The study exposed 20 ash trees to various radiation sources for a period of three months. Trees placed closest to the Wi-Fi radio demonstrated a "lead-like shine" on their leaves that was caused by the dying of the upper and lower epidermis of the leaves. This would eventually result in the death of parts of the leaves. The study also found that Wi-Fi radiation could inhibit the growth of corn cobs [René Schoemaker, "Wi-Fi Makes Trees Sick, Study Says," PC World, 2010.11.19].
Corn cobs?! Could we bloggers be reducing crop yields? Oh no!
But hold the iPhone: the media is headlining these results a little more confidently than are the Dutch researchers. Lead researcher Dr. Andre van Lammeren says the results are preliminary:
I think it's too early for alarm about this. The study that we have completed was a pilot study over three to four months, and we want to continue work on the issue now with more controls [Dr. Andre van Lammeren, in Greg Wiser, "Wireless Internet Hubs May Damage Trees, Study Finds," Deutsche Welle, 2010.11.26].
The research summary notes that the leaves manifesting the apparent damage sat 50 cm away from the Wi-Fi source for a few months. So even if this study demonstrates actual harm, it just says don't set your houseplant on the same table as your router.
Deutsche Welle also reports contradictory prior research from a Swiss forestry agency that found wireless Internet signals causing harm to spruce and beech trees only when researchers cranked up the wattage past elgal levels... and even then the harm came from thermal effects, not the signal itself.
Also not addressed in the Dutch research: the comparative harm to trees if we converted all our e-mails and blog posts and research reports back to paper.