10.5061/DRYAD.PG4F4QRR5
Zhou, Yong
0000-0003-2546-8462
Yale University
Singh, Jenia
Harvard University
Butnor, John
US Forest Service
Coetsee, Corli
Scientific Services, Kruger National Park
Boucher, Peter
Harvard University
Case, Madelon
Yale University
Hockridge, Evan
Harvard University
Davies, Andrew
Harvard University
Staver, Carla
Yale University
Limited increases in savanna carbon stocks over decades of fire suppression
Dryad
dataset
2021
FOS: Natural sciences
Yale University
https://ror.org/03v76x132
Harvard University
https://ror.org/03vek6s52
US Forest Service
https://ror.org/03zmjc935
2022-01-13T00:00:00Z
2022-01-13T00:00:00Z
en
https://doi.org/10.5281/zenodo.5842435
1085419433 bytes
5
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Savannas cover a fifth of the land surface and contribute a third of
terrestrial net primary production, accounting for three quarters of
global area burned and over half of global fire-driven carbon emissions.
Fire suppression and afforestation have been proposed as tools to increase
carbon sequestration in these ecosystems. A robust quantification of
whole-ecosystem carbon storage in savannas is lacking, however, especially
under altered fire regimes. Here, we provide the first direct estimates of
whole-ecosystem carbon response to over 60 years of fire exclusion in a
mesic African savanna. We found that fire suppression increased
whole-ecosystem carbon storage by only 35.4 ± 12% (mean ± standard error),
even though tree cover increased by 78.9 ± 29.3%, corresponding to total
gains of 23.0 ± 6.1 Mg C ha-1 at an average ~0.35 ± 0.09 Mg C ha-1 yr-1,
more than an order of magnitude lower than previously assumed. Frequently
burned savannas had substantial belowground carbon, especially in biomass
and deep soils. These belowground reservoirs are not fully considered in
afforestation or fire suppression schemes but may mean that the decadal
sequestration potential of savannas is negligible, especially weighed
against concomitant losses of biodiversity and function.
Study site: Kruger National Park (latitude: 22°20ʹ - 25°30ʹS; longitude:
31°10ʹ - 32°00ʹE) in South Africa Experimental design: Kruger maintains
one of a handful of long-term burning experiments in tropical savannas.
The experimental burning plots (EBPs) were initiated in 1954, making them
the longest-running fire ecology research project in African savannas. The
EBPs are distributed across four different landscapes of Kruger (i.e.,
Mopani, Satara, Skukuza, Pretoriuskop) with different dominant tree
species, parent materials, and rainfall. Each landscape can be considered
as an independent factorial design with four replicates (hereafter,
strings). Within each string, there are 12 treatments with the fire return
interval of each treatment representing a different combination of
frequency and season. For this study, we selected the Pretoriuskop
landscape receiving ~700 m rainfall, which broadly represents African
savannas that have the potential to reach full tree cover. Among these 12
treatments, we selected plots burned every year in August (hereafter,
annual) to represent an extreme fire regime; plots burned every three
years in August (hereafter, triennial) to represent the near-natural fire
return interval of African savannas; and plots that have not burned since
1954 (hereafter, unburned) to represent savannas with fire-suppressed
status. Light detection and ranging (LiDAR) data collection: Woody biomass
was estimated using LiDAR. We used Riegl VUX-1LR LiDAR unit integrated
onto a DJI Matrice 600 PRO unoccupied aerial system (UAS) to collect
high-resolution airborne LiDAR data. We carried out the LiDAR survey
during the middle of the wet season (i.e., January) of 2020 when
vegetation was at full leaf-on stage. The flight altitude was 100 m above
ground level, flight speed was 8 m s-1, and the LiDAR scan rate was 78.1
lines/second (see Supplementary Table 4 for other parameter settings). The
UAS maintained consistent elevation above the ground by using 30 m × 30 m
elevational data from the shuttle radar topography mission (SRTM) to
adjust flight altitude in real time during the survey. All treatments
within each string were surveyed with transects of identical heading to
decrease the probability of introducing confounding variables and remote
sensing artifacts created by differing survey methodologies or LiDAR scan
directions. Ground penetrating radar data collection: Coarse lateral root
biomass from woody plants was estimated using the ground penetrating radar
(GPR). GPR profiles were acquired using the Subsurface Interface Radar
(SIR) System-4000 with 1.6 GHz shielded antenna and odometer wheels for
position recording (Geophysical Survey Systems Inc., NH, USA). Prior to
the survey, the grass layer was carefully removed to avoid any
interference in the transmission of electromagnetic energy from antenna to
soils. The survey was conducted during the dry season (September to
November) of 2018 with soil water content less than 5%. At each 10 m × 10
m plot, GPR profiles were collected on a 20-cm grid. If a tree was present
on a scanning line, the rest of the GPR profile was obtained from the
opposite direction. The topography across all plots was relatively flat
with minimal surface relief (< 5 cm). Extra care was taken to
ensure the accurate position of each GPR profile with a guide rope and the
difference in the length of GPR profile was less than 1% (i.e., 10 cm) of
the supposed distance (i.e., 10 m).
This data is comprised of two components: (1) data and code for light
detection and ranging (LiDAR) processing; (2) data and code for ground
penetrating radar (GPR) processing. Please refer to the paper for more
details on data analysis.