by Marie-Claude Boileau | 30 January 2019
Published in Forests 6: 510-532. https://doi.org/10.3390/f6020510
We evaluated the effectiveness of commercial thinning mainly from below (CT; 0, 26%, 32% and 40% merchantable basal area removals) in meeting wood production demands and developing structural heterogeneity in a balsam fir (Abies balsamea (L.) Mill) and spruce (Picea spp.) stand. After 10 years, 32%–40% removals showed a 12%–18% increase in mean diameter and 27%–38% increase in gross merchantable volume (GMV) per tree compared to the unthinned control. At the stand level, all thinning treatments generated as much cumulative GMV (harvested volume + GMV after 10 years) and gross sawlog volume per hectare as the unthinned control. As for stand structure, eight out of nine thinned experimental units showed increased structural heterogeneity after 10 years, i.e., irregular, positively-skewed diameter distribution with an elongated right tail toward larger trees. The diameter distribution in the unthinned control became more symmetric, unimodal and regular over time, with fewer saplings than at the beginning of the experiment and lower density of larger trees compared to CT. Regeneration density and stocking were abundant in all treatments, largely dominated by balsam fir. Results indicate that thinning can be used to meet wood production objectives and help develop structural heterogeneity in this forest.
by Svetlana Savin | 30 January 2019
Published in New Forests 46: 409-425. https://doi.org/10.1007/s11056-015-9468-6
We established a long-term experiment in a temperate mixedwood stand to evaluate the effectiveness of silvicultural treatments in regenerating a mixed-species cohort while maintaining the dominance of conifers. Silvicultural treatments included clearcutting using careful logging around advanced growth (CLAAG), uniform shelterwood (US), group shelterwood with (GS-s) or without scarification (GS), and an uncut control (control). After 10 years, height and ground-line diameter growth responses of advanced balsam fir (Abies balsamea [L.] Mill.) regeneration were substantial in CLAAG and GS compared to the control, and intermediate in US. Growth responses were proportional to increases in canopy light transmittance resulting from harvest. Advanced balsam fir regeneration had low mortality (<10 %) and a high potential for release as measured by the apical dominance ratio. At the stand level, however, a shift in species composition occurred in the regenerating cohort. Over the 10-year period, composition changed from conifer-dominated to hardwood-dominated in CLAAG, GS, and GS-s compared to the control. Scarification increased the magnitude of this shift by favoring shade-intolerant hardwoods. Results highlight the need to find a balance between releasing advance conifer regeneration and limiting competition from less desirable species.
by Claire Morin | 30 January 2019
Published in Ecosphere 6(5): 1-22. https://doi.org/110.1890/ES14-00209
Long-term forest soil monitoring and research often require a comparison of laboratory data generated at different times and in different laboratories. Quantifying the uncertainty associated with these analyses is necessary to assess temporal changes in soil properties. Forest soil chemical properties, and methods to measure these properties, often differ from agronomic and horticultural soils. Soil proficiency programs do not generally include forest soil samples that are highly acidic, high in extractable Al, low in extractable Ca and often high in carbon. To determine the uncertainty associated with specific analytical methods for forest soils, we collected and distributed samples from two soil horizons (Oa and Bs) to 15 laboratories in the eastern United States and Canada. Soil properties measured included total organic carbon and nitrogen, pH and exchangeable cations. Overall, results were consistent despite some differences in methodology. We calculated the median absolute deviation (MAD) for each measurement and considered the acceptable range to be the median 6 2.5 3 MAD. Variability among laboratories was usually as low as the typical variability within a laboratory. A few areas of concern include a lack of consistency in the measurement and expression of results on a dry weight basis, relatively high variability in the C/N ratio in the Bs horizon, challenges associated with determining exchangeable cations at concentrations near the lower reporting range of some laboratories and the operationally defined nature of aluminum extractability. Recommendations include a continuation of reference forest soil exchange programs to quantify the uncertainty associated with these analyses in conjunction with ongoing efforts to review and standardize laboratory methods.
by Claire Morin | 30 January 2019
Published in Ecology 96(6): 1480-1491 http://dx.doi.org/10.1890/13-2366.1
Climate change is altering insect disturbance regimes via temperature-mediated phenological changes and trophic interactions among host trees, herbivorous insects and their natural enemies in boreal forests. Range expansion and increase in outbreak severity of forest insects are occurring in Europe and North America. The degree to which northern forest ecosystems are resilient to novel disturbance regimes will have direct consequences for the provisioning of goods and services from these forests and on long-term forest management planning. Among major ecological disturbance agents in the boreal forests of North America is a tortricid moth, the eastern spruce budworm, which defoliates fir (Abies spp.) and spruce (Picea spp.). Northern expansion of this defoliator in eastern North America and climate-induced narrowing of the phenological mismatch between the insect and its secondary host, black spruce (Picea mariana), may permit greater defoliation and mortality in extensive northern black spruce forests. Although spruce budworm outbreak centers have appeared in the boreal black spruce zone historically, defoliation and mortality were minor. Potential increases in outbreak severity and tree mortality raise concerns about the future state of this northern ecosystem. Severe spruce budworm outbreaks could decrease stand productivity compared with their occurrence in more diverse, southern balsam fir forest landscapes that have coevolved with outbreaks. Furthermore, depending on the proportion of balsam fir and deciduous species present and fire recurrence, changes in regeneration patterns and in nutrient cycling could alter ecosystem dynamics and replace black spruce by more productive mixed-wood forest, or by less productive ericaceous shrublands. Long-term monitoring, manipulative experiments and process modeling of climate-induced phenological changes on herbivorous insect pests, their host tree species and natural enemies in northern forests are therefore crucial to predicting species range shifts and assessing ecological and economic impacts.
