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Publications

NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.

2021

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Abstract

We compiled data from several independent, long-term silvicultural studies on USDA Forest Service experimental forests across a latitudinal gradient in the northeastern and north-central U.S.A. to evaluate factors influencing aboveground live-tree carbon sequestration and mortality. Data represent five sites with more than 70,000 repeated tree records spanning eight decades, five ecoregions, and a range of stand conditions. We used these data to test the relative influence of factors such as climate, treatment history (uneven-aged or no management), species composition, and stand structural conditions on aboveground live-tree carbon sequestration and mortality in repeatedly measured trees. Relative to no management, we found that uneven-aged management tended to have a positive effect on carbon sequestration at low stocking levels and in areas of favorable climate (expressed as a combination of growing season precipitation and annual growing degree days > 5 ◦C). In addition, losses of carbon from the aboveground live-tree pool due to tree mortality were lower in managed than unmanaged stands. These findings suggest that there may be conditions at which rate of sequestration in living trees is higher in stands managed with uneven-aged silviculture than in unmanaged stands, and that this benefit is greatest where climate is favorable.

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Abstract

Across North America, forests dominated by Quercus rubra L. (northern red oak), a moderately shade-tolerant tree species, are undergoing successional replacement by shade-tolerant competitors. Under closed canopies, Q. rubra seedlings are unable to compete with these shade-tolerant species and do not recruit to upper forest strata. In Europe, natural regeneration of introduced Q. rubra is often successful despite the absence of fire, which promotes regeneration in the native range. Considering that understorey light availability is a major factor affecting recruitment of seedlings, we hypothesized that Q. rubra seedlings are more shade tolerant in the introduced range than in the native range. Morphological traits and biomass allocation patterns of seedlings indicative of shade tolerance were compared for Q. rubra and three co-occurring native species in two closed-canopy forests in the native range (Ontario, Canada) and introduced range (Baden-Württemburg, Germany). In the native range, Q. rubra allocated a greater proportion of biomass to roots, while in the introduced range, growth and allocation patterns favored the development of leaves. Q. rubra seedlings had greater annual increases in height, diameter and biomass in the introduced range. Q. rubra seedlings in the introduced range were also younger; however, they had a mean area per leaf and a total leaf area per seedling that were five times greater than seedlings in the native range. Such differences in morphological traits and allocation patterns support the hypothesis that Q. rubra expresses greater shade tolerance in the introduced range, and that natural regeneration of Q. rubra is not as limited by shade as in the native range. The ability of Q. rubra seedlings to grow faster under closed canopies in Europe may explain the discrepancy in regeneration success of this species in native and introduced ranges. Future research should confirm findings of this study over a greater geographical range in native and introduced ecosystems, and examine the genetic and environmental bases of observed differences in plant traits.