Periodic Reporting for period 4 - GlacialLegacy (Glacial Legacy on the establishment of evergreen vs. summergreen boreal forests)
Periodo di rendicontazione: 2023-05-01 al 2024-10-31
Boreal forests, which make up roughly one‐third of the world's total forested area, provide critical ecosystem services including carbon stocks, climate‐feedbacks, permafrost‐stability, biodiversity, and economic benefits. The Siberian boreal forest is the largest continuous forest region on Earth and plays a crucial role in regulating global climate. However, the distribution and environmental processes behind this ecosystem are still not well understood. The GlacialLegacy project assessed whether summergreen and evergreen needle‐leaf forests represent alternative quasistable states that occur today under similar climatic conditions, but were triggered by different environmental conditions and gene pools during the Last Glacial. GlacialLegacy used coherent empirical and modelling approaches to investigate this hypothesis across the entire Northern Hemisphere.
Our combined pollen and sedimentary ancient DNA analyses showed that larch, a summergreen coniferous tree, was able to survive with substantial populations in northeastern Siberia, and was able to spread out of these refugia during the late Glacial period. Evergreen tree taxa, including spruce and pine only expanded during the Holocene from southern refugia. Our investigations yielded support for vegetation-permafrost interaction at the local-scale. However, our vegetation assessment did not find evidence for stable states in forest composition as a first order signal at the larger scale. In addition to permafrost, we found that fire was in a complex way connected with forest composition and human impact in Siberia during the Holocene. Our predictions also indicate that forest changes are slow and characterized by substantial lag times which is also of relevance for ongoing forest changes. Furthermore, we found that forest composition has a substantial impact on lake water quality, which is of relevance for drinking water quality particularly in the densely populated arid areas of Central Yakutia. So our results contribute substantial knowledge to the potentially critical future ecosystem service changes required for adaptation strategies to be prepared.
Our combined pollen and sedimentary ancient DNA analyses showed that larch, a summergreen coniferous tree, was able to survive with substantial populations in northeastern Siberia, and was able to spread out of these refugia during the late Glacial period. Evergreen tree taxa, including spruce and pine only expanded during the Holocene from southern refugia. Our investigations yielded support for vegetation-permafrost interaction at the local-scale. However, our vegetation assessment did not find evidence for stable states in forest composition as a first order signal at the larger scale. In addition to permafrost, we found that fire was in a complex way connected with forest composition and human impact in Siberia during the Holocene. Our predictions also indicate that forest changes are slow and characterized by substantial lag times which is also of relevance for ongoing forest changes. Furthermore, we found that forest composition has a substantial impact on lake water quality, which is of relevance for drinking water quality particularly in the densely populated arid areas of Central Yakutia. So our results contribute substantial knowledge to the potentially critical future ecosystem service changes required for adaptation strategies to be prepared.
The hypothesis of the project i.e. a substantial Glacial Legacy on boreal forests was presented to the scientific community in a peer‐reviewed paper and in a palaeodata synthesis study. Field works in Siberia and North America were implemented as well as laboratory works. Furthermore, we investigated synthesized pollen data in terms of climate and ecological change to investigate the trajectories. We set and applied a model that couples forest dynamics and permafrost which can assess Larix forests may self‐stabilize due to complex feedbacks. Furthermore, we implemented variation and adaptation of traits in this model to investigate whether larches of central Siberia can withstand future drought even if they adapted.
The GlacialLegacy hypothesis was also assessed using vegetation and remote sensing data collected along a southwest-northeast transect in eastern Siberia (Enguehard et al., 2024, 10.1088/1748-9326/ad5742). Our findings suggest that boreal forest distribution and composition in eastern Siberia are mainly driven by current climate and topographical factors, but that there remains a portion of the variability that cannot be fully accounted for by these factors alone. We hypothesize that this unexplained variance may be linked to legacies of the Late Glacial.
We also assessed the existence of alternative stable forest cover states in the boreal forest and its adjacent biomes by using a multimodality measure on time series of reconstructed tree cover (Schild et al., 2024, 10.1088/1748-9326/ad9508). We found that the response of tree cover to climate is rather gradual and not as abrupt. Even though current and upcoming shifts in the boreal forest are indisputable and a reason for strong concern, these changes could happen gradually without going through large-scale tipping between alternative stable states. To aid adaptation and conservation measures, more knowledge is needed about boreal forest drivers and their spatial heterogeneity.
The GlacialLegacy hypothesis was also assessed using vegetation and remote sensing data collected along a southwest-northeast transect in eastern Siberia (Enguehard et al., 2024, 10.1088/1748-9326/ad5742). Our findings suggest that boreal forest distribution and composition in eastern Siberia are mainly driven by current climate and topographical factors, but that there remains a portion of the variability that cannot be fully accounted for by these factors alone. We hypothesize that this unexplained variance may be linked to legacies of the Late Glacial.
We also assessed the existence of alternative stable forest cover states in the boreal forest and its adjacent biomes by using a multimodality measure on time series of reconstructed tree cover (Schild et al., 2024, 10.1088/1748-9326/ad9508). We found that the response of tree cover to climate is rather gradual and not as abrupt. Even though current and upcoming shifts in the boreal forest are indisputable and a reason for strong concern, these changes could happen gradually without going through large-scale tipping between alternative stable states. To aid adaptation and conservation measures, more knowledge is needed about boreal forest drivers and their spatial heterogeneity.
Larix forest functioning is still poorly investigated originates from the lack of data and models specifically from eastern Siberia. We made substantial progress in this respect by publishing unique datasets on the forest structure and forest development in relation with climate change. Also, we investigated the specific feedbacks that stabilize forest in Central Yakutia in two studies focusing on the adaptability of Larix trees to drought and on the biophysical feedbacks between permafrost soils and Larix. This was not addressed before. In addition, we made use of the pollen data synthesized a part of this project, we could perform high level paleoclimate reconstructions. Based on these data we were able to assess two hypotheses about temperature-precipitation relationships in time and space (Herzschuh et al., 2022) as well as temperature variability (Herbert et al., 2022). We were the first that established hybridization capture of genomes from sedimentary ancient DNA (Schulte et al. (https://onlinelibrary.wiley.com/doi/10.1111/1755-0998.13311(si apre in una nuova finestra)). Furthermore, we included adaptation in an individual-based vegetation model, this has not been done before. (Gloy et al., 2023 https://doi.org/10.1016/j.ecolmodel.2023.110278(si apre in una nuova finestra))