Leaves to landscapes

The modifiable areal unit problem (MAUP) warns that the ""smoothing""

Jill
Kelly
Kroon 319
2:45pm
The modifiable areal unit problem (MAUP) warns that the ""smoothing"" of data at coarse aggregations can inflate indicators of model quality. Lidar point data are sometimes used for forest biomass estimation. The lidar height measurements are usually summarized to areal units -- sometimes to circular forest inventory plots for developing a model, and sometimes to a regular grid for prediction and mapping. Some recent biomass studies show improved model fit and prediction errors at coarser resolutions, and therefore their authors advocate for larger inventory plots and coarser prediction surfaces. I argue that some of this ""improvement"" can be attributed to MAUP. This cautionary tale will be of interest to anyone who works with data at multiple scales (leaves to landscapes).

Both light and soil fungi are important determinants of early regeneration

Meghna
Krishnadas
Kroon 319
2:45pm
Both light and soil fungi are important determinants of early regeneration success in tree species, but few studies have examined their role simultaneously. The ability to withstand pathogens in the shaded conditions of closed-canopy forests can reinforce species' shade-tolerance. For four species of tropical trees with varying life history strategies'two shade-tolerant and two shade-intolerant'we conducted an in situ field experiment to examine the interactive effects of fungal pathogens, light, and seed density on germination and early seedling establishment in a fragmented forest in Western Ghats, India. For each species, seeds were sown into 1x1 m plots containing soil from underneath parent trees, with each plot assigned to high light or shaded understory, high or low density, and fungicide or no fungicide application, in a fully factorial design. We analyzed probabilities of cumulative seedling emergence and final seedling establishment using generalized linear mixed-models with a logit link. Shade-intolerant species were strongly constrained by light. Fungicide application improved seedling emergence, but not final seedling establishment, for shade-intolerant Toona ciliata, and gains from fungicide application were significantly higher in shade. Light was the only factor affecting seedling emergence of shade-intolerant Macaranga peltata, but seedlings finally survived only in plots in high light treated with fungicide. Conversely, shade-tolerant Olea dioica and Heritiera papilio recruited equally well in light and shade. Recruitment of both shade-tolerant species improved with fungicide application, suggesting benefits from dispersal to locations where pathogens are low. Notably, fungicide application improved recruitment of Olea to a greater degree in high light, indicating that this species could colonize high-light locations far from conspecifics. Although changes to both light availability and plant-soil feedback can potentially affect species' regeneration success, the combined role of light and pathogens is yet to be examined in the context of plant community dynamics in human-impacted forests.

Hickory (Carya spp.) is an abundant and important component

Aaron
Lefland
Kroon 319
2:45pm
Hickory (Carya spp.) is an abundant and important component of the southern New England forest. The four species found in the region include shagbark, pignut, mockernut, and bitternut hickories, all of which comprise the late successional component of the oak-hickory type that extends north into Central New England. These species are economically and ecologically important, providing high quality timber for wood working, and both habitat and mast for many species of birds and mammals. To date, little work has been done to investigate the demographics and regeneration dynamic of these species, and what research has been done has been outside of New England. To better understand these hickory demographics and stand dynamics we analyze data collected at three different spatial scales ' i) the New England regional landscape; ii) forest-scale; and iii) stand scale. First, we conduct a landscape-scale analysis to determine the abundance of the four hickory species throughout southern New England and analyze their spatial distribution in relation climate and underlying physiography. Second, we conduct a forest-scale analysis to determine the meso-scale factors that promote the establishment of hickory stands, and thirdly, we examine the structure and age-class distribution of hickory dominated stands and the spatial correlation between adult hickories and seedlings. Our results have implications for land managers within the region, as the first comprehensive study to examine the structure, demographics and regeneration dynamics of hickory in southern New England.

Herbivores and detritivores'species that consume decaying material

Robert
Buchkowski
Kroon 319
2:45pm
Herbivores and detritivores'species that consume decaying material'are ecologically linked through their participation in nutrient cycling and shared consumption of plant tissue. Herbivores can influence the quality of plant litter available to detritivores by feeding on living plants and inducing plant defensive responses. We typically assume that detritivores respond to these herbivory-induced differences in litter quality in the same way that they respond to other differences in litter quality. However, herbivore-induced changes in litter chemistry might influence detritivore litter processing differently than other changes in litter quality. I tested the impact of herbivory history on detritivore litter consumption and the transfer of those nutrients back into plant biomass in old-field experimental mesocosms. I added leaf litter with a factorial legacy of grasshopper herbivory and nitrogen fertilization to mesocosms with different densities of a common detritivorous woodlouse. After a growing season, I quantified differences in plant, microbial, and woodlouse biomass across the litter history x woodlouse treatments. The differences in litter quality across herbivory and fertilization treatments interacted with woodlouse abundance to influence total plant biomass at the end of the growing season. Woodlice decreased plant biomass when litter had a history of herbivory, but had no effect on plant biomass when litter was not fed on by herbivores. The opposite trend was observed for microbial biomass. Woodlice decreased microbial biomass when litter had no past herbivory. The woodlice consumed fertilized plant litter more than unfertilized plant litter and the liberation of nutrients from fertilized litter resulted in a grass-dominated plant community. My results provide a novel demonstration of strong feedbacks between herbivores and detritivores under field conditions. They also suggest that differential detritivore litter processing might modify the longer-term effects of herbivores on plant litter quality and plant communities.