Understanding the causes of variation in herbivore damage to plants is very important in that crop loss can be reduced, and damage may be manipulated to limit population growth of invasive weed species. My research focuses on variation of damage by insects to leaf tissues of tall thistle (Cirsium altissimum) rosettes under differing levels of ecosystem productivity and habitat complexity. I address four specific questions in my research. First, does ecosystem productivity affect the amount of tissue loss to insect herbivory? Second, does habitat complexity, in terms of litter and local species richness, affect tissue loss to insect herbivory? Third, is there any interaction effect between ecosystem productivity and habitat complexity on plant tissue loss to insect herbivores? Fourth, do ecosystem productivity and habitat complexity affect the fresh biomass of insect carnivores and herbivores? At each of two sites four 40 m X 40 m plots were established for ecosystem productivity manipulations and subplots within the 40 m X 40 m plots are used for manipulations of habitat complexity. Nitrogen was added to experimentally increase ecosystem productivity and litter (dead plant parts that are lying down) and plant species richness were manipulated for habitat complexity. Preliminary results from the first year of field work showed that the mean (± standard error) proportions of leaves damaged severely (>50% leaf area damaged) in control plots were 0.06 ± 0.01 in May, 0.25±0.01 in August and 0.10±0.07 in October. In nitrogen addition plots mean proportions of leaves damaged severely were 0.04±0.01 in May, 0.22±0.04 in August and 0.06±0.01 in October. Although nitrogen addition increased plant standing crop by 16.7%, differences in proportion of leaves damaged severely between control and N-addition plots were not statistically significant at any of the three months. Statistical analysis of these data is on-going.