Tree-ring formation of eastern white-cedar (Thuja occidentalis L.) at a boreal lake in northwestern Quebec, Canada, was monitored using manual band dendrometers to (i) retrace cambial activity phases, (ii) evaluate the effects of flooding on radial growth, and (iii) analyze the relationships with meteorological factors. The daily circumferential activity of four trees at each of two sites, a riparian and an upland site, was recorded during the growing season of 1996, a year with an extreme spring flood. First cambium cell divisions occurred near June 9, followed by a distinct and sustained upward trend in the stem basal area until mid-July that reflected the earlywood formation. The strongly synchronous circumferential activity at both sites suggests no adverse flooding effect on growth of the riparian trees, which is explained by the rapid retreat of the water just before growth initiation in early June. The following month until mid-August was characterized by strong short-term fluctuations caused by alternating drought and rain periods and a slight downward trend of the basal area for six of the eight banded white-cedars. The dendrometers of two trees, the closest to the lake, showed a slight upward trend probably reflecting latewood formation. Pearson correlation with meteorological data indicated that precipitation was positively related to the daily changes in basal area of all trees except during the period of earlywood formation, which probably resulted from the high soil moisture after spring snow-melting. Mean and minimum air humidity were positively related and maximum temperature negatively related to the daily variations in stem circumference during the whole monitoring period, emphasizing the importance of the internal water status on stem size.

Human activities are changing wildfire regimes globally through ignition, spread of invasive species, fire suppression, and climate change. Because of this, ecosystems are experiencing novel fire regimes that may alter plant growth and patterns of succession. Annual growth rings are one metric that can track changes in tree and shrub growth patterns over time in response to changing fire frequency. In Chapter 1 we explored the effects of fire on resprouting native shrubs in the Mojave Desert. Fires are becoming increasingly frequent due to the spread of highly flammable invasive grasses in the region. We monitored growth and fruit production of Larrea tridentata D.C. (creosote bush) on burned and unburned transects from three independent 2005 wildfires. Even though creosote has a high fire mortality rate, we found that resprouting creosote produced 4.7 times the amount of fruit and had stems that grew nearly twice as fast compared to creosote in unburned areas. Our data suggest that creosote can resprout after fire and thrives in its growth rates and reproduction in post-fire environments. In Chapter 2 we used annual Basal Area Increment to investigate how fire suppression has altered facilitation and competition interactions through stages of succession in mixed aspen-conifer forests. We found that aspen had lower growth rates in mixed aspen-conifer stands compared to aspen dominant stands. We also found that aspen growing with an associated fir tree due to facilitation had increasingly lower growth rates over time than those growing independently. Fir trees in mixed stands were facilitated over time by associated aspen trees while fir trees growing in association and independently in aspen stands showed no statistical difference from each other but grew better than independent fir trees in mixed stands. Our data suggest that restoring a more frequent fire regime will balance competitive interactions between aspen and conifer in subalpine forests.