Unapparent trees: escaping enemies in time by being discreet, unpredictable and inaccessible

For half a century, biologists considered trees as particularly apparent to their enemies. But why then do some trees escape herbivorous enemies by bursting buds either too early or too late, leading to phenological mismatch? We hypothesize that such mismatches occur on trees that are unapparent in time – those that burst buds ‘discreetly' (slowly) and unpredictably (inconsistently across years), and are difficult to access (host trees among non‐hosts). We studied herbivores on oaks in western France. We for the first‐time characterized phenology matching of an entire guild of herbivores, early spring ectophagous caterpillars (45 species). We examined whether, on a given date, caterpillars have a large body size and impact (herbivory), and whether this size or impact are largest on trees that burst buds earliest. Furthermore, we distinguished the contributions of within‐guild sorting of species and within‐population selection of individuals to phenology matching, we investigated whether present phenology matching was determined during past generations by testing if caterpillars from trees with early‐maturing foliage pupate early, even when transferred into a common garden. We found that caterpillar size and herbivory impact in the field and pupation date in the lab generally matched leaf phenology in the field. Such phenology matching was consistently observed at the intraspecific level but was less evident at the interspecific level. Together this indicates that phenology matching is mainly driven by past within‐population selection rather than present, within‐guild sorting. Furthermore, herbivores size and impact were most constrained by late bursting of host trees if these trees burst buds slowly and unpredictably and are difficult to access. We suggest that, during the assembly of early‐spring herbivore guilds, trees can best constrain development of herbivore populations by late budburst and remaining unapparent in time – bursting buds discreetly, unpredictably across years, or in inaccessible neighbourhoods.