Merging plant sociology with sustainable design to transform urban stormwater management
Stormwater Management
Plant Communities
Pollution Control
Urban Resilience
In the heart of Nanchang, a city known for its vibrant urban life and challenging red soil, a quiet revolution is taking root.
This revolution merges the ancient principles of plant sociology with the modern urgency of sustainable design, all within the confines of a rain garden. Phytocoenosis, a concept describing a specific, interacting plant community, is no longer just a subject for ecologists. It has become a powerful tool for urban planners, transforming simple green spaces into sophisticated, living systems that manage stormwater, combat pollution, and enhance biodiversity 2 .
This article explores how scientists in Nanchang are configuring these complex plant alliances to create rain gardens that are not only beautiful but are also highly engineered solutions to urban environmental challenges.
A stable, natural plant community where species coexist and interact through competition and other ecological processes.
A shallow, landscaped depression designed to capture and filter stormwater runoff from impervious surfaces.
To understand the innovation in Nanchang's landscapes, one must first grasp the concept of phytocoenosis. In essence, a phytocoenosis is a stable, natural plant community where species coexist and interact through competition and other ecological processes 2 .
Think of a mature, undisturbed forest where specific trees, shrubs, and groundcover plants are always found together—this is a phytocoenosis. Scientists study these communities through a discipline called phytosociology, which classifies them into a hierarchical system, much like how biologists classify species 5 8 .
The core method involves taking a relevé—a detailed record of all plant species in a defined plot, noting their abundance and the vertical layers they occupy, alongside data on geography and soil conditions 2 8 .
A rain garden is a shallow, landscaped depression designed to capture and filter stormwater runoff from impervious surfaces like roofs, roads, and parking lots 3 6 .
Unlike traditional gardens, they are engineered ecosystems. They use a special soil medium and deep-rooted native plants to:
In doing so, they mimic natural hydrology that has been disrupted by urbanization.
Nanchang presents a unique set of challenges:
Simply building a rain garden with random plants is not enough. The question is: which specific combination of plants will thrive in these conditions while maximizing the garden's performance?
This is where phytocoenosis configuration comes in. By designing a rain garden based on the principles of a stable, natural plant community, engineers can create a system that is more resilient, self-sustaining, and effective at its job.
Intense, uneven rainfall
Red soil with low permeability
A pivotal experiment in this field was a full-scale rain garden constructed on the campus of Nanchang University in 2016 1 .
The researchers' goal was to create a rain garden that could thrive in Nanchang's red soil area. Their approach was meticulous 1 :
The garden was designed to collect runoff from a 1,533 m² area of concrete pavement.
Since native red soil was not conducive to infiltration, the team created a special blended matrix for the garden's filter media layer. The blend was 60% laterite (a type of red soil), 30% sand, and 10% compost. This mixture achieved a permeability coefficient of 1.48 × 10⁻⁵ m/s, a crucial improvement over the native soil.
Using the water balance method, the garden was sized to capture 85% of the annual rainfall, with a design rainfall depth of 38.9 mm.
From September 2016 to January 2018, the team collected water samples from the inlet and outlet during rainfall events. They tested these samples for key pollutants, providing nearly two years of performance data.
The field data demonstrated outstanding performance. The rain garden successfully captured 78.9% of the annual rainfall volume, effectively mitigating urban flooding 1 .
Most impressively, it acted as a powerful filter. The table below shows the mean load removal rates for various pollutants, which far exceed the requirements of Nanchang's Sponge City technical guidelines 1 .
| Pollutant | Mean Load Removal | Visualization |
|---|---|---|
| Total Suspended Solids (TSS) | 92.5% |
|
| Ammonia Nitrogen (NH₃-N) | 85.3% |
|
| Total Phosphorus (TP) | 82.9% |
|
| Total Nitrogen (TN) | 80.5% |
|
| Chemical Oxygen Demand (COD) | 79.8% |
|
| Nitrate Nitrogen (NO₃-N) | 77.5% |
|
This high level of pollutant removal can be attributed to the well-designed system. The custom soil matrix provided a physical filter and a medium for microbial activity, while the plants' roots facilitated absorption and biodegradation. The garden transformed from a simple depression into a functioning phytocoenosis, where plants, soil, and microbes worked in concert to purify water 1 .
Designing an effective rain garden, especially in a challenging environment like Nanchang, requires more than just plants and soil.
A specially engineered blend of soils and amendments designed to overcome native soil limitations and achieve the required permeability and nutrient levels 1 .
A system that assigns plants numerical values based on their ecological preferences for factors like moisture, soil reaction, and nutrients 8 .
Measuring the rate at which water moves through the soil medium. This is a critical parameter for ensuring the garden functions as a stormwater infiltration device 1 .
Comprehensive study of plant interactions, nutrient cycles, and ecosystem functions to optimize rain garden performance.
The principles of phytocoenosis configuration are being applied beyond individual rain gardens to enhance Nanchang's entire urban fabric. Research has expanded to understand how green spaces function along the city's urban-to-rural gradient 7 .
Studies now analyze the ecological stoichiometry—the balance of carbon (C), nitrogen (N), and phosphorus (P)—in the soils of different green spaces. For instance, research has found that urban areas often have lower soil C:N ratios and higher phosphorus levels due to human activity, disrupting nutrient cycles 7 .
Carbon
Lower in urban areasNitrogen
Variable levelsPhosphorus
Higher in urban areasThis knowledge is crucial for configuring plant communities that can rebalance these nutrients. A designer might select species with specific leaf litter qualities to increase soil organic carbon in depleted urban parks.
Furthermore, the selection of native versus non-native species is a key consideration. Studies in other temperate regions have shown a tendency to use non-native species in urban parks to increase species richness 4 .
However, there is a growing push for using native species, which are often better adapted to local stressors and provide more support for local biodiversity 4 . The most successful designs will likely strike a balance, using a core of native species to ensure resilience while incorporating carefully vetted non-natives for specific functions or aesthetic value.
The work in Nanchang is a powerful demonstration that the solutions to our most pressing urban environmental problems are not always found in high-tech, grey infrastructure.
By looking to the inherent wisdom of natural plant communities—the science of phytocoenosis—we can design landscapes that are both functional and beautiful. The city's rain gardens are more than just patches of greenery; they are carefully calibrated, living machines that filter water, prevent floods, and provide habitat.
As Nanchang and cities worldwide continue to grow, this thoughtful alliance between ecology and engineering will be essential for building sustainable, resilient, and livable urban environments for the future.