Jack T. Tessier

Vernal nitrogen and phosphorus retention by forest understory vegetation and soil microbes

Northern hardwood forests experience annual maximal loss of nutrients during spring. The vernal dam hypothesis predicts that spring ephemeral herbs in northern hardwood forests serve as sinks for nutrients during this season and reduce the loss of nutrients from the terrestrial ecosystem. Soil microbes of northern hardwood forests also sequester nutrients during spring. We compared the vernal nutrient acquisition ability of a soil microbial community and an understory plant community with species of mixed leaf phenology. We monitored nitrogen and phosphorus pool sizes in understory vegetation and soil microbes during spring from 1999 through 2001 in a northern hardwood forest in the Catskill Mountains, New York. Vegetation nutrient content increased during two spring seasons by an average of 3.07 g N m−2 and 0.19 g P m−2 and decreased during one spring by 0.81 g N m−2 and 0.10 g P m−2. Evergreen, wintergreen, and deciduous plant species were able to sequester nutrients during spring. Soil microbial nutrient content decreased during one spring by 1.29 g N m−2 and remained constant during the other two springs. Streamwater nitrogen losses were not correlated with biotic nutrient uptake suggesting a temporal disconnect between the two processes. We conclude that understory vegetation is a larger potential sink for vernal nutrients than are soil microbes in this northern hardwood forest and understory and species representing multiple phenologies are capable of vernal nutrient uptake.

Creating Significant Learning Experiences Across Disciplines

The purpose of this study was to use Finks (2003) taxonomy of significant learning to redesign courses and assess student learning. Significant improvements were found across the semester for students in the six courses, but there were differences in which taxa showed improvement in each course. The meta-analysis showed significant, positive changes across disciplines in the areas of foundational knowledge, application, human dimension, and learning how to learn. This study provides support for Finks taxonomy in which significant learning can be achieved through course redesign.

Classroom Debate Format

To assess the effect of debate format on learning, four formats were separately employed in an environmental issues course. Learning was greatest when students wrote about a debate they witnessed, the teacher provided debate questions, and students received a reward for winning. Students valued debates for developing their arguing skills, used the Internet as a primary source, and placed trust in sources based on the author more than on their critical reading of the source.

Vernal Photosynthesis and Nutrient Retranslocation in Dryopteris intermedia

Abstract The value of preserving wintergreen fronds into the spring by forest understory fern species is unknown. In this study, net photosynthetic rates and nitrogen and phosphorus contents were monitored in a population of Dryopteris intermedia throughout a spring season to explore potential photosynthetic and retranslocational benefits of wintergreen fronds. Net photosynthesis occurred throughout the study indicating a potential for movement of fixed carbon from wintergreen fronds to other parts of the plant. Nitrogen and phosphorus content in the old fronds did not change through spring, thus no evidence for net retranslocation of these nutrients from wintergreen fronds to the rest of the plant was obtained. Maintenance of the wintergreen fronds may simply increase retention time and thus nutrient use efficiency of limiting nutrients. Other possible benefits of wintergreen fronds exist and should be investigated.

Old fronds serve as a vernal carbon source in the wintergreen fern Dryopteris intermedia (Aspleniaceae)

Maintaining green leaves beyond the growing season has been hypothesized to benefit plants by supplying either a nutrient or a carbon source. Understanding such ecophysiological aspects of plants will help us to appreciate how a species functions in its environment and predict how it might be affected by future changes in that environment. The wintergreen fern species Dryopteris intermedia does not retranslocate nitrogen and phosphorus from old fronds in spring, but photosynthesis does take place in the old fronds during this season. To determine if carbon fixed in the old fronds is translocated to other parts of the plant, we labeled old fronds with (13)C via photosynthetic uptake and examined old fronds, new fronds, fine roots, and rhizomes for (13)C content 1 day and 1 month after labeling the old fronds. Vernally fixed carbon was translocated to the new fronds but not significantly to the below ground tissues. Old fronds in this species, therefore, serve as a carbon source for vernal growth of new fronds. This is the first study in which a fern was labeled with (13)C to track vernally fixed carbon from old fronds to the rest of the plant in a wintergreen species. Future research should examine the precise timing of this carbon movement and examine other species for a similar or contrasting strategy.

Changes in base cation deposition across New York State and adjacent New England following implementation of the 1990 Clean Air Act amendments

To reduce atmospheric deposition, in 1990 Congress passed amendments to the Clean Air Act requiring electric utility power plants to decrease emissions of sulfur dioxide and nitrogen oxides, with Phase I beginning in 1995. We analyzed precipitation volume, wet deposition, and concentration of the sum of base cations measured at 12 National Atmospheric Deposition Program sites in Massachusetts, New Hampshire, New York, and Vermont. We compared five-year means prior to and following passage of the amendments and for five years after the implementation of Phase I. Whereas only one of the monitoring stations recorded a decline in base cation deposition, three sites out of the 12 showed a decline in base cation concentration. None of the sites exhibited a significant change in precipitation volume. Continued deposition of base cations may help to reduce the detrimental effects of acidic deposition.

Re-establishment of three dominant herbaceous understory species following fine-scale disturbance in a Catskill northern hardwood forest

Abstract At the landscape scale, herbaceous understory plant species are limited in return to forested settings by dispersal. At fine-scales, microhabitat characteristics are known to be important in determining the distribution of herbaceous understory plant species. Fine-scale manipulative experiments to determine responses of understory species to disturbance, however, are few and limited to Europe and the Pacific northwest. The Unified Neutral Theory of Biodiversity (UNT) predicts that species enter disturbed habitat in abundances proportional to their neighboring abundance. I assessed the reestablishment of dominant understory plant species (Dryopteris intermedia, Lycopodium lucidulum, and Oxalis acetosella) following small-scale disturbance in a Catskill northern hardwood forest. While reestablishment of all species was significantly and positively correlated with the presence of each species in surrounding areas indicating the importance of dispersal limitation of reestablishment, rates of recovery were species specific. Reestablishment of O. acetosella was far greater than that of the other species. In fact, no sexual reproduction was observed for D. intermedia and L. lucidulum. Cover of D. intermedia and L. lucidulum was significantly and positively correlated with pre-disturbance cover but this was not true for O. acetosella, indicating that for the pteridiophytes, habitat quality (as well as dispersal) was an important factor in reestablishment. Reestablishment therefore was influenced by dispersal and habitat characteristics, was species specific, and did not follow the predictions of the UNT. Thus, small-scale disturbance can have an important effect on the composition of the herbaceous community in northern hardwood forests.

Applying Plant Identification Skills To Actively Learn the Scientific Method

efforts to improve the quality of science education in the United States (George et al., 1996; Moore et al., 1997). Students who actively participate in their learning retain information better (Christian & Fisher, 1999) and develop more independent learning strategies (Goodwin et al., 1991) than their counterparts who experience primarily lecture style instruction. Active learning provides multiple teaching and learning strategies that can be applied in the science classroom (Chiappetta, 1997). Educators are therefore using active learning techniques in various fields of science (e.g., Anthony et al., 1998; Johnson, 1998; Stadler, 1998).

Ecological Problem-Based Learning: An Environmental Consulting Task.

Eroblem-based learning is touted as an effective way to promote active learning and encourage students to develop life-long learning skills (Groh et al., 1997; Uyeda et al., 2002). In science courses, problem-based learning is becoming a popular and effective approach (Arambula-Greenfield, 1996; Eggebrecht et al., 1996; Allen 1997; Woolverton & Liliestedt 1999; Singletary, 2000; Baldwin, 2001; Cruickshank & Olander, 2002, Kalischuk & Thorpe, 2002). Similar to undergraduate research (Mervis, 2001; Gonzalez, 2001; Marchaim, 2001), problem-based learning can expose students to professional activities (Abrahamson et al., 2000) and give them a greater appreciation for the applied aspects of the topics that they study. While some biology majors will enter careers involving laboratory research, many enter occupations related to environmental consulting and other forms of ecological field research. Two problems in particular that are faced by natural ecosystems, and in turn by environmental consultants, are urban sprawl and ecosystem fragmentation (e.g., McMahon & Harned, 1998; Wear et al., 1998; McKinney, 2002). There is ever increasing pressure for localities to use natural areas for development in an effort to perpetuate economic growth and accommodate the expanding human population (McKinney, 2002).

Methods of Belowground Movement in Erythronium americanum

Abstract As the climate changes, plants will need to respond to new environmental scenarios to survive. Belowground movements are one way in which plants respond to lethal temperatures. Plants use various methods to control belowground movements, notably contractile roots and droppers. I monitored populations of Erythronium americanum (Trout Lily) for contractile roots and documented the capacity of both annual corm growth and droppers to move the corm deeper in the soil. There was no evidence of contractile roots. While both corm growth and droppers lowered the corms, droppers provided for greater movement. Shallower corms produced longer droppers, and the average depth of a new corm formed from a dropper was consistent among corms of various original depths. Erythronium americanum can, therefore, use droppers to control corm depth, thus providing it a mechanism with which to escape potentially dangerous soil temperatures.