The inadequacy of current carbon storage assessment methods for rewilding: A Knepp Estate case study

In the context of global climate change mitigation, carbon storage in woody vegetation plays a crucial role. Recognising the value of the i-Tree Eco model for carbon storage in urban and forestry settings, this study aimed to explore its applicability to rewilded landscapes. Using direct measurements from destructively sampled scrub from the Knepp Estate, our goal was to determine the model's suitability to this landscape.Our findings reveal that these methods are not appropriate for multi-stemmed trees below browsing height, as we observed no significant relationship between stem basal diameter and height. The i-Tree tool's assumption of below-ground biomass being 26% of above-ground biomass may not be applicable to herbivore-influenced landscapes. Additionally, we found that, on average, scrub at Knepp had more biomass below the ground than above, with a root:shoot ratio of 1.07, which is more than four times the amount predicted by current models using the 0.26 estimate ratio.This study underscores the need for novel allometric approaches that consider species-specific biomass and the impact of external factors, such as herbivory, on carbon storage. Accurate carbon accounting in future rewilding projects is essential for their contribution to both biodiversity enhancement and climate change mitigation.While the i-Tree Eco model provides valuable insights for many ecosystems, our findings suggest that its applicability may be limited in scrubland ecosystems, especially in rewilded landscapes where natural processes create semi-stable scrub and open wood pastures. Nonetheless, with suitable adjustments or when complemented with other methods, the i-Tree Eco model could be a valuable tool for specific scrub or rewilding scenarios. Our study at the Knepp Estate challenges existing models by revealing that scrublands in rewilded areas allocate more carbon to belowground biomass than previously understood, with a root: shoot ratio significantly higher than i-Tree Eco model estimates. This discrepancy highlights the necessity for developing refined allometric equations that account for the unique structural complexities and herbivory impacts in rewilded landscapes. Accurate carbon quantification in such ecosystems is vital for their recognised role in biodiversity conservation and climate change mitigation.image