Woody plant encroachment intensifies under climate change across tundra and savanna biomes

CITATION: Garcia Criado, M. et al. 2020. Woody plant encroachment intensifies under climate change across tundra and savanna biomes. Global Ecology and Biogeography, 229(5): 925–943. doi:10.1111/geb.13072The original publication is available at https://onlinelibrary.wiley.com/journal/14668238Aim: Biomes worldwide are shifting with global change. Biomes whose extents are limited by temperature or precipitation, such as the tundra and savanna, may be particularly strongly affected by climate change. While woody plant encroachment is prevalent across both biomes, its relationship to temperature and precipitation change remains unknown. Here, we quantify the degree to which woody encroachment is related to climate change and identify its main associated drivers. Location: Tundra and savanna biomes. Time period: 1992 ± 20.27–2010 ± 5.62 (mean ± SD). 1876–2016 (range). Major taxa studied: Woody plants (shrubs and trees). Methods: We compiled a dataset comprising 1,089 records from 899 sites of woody plant cover over time and attributed drivers of woody cover change across these two biomes. We calculated cover change in each biome and assessed the degree to which cover change corresponds to concurrent temperature and precipitation changes using multiple climate metrics. Finally, we conducted a quantitative literature review of the relative importance of attributed drivers of woody cover change. Results: Woody encroachment was widespread geographically and across climate gradients. Rates of woody cover change (positive or negative) were 1.8 times lower in the tundra than in the savanna (1.8 vs. 3.2%), while rates of woody cover increase (i.e., encroachment) were c. 1.7 times lower in the tundra compared with the savanna (3.7 vs. 6.3% per decade). In the tundra, magnitudes of woody cover change did not correspond to climate, while in the savanna, greater cover change corresponded with increases in precipitation. We found higher rates of woody cover change in wetter versus drier sites with warming in the tundra biome, and higher rates of woody cover change in drier versus wetter sites with increasing precipitation in the savanna. However, faster rates of woody cover change were not associated with more rapid rates of climate change across sites, except for maximum precipitation in the savanna. Main conclusions: Woody encroachment was positively related to warming in the tundra and increased rainfall in the savanna. However, cover change rates were not predicted by rates of climate change, which can be partially explained by climate interactions in both biomes. Additional likely influences include site-level factors, time-lags, plant-specific responses, and land use and other non-climate drivers. Our findings highlight the complex nature of climate change impacts in biomes limited by seasonality, which should be accounted for to realistically estimate future responses across open biomes under global change scenarios.https://onlinelibrary.wiley.com/doi/10.1111/geb.13072Publishers versio

Status and trends in Arctic vegetation: Evidence from experimental warming and long-term monitoring

Changes in Arctic vegetation can have important implications for trophic interactions and ecosystem functioning leading to climate feedbacks. Plot-based vegetation surveys provide detailed insight into vegetation changes at sites around the Arctic and improve our ability to predict the impacts of environmental change on tundra ecosystems. Here, we review studies of changes in plant community composition and phenology from both long-term monitoring and warming experiments in Arctic environments. We find that Arctic plant communities and species are generally sensitive to warming, but trends over a period of time are heterogeneous and complex and do not always mirror expectations based on responses to experimental manipulations. Our findings highlight the need for more geographically widespread, integrated, and comprehensive monitoring efforts that can better resolve the interacting effects of warming and other local and regional ecological factors

Arctic tundra shrubification: a review of mechanisms and impacts on ecosystem carbon balance

Vegetation composition shifts, and in particular, shrub expansion across the Arctic tundra are some of the most important and widely observed responses of high-latitude ecosystems to rapid climate warming. These changes in vegetation potentially alter ecosystem carbon balances by affecting a complex set of soil-plant-atmosphere interactions. In this review, we synthesize the literature on (a) observed shrub expansion, (b) key climatic and environmental controls and mechanisms that affect shrub expansion, (c) impacts of shrub expansion on ecosystem carbon balance, and (d) research gaps and future directions to improve process representations in land models. A broad range of evidence, including in-situ observations, warming experiments, and remotely sensed vegetation indices have shown increases in growth and abundance of woody plants, particularly tall deciduous shrubs, and advancing shrublines across the circumpolar Arctic. This recent shrub expansion is affected by several interacting factors including climate warming, accelerated nutrient cycling, changing disturbance regimes, and local variation in topography and hydrology. Under warmer conditions, tall deciduous shrubs can be more competitive than other plant functional types in tundra ecosystems because of their taller maximum canopy heights and often dense canopy structure. Competitive abilities of tall deciduous shrubs vs herbaceous plants are also controlled by variation in traits that affect carbon and nutrient investments and retention strategies in leaves, stems, and roots. Overall, shrub expansion may affect tundra carbon balances by enhancing ecosystem carbon uptake and altering ecosystem respiration, and through complex feedback mechanisms that affect snowpack dynamics, permafrost degradation, surface energy balance, and litter inputs. Observed and projected tall deciduous shrub expansion and the subsequent effects on surface energy and carbon balances may alter feedbacks to the climate system. Land models, including those integrated in Earth System Models, need to account for differences in plant traits that control competitive interactions to accurately predict decadal- to centennial-scale tundra vegetation and carbon dynamics

Plant traits poorly predict winner and loser shrub species in a warming tundra biome

Climate change is leading to species redistributions. In the tundra biome, shrubs are generally expanding, but not all tundra shrub species will benefit from warming. Winner and loser species, and the characteristics that may determine success or failure, have not yet been fully identified. Here, we investigate whether past abundance changes, current range sizes and projected range shifts derived from species distribution models are related to plant trait values and intraspecific trait variation. We combined 17,921 trait records with observed past and modelled future distributions from 62 tundra shrub species across three continents. We found that species with greater variation in seed mass and specific leaf area had larger projected range shifts, and projected winner species had greater seed mass values. However, trait values and variation were not consistently related to current and projected ranges, nor to past abundance change. Overall, our findings indicate that abundance change and range shifts will not lead to directional modifications in shrub trait composition, since winner and loser species share relatively similar trait spaces

Macroecological patterns of vegetation change across a warming tundra biome

The climate is changing across the globe at unprecedented magnitudes, and temperatures in the Arctic are increasing at three times the rate of the global average. Climate change impacts are being felt across the tundra biome, both at northern latitudes and high elevations. Examples of these impacts include northward species range shifts, changing community composition and increasing shrub growth, height and expansion, a phenomenon also known as shrubification. While multiple reports of plot- and landscape-level transformations have been described from locations across the tundra biome, uncertainty remains about 1) the extent of climate as a driver of biotic change, 2) the identity and traits of species that are currently shifting their ranges, and 3) how precisely is plant diversity changing over time. By combining decades-long large-scale tundra datasets of community composition, abundance, change over time, functional traits, species distributions and gridded climate data, I delve into these key questions about how climate change is reshaping the tundra biome. My research has demonstrated that, while rates of woody encroachment do not generally correspond with rates of climatic change, climate is still a driver of shrub expansion in the tundra. I found that warmer and wetter sites have provided fertile ground for shrubs to expand across tundra landscapes. Increased precipitation at dry sites was also associated with greater woody encroachment in a structurally similar open biome, the savanna. Contrary to initial expectations, trait values and intraspecific variation in three key functional traits (plant height, specific leaf area and seed mass) were not consistently related to current and projected tundra shrub species ranges. Likewise, the identity of climate change ‘winner’ and ‘loser’ shrub species differed depending on whether they were considered through past-observed change or projected range shifts, highlighting discrepancies arising from the use of different methods. Additionally, I found that there is a latitudinal biodiversity gradient in the tundra, with greater species richness at lower latitudes, and that tundra species richness has increased by a small amount over the last four decades. Climate influenced species trajectories, with warmer and drier areas containing more persisting and less extinct species. Species abundance has shifted, with consistent winner and loser functional groups, including an increasing dominance of shrubs influencing biodiversity change over time across plots. However, some sites appear resistant to change, with more resilient plant communities at plots that are more diverse and have a more even composition. Overall, my findings indicate that the tundra biome is experiencing a transformation that is heavily underpinned by the expansion of shrubs, partly due to a warming climate, although microclimate, non-climate drivers and time lags can also influence woody encroachment rates. Species’ abundance changes and projected range shifts will likely not lead to directional modifications in shrub functional trait composition or variation with future warming, since ‘winner’ and ‘loser’ species share relatively similar trait compositions. Importantly, I observed heterogeneous individual-level responses when examining traits, distributions and biodiversity patterns. This might be partly due to site-level conditions not being sufficiently captured by large-scale climate and species monitoring data, which are essential to adequately represent and predict biome-level shifts. Taken together, my results suggest biodiversity change driven by shifts in plant composition across the tundra biome, and indicate early signs of directional biotic changes that could ultimately result in tipping points in tundra biodiversity. These can alter the carbon cycle and ecosystem feedbacks, leading to further temperature increases, thawing of the permafrost, and its consequent release of carbon and methane in the Arctic. Ultimately, these could pose serious threats to the biotic communities, human populations and ecosystem services across the tundra biome and beyond

Localization and survival of Azospirillum brasilense Az39 in soybean leaves

In recent years, foliar inoculation has gained acceptance among the available methods to deliver plant beneficial micro-organisms to crops under field conditions. Colonization efficiency by such micro-organisms largely depends on their ability to survive when applied on the leaves. In this work, we evaluated the survival and localization of Azospirillum brasilense Az39 (Az39) in excised soybean leaves. Scanning electron microscopy and confocal laser scanning microscopy of a red fluorescent-transformed variant of Az39 were used to determine bacterial localization, while the most probable number and plate count methods were applied for bacterial quantification. Microscopic observations indicated a decrease in the number of Az39 cells on the leaf surface at 24 h after treatment, whereas midribs and cell–cell junctions of the inner leaf epidermis became highly populated zones. The presence of Az39 inside xylem vessels was corroborated at 6 h after bacterization. Az39 population did not significantly decrease throughout 24 h. We could visualize Az39 cells on the surface and in internal tissues of soybean leaves and recover them through culture methodologies. These results evidence the survival capacity of Az39 on and inside leaves and suggest a previously unnoticed endophytic potential for this well-known plant growth-promoting rhizobacteria strain.Fil: Puente, Mariana Laura. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Microbiología y Zoología Agrícola; ArgentinaFil: Maroniche, Guillermo Andrés. Universidad Nacional de Mar del Plata. Facultad de Cs.agrarias. Departamento de Introducción A Las Cs.agrarias. Area Biomolecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Panepucci, Marina Gabriela. Universidad de Buenos Aires; ArgentinaFil: Sabio y Garcia, Julia Veronica. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Microbiología y Zoología Agrícola; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: García, Jorge Eduardo. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Microbiología y Zoología Agrícola; ArgentinaFil: Criado, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Grupo Vinculado Centro de Estudios de Biodiversidad y Biotecnología MdP- INBA; ArgentinaFil: Molina, Romina Micaela. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones Agrobiotecnológicas - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Agrobiotecnológicas; ArgentinaFil: Cassan, Fabricio Dario. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones Agrobiotecnológicas - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Agrobiotecnológicas; Argentin

Woody plant encroachment intensifies under climate change across tundra and savanna biomes

Aim Biomes worldwide are shifting with global change. Biomes whose extents are limited by temperature or precipitation, such as the tundra and savanna, may be particularly strongly affected by climate change. While woody plant encroachment is prevalent across both biomes, its relationship to temperature and precipitation change remains unknown. Here, we quantify the degree to which woody encroachment is related to climate change and identify its main associated drivers. Location Tundra and savanna biomes. Time period 1992 ± 20.27–2010 ± 5.62 (mean ± SD). 1876–2016 (range). Major taxa studied Woody plants (shrubs and trees). Methods We compiled a dataset comprising 1,089 records from 899 sites of woody plant cover over time and attributed drivers of woody cover change across these two biomes. We calculated cover change in each biome and assessed the degree to which cover change corresponds to concurrent temperature and precipitation changes using multiple climate metrics. Finally, we conducted a quantitative literature review of the relative importance of attributed drivers of woody cover change. Results Woody encroachment was widespread geographically and across climate gradients. Rates of woody cover change (positive or negative) were 1.8 times lower in the tundra than in the savanna (1.8 vs. 3.2%), while rates of woody cover increase (i.e., encroachment) were c. 1.7 times lower in the tundra compared with the savanna (3.7 vs. 6.3% per decade). In the tundra, magnitudes of woody cover change did not correspond to climate, while in the savanna, greater cover change corresponded with increases in precipitation. We found higher rates of woody cover change in wetter versus drier sites with warming in the tundra biome, and higher rates of woody cover change in drier versus wetter sites with increasing precipitation in the savanna. However, faster rates of woody cover change were not associated with more rapid rates of climate change across sites, except for maximum precipitation in the savanna. Main conclusions Woody encroachment was positively related to warming in the tundra and increased rainfall in the savanna. However, cover change rates were not predicted by rates of climate change, which can be partially explained by climate interactions in both biomes. Additional likely influences include site‐level factors, time‐lags, plant‐specific responses, and land use and other non‐climate drivers. Our findings highlight the complex nature of climate change impacts in biomes limited by seasonality, which should be accounted for to realistically estimate future responses across open biomes under global change scenarios