Abstract
Managing competing vegetation is crucial in stand establishment strategies; forecasting the abundance, composition, and impact of competing vegetation after harvesting is needed to optimize silviculture scenarios and maintain long-term site productivity. Our main objective was to identify factors influencing the short-term abundance and composition of competing vegetation over a large area of the Canadian boreal forest. Our second objective was to better understand the mid-term evolution of the regeneration/competing vegetation complex in cases of marginal regeneration conditions. We used operational regeneration surveys of 4471 transects sampled ≈5 years after harvesting that contained data on regeneration, competing vegetation, elevation, ecological classification, soil attributes, and pre-harvest forest stands. We performed a redundancy analysis to identify the relationships between competing vegetation, harvesting and biophysical variables. We then estimated the probability of observing a given competing species cover based on these variables. In 2015, we re-sampled a portion of the sites, where conifer regeneration was marginal early after harvesting, to assess the temporal impact of different competing levels and species groups on the free-to-grow stocking, vigour and basal area of softwood regeneration. Results from the first inventory showed that, after careful logging around advance growth, ericaceous shrubs and hardwoods were not associated with the same sets of site attributes. Ericaceous shrubs were mainly found on low fertility sites associated with black spruce (Picea mariana (Mill.) BSP) or jack pine (Pinus banksiana Lamb.). The distinction between suitable environments for commercial shade-intolerant hardwoods and non-commercial hardwoods was less clear, as they responded similarly to many variables. Analysis of data from the second inventory showed a significant improvement in conifer free-to-grow stocking when commercial shade-intolerant hardwood competing levels were low (stocking 0%–40%) and when ericaceous shrubs competing levels were moderate (percent cover 26%–75%). In these conditions of marginal regeneration, the different types and intensities of competition did not affect the vigour or basal area of softwood regeneration, 9–14 years after harvesting.
Highlights
Stand renewal is a crucial step in any silvicultural system
Axis 1, which contains most of the information, contrasts conditions associated with ericaceous shrubs and those associated with other competing vegetation types
The ericaceous shrubs were positively correlated with imperfect drainage, altitude, hills of Lake Péribonka and pre-harvest stands dominated by black spruce (Figure 3)
Summary
Stand renewal is a crucial step in any silvicultural system. At this stage, desired species can experience competition by a suite of species that can impact longer-term stand composition and Forests 2019, 10, 177; doi:10.3390/f10020177 www.mdpi.com/journal/forestsForests 2019, 10, 177 productivity. Stand renewal is a crucial step in any silvicultural system. At this stage, desired species can experience competition by a suite of species that can impact longer-term stand composition and Forests 2019, 10, 177; doi:10.3390/f10020177 www.mdpi.com/journal/forests. These effects are a function of the silvics of the desired species and the nature of competing vegetation. Competing problems seem to occur when hardwoods reach a certain density threshold that varies depending on species [4,5,6]. They can facilitate conifer growth and survival. Facilitation can result from better protection against insects, disease, photoinhibition, photooxidation, temperature and moisture extremes [7,8], by improving soil productivity [9], or by nutrient gains through associations with mycorrhizae [10]
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