Understanding Fungal-Dominant vs Bacterial-Dominant Soil Ecosystems: Implications for Landscape Specification

Soil biology underpins every plant choice and strategy in land management, both in agricultural contexts and urban landscape design. One of the most influential dynamics within soil ecosystems is the balance between fungal and bacterial life.

For landscape specifiers, understanding how this balance affects nutrient cycling, plant longevity, and maintenance requirements can help guide both species selection and soil treatment strategies.

Fungal vs Bacterial Soils: What’s the Difference?

Bacterial-Dominant Soils

• Characteristic of early successional systems (e.g. native grasslands, lawns, annual beds, disturbed urban soils).
• Rapidly decompose fresh, nitrogen-rich organic matter like grass clippings, herbaceous material or composted manure.
• Release quick-acting nutrients, especially ammonium nitrogen, useful for fast-growing, shallow-rooted species.
• Support opportunistic species—but often require frequent inputs and intervention.
• Essentially, bacterial dominant soil systems can be thought of as a bonfire: lots of activity happening right now with little consideration for future resources.

Fungal-Dominant Soils

• Found in mature ecosystems like shrublands and forests.
• Break down woody, carbon-rich material such as logs, bark and dry leaf litter.
• Foster slow-release, stable nutrient cycling, particularly in nitrate and phosphorus forms.
• Essential for deep-rooted, perennial species (e.g. native trees, shrubs, and strappy plants) that depend on long-term resilience.
• Essentially, fungal dominant soil systems are like cooking with hot coals: they burn low and slow, with a stable and reliable stockpile to work with over a long period.

Why Landscape Systems Need Both—But with a Fungal Backbone

In an ideal landscape ecosystem, both bacteria and fungi play essential roles.

• Bacteria provide fast nutrient availability, ideal for establishment phases and high-turnover areas.
• Fungi, however, offer nutrient stability, soil structure, and resilience.
• A fungal backbone—a dominant, but not exclusive, fungal presence—helps reduce plant mortality, cut maintenance inputs, and buffer against environmental stress (e.g. drought, nutrient leaching, pest pressure).

Implications for Urban and Public Landscapes

• Woody mulches and reduced disturbance favour fungi, improving plant health and soil structure long-term. (Chop and drop pruning and mulching strategies are ideal but may be not meet ornamental standards on high profile projects)
• Disturbed or compacted soils (common in urban works) often become bacteria-skewed—leading to more weed pressure, root pathogens, and greater need for fertilisers. (This often happens through constant hand weeding, foot traffic, or unsuitable plant guilds that cannot hold their position strongly)
• Establishing a fungal base early in a project (via fungal-dominant composts, woody inputs, and compatible plant species) allows for:
  • Lower irrigation and fertilisation needs
  • Reduced pest and disease outbreaks
  • Enhanced plant longevity and reduced replacement costs

Nitrogen Fixers as Functional Bridge Plants

Species like Hardenbergia violacea and Acacia spp. are not just beautiful native additions—they also fix atmospheric nitrogen, feeding soil microbes and aiding early fungal establishment.

• Hardenbergia, a mycorrhizal climber, groundcover and sometimes shrubby hedge, forms part of the transition phase from early successional bacterial systems to more stable fungal-dominant systems.
• Acacias, often pioneer trees or shrubs, actively improve soil fertility, particularly in degraded or low-nitrogen soils, while encouraging the fungal networks that later-stage trees and shrubs depend upon.

These plants serve as ecological scaffolds, setting the stage for broader plant diversity and a self-regulating soil food web.

The nitrogen held in their tissues, particularly thicker woody stems, is released much more slowly than is released through manure, compost and green grass clippings. Nitrogen fixers perform this function much more reliably when resources are scarce, as opposed to in fertile positions.

Key Design Recommendations for Specifiers

Conclusion

A resilient, low-input landscape does not rely solely on plants—it begins with soil life.

While bac-terial activity drives quick change, fungal systems create lasting structure and function. For long-term performance, a fungal-dominant—but biologically diverse—soil ecology is the foun-dation of healthier plants, lower maintenance, and greater ecological stability.

Landscape architects and designers are able to book a free one-on-one consultation with me to learn more about the concept of succession from unstable soil systems to stable ones. Ozbreed are committed to improving urban ecological conditions around Australia, so please reach out to me (Daniel Fuller, Ozbreed’s horticulture expert) to learn more.