Revealing the causes and temporal distribution of tree mortality in Central Amazonia

Abstract

Tree mortality is a critical process in forest ecosystems, as it influences floristic composition, structure, dynamics, carbon storage, and forest nutrient cycling. However, the mechanisms behind tree death in tropical regions are still poorly characterized. This lack of information is mainly because tree mortality data come from long-interval inventories and studies that measured tree death seasonally are scarce. Here we offer novel insights into the power of fine temporal scale observations and we use a natural history approach to understand the processes and mechanism of tree mortality. We monitored tree mortality every month during one year, in 10 ha of terra-firme forest. To determine the pathways of mortality, we considered the state of the tree at the start of the investigation and the pre and post-mortem characteristics. From November 2010 to October 2011, 67 out of 5808 trees died. Despite the 2010 drought, mortality was highly correlated with monthly rainfall (r = 0.85). In total, six pathways of mortality were assessed. Storms were the main cause of mortality, killing 45% of all dead trees, followed by Biotic/abiotic factors accounting for 30% of tree mortality. The high mortality registered in the rainy season was mostly (78%) due to healthy trees dying uprooted or snapped. Finally, we would benefit from studies that assess mortality on a monthly basis and in combination with quantitative long-term data, we can substantially improve our understanding of the mechanisms behind tree death in the tropics.

Tree mode of death and mortality risk factors across Amazon forests

“…Nevertheless, direct observations of the exact processes and conditions that cause tree death are extremely rare (but see refs. 13,14 ), making information from standardised, long-term forest monitoring plots the principal means we have to derive large-scale geographical patterns and differentiate among the potential drivers of tree mortality. In plots, the inferred mode of death (standing vs. broken or uprooted) can be used to provide the basis for understanding the causes of death.…”

Lightning is a major cause of large tree mortality in a lowland neotropical forest

“…Smith et al , ; Sherman et al , ; Amir & Duke, ), and we expect that it will prove to be a similarly important mechanism of tree mortality at other tropical forest sites (Anderson, ; Magnusson et al , ). The only other quantitative assessment of lightning‐caused mortality in a terrestrial tropical forest found a similar contribution to total tree mortality (Fontes et al , ). Specifically, bimonthly assessments of 5808 trees near Manaus in central Amazonia for one year showed that 4.5% of deaths of trees > 10 cm in diameter were due to lightning (Fontes et al , ), which was equal to our finding of 4.5% for this size class.…”

“…The only other quantitative assessment of lightning‐caused mortality in a terrestrial tropical forest found a similar contribution to total tree mortality (Fontes et al , ). Specifically, bimonthly assessments of 5808 trees near Manaus in central Amazonia for one year showed that 4.5% of deaths of trees > 10 cm in diameter were due to lightning (Fontes et al , ), which was equal to our finding of 4.5% for this size class. Moreover, lightning frequency is high in most tropical forests; 68% of evergreen broadleaf tropical forests experience ≥ 50% of the lightning frequency recorded for BCI (Cecil et al , ; Friedl & Sulla‐Menashe, ).…”

Necromass Carbon Stock in a Secondary Atlantic Forest Fragment in Brazil

“…In addition, the increased presence of necromass in later stages of decomposition indicates that tree mortality may have occurred at more distant times. This fact highlights the need to carry out more frequent forest inventories and to monitor the phytosanitary conditions of the trees while alive to determine more precisely when a tree dies [54].…”