Does fertilization influence herbivory during tropical forest restoration? Emma Rosenfield (‘16), Arianna Porter (‘15), Julia Rogers (‘16), Omari Matthew (‘14), Susan Gagliardi, Lauren Bizzari, Cathy Collins Introduction Globally, about 13 million hectares of forests were converted to other uses or lost through natural causes each year between 2000 and This includes tropical forests that provide the plant with numerous resources and services. Therefore, it is critical that we actively try to restore these landscapes. Our restoration study is focused on the Firestone Center for Restoration Ecology in Costa Rica. The land on this property was originally a healthy tropical rainforest. However, after clearing for grazing, a non-native bamboo (Guadua angustifolia), was planted and now dominates the landscape. In order to study the conditions under which healthy rainforests can be restored, we designed an experiment in this disturbed landscape. In our study, we asked whether herbivore pressure responds to fertilizer added to tree seedlings in a tropical rainforest environment. Methods With the intension of studying rainforest restoration, we set up the experiment by clearing 16 plots within a monoculture of non-native bamboo and planted 16 native trees per plot. On June 3 rd, 2013, 150g of fertilizer was added to 8 plots each in a ratio of 10:30:10 (N:P:K). Fertilizer was added again in August and October We chose this ratio based on evidence that suggests that lowland sites are limited by Phosphorous and that Potassium is important. Each plot contained seven native trees species present in different relative abundances. To measure herbivory, we estimated the extent and intensity of herbivory at the tree, branch, and leaf level in June 2013 and January Extent is the number of leaves that are affected by herbivory, while intensity is the amount of biomass missing from the tree (Figure 1). To generate leaf nutrient composition, we collected leaf tissue samples and set them to a laboratory for nutrient chemical analysis. Results Conclusions Differences in nutrient content of leaf tissue across seasons may be due to the fact that fertilizer was added closer to sampling in the wet season. In the dry season, sampling was carried out three months post fertilization. Therefore, the seedlings did not have the fertilizer nutrients still in their leaves because they had already processed them. Additionally, during the dry season trees may shunt nutrients to their roots to preserve tree health. Fertilizer increased herbivory intensity across all species in the wet season, but not in the dry season (Figure 3). This difference with season may be due to the gap between fertilization and sampling in the dry season. As the wet season data show, insects may concentrate their herbivory on tissues with higher nutrient content. Fertilization does not influence the extent of herbivory. This may be due to the fact that insects are locating leaves of higher quality and eating more of them, thus increasing the intensity of herbivory, but not the extent. In the wet season, herbivores preferred certain tree species (Figure 4). Difference in herbivory across species may be due to differences in nutrient uptake. For example, we noticed higher leaf cutter ant damage on Maya Colorado seedlings. These results indicate that fertilizer influences species interactions in the early stages of rainforest restoration. 1 Guiding Question 1.In the context of a tropical forest restoration experiment, a.Does fertilization influence herbivory? b.Does fertilization alter leaf tissue nutrients? Extent Intensity Extent Intensity Extent Intensity Extent Intensity Figure 1. Explanation of extent and intensity measurements Acknowledgements We would like to thank Dr. Cathy Collins and the rest of the lab team for their support and guidance, as well as the Firestone Center for Restoration Ecology. Figure 2. Comparison between nutrient content of plant tissue in fertilized and non-fertilized plots in the wet and dry seasons. Species sampled was Maya Colorado. Nutrients analyzed were Nitrogen (N), Phosphorus (P), and Potassium (K). Errors bars show standard error. Figure 3. Comparison of herbivory intensity between fertilized and non-fertilized tree species in the wet and dry season. Species sampled was Maya Colorado. Error bars show standard error. Figure 4. Comparison between percent herbivory, extent and intensity, in all planted tree species. Species codes stand for names of native trees: Amarillon (Am), Cenazaro (Cen), Guapinol (Guap), Kapok (K), Manglio (Mang), Maya Colorado (MC), Ron Ron (RR), and Vaco (V). Error bars show standard error. This figure shows that percent intensity and extent of herbivory vary among species (p i <0.0001, p e <0.001). Furthermore, percent extent of herbivory was higher than percent intensity in all species. There was a significant difference in percent intensity between fertilized plots and those not fertilized in the wet season (p=0.009). However, this difference was not seen in the dry season (p=0.0706) (Figure 3). Fertilization increased nitrogen and phosphorous content in the tree leaves in the wet season (p N =0.0012, p P =0.0281), but not in the dry season (p N =0.0813, p P =0.484) (Figure 2). Potassium showed no significant differences in the wet (p=0.5798) or dry (p=0.3883) season.