| 1. |
- Zani, Deborah, et al.
(författare)
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Climate and dispersal limitation drive tree species range shifts in post-glacial Europe : results from dynamic simulations
- 2023
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media SA. - 2296-701X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: The ability of species to colonize newly suitable habitats under rapid climate change can be constrained by migration processes, resulting in a shift of the leading edge lagging behind the ameliorating climate, i.e. migration lag. The importance and extent of such migration lags during the forest expansion after the Last Glacial Maximum (LGM) are still debated. Similarly, the relative importance of the main drivers of post-glacial vegetation dynamics (temperature, dispersal limitation, and competition) is still discussed in the literature. Methods: We used the dynamic global vegetation model LPJ-GM 2.0 to reconstruct the range shifts of 16 competing major European tree species after the LGM (18.5 ka BP) until recent times (0 ka BP). We simulated two dispersal modes by allowing free establishment whenever the climatic conditions suited the species (free dispersal), or by accounting for migration processes in the simulated vegetation dynamics (dispersal limitation). We then calculated thermal and range shift velocities, competition at establishment, thermal and dispersal lags for each species and dispersal mode. Finally, we compared our simulated range shift velocities with pollen-derived migration rates. Results: The simulation assuming limited dispersal resulted in more accurate migration rates as compared to pollen-derived migration rates and spreading patterns. We found no marked migration lags in the post-glacial establishment of pioneer species (Pinus sylvestris and Betula pubescens). Under the free dispersal mode, the remaining temperate species expanded rapidly and almost synchronously across central Europe upon climate warming (Bølling-Allerød interstadial). Differently, the northward spread of temperate species simulated under dispersal limitation happened mainly during the Holocene and in successive waves, with late spreaders (e.g. Fraxinus excelsior) experiencing multi-millennial dispersal lags and higher competition. Discussion: Our simulation under dispersal constraints suggests that the post-glacial tree expansion in Europe was mainly driven by species-specific thermal requirements and dispersal capacity, which in turn affected the order of taxa establishment and thus the degree of competition. Namely, taxa with less cold-tolerance and relatively low dispersal ability experienced the highest migration lags, whereas the establishment of pioneer species was mostly in equilibrium with the climate.
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| 2. |
- Zani, Deborah
(författare)
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Extending dynamic vegetation models to simulate range shifts
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In response to rapid climate change and increasing human pressure, a wide variety of taxa have shifted their distribution in the past decades (range shift), with important consequences for ecosystem services and human health and economy. However, it is not yet clear whether most species will be able to track their favourable habitats or lag behind the climate signal (migration lag). Studying the paleo-vegetation response to past climatic fluctuations may help to understand the ecological processes underlying range shift dynamics. This thesis aims to implement an efficient model to hind- and fore-cast the range shift of the vegetation at large temporal and spatial scales. To this end, we used the dynamic global vegetation model (DGVM) LPJ-GM, which couples a migration module to the widely-used DGVM LPJ-GUESS, thus allowing plant species to migrate while interacting with each other. First, we assessed and calibrated the migration module of LPJ-GM 1.0 by using estimates of migration rates derived from pollen records of major European tree species, resulting in the parametrized model LPJ-GM 1.1. In agreement with previous modelling studies and ecological theory (Reid’s paradox), long-distance dispersal events were found to be crucial in realizing the high spreading rates of migrating trees during the last deglaciation. Next, we upgraded the existing migration routine of LPJ-GM 1.1 (henceforth the SEEDISP option) and implemented a second migration routine (henceforth the FIXSPEED option) to decrease the computational cost of range shift simulations at larger scales. These implementations resulted in the model LPJ-GM 2.0. We then applied LPJ-GM 2.0 to simulate the paleo-vegetation dynamics during the last (inter-)stadial cycles (Europe after the Last Glacial Maximum and the Northern Hemisphere, NH, for the last 50 ky) under two dispersal modes, where plant establishment was determined by: (1) the standard LPJ-GUESS routine (free dispersal), or (2) additionally constrained by “seed” availability (dispersal limitation of LPJ-GM 2.0; SEEDISP for Europe and FIXSPEED for the NH). Applying migration constraints to vegetation dynamics altered the paleo-vegetation distribution at points of rapid climate change. A number of tree taxa and forested biomes experienced multi-millennia migration lags during the sudden warming events following the cold spells of the Older Dryas (around 14.5 ka) and the Younger Dryas (around 11.5 ka). We found the highest migration lags (>3 millennia) in the boreal forests colonizing Central Siberia across the Holocene, and in the post-glacial expansion of European temperate forests. The magnitude of migration lags of forested biomes and tree taxa depended on the presence of dispersal barriers, distance to glacial refugia, the configuration of the migrant population, thermal requirements for establishment and species-specific dispersal ability (and subsequent competition). The performance of both SEEDISP and FIXPSEED was higher than “free dispersal” simulations when compared with pollen reconstructions. Altogether, our results suggest that accounting for migration processes in vegetation models will increase our confidence in future projections of plant range shifts and thus, of ecosystem services and climate-vegetation feedback.
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| 3. |
- Zani, Deborah, et al.
(författare)
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Response to comment on "increased growing-season productivity drives earlier autumn leaf senescence in temperate trees
- 2021
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 371:6533
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Forskningsöversikt (refereegranskat)abstract
- Our study showed that increases in seasonal productivity drive earlier autumn senescence of temperate trees. Norby argues that this finding is contradicted by observations from free-air CO2 enrichment (FACE) experiments, where elevated CO2 has been found to delay senescence in some cases. We provide a detailed answer showing that the results from FACE studies are in agreement with our conclusions.
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| 4. |
- Zani, Deborah, et al.
(författare)
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The role of dispersal limitation in the forest biome shifts of Europe in the last 18,000 years
- 2024
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Ingår i: Journal of Biogeography. - : Wiley. - 0305-0270 .- 1365-2699. ; 51:8, s. 1438-1457
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Tidskriftsartikel (refereegranskat)abstract
- Aim: How the ability of plants to move towards newly favourable habitats (dispersal limitation) impacts the change of biome distribution and transition under fast climate warming is still debated. Analysing vegetation change in the past may help to clarify the relative importance of underlying ecological processes such as climate, biotic interactions, and dispersal. In this study, we investigated how dispersal limitation affected the distribution of European forests in the last 18,000 years. Location: Southern and Central Europe. Taxon: Spermatophyta. Methods: Using the LPJ-GM 2.0 model (an extension of LPJ-GUESS), we simulated European vegetation from the end of the Last Glacial Maximum (18.5 ka) to the current time (0 ka). Using biome reconstructions from pollen data as reference, we compared the performance of two dispersal modes: with no migration constraints or seed limitation (free dispersal mode), and with plant establishment depending on seed dynamics and dispersal (dispersal limitation mode). Results: The model run, including migration processes, was better at capturing the post-glacial expansion of European temperate forests (and the longer persistence of boreal forests) than the setting assuming free dispersal, especially during periods of rapid warming. This suggests that a number of (temperate) tree taxa experienced delayed occupancy of climatically suitable habitats due to a limited dispersal capacity, i.e., post-glacial migration lags. Main Conclusions: Our results show that including migration processes in model simulations allows for more realistic reconstructions of forest patterns under rapid climate change, with consequences for future projections of carbon sequestration and climate reconstructions with vegetation feedback, assisted migration and forest conservation.
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| 5. |
- Zani, Deborah, et al.
(författare)
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Tree migration in the dynamic, global vegetation model LPJ-GM 1.1 : efficient uncertainty assessment and improved dispersal kernels of European trees
- 2022
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 15:12, s. 4913-4940
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Tidskriftsartikel (refereegranskat)abstract
- The prediction of species geographic redistribution under climate change (i.e. range shifts) has been addressed by both experimental and modelling approaches and can be used to inform efficient policy measures on the functioning and services of future ecosystems. Dynamic global vegetation models (DGVMs) are considered state-of-the art tools to understand and quantify the spatio-temporal dynamics of ecosystems at large scales and their response to changing environments. They can explicitly include local vegetation dynamics relevant to migration (establishment, growth, seed (propagule) production), species-specific dispersal abilities and the competitive interactions with other species in the new environment. However, the inclusion of more detailed mechanistic formulations of range shift processes may also widen the overall uncertainty of the model. Thus, a quantification of these uncertainties is needed to evaluate and improve our confidence in the model predictions. In this study, we present an efficient assessment of parameter and model uncertainties combining low-cost analyses in successive steps: local sensitivity analysis, exploration of the performance landscape at extreme parameter values, and inclusion of relevant ecological processes in the model structure. This approach was tested on the newly implemented migration module of the state-of-the-art DGVM LPJ-GM, focusing on European forests. Estimates of post-glacial migration rates obtained from pollen and macrofossil records of dominant European tree taxa were used to test the model performance. The results indicate higher sensitivity of migration rates to parameters associated with the dispersal kernel (dispersal distances and kernel shape) compared to plant traits (germination rate and maximum fecundity) and highlight the importance of representing rare long-distance dispersal events via fat-tailed kernels. Overall, the successful parametrization and model selection of LPJ-GM will allow plant migration to be simulated with a more mechanistic approach at larger spatial and temporal scales, thus improving our efforts to understand past vegetation dynamics and predict future range shifts in a context of global change.
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