The short-term responses of Cassiope tetragona, a high arctic evergreen shrub, to
variations in growing season climate were examined using experimental manipulations of
temperature and growing season length at Alexandra Fiord, Ellesmere Island. Surface
temperatures in the field were increased an average of 1-2 °C in two communities using open-top
greenhouses. Growing season length was altered in a snowbed community by using
manual snow manipulations to change the date of snowmelt. Growth and reproductive
responses of Cassiope tetragona to these manipulations were observed over two field seasons
following treatment establishment. Natural variations in vegetative and reproductive
characteristics of Cassiope tetragona were also monitored in unmanipulated communities
selected to represent a range of environmental conditions at the study site. Retrospective
analysis of past Cassiope growth and reproduction was used to provide a record of variations
in productivity spanning 25-35 years which could be related to climate records from
Ellesmere Island. For the retrospective analysis, patterns of internode lengths were used to
delimit sections of annual growth and chronologies of annual stem elongation, leaf number
and flower number were then analyzed using methods similar to those applied to tree-ring
studies.
In general, the reproductive parameters of Cassiope tetragona were observed to be
highly responsive to short-term variations in growing season climate, while vegetative
production exhibited a much more conservative response. Flower production and rates of
reproductive development were significantly stimulated by experimental warming.
Retrospective analysis of flower production support field observations indicating that flower
production is highly sensitive to annual variations in growing season temperatures. In
contrast, shoot growth showed moderate responses to experimental warming. Records of
past growth indicate that although vegetative production appears to be sensitive to annual
variations in summer temperatures, the degree of responsiveness is much lower than for reproductive parameters. Net growth and reproduction were not stronly affected by natural
or experimental variations in snowmelt timing, although phenology timing was
significantly altered.
The conservative growth response of Cassiope tetragona to short-term variations in
climate is suggested to be related to constraints on plant phenology which may restrict
flexibility in the period utilized by plants for aboveground growth. Preferential allocation
of within-plant resources to reproductive structures during periods of ameliorated growing
season climate may account for the observed strong reproductive responses to climate
variations. Trade-offs betweeen growth and reproduction have important implications for
predicting the long-term response of Cassiope tetragona to climate change. An
understanding of within-plant allocation strategies is also important to the interpretation of
past variations in growth and reproduction. Retrospective analysis of past Cassiope
production is likely to be a very useful tool for investigating ecological relationships and
past climate change.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/3845 |
| Date | 11 1900 |
| Creators | Johnstone, Jill F. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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