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 belowground biomass being 26% of aboveground 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 4 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.