Abstract
BackgroundAmazon palm swamp peatlands are major carbon (C) sinks and reservoirs. In Peru, this ecosystem is widely threatened owing to the recurrent practice of cutting Mauritia flexuosa palms for fruit harvesting. Such degradation could significantly damage peat deposits by altering C fluxes through fine root productivity, mortality, and decomposition rates which contribute to and regulate peat accumulation. Along a same peat formation, we studied an undegraded site (Intact), a moderately degraded site (mDeg) and a heavily degraded site (hDeg) over 11 months. Fine root C stocks and fluxes were monthly sampled by sequential coring. Concomitantly, fine root decomposition was investigated using litter bags. In the experimental design, fine root stocks and dynamics were assessed separately according to vegetation type (M. flexuosa palm and other tree species) and M. flexuosa age class. Furthermore, results obtained from individual palms and trees were site-scaled by using forest composition and structure.ResultsAt the scale of individuals, fine root C biomass in M. flexuosa adults was higher at the mDeg site than at the Intact and hDeg sites, while in trees it was lowest at the hDeg site. Site-scale fine root biomass (Mg C ha−1) was higher at the mDeg site (0.58 ± 0.05) than at the Intact (0.48 ± 0.05) and hDeg sites (0.32 ± 0.03). Site-scale annual fine root mortality rate was not significantly different between sites (3.4 ± 1.3, 2.0 ± 0.8, 1.5 ± 0.7 Mg C ha−1 yr−1 at the Intact, mDeg, and hDeg sites) while productivity (same unit) was lower at the hDeg site (1.5 ± 0.8) than at the Intact site (3.7 ± 1.2), the mDeg site being intermediate (2.3 ± 0.9). Decomposition was slow with 63.5−74.4% of mass remaining after 300 days and it was similar among sites and vegetation types.ConclusionsThe significant lower fine root C stock and annual productivity rate at the hDeg site than at the Intact site suggests a potential for strong degradation to disrupt peat accretion. These results stress the need for a sustainable management of these forests to maintain their C sink function.
Highlights
Amazon palm swamp peatlands are major carbon (C) sinks and reservoirs
The reduction in vegetation density with increasing degradation was drastic with twice fewer M. flexuosa seedlings and juveniles, five times fewer M. flexuosa adults and three times fewer trees at the heavily degraded site (hDeg) site compared to the Intact site
Trees dominated the stands at the Intact and hDeg sites while at the moderately degraded site (mDeg) site the share tree: M. flexuosa was close to 50:50
Summary
Amazon palm swamp peatlands are major carbon (C) sinks and reservoirs. In Peru, this ecosystem is widely threatened owing to the recurrent practice of cutting Mauritia flexuosa palms for fruit harvesting. Peat-forming vegetation communities are for the most part (78%) swamp forests (permanently or semi-permanently flooded forests) dominated by the palm Mauritia flexuosa, a dioecious species that can establish nearly monodominant stands [8,9,10]. Local communities cut the palms because their height (often up to 40 m) and the slippery nature of their bark render their climbing difficult [14] This unsustainable harvesting practice undermines the economic potential of M. flexuosa for rural communities [15], it induces a male dominance in degraded stands [13, 16], modifies the structure and floristic composition of the forest [10, 12, 17] and likely disrupts a wide range of ecological patterns and processes, including belowground C dynamics [18, 19]
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