Look up in Bwindi Impenetrable Forest and the branches above you are not bare. Every surface — every horizontal branch, every fork in a large tree, every patch of rough bark — is colonised by plants growing on the tree itself rather than in the soil below. These are the epiphytes: plants that use other plants as their physical substrate, drawing their water from rainfall and mist, their nutrients from decomposing organic matter trapped in bark crevices, and their light from whatever reaches them in the forest’s layered canopy.
Epiphytes are one of the defining features of tropical montane forest. In temperate forests, tree branches are largely bare between the growing season. In Bwindi’s evergreen montane forest, there is no bare season — the moisture is constant, the temperatures stable, and the growth opportunities never close. The result is a forest where the trees themselves support entire communities of secondary plants — ferns, mosses, lichens, bromeliads, and orchids — that live their entire lives above the ground without ever contacting the soil. Understanding this vertical dimension of the forest ecosystem transforms how you see the canopy on a gorilla trek.
What is an epiphyte and how do they live
The word epiphyte derives from the Greek epi (upon) and phyton (plant) — a plant upon a plant. Epiphytes are not parasites; they do not draw water or nutrients from the host tree’s vascular tissue. Instead, they colonise the host’s surface and make their own living entirely from what they can capture from the air, rainfall, and the organic debris that accumulates around their roots. This is a genuinely remarkable ecological strategy that requires specific adaptations to the challenges of life without soil.
Water capture is the primary challenge for epiphytes. Unlike terrestrial plants that draw water from the soil through a root system, epiphytes must harvest water from rain, mist, dew, and the runoff that flows along branches and trunks during rainfall events. Many epiphytes have adapted their root systems into specialised structures called velamen — thick, spongy, multi-layered root coverings that absorb water rapidly during rain events and reduce water loss between rains. Orchid roots with velamen have a distinctive silvery-white appearance when dry; they turn green with a visible inner layer when wet.
Nutrient acquisition requires equal ingenuity. The organic debris — dead leaves, insect material, bark fragments — that accumulates in branch forks and bark crevices provides a nutrient source if the epiphyte can grow its roots into these deposits. Some epiphytes actively trap debris by growing basket-like arrangements of leaves that collect falling organic matter from above, creating their own nutrient trap. Lichens begin the colonisation of bare bark by fixing atmospheric nitrogen and weathering mineral nutrients from the rock or bark surface, then die and decompose to provide a thin organic layer for subsequent plant colonisers.
Orchids of Bwindi: the forest’s most diverse epiphyte family
The family Orchidaceae is the largest family of flowering plants on earth, with approximately 28,000 species — and Bwindi Impenetrable Forest harbours a significant representation of this diversity. Uganda as a whole contains over 500 orchid species; Bwindi’s montane forest environment, with its combination of high moisture, stable temperatures, and diverse forest structure, supports a particularly rich orchid community.
Most of Bwindi’s orchids are epiphytic, growing on tree branches and trunks rather than in the soil. They are not typically showy in the way that horticultural orchids are — the wild forest orchids of Bwindi are often small, their flowers subtle and intricate rather than large and dramatic, and their colouration ranges through greens, yellows, whites, and purples that blend with the bark and moss rather than standing out from it. Finding them requires the slow, attentive observation that gorilla trekkers are not always in the mood for after a demanding uphill climb.
Several orchid genera are particularly well represented in Bwindi. Bulbophyllum — the largest genus of orchids globally — includes dozens of species in Bwindi with an enormous range of floral forms. Their flowers are often bizarre by the standards of familiar orchid aesthetics: some have long, thread-like petals, others have fused structures that resemble insects, and many are pollinated by flies attracted to compounds that mimic rotting organic matter. Polystachya is another large and diverse genus at Bwindi, with pseudobulbs and small but intricate yellow or greenish flowers. Angraecoid orchids — including Angraecum species pollinated by hawkmoths attracted to their powerful night fragrance — occur in the forest margins and clearings.
Ferns: the most ancient epiphytes
Ferns are among the most successful epiphytes in montane tropical forests, and Bwindi’s canopy is colonised by dozens of species. They are evolutionarily ancient — ferns diversified long before flowering plants existed, and their basic reproductive strategy using spores rather than seeds has proven durable across hundreds of millions of years of environmental change. The epiphytic ferns of Bwindi have developed specific adaptations to canopy life that distinguish them from terrestrial ferns in the forest understorey.
The platycerium ferns — staghorn ferns — are among the most dramatic. They produce two distinct types of fronds: flat, shield-shaped basal fronds that press against the host tree’s bark and trap organic debris, and pendulous, antler-shaped fertile fronds that bear spores on their undersides. The basal fronds create their own debris trap, decomposing over time to provide nutrients for the plant’s root system. A large, mature platycerium can weigh tens of kilograms and may colonise its host branch for decades.
Drynaria ferns have a similar dual-frond strategy. Nest fronds that are dry and brown cup the base of the plant and trap falling debris; fertile fronds are large, deeply lobed, and distinctly green. The combination creates a self-fertilising system where the plant generates its own nutrient supply independent of the host’s soil. Walking through Bwindi’s forest and seeing large drynaria clusters in the canopy — dark, cup-shaped leaf accumulations draped across branch junctions — is one of the visual signatures of mature montane forest.
Mosses and liverworts: the base layer of the epiphyte community
Before orchids and ferns can colonise bare bark, the surface must first be prepared by pioneering organisms. Mosses and liverworts are the primary colonisers of tree surfaces in Bwindi’s moist environment, covering bark with thick green or gold-green mats that trap moisture, accumulate organic material, and create the substrate conditions that allow more complex epiphytes to establish. The moss coverage on mature trees in the wetter parts of Bwindi is so complete that bark is rarely visible — the tree trunks are entirely sheathed in green.
This moss layer is an ecosystem in itself. Insects live within the moss mats — mites, springtails, beetle larvae, and numerous other invertebrates that feed on the moss itself or on the microfungi and bacteria that live within it. These invertebrates are food for small birds — flycatchers, warblers, sunbirds — that forage through the moss layer systematically, gleaning prey from within the mat rather than from open air. The moss layer thus feeds an entire trophic chain that is invisible from below but active throughout the canopy throughout every daylight hour.
Ecological importance of epiphytes in the forest system
Epiphytes contribute to the forest ecosystem in ways that go beyond their individual plant function. The combined water-holding capacity of epiphyte mats on trees is enormous — a single large tree covered in moss and orchid roots can retain litres of water after rainfall, releasing it slowly through evaporation and stem flow over the following days. This water-retention function moderates stream flow in montane catchments: forests with abundant epiphytes release water more slowly after rains, reducing flood peaks and maintaining dry-season flows more reliably than forests without this epiphyte layer.
The contribution of epiphytes to nutrient cycling is also significant. As epiphyte mats die, decompose, and fall from the canopy, they deliver a steady rain of organic material to the forest floor. This material enriches the forest floor nutrient budget and provides food for the invertebrate communities in the leaf litter that themselves feed the forest floor fauna — including the red-tailed monkeys and small rodents that gorillas occasionally encounter while feeding.
Looking for epiphytes on your gorilla trek
The approach trek to a gorilla family is the best time to observe epiphytes, because the trek covers forest at multiple elevations and across different forest types. The lower slopes — where the trail passes through more disturbed secondary forest — have different epiphyte communities from the older primary forest at higher elevations where the oldest trees carry the most diverse and established epiphyte communities.
Binoculars are the most useful tool for epiphyte observation — many of the most interesting orchid and fern species are at heights that make detail impossible to see with the naked eye. A quick scan of branch surfaces with binoculars during a rest break on the approach trail will almost always reveal orchid pseudobulbs, fern fronds, or moss communities that are invisible when walking. This habit of looking up rather than forward occasionally produces the additional reward of an unexpected bird or primate sighting in the canopy — the forest’s vertical dimension is consistently rewarding for observers who remember to use it.
