Drivers of Vegetation Structure Differ Between Proposed Natural Reference Conditions for Temperate Europe

Aim

Pre-degradation baseline conditions (references) provide crucial context for restoration actions. Here, we compare vegetation structure and its driving processes across the main pre-agricultural references discussed for temperate Europe: the Last Interglacial and the early-mid Holocene—before and after the arrival of Homo sapiens, respectively.

Location

Temperate Europe.

Time Period

The first ~4000–6000 years, excluding the initial early-successional phases, of the Last Interglacial (PAAZ III) and Holocene (8700–5700 BP).

Major Taxa Studied

Plants.

Methods

We use large datasets of pollen-based vegetation reconstructions (REVEALS) to compare open vegetation, light woodland and closed forest between the two periods. We use Random Forest modelling and downscaled climate data to assess whether climate-vegetation relations were consistent between periods, as expected if they reflected direct climatic effects on vegetation.

Results

Open vegetation was slightly higher in the early–mid Holocene than in the Last Interglacial, averaging 20% versus 16% in paired grid cells, respectively. In contrast, light woodland cover was lower in the early–mid Holocene, with mean values of 49% compared to 57% in paired cells. The combined open vegetation and light woodland cover was high in both periods, averaging 73% in the Last Interglacial and 69% in the early–mid Holocene. Closed forest cover was similar across both periods (Holocene = 24%; Last Interglacial = 23%). Notably, openness –climate relations from the early–mid Holocene cannot predict open vegetation in the Last Interglacial.

Main Conclusions

These findings suggest that vegetation in the early–mid Holocene and Last Interglacial was affected by persistent, substantial disturbances, which were not controlled by direct climate effects, and that the main drivers differed between the periods, with the rich megafauna of the Last Interglacial and Mesolithic people as the primary candidates. Our findings support that early–mid Holocene ecosystems were already strongly shaped by Homo sapiens and differed from earlier temperate ecosystems.