by Claire Morin | 30 January 2019
Published in Journal of Climate 25: 7690-7701. https://doi.org/10.1175/JCLI-D-11-00440.1
The impacts of climate change on future soil temperature Ts and soil moisture Ms of northern forests are uncertain. In this study, the authors first calibrated Ts and Ms models [Forest Soil Temperature Model (ForSTeM) and Forest Hydrology Model (ForHyM), respectively] using long-term observations of Ts and Ms at different depths measured at three forest sites in eastern Canada. The two models were then used to project Ts and Ms for the period 1971–2100 using historical and future climate scenarios generated by one regional and five global climate models. Results indicate good model performance by ForSTeM and ForHyM in predicting observed Ts and Ms values at various depths for the three sites. Projected annual-mean Ts at these sites increased between 1.1° and 1.9°C and between 1.9° and 3.3°C from the present 30-yr averages (1971–2000) to the periods 2040–69 and 2070–99, respectively. Increases as high as 5.0°C were projected at the black spruce site during the growing season (June) for the period 2070–99. Changes in annual-mean Ms were relatively small; however, seasonally Ms is projected to increase in April, because of earlier snowmelt, and to decrease during the growing season, mainly because of higher evapotranspiration rates. Soil moisture in the growing season could be reduced by 20%–40% for the period 2070–99 compared to the reference period. The projected warmer and drier soil conditions in the growing season could have significant impacts on forests growth and biogeochemical cycles.
by Claire Morin | 30 January 2019
Published in Biological Conservation 159: 458-467. https://doi.org/10.1016/j.biocon.2012.12.019
In boreal forests, partial cutting is increasingly proposed as a suitable alternative to the widespread use of clearcutting in order to conciliate forest management with habitat conservation for epiphytic species. We compared the growth of two epiphytic lichen species, Bryoria nadvornikiana and Evernia mesomorpha, in old forest stands recently treated by partial cutting and untreated controls, located in black spruce boreal forests of western Québec. Lichen growth rates were measured over a period of tow years from transplants of the two species, and several environmental variables (e.g., canopy openness, thallus temperature, and tallus wetness) were also measured directly at the sampling sites. Despite important within-treatment variation in growth rates among transplants, we observed reduced growth rates in partial cuts for both species. Canopy openness measurements of more than 40% resulted in negative growth rates for B. nadvornikiana, a species typically associated with relatively closed canopies, and canopy openness over 70% resulted in negative growth rates for E. mesomorpha, a species that tends to be associated with open canopies. This negative growth response contrasts with what is generally reported in the literature about the effect of canopy opening creation on epiphytic lichen growth. As a function of the environmental parameters that were measured on site, we suggest that a reduction in the duration of hydration periods, and an increased risk of thallus fragmentation in partially cut stands, especially for B. nadvornikiana, could explain this result. Because this negative effect could be more likely to occur during dry periods, future trends in the response of epiphytic lichens to the creation of canopy openings could be influenced by climate change. This study suggest that even if partial cuts can be a good alternative to clearcutting for the conservation of epiphytic lichen species, they are more likely to succeed if dense clumps of residual trees (canopy cover > 70%) are retained in the treated stands.
by Marie-Claude Boileau | 30 January 2019
Published in Northern Journal of Applied Forestry 30(1): 28-36
In northeastern North America, a growing number of studies report on the regeneration failure of sugar maple (SM, Acer saccharum Marsh.) in some SM-dominated stands coupled with a marked increase in abundance of American beech (AB, Fagus grandifolia Ehrh.) in the regeneration stratum, suggesting change in forest composition toward AB dominance. The effect of release (removing all competitors within 1 m of their crown perimeters) and liming (3 Mg ha-1 of CaCO3) on growth of SM and AB saplings was experimentally tested to partition the effect of intertree competition and soil fertility on the growth dynamics of these two species at the sapling stage. Lime application had the desired effect on soil chemistry, expressed notably as a four-fold increase in calcium concentrations of the upper soil layer (0 –12 cm) and a 63% decrease in exchangeable acidity. Seven years following treatments, biomass growth response of AB saplings to release was 1.5 times higher than that of SM. In contrast, liming increased biomass growth of SM saplings (approximately 2 times compared with unlimed saplings), while there was no effect on AB growth. Also, the availability of light and of soil Ca interacts to increase growth of SM saplings. Our results confirm that SM is more sensitive to calcium availability than AB. Various forest management strategies are discussed in light of these experimental results.
by Claire Morin | 30 January 2019
Published in Biogeochemistry 111: 393-409 https://doi.org/10.1007/s10533-011-9664-1
Within the southeast Canada and northeast USA region, a peak in sulphate (SO42-) concentration has been reported for some streams following periods of substantial catchment drying during the summer months (ON, Canada; VT, NH and NY, USA). However, it is currently unclear if a SO42- response to seasonal drying is widespread across the broader region, or to what extent the level of response varies among catchments. In our study, SO42- response to seasonal drying was compared in 20 catchments from 11 locations across southeastern Canada (ON, QC and NS) and northeastern USA (NH, NY, VT, WV and ME). Using long-term monitoring data of stream discharge and chemistry, the number of days for each month of the dry season (# d) when discharge (Q) was below a threshold level (25th percentile; Q25) was calculated for each catchment to give a measure of ‘seasonal dryness’ (# d Q < Q25). A SO42- response score (rs) was then calculated for each catchment based on linear regression analysis of # d Q < Q25 versus either the annual SO42- concentration, or the residual of annual SO42- concentration as a function of time (year). The final rs values for each catchment provided an estimate of the proportion of variation in annual SO42- concentration which could be explained by seasonal drying (possible rs range = 0–1). Of the 20 catchments, 13 exhibited some level of a SO42- response to seasonal drying (rs = 0.04–0.72) with an additional two catchments exhibiting a SO42- response for one or more seasons. SO42- response scores were positively related to percent wetland area(w) (rs = 1.000 – 0.978e-0.054*w, r2 = 0.44) and percent saturated area (sat) (rs = 0.481 – 0.488e-0.101*sat, r2 = 0.54) indicating that wetlands/saturated areas were an important driver of regional variation in the SO42- response to seasonal drying. Our results suggest that any shift towards drier summers as a result of climate change could impact SO42- dynamics in a large number of catchments throughout the region.
by Claire Morin | 30 January 2019
Published in Canadian Journal of Forest Research 42: 1204-1212. https://doi.org/10-1139/x11-176
Observed modifications of ectomycorrhizal (ECM) communities have been connected to the increased N depositions of the 20th century. Because of their narrow niche width, small disturbances of soil conditions can produce greater effects on the fungal species than on their host trees. This study investigated the ECM community in a black spruce (Picea mariana (Mill.) BSP) stand subjected to long-term additions of 9 and 30 kg N·ha–1·year–1 of ammonium nitrate, representing 3 and 10 times the atmospheric N deposition at the site, respectively. Root tip vitality and ECM presence were detected on samples collected from the organic horizon and ECM were classified into morphotypes according to their morphological and anatomical characters. In the control, 80.6% of the root tips were vital, 76.5% of them showing ECM colonization. Higher root tip vitality and mycorrhization were observed in the treated plots. Forty-one morphotypes were identified, most of them detected at the higher N inputs. Results diverging from the expectations of a reduction in ECM presence and diversity could be related to a higher growth rate of the trees following fertilization. The repeated application of small N doses could have been a better imitation of natural inputs from atmospheric deposition and could have provided more reliable responses of ECM to treatment.
