Plant Biosystems, 2010, 1–12, iFirst Article ISSN 1126-3504 print/ISSN 1724-5575 online © 2010 Società Botanica Italiana DOI: 10.1080/11263500903560512 OLD-GROWTH FORESTS: AN ECOSYSTEM APPROACH Structural characteristics and aboveground biomass of old-growth spruce–fir stands in the eastern Carpathian mountains, Ukraine W. S. KEETON 1 , M. CHERNYAVSKYY 2 , G. GRATZER 3 , M. MAIN-KNORN 4 , M. SHPYLCHAK 5 , & Y. BIHUN 6 1 Rubenstein School of Environment and Natural Resources, University of Vermont, USA, 2 Department of Ecology, Ukrainian National Forestry University, Ukraine, 3 Department of Forest and Soil Sciences, Institute of Forest Ecology, BOKU – University of Natural Resources and Applied Life Sciences, Austria, 4 Geomatics Department, Institute of Geography, Humboldt-Universität zu Berlin, Germany, 5 Nature Reserve Gorgany, Ukraine, and 6 Shelterwood Systems, USA Taylor and Francis Ltd Abstract Temperate old-growth forests are known to have ecological characteristics distinct from younger forests, but these have been poorly described for the remaining old-growth Picea abies–Abies alba forests in the eastern Carpathian mountains. In addition, recent studies suggest that old-growth forests may be more significant carbon sinks than previously recognized. This has stimulated interest in quantifying aboveground carbon stocks in primary forest systems. We investigated the structural attributes and aboveground biomass in two remnant old-growth spruce–fir stands and compared these against a primary (never logged) mature reference stand. Our sites were located in the Gorgany Nature Reserve in western Ukraine. Overstory data were collected using variable radius plots; coarse woody debris was sampled along line intercept transects. Differences among sites were assessed using non-parametric statistical analyses. Goodness-of-fit tests were used to evaluate the form of diameter distributions. The results strongly supported the hypothesis that old-growth temperate spruce–fir forests have greater structural complexity compared to mature forests, including higher densities of large trees, more complex horizontal structure, and elevated aboveground biomass. The late-successional sites we sampled exhibited rotated sigmoid diameter distributions; these may reflect natural disturbance dynamics. Old-growth Carpathian spruce–fir forests store on average approximately 155–165 Mg ha -1 of carbon in aboveground tree parts alone. This is approximately 50% higher than mature stands. Given the scarcity of primary spruce–fir forests in the Carpathian region, remaining stands have high conservation value, both as habitat for late-successional species and as carbon storage reservoirs. Keywords: Old-growth, temperate spruce–fir, forest carbon, stand structure, forest development, ecosystem services Introduction Temperate old-growth forests are recognized as having ecological characteristics distinct from younger forests, including high levels of carbon storage (Luyssaert et al. 2008; Keith et al. 2009), structurally complex habitats for late-successional species (Stoyko 1998; Lindenmayer & Franklin 2002), and effects on habitat structure in forested streams (Keeton et al. 2007). There is growing understanding of the processes associated with development of these characteristics over time, such as interactions between successional dynamics and natural disturbances (Franklin et al. 2002). As our knowledge of these dynamics has advanced, scientists have experimented with new silvicultural systems designed to reproduce or restore a degree of old-growth character in actively managed forests (Keeton 2006; Bauhus et al. 2009; Chernyavskyy 2009). The objective is to increase ecological connectivity, for instance, linking and buffering reserves, by providing late-successional habitat characteristics where these are currently under- represented on the landscape (Keeton 2007). The development of restorative silvicultural systems is guided by improved understanding of the structural characteristics associated with old-growth forests. Similarly, efforts to protect high conservation value forests require information on the ecosystem services provided by different forest types and Correspondence: W. S. Keeton, Rubenstein School of Environment and Natural Resources, University of Vermont, 343 Aiken Center, Burlington, VT 05405, USA. Tel: +011 802 656 2518. Fax: +011 802 656 2623. Email: william.keeton@uvm.edu Downloaded By: [Keeton, W. S.] At: 14:58 7 March 2010