The impact and significance of tephra deposition on a Holocene forest environment in the North Cascades, Washington, USA.

© 2016 Elsevier Ltd. High-resolution palaeoecological analyses (stratigraphy, tephra geochemistry, radiocarbon dating, pollen and ordination) were used to reconstruct a Holocene vegetation history of a watershed in the Pacific Northwest of America to evaluate the effects and duration of tephra deposition on a forest environment and the significance of these effects compared to long-term trends. Three tephra deposits were detected and evaluated: MLF-T158 and MLC-T324 from the climactic eruption of Mount Mazama, MLC-T480 from a Late Pleistocene eruption of Mount Mazama and MLC-T485 from a Glacier Peak eruption. Records were examined from both the centre and fringe of the basin to elucidate regional and local effects. The significance of tephra impacts independent of underlying long-term trends was confirmed using partial redundancy analysis. Tephra deposition from the climactic eruption of Mount Mazama approximately 7600 cal. years BP caused a significant local impact, reflected in the fringe location by changes to open habitat vegetation (Cyperaceae and Poaceae) and changes in aquatic macrophytes (Myriophyllum spicatum, Potamogeton, Equisetum and the alga Pediastrum). There was no significant impact of the climactic Mazama tephra or other tephras detected on the pollen record of the central core. Changes in this core are potentially climate driven. Overall, significant tephra fall was demonstrated through high resolution analyses indicating a local effect on the terrestrial and aquatic environment, but there was no significant impact on the regional forest dependent of underlying environmental changes

Lexical development in bilingual infants and toddlers: Comparison to monolingual norms

This study compares lexical development in a sample of 25 simultaneous bilingual and 35 monolingual children for whom semilongitudinal data were collected between the ages of 8 and 30 months. A standardized parent report form, the MacArthur Communicative Development Inventory (1989), was used to assess the children\u27s receptive and productive vocabulary in English and/or Spanish. A methodology was devised to assess the degree of overlap between the bilingual children\u27s lexical knowledge in one language and their knowledge in the other. Using the measures presented here, there was no statistical basis for concluding that the bilingual children were slower to develop early vocabulary than was the monolingual group. The wide range of vocabulary sizes observed at these ages in normally developing children (Fenson et al. 1991) was observed in these bilingual children as well. The close correspondence of the pattern of the bilinguals\u27 growth in two languages at once to monolinguals\u27 growth in one suggests that norms for lexical development in bilinguals should be made with reference to the children\u27s performance in two languages together