Stephenson et al. 2014, Nature, 507
log [mass (Mg)] AGB growth rate Africa Asia
But, the bigger the tree
the higher its above-ground biomass (AGB) growth rate
Neotropics
Conclusion
Despite large trees have high individual growth rate and stock substantial amount of biomass, we showed that stand-level biomass production likely decreases with the abundance of large trees in unlogged and logged natural forests. The
contribution of large trees to annual stand-level biomass production at the stand level appeares limited in comparison to that of the small trees. This pattern does not only originate from differences in abundance of small versus large trees or
differences in initial biomass stocks among tree size classes but also from a low efficiency of large trees to produce biomass and a relatively constant mortality rate among tree size classes.
200 400 600
0 20 40 60 80
control 4-ha plots
logged 4-ha plots
logged and thinned 4-ha plots
observations in 0.25-ha subplots % % Initial biomass stock
Abundance of large trees (% of biomass in large trees)
a cde de e a b c cd a ab ab ab a ab ab b a de e e b c c d a abc bc c a ab abc c a e e e b c cd de a b b c a bc b bc
Control Logged Logged + Thinned
10-30 30-50 50-70 70-9090-110110-130130-150 150+ 10-30 30-50 50-70 70-9090-110110-130130-150 150+ 10-30 30-50 50-70 70-9090-110110-130130-150 150+ -2.5 0.0 2.5 1 1 Biomass gains and losses Biomass gain Biomass loss Biomass net change
Abundance of large trees (% of biomass in large trees)
Total biomass varied
significantly among plots and, as expected, we found that biomass stock increased with the abundance of large trees (r=0.816).
But biomass production decreased with the abundance of large trees mainly because of a reduction in biomass gains with the abundance of large trees rather than variation of biomass losses.
Accept hypothesis 3. losses (tree mortality)
gains (tree growth)
Tree diameter classes (cm)
Key element of
numerous ecological processes (e.g. : nutrient cycle, hydrological
regime)
Huge amount of standing biomass
Under the assumption of steady state, the metabolic theory of ecology
predicts that tree growth increases with size
whereas mortality rate decreases with tree size
In natural tropical forests, large trees are rare and particular,
e.g. in terms of species (pioneer species) and life history
Tree mortality can be the driving process of biomass dynamics,
and particularly the mortality of large trees
Rutishauser et al. 2014, J. Veg. Sci, 21
High socio-economic value Unique habitat
for biodiversity
The more the large trees, the greater
the above-ground biomass (AGB) accross tropical forests
Slik et al. 2013, Glob. Ecol. Biogeo., 22
Density of large trees AGB
Neotropics
Africa
Asia
The role of large trees in the biomass production
of heterogeneous forest
Gauthier LIGOT, gligot@ulg.ac.be
Sylvie GOURLET-FLEURY, Dakis-Yaoba OUEDRAOGO, Sébastien BAUWENS, Yves BROSTAUX, Xavier MORIN, Fidèle BAYA, Jean-Louis DOUCET, Adeline FAYOLLE
At the stand level At the tree level
Content may not reflect National Geographic's current map policy. Sources: National Geographic, Esri, DeLorme, HERE, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, increment P Corp.
20°0'0"E 20°0'0"E 15°0'0"E 15°0'0"E 10°0'0"E 10°0'0"E 5°0'0"N 5°0'0"N 0°0'0" 0°0'0"
Experimental forest of M'Baiki
4 ha 4 ha 4 ha 4 ha 4 ha 4 ha 4 ha 4 ha 4 ha 4 ha Control Logged in 1984-1986 Logged + Thinned in 1984-1986
Tree monitoring in 10 plots of 4 ha monitored 1992-2012
29,729 trees, 255 taxa
Computation and statistics
200 m
50 m
tree agb = f(tree diameter, wood density)
Estimation of tree AGB with allometric equations Chave et al. 2009, Zanne et al. 2009
Biomass gains = sum of the biomass growth of all surviving and recruited trees during the census interval (1992-2012) Biomass losses = sum of the biomass of all trees that died during the census interval
Biomass net change = the difference between stand biomass in 1992 and 2012
Spatial bootstrap
160 subplots of 0.25 ha
Compute biomass gains and losses for each plot, subplot,
and diameter classes
Compute confidence intervals of 4-ha plot estimates bootstrapping over the 0.25-ha subplots
Accross all treatments,
there was a significant decrease in contribution to stand-level biomass gains with tree size Accept hypothesis 1.
Contribution to stand-level biomass losses depended more on treatment and initial
biomass stock than tree size. Contribution to biomass losses did not increased with tree size.
Reject hypothesis 2.
Control Logged Logged + Thinned
0 20 40 60 80 0 20 40 60 80 0 20 40 60 80 -2.5 0.0 2.5 5.0 7.5 Biomass gain (growth + recruitment) Biomass loss (mortality) Net change
Large trees play numerous key ecological roles, but they likely play a minor role
for the annual biomass production or carbon capture.
Preserving large trees might be a poor strategy to maximize biomass production or carbon capture.
Photo credits : © Jean-Louis Doucet,
Jean-Yves de Vleeschouwer,
Dakis-Yaoba Ouédraogo, Adeline Fayolle
TAKE HOM E
MESSAGE
While the role of large trees to the stock of biomass is clear,
their contribution to the annual production of biomass per area unit (at the stand level) is unclear.
We aim at disentangling the contribution of large trees to stand-level biomass production
Hypothesis 3
Biomass net change
(growth + recruitment - mortality)
Abundance of large trees Hypothesis 1
Biomass gains
(tree growth)
sum of the biomass gains of every large trees
per area unit
Small trees
Medium trees Large trees
Hypothesis 2
Biomass losses
(tree mortality)
Small trees
Medium trees Large trees
Freiburg 20 September 2017
