Plants utilize a mixture of defence types in response to herbivores, including physical, chemical, and biological defences. Among chemical defences, phenolics are well-known to inhibit digestion and are highly variable across plant species and resource gradients. There are prominent hypotheses predicting the potential change of phenolics in response to soil nutrients, but most focus on nitrogen (N) and none consider their interaction with defence strategies. We proposed an updated theoretical model that incorporates defence types and predicts their relative advantages under herbivore attack. We studied intraspecific leaf chemistry of several architecturally defended and non-architecturally defended species growing together across four sites with varying soil chemistry. We measured individual-level leaf concentrations of carbon, nitrogen, phosphorus (P), potassium (K), and phenolics, and site-level soil N, P, and K. We found that architectural defenders had lower phenolics and higher P than non-architectural defenders across locations. Relationships between soil nutrients and leaf chemistry were steeper in architectural defenders. Most leaf nutrients and phenolics showed significant relationships with soil P, and only leaf P was related to its respective soil resource. Within leaves, phenolics were negatively related to leaf N in both groups but only negatively related to leaf P for architectural defenders. Our results suggest that architectural defenders are less able to accumulate phenolic defences in high P soils than non-architectural defender. One possible explanation is that phenolic production is limited in P-rich soils via active phloem loading, but only in architectural defenders that have defence options other than chemical ones.

Current widely used climate envelope approaches, i.e., correlations between climatic variables and the presence of a species, simulate responses for the whole species and predict future ranges based mainly on climatic suitability. However, short-term tree responses to climate change will take place within current populations, and these populations, acclimated to their local environments, are not likely to respond similarly to climate change. Thus, to develop reliable forecasts of forest responses to climate change, this variability among populations needs to be considered. In this study, we tested the effect of environmental conditions on the growth of two common maple species (Acer rubrum L. and A. saccharum Marshall) at two different latitudes within their northern distributional ranges. We collected increment cores, and analyzed year to year variabilities in tree growth as a function of temperature and precipitation. The results suggest divergent responses between species and between populations of the same species. Predicted growth under different climate scenarios for the region suggested that the growth of southern populations might decrease, while northern populations might still be able to retain their current growth. These results document the population-level responses to environmental conditions of these two species, providing latitude-specific guidance for future forest distribution prediction.