Effect of seasonality, climate, and leaf traits on insect herbivory and arthropod dynamics across a vertical forest stratification in Papua New Guinea’s lowland rainforest

Abstract Determining factors that regulate insect–plant interactions is of great interest in tropical forest ecology. However, our understanding of these factors across vertical stratification in tropical rainforests remains limited. We examined the effects of seasonality, microclimate, and leaf traits on insect herbivory and arthropod dynamics across vertical forest stratification in a weakly seasonal tropical rainforest in Papua New Guinea. We surveyed insect herbivory and arthropods on seven dominant tree species at 5 m increments from 1 m to 30 m, three times during both dry and wet seasons. We assessed insect herbivory on 9,425 leaves and collected 3,445 arthropods from 407.07 m 2 of foliage. Herbivory decreased non-linearly with forest height and was highest during the wet season. Herbivorous arthropod density mirrored this pattern, peaking at the onset of the rainy season and remaining low at the start of the dry season and the end of the wet season. Predatory arthropod densities peaked in the canopy at the beginning of the wet season. Temperature, leaf dry matter content, and leaf toughness increased with forest height, while specific leaf area decreased. We conclude that forest stratification and seasonality play vital roles in mediating the rate of insect herbivory and arthropod community dynamics in the tropical lowland rainforest of Papua New Guinea.