Abstract Detail

Forest Tree Responses to a Changing Climate

Guy, Robert [1], McKown, Athena [2], Soolanayakanahally, Raju [3].

To everything there is a season, and a time to set bud under heaven.

Vegetative phenology plays an enormous role in determining tree growth and adaptation to climate and, not surprisingly, varies extensively between and within north-temperate and boreal tree species. Temperate and boreal trees use photoperiod to cue height growth cessation, bud set and leaf senescence. Photoperiodic regime, which is of course fixed with latitude, may limit the ability of tree species to respond to climate warming. To explore patterns of photoperiodic adaptation and other latitudinal clines in trees, we have been using two extensive poplar collections: the BC MoFLNRO collection of >500 genotypes of black cottonwood (Populus trichocarpa) and the AgCanBaP collection of over 960 balsam poplar (P. balsamifera) genotypes. The black cottonwood collection is maintained on campus in Vancouver, BC. We also grow part of the balsam poplar collection for comparison with the same clones in another common garden at Indian Head, SK, near the southern limit of the species. These common gardens, in very different climates, have similar latitude and photoperiod. In both poplar species there are strong clines in photosynthetic rate, being higher in northern accessions, and we speculate that populations from colder climates may compensate for shorter growing seasons by having higher photosynthesis. In fact, when photoperiodic constraints are removed under greenhouse conditions, northern genotypes tend to be the faster growers. Quite the opposite is true when these collections are grown in the outdoor common gardens. Near-arctic and continental genotypes of balsam poplar, and northern genotypes of black cottonwood, grow very poorly in Vancouver because they set bud too early, well before the summer solstice. Bud set in their native environments is normally induced by the shorter days of late summer. However, it is important for trees not to respond to similar photoperiods in early spring. Formerly it was thought that directionality in the change in photoperiod (i.e., increasingly longer days in spring) prevented height growth cessation, but this is not the case. Rather, young vegetative shoots are simply insensitive to photoperiod. This period varies from 2-6 weeks, depending on genotype, and occurs after the transition to neoformed leaf production. Early springs result in early sensitivity, which, if days are short enough, stops growth. Consequently, in the context of climate warming, native poplars may start growth sooner to take advantage of early springs, but they may also capture less of a longer summer. Fortunately, considerable within population variation in critical photoperiod will buffer the impact.

1 - University of British Columbia, Forest and Conservation Sciences, 2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada
2 - University Of British Columbia, Forest Sciences Centre, 2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada
3 - Agriculture and Agri-Food Canada, Agroforestry Development Centre, No. 2 Government Rd., Indian Head, SK, S0G 2K0, Canada

Keywords:
phenology
local adaptation
photoperiod
Populus
latitude.

Presentation Type: Symposium Presentation
Session: SY13
Location: Hall A/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 10:15 AM
Number: SY13006
Abstract ID:1359
Candidate for Awards:None