How Dead Foundation Species Shape Ecosystem Recovery

Storms and heatwaves can leave devastation in their wake: a coral skeleton bleached white or a tree trunk flattened into the mud.

It is easy to assume that, once an organism dies, its remains simply lie in place and gradually decay.

However, a new study covering a broad selection of ecosystems indicates that this assumption is mistaken.

Long after death, those remains continue to have an effect, often in ways that are far from obvious.

Defining death

The organisms examined are known to ecologists as foundation species: trees, grasses, corals and oysters that create a habitat’s physical framework and support innumerable other organisms.

When these species flourish, so does the wider community that depends on them.

Kai Kopecky, an ecologist and postdoctoral researcher at the University of Colorado Boulder (CU Boulder), led a team investigating a less frequently asked question.

Rather than examining what foundation species do during life, the researchers examined what their remains do after death.

Ecologists use the term ecological memory to describe the persistence of the past within a system. It is partly created by material legacies - the structural or resource remnants left by an organism.

Previous research found that the loss of a living foundation species can cause an entire community to fall apart. Its remains, however, had received little attention.

Evidence from ten ecosystems

For a broad test, the researchers combined long-term datasets from ten ecosystems, chiefly in the United States as well as one reef in the South Pacific.

Some sites lay close to the Arctic Circle, whereas others were located in warm tropical waters.

The records covered periods ranging from two years to more than three decades, combining field experiments with observations.

This extended perspective revealed what occurred when fires, storms or heatwaves left dead material across the landscape.

Kopecky had anticipated a clear split, perhaps with marine ecosystems behaving differently from terrestrial ones. Instead, no such boundary emerged.

Dead material exerted a substantial influence in habitats that otherwise had very little in common.

Dead foundation species can support new life

In five of the ten ecosystems, dead organisms gave living ones an advantage.

On tidal flats, accumulated old oyster shells provided the firm surface needed by young oysters to attach themselves, allowing reefs to rebuild on the remains of the preceding generation.

In temperate forests, standing dead hemlock trees provided a place where new saplings could establish roots. The same pattern appeared farther north.

Trees killed by fire remained standing before eventually releasing stored seeds, which reseeded the burned land.

Along subtropical coastlines, leaf litter from mangroves damaged by storms appeared to enrich the soil, prompting the surviving trees to produce fresh roots.

In one example, the dead material increased new growth by more than tenfold. The team could only suggest that extra nutrients were responsible.

When debris takes over

In four other ecosystems, dead remains became an obstacle. Dense layers of dead grass in tallgrass prairies shut out sunlight and restricted new shoots emerging from roots beneath the surface.

On South Pacific coral reefs, branching skeletons left by heatwaves favoured weedy competitors, which crowded out the living coral attempting to recover.

As a study monitoring an ocean heatwave showed, heatwaves have previously wiped out reef-builders.

In salt marshes, floating debris came to rest on living grasses and smothered them. In tropical rainforests, fallen canopy litter took the light and space required by young seedlings.

One kelp forest in California showed no meaningful effect in either direction.

The shared pattern

When the team compared the examples, it found that dead material operated in one of two main ways.

Some remains altered a location’s physical structure, as with a shell bed or a mass of skeletons. Others changed the availability of light or nutrients; either process could be beneficial or damaging.

What most impressed the researchers was not any individual example.

Across systems with almost nothing in common, the dead influenced recovery both frequently and powerfully, making that broad pattern the central finding. Its prevalence had not previously been quantified.

“The most striking takeaway is not the effect of any particular dead organism within its respective ecosystem, but how commonly and strongly the dead influence the living,” said Kopecky.

The idea itself was not entirely new. A 2023 review had argued that dead foundation species should hold a genuine place in ecology rather than being treated as a footnote.

This study provides the firm evidence, presenting the dead as active participants rather than passive debris.

Managing the aftermath

The findings arrive at a particularly relevant time. John Kominoski, a biologist at Florida International University (FIU), is a co-author of the study.

He noted that storms, fires and heatwaves are becoming more severe, each leaving behind greater quantities of dead material.

Some land managers already apply this approach without giving it that name.

Prescribed burns remove dead grass to enable prairies to green up, while restoration teams place old oyster shells in the water to provide a foundation for new reefs.

What is new is the evidence. These effects occur often enough to be relied upon as a genuine part of ecosystem recovery.

Armed with this understanding, restoration efforts can make greater use of helpful remains and remove harmful material before it entrenches the damage.