Why Does Early-Season Herbivory Affect Subsequent Budburst?

Abstract

Delays in budburst in the year following herbivory have previously been attributed to a defensive response to early-season herbivory or localized resource deficiencies (resource availability hypothesis) limiting bud development. We carried out field experiments to test the resource availability hypothesis as well as the crown architecture hypothesis, which attributes changes in the time of budburst in the year following herbivory to changes in the proportion of different bud types. We examined predictions from these hypotheses using a defoliator, Choristoneura fumiferana; a defoliator/stem feeder, Zeiraphera canadensis; and a stem galler, Adelges abietis; on white spruce, Picea glauca. The time of budburst and final leaf size of unexploited midcrown shoots of white spruce were compared to those of adjacent exploited shoots. We also evaluated budburst in a manipulated field study, in which tree growth was reduced through root pruning and increased through fertilization.Partial defoliation by C. fumiferana and Z. canadensis did not affect budburst, but did result in smaller leaves. Almost complete defoliation of shoots by C. fumiferana and galling by A. abietis resulted in delayed budburst. Reductions in leaf size were directly related to the amount of herbivory (i.e., low or high) by C. fumiferana and Z. canadensis. Budburst of trees whose growth rate had been decreased by root pruning or increased by fertilizing occurred later and sooner, respectively, than budburst on unmanipulated trees. The time of budburst was inversely correlated with foliar nitrogen and water content and the length of unexploited shoots. These results supported the resource availability hypothesis. The influence of resource availability on time of budburst was observed at the shoot, branch, and whole-tree levels. When Ͼ50% of stems were destroyed by Z. canadensis, budburst occurred earlier or at the same time in the following spring. This was due to the production of basal buds, which burst before all other buds on a shoot. The production of early-bursting basal buds more than compensated, or just compensated, for a small delay in budburst of terminal, distal-lateral, and medial-lateral buds. Thus, changes in the time of budburst in the year following herbivory were due to changes in crown architecture as well as to changes in resource availability. We predict that increased intra-tree heterogeneity in the time of budburst should make P. glauca more, rather than less, susceptible to two of the herbivores studied because of the presence of a highly nutritious food source, newly burst buds, for a longer period of time. We suggest that the influence of previous herbivory on the time of budburst in the next growing season is a commonly overlooked factor that may have a large influence on herbivore abundance and distribution.

Variation in Lupinus arboreus alkaloid profiles and relationships with multiple herbivores

“…Maddox and Root (1987) found consistent heritable resistance for multiple species of stem galling insects but not other herbivore guilds, although traits associated with resistance were not identified. Although stem and bud gallers can have clear impacts on plant fitness (Quiring and McKinnon, 1999), the relationship between leaf gallers and plant fitness is not as clear. There are still remarkably few studies that have demonstrated selection by herbivores on specific plant chemical defenses (but see Mauricio and Rausher, 1997;Shonle and Bergelson, 2000).…”

Effects of drought and heat on forest insect populations in relation to the 2003 drought in Western Europe

“…Lepidoptera hatching during a drought period are negatively affected by leaf texture changes; leaves become tougher because of the decline in water content (see ref. in [5,60,74]. However, senescing foliage also provides insects with high quality food containing high nitrogen concentration [44].…”

Effects of Natural Winter Browsing and Simulated Summer Browsing by Moose on Growth and Shoot Biomass of Birch and Its Associated Invertebrate Fauna

“…Herbivory on leaves may also affect the timing of budburst in the next growing season (Tuomi et al 1989, Quiring & McKinnon 1999. The spring emergence of many leaf-feeding insects is closely synchronized with budburst of their host trees.…”

“…As a result, trees where budburst occurs earlier or later may often be less defoliated by herbivorous insects (see e.g. Tuomi et al 1989, Quiring & McKinnon 1999, and references therein).…”