by Svetlana Savin | 30 January 2019
Published in Forest Science 58(1): 24-33
Spruce budworm (Choristoneura fumiferana Clem.) (SBW) outbreaks have caused considerable damage to coniferous forests dominated by balsam fir (Abies balsamea [L.] Mill.) or black spruce (Picea mariana [Mill.]). Hence, forecasting SBW-caused mortality of these species is an important step in allowable annual cut calculations of the forest industry in northeastern North America. This study developed prediction models of balsam fir and black spruce mortality caused by SBW and compared SBW-caused mortality of fir and spruce that were growing under similar stand conditions. Zero-inflated models were estimated for the entire range of balsam fir and black spruce in Québec, Canada, using historical records of insect defoliation and permanent sample plot inventories from 1970 to 2006. Fir and spruce mortality caused by SBW was successfully related to historical records of defoliation through a growth reduction index. Fir mortality increased with the number of years of severe defoliation and was always greater than that of spruce, which appeared to be weakly affected by SBW defoliation. In mixed spruce-fir stands, the total volume of mortality decreased almost linearly with increasing proportions of black spruce. This suggests that thinning aimed to increase spruce proportions could be efficient in reducing overall stand mortality during an SBW outbreak.
by Svetlana Savin | 30 January 2019
Published in Journal of Vegetation Science https://doi.org/10.1111/j.1654-1103.2012.01488.x
Question: Recent studies revealed by indirect evidence that lichen–spruce woodlands in the closed-crown boreal forest are an alternative stable state of black spruce–feathermoss stands. This paper aims to demonstrate and quantify black spruce forest cover regression following successive wildfire events in the closed-crown forest zone during the 20th century. A case study in north-eastern North American closed-crown forest zone is presented.
Location: The study area is at the centre of the closed-crown boreal forest zone of eastern Canada (49°59′ N, 71°59′ W).
Methods: A burned area of 25 ha was selected in which three tree cohorts were visible. The first cohort contains partly buried trunks and stumps of a stand destroyed by a forest fire in 1920, the second contains standing dead trees from a 1995 forest fire and the third contains seedlings established after the 1995 fire. Fires were dated by scar analyses of living trees at the edge of the site. An array of sample plots was established in autumn 1997 to evaluate each cohort in terms of stocking and tree density.
Results: Black spruce stocking decreased significantly between cohorts, from 43.5% in Cohort 1 (all coniferous trees) to 25.6% in Cohort 2 and 11.5% in Cohort 3 (2011). Jack pine showed an inverse tendency, from 0% in Cohort 1 (not determined) to 0% in Cohort 2 and 3.8% in Cohort 3. Black spruce stems per hectare also dropped significantly from a minimum of 1322 in Cohort 1 to 1088 in Cohort 2 and 976 in Cohort 3.
Conclusions: This study is the first quantitative demonstration that lichen–spruce woodlands in the closed-crown boreal forest zone are an alternative stable state of black spruce–feathermoss stands. Stocking levels and densities markedly declined after each of the two fires (1920 and 1995) that both occurred after spruce budworm outbreaks (1910 and 1980) and are most likely responsible for the shift from a closed-crown to an open woodland.
by Svetlana Savin | 30 January 2019
Published in HortScience 47(2): 205-211
Two complementary greenhouse studies were conducted to examine the effects of different root zones and fertilization regimes on ‘SR7200’ velvet bentgrass (Agrostis canina L.) and L-93 creeping bentgrass (Agrostis stolonifera L.). In the first study, in which only velvet bentgrass was studied, peat content in the root zone mixture contributed significantly to initial establishment of this species and high seeding rates increased cumulative shoot dry weight early in establishment but became less significant as the turfgrass matured. Higher phosphorus rates contributed to increased cumulative shoot dry weight over the first 4 weeks of the experiment. Nitrogen rate was the most significant factor positively affecting both cumulative shoot dry weight and turfgrass quality. In the second experiment with both velvet bentgrass and creeping bentgrass, nitrogen rate significantly increased turfgrass quality when measured at Week 5, halfway through the experiment. Over time, however, turf growth and quality were negatively impacted in both species with increasing nitrogen rates. Root zone composition had a significant effect on initial establishment of both bentgrasses with greater peat content leading to higher quality early on. Cumulative shoot dry weight increased with increasing nitrogen rate but at higher rates, there was a concomitant decrease in root production.
by Marie-Claude Boileau | 30 January 2019
Published in Ecoscience 18(4): 382-393. https://doi.org/10.2980/18-4-3432
The present study investigates potential differences in trait plasticity as an additional contributing mechanism explaining ericaceous shrub dominance during different periods after logging. Two ericaceous species (Kalmia angustifolia, Rhododendron groenlandicum), and black spruce plants (Picea mariana), were submitted to combinations of 3 light levels and 2 levels of nitrogen addition during a simulated growing season of 9 weeks under greenhouse conditions. Plant traits related to light (photosynthesis, leaf mass per unit of area, leaf and aboveground biomass allocation, foliar N concentration) and nutrient acquisition (root mass ratio, specific absorption ratio, absorption of 15N) were measured in response to the manipulation of these resources. The leaf mass per unit of area (LMA) of both ericaceous species was significantly reduced by shading; LMA of Rhododendron and Kalmia was, respectively, 54% and 31% higher in the highest light treatment. The LMA of black spruce was unchanged in response to light level. There were few differences among species in trait response to N addition. Black spruce was characterized by higher nutrient absorption rate and specific absorption rate at higher N levels compared to the 2 ericads. With the exception of LMA, plasticity to light was higher for Kalmia; in contrast, plasticity to N addition was higher for Rhododendron and black spruce. Finally, LMA appears to be a key trait explaining the competitive advantage of ericaceous species (especially Rhododendron) and potential encroachment on forested sites after disturbance.
by Claire Morin | 30 January 2019
Published in Hydrology and Earth System Sciences 16: 685-697. https://doi.org/10.5194/hess-16-685-2012
Soil mineral weathering represents an essential source of nutrient base cation (Ca, Mg and K) for forest growth in addition to provide a buffering power against precipitation acidity for soils and surface waters. Weathering rates of base cations were obtained for 21 catchments located within the temperate and the boreal forest of the Canadian Shield with the geochemical model PROFILE. Weathering rates ranged from 0.58 to 4.46 kmolc ha−1 yr−1 and their spatial variation within the studied area was mostly in agreement with spatial variations in soil mineralogy. Weathering rates of Ca and Mg were significantly correlated (r = 0.80 and 0.64) with their respective lake concentrations. Weathering rates of K and Na did not correlate with lake concentrations of K and Na. The modeled weathering rates for each catchment were also compared with estimations of net catchment exportations. The result show that modeled weathering rates of Ca were not significantly different than the net catchment exportations while modeled weathering rates of Mg were higher by 51 %. Larger differences were observed for K and Na weathering rates that were significantly different than net catchment exportations being 6.9 and 2.2 times higher than net exportations, respectively. The results for K were expected given its high reactivity with biotic compartments and suggest that most of the K produced by weathering reactions was retained within soil catchments and/or above ground biomass. This explanation does not apply to Na, however, which is a conservative element in forest ecosystems because of the insignificant needs of Na for soil microorganisms and above ground vegetations. It raises concern about the liability of the PROFILE model to provide reliable values of Na weathering rates. Overall, we concluded that the PROFILE model is powerful enough to reproduce spatial geographical gradients in weathering rates for relatively large areas as well as adequately predict absolute weathering rates values for the sum of base cations, Ca and Mg.
