Review papers by their claims

Central claim (and what is actually measured)

What the authors measured: In 2021 they collected 54 TreM samples spanning 18 TreM-types (3 replicates each) on Fagus sylvatica in the Massane old-growth beech forest and extracted micro-invertebrates using a modified Baermann technique; nematodes were identified to species-level, while other groups were quantified at broader levels. They counted nematodes/rotifers/tardigrades/mites (minimum 200 individuals counted per sample/sub-sample) and used stable isotope analysis (δ13C, δ15N) on basal resources and micro/macro invertebrates to infer trophic structure. Methods overview

What supports the claim: TreMs were reported as high-abundance hotspots (mean 195 individuals per gram dry TreM substrate; range 4–1698) with nematodes dominating (80% of individuals; rotifers 10%, tardigrades 7.5%). The authors report significant TreM-form / TreM-type effects on community composition and nematode functional indices (e.g., maturity and trophic diversity) and report non-overlapping isotopic niches among the three main TreM-forms (cavities, epiphytes, fungi) with form-specific niche metrics. Key quantitative findings

Limitations or alternative interpretations (what could break the inference)

• Temporal confounding: TreM-types were not sampled with within-type temporal replication; sampling seasons differed by TreM accessibility/availability. The authors explicitly discuss this as a potential confound (“TreM tempo”). This means part of “TreM-type” differences could reflect seasonal turnover rather than TreM-structure. Season confounding limitation
• Trophic inference is indirect: δ13C/δ15N are powerful for trophic positioning and isotopic niche separation, but they do not directly prove who eats whom. Baseline variation, trophic enrichment factors, and resource mixture effects can produce isotopic patterns that are consistent with multiple food-web configurations. The authors partially address this by focusing on isotopic niches and form-specific metrics, but the “complex food webs” phrasing is still supported indirectly by isotopes and functional guild indices rather than direct interaction data. Isotopic inference basis
• Partial isotopic sampling: Isotopic analyses were not available for all TreM-types (reported as present in 11 of 18 types). That can bias which TreM-types contribute to the food-web separation conclusions and may alter the “support” strength for rare/atypical types. Isotope sample coverage

Practical implications (what a reader can take forward)

Most actionable contribution: The study connects TreM typology (structural microhabitat classes) to measurable micro-invertebrate community properties (abundance/diversity) and isotopic niche differentiation among TreM-forms. If replicated across sites and with within-type temporal designs, this strengthens the case for TreMs as biodiversity indicators and as mechanistic “microhabitat-function” units relevant to conservation/forest management planning. Implication statements