Tall Amazonian forests are less sensitive to precipitation variability

Giardina, Francesco; Konings, Alexandra G.; Kennedy, Daniel; Alemohammad, Seyed Hamed; Oliveira, Rafael S.; Uriarte, María; Gentine, Pierre

doi:10.1038/s41561-018-0133-5

Cited by 137 publications

(109 citation statements)

References 54 publications

Supporting

Mentioning

102

Contrasting

Order By: Relevance

“…Indeed, the distributions of leaf area and light environments are strongly related to DBH distribution of trees in Tapajós, as individuals optimize their productivity over the vertical gradient to create consistent relationships between canopy light environments and biomass growth (Stark et al., , ). Our results further suggest that rooting depth increases with tree height, compensating for the greater evaporative demand at the top of the canopy (McDowell & Allen, ) and allowing larger trees to be photosynthetically active during the dry season (Giardina et al., ). The greater light interception of taller trees may allow them to afford the carbon costs of growing deeper roots.…”

Section: Discussionsupporting

confidence: 52%

“…Nearly half the Amazon exhibits marked seasonality in rainfall and is subject to additional high‐magnitude water deficits caused by positive phases of the El Niño–Southern Oscillation (ENSO) (Jiménez‐Muñoz et al., ; Marengo, Tomasella, Alves, Soares, & Rodriguez, ). Despite these periodically adverse conditions for plant growth, trees can sustain transpiration, start new leaf flushing and maintain photosynthesis during dry periods, though the mechanisms underlying this high drought resistance are still under debate (Giardina et al., ; Huete et al., ; Malhi et al., ; Oliveira, Dawson, Burgess, & Nepstad, ; Restrepo‐Coupe et al., ; Saleska et al., ; Wu et al., ).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Hydrological niche segregation defines forest structure and drought tolerance strategies in a seasonal Amazon forest

et al. 2018

Self Cite

View full text Add to dashboard Cite

The relationship between rooting depth and above‐ground hydraulic traits can potentially define drought resistance strategies that are important in determining species distribution and coexistence in seasonal tropical forests, and understanding this is important for predicting the effects of future climate change in these ecosystems. We assessed the rooting depth of 12 dominant tree species (representing c. 42% of the forest basal area) in a seasonal Amazon forest using the stable isotope ratios (δ18O and δ2H) of water collected from tree xylem and soils from a range of depths. We took advantage of a major ENSO‐related drought in 2015/2016 that caused substantial evaporative isotope enrichment in the soil and revealed water use strategies of each species under extreme conditions. We measured the minimum dry season leaf water potential both in a normal year (2014; Ψnon‐ENSO) and in an extreme drought year (2015; ΨENSO). Furthermore, we measured xylem hydraulic traits that indicate water potential thresholds trees tolerate without risking hydraulic failure (P50 and P88). We demonstrate that coexisting trees are largely segregated along a single hydrological niche axis defined by root depth differences, access to light and tolerance of low water potential. These differences in rooting depth were strongly related to tree size; diameter at breast height (DBH) explained 72% of the variation in the δ18Oxylem. Additionally, δ18Oxylem explained 49% of the variation in P50 and 70% of P88, with shallow‐rooted species more tolerant of low water potentials, while δ18O of xylem water explained 47% and 77% of the variation of minimum Ψnon‐ENSO and ΨENSO. We propose a new formulation to estimate an effective functional rooting depth, i.e. the likely soil depth from which roots can sustain water uptake for physiological functions, using DBH as predictor of root depth at this site. Based on these estimates, we conclude that rooting depth varies systematically across the most abundant families, genera and species at the Tapajós forest, and that understorey species in particular are limited to shallow rooting depths. Our results support the theory of hydrological niche segregation and its underlying trade‐off related to drought resistance, which also affect the dominance structure of trees in this seasonal eastern Amazon forest. Synthesis. Our results support the theory of hydrological niche segregation and demonstrate its underlying trade‐off related to drought resistance (access to deep water vs. tolerance of very low water potentials). We found that the single hydrological axis defining water use traits was strongly related to tree size, and infer that periodic extreme droughts influence community composition and the dominance structure of trees in this seasonal eastern Amazon forest.

show abstract

Section: Discussionsupporting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Hydrological niche segregation defines forest structure and drought tolerance strategies in a seasonal Amazon forest

et al. 2018

Self Cite

View full text Add to dashboard Cite

show abstract

“…Condit, Hubbell, & Foster, 1996;Enquist & Enquist, 2011;Fauset et al, 2012;Feeley, Davies, Perez, Hubbell, & Foster, 2011). Although the link between rooting depth and tree size is still unclear (Stahl et al, 2013), this hypothesis is consistent with wetter areas tending to have more densely populated understoreys (Malhi et al, 2002;Pitman et al, 2002) and taller forests being less sensitive to precipitation variability (Giardina et al, 2018). Although the link between rooting depth and tree size is still unclear (Stahl et al, 2013), this hypothesis is consistent with wetter areas tending to have more densely populated understoreys (Malhi et al, 2002;Pitman et al, 2002) and taller forests being less sensitive to precipitation variability (Giardina et al, 2018).…”

Section: Introductionmentioning

confidence: 80%

Compositional response of Amazon forests to climate change

Esquivel‐Muelbert

Baker

Dexter

et al. 2018

Global Change Biology

303

251

View full text Add to dashboard Cite

Most of the planet's diversity is concentrated in the tropics, which includes many regions undergoing rapid climate change. Yet, while climate‐induced biodiversity changes are widely documented elsewhere, few studies have addressed this issue for lowland tropical ecosystems. Here we investigate whether the floristic and functional composition of intact lowland Amazonian forests have been changing by evaluating records from 106 long‐term inventory plots spanning 30 years. We analyse three traits that have been hypothesized to respond to different environmental drivers (increase in moisture stress and atmospheric CO 2 concentrations): maximum tree size, biogeographic water‐deficit affiliation and wood density. Tree communities have become increasingly dominated by large‐statured taxa, but to date there has been no detectable change in mean wood density or water deficit affiliation at the community level, despite most forest plots having experienced an intensification of the dry season. However, among newly recruited trees, dry‐affiliated genera have become more abundant, while the mortality of wet‐affiliated genera has increased in those plots where the dry season has intensified most. Thus, a slow shift to a more dry‐affiliated Amazonia is underway, with changes in compositional dynamics (recruits and mortality) consistent with climate‐change drivers, but yet to significantly impact whole‐community composition. The Amazon observational record suggests that the increase in atmospheric CO 2 is driving a shift within tree communities to large‐statured species and that climate changes to date will impact forest composition, but long generation times of tropical trees mean that biodiversity change is lagging behind climate change.

show abstract

“…Just as all species are not equally susceptible to drought, individuals within species also vary in the extent to which they suffer mortality during droughts. Across forested ecosystems, susceptibility is often skewed towards the smallest and/or largest size classes (Bennett, Mcdowell, Allen, & Anderson‐Teixeira, ; Choat et al, ; Giardina et al, ; Greenwood et al, ; McDowell et al, ; O'Brien et al, ; Phillips et al, ). Seedlings and young individuals have poorly developed root and vascular systems and limited carbohydrate reserves, while larger individuals may be more vulnerable because of their greater overall water requirements, greater inherent vulnerability to hydraulic stress, or because of the greater cumulative effects of earlier exogenous stressors such as fires, herbivory, pathogens and competition in larger, older individuals (Allen et al, ; Anderegg, Berry, et al, ; Bennett et al, ; Rice et al, ; Zhang et al, ).…”

Section: Direct Effects Of Droughts On Savanna Tree Mortalitymentioning

confidence: 99%

“…Differences in mortality can arise even in the absence of any size‐related differences in drought tolerance per se if different sized individuals “experience” droughts to different degrees. For example, larger individuals with access to the water table might not “experience” droughts to the same extent as smaller, shallow rooted individuals, and vice versa (Chitra‐Tarak et al, ; Giardina et al, ).…”

Section: Direct Effects Of Droughts On Savanna Tree Mortalitymentioning

confidence: 99%

Droughts and the ecological future of tropical savanna vegetation

Sankaran

2019

Journal of Ecology

View full text Add to dashboard Cite

Climate change is expected to lead to more frequent, intense and longer droughts in the future, with major implications for ecosystem processes and human livelihoods. The impacts of such droughts are already evident, with vegetation dieback reported from a range of ecosystems, including savannas, in recent years. Most of our insights into the mechanisms governing vegetation drought responses have come from forests and temperate grasslands, while responses of savannas have received less attention. Because the two life forms that dominate savannas—C3 trees and C4 grasses—respond differently to the same environmental controls, savanna responses to droughts can differ from those of forests and grasslands. Drought‐driven mortality of savanna vegetation is not readily predicted by just plant drought‐tolerance traits alone, but is the net outcome of multiple factors, including drought‐avoidance strategies, landscape and neighborhood context, and impacts of past and current stressors including fire, herbivory and inter‐life form competition. Many savannas currently appear to have the capacity to recover from moderate to severe short‐term droughts, although recovery times can be substantial. Factors facilitating recovery include the resprouting ability of vegetation, enhanced flowering and seeding and post‐drought amelioration of herbivory and fire. Future increases in drought severity, length and frequency can interrupt recovery trajectories and lead to compositional shifts, and thus pose substantial threats, particularly to arid and semi‐arid savannas. Synthesis. Our understanding of, and ability to predict, savanna drought responses is currently limited by availability of relevant data, and there is an urgent need for campaigns quantifying drought‐survival traits across diverse savannas. Importantly, these campaigns must move beyond reliance on a limited set of plant functional traits to identifying suites of physiological, morphological, anatomical and structural traits or “syndromes” that encapsulate both avoidance and tolerance strategies. There is also a critical need for a global network of long‐term savanna monitoring sites as these can provide key insights into factors influencing both resistance and resilience of different savannas to droughts. Such efforts, coupled with site‐specific rainfall manipulation experiments that characterize plant trait–drought response relationships, and modelling efforts, will enable a more comprehensive understanding of savanna drought responses.

show abstract

Tall Amazonian forests are less sensitive to precipitation variability

Cited by 137 publications

References 54 publications

Hydrological niche segregation defines forest structure and drought tolerance strategies in a seasonal Amazon forest

Hydrological niche segregation defines forest structure and drought tolerance strategies in a seasonal Amazon forest

Compositional response of Amazon forests to climate change

Droughts and the ecological future of tropical savanna vegetation

Contact Info

Product

Resources

About