Trees that talk?

Still lots of snow, but still managed to get out, and here's some leftovers from last summer:

Gray Alder (Alnus incana rugosa), Van Patton Woods FP,
Lake Co, IL 3/9/2014

Gray Alder (Alnus incana rugosa), Van Patton Woods FP,
Lake Co, IL 3/9/2014

These are male (skinny) and female (round) catkins from a Gray Alder, (Alnus incana rugosa). Although they look like hemlock cones, alders are actually flowering plants. In contrast to birches or willows, though, these catkins develop woody tissue and remain on the tree through the winter.

Alders are interesting plants. They grow nodules on their roots that host nitrogen-fixing bacteria (1), just as legumes do, so they enrich the soil where they grow.

They also, apparently, talk to each other! When European Alders (A. glutinosa) are attacked by leaf beetles (Agelastica alni), they alter their leaf chemistry, adding phenols and increasing the activity of various oxidative enzyme pathways. They also emit ethylene and various terpenes. Beetle activity after this occurred was found to decrease not only on the affected tree but on trees some distance away, as did other specialist herbivorous insects. Generalist herbivores were apparently not affected. When other trees were exposed to the mix of emitted chemicals, they saw similar results, even though those other trees hadn't been attacked. (2) The authors rightly point out that this is a form of communication -- between trees!

Tolkien may have exaggerated their liveliness, but apparently trees can talk to each other.

(1) Akkermans, A. D. L. (1971). Nitrogen fixation and nodulation of Alnus and Hippophaë under natural conditions. Meded. bot. Lab. Rijks-Univ., Leiden.

(2) Tscharntke, T., Thiessen, S., Dolch, R., & Boland, W. (2001). Herbivory, induced resistance, and interplant signal transfer in Alnus glutinosa.Biochemical Systematics and Ecology, 29(10), 1025-1047.