allows it to establish quickly in disturbed soils. The roots are fibrous and spread out horizontally just beneath the soil surface.

Growth and Spread:

Cheatgrass is an annual plant, completing its life cycle within a single growing season. It germinates early in the spring or fall, often before native grasses and other vegetation have a chance to emerge. This early growth gives Cheatgrass a competitive advantage, allowing it to dominate landscapes where it becomes established. As the plant matures, it dries out and becomes highly flammable, significantly increasing the risk of wildfires.

One of the most concerning aspects of Cheatgrass is its ability to produce a large number of seeds, which are easily dispersed by wind, water, and animals. These seeds can remain viable in the soil for several years, contributing to the persistence and spread of the species. After a fire, Cheatgrass is often one of the first plants to reestablish, creating a vicious cycle of fire and reinvasion that further degrades the ecosystem.

Ecological Impact:

Cheatgrass poses a significant threat to native ecosystems, particularly in arid and semi-arid regions. Its ability to outcompete native vegetation reduces biodiversity and alters habitat structure, impacting wildlife that depends on native plants for food and shelter. Moreover, its tendency to create highly flammable fuel beds increases the frequency and intensity of wildfires, which can further devastate native plant communities and alter the natural fire regimes.

Control Methods:

Controlling Cheatgrass is challenging due to its aggressive growth and prolific seed production. Effective management often requires a combination of strategies, including:

• Mechanical Control: Mowing or grazing can reduce seed production if done before the plant sets seed. However, timing is critical, as cutting too early or too late may not prevent seed dispersal.

• Herbicide Application: Pre-emergent herbicides can be effective in reducing Cheatgrass seed germination, while post-emergent herbicides may be used to kill existing plants. Herbicide treatments are often combined with reseeding efforts to promote the growth of native or more desirable vegetation.

• Prescribed Burning: In some cases, controlled burns can help reduce Cheatgrass seed banks and give native plants a competitive advantage. However, this method must be used with caution, as it can also promote further Cheatgrass invasion if not carefully managed.

• Reseeding: Restoring native vegetation through reseeding can help outcompete Cheatgrass over time, particularly in areas where the soil has been disturbed.

In summary, Cheatgrass (Bromus tectorum) is a highly invasive and ecologically disruptive plant that poses significant challenges to land managers. Its ability to alter fire regimes and outcompete native vegetation makes it one of the most problematic invasive species in North America. Effective control and management are essential to protect the integrity of affected ecosystems.

Smooth Brome (Bromus inermis)

Smooth Brome is a perennial grass that forms dense monocultures, displacing native species in grasslands and riparian areas. This invasive grass alters habitats and reduces the availability of resources for native wildlife.

Control Methods: Management strategies include mechanical removal, prescribed fire. Restoration may involve reseeding native grasses and forbs after Smooth Brome removal.

Johnson Grass (Sorghum halepense)

Johnson Grass is a fast-growing perennial grass that invades wetlands, riverbanks, and disturbed areas. It spreads through both seeds and rhizomes, creating dense stands that outcompete native plants and alter soil conditions.

Control Methods: Johnson Grass can be controlled through a combination of mowing, mechanical removal. Long-term control often requires persistent efforts due to its aggressive nature.

Weeping Lovegrass (Eragrostis curvula)

Weeping Lovegrass was introduced for erosion control but has become invasive in many areas of the Gila Wilderness. It forms dense, competitive stands that suppress native grasses and forbs, reducing habitat quality.

Control Methods: Effective control includes prescribed burning and mowing and mechanical removal. Repeated treatments may be necessary to prevent regrowth.

Dandelion (Taraxacum officinale)

Dandelion is a well-known invasive species that thrives in disturbed areas. While often considered a simple weed, Dandelion can outcompete native plants, particularly in meadows and grasslands. Its deep taproot makes it difficult to eradicate once established.

Control Methods: Control typically involves mechanical removal, ensuring the entire taproot is removed.

Nettles (Urtica dioica)

Nettles, particularly Stinging Nettles, are invasive in disturbed soils and along waterways. While they have some medicinal and culinary uses, their aggressive nature allows them to form dense stands that outcompete native vegetation.

Control Methods: Nettles can be controlled through regular mowing, mechanical removal and improving soil health to support native plant growth.

The Impact of Invasive Species

The invasion of non-native species such as Bull Thistle, Horehound, Horseweed, Mullein, Prickly Lettuce, White and Yellow Sweet Clover, Cheatgrass, Smooth Brome, Johnson Grass, Weeping Lovegrass, Dandelion, Nettles, and Yellow Salsify presents significant challenges to the Gila Wilderness. These invasive plants reduce biodiversity, alter soil and water conditions, and increase the frequency and intensity of wildfires, ultimately threatening the ecological integrity of this unique wilderness area.

What You Can Do to Help

Preventing the spread of invasive species requires collective action. Here’s how you can contribute:

• Clean Your Gear: Before entering and leaving the wilderness, clean your boots, clothing, and equipment to prevent the spread of invasive seeds.
• Stay on Designated Trails: Stick to established trails to minimize disturbance to native vegetation and reduce the spread of invasive plants.
• Report Sightings: If you encounter invasive species, report them to local land management agencies. Early detection and rapid response are key to controlling their spread.
• Volunteer: Join local conservation groups in efforts to remove invasive species and restore native habitats in the Gila Wilderness.