DOI: 10.5061/dryad.76hdr7t31
title: The inadequacy of current carbon storage assessment methods for rewilding: A Knepp Estate case study

description: 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.
description: # **The Inadequacy of Current Carbon Storage Assessment Methods for
 Rewilding: A Knepp Estate Case Study**
 **Brief Summary of Dataset
 Contents:** The dataset from the study conducted at Knepp Estate primarily
 involves direct measurements of scrubland vegetation, focusing on
 evaluating the i-Tree Eco model's applicability to rewilded
 landscapes. The study's findings revealed limitations of current
 methods in estimating carbon storage for multi-stemmed trees in
 herbivore-influenced landscapes, suggesting the need for novel allometric
 approaches. The data has been split into two datasets, here's a brief
 overview of each: **Data Set 1: Total_Opwall_Adj Dbh_Feb23** *
 **Purpose**: Utilises an allometric model by iTree Eco to assess tree
 biomass at the Knepp Wildland project. * **Data Collected**: Includes
 species, scientific name, height (in meters), diameter at breast height
 (DBH) (in centimeters), number of stems, and presence of species-specific
 allometric equations. * **Columns**: * species: The common name of the
 tree or shrub. * scientific name: The scientific nomenclature. * height
 (m): The height of the tree/shrub. * dbh (cm): Diameter at breast height.
 * no_stems: Count of stems for each tree/shrub. * present: Indicates if a
 species-specific allometric equation is available. * proxy: Refers to the
 phylogenetic class used by iTree for biomass estimation. **Data
 analysis:** * **Software:** i-Tree Forecast Eco v6.0.22 * **Description**:
 Used for estimating potential carbon storage. It allows for adjustments in
 measurement techniques, such as measuring the diameter at ground level
 when standard diameter at breast height (DBH) cannot be taken​​. *
 **Statistical analysis**: * **Tree Height and DBH Relationship Analysis:**
 Using R studio version 2022.7.2.576 - Spearman’s Rank Correlation and
 Siegel nonparametric linear regression analysis were employed to evaluate
 the relationship between tree height and DBH. Trees were divided into two
 height categories: above and below 2.5 meters, corresponding to the browse
 line height​.   **Data Set 2: Above Vs Below_Total_Pt1_Feb23** *
 **Purpose**: To compare aboveground and belowground biomass weights for a
 sample of trees and evaluate the i-Tree model's root:shoot ratio
 assumption. * **Data Collected**: Biomass weights (in grams) of 39
 destructively sampled trees and shrubs, to compare the aboveground (AGB)
 and belowground biomass (BGB) to the predicted estimate of the i-Tree
 model. * **Columns**: * species: The common name of the tree or shrub. *
 agb_weight (g): Aboveground biomass weight. * Bgb_weight (g): Belowground
 biomass weight. * I_tree bgb (g): The predicted belowground biomass using
 the i-Tree model, calculated as 0.26 times the aboveground biomass. *
 *root:shoot ratio: A comparison metric of belowground to aboveground
 biomass.* **Destructive Sampling Methodology:** The extraction of above-
 and belowground plant material. **Statistical analysis:** * **Statistical
 Analysis Software:** R Studio version 2022.7.2.576 * **Graph Creation:**
 ggplot2 package in R Studio * **Analytical Techniques:** * Root:Shoot
 Ratio Evaluation: A one-sample t-test was used to compare the measured
 root:shoot ratio with the i-Tree Eco model's predicted ratio of 0.26.
 This was crucial for assessing the model's accuracy in predicting
 belowground biomass​​. **Sharing/Access Information:** **- Links to Other
 Publicly Accessible Locations of the Data:** Currently not provided in the
 document. **- Data Derived From Sources:** The study references several
 external sources, including publications and databases like GlobAllomeTree
 and the i-Tree database, which informed the methodology and analysis. *