Seed–litter–position drives seedling establishment in grassland species under recurrent drought

Changes in land use and climate interfere with grassland ecosystem processes. Here I experimentally investigated the combined effects of land‐use change related litter cover and contrasting water supply on seedling emergence. In this context, the role of the initial relative position of seeds, i.e. seeds on top of the litter versus seeds beneath the litter in interaction with water supply has not been investigated so far. I hypothesised that facilitative effects of litter on seedling emergence occur when seeds are covered by litter and deteriorate when litter covers the ground and seeds fall on it (seeds on top of the litter). Further, I hypothesised that the importance of seed position for seedling emergence will increase under conditions of recurrent drought. I performed a controlled pot experiment on seedling emergence of three common European grassland species (Pimpinella saxifraga, Leontodon autumnalis, Sanguisorba officinalis) by experimental manipulations of litter and water availability. Seedling emergence under moist conditions showed no significant differences between each litter position compared to the control across species. In contrast, under recurrent drought, seedling emergence was significantly higher below the litter compared to seeds on top of the litter and the control (i.e. no litter). In abandoned land, seedling emergence may be limited when seeds fall on ground‐covering litter. In contrast, in grasslands with regular low‐intensity land use, seedling emergence may be enhanced when a moderate level of litter covers seeds at the end of the growing season. Protective mechanisms that occur with seeds positioned beneath litter are particularly important under recurrent drought.     

Climate change and the incidence of food poisoning in England and Wales

In recent years there have been several spells of high temperatures providing analogues for the conditions that might become more common as a result of the enhanced greenhouse effect. Statistical models were developed of the relationship between the monthly incidence of food poisoning and temperatures and these were then used to provide estimates of the possible effects of future warmer summers. Routinely collected data on the number of reported cases of food poisoning were analysed for the years 1982–1991. Regression analysis was used to establish the relationship between the monthly incidence of food poisoning and temperatures of the same and the previous month. Published scenarios for future temperatures were applied to these statistical models to provide estimates of the possible impacts of warmer conditions. The monthly incidence of food poisoning was found to be significantly associated with the temperature of the same and of the previous month with the latter having the stronger effect. Using published data on the relationship between reported and actual numbers of cases of food poisoning, it is estimated that annually there might be an additional 179 000 cases of food poisoning by the year 2050 as a result of climate change. The observed relationship with the same month's temperature underlines the need for improvements in storage, preparation and hygiene close to the point of consumption. However, there was a much stronger relationship with the temperature of the previous month, indicating the importance of conditions earlier in the food production process. Improvements in areas such as animal husbandry and slaughtering may also be necessary to avoid the adverse effects of a warmer climate.     

Plant community dynamics in a calcareous grassland under climate change manipulations

This study investigates the effects of field manipulations of local climate to determine the potential impact of climate change on plant community dynamics in a calcareous grassland. The experimental site is located in a grassland at the Wytham estate, Oxfordshire, UK. The one hectare study area is within a 10 ha abandoned arable field on Jurassic corallian limestone. Two climate change scenarios were used: warmer winters with increased summer rainfall and warmer winters with summer drought. Plant cover and species richness were significantly increased in plots receiving supplemented summer rainfall, while the amount of litter was significantly reduced. Litter formation was significantly increased by winter warming and drought. The responses of the plant community to the climate manipulations were related to the life-history attributes of the dominant species. Seedling recruitment was limited by microsite availability, which also varied in the different climate manipulations. The results are discussed in terms of successional dynamics. They suggest that warmer winters may delay succession, as gap formation in the sward will provide sites for colonisation of annuals, thereby enabling their persistence in the sward. Under wetter conditions during summer, perennial grasses tend to close the sward, thereby inhibiting the establishment of later successional species.     

The effect of birthplace on heat tolerance and mortality in Milan, Italy, 1980–1989

The temperature–mortality relationship follows a well-known J-V shaped pattern with mortality excesses recorded at cold and hot temperatures, and minimum at some optimal value, referred as Minimum Mortality Temperature (MMT). As the MMT, which is used to measure the population heat-tolerance, is higher for people living in warmer places, it has been argued that populations will adapt to temperature changes. We tested this notion by taking advantage of a huge migratory flow that occurred in Italy during the 1950s, when a large number of unemployed people moved from the southern to the industrializing north-western regions. We have analyzed mortality–temperature relationships in Milan residents, split by groups identified by area of birth. In order to obtain estimates of the temperature-related risks, log-linear models have been used to fit daily death count data as a function of different explanatory variables. Results suggest that mortality risks differ by birthplace, regardless of the place of residence, namely heat tolerance in adult life could be modulated by outdoor temperature experienced early in life. This indicates that no complete adaptation might occur with rising external environmental temperatures.     

Resilience of Mediterranean shrubland to a severe drought episode: the role of seed bank and seedling emergence

Extreme climate events, such as severe drought episodes, may induce changes in vegetation if they induce species‐specific adult mortality and changes in the seedling recruitment pattern. In 2005 a severe drought occurred in Doñana National Park (south Spain) causing extensive shrubland mortality. Over the following years we monitored the soil seed bank and seedling emergence via a gradient of canopy dieback induced by the drought episode. The canopy dieback corresponded to an increase in emergence of seedlings of woody species in 2007, probably because of the reduced competition induced by canopy loss. The soil seed bank of woody species sampled in 2008 was less abundant on plots with a higher proportion of dead vegetation, probably because of depletion of the seed bank as a result of the increased germination in the previous year and also as a result of a reduction in seed supply in these sites. Accordingly, in 2009 we detected reduced emergence of woody species on plots that had suffered the greatest shrub mortality. We failed to find any significant changes in patterns of the soil seed bank and seedling emergence of short‐lived herbaceous species, indicating greater resilience in these types of species. This study highlights the resilience of Mediterranean shrublands to climate fluctuations at one extreme of the variability characteristic of these ecosystems. An increase in the frequency of severe drought episodes – increasingly probable under the new climate conditions – does have the potential, however, to induce changes in vegetation, especially in woody communities that need more time to replenish their seed banks.     

Implications of climate warming on seedling emergence and mortality of African savanna woody plants

Seedling emergence from scarified seeds and mortality of different seedling cohorts of five African savanna woody species (Acacia polyacantha, A. sieberana, Bauhinia thonningii, Dichrostachys cinerea and Ziziphus abyssinica) were studied under field conditions at a site in central Zambia. The study was conducted over a 4-year period, from 2003 to 2007. The objectives of the study were to determine climate factors that significantly influence seedling emergence rate and mortality in order to assess likely responses of the studied species to a warmer climate. Mean seedling emergence rate was 12% in D. cinerea and Z. abyssinica, 17% in B. thonningii, 47% in A. poyacantha and 62% in A. sieberana. Climate factors did not significantly affect seedling emergence in A. sieberana while temperature significantly influenced seedling emergence rate in the other species. Under a 1° warmer climate, seedling emergence rate was predicted to decline in A. polyacantha, B. thonningii and Z. abysssinica but is likely to increase slightly in D. cinerea. Time of seedling emergence during the wet season did not appear to affect seedling survival. Temperature also significantly influenced seedling mortality in all the studied species such that under a warmer climate, mortality was predicted to increase in A. sieberana and D. cinerea but decrease in A. polyacantha, B. thonningii and Z. abyssinica. As the studied species exhibited differential optimum temperature conditions for seedling emergence and seedling survival, they are likely to respond to climate warming in different but predictable ways. The results of the study are useful to forest management and development of climate change adaptation strategies in southern Africa.     

Potential impact of temperature change on epibenthic predator–bivalve prey interactions in temperate estuaries

Temperate estuaries are indispensable as refuelling areas for long-distance shorebirds, where they depend on intertidal benthic fauna, such as bivalves, as food source. Bivalve recruitment is thought to be, at least partly, top-down regulated by epibenthic predators (the shrimp Crangon crangon and the crab Carcinus maenas) but this interaction is part of a complex predator–prey system since various fish species prey upon the crustaceans.