Effects of Warming on Dense Stands of Young Faxon Fir Trees

Introducting their study, Wang et al. (2012) write that "competition with neighboring plants is one of the most important biotic factors limiting plant growth," noting that "plants in a stand compete with each other for resources" and that "competition alters morphological and physiological traits of plants," citing Hikosaka et al. (1999, 2003, 2005) and Nagashima et al. (2003). And they state that these alterations, in turn, "result in changes in the microclimate and resource acquisition in the stand, and consequently influence the growth and development of individuals," which lead them to conclude that "it is indispensable to study temperature responses of plants growing in a stand instead of growing individually," which they proceeded to do.

Within each of six enclosed-top fumigation chambers erected out-of-doors at the Maoxian Ecological Station in southwest China, Wang et al. placed a single wooden box filled with surface sandy soil taken from a 30-year-old Aibes faxoniana forest; and they planted within each of them same-size 7-year-old A. faxoniana seedlings at a density of 16 plants per square meter, while draping high-density shade cloths over the tops of the chambers so that the light intensity received by the seedlings was about 35% of ambient top-of-the-forest light intensity, in order to mimic the understory light environment in which A. faxoniana seedlings typically grow. And for the following six years, they monitored numerous plant properties, while half of the chambers were maintained at the ambient outdoor temperature (T) and the other half were maintained at T + 2.2°C.

At the end of their study, the three Chinese scientists were able to report that "warming caused statistically significant increases in the specific leaf area, leaf area ratio, root biomass, leaf biomass, branch biomass, stem biomass, and total mass of the seedlings," as well as "total chlorophyll concentrations, specific chlorophyll pigments, and Chlorophyll a/b ratios," and they say that these changes in branch growth and needle chemistry enhance the light-capture potential of seedlings growing in the low-light environment characteristic of Faxon fir understories. Given such findings, Wang et al. conclude that "future elevated temperature may adjust trees' morphology and physiology to enable the capture of more light to support seedling growth under growth-limiting light, intra-specific competition and nutritional conditions."

Additional References
Hikosaka, K., Sudoh, S. and Hirose, T. 1999. Light acquisition and use by individuals competing in a dense stand of an annual herb, Xanthium canadense. Oecologia 118: 388-396.

Hikosaka, K., Yamano, T., Nagashima, H. and Hirose, T. 2003. Light-acquisition and use of individuals as influenced by elevated CO2 in even-aged monospecific stands of Chenopodium album. Functional Ecology 17: 786-795.

Hikosaka, K., Onoda, Y., Kinugasa, T., Nagashima, H., Anten, N.P.R. and Hirose, T. 2005. Plant responses to elevated CO2 concentration at different scales: leaf, whole plant, canopy, and population. Ecological Research 20: 243-253.

Nagashima, H., Yamano, T., Hikosaka, K. and Hirose, T. 2003. Effects of elevated CO2 on the size structure in even-aged monospecific stands of Chenopodium album. Global Change Biology 9: 619-629.