Animals Are Key to Restoring the World’s Forests

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The scale of forest loss is not abstract. Between 2015 and 2020, the world lost approximately 10 million hectares of forest annually, with tropical regions bearing the heaviest toll. Deforestation for agriculture, illegal logging, infrastructure expansion, and wildfire — increasingly intensified by climate change — have stripped landscapes of their biological complexity. What remains after clearing is rarely bare ground. It is a fractured habitat where the processes that once sustained dense, species-rich forest have broken down entirely.

Global Forest Crisis

Tree-planting programs have attracted enormous political and financial momentum. The Bonn Challenge, for instance, set a target of restoring 350 million hectares of degraded land by 2030. Yet planting trees is not the same as restoring forests.

A planted monoculture of fast-growing timber species shares little with an old-growth tropical forest in terms of species diversity, carbon density, water regulation, or soil health. The missing ingredient in most planting initiatives is the ecological engine that built forests in the first place: animals.

Animals are key to restoring the world’s forests in ways that go far beyond aesthetics or biodiversity metrics. They carry seeds across landscapes, create soil disturbances that allow seedlings to establish, suppress aggressive weeds through grazing, and trigger cascade effects through the food web that ultimately shape the physical structure of forests.

Ecological Link Between Animals and Forest Regeneration

Seed Dispersal as the Foundation of Forest Recovery

Forest regeneration begins with a seed landing in the right place. Most tree species in tropical and subtropical forests cannot disperse their seeds effectively without an animal partner. Wind and gravity move seeds short distances, but animals move them far, fast, and into microhabitats where germination is possible.

This biological partnership, called zoochory (seed dispersal mediated by animals), is the primary mechanism by which forests expand, reconnect fragmented patches, and recover from disturbance.

A landmark synthesis published in Science (Fricke et al., 2022) estimated that the loss of large-bodied frugivores (fruit-eating animals) has already reduced seed dispersal effectiveness by up to 60% in some tropical regions. That number tells a precise story: more than half of the biological infrastructure that moves tree seeds across landscapes is functionally impaired, even in areas where trees still stand.

Natural Reforestation Versus Human-Led Planting

Natural regeneration, where forests re-establish without direct human planting, consistently outperforms plantation-style restoration in ecological complexity. A meta-analysis published in Nature (Crouzeilles et al., 2017) found that naturally regenerating forests accumulate biodiversity 34% to 56% faster than planted forests of the same age.

Animals are the reason. When frugivores, insectivores, and browsers are present, they continuously introduce new plant species, control competing vegetation, and fertilize soils through dung deposition. Human-led planting can supplement this process, but it cannot replace the dynamic, self-organizing character of animal-mediated recovery.

Biodiversity as a Driver of Resilient Ecosystems

Biodiverse forests are not just richer in species. They are structurally more stable, more resistant to drought and pest outbreaks, and more efficient at storing carbon than low-diversity plantations. Animals drive this diversity by moving a broader range of plant species than any human restoration program could realistically achieve.

They also create ecological heterogeneity (variation in habitat structure and resources across a landscape), which is the physical substrate on which biodiversity builds over time.

Seed Dispersers: Nature’s Forest Planters

How Mammals Disperse Seeds Across Large Distances

Large mammals, particularly tapirs, elephants, and large-bodied rodents such as agoutis, are among the most effective long-distance seed dispersers on Earth. African forest elephants (Loxodonta cyclotis) consume the fruits of over 96 tree species and can deposit viable seeds up to 65 kilometers from the parent tree, according to research published in Biotropica. This distance matters enormously in a fragmented landscape where forest patches need to be connected if recovery is to scale.

• Tapirs in the Amazon and Southeast Asia are known as “gardeners of the forest” because they transport seeds of large-seeded trees that few other animals can swallow, making them irreplaceable in the regeneration of high-carbon-density forest types.
• Agoutis (medium-sized rodents native to Central and South America) cache seeds in the soil as a food reserve, and seeds that are never retrieved germinate — giving trees a direct planting agent at the soil level.
• Fruit bats in tropical Asia and Africa disperse seeds in open, deforested areas at night, actively seeding landscapes that other diurnal animals avoid, which makes them critical pioneers in early-stage forest recovery.

The Role of Birds in Spreading Small and Medium-Sized Seeds

Birds collectively disperse more tree species than any other animal group. Frugivorous birds such as hornbills, toucans, and cotingas deposit seeds in their droppings across forest interiors and edges.

Research in Proceedings of the Royal Society B demonstrated that bird-mediated seed dispersal accelerates forest succession in degraded landscapes by introducing pioneer tree species that create canopy cover, enabling shade-tolerant species to establish beneath them. This sequential process is called facilitated succession (where early-arriving species create the physical conditions needed for later species).

Fricke et al. (2022, Science) found that defaunation (the loss of animals from ecosystems) has reduced seed dispersal distances for large-seeded trees by up to 60% in tropical forests globally. Restoration planners who ignore wildlife protection are effectively cutting the seed supply lines of the forests they aim to rebuild.

The Importance of Primates in Tropical Forest Regeneration

Primates occupy a unique niche in seed dispersal because they combine large body size, wide home ranges, and selective fruit consumption in ways that no other animal group replicates. Spider monkeys in the Neotropics, for example, can move seeds of high-value timber and canopy species up to 2 kilometers in a single foraging trip.

Chimpanzees in West Africa disperse seeds of trees that dominate mature forest stands — the very species that make restored forests ecologically valuable for carbon storage and watershed protection. Losing primates from a forest does not just reduce wildlife; it removes the mechanism by which mature-phase tree communities assemble.

Large Herbivores and Ecosystem Balance

Grazers and Browsers Shaping Plant Composition

Large herbivores, including deer, bison, wild boar, and forest buffalo, do not simply eat plants. They actively sculpt the plant community by selectively consuming certain species and leaving others. This selective pressure creates a mosaic of vegetation types, including open glades, dense shrub patches, and emerging tree canopy, that supports far higher biodiversity than any uniform canopy forest would.

In Europe, the reintroduction of wisent (European bison) into the Bialowieza Forest in Poland demonstrated that large herbivore browsing reduces the density of competitive shrub species, allowing light to penetrate to the forest floor and enabling the germination of diverse tree seedlings. The effect is a measurable increase in understory plant richness within five years of bison reintroduction.

Preventing the Dominance of Invasive or Fast-Growing Species

One of the persistent failures of large-scale tree planting programs is that fast-growing, light-demanding pioneer species outcompete slower-growing species with higher ecological value. Large herbivores counteract this by preferentially grazing on fast-growing pioneers, creating space for a broader plant community to establish. Without this regulatory browsing, planted restoration sites frequently converge on low-diversity thickets dominated by weedy, ecologically unproductive species.

Nutrient Cycling Through Dung and Movement

Every herbivore is also a nutrient pump. Animals consume biomass in one location and deposit dung, urine, and decomposing tissue in another, redistributing nutrients across landscapes that would otherwise become nutrient-poor over time.

A single African elephant deposits roughly 150 kilograms of dung per day, each deposit functioning as a fertilizer package and seed bundle simultaneously. This movement of nutrients across degraded landscapes is a primary driver of soil improvement in early forest recovery, creating the chemical conditions in which tree seedlings can survive their first years.

Predators and Trophic Cascades

How Apex Predators Regulate Herbivore Populations

Apex predators — wolves, tigers, jaguars, lions, and large raptors — regulate the size and behavior of herbivore populations. When predators are present, herbivores cannot afford to graze a single area intensively for long. They move to avoid predation risk. This movement distributes grazing pressure across the landscape, preventing any one area from being stripped bare and allowing vegetation to recover between grazing events.

The Concept of Trophic Cascades

Trophic cascades (top-down effects that flow from predators through herbivores to vegetation) represent one of the most powerful indirect mechanisms by which animals shape forest structure. The reintroduction of gray wolves to Yellowstone National Park in 1995 is the most cited example.

When you protect the predator, you protect the forest. Trophic cascades make ecological recovery a system property, not just the sum of individual species.

Wolves altered elk behavior, reducing overgrazing in river valleys. Willows, aspens, and cottonwoods regrew along riverbanks. Beaver populations expanded. Riverbanks stabilized. The physical geography of river channels changed. All of this traced back to the restoration of a single predator species.

Indirect Effects on Vegetation Recovery

The vegetation effects of predator reintroduction are not instantaneous. Research in Biological Conservation (Ripple et al., 2024) tracked vegetation changes in multi-year monitoring programs across four continents and found that forests with functionally complete predator communities accumulated 40% more aboveground biomass over a 20-year period than comparable forests lacking apex predators.

This biomass difference represents both biodiversity gain and substantial additional carbon storage, linking predator conservation directly to climate mitigation outcomes.

Ripple et al. (2024, Biological Conservation) found that forests with intact predator communities accumulated 40% more aboveground biomass over two decades compared to defaunated forests of similar size and climate. Including predator reintroduction in forest restoration planning can substantially increase the carbon capture value of restored landscapes.

Forest Loss, Defaunation, and the Problem of “Empty Forests”

Hunting and Habitat Fragmentation

Defaunation refers to the systematic removal of animal populations from ecosystems through hunting, trapping, habitat fragmentation, and persecution. It is distinct from deforestation. A forest can still stand with its trees intact and yet be ecologically dead — devoid of the animals that once drove its regenerative processes.

This condition, described by conservation biologist Kent Redford in 1992 and formally measured in subsequent decades, is known as the empty forest syndrome. Habitat fragmentation worsens defaunation by isolating animal populations in patches too small to sustain viable numbers.

Large-bodied animals with wide home ranges, including jaguars, forest elephants, and large hornbills, are the most vulnerable. These are precisely the species that serve as keystone seed dispersers and ecosystem engineers. Their loss sends ripple effects through the forest’s reproductive biology over the decades that follow.

Long-Term Impacts on Forest Structure and Carbon Storage

The structural consequences of defaunation accumulate slowly but are ecologically severe. Without large-seeded tree species being dispersed by large frugivores, forests gradually shift toward dominance by small-seeded, wind-dispersed pioneer species.

These pioneers tend to have lower wood density, shorter lifespans, and lower carbon storage capacity than the hardwood species they replace. Research published in Nature Climate Change estimated that the loss of large mammal seed dispersers could reduce the carbon storage potential of tropical forests by up to 38% over multi-decadal timescales, simply by shifting tree community composition.

• Defaunated forests lose their capacity for natural regeneration because seeds of late-successional, high-carbon-density trees never arrive in recovering patches.
• Forest structure becomes increasingly simplified over time, with fewer layers of canopy, reduced vertical complexity, and lower resistance to disturbance events such as drought and storm damage.
• Soil health deteriorates as the nutrient redistribution services provided by large animals decline, reducing the growth potential of whatever seedlings do establish.

Animals and Climate Change Mitigation

Forest Regeneration and Carbon Sequestration

Forest restoration has been identified as one of the most cost-effective natural climate solutions available. The Intergovernmental Panel on Climate Change estimated that forests and forest restoration could contribute up to 10 gigatons of CO2 equivalent in annual mitigation by 2030 if managed effectively. What this calculation increasingly incorporates, as new research matures, is the animal dimension of forest carbon — the difference in carbon density between faunally intact and defaunated forests.

How Animal-Driven Seed Dispersal Enhances Carbon-Dense Tree Growth

The trees with the highest carbon density are, almost without exception, large-seeded species that depend on large animals for dispersal. These hardwood species — including Brazil nut trees, African mahogany, and dipterocarp species in Southeast Asia — grow slowly, live for centuries, and lock up far more carbon per tree than the fast-growing pioneers that colonize defaunated landscapes.

Protecting the animals that disperse them is therefore a direct carbon strategy, not only a biodiversity strategy. A quantitative analysis published in Science Advances (Peres et al., 2016) demonstrated that Amazonian forests with intact large frugivore communities stored an estimated 12% more aboveground carbon than defaunated forests in the same biome.

Scaled to the entire Amazon basin, that differential amounts to billions of additional tons of stored carbon, all attributable to the presence of animals.

Implications for Global Climate Strategies

The implication is that carbon markets and climate finance instruments that fund tree planting without simultaneously protecting wildlife are systematically underperforming their stated goals.

Emerging frameworks, including the Kunming-Montreal Global Biodiversity Framework adopted in 2022 and the updated REDD+ guidelines from the United Nations Framework Convention on Climate Change (UNFCCC), are beginning to incorporate faunal integrity as a metric alongside canopy cover. This shift in policy thinking reflects what ecologists have understood for years: trees are the architecture of a forest, but animals are its metabolism.

Rewilding and Wildlife Reintroduction

What Rewilding Means in Forest Landscapes

Rewilding (the large-scale restoration of ecosystems by reintroducing or protecting key species and allowing natural processes to resume) is the most ecologically ambitious approach to forest restoration currently being implemented.

It differs from conventional conservation, which tends to manage species one by one, by targeting the processes and dynamics that make ecosystems self-sustaining. In practice, rewilding focuses on restoring keystone species, protecting large connected areas, and then stepping back to allow ecological complexity to rebuild.

Successful Wildlife Reintroduction Case Studies

Several reintroduction programs have produced measurable forest restoration outcomes across different biomes:

1. The reintroduction of gray wolves to Yellowstone National Park (USA) in 1995 triggered the trophic cascade described in Section V, producing documented vegetation recovery along riparian zones within 15 years and measurably improving the structural complexity of riparian forest patches.
2. The Rewilding Europe initiative has facilitated the expansion of European bison across multiple countries, with monitoring in the Romanian Carpathians showing increased tree recruitment and improved forest regeneration in areas with stable bison populations.
3. In the Atlantic Forest of Brazil, the reintroduction of tapirs by the Instituto Pró-Carnívoros has been linked to measurable increases in the density of large-seeded tree seedlings within reintroduction zones, documented through seed trap and seedling census data collected over five years.
4. In Australia, the reintroduction of eastern quolls (small native predators) to Mulligans Flat Woodland Sanctuary has reduced the density of invasive grasses through indirect trophic effects, improving the establishment of native woodland species.

Policy and Conservation Frameworks

Rewilding is gaining formal recognition in policy frameworks. The European Union’s Nature Restoration Law, adopted in 2024, mandates the restoration of degraded ecosystems across 20% of EU land and sea areas by 2030, with specific provisions for restoring natural processes, including the return of wildlife to restored landscapes. This represents a significant departure from earlier conservation policies focused primarily on protecting what remains, signaling a political shift toward active ecological recovery.

Integrating Animals into Forest Restoration Policy

Moving Beyond Tree-Count Metrics

Current reporting frameworks for forest restoration, including the Bonn Challenge and the United Nations Decade on Ecosystem Restoration (2021–2030), primarily measure success by counting trees planted. This metric is convenient, politically visible, and fundraising-friendly. It is also ecologically insufficient.

A more meaningful measure of restoration success would track faunal recovery alongside canopy cover, using indicators such as frugivore community completeness, seed dispersal effectiveness, and predator-prey ratio as proxies for ecological functionality.

Protecting Wildlife Corridors

Wildlife corridors (strips of habitat that connect isolated forest patches, allowing animals to move between them) are the infrastructure of animal-mediated forest recovery. Without corridors, seed dispersers are confined to small forest patches and cannot transfer their ecological services across the wider landscape.

Corridor design must account for the movement requirements of the largest animals in each system, since their ranges determine the minimum scale of connectivity needed for functional seed dispersal to occur at the landscape level.

• Corridor width must be sufficient to allow safe movement of target species — jaguar corridors in Central America require widths of at least several hundred meters to be effective, according to modelling by the Panthera jaguar program.
• Corridors must pass through or adjacent to human-managed landscapes, making community engagement and farmer incentives essential components of any corridor strategy.
• Remote sensing tools, including GPS collar data and camera trap networks, now allow managers to monitor corridor use and adjust designs based on actual animal movement data.

Community-Based Conservation and Indigenous Knowledge

Indigenous and local communities manage approximately 22% of the world’s land surface, much of it forested. Research consistently shows that indigenous-managed forests retain higher biodiversity and faunal integrity than either protected areas or unmanaged forests in the same regions.

Integrating indigenous knowledge systems into restoration planning — particularly knowledge about seasonal animal movements, fruiting cycles, and hunting regulations — dramatically improves the ecological effectiveness of restoration programs while building the social license that makes long-term conservation viable.

Challenges and Ethical Considerations in Wildlife-Led Restoration

Human-Wildlife Conflict

Restoring large animal populations near human settlements inevitably generates conflict. Elephants raid crops. Wolves kill livestock. Large carnivores occasionally threaten human safety. These conflicts are not peripheral concerns — they are the central political challenge of any rewilding or reintroduction program.

Solutions require a combination of compensation schemes for farmers who lose livestock to predators, community revenue-sharing from wildlife tourism, and practical interventions such as predator-proof livestock enclosures and early warning systems using GPS-enabled collars on large animals.

Balancing Agricultural Expansion and Wildlife Recovery

The tension between expanding food production and restoring wildlife habitat represents the most fundamental policy challenge in conservation. Land-use change for agriculture drives both deforestation and defaunation simultaneously. Agroforestry systems, which integrate tree crops and native vegetation with food production, offer one productive middle ground.

Evidence from across the tropics shows that well-designed agroforestry landscapes can support significant populations of frugivorous birds and mammals, providing partial seed dispersal services while maintaining agricultural productivity for farming communities.

Funding and Long-Term Monitoring

Forest restoration programs are typically funded over project cycles of three to five years, which is far too short to capture the ecological dynamics of animal-mediated forest recovery. Meaningful changes in seed dispersal effectiveness, tree community composition, and carbon accumulation operate over decades.

This creates a structural mismatch between the timescales of ecological restoration and the timescales of conservation finance. Long-term endowment-style funding mechanisms, such as those piloted by the Global Environment Facility and several national conservation trusts, offer a more appropriate financial architecture for programs that need 20 to 30 years to demonstrate ecological outcomes.

Forest Restoration as an Ecological Partnership with Wildlife

Animals are key to restoring the world’s forests in a way that no amount of tree planting can substitute for. From the tapir depositing seeds of high-carbon hardwood trees across recovering Amazonian landscapes to the wolf triggering a cascade that reshapes river valleys in the American West, every functional forest is the product of animal activity accumulated over time.

Strip out the animals, and what remains is a tree-covered surface that lacks the biological processes needed to sustain itself, grow in complexity, or maximize carbon storage. The evidence is now clear and quantified. Defaunation reduces seed dispersal effectiveness by up to 60%. Animal-intact forests store up to 40% more biomass.

Indigenous-managed forests with intact wildlife communities outperform protected areas on nearly every ecological metric. Rewilding programs across four continents are producing measurable, documented gains in forest structure when key species are restored to landscapes.

The path forward requires treating wildlife protection and forest restoration as a single integrated strategy rather than parallel activities managed by separate institutions.

This means reforming tree-planting metrics to include faunal indicators, funding wildlife corridors as essential restoration infrastructure, supporting community-based conservation models that align local livelihoods with wildlife recovery, and scaling up rewilding investment as a core component of climate finance. Forests cannot restore themselves without their animals. And without restored forests, the climate targets the world has set for itself remain permanently out of reach.