. 2016. Twenty-five-year response of the herbaceous layer of a temperate hardwood forest to elevated nitrogen deposition. Ecosphere 7(4):e01250. 10. 1002/ecs2.1250 Abstract. Increasing rates of atmospheric deposition of nitrogen (N) present a novel threat to the biodiversity of terrestrial ecosystems. Many forests are particularly susceptible to excess N given their proximity to sources of anthropogenic N emissions. This study summarizes results of a 25-yr treatment of an entire central Appalachian hardwood forest watershed via aerial applications of N with a focus on effects of added N on the cover, species richness, and composition of the herbaceous layer. Research was carried out on two watersheds of the Fernow Experimental Forest (FEF), West Virginia. The long-term reference watershed at FEF (WS4) was used as a reference; WS3 was experimentally treated, receiving three aerial applications of N per year as (NH 4 ) 2 SO 4 totaling 35 kg N ha −1 yr −1 , beginning in 1989. Cover of the herbaceous layer (vascular plants ≤1 m in height) was estimated visually in five circular 1-m 2 subplots within each of seven circular 400-m 2 sample plots spanning all aspects and elevations of each watershed. Sampling was carried out in early July of each of the following years : 1991, 1992, 1994, 2003, and 2009-2014, yielding 10 yr of data collected over a 23-yr period. It was anticipated that the N treatment on WS3 would decrease species richness and alter herb layer composition by enhancing cover of a few nitrophilic species at the expense of numerous N-efficient species. Following a period of minimal response from 1991 to 1994, cover of the herb layer increased substantially on N-treated WS3, and remained high thereafter. There was also a coincidental decrease in herb layer diversity during this period, along with a sharp divergence in community composition between WS4 and WS3. Most changes appear to have arisen from unprecedented, N-mediated increases of Rubus spp., which are normally associated with the high-light environment of openings, rather than beneath intact forest canopies. These findings support the prediction that N-mediated changes in the herbaceous layer of impacted forests are driven primarily by increases in nitrophilic species.
In this study, we used targeted active-learning activities to help students improve their ways of reasoning about carbon flow in ecosystems. The results of a validated ecology conceptual inventory (diagnostic question clusters [DQCs]) provided us with information about students' understanding of and reasoning about transformation of inorganic and organic carbon-containing compounds in biological systems. These results helped us identify specific active-learning exercises that would be responsive to students' existing knowledge. The effects of the active-learning interventions were then examined through analysis of students' pre- and postinstruction responses on the DQCs. The biology and non–biology majors participating in this study attended a range of institutions and the instructors varied in their use of active learning; one lecture-only comparison class was included. Changes in pre- to postinstruction scores on the DQCs showed that an instructor's teaching method had a highly significant effect on student reasoning following course instruction, especially for questions pertaining to cellular-level, carbon-transforming processes. We conclude that using targeted in-class activities had a beneficial effect on student learning regardless of major or class size, and argue that using diagnostic questions to identify effective learning activities is a valuable strategy for promoting learning, as gains from lecture-only classes were minimal.
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