Tree Mortality After a Hot Drought: Distinguishing Density-Dependent and -Independent Drivers and Why It Matters

Crouchet, Sarah E.; Jensen, Jennifer; Schwartz, Benjamin; Schwinning, Susanne

doi:10.3389/ffgc.2019.00021

Cited by 46 publications

(44 citation statements)

References 63 publications

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“…The ecological relationships leading to this observation may not be intuitive. A larger number of live trees might be explained by resprouting, and more standing-dead trees and C found in dead and soils pools as a consequence to higher mortality rates 56 . It is worth mentioning that differences in localized drought effects might also be influenced by recent precipitation events, among other contemporary and legacy factors, such as species composition and soil characteristics (e.g.…”

Section: Resultsmentioning

confidence: 99%

Expansion of US wood pellet industry points to positive trends but the need for continued monitoring

Aguilar

Mirzaee

McGarvey

et al. 2020

Sci Rep

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Implementation of the European Union Renewable Energy Directive has triggered exponential growth in trading of pelletized wood fibers. Over 18 million tons of wood pellets were traded by EU member countries in 2018 of which a third were imported from the US. Concerns exist about negative impacts on US forests but systematic assessments are currently lacking. We assessed variability in fundamental attributes for timberland structure and carbon stocks within 123 procurement landscapes of wood pellet mills derived from over 38 thousand forest inventory plots in the eastern US from 2005 to 2017. We found more carbon stocks in live trees, but a fewer number of standing-dead trees, associated with the annual operation of large-scale wood pellet mills. In the US coastal southeast—where US pellet exports to the EU originate—there were fewer live and growing-stock trees and less carbon in soils with every year of milling operation than in the rest of the eastern US—which supplies the domestic market. Greater overlap of mills’ procurement areas exhibited discernible increments across selected carbon stocks. These trends likely reflect more intensive land management practices. Localized forest impacts associated with the wood pellet industry should continue to be monitored.

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Section: Resultsmentioning

confidence: 99%

Expansion of US wood pellet industry points to positive trends but the need for continued monitoring

Aguilar

Mirzaee

McGarvey

et al. 2020

Sci Rep

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“…The resprouting capacity of defoliated trees is higher in trees with high DBH (Matula et al, 2019), but it declines with age (Clarke et al, 2013). According to Crouchet et al (2019), the impact of the drought is higher on the dense stands and affects the less competitive trees, including smaller and older plants. Mediterranean coppices are very complex and dynamic systems (Fabbio, 2016) rich in diversity, in which increasing drought conditions may affect competition processes with changes in structure and composition.…”

Section: Discussionmentioning

confidence: 99%

Widespread Crown Defoliation After a Drought and Heat Wave in the Forests of Tuscany (Central Italy) and Their Recovery—A Case Study From Summer 2017

Pollastrini

Puletti²,

Selvi

et al. 2019

Front. For. Glob. Change

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An anomalous event of drought and heat occurred in central Italy during the summer of 2017. Based on the SPI (Standardized Precipitation Index) and data from the European Space Agency, this event started in November 2016 and was characterized by a strong reduction of precipitation and soil moisture, especially in lowland areas with Mediterranean climate. The aim of this case report were to describe the impact of this event on representative forest communities in central Italy, to analyze the different responses of deciduous and evergreen tree and shrub species in contrasting environmental conditions and to assess their subsequent capacity of recovery or, if not, mortality. Trees suffered severe impacts consisting of widespread crown defoliation, leaf desiccation, crown dieback and whole tree mortality. Deciduous tree species (Fagus sylvatica, Quercus pubescens, Quercus cerris) shed their leaves during the summer, but apical buds and twigs were preserved. This allowed these species to produce new shoots in the following year (2018) and to restore the canopy closure of the stands. Mediterranean evergreen broadleaves, such as Quercus ilex and Phillyrea latifolia suffered of total or partial crown desiccation with wilting leaves and branch dieback. These species partially resprouted in 2018 from axillary and latent buds. The case presented here is discussed within the wider context of the impacts of climate change on Mediterranean forests. Future research directions should include an effective forest monitoring system that combines terrestrial and remote sensing surveys, ad hoc field climate change experiments and silvicultural trials from the perspective of proactive management for the adaptation of forests to future climatic conditions.

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“…The response of tree species to drought can vary at the intraspecific level depending on both, regional and local factors (Orwig and Abrams, 1997;Gazol et al, 2017Gazol et al, , 2018Aragão et al, 2019;Baker et al, 2019;Crouchet et al, 2019). It is expected that tree species will be more vulnerable to drought near the rearedge (equatorward) and xeric limits of their distribution ranges (Sánchez-Salguero et al, 2017) where stronger legacy effects of drought on growth can be expected (Anderegg et al, 2015;Gazol et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Tree Species Are Differently Impacted by Cumulative Drought Stress and Present Higher Growth Synchrony in Dry Places

Gazol

Camarero

Sangüesa‐Barreda

et al. 2020

Front. For. Glob. Change

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The increase in frequency and intensity of droughts due to climate change might threaten forests under stress levels causing dieback and mortality episodes. Thus, deciphering how tree species from within a region respond to drought along environmental gradients should help us to understand forest vulnerability to climate change. To enlighten contrasting drought responses of dominant tree species, we reconstructed vegetation activity using Normalized Difference Vegetation Index (NDVI) and radial growth using tree-ring width series. We studied six tree species, three angiosperms (Fagus sylvatica, Quercus humilis, and Quercus ilex) and three gymnosperms (Pinus sylvestris, Pinus nigra, and Pinus halepensis), inhabiting a Mediterranean region in north-eastern Spain. We investigated if reduced growth resilience and increased growth synchrony after successive droughts (1986, 1989, 2005, and 2012): (i) were related to cumulative drought stress and (ii) preceded forest dieback in dry sites as compared to wet sites. In 2016, dieback affected Q. ilex and P. sylvestris stands in dry sites showing lower growth rates and NDVI. No dieback symptoms were observed in other species from dry (P. nigra, P. halepensis) or wet (F. sylvatica, Q. humilis, P. sylvestris) sites. Hot and dry summer conditions constrained growth and reduced NDVI. During 2005, a severe drought affected all species, but growth drops were more marked in dry places. All species were able to recover after extreme droughts, albeit angiosperms displayed lower than expected values of growth after the 2012 drought. Growth synchrony was higher in dry sites than in wet sites, and the differences were higher after the 2005 drought. This study reveals that the sensitivity of tree species to drought in species inhabiting the same region is species dependent, and it is contingent on local conditions with higher effects in dry sites than in wet sites. We describe how a cumulative impact of successive droughts increases growth synchrony and triggers the occurrence of dieback events in Mediterranean forests.

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Tree Mortality After a Hot Drought: Distinguishing Density-Dependent and -Independent Drivers and Why It Matters

Cited by 46 publications

References 63 publications

Expansion of US wood pellet industry points to positive trends but the need for continued monitoring

Expansion of US wood pellet industry points to positive trends but the need for continued monitoring

Widespread Crown Defoliation After a Drought and Heat Wave in the Forests of Tuscany (Central Italy) and Their Recovery—A Case Study From Summer 2017

Tree Species Are Differently Impacted by Cumulative Drought Stress and Present Higher Growth Synchrony in Dry Places

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