单选题 .  ①Exotic insect pests can produce both short-and long-term effects on forest ecosystems. ②Short-term effects include the disturbances directly associated with the action of the pest, which may cause the defoliation, loss of vigor, or death of trees. ③Long-term effects involve changes in tree species composition and the consequent alterations of forest structure, productivity, and nutrient uptake. ④Exotic pests are more efficient than most abiotic disturbances (e.g., fire or wind) at producing long-term changes in species composition. ⑤Pests often target specific tree species and, if they become established, they usually remain as permanent components of the ecosystem. ⑥Shifts in forest species composition ramify through the ecosystem in many ways because tree species have different, often unique properties.32.  The passage mentions which of the following as effects of exotic pests on forest ecosystems? ______