Rethinking the native-invader paradigm in Turkish ecosystems
Turkey is home to approximately 12,000 plant species, with about 1.5% estimated to be alien species 8 .
Imagine a tranquil Turkish landscape where vibrant wildflowers dance in the breeze alongside majestic ancient trees. This picturesque scene embodies ecological harmony—until certain plants begin behaving badly, elbowing out their neighbors and disrupting the delicate balance. For decades, scientists and conservationists have sounded alarms about non-native invasive species that hitch rides across continents through human activities. But what if the threat isn't always foreign? What if some native species, empowered by environmental changes, begin exhibiting the same destructive behaviors as their non-native counterparts?
This question forms the core of a fascinating scientific investigation in Turkey, where researchers have made a startling discovery: some native plants can pose similar ecological risks as notorious invasive species from other continents. This finding challenges long-held assumptions in conservation biology and forces us to rethink what it means to be "invasive" in an era of rapid global change.
Before delving into the Turkish case study, let's clarify some key terminology:
Species that have evolved naturally in a particular region over thousands of years, developing complex relationships with other elements of the ecosystem.
Example: Turkish pine (Pinus brutia) and Anatolian black pine (Pinus nigra subsp. pallasiana) 5
Plants or animals living outside their natural range due to human introduction.
Example: Domestic cows (Bos taurus) and bell peppers (Capsicum annuum) in Turkey 5
Non-native organisms that cause harm to the environment, economy, or human health.
Example: Burmese python in Florida's Everglades and kudzu vine in the southern United States 5
Organisms whose current ranges are growing or shifting over time, which can include both native and non-native species.
Example: Nine-banded armadillos expanding northward from Mexico into the United States 5
The conventional wisdom has long held that non-native species are inherently more dangerous than native ones because they lack natural predators and controls in their new environments. But as we'll see, this distinction may be less clear-cut than previously believed.
Turkey represents a perfect natural laboratory for studying invasion biology. With approximately 12,000 plant species (of which about 1.5% are estimated to be alien), Turkey sits at the crossroads of Europe and Asia, featuring diverse climates and ecosystems 8 . This biodiversity hotspot faces increasing pressure from both introduced species and changing environmental conditions.
A team of Turkish researchers designed a pioneering study to answer a provocative question: Do non-native and dominant native species carry a similar risk of invasiveness? Their investigation, published in 2022, directly compared the invasive potential of five non-native and five native plant species known to be problematic in various parts of the world 1 3 .
The researchers selected ten plant species with notorious reputations:
| Species Name | Common Name | Origin Status | Native Range |
|---|---|---|---|
| Ailanthus altissima | Tree of heaven | Non-native | Asia |
| Cuscuta campestris | Field dodder | Non-native | North America |
| Phytolacca americana | American pokeweed | Non-native | North America |
| Robinia pseudoacacia | Black locust | Non-native | North America |
| Sicyos angulatus | Bur cucumber | Non-native | North America |
| Cirsium arvense | Canadian thistle | Native | Europe/Asia |
| Hedera helix | English ivy | Native | Europe/Turkey |
| Onopordum acanthium | Scotch thistle | Native | Europe/Turkey |
| Phragmites australis | Common reed | Native | Cosmopolitan |
| Sorghum halepense | Johnson grass | Native | Mediterranean |
To evaluate these species objectively, the researchers employed a standardized risk assessment protocol—the Australian Weed Risk Assessment (WRA) system, specially adapted for Turkey's geographical and climatic conditions 1 . This sophisticated tool functions like an ecological personality test, examining multiple facets of each species' biology and behavior.
The WRA evaluates species through 49 detailed questions across several categories:
Where did the species originate? How many countries has it invaded? How wide is its climatic tolerance?
How does it reproduce? How fast does it grow? What makes it resilient?
What environmental or economic harm does it cause? How difficult and costly is it to control?
How well does Turkish climate match species' needs? How might climate change affect its spread?
| Assessment Category | Sample Questions | Purpose |
|---|---|---|
| Biogeography & History | How many countries has the species invaded? What climate types does it tolerate? | Evaluate invasion history and environmental flexibility |
| Biology & Ecology | How does the species reproduce? How long until maturity? How many offspring does it produce? | Understand reproductive strategy and dispersal ability |
| Impact & Management | What ecosystem changes does it cause? How does it affect agriculture? How difficult is control? | Assess ecological and economic consequences |
| Climate Compatibility | How well does Turkish climate match species' needs? How might climate change affect its spread? | Predict future expansion potential |
Each response contributes to a cumulative risk score that places species into categories: low risk, intermediate risk, or high risk. This systematic approach allows researchers to compare species objectively, regardless of their origin .
The findings challenged conventional expectations. All ten species evaluated—both native and non-native—received high-risk scores 1 3 . This alone was remarkable, but the results revealed even more interesting patterns:
Among non-native species, Robinia pseudoacacia (black locust) scored highest, followed by Cuscuta campestris, Phytolacca americana, Sicyos angulatus, and Ailanthus altissima.
Among native species, Phragmites australis (common reed) ranked highest, followed by Sorghum halepense, Cirsium arvense, Onopordum acanthium, and Hedera helix.
When researchers analyzed the risk scores using statistical ordination techniques, they found significant similarities between invasive non-natives and "expanding" native species 1 4 . The traits that made plants problematic—rapid growth, efficient reproduction, ecosystem alteration, and resistance to control measures—appeared regardless of origin.
| Species | Origin | Risk Score | Risk Category | Rank Within Group |
|---|---|---|---|---|
| Robinia pseudoacacia | Non-native | High | Invasive | 1 |
| Cuscuta campestris | Non-native | High | Invasive | 2 |
| Phytolacca americana | Non-native | High | Invasive | 3 |
| Sicyos angulatus | Non-native | High | Invasive | 4 |
| Ailanthus altissima | Non-native | High | Invasive | 5 |
| Phragmites australis | Native | High | Expanding | 1 |
| Sorghum halepense | Native | High | Expanding | 2 |
| Cirsium arvense | Native | High | Expanding | 3 |
| Onopordum acanthium | Native | High | Expanding | 4 |
| Hedera helix | Native | High | Expanding | 5 |
These results suggest that the biological traits of species—not their geographic origin—may be the best predictor of ecological impact 1 . Under the right conditions, native species can exhibit the same problematic behaviors typically associated with invasive non-natives.
This research raises a crucial question: Why would native species suddenly become problematic in ecosystems where they've existed for millennia? The answer appears to lie in environmental disruption that creates opportunities for certain species to dominate.
Global changes—including climate change, habitat fragmentation, pollution, and altered disturbance regimes—can fundamentally shift the competitive balance in ecosystems 1 . Native species with traits that allow them to capitalize on these changes may expand beyond their historical ranges or densities.
For example, a native plant might have evolved to thrive after natural wildfires. When human activities increase fire frequency or intensity, that species may suddenly have an unfair advantage over others. Similarly, nitrogen pollution from agriculture and industry can favor native plants that thrive in nutrient-rich soils, allowing them to outcompete neighbors adapted to lower nutrient conditions.
This phenomenon isn't limited to Turkey. In North America, native species like the mountain pine beetle have expanded their populations dramatically due to climate change and forest management practices, causing widespread tree mortality 5 . In Washington state, native wild ginger (Asarum caudatum) demonstrates better adaptation to local dry summer conditions than its European counterpart 6 .
The Turkish study carries significant implications for how we approach conservation and ecosystem management:
Conservation policies traditionally focus on eliminating non-native species while presuming native species are beneficial. This research suggests we should prioritize management based on ecological impact rather than geographic origin 1 .
The researchers proposed classifying high-risk native species as "expanding" rather than invasive, acknowledging that while they're native, they're behaving in ecologically disruptive ways 3 .
Risk assessment tools like the adapted WRA can help identify potentially problematic native species before they cause significant harm, allowing for proactive management .
Effective conservation requires addressing the underlying environmental changes that enable species—both native and non-native—to become problems, rather than simply focusing on the species themselves.
This perspective aligns with emerging views in ecology that emphasize functional traits over evolutionary history when evaluating species' roles in ecosystems. As one study noted, "dominant species with highly negative environmental and socioeconomic impacts in their habitats should be included in priority lists for management measures irrespective of their origin" 1 .
The field of invasion biology continues to evolve, developing more sophisticated tools to predict and manage problematic species. The second-generation Terrestrial Plant Species Invasiveness Screening Kit (TPS-ISK) builds upon the WRA approach used in the Turkish study, offering enhanced capabilities for screening terrestrial plants under current and future climate scenarios .
These advanced assessment tools consider how climate change might alter invasion risks, recognizing that species currently confined to certain ranges may expand as temperatures shift. This is particularly relevant for Turkey, which encompasses diverse climatic zones from Mediterranean to temperate regions.
Future research directions include:
The Turkish case study on native and non-native plant species offers a nuanced perspective on invasion biology. It reveals that the ecological lines between "native" and "invasive" are more blurred than traditionally thought—that under the right conditions, even species that have called a region home for millennia can become disruptive forces.
This doesn't mean we should abandon concerns about non-native species, which remain a significant threat to global biodiversity. Rather, it suggests we need a more sophisticated and context-dependent approach to conservation—one that recognizes that both native and non-native species can cause ecological harm when environmental conditions change.
As we continue to reshape our planet through climate change, habitat modification, and species movements, we must develop a more flexible understanding of ecological relationships. The goal isn't to preserve ecosystems in some idealized historical state, but to manage change in ways that maintain ecological function, biodiversity, and the services that ecosystems provide to humanity.
The fascinating research from Turkey reminds us that in ecology, as in life, things are rarely as simple as they first appear. Sometimes, the most dangerous threats come from unexpected places—even from those we consider our neighbors.