The effects of herbivory and soil fertility on the growth patterns of <i>Quercus serrata</i> and <i>Q. crispula</i> saplings at the shoot and individual levels

Abstract We investigated the combined effects of herbivore damage and soil fertility on shoot growth patterns of Quercus serrata and Q. crispula saplings at both the shoot and individual levels. Saplings were grown in herbivore‐damaged or undamaged areas of the greenhouse with the two fertilization treatment levels, low or high. We measured the leaf area loss, number of flushes, length of extension units (EUs; the first vs the higher), number of leaves on each individual, and number of EUs. At the shoot level, the leaf area loss at high soil fertility was significantly greater than that at low soil fertility among the highest EUs of Q. serrata , while this difference was not significant in Q. crispula , suggesting that effect of soil fertility on leaf area loss is species‐specific. Furthermore, herbivore damage was associated with a significant increase in the number of EUs and a reduction in the length of the higher EUs under both soil fertility treatments, although saplings had a tendency to produce significantly more flushes and longer individual EUs under the high soil fertility. At the individual level, herbivore‐damaged saplings exhibited a significant increase in leaf numbers; however, the total length of the EUs in Q. serrata or Q. crispula was not significantly affected by herbivore damage, regardless of soil fertility. These results suggest that Q. serrata and Q. crispula saplings produce shorter EUs in response to herbivore damage in order to reduce the cost of mechanical support and spread the risk for any subsequent herbivore damage.