Operationalizing closer-to-nature forest management: application of the energy-equivalence principle in a holm oak (Quercus ilex L.) Mediterranean forest

Recent European Commission documents emphasize the need for guidelines to implement Closer-to-Nature Forest Management (CNFM). However, current technical guidelines miss providing detailed practices suited to diverse environmental contexts. We propose a simple, universal tool to complement existing strategies for implementing CNFM. Empirical data and theoretical models suggest that old-growth forests tend to achieve a structure consistent with the Energy Equivalence Principle (EEP), where changes in size-class abundance are balanced by changes in individual resource use. We applied the EEP approach as a management tool in two Mediterranean evergreen holm oak forests in Sardinia, Italy: one old-growth (OG) and one recently disturbed (IoS). Using basic tree metrics—height, diameter, crown length, radius and crown volume (as a proxy for resource use)—we predicted EEP individual tree distributions. Results showed that holm oak dominated the top layer of both forest types (98 %), but species diversity was higher in the OG regeneration. The scaling of holm oak crown volume with height was α = 3.00 (CI±0.19). The exponent of potential EEP diameter distribution was β = -2.44, while the actual status of the forest structure was represented by significantly different slopes β = -1.99 (CI±0.11) and β= -1.36 (CI±0.21) for OG and IoS respectively. OG structure closely resembled EEP distribution, whereas IoS reflected the typical intermediate stage structure found in forest stands. Comparing EEP-based distribution with current forest structures enabled identification of precise intervention targets in each silvicultural class, guiding forest managers to design community structures more aligned with natural processes, enhancing forest multifunctionality.