Russian olive is a beautiful shrub, but in North America it’s declared unwelcome! This invasive shrub tends to out-compete native plants. In time, entire ecosystems are altered forever. So what makes Russian olive invasive? It hurts the environment!
Russian olive does not displace native vegetation in a single way: it changes the soil, the light, the seed supply and simply outlasts hard weather. Here is how each mechanism works and what it costs the plants around it.
| Mechanism | How it works | Consequence for native plants |
|---|---|---|
| Nitrogen fixation in the roots | A bacterial partner on its wide-ranging roots captures nitrogen and feeds it to the shrub | Soil nutrient balance is altered, and nearby water bodies gain nutrients that favour smothering algae |
| Dense shading underbrush | Seedlings start in the part shade of sparse native canopies, then thicken into impenetrable growth | Native seeds lack the light, water and nutrients they need to sprout and grow |
| Seed dispersal by birds and animals | Berries are eaten and the seeds expelled near and far, germinating early and growing fast | A single fruit-bearing shrub can colonise vast distances away from the parent plant |
| Sheer resilience | Hardy to -40°F (-40°C), drought-tolerant, heat-tolerant and vigorous when cut down | After a severe frost or dry spell it recovers far faster than the natives it replaces |
Taken together, these four traits explain why the flora of an entire area can be replaced within a couple of decades.
Local fauna and flora are affected by Russian olive as it spreads. This fast-growing plant crowds vegetation out and native plants have trouble germinating, growing, and spreading their own seeds.
Whenever a particularly severe frost spell or dry spell kills native plants off, this hardy and drought-resistant plant bounces back much faster.
Russian olive tends to alter nitrogen reserves in the soil, fixating it in the roots and wood. This reduces the amounts of nutrients available for other plants who often can’t compete with the newcomer.
It does this by latching a special bacteria to its wide-ranging root system: Actinobacteria frankia. This bacteria captures nitrogen and makes it available to the shrub. It does this so effectively that the amount of nutrients in the soil is altered. Even nearby bodies of water are impacted, and the changes create a favorable environment for water flora-smothering algae.
Russian olive has been shown to outgrow and crowd out native willow, black cottonwood, poplar, elm, and even other invasive species such as saltcedar (also called tamarisk) and more.
In most cases, Russian olive grows dense and lush and keeps other seeds from germinating under it. Since the canopy of native species are more sparse and let the sunlight through, the following cycle develops:
Native trees are only left with perilous and unstable places to germinate like riverbanks and temporary islands within the riverflow.
Within a couple decades, the flora of an entire area can be replaced.
Russian olive is hardy down to -40°F (-40°C)! It also survives periods of drought and warm to hot temperatures too. It is an extremely vigorous tree that doesn’t have any natural competitors.
To sum it up, Russian olive:
Additionally, Russian olive berries are prized by many bird species who eat them throughout the winter. Birds then expel the seeds near and far, and these germinate early and grow fast. One single fruit-bearing shrub can thus spread over vast distances.
