My apologies to Nico, and others if my assertions were overly abrupt. And my thanks to Hennie, and others for you're affirmation. I must agree with Nico, trees will never talk, at least in any anthropocentric way. They dont have vocal chords. Writing accurately and specifically, much of the current research, based on the recognized hard sciences is not looking at "trees" and "talking" but rather "communication" more generally than "talking"; and at "plants" more generally than just "trees". Further, the more specific knowledge details communication within a single plant, though there is some evidence of communication between plants; and between plants and the community of soil based micro-organisms at the roots.
I am certainly not an expert, nor do I know all of the research; my comment of sending the trees off to war was a bit over the top, but not entirely uninformed. As a species, we do tend to find some way to abuse most of what we acquire dominion over. However, as this is the list for skeptical druids; I post below a sampler of citations. These are meant more to suggest the direction of further research than to post complete objective evidence. Much of this work is published under subscription and copyright. Hence, I include here the (Harvard form) citations, along with relevant samples from the text.
Witzany, G. 2008, "The Biosemiotics of Plant Communication", The American Journal of Semiotics, vol. 24, no. 1-3, pp. 39-39-56,208.
This contribution demonstrates that the development and growth of plants depends on the success of complex communication processes. These communication processes are primarily sign-mediated interactions and are not simply an mechanical exchange of information) as that term has come to be understood (or misunderstood) in science. Rather, such interactions as I will be describing here involve the active coordination and organisation of a great variety of different behavioural patterns - all of which must be mediated by signs.
Thus proposed, a biosemiotics of plant communication investigates communication processes both within and among the cells, tissues, and organs of plants as sign-mediated interactions which follow (1) combinatorial (syntactic), (2) context-sensitive (pragmatic) and (3) content-specific (semantic) levels of rules. As will be seen in the cases under investigation, the context of interactions in which a plant organism is interwoven determines the content arrangement of its response behaviour. And as exemplified by the multiply semiotic roles played by the plant hormone auxin that I will discuss below, this means that a molecule type of identical chemical structure may function in the instantiation of different meanings (semantics) that are determined by the different contexts (pragmatics) in which this sign is used.
Biosemiotics investigates the use of signs within and between organisms. Such signs may be signals or symbols, and many of them are chemical molecules. In the highly developed eukaryotic kingdoms, the behavioural patterns of organisms may also serve as signs, as for example, the dances of bees. Such signs obey the semiotic rules appropriate to their three level types. Thus: (1) their syntax determines the combinatory possibilities of a given set of signs - whether physical and chemical (e.g., Watson-Crickbase-pairing), or spatial, temporal, and rhythmical (i.e., the relationship among the signs); (2) their pragmatics determines the relationship between a sign-user (within its interactional context) and the signs to be negotiated, and (3) their semantics (which is to say: their meanings) depend on the pragmatic interactional contexts within which a sign-using individual is, by necessity, interwoven - and, therefore, on the particular relation between the signs and the signified content that is required in the specific context.
Recent investigation into the biosemiotics of plant communication provides robust empirical evidence about sign-mediated interactions taking place incessantly both within and between plants, as well as between plants and non-plant organisms. As can be seen, there is a great variety of signalling processes in the organismic kingdom of plants, and this argues against the notion, held for too long now, that plants can be considered as automation-like organisms. With this article I hope to show that further investigation into the biosemiotics of plant communication may help us to better understand these fascinating organisms, in all of their communicative competence.
Zimmermann, M.R., Maischak, H., Mithöfer, A., Boland, W. & Felle, H.H. 2009, "System Potentials, a Novel Electrical Long-Distance Apoplastic Signal in Plants, Induced by Wounding1", Plant Physiology, vol. 149, no. 3, pp. 1593-1593-600.
Understanding systemic signaling in plants has long been recognized as a major scientific challenge. In principle, the systemic signaling induced by wounding and/or pathogen or herbivore attack may be realized by either chemical or electrical signals. Chemical signals have been shown to be involved in long distance signaling, propagating likely from organ to organ either through the vascular system or as volatiles that are released into the atmosphere, carrying the message not only to organs within a plant but possibly to neighboring plants as well (Heil and Silva Bueno, 2007; Heil and Ton, 2008; Howe and Jander, 2008; Mithöfer et al., 2009). Other studies suggest that upon wounding, electrical signals may travel through phloem and/or xylem elements (Davies, 1987; Rhodes et al., 1996). Interestingly, such electrical signals have also been shown to affect systemic leaves, for example, by regulating genes (Graham et al., 1986;Wildon et al., 1992; Stankovic and Davies, 1997; Herde et al., 1998). Among other genes, proteinase inhibitor (Pin) and calmodulin mRNA have been up-regulated in tomato (Solanum lycopersicum) upon wounding and the application of heat stimuli (Stankovic and Davies, 1997). Plants that elicited no electrical signal did not accumulate Pin mRNA (Stankovic and Davies, 1997). In particular, the induction of Pin genes is striking because these proteinase inhibitors are induced upon insect herbivory as a defense reaction (Green and Ryan, 1972). Proteinase inhibitors either harm the attackers or simply prevent insects from feeding (Koiwa et al., 1997). Although, in principle, cellular reactions in plants have also been demonstrated to follow the release of electrical signals induced by heat, chilling, or electric voltage, to what extent such signals carry specific information in nonspecialized plants or organs is disputed.
Karban, R., Shiojiri, K. & Ishizaki, S. 2010, "An Air Transfer Experiment Confirms the Role of Volatile Cues in Communication between Plants", The American Naturalist, vol. 176, no. 3, pp. 381.
Previous studies reported that sagebrush plants near experimentally clipped neighbors experienced less herbivory than did plants near unclipped neighbors. Blocking air flow with plastic bags made this effect undetectable. However, some scientists remained skeptical about the possibility of volatile communication between plants since the existence and identity of a cue that operates in nature have never been demonstrated. We conducted an air transfer experiment that collected air from the headspace of an experimentally clipped donor plant and delivered it to the headspace of an unclipped assay plant. We found that assay plants treated with air from clipped donors were less likely to be damaged by naturally occurring herbivores in a field experiment. This simple air transfer experiment fulfills the most critical of Koch's postulates and provides more definitive evidence for volatile communication between plants. It also provides an inexpensive experimental protocol that can be used to screen plants for interplant communication in the field.