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Plant dispersal and persistence strategies play an increasingly important role in the face of changing climate. Evaluating the restoration potential of soil seed banks as an important component of community resilience is crucial for developing effective grassland conservation and restoration strategies under climate change. Soil seed banks can act as a source for vegetation recovery by preserving species and supporting their establishment by assisting persistence and recolonization. In a systematic review of field and experimental seed bank studies, we evaluated the potential of seed banks in buffering climatic extremities and fluctuations. We found 42 papers testing the first‐order (temperature and precipitation changes) and second‐order effects of climate change (flooding and fire) on the seed bank in grasslands. We showed that persistent seed banks can support passive restoration especially in wetlands and habitats where unpredictable and frequent disturbance was typical in the historical timescale. We found that active restoration by seed addition will be most important in less disturbance‐adapted habitats characterized by species with transient seed banks. In such cases, the introduction of native matrix species that can tolerate the predicted climatic change should be prioritized at degraded sites. [ABSTRACT FROM AUTHOR]

1. Grasses using the C4 photosynthetic pathway dominate today's savanna ecosystems and account for ~20% of terrestrial carbon fixation. However, this dominant status was reached only recently, during a period of C4 grassland expansion in the Late Miocene and Early Pliocene (4–8 Myr ago). Declining atmospheric CO2 has long been considered the key driver of this event, but new geological evidence casts doubt on the idea, forcing a reconsideration of the environmental cues for C4 plant success. 2. Here, I evaluate the current hypotheses and debate in this field, beginning with a discussion of the role of CO2 in the evolutionary origins, rather than expansion, of C4 grasses. Atmospheric CO2 starvation is a plausible selection agent for the C4 pathway, but a time gap of around 10 Myr remains between major decreases in CO2 during the Oligocene, and the earliest current evidence of C4 plants. 3. An emerging ecological perspective explains the Miocene expansion of C4 grasslands via changes in climatic seasonality and the occurrence of fire. However, the climatic drivers of this event are debated and may vary among geographical regions. 4. Uncertainty in these areas could be reduced significantly by new directions in ecological research, especially the discovery that grass species richness along rainfall gradients shows contrasting patterns in different C4 clades. By re-evaluating a published data set, I show that increasing seasonality of rainfall is linked to changes in the relative abundance of the major C4 grass clades Paniceae and Andropogoneae. I propose that the explicit inclusion of these ecological patterns would significantly strengthen climate change hypotheses of Miocene C4 grassland expansion. Critically, they allow a new series of testable predictions to be made about the fossil record. 5. Synthesis. This paper offers a novel framework for integrating modern ecological patterns into theories about the geological history of C4 plants. [ABSTRACT FROM AUTHOR]

Abstract: Over the past 15 years, 3 million hectares of forests have been converted into shrublands or grasslands in the Mediterranean countries of the European Union. Fire and drought are the main drivers underlying this deforestation. Here we present a conceptual framework for the process of fire‐induced deforestation based on the interactive effects of fire and drought across three hierarchical scales: resistance in individuals, resilience in populations, and transitions to a new state. At the individual plant level, we review the traits that confer structural and physiological resistance, as well as allow for resprouting capacity: deforestation can be initiated when established individuals succumb to fire. After individuals perish, the second step toward deforestation requires a limited resilience from the population, that is, a reduced ability of that species to regenerate after fire. If individuals die after fire and the population fails to recover, then a transition to a new state will occur. We document trade‐offs between drought survival and fire survival, as embolism resistance is negatively correlated with fire tolerance in conifers and leaf shedding or drought deciduousness, a process that decreases water consumption at the peak of the dry season, temporally increases crown flammability. Propagule availability and establishment control resilience after mortality, but different hypotheses make contrasting predictions on the drivers of post‐fire establishment. Mycorrhizae play an additional role in modulating the response by favoring recovery through amelioration of the nutritional and water status of resprouts and new germinants. So far, resprouter species such as oaks have provided a buffer against deforestation in forests dominated by obligate seeder trees, when present in high enough density in the understory. While diversifying stands with resprouters is often reported as advantageous for building resilience, important knowledge gaps exist on how floristic composition interacts with stand flammability and on the “resprouter exhaustion syndrome,” a condition where pre‐fire drought stress, or short fire return intervals, seriously restrict post‐fire resprouting. Additional attention should be paid to the onset of novel fire environments in previously fire‐free environments, such as high altitude forests, and management actions need to accommodate this complexity to sustain Mediterranean forests under a changing climate. [ABSTRACT FROM AUTHOR]

Dynamic global vegetation models ( DGVMs) can disentangle causes and effects in the control of vegetation and fire. We used a DGVM to analyse climate, CO2 and fire influences on biome distribution and net primary production ( NPP) in last glacial maximum ( LGM) and pre-industrial ( PI) times., The Land surface Processes and eXchanges ( LPX) DGVM was run in a factorial design with fire 'off' or 'on', CO2 at LGM (185 ppm) or PI (280 ppm) concentrations, and LGM (modelled) or recent climates. Results were analysed by Stein-Alpert decomposition to separate primary effects from synergies., Fire removal causes forests to expand and global NPP to increase slightly. Low CO2 greatly reduces forest area (dramatically in a PI climate; realistically under an LGM climate) and global NPP. NPP under an LGM climate was reduced by a quarter as a result of low CO2. The reduction in global NPP was smaller at low temperatures, but greater in the presence of fire., Global NPP is controlled by climate and CO2 directly through photosynthesis, but also through biome distribution, which is strongly influenced by fire. Future vegetation simulations will need to consider the coupled responses of vegetation and fire to CO2 and climate. [ABSTRACT FROM AUTHOR]

Various environmental factors, including atmospheric CO2 (pCO2), regional climate, and fire, have been invoked as primary drivers of long-term variation in C4 grass abundance. Evaluating these hypotheses has been difficult because available paleorecords often lack information on past C4 grass abundance or potential environmental drivers. We analyzed carbon isotope ratios (δ13C) of individual grains of grass pollen in the sediments of two East African lakes to infer changes in the relative abundance of C3 vs. C4 grasses during the past 25 000 years. Results were compared with concurrent changes in pCO2, temperature, moisture balance, and fire activity. Our grass-pollen δ13C analysis reveals a dynamic history of grass-dominated vegetation in equatorial East Africa: C4 grasses have not consistently dominated lowland areas, and high-elevation grasses have not always been predominantly C3. On millennial timescales, C4 grass abundance does not correlate with charcoal influx at either site, suggesting that fire was not a major proximate control of the competitive balance between C3 and C4 grasses. Above the present-day treeline on Mt. Kenya, C4 grass abundance declined from an average of ~90% during the glacial period to less than ~60% throughout the Holocene, coincident with increases in pCO2 and temperature, and shifts in moisture balance. In the lowland savanna southeast of Mt. Kilimanjaro, C4 grass abundance showed no such directional trend, but fluctuated markedly in association with variation in rainfall amount and seasonal-drought severity. These results underscore spatiotemporal variability in the relative influence of pCO2 and climate on the interplay of C3 and C4 grasses and shed light on an emerging conceptual model regarding the expansion of C4-dominated grasslands in Earth's history. They also suggest that future changes in the C3/C4 composition of grass-dominated ecosystems will likely exhibit striking spatiotemporal variability as a result of varying combinations of environmental controls. [ABSTRACT FROM AUTHOR]

• The importance of fire in the creation and maintenance of mesic grassland communities is well recognized. Improved understanding of how grasses - the dominant clade in these important ecosystems - will respond to alterations in fire regimes is needed in the face of anthropogenically driven climate and land-use change. • Here, we examined how grass communities shift in response to experimentally manipulated fire regimes at multiple levels of community diversity - taxonomic, phylogenetic and functional - in C4-dominanted mesic savanna grassland sites with similar structure and physiognomy, yet disparate biogeographic histories. • We found that the grass communities were similar in their phylogenetic response and aspects of their functional response to high fire frequency. Both sites exhibited phylogenetic clustering of highly abundant species in annually burned plots, driven by species of the Andropogoneae, and a narrow range of functional strategies associated with rapid post-fire regeneration in a high-light, nitrogen-limited environment. • By examining multiple facets of diversity in a comparative context, we identified convergent phylogenetic and functional responses to altered fire regimes in two mesic savanna grasslands. Our results highlight the importance of a common filtering process associated with fire that is consistent across grasslands of disparate biogeographic histories and taxonomic representation. [ABSTRACT FROM AUTHOR]

Degraded grasslands resulting from intensive land use appear to be highly resistant to tree invasion due to interactions between land use, climate, grazing and fire. We describe long-term patterns of tropical montane forest regeneration into degraded grasslands and analyze their relationships with historical changes in rainfall, grazing and fire in Los Toldos valley (Northwest Argentina), cloud forest life zone (1600 m asl). We used dendrochronological techniques to reconstruct spatial and temporal patterns of Podocarpus parlatorei establishment (the dominant tree species in secondary forests) and grassland fires for the last 150 yr. We assessed current livestock spatial distribution along the valley through feces sampling. Inferred tree establishment patterns ( i.e., considering age structure and mortality) were analyzed in relation to temporal and spatial patterns of grazing and fire derived from our own analyses and from government statistics, and to rainfall patterns derived from previous dendrochronological reconstructions. Current grazing intensity was higher close to the local township. Fire occurrence increased with periods of above-average rainfall (higher fuel productivity), and tended to increase with distance to township (less grazing). Tree establishment in grasslands was spatially associated with high grazing intensity and low fire frequency, and temporally associated with periods of high grazing intensity and below-average rainfall. Despite climatic and land-use changes leading to conditions potentially favorable for trees ( i.e., more rainfall, less grazing), grasslands persist in this study area, likely due to the direct (saplings burning) and indirect (soil degradation and desiccation) effects of recurrent fires, enhanced by decreasing grazing and increasing rainfall. Abstract in Spanish is available at [ABSTRACT FROM AUTHOR]