How Do Pioneer Species Support Habitat Recovery?

• Small pioneer plant
• Broken-up rock
• Soil layer
• Leaf litter

What you will learn

• Recognise which species are pioneers and what kind of places they live in.
• Describe what pioneers do to help a habitat recover.
• Explain why pioneers do not stay forever.

Before you start

No prior knowledge is needed. You only need to know that a habitat is a place where living things live.

What are pioneer species?

According to the chapter "Pioneer Species" in the Encyclopedia of Ecology, summarised on the University of Illinois research portal, pioneers are the species that first colonize new habitats created by disturbance. The term is usually applied to plants, but microbial and invertebrate pioneers are also sometimes recognized.

The chapter separates two groups. One colonizes sites lacking developed organic soil and starts primary succession. The other starts secondary succession, often from propagules already in the soil.

How do they cope on freshly disturbed ground?

It depends on the site. The same chapter says pioneers of primary succession must cope with unfavorable conditions for establishment. Their growth and distribution are often restricted by the nutrient supply, because soil development is limited.

Pioneers of secondary succession often meet resource-rich environments where competition with existing vegetation is reduced. Some of the fastest-growing plant species are pioneer herbs and shrubs.

• No soil yet: unfavorable conditions
• Soil remains: plenty of resources
• Open space, little competition

How do they help a habitat recover?

They help the place gain soil and nutrients. The Kenai Fjords National Park page on plant succession says organisms from nearby habitats begin to build soil by breaking down exposed bedrock. Once a sufficient substrate has developed, new vegetation can take root.

Alders are another example. The same page says they form a symbiotic relationship with nitrogen-fixing bacteria that live in their root nodules. The bacteria transform atmospheric nitrogen, which plants cannot use, into a plant-available form.

• Alder tree
• Root nodules with bacteria
• Nitrogen from the air
• Nitrogen-rich leaf litter

Nitrogen-rich leaf litter from alders helps create a more fertile soil. The page says that soil will ultimately allow the larger trees of the next stage to supplant the alders.

Why do they not stay forever?

Because light and shade call for two different ways of living. The University of Illinois chapter describes a trade-off between growth in high light and survival in the shade. It limits the habitat range of secondary-succession pioneers and prevents their populations from persisting long after the disturbance has passed.

Kenai Fjords says much the same in another way: species suited to one set of conditions gradually alter their own environment until other species that thrive in the new conditions outcompete them.

• Strong light
• Pioneer sprout growing fast
• Large trees casting shade
• Pioneer sprout in shade

Real-world example

A glacier at Kenai Fjords National Park retreats and leaves bare rock. The park's page describes mosses and lichens beginning to colonize and break down the rock. Alders grow afterwards, working with bacteria in their roots and dropping nitrogen-rich leaf litter on the ground. The more fertile soil is what lets larger trees replace them.

Common misunderstandings

Pioneers are just weeds. The term is usually applied to plants, but microbes and invertebrates are also sometimes recognized as pioneers.

All pioneers start on bare rock. One group starts where there is no soil. The other starts secondary succession, often from propagules already in the soil.

Pioneers last forever. The trade-off between light and shade prevents pioneer populations from persisting long after the disturbance has passed.

Frequently asked questions

What is a pioneer species?

A species that first colonizes a new habitat created by disturbance.

How do pioneer species help habitat recovery?

They help build soil, as mosses and lichens break down rock, and add nutrients, as alders drop nitrogen-rich leaf litter.

Why do pioneer species disappear after a while?

Other species that thrive in the new conditions outcompete them, and a trade-off between light and shade stops them persisting long.

Summary

• Pioneers are the first species to arrive in a new habitat created by disturbance.
• They help recovery by forming soil and adding nutrients for later arrivals.
• They give way because the environment changes and shade limits them.