Effect of ecosystem warming on boreal black spruce bud burst and shoot growth

Abstract

The boreal forest is predicted to experience the greatest warming of any forest biome during the next 50-100 years, but the effects of warming on vegetation phenology are not well known. The objectives of this study were to (1) examine the effects of whole ecosystem warming on bud burst and annual shoot growth of black spruce trees in northern Manitoba, Canada and (2) correlate bud burst to cumulative degree-days (CDD). The experimental design was a complete randomized block design that consisted of four replicated blocks. Each replicate block contained four treatments: soil warming only (heated outside, HO), soil and air warming (heated inside, HI), control outside (no chamber, no heating, CO), and inside a chamber maintained at ambient conditions (no soil or air warming, control inside, CI). Bud burst was measured during the first and second years of the experiment, starting in 2004, and annual shoot growth was measured for the first 3 years (2004)(2005)(2006) of the study. On average, shoot bud burst occurred 11 and 9 days earlier in 2004 and 2005, respectively, for HI than for other treatments. However, mean CDD required for bud burst for HI was within the standard deviation of CO for both years. In year 1 of the treatments, shoot bud burst occurred earlier for HI than other treatments (CI, CO, HO), but final shoot length of HI trees was less than in CO trees. In the second year of warming, final shoot length was not different for HI than CO. By the third year of warming final shoot length was significantly greater for HI than all other treatments. Empirical results from this study suggest that soil and air warming causes an earlier bud burst for all years of observation and greater shoot lengths by the third season of warming. A longer growing season and greater annual shoot growth should increase carbon uptake by boreal black spruce trees in a warmer climate.

Ecophysiological modeling of photosynthesis and carbon allocation to the tree stem in the boreal forest

“…According to the simulations, the onset of the growing season shifted by 7 days from 14 June to 7 June between the 1950-1970and 1990. This result is consistent with the study of Bronson et al (2009) on the effect of warming on black spruce budburst. During phase 3, which corresponds to budburst, a portion of the available carbon simulated by MAIDEN comes from stored non-structural carbohydrates that are from the current and previous years (parameter Cbud; see Table 1).…”

“…However, because we added a mechanism to smooth yearly variations (see the day23_flex parameter), more years were needed by the plants to acclimate to variable GDD accumulations in winter-spring. With the selected parameters to simulate stem growth, the median onset of the growing season was 10 June (similar to observations for black spruce in northern Mani- toba, Canada; Bronson et al, 2009), with a standard deviation of 7.8 days. If the smoothing term was excluded, then the standard deviation increased to 9.4 days (see Fig.…”

Effects of soil warming and nitrogen foliar applications on bud burst of black spruce

“…Independently of year, bud burst started on average on DOY 150 and soil warming didn't affect the onset. Considering the similar photoperiod between the two sites, air temperature probably plays a predominant role in determining the initiation of bud development in SIM, confirming the finding of Bronson et al (2009). Overall, independently of study site, the bud burst process lasted longer in 2013 than 2012, 3 and 6 days more on average at BER and SIM, respectively.…”

“…Although in the short-term a previous study revealed that a 5 °C increase in the soil temperature does not significantly affect the onset of bud burst and the shoot growth of 12 years old black spruce trees, from the third year of treatment the final shoot length showed an increase in the order of 14% (Bronson et al, 2009).…”

“…Modifications of the conditions in one of these two systems might lead to physiological responses in the other through the long-distance communication by hormonal signals and sugar remobilization (Puig et al, 2012). Although localized heating experiments revealed a local modification in stem and root growth (Begum et al, 2012;Lupi et al, 2012b), the effect on other parts of the plant, including the timings of the bud burst process, appears limited, at least in the short term (Bronson et al, 2009). For technical reasons, the materials used to analyze the responses of tree species to warming experiments are generally juvenile trees, as saplings or seedlings (Rossi and Bousquet, 2014).…”