A fire history of a subalpine forest in south-eastern Wyoming, USA

Fire history was determined for part of the Routt‐Medicine Bow National Forest in south‐eastern Wyoming using fire‐scar and age‐class analysis. A composite chronology of fire events was used to determine mean fire intervals (MFI) for pre‐EuroAmerican settlement, EuroAmerican settlement (before 1868 ad ), EuroAmerican settlement and modern (after 1912) periods, for all fires and stand‐replacing fires. Point‐scale MFI was also determined using grand means from individual trees. Stand‐replacing fires were reconstructed to determine fire rotation. MFI for the entire time period is 5.5–8.4 years. MFI decreased from 9.3 to 15.7–1.9–2.9 years from the preto post‐EuroAmerican settlement periods, and increased during the modern period. Point‐scale MFIs are longer than MFI of the study area. Fire rotation is 182 years for the total period of record, but increased from 127 years during the pre‐EuroAmerican settlement period to 170 years during the EuroAmerican settlement period. Fire rotation during the modern period dramatically increased to 27,035 years. Results suggest fire suppression may have influenced the fire regime. Comparison of regional fire events with fire events from this study indicate regional weather has an important influence on Rocky Mountain fire regimes.     

Making a mark: two thousand years of ecology, economy and worldview

We can make a history of the world as an ecological history of an empirical nature. But parallelling that is the history of human thought about nature. The two interact at both pragmatic and abstract levels but in essence the outcome is unpredictable and more akin to chaos theory than to environmental or technological determinism. So the pursuit of either environmentalist or cornucopian Utopias seems not only doomed to failure but likely to cause destruction along the way; a step by step improvisatory strategy seems the best we can do.     

脓疮草复合体的生物学特性研究

通过野外和移栽实验观测,对脓疮草复合体（Ｐａｎｚｅｒｉａｎ ｌａｎａｔａ ｃｏｍｐｌｅｘ）居群进行了生物学特性研究。结果表明：浓疮草复合体居群在生活史方面无明显差异,移栽的１０个复合体居群生活史十分 相似：脓疮草复合本的花量大,花期可达３个月左右,花为雌雄异熟,以异花授粉为主,自交（同株异花授粉）亲合;叶裂程度、花萼裂片宽窄等性状,在天然居群中是连续变化的,而且移栽后可逆性较大,性状不稳定。     

Land-Use History in Ecosystem Restoration: A 40-Year Study in the Prairie-Forest Ecotone

Land‐use history, recent management, and landscape position influence vegetation at the Rockefeller Experimental Tract (RET), a 40‐year‐old restoration experiment in northeast Kansas. RET is representative of the prairie‐forest ecotone, containing native tallgrass prairie and oak‐hickory forest, but unique in having tracts of replanted prairie, seeded in 1957, that have undergone long‐term restoration treatments: burned, grazed, mowed, or untreated. A land‐use history database for RET was compiled using a geographic information system to integrate historic and contemporary sources of information. Restoration management on the reseeded prairie has had a profound effect on forest development: mowing or burning precluded forest establishment (<3% forest cover), whereas portions of untreated or grazed areas became heavily forested (>97% forest cover). Forest colonization depends upon biotic and edaphic conditions at the time restoration was initiated: for areas replanted to prairie and managed by grazing, forestation was 6% on land in cultivation prior to replanting, 20% on former pastureland, and 98% on land deforested just before replanting. Patterns of forest colonization were also significantly associated with three landscape positions: near existing forest, along water courses, and along ridge tops. Additionally, land‐use history analyses showed that the presence of various prairie and forest species resulted from persistence and not from colonization following restoration. Because of the lasting imprint of historic land use on the landscape, our results indicate that it is essential that restoration studies be evaluated within a site‐specific historical context.     

Variable demography in relation to germination time in the annual plant Tagetes micrantha Cav. (Asteraceae)

This study tests whether variability in a life history trait such as emergence time has ecological and evolutionary significance in seasonal environments due to their relationship with fitness components. The population dynamics of nine different cohorts of seedlings emergence were analyzed in a natural population of the annual herb Tagetes micrantha Cav. (Asteraceae). Temporal variation in seedling emergence was related to the pattern of precipitation, while spatial variation could be related to topographical heterogeneity. Plants that emerged at the beginning of the season (early germination) had lower probabilities of survivorship than those that emerged at the end of the season (late germination). In contrast, plants that emerged early had, on average, higher fecundity than those that emerged late. The net result of these contrasting patterns of survival and fecundity constitute a life history trade-off in T. micrantha.     

Optimal time to patency in parasitic nematodes: host mortality matters

We develop an optimality model based on classical epidemiological models to investigate the optimal time to patency in parasitic nematodes in relation to host mortality and parasite mortality. We found that the optimal time to patency depends on both host longevity and prepatent mortality of nematodes. We tested our models using a comparative analysis of the relationships between nematode time to patency, nematode mortality and host mortality. Although we confirmed the importance of prepatent mortality, we also found a significant positive influence of host mortality. Host mortality rate affects parasite survivorship and life history strategies in the same way that habitat-specific mortality regimes drive the evolution of life histories in free-living organisms.     

Human impact on mid- and late Holocene vegetation in south Cumbria, UK

The use of 9 pollen sampling sites and 56 14C dates has identified hitherto unsuspected or poorly-defined sequences of mid- to late Holocene (late Neolithic to post-Medieval) anthropogenic vegetation changes in south Cumbria, U.K. A series of small-scale, but significant woodland clearance episodes are recorded throughout the Bronze Age, followed by a marked recession in activity during the early Iron Age. The late Iron Age-Roman periods witnessed the first major clearance of woodland in the region which was succeeded by woodland regeneration in the post-Roman/early Medieval period. Woodland clearance intensified in the later Medieval period culminating in large areas of permanently open landscape. The results show that high-resolution, independently date pollen analysis is necessary to reveal regional evidence of small, temporary Bronze Age clearances. A well-documented prehistoric wooden trackway from Foulshaw Moss is shown to be significantly older than previously thought, dating to the mid-Bronze Age, ca. 1550–1250 cal B.C. Pre-Roman cereal cultivation in the area is also confirmed.The Department of Earth Sciences     

Cues and the optimal timing of activities under environmental changes

Organisms time activities by using environmental cues to forecast the future availability of important resources. Presently, there is limited understanding of the relationships between cues and optimal timing, and especially about how this relationship will be affected by environmental changes. We develop a general model to explore the relation between a cue and the optimal timing of an important life history activity. The model quantifies the fitness loss for organisms failing to time behaviours optimally. We decompose the immediate change in fitness resulting from environmental changes into a component that is due to changes in the predictive power of the cue and a component that derives from the mismatch of the old response to the cue to the new environmental conditions. Our results show that consequences may range from negative, neutral to positive and are highly dependent on how cue and optimal timing and their relation are specifically affected by environmental changes.