Reply to Skole et al.: Regarding high-resolution carbon stocks and emissions in the Amazon

Abstract

Skole et al.(1) claim that we do not make a case for highresolution carbon stock and emissions mapping in tropical forests. Specifically, they argue that (i) our Intergovernmental Panel on Climate Change (IPCC) Tier 1 estimates for the Peruvian Amazon study are biased, (ii) our plot-level carbon estimates used to calibrate airborne Light Detection and Ranging (LiDAR) are flawed, and (iii) our regional mapping of carbon stocks is low compared with a their estimate using field data from a previous local-scale study. However, their critique is based on misstatements about our methods and a misunderstanding of carbon stock variation throughout the region. (1) present a Tier 1 estimate, downscaled with forest fractional cover, of 538 teragrams (Tg) C. This reduces our purportedly biased estimate of 587 Tg by only 8%. However, far more importantly, we showed that these Tier 1 estimates have uncertainties exceeding 90%, rendering them extremely tenuous for use in monitoring carbon emissions.Skole et al.(1) also incorrectly state the allometries used in our field plots. As reported, 10 or more trees were measured for height in every plot distributed across the range of forest types found throughout the region. We measured the heights of the three largest trees in every plot, and these values were used in the model by Chave et al. (5). Because larger trees contribute far greater biomass to plot totals, our measurements accounted for the majority of biomass in all plots. Skole et al. (1) also suggest that an alternative allometric model from Winrock International (6) would be more appropriate for our area. They argue that the model of Chave et al. (5) was not calibrated to the height variation of locally measured trees, which is not true. Far from dismissing the Winrock International (6) model, we tested and rejected it, along with two other models, because each lacks parameters to account for height and/or wood density of individual trees.Skole et al. (1) next assume that the Winrock International (6) study was representative of our much larger study region. However, airborne LiDAR sampling revealed 20-35% lower carbon stocks in forests to the north and south of the local Winrock study, showing that the Winrock plots were placed in an area of locally high biomass. Extrapolating those local values to our entire study region misses critical carbon variation and produces an erroneous result. By substituting a locally derived carbon density value based on just 4 of 26 vegetation types found throughout the region, Skole et al.(1) overestimate regional carbon stocks by 25%-and ironically-underscore the importance of using a rigorous high-resolution method such as ours (2).The criticisms leveled by Skole et al. (1) reinforce the importance of our key findings: (i) forest carbon density varies significantly by factors operating at differing geological, ecological, and land-use scales, (ii) these variations in carbon density are invisible using IPCC Tier 1 mapping techniques but can be accounted for with a combination of airborne...

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“…For example, in the Peruvian Amazon, data from the Los Amigos Conservation Concession [ 31 ] were shown not to be representative of forests nationally. Nearby forests situated to the north and south of this local study are estimated to contain 20-35% less carbon per unit area [ 32 ], suggesting that Los Amigos Conservation Concession is an area of locally high biomass. Since Tier 3 methods account for variation observed within biomes and countries, the representativeness of the carbon estimates is higher than those associated with Tier 1 and 2 methodologies [ 32 , 33 ].…”

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“…Until now, the known evolutionary and ecological roles of sperm chemoattractants were limited to (i) providing remote chemical signals that increase the effective target size of eggs and thereby promote sperm-egg encounters [4,5] and (ii) providing an efficient mechanism of avoiding costly interspecific hybridization [8,9]. The latter of these two functions emphasizes the variation that must exist among sperm chemoattractants among divergent taxa.…”

“…Although prevalent across most metazoans [3], sperm chemotaxis is best documented in broadcast spawning marine invertebrates, where males and females release gametes into the external environment. In these taxa, the evolutionary and ecological functions of sperm chemotaxis include increasing the effective target size of eggs, thereby enabling sperm to remotely orient towards fertile eggs via chemical signals [4][5][6][7], and maintaining species integrity by facilitating species recognition [8,9]. Although these naturally selected functions of sperm chemotaxis are highly relevant to broadcast spawning marine invertebrates, particularly in species with overlapping distributions and breeding seasons [4], the potential for chemoattractants to also mediate sperm -egg interactions within species remains enigmatic [10].…”

Reply to Comment on ‘A first map of tropical Africa’s above-ground biomass derived from satellite imagery’

“…degraded areas) that are captured in the satellite observations, and thus may tend to overestimate AGB in forest and woodland areas (as has been well documented; see e.g. Asner et al 2011). Finally, although it is probably obvious to anyone who has worked with such data sets, the satellite data that we used were based on 1 km 2 (100 ha) pixels whereas the plot data of Mitchard et al always covered a smaller proportion of the MODIS pixels (as did, we note, the field data that we calibrated our initial model on).…”