@article{fdi:010085886,
  title = {{M}onitoring vegetation dynamics with open earth observation tools : the case of fire-modulated savanna to forest transitions in {C}entral {A}frica},
  author = {{S}agang, {L}. {T}. and {P}loton, {P}ierre and {V}iennois, {G}. and {F}eret, {J}. {B}. and {S}onke, {B}. and {C}outeron, {P}ierre and {B}arbier, {N}icolas},
  editor = {},
  language = {{ENG}},
  abstract = {{W}oody encroachment and forest progression are widespread in forest-savanna transitional areas in {C}entral {A}frica. {Q}uantifying these dynamics and understanding their drivers at relevant spatial scales has long been a challenge. {R}ecent progress in open access imagery sources with improved spatial, spectral and temporal resolution combined with cloud computing resources, and the advent of relatively cheap solutions to deploy laser sensors in the field, have transformed this domain of study. {W}e present a study case in the {M}pem & {D}jim {N}ational {P}ark ({MDNP}), a 1,000 km(2) protected area in the {C}entre region of {C}ameroon. {U}sing open source algorithms in {G}oogle {E}arth {E}ngine ({GEE}), we characterized vegetation dynamics and the fire regime based on {L}andsat multispectral imagery archive (1975-2020). {C}urrent species assemblages were estimated from {S}entinel 2 imagery and the open source biodiv{M}ap{R} package, using spectral dissimilarity. {V}egetation structure (aboveground biomass; {AGB}) was characterized using {U}nmanned {A}erial vehicle ({UAV}) {L}i{DAR} scanning data sampled over the study area. {S}avanna vegetation, which was initially dominant in the {MDNP}, lost about 50% of its initial cover in <50 years in favor of forest at an average rate of ca. 0.63%.year(-1) (6 km(2).year(-1)). {S}pecies assemblage computed from spectral dissimilarity in forest vegetation followed a successional gradient consistent with forest age. {AGB} accumulation rate was 3.2 {M}g.ha(-1).year(-1) after 42 years of forest encroachment. {I}n savannas, two modes could be identified along the gradient of spectral species assemblage, corresponding to distinct {AGB} levels, where woody savannas with low fire frequency store 40% more {AGB} than open grassy savannas with high fire frequency. {A} fire occurrence every five year was found to be the fire regime threshold below which woody savannas start to dominate over grassy ones. {A} fire frequency below that threshold opens the way to young forest transitions. {T}hese results have implications for carbon sequestration and biodiversity conservation policies. {M}aintaining savanna ecosystems in the region would require active management actions to limit woody encroachment and forest progression, in contradiction with global reforestation goals.},
  keywords = {{F}orest-savanna transition ; {G}oogle {E}arth {E}ngine ; {F}ire ; {UAV}-{L}i{DAR} ; {A}boveground biomass ; {S}pecies assemblage ; {AFRIQUE} {CENTRALE}},
  booktitle = {},
  journal = {{ISPRS} {J}ournal of {P}hotogrammetry and {R}emote {S}ensing},
  volume = {188},
  numero = {},
  pages = {142--156},
  ISSN = {0924-2716},
  year = {2022},
  DOI = {10.1016/j.isprsjprs.2022.04.008},
  URL = {https://www.documentation.ird.fr/hor/fdi:010085886},
}