by Claire Morin | 30 January 2019
Paru dans BioScience 60(10) : 788-797. https://doi.org/10.1525/bio.2010.60.10.5
A critical variable in the estimation of gross primary production of terrestrial ecosystems is light-use efficiency (LUE), a value that represents the actual efficiency of a plant’s use of absorbed radiation energy to produce biomass. Light-use efficiency is driven by the most limiting of a number of environmental stress factors that reduce plants’ photosynthetic capacity; these include short-term stressors, such as photoinhibition, as well as longer-term stressors, such as soil water and temperature. Modeling LUE from remote sensing is governed largely by the biochemical composition of plant foliage, with the past decade seeing important theoretical and modeling advances for understanding the role of these stresses on LUE. In this article we provide a summary of the tower-, aircraft-, and satellite-based research undertaken to date, and discuss the broader scalability of these methods, concluding with recommendations for ongoing research possibilities.
by Svetlana Savin | 30 January 2019
Published in Ecological Modelling 243: 123-132
Studies relating site index to climatic variables basically assume that the sensitivity of a species to climate remains stable across the geographic range of their study area. Yet, provenance trials speak to the contrary and show that populations are adapted to their local climatic conditions and tend to respond differently to climate. Spatial and temporal complexity of forest productivity and climate-relationships has been globally reported and recent studies have emphasized the necessity for regional studies on forest growth dynamics of current and future populations. The objective of this study was to determine whether the main climatic and non-climatic drivers of trembling aspen (Populus tremuloides Michx.) growth in Québec should be treated as regional (the study area reacts as a unique population) or local factors (the area is composed of different populations) when modeling the spatio-temporal variability of aspen productivity as measured with site index. Stem analysis data was collected from 124 trees (32 stands) that span a north-south (latitude 46–51◦N) transect in western boreal Québec. Most stands were dense with cover density above 60%, even-aged, 50–90 years old, and very often mixed. The northernmost regions (latitude 48–51◦N) are characterized by either organic or clay deposits, while in the south (latitude 46–48◦N) till or clay deposits predominate. Climate variables that met selection criteria as major regional or local factors that influence aspen productivity were selected. A mixed modeling approach was subsequently employed to identify the categorization unit that could be defined as a population. We then predicted variation in the random error with prior information obtained at stand level. Our results show that aspen height growth is mainly driven by annual sums of degree days and stand age. Surface deposit type, which is an indicator of soil nutritive status and moisture potential, was found to have modulated climate influence. Finally, aspen productivity is better explained with a model that assumes that specific populations have a different response function to climate and are adapted to their local climatic conditions. This has implications when predicting the response to climatic change for forest growth models that assume that conspecifics respond to climate similarly.
by equipewp | 30 January 2019
Published in Tree Seed Working Group – News Bulletin 55(June): 4-5.
by Marie-Claude Boileau | 30 January 2019
General Technical Report NRS-98. United States Department of Agriculture, Forest Service, Northern Research Station. 75 p.
Northern white-cedar (eastern white cedar; Thuja occidentalis L.) is an important tree species in the northeastern United States and adjacent Canada, occurring both in pure stands and as a minor species in mixed stands of hardwoods or other softwoods. Yet practitioners have little and often contradictory information about cedar ecology and silviculture. In response to this information need, a group of university and government researchers in the United States and Canada embarked on more than a decade of collaborative research; this guide is a compilation of the knowledge generated by that effort. (…)
by Marie-Claude Boileau | 30 January 2019
Published in New Forests 44: 533–546. https://doi.org/10.1007/s11056-012-9361-5
Conserving forest biodiversity has become a significant global concern. A change in forest composition, compared to pre-industrial values, is an important biodiversity issue. In this regard, there is a significant decrease in Picea glauca densities at the landscape level in boreal mixedwoods of northeastern Canada, compared to pre-industrial abundance. Enrichment planting is considered a promising silvicultural approach for improving P. glauca stocking and re-establishing its natural co-dominance with Abies balsamea. However, optimal enrichment scenarios must be identified, notably regarding site preparation treatments that can enhance planted seedling survival and growth while protecting Abies advance regeneration. We established a field trial in Québec (Canada), laid out as a complete block split-plot design. Picea glauca and P. mariana seedlings (main plot) were planted according to 3 ‘‘microsite’’ treatments (subplot): (1) planting in the humus layer; (2) planting in the mineral soil, with minimal humus disturbance; and (3) planting in a microsite mechanically-prepared using modified brushsaws. After 3 growing seasons, P. mariana seedlings were taller than P. glauca seedlings, but had smaller ground-level diameters. Seedlings planted in the mineral soil had overcome the initial height difference they had with seedlings planted in the humus and mechanically-prepared microsites, with no interaction with species. Ground-level diameter was similar for seedlings planted in the humus and mechanically-prepared microsites, but smaller for seedlings planted in the mineral soil. Water potentials, available light, and foliar nutrient concentrations were not influenced by treatments or species; survival was >90 %. Our results indicate that P. glauca can be established through enrichment planting in boreal mixedwoods. Localized site preparation is not required to limit initial plantation stress in this ecosystem.
