In the world of ecology, plant species are often categorized based on their behavior and impact on the environment. Two common terms that can be confusing are "invasive" and "aggressive" plant species. While they may seem similar, they refer to different types of plant behaviors. Understanding the difference is important for gardeners, environmentalists, and anyone concerned with plant ecology. It is especially important in deciding what plants to add to to the local landscape. Here's a detailed breakdown of the two:

Invasive Plant Species

An invasive plant species is one that is non-native to a specific ecosystem and, when introduced, causes harm to the environment, economy, or human health. Invasive species typically spread rapidly and aggressively, outcompeting local or native plant species. Another consideration is the ability of a non-native species to be able to hybridize a native species.

Invasive plant species to Florida can be found on the Florida Invasive Species Council Website.

Plants are categorized into either non-invasive, Category I Invasive Species, and Category II Invasive Species. Non-invasive is self-explanatory.

Category I plants are defined as "altering native plant communities by displacing native species, changing community structures or ecological functions, or hybridizing with natives."

Category II plants are defined as those that "have increased in abundance or frequency but have not yet altered Florida plant communities to the extent shown by Category I species. These species may become Category I if ecological damage is demonstrated."

Key characteristics of invasive plants:

• Non-native: They do not naturally occur in the ecosystem to which they've been introduced.

• Rapid spread: They reproduce quickly, often with a high seed output or vegetative reproduction.

• Ecological harm: They disrupt local ecosystems by crowding out native species, altering soil composition, water availability, and habitat structures. This can lead to a decline in biodiversity.

• Economic and health impact: Invasive plants can also affect agriculture, forestry, and human health. For example, they may become agricultural pests or introduce allergens.

• Ability to hybridize with native species: There are many non-native species that can hybridize with native species through cross pollination. The seeds produced through cross pollination will result in a hybrid plant which can eventually lose characteristics of the parent plants.

  
  

Examples:

• Air Potato Vine - a non-native vining plant that has rapid growth and spread. Due to it's growth characteristics, it can crowd out native species. Removal of this species is not easy by both mechanical or chemical methods.

• Brazilian Pepper Trees - a non-native large shrub that was originally planted for its aggressive growth habit in order to establish hedges along roadways and other areas. It spreads easily through seed and is difficult to remove. The costs of removing this plant has been deemed expensive enough to be determined a high enough economic impact for it to be invasive.

• Mexican Petunia - a non-native aggressive purple flowering plant that has become popular in Florida because it is easy to grow and flowers all year. It is difficult to remove and can hybridize with native wild petunias.

  
  

Aggressive Plant Species

An aggressive plant species, on the other hand, refers to any plant that grows and spreads rapidly, often outcompeting others for resources like sunlight, water, and nutrients. However, aggressive plants are not necessarily non-native. They may be native to the region, but their behavior can still cause problems for other plants.

Key characteristics of aggressive plants:

• Can be native or non-native: Unlike invasive species, aggressive plants may or may not be foreign to the region.

• Rapid growth: These plants grow quickly and can dominate a particular area, potentially reducing the diversity of other plant species.

• Competition for resources: They are simply fast growers that can overwhelm other plants in the immediate vicinity. They may not cause the large-scale environmental harm that invasive species do, but they can still reduce the variety of plant life in a particular area.

  
  

Examples:

• Sunshine mimosa - a FL native groundcover that can grow rapidly and establish itself outside of the original area it was planted in.

• Tropical sage - a FL native wildflower that can aggressively seeds itself wherever seeds are spread.

  
  

Key Differences

1. Origin:

   • Invasive: Always non-native.

   • Aggressive: Can be either native or non-native.

2. Impact:

   • Invasive: Causes significant ecological harm, reduces biodiversity, and often leads to long-term changes in the ecosystem.

   • Aggressive: Primarily competes for space and resources but may not lead to the same level of ecosystem disruption.

3. Spread:

   • Invasive: Has the potential to spread far beyond the area where it was introduced, often altering entire ecosystems.

   • Aggressive: Usually spreads within a local area and competes with other species, but may not have the same widespread ecological impact.

4. Control and Management:

   • Invasive: Often requires active management or eradication because of the severe impact on the ecosystem.

   • Aggressive: Can sometimes be managed through pruning or regular maintenance, especially in garden settings, without drastic measures.

5. Ability of a Non-Native to Hybridize with Native Plants

   
   

Conclusion

Understanding the distinction between invasive and aggressive plant species helps in managing landscapes and conserving native ecosystems. Invasive plants pose a serious threat to biodiversity and require significant intervention, whereas aggressive plants, although competitive, don't always warrant the same level of concern—unless they start displacing native flora or disrupting important local habitats.

Being mindful of both types of species is crucial for maintaining healthy and balanced ecosystems, whether you're tending to your garden or working on a larger conservation project.

Let’s work together to protect our native flora and fauna by recognizing and managing both invasive and aggressive plant species!