by Audrey Verreault | 27 April 2020
Published in Journal of Environmental Quality 42: 623-639. doi: 10.2134/jeq2012.0378
Environmental change is monitored in North America through repeated measurements of weather, stream and river flow, air and water quality, and most recently, soil properties. Some skepticism remains, however, about whether repeated soil sampling can effectively distinguish between temporal and spatial variability, and efforts to document soil change in forest ecosystems through repeated measurements are largely nascent and uncoordinated. In eastern North America, repeated soil sampling has begun to provide valuable information on environmental problems such as air pollution. This review synthesizes the current state of the science to further the development and use of soil resampling as an integral method for recording and understanding environmental change in forested settings. The origins of soil resampling reach back to the 19th century in England and Russia. The concepts and methodologies involved in forest soil resampling are reviewed and evaluated through a discussion of how temporal and spatial variability can be addressed with a variety of sampling approaches. Key resampling studies demonstrate the type of results that can be obtained through differing approaches. Ongoing, large-scale issues such as recovery from acidification, long-term N deposition, C sequestration, effects of climate change, impacts from invasive species, and the increasing intensification of soil management all warrant the use of soil resampling as an essential tool for environmental monitoring and assessment. Furthermore, with better awareness of the value of soil resampling, studies can be designed with a long-term perspective so that information can be efficiently obtained well into the future to address problems that have not yet surfaced.
by Marie-Claude Boileau | 27 April 2020
Published in Soil Science Society of America Journal 78(S1): S196-S207. doi: 10.2136/ssaj2013.08.0373nafsc
While post-harvest residue (“slash”) is increasingly viewed as a source of biofuel, few studies have considered the potential ecological impact of the spatial distribution of forest harvest residue. We hypothesized that slash pilescreate islands of high soil fertility and light, leading to greater abundance, growth, and reproduction of plants. In 6-yr-old intensively managed hybrid poplar (Populus balsamifera L. ´ P. maximowiczii A. Henry) plantations, we showed that soluble organic N, NO3–N, NH4–N, and P decreased as a negative exponential function with distance from the pile. Pin cherry (Prunus pensylvanica L. f.) relative growth rate was fastest near piles in the first few years after harvest. We found significantly greater stem size, flowers per plant, and foliar P near piles for cherry, and this inverse gradient sharpened in a 16-yr-old white spruce [Picea glauca (Moench) Voss] plantation. For the two other flowering species, strawberry (Fragaria virginiana Mill.) and raspberry (Rubus idaeus L.), flower and fruit abundance were also significantly and strongly negatively correlated with distance to the pile. Further, directly correlating soil nutrient availability with plant traits, we found significant positive relationships between plant growth, reproductive output, and N availability. Partial correlation analysis indicated that more of the variance in plant traits was explained by distance than by soil nutrition. We conclude that in industrial forests, piles replace canopy gaps as sites where understory plant species can episodically reproduce and are therefore important for many plant species as well as the pollinators and frugivores dependent on them.
by Marie-Claude Boileau | 23 April 2020
Publisher in Remote Sensing 11(23): 2745. https://doi.org/10.3390/rs11232745
Satellite remote sensing is a widely accessible tool to investigate the spatiotemporal variations in the bud phenology of evergreen species, which show limited seasonal changes in canopy greenness. However, there is a need for precise and compatible data to compare remote sensing time series with field observations. In this study, fortnightly MODIS-NDVI was fitted using double-logistic functions and calibrated using ordinal logit models with the sequential phases of bud phenology collected during 2015, 2017 and 2018 in a black spruce stand. Bud break and bud set were spatialized for the period 2009–2018 across 5000 stands in Quebec, Canada. The first phase of bud break and the last phase of bud set were observed in the field in mid-May and at the beginning of September, when NDVI was 80.5% and 92.2% of its maximum amplitude, respectively. The NDVI rate of change was estimated at 0.07 in spring and 0.04 in autumn. When spatialized on the black spruce stands, bud break was detected earlier in the southwestern regions (April–May), and later in the northeastern regions (mid to end of June). No clear trend was observed for bud set, with different patterns being detected among the years. Overall, the process bud break and bud set lasted 51 and 87 days, respectively. Our results demonstrate the potential of satellite remote sensing for providing reliable timings of bud phenological events using calibrated NDVI time series on wide regions that are remote or with limited access.
by Marie-Claude Boileau | 23 April 2020
Published in FACETS 5(1): 166-181.
Sustainable forest management implies successful regeneration after disturbances. Low N availability and competition can, however, limit tree establishment in boreal ecosystems. To develop silviculture strategies that maintain productivity in such context, we established a field trial in northern Québec, Canada. We evaluated if a companion N2-fixing species (Alnus alnobetula) promotes or hinders Picea mariana and Pinus banksiana establishment over six growing seasons. We tested if Alnus has a facilitation effect through nutritional processes and a competition effect through light interception. Foliar stable nitrogen isotope ratio (δ15N=15N/14N, ‰) results confirmed that Alnus obtains a substantial part of its N through biological fixation and represents an N source in this system. Although we did not observe increased foliar N concentrations in either conifer species in the presence of Alnus, Pinus growth was nonetheless higher in presence of Alnus, whereas no difference was observed for Picea. In the plots where Alnus cohabited with the conifers, the former had a negative impact on seedling growth, suggesting a significant competition for light. Overall, the net effect of Alnus was positive for Pinus and neutral for Picea. Our results have significant implications for silviculture in N-limited systems, especially in the context of climate change that imposes increased levels of stress on regeneration.
by Audrey Verreault | 17 April 2020
Published in Forests 7(9): 205. doi:10.3390/f7090205
This study presents the long-term (over the last 8000 years) natural variability of a portion of the Picea mariana-moss bioclimatic domain belonging to Québec’s Clay Belt. The landscapes are dominated by mesic-subhydric clay and early successional forests composed of Populus tremuloides, Pinus banksiana and Picea mariana. The natural variability (fires and vegetation) of one of these landscapes was reconstructed by means of pollen and macroscopic charcoal analysis of sedimentary archives from two peatlands in order to assess when and how such landscapes were formed. Following an initial afforestation period dominated by Picea (8000–6800 cal. Years BP), small and low-severity fires favored the development and maintenance of landscapes dominated by Picea and Abies balsamea during a long period (6800–1000 BP). Over the last 1000 years, fires have become more severe and covered a larger area. These fires initiated a recurrence dynamic of early successional stands maintained until today. A decline of Abies balsamea has occurred over the last centuries, while the pollen representation of Pinus banksiana has recently reached its highest abundance.
We hypothesize that the fire regime of the last millennium could characterize Québec’s Clay Belt belonging to the western Picea mariana-moss and Abies balsamea–Betula papyrifera domains.
