VINES AND LIANAS

Rainforest Vines and Lianas

The tropical rainforest is a dense and complex ecosystem where competition for light is fierce. To overcome this challenge, many plants have evolved to climb rather than grow upright, using trees as structural support. Vines and lianas—woody climbing plants—are abundant in rainforests and play a crucial role in the forest’s ecology. There are over 2,500 species of vines from approximately 90 plant families, ranging from small creeping plants to massive, rope-like lianas that span the forest canopy.

What Are Lianas?

Lianas are a type of woody vine that begin life as small, self-supporting shrubs on the forest floor. As they grow, they rely on surrounding trees to reach the light-rich environment of the upper canopy. By climbing instead of investing in thick, self-supporting trunks, lianas allocate more energy to rapid growth, leaf production, and extensive root systems.

Some lianas, such as rattan, are economically valuable. Rattan is widely used in furniture, rope-making, and handicrafts. It also produces large, edible fruits that are a favorite of many primates.

How Lianas Climb

Lianas use various adaptations to ascend toward the canopy:

• Stem twining: Some lianas wrap their flexible stems around tree trunks and branches.
• Tendrils: These specialized appendages emerge from stems, leaves, or branches, allowing the liana to latch onto supports.
• Thorns and spikes: Some lianas have hook-like structures that anchor them to host trees.
• Adhesive roots: Certain species develop small, sticky roots that attach directly to tree bark.

Once lianas reach the canopy, they spread horizontally, linking multiple trees together. In some forests, liana leaves make up nearly 40 percent of total canopy foliage.

Other Climbing Plants in the Rainforest

Hemiepiphytes

Unlike true lianas, hemiepiphytes begin their lives as epiphytes—plants that grow on other trees without taking nutrients from them. These plants eventually send roots downward to establish contact with the soil. Strangler figs are a well-known example of hemiepiphytes. These plants start in the canopy and slowly envelop their host tree, often outcompeting and eventually killing it.

Creepers

Creepers are another group of climbing plants that begin as small shrubs on the forest floor. They grow toward tree trunks and climb upward, using flattened, triangular leaves to cling to surfaces. As they reach higher into the canopy, their leaf structure changes, spreading outward to capture more sunlight.

The Impact of Lianas on Rainforest Trees

Although lianas contribute to rainforest biodiversity, they also pose challenges for trees. Since they do not need to invest in thick trunks for support, lianas can outcompete trees by growing rapidly and monopolizing light, space, and nutrients.

Some trees have evolved mechanisms to counteract liana growth:

• Self-pruning fronds: Palms and tree ferns shed fronds regularly to prevent lianas from taking hold.
• Branch shedding: Some trees intentionally drop branches to rid themselves of climbing plants.
• Canopy movement: Research suggests that trees swaying independently of their neighbors may break liana connections.

Some lianas have adapted to these countermeasures by developing flexible, coiling stems that absorb movement without breaking.

The Ecological Role of Lianas

Lianas play several crucial roles in rainforest ecosystems:

1. Providing Habitat for Animals

The thick networks of lianas create canopy bridges, allowing arboreal animals such as monkeys, sloths, and tree frogs to move between trees without descending to the forest floor, where predators lurk.

2. Suppressing Tree Regeneration

Lianas can inhibit tree growth by competing for sunlight and nutrients. This is especially pronounced in disturbed or regenerating forests, where lianas proliferate due to increased light availability.

3. Contributing to Carbon Sequestration

Despite their competitive nature, lianas store large amounts of carbon due to their rapid growth rates and extensive biomass, making them an important factor in rainforest carbon dynamics.

Research on Lianas

Recent studies have provided new insights into how lianas thrive in the rainforest. In a study conducted across 69 tropical forests, researchers found that liana abundance is negatively correlated with precipitation and positively correlated with seasonal variation. This finding contrasts with most other plant groups, which thrive in consistently wet environments.

Biologist Stefan Schnitzer of the University of Wisconsin-Milwaukee hypothesizes that lianas have deep roots and highly efficient vascular systems, allowing them to outcompete trees during seasonal droughts. In one study conducted in Panama, Schnitzer found that lianas grew seven times faster than trees during the dry season but only twice as fast during the wet season. This advantage helps explain their dominance in seasonal rainforests.

Another study by Schnitzer and his colleagues revealed that lianas significantly reduce tree sapling growth in disturbed and secondary forests. By competing for light, nutrients, and physical space, lianas slow forest regeneration and may influence long-term forest composition.

Conclusion

Rainforest vines and lianas are an essential yet often overlooked component of tropical forests. While they can suppress tree growth, they also provide habitat, enhance biodiversity, and play a role in carbon sequestration. As scientists continue to study their ecological impact, it becomes increasingly clear that these climbing plants are key players in the complex web of rainforest life.