Guy S. Robinson

Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America

Demise of the Megafauna Approximately 10,000 years ago, the Pleistocene-Holocene deglaciation in North America produced widespread biotic and environmental change, including extinctions of megafauna, reorganization of plant communities, and increased wildfire. The causal links and sequences of these changes remain unclear. Gill et al. (p. 1100; see the Perspective by Johnson) unravel these connections in an analysis of pollen, charcoal, and the dung fungus Sporormiella from the sediments of Appleman Lake, Indiana. The decline in Pleistocene megafaunal population densities (inferred from fungal spore abundances) preceded both the formation of the lateglacial plant communities and a shift to an enhanced fire regime, thus contradicting hypotheses that invoke habitat change or extraterrestrial impact to explain the megafaunal extinction. The data suggest that population collapse and functional extinction of the megafauna preceded their final extinction by several thousand years. The decline in Pleistocene megafauna led to the formation of novel plant communities and increased fire. Although the North American megafaunal extinctions and the formation of novel plant communities are well-known features of the last deglaciation, the causal relationships between these phenomena are unclear. Using the dung fungus Sporormiella and other paleoecological proxies from Appleman Lake, Indiana, and several New York sites, we established that the megafaunal decline closely preceded enhanced fire regimes and the development of plant communities that have no modern analogs. The loss of keystone megaherbivores may thus have altered ecosystem structure and function by the release of palatable hardwoods from herbivory pressure and by fuel accumulation. Megafaunal populations collapsed from 14,800 to 13,700 years ago, well before the final extinctions and during the Bølling-Allerød warm period. Human impacts remain plausible, but the decline predates Younger Dryas cooling and the extraterrestrial impact event proposed to have occurred 12,900 years ago.

Sporormiella and the late Holocene extinctions in Madagascar

Fossil spores of the dung fungus Sporormiella spp. in sediment cores from throughout Madagascar provide new information concerning megafaunal extinction and the introduction of livestock. Sporormiella percentages are very high in prehuman southwest Madagascar, but at the site with best stratigraphic resolution the spore declines sharply by ≈1,720 yr B.P. (radiocarbon years ago). Within a few centuries there is a concomitant rise in microscopic charcoal that probably represents human transformation of the local environment. Reduced megaherbivore biomass in wooded savannas may have resulted in increased plant biomass and more severe fires. Some now-extinct taxa persisted locally for a millennium or more after the inferred megafaunal decline. Sites in closed humid forests of northwest Madagascar and a montane ericoid formation of the central highlands show only low to moderate Sporormiella percentages before humans. A subsequent rise in spore concentrations, thought to be evidence for livestock proliferation, occurs earliest at Amparihibe in the northwest at ≈1,130 yr B.P.

Predictability of biomass burning in response to climate changes

Climate is an important control on biomass burning, but the sensitivity of fire to changes in temperature and moisture balance has not been quantified. We analyze sedimentary charcoal records to show that the changes in fire regime over the past 21,000 yrs are predictable from changes in regional climates. Analyses of paleo- fire data show that fire increases monotonically with changes in temperature and peaks at intermediate moisture levels, and that temperature is quantitatively the most important driver of changes in biomass burning over the past 21,000 yrs. Given that a similar relationship between climate drivers and fire emerges from analyses of the interannual variability in biomass burning shown by remote-sensing observations of month-by-month burnt area between 1996 and 2008, our results signal a serious cause for concern in the face of continuing global warming.

LANDSCAPE PALEOECOLOGY AND MEGAFAUNAL EXTINCTION IN SOUTHEASTERN NEW YORK STATE

Stratigraphic palynological analyses of four late Quaternary deposits com- prise a landscape-level study of the patterns and processes of megafaunal extinction in southeastern New York State. Distinctive spores of the dung fungus Sporormiella are used as a proxy for megafaunal biomass, and charcoal particle analysis as a proxy for fire history. A decline in spore values at all sites is closely followed by a stratigraphic charcoal rise. It is inferred that the regional collapse of a megaherbivory regime was followed by landscape transformation by humans. Correlation with the pollen stratigraphy indicates these devel- opments began many centuries in advance of the Younger Dryas climatic reversal at the end of the Pleistocene. However, throughout the region, the latest bone collagen dates for Mammut are considerably later, suggesting that megaherbivores lasted until the beginning of the Younger Dryas, well after initial population collapse. This evidence is consistent with the interpretation that rapid overkill on the part of humans initiated the extinction process. Landscape transformation and climate change then may have contributed to a cascade of effects that culminated in the demise of all the largest members of North Americas mammal fauna.

Climatic control of the biomass-burning decline in the Americas after ad 1500:

The significance and cause of the decline in biomass burning across the Americas after ad 1500 is a topic of considerable debate. We synthesized charcoal records (a proxy for biomass burning) from the Americas and from the remainder of the globe over the past 2000 years, and compared these with paleoclimatic records and population reconstructions. A distinct post-ad 1500 decrease in biomass burning is evident, not only in the Americas, but also globally, and both are similar in duration and timing to ‘Little Ice Age’ climate change. There is temporal and spatial variability in the expression of the biomass-burning decline across the Americas but, at a regional–continental scale, ‘Little Ice Age’ climate change was likely more important than indigenous population collapse in driving this decline.

The associations between daily spring pollen counts, over-the-counter allergy medication sales, and asthma syndrome emergency department visits in New York City, 2002-2012.

BackgroundMany types of tree pollen trigger seasonal allergic illness, but their population-level impacts on allergy and asthma morbidity are not well established, likely due to the paucity of long records of daily pollen data that allow analysis of multi-day effects. Our objective in this study was therefore to determine the impacts of individual spring tree pollen types on over-the-counter allergy medication sales and asthma emergency department (ED) visits.MethodsNine clinically-relevant spring tree pollen genera (elm, poplar, maple, birch, beech, ash, sycamore/London planetree, oak, and hickory) measured in Armonk, NY, were analyzed for their associations with over-the-counter allergy medication sales and daily asthma syndrome ED visits from patients’ chief complaints or diagnosis codes in New York City during March 1st through June 10th, 2002-2012. Multi-day impacts of pollen on the outcomes (0-3 days and 0-7 days for the medication sales and ED visits, respectively) were estimated using a distributed lag Poisson time-series model adjusting for temporal trends, day-of-week, weather, and air pollution. For asthma syndrome ED visits, age groups were also analyzed. Year-to-year variation in the average peak dates and the 10th-to-90th percentile duration between pollen and the outcomes were also examined with Spearman’s rank correlation.ResultsMid-spring pollen types (maple, birch, beech, ash, oak, and sycamore/London planetree) showed the strongest significant associations with both outcomes, with cumulative rate ratios up to 2.0 per 0-to-98th percentile pollen increase (e.g., 1.9 [95 % CI: 1.7, 2.1] and 1.7 [95 % CI: 1.5, 1.9] for the medication sales and ED visits, respectively, for ash). Lagged associations were longer for asthma syndrome ED visits than for the medication sales. Associations were strongest in children (ages 5-17; e.g., a cumulative rate ratio of 2.6 [95 % CI: 2.1, 3.1] per 0-to-98th percentile increase in ash). The average peak dates and durations of some of these mid-spring pollen types were also associated with those of the outcomes.ConclusionsTree pollen peaking in mid-spring exhibit substantive impacts on allergy, and asthma exacerbations, particularly in children. Given the narrow time window of these pollen peak occurrences, public health and clinical approaches to anticipate and reduce allergy/asthma exacerbation should be developed.

The Association of Tree Pollen Concentration Peaks and Allergy Medication Sales in New York City: 2003–2008

The impact of pollen exposure on population allergic illness is poorly characterized. We explore the association of tree pollen and over-the-counter daily allergy medication sales in the New York City metropolitan area. Dates of peak tree pollen (maple, oak, and birch) concentrations were identified from 2003 to 2008. Daily allergy medication sales reported to the city health department were analyzed as a function of the same-day and lagged tree pollen peak indicators, adjusting for season, year, temperature, and day of week. Significant associations were found between tree pollen peaks and allergy medication sales, with the strongest association at 2-day lag (excess sales of 28.7% (95% CI: 17.4–41.2) over the average sales during the study period). The cumulative effect over the 7-day period on and after the tree pollen peak dates was estimated to be 141.1% (95% CI: 79.4–224.1). In conclusion, tree pollen concentration peaks were followed by large increases in over-the-counter allergy medication sales.

Correlation Between Aeroallergen Levels and New Diagnosis of Eosinophilic Esophagitis in New York City.

Objective: The relation between food allergies and eosinophilic esophagitis (EoE) is well established. Aeroallergens may also contribute to the development of EoE; however, there are limited data to support or refute this hypothesis. The objectives of this pilot study were to determine whether there is a seasonal variation in the onset of symptoms and/or diagnosis of EoE and whether these variations correlate with a specific pollen concentration within New York City. Methods: We performed a retrospective chart review to identify all pediatric patients at New York Presbyterian Weill Cornell Medical Center diagnosed with EoE between 2002 and 2012. Sixty-six patients were identified and 28 were excluded. Cases were classified by both date of initial symptoms and date of histologic diagnosis. Pollen counts from a certified New York City counting station and the percentage of EoE cases were collated monthly and seasonally and compared. Results: There was a seasonal variation in onset of symptoms and diagnosis of EoE, with the highest number of patients reporting onset of symptoms of EoE in July to September, and those being diagnosed with EoE in October to December. There was a seasonal correlation between peak levels of grass pollen and peak onset of EoE symptoms, which were both highest in July to September. The diagnosis of EoE peaked one season later. Conclusions: The study findings suggest that there is a correlation between specific aeroallergens and both the onset of symptoms and time of diagnosis of patients with EoE.

Levels and determinants of tree pollen in New York City

Exposure to allergenic tree pollen is a risk factor for multiple allergic disease outcomes. Little is known about how tree pollen levels vary within cities and whether such variation affects the development or exacerbation of allergic disease. Accordingly, we collected integrated pollen samples at uniform height at 45 sites across New York City during the 2013 pollen season. We used these monitoring results in combination with adjacent land use data to develop a land use regression model for tree pollen. We evaluated four types of land use variables for inclusion in the model: tree canopy, distributed building height (a measure of building volume density), elevation, and distance to water. When included alone in the model, percent tree canopy cover within a 0.5 km radial buffer explained 39% of the variance in tree pollen (1.9% increase in tree pollen per one-percentage point increase in tree canopy cover, P<0.0001). The inclusion of additional variables did not improve model fit. We conclude that intra-urban variation in tree canopy is an important driver of tree pollen exposure. Land use regression models can be used to incorporate spatial variation in tree pollen exposure in studies of allergic disease outcomes.