Exploring the limitations of traditional forest classification and the multidimensional approaches revolutionizing conservation
Walk into any forest, and you're immediately surrounded by life—but what appears as a uniform green blanket is actually a complex, multi-dimensional mosaic of species interacting in subtle ways. For decades, ecologists and conservationists have classified forests into community types based on their dominant tree species to simplify this complexity. But as we face unprecedented biodiversity loss worldwide, scientists are asking a crucial question: Do these broad categories actually capture what we need to know to protect biological diversity? Recent research suggests the answer is no, and the implications for conservation are profound.
With 8.1 million hectares of forest lost in 2024 alone—a rate 63% higher than needed to meet 2030 conservation targets—we can no longer afford oversimplified approaches to protecting what remains 3 .
The traditional approach of classifying forests by their dominant trees is increasingly revealing its limitations. Like describing a diverse neighborhood solely by the style of its houses while ignoring the people living inside, forest typing may miss the very elements that make ecosystems function.
The limitations of broad forest classifications become strikingly apparent in one of ecology's longest-running debates: should we protect Single Large Or Several Small (SLOSS) forest areas? This question has divided scientists since the 1970s, and a groundbreaking 2025 study has reignited the discussion with findings that challenge conventional approaches to conservation planning 2 .
The study, led by biologist Thiago Gonçalves-Souza and involving researchers from eight countries, analyzed data from 37 studies across six continents. The team discovered that fragmented forest landscapes harbor 12% less species diversity than large, continuous forests—even when the total area remains the same 2 .
Yet the debate remains unsettled. Prominent biologist Lenore Fahrig cautions that overemphasizing large forests could mistakenly suggest "small remnants hold little importance for biodiversity conservation," potentially leading to lost protections for vital fragments 2 .
Classifying a forest as "oak-hickory" or "pine-broadleaf" tells us something about its composition but misses crucial elements that determine its ecological value:
As Fernando Guedes Pinto of SOS Mata Atlântica notes, the Atlantic Rainforest—one of Earth's most biodiverse biomes—now exists mainly as small, isolated fragments, with only 24% of its original cover remaining. "The periphery of the forest isn't appropriate habitat for more ecologically demanding species," he explains, highlighting how fragmentation creates additional limitations beyond what forest type alone can reveal 2 .
When scientists evaluate biodiversity, they've moved far beyond simply counting species. Modern ecology recognizes three essential dimensions of biodiversity, each providing different insights into ecosystem health:
The traditional approach focused on species identity and richness—essentially who lives where and in what numbers.
This measures the evolutionary relationships among species, recognizing that communities with distantly-related species may represent more evolutionary history and potentially greater adaptability.
Perhaps the most practically significant, this dimension assesses the variety of ecological roles and traits represented in a community, from root depth to pollination strategy.
Research has demonstrated that these dimensions can respond differently to environmental changes. A 2019 study in the French Alps found that while species richness often shows a unimodal relationship with productivity (peaking at intermediate productivity levels), functional and phylogenetic diversity typically increase steadily with productivity in unconstrained environments like forests 7 . This divergence explains why forest types alone cannot predict biodiversity outcomes—different aspects of biodiversity follow different rules.
Quantifying these biodiversity dimensions requires sophisticated approaches that go beyond traditional visual assessment. Scientists now use methods that independently evaluate species richness and evenness—how equally individuals are distributed among species 4 .
A 2022 study introduced a new biologically meaningful measure called DRE that separates richness and evenness components, addressing limitations of traditional indices like the Shannon-Weaver and Simpson indices, which combine both aspects into a single value with limited biological interpretation 4 . This separation proves particularly important in conservation because richness and evenness may respond differently to human impacts and play distinct roles in ecosystem functioning.
| Aspect | Traditional Approach | Modern Approach | Conservation Implication |
|---|---|---|---|
| Focus | Dominant tree species | Multiple taxonomic groups & traits | Comprehensive protection |
| Scale | Single (local) | Multiple scales (local to landscape) | Maintains connectivity |
| Dimensions | Taxonomic only | Taxonomic, phylogenetic, functional | Preserves evolutionary potential |
| Measurement | Simple richness indices | Richness & evenness separated | Better predicts ecosystem function |
Table 1: Traditional vs. Modern Approaches to Biodiversity Assessment
A landmark 2019 study published in Nature Communications dramatically advanced our understanding of why forest community types provide insufficient bases for biodiversity evaluation 7 . The research team combined an enormous dataset of >11,000 community plots in the French Alps with a molecular phylogeny and trait information for >1,200 plant species. This comprehensive approach allowed them to simultaneously investigate relationships between satellite-sensed productivity (using NDVI) and all major biodiversity dimensions across different climate zones and ecosystem types.
Used to continuously increase the weight given to species dominance
With a weighting parameter balancing trait and evolutionary contributions
To emphasize different scales of similarity, from deep evolutionary splits to recent diversification
This methodological complexity enabled the team to test specific ecological hypotheses about how environmental filtering, competitive exclusion, and niche differentiation shape biodiversity patterns across different contexts 7 .
The study revealed that the relationship between productivity and biodiversity changes dramatically depending on which dimension of biodiversity is considered and the ecosystem context:
| Ecosystem Type | Species Richness | Functional Diversity | Phylogenetic Diversity | Primary Driver |
|---|---|---|---|---|
| Natural Forests | Unimodal | Increasing | Increasing | Niche differentiation |
| Managed Grasslands | Unimodal | Unimodal/Decreasing | Unimodal/Decreasing | External constraints |
| Alpine Systems | Unimodal | Variable | Variable | Environmental filtering |
Table 2: Biodiversity-Productivity Relationships Across Ecosystem Types 7
These findings fundamentally challenge the value of forest community typing alone because they demonstrate that:
Contemporary ecologists employ an array of sophisticated tools to capture biodiversity's multiple dimensions, moving far beyond traditional field sketches and pressed plants. These technologies provide data at appropriate scales and resolutions to make informed conservation decisions:
Using specialized camera systems like the Plant Canopy Imager CI-110, scientists quantify leaf area index (LAI) and photosynthetically active radiation (PAR) levels to understand forest structure and light environments 6 . These tools help capture the crucial vertical dimension of forests that traditional typing misses.
By sequencing DNA from collected specimens, researchers reconstruct evolutionary relationships among species, quantifying phylogenetic diversity and identifying evolutionarily distinct lineages that may merit conservation priority 7 .
Ecologists meticulously measure key plant traits like specific leaf area (SLA), height, and seed mass that indicate species' ecological strategies and contributions to ecosystem functioning 7 .
Comprehensive biodiversity assessment requires sampling across taxonomic groups, from vascular plants and birds to epiphytic lichens, bryophytes, wood-inhabiting fungi, and saproxylic beetles 5 . Each group provides unique insights into ecosystem health.
A 2025 analysis of forest multi-taxon biodiversity monitoring revealed stark differences in sampling requirements across taxonomic groups 5 . For precise species richness assessment alone, estimates range from 3 to 147 plots per site across 3 to 29 sites per forest category, with birds and epiphytic bryophytes requiring the least effort while saproxylic beetles need substantially more intensive sampling 5 .
| Taxonomic Group | Plots per Site (Species Richness) | Sites per Forest Category | Sampling Challenge |
|---|---|---|---|
| Birds | 3-5 | 3-5 | Low |
| Epiphytic Bryophytes | 5-10 | 5-8 | Low-Moderate |
| Vascular Plants | 15-25 | 10-15 | Moderate |
| Wood-inhabiting Fungi | 25-50 | 15-20 | High |
| Saproxylic Beetles | 100-147 | 20-29 | Very High |
Table 3: Sampling Efforts Required for Biodiversity Assessment Across Taxonomic Groups 5
These dramatically different sampling requirements explain why quick forest typing assessments cannot adequately capture true biodiversity patterns—the most meaningful elements often require the most intensive sampling efforts.
The evidence is clear: classifying forests by community types provides a helpful starting point but fails to capture the multidimensional reality of biological diversity. As we work against the clock to protect global forests, conservation strategies must evolve to incorporate:
that evaluates taxonomic, phylogenetic, and functional diversity
that moves beyond charismatic species and dominant trees
that considers connectivity between forest patches
that recognize how relationships vary across ecosystems
The challenge is significant, but the scientific tools now exist to guide smarter conservation. As Lucas Ferrante from the University of São Paulo wisely notes, "I think it's minimalist to defend either a single large area or many small ones as an ideal conservation model... If it's to protect endangered species, I have to look at where these species live within the landscape" 2 .
The future of forest conservation lies not in discarding classification systems altogether, but in enhancing them with sophisticated biodiversity assessment that respects the complexity of nature. Only then can we hope to protect the rich tapestry of life that forests harbor in an increasingly threatened world.