Plant characteristics drive ontogenetic changes in herbivory damage in a temperate forest

Understanding ontogenetic differences in plant defenses and herbivory
damage is crucial for obtaining a better understanding of plant
life-history strategies, community assembly, and dynamics. Although many
studies have compared plant defenses or herbivory damage between
ontogenetic stages (e.g., sapling vs. adult), how the effects of plant
characteristics on leaf herbivory damage change during plant ontogeny has
rarely been examined across species or in a species-rich natural
community. To elucidate the effects of plant characteristics, we compared
the relationships of leaf herbivory damage with stem density, plant size,
and leaf traits between saplings and adults for almost all co-occurring
woody species (56 species, ranging from rare to abundant) in a Japanese
temperate forest. In most species, adults were larger, fewer in number,
and had leaf traits that were potentially less favorable to herbivores
(e.g., stronger, or with more phenolics). In contrast, we observed
species-specific directions of changes in herbivory damage between adults
and saplings with plant phylogeny or density having no clear effect. The
relationships between some plant traits and herbivory damage were ontogeny
dependent, indicating a shift from chemical to physical defense as plants
mature, although most of the species characteristics studied were highly
correlated between stages. Such ontogeny-dependent relationships between
plant traits and herbivory damage could cause variation in the ontogenetic
changes in herbivory damage among species depending on the value of plant
traits. Moreover, the direction and magnitude of the effects of
ontogenetic differences in species traits on the ontogenetic differences
in herbivory damage varied depending on the traits. Together, these
factors could have caused the observed ontogenetic changes in herbivory
damage among species. Synthesis. Our study demonstrated how relationships
between plant characteristics and herbivory damage can change
ontogenetically across many coexisting woody species in a forest
community, suggesting that plant traits may perform different functions
related to herbivory at different ontogenetic stages. This has rarely been
considered in previous dualistic comparisons of individual traits and
herbivory damage between ontogenetic stages, and it is vital for
understanding plant life-history strategies across stages in relationships
with herbivores in natural communities.