Species-specific growth responses of black spruce and trembling aspen may enhance resilience of boreal forest to climate change

To understand how the future climate will affect the boreal forest, we studied growth responses to climate variability in black spruce (Picea mariana [Mill.] B.S.P.) and trembling aspen (Populus tremuloides Michx.) two major co-occurring boreal tree species of the eastern Canadian boreal forest. We analysed climate growth interaction during (i) periods of non-anomalous growth and (ii) in years with strong growth anomalies. We utilized paired tree level data for both growth and soil variables, which helped ensure that the studied growth variability was a function of species specific biology, and not of within stand variation in soil conditions. Redundancy analysis conducted on spruce and aspen tree ring chronologies showed that their growth was affected differently by climate. During non-anomalous years, growth of spruce was favoured by cooler temperatures and wetter conditions, while aspen growth was favoured by higher temperatures and drier conditions. Black spruce and trembling aspen also showed an inverse pattern in respect to expression of growth anomalies (pointer years). A negative growth anomaly in spruce tended to be associated with positive ones in aspen and vice versa. This suggested that spruce and aspen had largely contrasting species specific responses to both "average" weather conditions and extreme weather events. Synthesis. Species specific responses to environmental variability imply that tree responses to future climate will likely be not synchronized among species, which may translate into changes in structure and composition of future forest communities. In particular, we speculate that outcome of climate change in respect to relative abundance of black spruce and trembling aspen at the regional levels will be highly dependent on the balance between increasing temperatures and precipitation. Further, species specific responses of trees to annual climate variability may enhance the resilience of mixed forests by constraining variability in their annual biomass accumulation, as compared to pure stands, under periods with high frequency of climatically extreme conditions

Recovery of carbon stocks after wildfires in boreal forests : a synthesis

Book of abstracts Cool forests at risk? The Critical Role of Boreal and Mountain Ecosystems for People, Bioeconomy, and ClimatePeer reviewe

Soil characteristics mediate the distribution and response of boreal trees to climatic variability

We studied the effects of the soil organic layer (SOL) accumulation on growth and distribution of black spruce (Picea mariana (Mill.) BSP) and trembling aspen (Populus tremuloides Michx.) within the Quebec Clay Belt. At the landscape scale, spruce was present over a much larger gradient in SOL thickness (similar to 1 to 100 cm) than aspen (similar to 1 to 30 cm). For trees between 60 and 100 years old, SOL thickness had no effect on the basal area increment (BAI) of spruce but showed a strong and negative correlation with BAI in aspen. Radial growth of black spruce was favored by higher precipitation in June of the previous growing season, higher temperatures in early winter and in spring, and by low temperatures in summer. SOL thickness had statistically significant but moderate effects on the climate-growth relationships in spruce, apparently affecting root insulation during the dormant period and water availability during the growing period. In aspen, current-year June temperature was the most important factor positively correlated with growth. The SOL thickness affected the relationship between the aspen growth and (i) January temperature and (ii) June-August monthly drought code. We predict that the response of black spruce to climate change should be rather uniform across the study region, while the response of aspen is likely to be strongly mediated by SOL thickness

Effects of above- and belowground partial harvest disturbance on growth and water status of residual sugar maple

Partial forest harvesting is known to modify both\ud above- and belowground resource availability and may result in direct and indirect stress to the residual trees as a result of machinery traffic and sudden changes in irradiance.We studied sugar maple (Acer saccharum Marsh.) trees in stands that had undergone a selection harvest 11 years before sampling to verify whether sudden increases in light availability and soil disturbance caused by machinery influence growth rates and lead towater stress.We selected trees that had experienced either no disturbance from partial harvest, soil disturbance only, sudden increases in light availability only or both disturbances.We analyzed\ud stem radial growth rates and stable carbon isotope composition (δ13C) of stem wood with an annual resolution from 10 years before partial harvest until 10 years after partial harvest. Disturbances from partial harvest did not negatively affect growth rates or tree water status. Although trees that experienced increased light availability had higher (less negative) δ13C after harvest (indicating increased water-use efficiency), they also had higher growth rates, suggesting that they\ud experienced no pronounced water stress. Trees subjected to soil disturbance showed no sign of water stress. These results may partly be associated with favorable growth conditions(abundant precipitation and mild temperature) in the years following harvest and could differ from results that would be observed under more severe climatic conditions

Fire-induced changes of high and low intensity prescribed fires in a Canadian boreal forest

Geophysical Research AbstractsVol. 21, EGU2019-7859, 2019EGU General Assembly 2019The degree of fire-induced effects on boreal forest soils substantially depends on the intensityof fire. Especially high-intensity fires may drastically alter the quality and quantity of the soilorganic matter pool. In this study, we investigated the effects of low and high intensityprescribed fires on soil carbon and nitrogen contents, soil pH, soil temperature, and soilmoisture in a Canadian boreal forest. The study was based on intensive field sampling duringAugust 2018 in Jack pine (Pinus banksiana) forest stands located 50 km north of FortProvidence, Northwest Territories (61.582˚ ; -117.165˚). We measured the soil parametersfrom two short-term fire chronosequences — one with high-intensity prescribed fireshappening in years 2000, 2012, 2015, 2016, and 2017; and the other with low-intensityprescribed fires happening in years 2015, 2017, and 2018. Additionally, we measured soiltemperature and moisture before and after a low-intensity prescribed fire. In thehigh-intensity fire chronosequence, the study site burned in year 2012 had the lowest soiltemperature. Even though temperatures seemed slightly higher in the most recent years ofthe fire chronosequence (2015, 2016, and 2017), we did not identify a clear trend.Soil moisture was the lowest in the study site burned in year 2000, with mostly nosignificant differences between the following years. We did not find significantdifferences in soil moisture and soil temperature before and after a low-intensityprescribed fire. However, both time-after-fire and fire intensity were important forsoil moisture prediction, whereas only fire intensity was important for predictingsoil temperature. Soil pH in the humus layer of the study site burned in 2012 wassignificantly lower compared to the other age classes (no pH data for year 2000) of thehigh-intensity fire chronosequence. Neither C nor N content were significantly differentbetween the fire age classes at the humus layer or at the mineral layers. We believethat the small sample size did not allow the identification of further differencesbetween the age classes, and it prevented direct comparisons between high and lowintensity fires. Despite its exploratory nature, this study offers some insight intoshort-term effects of fire on some soil parameters, for example, the observed changeson soil moisture, soil temperature, and soil pH. Therefore, we will progress thiswork by increasing the sample size and analysing autotrophic and heterotrophic soilrespiration to directly infer on fire-induced changes on the soil organic matter pool.Non peer reviewe

Soil organic matter decomposition and temperature sensitivity after forest fire in permafrost regions in Canada

Non peer reviewe

Linking stem growth respiration to the seasonal course of stem growth and GPP of Scots pine

Current methods to study relations between stem respiration and stem growth have been hampered by problems in quantifying stem growth from dendrometer measurements, particularly on a daily time scale. This is mainly due to the water-related influences within these measurements that mask growth. A previously published model was used to remove water-related influences from measured radial stem variations to reveal a daily radial growth signal (ΔˆGm). We analysed the intra- and inter-annual relations between ΔˆGm and estimated growth respiration rates (Rg) on a daily scale for 5 years. Results showed that Rg was weakly correlated to stem growth prior to tracheid formation, but was significant during the early summer. In the late summer, the correlation decreased slightly relative to the early summer. A 1-day time lag was found of ΔˆGm preceding Rg. Using wavelet analysis and measurements from eddy covariance, it was found that Rg followed gross primary production and temperature with a 2 and 3 h time lag, respectively.This study shows that further in-depth analysis of in-situ growth and growth respiration dynamics is greatly needed, with a focus on cellular respiration at specific developmental stages, its woody tissue costs and linkages to source–sink processes and environmental drivers.Peer reviewe