By Mark E. Harmon, Chad T. Hanson and Dominick A. DellaSala
Abstract: Biomass combustion is a major biogeochemical process, but uncertain in magnitude. We examined multiple levels of organization (twigs, branches, trees, stands, and landscapes) in large, severe forest fires to see how combustion rates for live aboveground woody parts varied with tree species, size, and fire severity in Ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and mixed conifer-dominated forests of the Sierra Nevada, California, USA. In high severity fire patches, most combustion loss was from branches < 2 cm diameter; in low to moderate severity patches, most was from bole charring. Combustion rates decreased as fire severity declined and with increasing tree size. Pinus species had little branch combustion, leading them to have ≈50% the combustion rate of other taxa. Combustion rates could be 100% for small branch segments and up to 57% for small tree aboveground woody biomass in high severity fire patches. However, combustion rates are very low overall at the stand (0.1%–3.2%) and landscape level (0.6%–1.8%), because large trees with low combustion rates comprise the majority of biomass, and high severity fire patches are less than half of the area burned. Our findings of low live wood combustion rates have important implications for policies related to wildfire emissions and forest management.
(2022) Combustion of Aboveground Wood from Live Trees in Megafires, CA, USA.pdf
Abstract: Plantation forests are increasing rapidly in the world in order to alleviate deforestation and degradation of natural forests, along with providing various goods and services. While monoculture plantations have been the dominant type of plantation in practice and well recorded in research, in the face of intensifying climate change and resource scarcity, there is a growing interest in mixed-species plantations. Agroforestry systems are also catching the attention of foresters, smallholders and landowners. However, there are relatively limited number of studies on successful species mixtures. This paper first reviews the progression of monocultures and mixed-species, followed by the comparisons of advantages, disadvantages and effects on the surrounding natural ecosystems between these two types of plantations. The paper further investigates combinations of species with complementary traits for efficient use of limiting resources associated with improvement in growth development and production of tree species, as well as examining some other challenges in mixed-species. In addition, it is helpful to select and combine tree/crop species in mixtures based on complementary traits that maximize positive and minimize negative interactions and using the advance molecular technologies for genetic analysis. With careful design and proper management, mixed-species plantations with two, three or four species can be more productive and have more advantages in biodiversity, economy and forest health over monocultures. Many researchers are still working on different projects to explore the potential benefits and to promote the applications of mixed-species plantations and agroforestry.
Mixed-species versus monocultures in plantation forestry: Development, benefits, ecosystem services and perspectives for the future (2018).pdf
Abstract: Use of glyphosate-based herbicides (GBHs) increased ∼100-fold from 1974 to 2014. Additional increases are expected due to widespread emergence of glyphosate resistant weeds, increased application of GBHs, and pre-harvest uses of GBHs as desiccants. Current safety assessments rely heavily on studies conducted over 30 years ago. We have considered information on GBH use, exposures, mechanisms of action, toxicity and epidemiology. Human exposures to glyphosate are rising, and a number of in vitro and in vivo studies challenge the basis for the current safety assessment of glyphosate and GBHs. We conclude that current safety standards for GBHs are outdated and may fail to protect public health or the environment. To improve safety standards, the following are urgently needed: (1) human bio-monitoring for glyphosate and its metabolites; (2) prioritization of glyphosate and GBHs for hazard assessments, including toxicological studies that use state-of-the-art approaches; (3) epidemiological studies, especially of occupationally exposed agricultural workers, pregnant women and their children and (4) evaluations of GBHs in commercially used formulations, recognizing that herbicide mixtures likely have effects that are not predicted by studying glyphosate alone.
Is it time to reassess current safety standards for glyphosate-based herbicides? (2016).pdf
Abstract: British Columbia (BC), Canada is experiencing a severe mountain pine beetle (MPB) (Dendroctonus ponderosae) epidemic extending over an area of 135,000 km2. The widespread mortality of lodgepole pine (Pinus contorta var. latifolia) caused by the beetle has significant implications for BC’s timber supply and Canada’s carbon (C) budget. This study used the eddy-covariance technique to examine how the beetle is impacting the net ecosystem production (NEP) of two attacked lodgepole pine-dominated stands in the central interior of BC. MPB-06 is an 83-year-old stand that was first attacked in 2006. At the start of 2007 roughly 60% of the canopy had been attacked and by October 2008 only 21% of the trees remained healthy. MPB-03, a 110-year-old stand, had >95% pine canopy mortality as a result of a 2003 beetle attack, and also differed from MPB-06 in that it had a more developed secondary structure (consisting of tree seedlings and saplings and sub-canopy and canopy trees) that survived the beetle attack. Eddy-covariance measurements were also conducted in two stands near MPB-06 harvested in 2005 and 1997 (CC-05 and CC-97) for approximately three-week periods each during the 2007 growing season. MPB-06 had an annual NEP of 82 and 33 g C m2, while MPB-03 had an NEP of 56 and 4 g C m2 in 2007 and 2008, respectively. In the 2007 and 2008 growing seasons (May–September), MPB-06 was a sink of 12 and 52 g C m2, while MPB-03 was a sink of 17 and 68 g C m2, respectively. The productivity at MPB-06 resulted from an increase in photosynthesis by the remaining healthy trees and understory vegetation, while at MPB-03 the secondary structure and understory vegetation showed a strong capacity to sequester C due to an opening up of the stand as a result of canopy mortality. Average daily values of NEP during the measurement periods at CC-97 and CC-05 were 0.37 and 0.87 g C m2, respectively, showing that even 10 years following harvesting, these stands are likely to remain growing season C sources. That MPB-06 and MPB-03 were growing season C sinks suggests that deferring the harvest of stands with significant levels of secondary structure could prevent MPB-attacked forested areas from becoming C sources over extended periods.
Impact of mountain pine beetle on the net ecosystem production of lodgepole pine stands in British Columbia (2010).pdf
Abstract: Single-species planting of lodgepole pine (Pinus contorta var. latifolia) following clear-cut logging or wildfire has been common throughout interior British Columbia, Canada, but health problems with the species have been documented as it grows beyond the juvenile stage. We examined damage and stocking in twenty-seven 15- to 30-year-old lodgepole pine plantations that were previously declared free growing in the highly productive cedar hemlock forests in southeastern British Columbia, where lodgepole pine is absent from many primary forests. In order to be free growing, stands must meet minimum tree density, height, damage and brush competition criteria as legislated by the Provincial government. Overall, 44 per cent of lodgepole pine trees had unacceptable damage (causing them to be rejected as crop trees), and as a direct result, one-third of the plantations were no longer defined as free growing because there were insufficient crop trees remaining. Natural regeneration of other tree species partially compensated for the unhealthy pine. Logistic regression and odds ratio analysis associated increasing risk of damage from western gall rust with increasing soil moisture, more northerly aspects and mechanical site preparation, and decreasing risk with pre-commercial thinning treatment. Risk of damage from snow and ice was associated with increasing mean annual precipitation, decreasing longitude and broadcast burning. Risk of bear damage was associated with increasing soil moisture, pre-commercial thinning treatment and broadcast burning. Based on our results, we recommend that single-species planting of lodgepole pine be curtailed in the Interior Cedar–Hemlock zone in southeastern British Columbia.
Decline of planted lodgepole pine in the southern interior of British Columbia (2010).pdf
• The immediate environmental effects of postfire logging depend on the severity of the burn, slope, soil texture and composition, the presence or building of roads, type of logging system, and postfire weather conditions.
• Postfire logging can cause significant changes in the abundance and nest density of cavity-nesting birds, particularly those attracted to recently burned
• The probability that insect pest populations will build up and infest adjacent green-tree stands may be reduced through removal of vulnerable trees after fire.
• Fuel mass increased on the logged sites as a result of slash left over from harvest, and on the control site as the result of fire-killed trees falling over.
Post fire logging- Is it beneficial to a forest? (2002).pdf