This tree issue appears erroneous. First, the whole 金門 island is a huge piece of rock with very little top soil. It would not have supported forests of any size. And wood used in ship-building is not just any wood. There are different types of ships and each requires different materials. A search turns up this interesting reference: “...南林教授曾对南京明代宝船厂遗址出土的大量与造船有关的木材进行了鉴定，采集了236个出土朽木样品，其中有杉木、松木、柚木、格木、娑罗双树、 锥木、杯裂香、柿木8种树材。” In other words, these are all huge tall trees suitable for putting together large ocean-faring warships. In 金門? Probably only 相思樹 could grow, a recent photo is shown below:
|The "trees" in Kinmoy|
A good guess is that Koxinga's soldiers probably did chop them down for firewood; however, it would have been quite easy to re-grow these bushes unless the residents of 金門 chose not to. Some scholars appear to cite a certain 金門縣志 of the Qing era with regard to the "deforestation". Given the 清史's dubious nature as far as 鄭成功 (in fact, 胡說八道nonsensical smears), this record is also questionable.