| There is increasing interest to develop quantitative approaches to carbon accounting and determine carbon sequestration potential at both the site and landscape scales. Currently, our lack of understanding of fine root dynamics in northern temperate forest systems has hampered efforts to accurately parameterize any of the existing C budget models (e.g., CBM-CFS3). The objectives of this study were to: 1) describe the various approaches most commonly used to estimate fine root biomass, highlighting their strengths and limitations, 2) develop species- and diameter class-specific standard root lengths (i.e., factor for converting measured root lengths to biomass when using minirhizotron technologies) for selected northern temperate tree species, and 3) compare/contrast the estimates of fine root biomass, productivity, and turnover rates derived from the commonly applied indirect (i.e., used in most carbon accounting models) and direct (i.e., in situ stand-level measurements) methods. This study was conducted for three distinct northern temperate forest/stand types (i.e., northern hardwoods - sugar maple; northern coniferous -- jack pine; and boreal mixedwood -- aspen, spruce, balsam fir).;Keywords: fine root dynamics, minirhizotrons, sequential coring, ingrowth bags, sugar maple, jack pine, boreal mixedwoods;It was determined that there was a significant difference in fine root standard root length (SRL) between northern temperate tree species and diameter classes. Angiosperms tended to had significantly higher average SRLs compared to gymnosperms. Within these species groupings, tolerant, late successional species had higher SRLs compared to their intolerant, early successional counterparts. Standard root lengths dropped significantly (>200 %) as diameter class increased. The results suggest that the development of species- and diameter class-specific SRLs should provide better estimates of fine root biomass and productivity, leading to a better understanding of temperate forest C dynamics. The results from the comparison of the indirect and direct methods to estimate fine root biomass, productivity, and turnover accentuate the potential challenges associated with incorporating site specific fine root research into broader generalizations applied to large land masses. These constructs inevitably incorporate inherent errors associated with aboveground biomass estimates, conversions factors to belowground estimates (indirect methods), high within-site variability associated with direct measurements, and all the numerical accounting methods and assumptions needed to arrive at fine root estimates. A more thorough examination of fine root dynamics is required in order to ensure wider scientific acceptance of broad-based models and their ability to predict the impacts of forest management activities or climate change. |
