(altered pore size, water repellency, stability of
aggregates), biological composition (vegetation
loss, changes in microbial communities), and
chemical properties (increase in organic car-
bon due to combustion, volatilization of nitro-
gen and phosphorus), with detrimental effects
( 94 , 95 ). Burned soil may become hydrophobic
as a result of accumulation of hydrophobic
substances on the soil surface after burning of
organic materials ( 96 ). Moreover, the exposed
soil is much more vulnerable to wind ( 97 ) and
water ( 96 ) erosion during the first few years
following wildfires. Loss of topsoil due to ero-
sion is the primary risk of failure for forest
replanting. Another consequence of the wild-
fires is the formation of hazardous organic
compounds such as polycyclic aromatic hy-
drocarbons (PAHs) as a result of combustion
processes of the plant biomass ( 98 ). Soil micro-
organisms play an important role in soil func-
tion recovery after fire. PGPR have been shown
to enhance nutrient availability and promote
plant growth in fire-impacted soil ( 99 , 100 ).
The inoculation of soil with ectomycorrhizal
fungi in burned forest also stimulates plant
growth ( 101 ), making them attractive for as-
sisted forest regeneration in fire-damaged
soils. Alternatively, the growth of locally in-
digenous soil microorganisms can be stimu-
lated with organic matter, oxygen, specific
plant species, or other stimulating factors
through so-called biostimulation ( 102 ). Bio-
stimulation enhances the natural biodegrada-
tion potential of the indigenous microbial
community and has been shown to be a most
promising strategy for PAH removal from
burned forest soil ( 103 ) and from contami-
nated soil ( 104 ). To combat hydrophobicity
of soils, wax-degrading Actinobacteria have
successfully been used to reduce water re-
pellency, either via Actinobacteria inocula-
tion in soil ( 105 ) or when still present in soil
via their biostimulation ( 106 ), which is a more
practical and economical approach.Loss of soil fertility
SincetheGreenRevolutioninthe1950sand
1960s, agricultural production has increased
worldwide with the aim of feeding an in-
creasing world population. Global food de-
mand will rise by another 70% in the coming
decades, emphasizing the need for intensive
crop production ( 107 ). The intensive cultiva-
tion of crops can lead to the exhaustion of soil
organic matter and soil nutrient reserves, re-
sulting in soil degradation ( 108 ). Driven by
increased understanding of the role of micro-
organisms in soil health and crop productiv-
ity, the use of agronomic practices to restore
soil fertility through organic matter addition,
microbial N fixation, and nutrient recycling
(i.e., regenerative agriculture) is also increas-
ing rapidly. Such practices include no-tillage,
rotating crops and growing cover crops, re-
turning crop residue into the soil, using bio-
fertilizers or biopesticides, and applying organic
fertilizers such as manure, biochar, and com-
post ( 109 ). It has been shown that biofertil-
izers (i.e., inocula of fungi and bacteria) can
be combined with organic fertilizers to re-
duce the need for chemical fertilizers and to
use soil resources more efficiently ( 110 ). As
for the biopesticides, these are less toxic than
abiotic pesticides, reducing environmental pol-
lution, and can be more effective than chem-
ical pesticides in the long term ( 110 ). Soil organic
matter, biopesticides, and biofertilizers provideCobanet al.,Science 375 , eabe0725 (2022) 4 March 2022 4 of 10
Fig. 3. Main types of land degradation and main
types of useful bacteria.
Fig. 2. Development of land degradation estimations.Top left: Total estimated land degradation. Top right: Estimated land degradation per continent. These
graphs are based on data from Gibbs and Salmon (2015) and IPBES (2018) ( 177 , 178 ); Antarctica is excluded in both panels. Variations between these estimations
have not led to a conclusive estimate of spatial coverage and severity of land degradation at the global scale ( 179 ). For this reason, IPBES (2018) uses a convergence-
of-evidence approach based on global change issues.
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