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... The study site is a 1-ha (100 × 100 m) plot of mixed deciduous forest, nested within an 18-ha long-term forest inventory plot run by Oxford University and is part of the ForestGEO global network of forest inventory plots (Calders et al., 2018. The mean annual temperature and precipitation are 10 °C and 729 mm, respectively (Butt et al., 2009). In the studied plot, there were 550 standing trees in 2015/16. ...
... Wytham Woods is a semi-natural woodland, located on a gentle hill with the maximum elevation rising to 165 m in Oxfordshire, England (1 20′ W, 51 47′ N) (Butt et al., 2009). Since 2008, an 18-ha permanent inventory plot was established. ...
... The field sites were selected to represent contrasting ecosystems based on the availability of concurrent isoprene and temperature measurements. Tapajós National Forest is a protected Amazonian old-growth closed-canopy evergreen tropical forest (Sarkar et al., 2020), while the Wytham Woods site is a mixed temperate woodland where Quercus robur (European oak) is the dominant isoprene emitter (Butt et al., 2009). ...
Isoprene is a hydrocarbon emitted in large quantities by terrestrial vegetation. It is a precursor to several air quality and climate pollutants including ozone. Emission rates vary with plant species and environmental conditions. This variability can be modeled using the Model of Emissions of Gases and Aerosols from Nature (MEGAN). MEGAN parameterizes isoprene emission rates as a vegetation‐specific standard rate which is modulated by scaling factors that depend on meteorological and environmental driving variables. Recent experiments have identified large uncertainties in the MEGAN temperature response parameterization, while the emission rates under standard conditions are poorly constrained in some regions due to a lack of representative measurements and uncertainties in landcover. In this study, we use Bayesian model‐data fusion to optimize the MEGAN temperature response and standard emission rates using satellite‐ and ground‐based observational constraints. Optimization of the standard emission rate with satellite constraints reduced model biases but was highly sensitive to model input errors and drought stress and was found to be inconsistent with ground‐based constraints at an Amazonian field site, reflecting large uncertainties in the satellite‐based emissions. Optimization of the temperature response with ground‐based constraints increased the temperature sensitivity of the model by a factor of five at an Amazonian field site but had no impact at a UK field site, demonstrating significant ecosystem‐dependent variability of the isoprene emission temperature sensitivity. Ground‐based measurements of isoprene across a wide range of ecosystems will be key for obtaining an accurate representation of isoprene emission temperature sensitivity in global biogeochemical models.
... The forest is dominated by Fraxinus excelsior, A. pseudoplatanus and Corylus avellana. The mean annual rainfall is 726 mm, the mean annual temperature is 10 • C and the mean annual radiation is 118 W m −2 (Butt et al., 2009). Wytham Woods is a typical temperate forest site in southern Great Britain (Kirby et al., 2014;Savill et al., 2011), and its D distribution ( Scans were done in a larger 6 ha area using an approximate 20 m × 20 m grid to ensure the best possible data quality within our 1.4 ha study area (Wilkes et al., 2017). ...
... The carbon density of (dry) biomass is often approximated at 50% for trees found in British and European forests (Matthews, 1993;Nabuurs et al., 2007). Here, we use species-specific values of carbon density derived in Wytham Woods (Butt et al., 2009;Fenn et al., 2015). ...
... TLS-derived AGB was 573.8 tonnes in total for all live standing trees, which equates to 409.9 t ha −1 (Figure 3). This is significantly more than the 231.9 t ha −1 resulting from the Bunce allometric models that are commonly used in these temperate forests (Bunce, 1968;Butt et al., 2009;Forestry Commission, 2014a, 2014b and ...
Quantifying climate mitigation benefits of biosphere protection or restoration requires accurate assessment of forest above‐ground biomass (AGB). This is usually estimated using tree size‐to‐mass allometric models calibrated with harvested biomass data.
Using three‐dimensional laser measurements across the full range of tree size and shape in a typical UK temperate forest, we show that its AGB is 409.9 t ha⁻¹, 1.77 times more than current allometric model estimates. This discrepancy arises partly from the bias towards small trees in allometric model calibration: 50% of AGB in this forest was in less than 7% of the largest trees (stem diameter > 53.1 cm), all larger than the trees used to calibrate the widely used allometric model.
We present new empirical evidence that the fundamental assumption of tree size‐to‐mass scale‐invariance is not well‐justified for this kind of forest. This leads to substantial biases in current biomass estimates of broadleaf forests, not just in the UK, but elsewhere where the same or similar allometric models are applied, due to overdependence on non‐representative calibration data, and the departure of observed tree size‐to‐mass from simple size‐invariant relationships.
We suggest that testing the underlying assumptions of allometric models more generally is an urgent priority as this has wider implications for climate mitigation through carbon sequestration. Forests currently act as a carbon sink in the UK. However, the anticipated increase in forest disturbances makes the trajectory and magnitude of this terrestrial carbon sink uncertain. We make recommendations for prioritizing measurements with better characterized uncertainty to address this issue.
... Wytham Woods is a semi-natural woodland, located on a gentle hill with the maximum elevation rising to 165m in Oxfordshire, England (1°20' W, 51°47' N) (41). Since 2008, an 18 ha permanent inventory plot was established, which was the focus of this study (42 ...
Individual tree segmentation from airborne laser scanning data is a longstanding and important challenge in forest remote sensing. There are a number of segmentation algorithms but robust intercomparison studies are rare due to the difficulty of obtaining reliable reference data. Here we provide a benchmark data set for temperate and tropical broadleaf forests generated from labelled terrestrial laser scanning data. We compare the performance of four widely used tree segmentation algorithms against this benchmark data set. All algorithms achieved reasonable accuracy for the canopy trees, but very low accuracy for the understory trees. The point cloud based algorithm AMS3D (Adaptive Mean Shift 3D) had the highest overall accuracy, closely followed by the 2D raster based region growing algorithm Dalponte2016+. This result was consistent across both forest types. This study emphasises the need to assess tree segmentation algorithms directly using benchmark data. We provide the first openly available benchmark data set for tropical forests and we hope future studies will extend this work to other regions.
... The field sites were selected to represent contrasting ecosystems based on the availability of concurrent isoprene and temperature measurements. Tapajós National Forest is a protected Amazonian old-growth closed-canopy evergreen tropical forest (Sarkar et al., 2020), while the Wytham Woods site is a mixed temperate woodland where Quercus robur (European oak) is the dominant isoprene emitter (Butt et al., 2009). ...
... The study site was in Wytham Woods, Oxfordshire, UK (51 • 46 N, 1 • 20 W). Wytham Woods covers over 400 ha, with an altitude range of 60-164 m above sea level, a mean annual temperature of 10 • C and a mean annual rainfall of 726 mm [19,20]. The woodland compromises disturbed ancient woodland, naturally generated secondary woodland and plantations [21]. ...
... Birch is particularly susceptible to windthrow, which probably contributes to its decline in Wytham Woods, in addition to the low shade tolerance [42]. In Wytham Woods, most birches are in the disturbed semi-natural woodlands and others are scattered over the whole woodland in low numbers [20,42]. Apart from being a shade-intolerant species and getting outcompeted in closed canopy, our results show birch dispersal is also very sensitive to stand tree density. ...
Silver and downy birch (Betula pendula Roth and B. pubescens Ehrhs) are pioneer species which play an important role in forest regeneration in disturbed areas. Knowledge of birch seed production and dispersal is key to making good predictions of the persistence and colonization of birch. Both processes can be affected by the density of trees in the neighbourhood. In this study, we studied the seed production and dispersal of birch trees in two plots in Wytham Woods, UK, in 2015, and investigated the potential effect of neighbourhood tree density. We applied inverse modelling to seed trap data, incorporating tree density around the source tree and on the seed path to estimate birch fecundity and the dispersal kernel of the seeds. We show that the pattern of dispersed seeds was best explained by a model that included an effect of tree density on seed dispersal. There was no strong evidence that conspecific or heterospecific tree density had an effect on birch fecundity in Wytham Woods. A birch with diameter at breast height (DBH) of 20 cm is estimated to have produced ~137,000 seeds in 2015. Mean dispersal distance in an open area is estimated to be 65 m but would be reduced to 38 m in a closed stand. Both the mean dispersal distance and the probability of long-distance dispersal of birch decreases in dense environments. Areas with higher tree density also would intercept more seeds. These results highlight the importance of considering tree density in the neighbourhood and in the overall landscape when predicting the colonization and recruitment of birch.
... Within a closed canopy ancient semi-natural woodland, carbon is very unevenly distributed between trees and it is possible that wood pasture may store similar amounts of carbon in some circumstances. For example, in an 18 ha plot at Wytham Woods, Butt and others (2009) estimated that approximately 29 per cent of the carbon was in oak (Quercus robur) trees, which are mostly large old trees, and made up less than 2 per cent of the individual stems (photo 2.3). Wood pasture soils are often relatively undisturbed and may also be a valuable carbon store, depending on soil type and management history. ...
... Blue arrows represent carbon uptake through photosynthesis, red arrows represent carbon releases to the atmosphere from respiration. Measured values of stocks and fluxes of carbon in Wytham Woods from data inButt and others (2009) and Fenn and others (2015) ...
In this report, we review the scientific evidence base relating to carbon storage and sequestration by semi-natural habitats, in relation to their condition and/or management. This new report updates and expands previous work by Natural England on ‘Carbon storage by habitat’ published in 2012. We cover terrestrial, coastal and marine habitats, and the freshwater systems that connect them, in order to quantify their relative benefits for carbon management.
... Carbon gains were estimated separately for each species. This value is broadly in line with other studies of carbon sequestration in UK native woodlands, which average around 135 tC ha -1 (Patenaude et al. 2003;Butt et al., 2009;Morison et al., 2012;Hale, 2015;Hale et al., 2019). A c c e p t e d M a n u s c r i p t 4 We assumed this value represented an 80% canopy cover mature woodland. ...
Woodland creation sequesters carbon and contributes to climate change mitigation. Most previous assessments of the carbon sequestration of new UK woodlands have focused on tree planting, little is known about the scale of the potential contribution from natural regeneration. We used a Potential for Native Woodland Model to make the first estimate of carbon sequestration by large-scale native woodland expansion through natural regeneration in Scotland. We estimate native woodland could expand to cover an additional 3.9 million hectares of the Scottish uplands removing an average of 6.96 million tons of CO2 per year. This represents 35%–45% of the carbon removal target for UK woodlands that has been suggested by the UK Committee on Climate Change. Expanding woodlands to just 10% of this potential would double existing native woodland and could provide a multitude of benefits, including carbon removal equivalent to approximately 4% of this target. The next few decades are critical in terms of climate change mitigation, therefore further work is now required to improve these estimates and better constrain this potentially large contribution.
... no silvicultural management) since WWII (Fenn et al. 2015). Over the 1993-2008 time period, the site was characterized by a mean annual temperature of 10°C and a mean annual precipitation of 726 mm (Butt et al. 2009). The study took place on a 1.4 ha forest plot nested within the 18 ha long-term monitoring site part of the ForestGEO global network of forest inventory 115 plots. ...
Terrestrial Biosphere Modeling (TBM) is an invaluable approach for studying plant-atmosphere interactions at multiple spatial and temporal scales, as well as the global change impacts on ecosystems. Yet, TBM projections suffer from large uncertainties that limit their usefulness. A large part of this uncertainty arises from the empirical allometric (size-tomass) relationships that are used to represent forest structure in TBMs. Forest structure actually drives a large part of TBM uncertainty as it regulates key processes such as the transfer of carbon, energy, and water between the land and atmosphere, but remains challenging to measure and reliably represent. The poor representation of forest structure in TBMs results in models that are able to reproduce observed land fluxes, but which fail to realistically represent carbon pools, forest composition, and demography. Recent advances in Terrestrial Laser Scanning (TLS) techniques offer a huge opportunity to capture the three-dimensional structure of the ecosystem and transfer this information to TBMs in order to increase their accuracy. In this study, we quantified the impacts of integrating structural observations of individual trees (namely tree height, leaf area, woody biomass, and crown area) derived from TLS into the state-of-the-art Ecosystem Demography model (ED2.2) at a temperate forest site. We assessed the relative model sensitivity to initial conditions, allometric parameters, and canopy representation by changing them in turn from default configurations to site-specific, TLS-derived values. We show that forest demography and productivity as modelled by ED2.2 are sensitive to the imposed initial state, the model structural parameters, and the way canopy is represented. In particular, we show that: 1) the imposed openness of the canopy dramatically influenced the potential vegetation, the optimal ecosystem leaf area, and the vertical distribution of light in the forest, as simulated by ED2.2; 2) TLS-derived allometric parameters increased simulated leaf area index and aboveground biomass by 57 and 75 %, respectively; 3) the choice of model structure and allometric coefficient both significantly impacted the optimal set of parameters necessary to reproduce eddy covariance flux data.
