Online seminars

Our next seminar will take place on Tuesday, November 19th (2100 CET).

Brendan Choat

The impact of extreme drought on Australian forests and woodlands.

Abstract:

Severe droughts have caused widespread tree mortality across many forest biomes with profound impacts on ecosystem function and carbon balance. Climate change is expected to intensify regional scale droughts via the effects of higher temperatures and evaporative demand, with evidence suggesting that amplification of drought stress by anomalously high temperatures is already occurring. South-eastern Australia was subject to a severe drought from 2017–2020, with 2019 being both the hottest and driest year on record across the continent. This drought resulted in massive canopy die-off in forest and woodland vegetation throughout south-eastern Australia. Broadscale forest mortality events have focused attention on the physiological underpinnings of drought-induced tree death and our ability to forecast risk to forests from future extreme events. Catastrophic failure of the plant hydraulic system caused by the formation of gas emboli in the xylem is recognised as a principal mechanism associated with tree mortality during drought. Recent work has advanced our understanding of this process and identified species-specific physiological thresholds for tree death. I will explore our current understanding of tree response to drought, incorporating field data from the 2019 drought and the application of hydraulic failure thresholds to process-based models predicting mortality. At the whole plant level, developments in methodology used to evaluate the impacts of water stress on plant hydraulic function provide novel insights into hydraulic failure and mechanisms of recovery after drought.

Past seminars

Our #23 ITMN seminar took place on October 8th (1600 CEST).

Teja Kattenborn & Clemens Mosig

deadtrees.earth – a database of centimeter-scale aerial imagery as premier reference data for mapping global tree mortality

Abstract:

Quantifying tree mortality at global scale remains a major unsolved challenge. Earth observation satellites, such as the Copernicus Sentinel fleet have sufficient resolution to map even scattered tree mortality patterns. Coupled with supervised machine learning, they present a promising avenue to map standing dead trees at global scale. However, to train globally transferable machine learning models , we need a globally comprehensive reference dataset.

Here, we present the launch of the community-based deadtrees.earth database, compromising more than 1500 globally distributed centimeter-scale orthophotos of forests with delineated standing deadwood. This database acts as a foundation to a machine learning model ecosystem that leverages these drone orthophotos and labels as reference for satellite-based tree mortality mapping. Finally, we present a model that provides a yearly map, fractional cover of standing deadwood at 10 m resolution, across global ecosystems. These products will facilitate to reveal and understand global tree mortality dynamics across.

Here is the recording of Teja and Clemens’ presentation. Enjoy!

Our #22 ITMN seminar took place on May 28th (1600 CEST).

Lalasia Bialic-Murphy

The pace of life for forest trees

Abstract:

Tree growth and longevity trade-offs fundamentally shape the terrestrial carbon balance. Yet, we lack a unified understanding of how such trade-offs vary across the world’s forests. In this seminar, I will present results from a collaboration with an international team of researchers. By mapping life history traits for a wide range of species across the Americas, our findings reveal considerable variation in remaining life expectancies from 10 cm in diameter and show that the pace of life for trees can be accurately classified into four demographic functional types. We find emergent patterns in the strength of trade-offs between growth and longevity across a temperature gradient. Furthermore, we show that the diversity of life history traits varies predictably across forest biomes, giving rise to a positive relationship between trait diversity and productivity. Our pan-latitudinal assessment provides novel insights into the demographic mechanisms that govern the rate of carbon turnover across forest biomes.

Here is the recording of lalasia’s presentation. Enjoy!

Our #21 ITMN seminar took place on March 18th (1700 CET).

Pieter Zuidema

Pantropical tree growth responses to climatic variation and extremes.

Abstract:

Increasing drought stress under anthropogenic climate change jeopardizes the potential of tropical forests to capture carbon in woody biomass and act as CO2 sink. A pantropical quantification of drought impacts on tree stem growth is needed to evaluate this risk. We established and used the tropical tree-ring network to assess climate sensitivity and drought impacts.

Based on 477 tree-ring chronologies we found modest stem growth declines (median: 2-4%) during the 10% driest years. Growth declines were larger for dry-season than wet-season droughts, specifically for Gymnosperms, and at hotter and more arid sites.

Using empirical relationships between growth anomalies and tropical tree mortality, we estimate the pantropical growth reduction to induce a rise of 0.1% in annual tree mortality (compared to 1% baseline). Lagged growth reductions during post-drought years were rare. Over half of the growth reduction during drought years was mitigated during wet extreme years.

Drought impacts on tropical forest carbon sequestration through stem growth have been small and short-lived, but will aggravate under climate change, in particular through associated elevated mortality risks.

Here is the recording of Pieter’s presentation. Enjoy!

Our #20 ITMN seminar took place on January 17th (1700 CET).

Philippe Ciais

Harnessing big data and artificial intelligence for forest monitoring

Abstract:

The fusion of satellite data from different sensors allows to create new maps of forest biomass and height, and their changes over time, down to the level of individual trees. Philippe will present new deep learning models of forest attributes and applications, including an attribution of disturbances over France.

Here is the recording of Philippe’s presentation. Enjoy!

Our #19 ITMN seminar took place on November 21st (1700 CET).

Joanne White

Contributions of remote sensing to characterizing post-disturbance forest recovery in boreal forests

Abstract:

The success and rate of forest regeneration following disturbance has consequences for sustainable forest management, climate change mitigation, and biodiversity, among others. Systematically monitoring forest regeneration over large and often remote areas of the boreal forest is challenging. The application of remotely sensed data to characterize post-disturbance recovery in the boreal has been an active topic of research for more than 25 years. Innovations in sensors, data policies, curated data archives, and increased computational capacity have enabled new insights on the characterization of post-disturbance forest recovery, particularly following stand replacing disturbances. The past, current, and potential future contributions of remote sensing to the characterization of forest recovery in boreal forests will be highlighted.

Here is the recording of Joanne’s presentation. Enjoy!

Our #18 ITMN seminar took place on October 17th (1600 CEST).

Tommaso Jucker

Tracking forest dynamics across spatial, temporal and ecological scales using airborne LiDAR

Abstract:

Characterising the processes that shape forest dynamics across broad spatial and temporal scales remains a major challenge in ecology. Satellite remote sensing has played an important role in helping to fill this knowledge gap, providing us with a global picture of how forests have been changing over the past several decades. However, relating changes in forest cover observed from space to the growth, mortality and recruitment of individual trees that ecologists typically measure in the field is anything but straightforward. In this talk I will explore a number of ways in which airborne LiDAR can act as a go-between satellites and ground data when it comes to tracking forest responses to disturbance across spatial, temporal and ecological scales.

Here is the recording of Tommaso’s presentation. Enjoy!

Our #17 ITMN seminar took place on April 18th (1600 CET).

Arthur Gessler

New approaches for monitoring forest functioning in a changing climate – crossing scales from molecular mechanisms to stand wide processes.

Abstract:

Climate change is affecting forest functioning and jeopardizes the services forest ecosystems provide. Reduced water availability during drought events and increased temperatures affect photosynthetic carbon assimilation, tree growth and the defense capacity causing tree damage and mortality on the long-term.
Forest monitoring (as carried out e.g., within the framework of ICP Forests) provides important information on the changes and long-term trajectories of tree health and mortality. Novel techniques might, however, provide additional mechanistic insights that can complement classical monitoring.
Here we show how the characterization of crown defoliation (a standard ICP Forests metric) trajectories allow to predict the future mortality risk and how the leaf and needle metabolome in dying trees provides additional understanding of the mortality processes.
In addition, continuous determination of the origin of water uptake (based on water isotoplogues) and the tree water deficit (based on point dendrometers) helps nowcasting the immediate stress responses of trees to extreme events.
Finally, we explore how pre-visual stress signals from drone based remote sensing (e.g., the Photochemical Reflectance Index PRI) and its relationship to leaf level photo- and pigment chemistry might be implemented (and scaled to satellite based remote sensing) to better predict health and mortality risks in future.

Here is the recording of Arthur’s presentation. Enjoy!

Our #16 ITMN seminar took place on March 14th (1600 CET).

Anna Trugman

Integrating plant physiology and community ecology across scales through trait-based models to predict drought mortality

Abstract:

Climate change has the potential to massively disrupt terrestrial ecosystem productivity, impacting biodiversity, and driving Earth’s forests to release carbon into the atmosphere, which would further exacerbate climate change. Plant functional traits, such as those that determine tree drought vulnerability, and the diversity in traits within a forest, modulate surface water, carbon, and energy fluxes. Yet, we do not know how species composition and their accompanying traits will change with climate change. In this talk, I leverage plant physiological observations, large observational databases, and trait-based ecosystem models to understanding the extent to which plant trait diversity can impact ecosystem resilience to drought events in the continental United States. I then discuss predictions and ecological uncertainties in a changing climate.

Here is the recording of Anna’s presentation. Enjoy!

Our #15 ITMN seminar took place on January 18th (1630 CET).

Miroslav Svoboda

Past disturbance history, tree longevity, and recent tree mortality in temperate primary forests of east and south-east Europe

Abstract:

Primary forests provide important baseline information for our managed forests. Despite intensive use, primary forests still exist in east and south-east Europe. Their past disturbance history provides important reference information for current attempt on application of closer-to-nature forest management in the region. Recent tree mortality and tree longevity patterns in primary forests provide important feedback about ability of the natural forests to cope with ongoing climate change.

Here is the recording of Miroslav’s presentation. Enjoy!

Our #14 ITMN seminar took place on December 6th (1600 CET).

Daniel Zuleta

Tree mortality and damage links in tropical forests

Abstract:

Large uncertainties remain on how tropical forests will respond to a rapidly changing climate. This uncertainty is primarily attributed to spatial variation in woody residence times (i.e., biomass losses via tree mortality and branchfall), which occur more abruptly than tree growth and recruitment. We used data from the ForestGEO annual monitoring program to study the relative importance of multiple tree-level factors involved in tree death, their physiological consequences, and their implications for aboveground biomass dynamics. While tree-level damage is the most common condition preceding death in tropical trees, non-lethal damage can contribute to significant amounts of aboveground biomass losses that are not necessarily captured by studies focused only on tree mortality. Ongoing efforts to resolve the timing of lethal and non-lethal biomass losses, their climatic drivers, and physiological consequences will improve our understanding of carbon woody residence time and predictions of the fate of forests in vegetation models.

Helene Muller-Landau

Quantifying spatial and temporal variation in canopy tree mortality and branchfalls in a tropical forest using repeat drone photogrammetry

Abstract:

Tropical tree mortality and branchfall rates vary widely among sites and over time, in part in relation to climate. However, we still have a relatively poor understanding of the drivers of tree mortality and branchfall, because their rates are low, requiring frequent and large-scale observations to quantify variation, which is infeasible with labor-intensive traditional field methods. We used repeat drone photogrammetry to quantify temporal and spatial variation in canopy tree mortality and branchfall at high resolution and over large scales at Barro Colorado Island, Panama. We documented high temporal and spatial variability, and found that temporal variability was related to strong rainfall events whereas spatial variability was related to soil type, topography, and stand age.

Here is the recording of their presentations. Enjoy!

Our #13 ITMN seminar took place on July 5th (1600 CEST).

David Galbraith

How does sensitivity to climate change vary across Amazon forests? Insights from ecophysiology, forest dynamics, remote sensing and modelling.

Abstract: There is a pressing need to better understand and predict the impacts of climate change on Amazon forests, given their important role in the Earth System. In this talk, I present new results that reveal how the sensitivity of Amazon forests to climate stressors varies across the Basin, drawing upon new plant functional trait data collection, forest inventory data analyses, remote sensing and ecosystem modelling.

Here is the recording of David’s presentation. Enjoy!

Our #12 ITMN seminar took place on April 26th (1600 CET).

Andreas Bolte

Forest mortality dynamics in Germany – how can we cope with it?

Abstract: In the last years forests in Germany haved faced vitality decreases and mortality dynamics never seen before. About 25% of German forests are projected to be at risk for extensive disturbance events and ecosystem service losses within the next 30 years; their transformation to future resilient forests will cost billions of Euros. Based on an analysis of ongoing mortality dynamics and options for an adaptive forest management, solutions for future forest management will be discussed.

Here is the recording of Andreas’ presentation. Enjoy!

Our #11 ITMN seminar took place on March 15th (1600 CET).

Bonaventure Ntirugulirwa

Mortality of Afrotropical trees in a temperature manipulation experiment: Result from the Rwanda TREE project

Abstract: Knowledge on mortality responses of tropical trees and communities under projected warmer climate is limited. Trees in tropical montane forests (TMFs) are considered particularly vulnerable to climate change, but this hypothesis remains poorly evaluated due to data scarcity. To reduce the knowledge gap on the warming response of TMFs, we have established a field experiment along an elevation gradient ranging from 2400 m a.s.l. (15.2 °C mean temperature) to 1300 m a.s.l. (20.6 °C mean temperature) in Rwanda. Twenty tree species, native to East and Central Africa, from two forest types of origin (transitional rainforest at 1600 – 2000 m a.s.l, and TMF at 2000 – 3000 m a.s.l.) and two successional groups, early (ES) and late succession (LS), were planted in multispecies plots at three sites along the gradient. Tree growth and survival of 5400 trees was monitored regularly over two years. The results showed that ES trees from lower elevations grew faster at warmer sites while several of the LS species, especially from higher elevations, did not respond or grew slower. Moreover, tree mortality increased in a warmer climate and this was more pronounced in high-elevation and LS species compared to lower-elevation and ES tree species. ES species with transitional rainforest origin strongly increased in proportion of stand basal area at warmer sites, while tropical montane forest species declined, suggesting that higher-elevation and LS species are at risk to be outcompeted by lower-elevation and ES species in a warmer climate. We conclude that tree mortality and growth responses combined may lead to modified tree community composition in a warmer climate, favouring lower-elevation and ES tree species. This has important implications for biodiversity and carbon storage of Afromontane forests.

Here is the recording of Bonaventure’s presentation. Enjoy!

Our #10 ITMN seminar took place on February 15th (1600 CET).

Ana Bastos

Climate variability, extremes, and attribution of high-impact ecological events: challenges and ways forward

Abstract: Climate and weather extremes impact tree functioning directly and can further trigger forest disturbances, thus affecting forest functioning and dynamics over periods much longer than the extreme per-se. With increased frequency or intensity of extreme events projected in the coming decades, extreme events might cluster in periods shorter than recovery times, thereby amplifying impacts and potentially inducing degradation and mortality trajectories. Understanding the links between atmospheric variability controlling extreme event occurrence and downstream impacts on forests is, therefore, crucial to: (i) separate trends in disturbance/mortality events due to natural vs. anthropogenically forced climate variability, (ii) improve process understanding about the drivers of high-impact ecological events and (iii) increase the robustness of future projections of forest dynamics.

Here is the recording of Ana’s presentation. Enjoy!

Our #9 ITMN seminar took place on January 25th (1700 CET).

Barbara Bentz

Recipes for Climate-Induced Bark Beetle-Caused Tree Mortality

Abstract: Globally, native bark beetles are contributing to increases in tree mortality and changes in climate are playing significant roles. Projecting future trends will be complicated by environmentally determined, evolved traits in both host trees and insects. Ingredients for bark beetle population success in future climates will be discussed.

Here is the recording of Barbara’s presentation. Enjoy!

Our #8 ITMN seminar took place on December 9 2021 (1400 CET).

Viacheslav Kharuk

Conifer decline and mortality in Siberia

Abstract: Conifer decline and mortality in the 21st century has been observed all over the boreal forests zone (e.g., Boyd et al., 2019), Europe (e.g., Hasenauer, & Seidl, 2017), and Russia (e.g., Kharuk et al., 2020). This report focused mostly on the causes of Siberian pine (Pinus sibirica Du Tour.) and fir (Abies sibirica Ledeb) decline and mortality in Siberia. In addition, recent insect (Zeiraphera griseana) and fungi (Melampsora sp.) attacks on the Larix sibirica stands are considered.

Results
1. Warming caused northward and uphill migration of the Siberian moth (Dendrolimus sibiricus Tschetv.) outbreaks range into the former pristine taiga.
2. Siberian fir mortality caused by the synergy of bark-beetles (Polygraphus proximus Blandford.) attacks and water stress.
3. Siberian pine and fir forest mortality preceded by trees growth index (GI) reduction caused by elevated air temperatures, acute droughts and following on insect attacks.
4. In mountains forest mortality observed mostly at low elevations, whereas within the areas with sufficient moisture availability (i.e., at elevations above ~1000 m) trees GI and forest area are increasing.
5. Consecutive years with elevated air temperature provoked immense insect (Zeiraphera griseana) outbreak within relatively dry larch habitat and fungi (Melampsora sp.) outbreak within moisture larch habitat.
6. With the projected drought increase, precipitation-sensitive Siberian pine and fir would retreat from its southern low elevation ranges and substitute by tolerant species (e.g., Betula spp, Larix sibirica, Pinus sylvestris).

Here is the recording of Viacheslav’s presentation. Enjoy!

Our #7 ITMN seminar took place on November 23 2021 (1600 CET).

Yude Pan

Impacts of disturbances on leaf area index and productivity of terrestrial ecosystems

Abstract: An empirical model depicting the relationship between changes in leaf area index (LAI) and aboveground net primary productivity (ANPP) of terrestrial ecosystems provides an opportunity exploring these changes at a global scale. As LAI can be an effective indicator for ANPP, it also facilitates observations of larger scaled disturbances on terrestrial ecosystems and evaluating consequences in ANPP. These disturbances were originated from both human activities and natural forces. Human disturbances such as deforestation around tropical rainforests evidenced losses in LAI. Natural disturbances related to changing climate are recognisable from intensified wildfires and droughts, which left marks in fire-prone regions and extremely dry lands. Although elevated atmospheric CO2 appeared to have enhanced global ANPP, disturbances and relevant tree mortality caused 30% of vegetated lands with reduced LAI and 14% with decreased ANPP.

Here is the recording of Yude’s presentation. Enjoy!

Our #6 ITMN seminar took place on June 22 (1700 CEST).

CRAIG D. ALLEN

The global emergence of hotter-drought drivers of forest disturbance tipping points

Abstract: Current research is presented on global-scale patterns and trends of forest responses to increasingly hotter droughts, particularly extensive tree mortality and forest die-offs involving a range of interactive disturbances (e.g., water stress, insect outbreaks, high-severity wildfire). Diverse cross-scale observations and empirical findings increasingly indicate that amelioration of hotter-drought stress via fertilization of photosynthesis from elevated atmospheric CO2 concentrations may soon be overwhelmed by heat and accelerated atmospheric drought. These findings highlight some current challenges in realistically projecting the future of global forest ecosystems (and their associated carbon pools and fluxes) with process-based Earth system models. In particular there is substantial evidence that forests dominated by larger, older trees may be disproportionately vulnerable to increased growth stress and mortality under hotter-drought conditions. The fates of these old trees in response to global change are of vital importance, given that they are essential as: a) disproportionately large carbon sinks; b) among the most biodiverse and rare terrestrial ecosystems; c) irreplaceable archives of environmental history; and d) venerated for many cultural reasons. Key scientific uncertainties that impede modeling progress are outlined, and examples of promising empirical modeling approaches are illustrated.

Here is the recording of Craig’s presentation. Enjoy!

Our #5 ITMN seminar took place on May 6 (1700 CEST).

LISA HÜLSMANN

Tree mortality modeling – a tool for ecological inference and a challenge for projecting forest dynamics

Abstract: Tree death is ubiquitous in forests, even without climate change, and has a lasting impact on forest structure, species composition, biomass, and biodiversity. By relating tree mortality and other vital rates to tree, forest, and environmental conditions, we can therefore identify the mechanisms that govern the shape of forest ecosystems. In turn, these empirical relationships can be useful for projecting future forest dynamics and range limits of tree species. In the talk, I will discuss empirical tree mortality models as a diagnostic opportunity and a modeling challenge through two examples: the role of conspecific negative density dependence (Janzen-Connell effects) for tree diversity and the tighter coupling of dynamic vegetation models to forest data.

Here is the recording of Lisa’s presentation. Enjoy!

Our #4 ITMN seminar took place on Mar 24 (900 MDT).

NATE MCDOWELL

Rising tree mortality in the Anthropocene

Abstract: Tree mortality is rising in most documented locations but the drivers and mechanisms of this trend are unknown. Changes in atmospheric carbon dioxide, temperature, and vapor pressure deficit, along with drought, are primary potential drivers. Mechanisms linking these drivers to mortality include water, carbon, and pathogen defense processes. These processes are interdependent such that failure of one can lead to failure of the others. Prediction of future mortality is challenged by our understanding of the mechanisms, however, some evidence suggests the growing mortality rates are likely to continue well into the future. I conclude by reviewing the numerous challenges and opportunities for predicting future tree mortality.

Here is the recording of Nate’s presentation. Enjoy!

Our #3 ITMN seminar took place on Feb 23 (900 Sydney).

BELINDA MEDLYN

Tree mortality in Australian ecosystems: past, present and future

Abstract: Australia is not only the driest inhabited continent, it also experiences high interannual variability in rainfall, and severe multi-year droughts. Tree death from drought is thus a recurring feature of the Australian landscape. In this talk I will review our current understanding of drought mortality in Australian ecosystems, including the historical context, current field research on the extent and mechanisms of drought dieback and recovery, and the development of models to predict future drought mortality risk.

Here is the recording of Belinda’s presentation. Enjoy!

Our #2 ITMN meeting took place on Jan 19 (4 pm, CET).

FLÁVIA COSTA

Tree mortality in the Amazon across local hydrological gradients: how water table depth may save or condemn trees as climate changes

Abstract: Dr Costa will present results of 20 years of investigation on patterns of forest response to soil hydrology (more specifically water table depth) during normal and extreme climatic years to examine the hypothesis that shallow water tables buffer forests from droughts and forests in these conditions may even be benefited by droughts. Dr Costa will also present some data on the hydraulic trait distributions along hydrological gradients to analyse the shifting implications to mortality during moderate to strong droughts.

Here is the recording of Flavia's presentation. Enjoy!

Our kick-off meeting was taking place on Nov 17 (5 pm, CET) with our first speaker:

MATT HANSEN

Global forest monitoring using satellite data

Abstract: Earth observation data enable the monitoring of forest extent and change from national to global scales. Consistent processing of time-series images has made possible the operational production of global tree cover extent, loss and gain products. However, attribution of dynamics in the context 1) reference state, for example forest type, 2) change factor, for example fire or logging, and 3) outcome, for example land use type or natural recovery, is more challenging. In addition to mapping, the requirement to perform robust sample-based analyses to report on all themes is underappreciated. This talk will review our work on characterizing forest dynamics at the global scale using multi-source satellite imagery, including mapping and sampling, in the context of current operational versus future aspirational capabilities.