  Citation: Chivulescu, S , .; Pitar, D.; Apostol, B.; Leca, S , .; Badea, O. Importance of Dead Wood in Virgin Forest Ecosystem Functioning in Southern Carpathians. Forests 2022, 13, 409. https://doi.org/10.3390/ f13030409 Academic Editor: Romà Ogaya Received: 4 February 2022 Accepted: 1 March 2022 Published: 3 March 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Importance of Dead Wood in Virgin Forest Ecosystem Functioning in Southern Carpathians S , erban Chivulescu 1 , Diana Pitar 1, *, Bogdan Apostol 1 ,S , tefan Leca 1 and Ovidiu Badea 1,2 1 National Institute for Research and Development in Forestry “Marin Drăcea”, 077191 Voluntari, Romania; serban.chivulescu@gmail.com (S , .C.); bogdanap_ro@yahoo.com (B.A.); stefan.leca@icas.ro (S , .L.); obadea@icas.ro (O.B.) 2 Faculty of Silviculture and Forest Engineering, “Transilvania” University of Bras , ov, 500123 Bras , ov, Romania * Correspondence: diana.silaghi@icas.ro Abstract: Dead wood (DW) is an important component of sustainable forest management and climate change mitigation. Three research plots (each with an area of 1 ha), located in virgin forests in the Southern Carpathians (Semenic P20, Retezat–Zănoaga, and Făgăras , –S , inca), were installed in order to study the synergies between DW and climate change mitigation effects. Data on the dendrometric characteristics of standing and lying DW, the species, and the degree of decay were recorded. The aboveground biomass (AGB) and carbon stock (CS) of the DW were also determined. The DW volume was between 48 m 3 ·ha −1 and 148 m 3 ·ha −1 , with the total volume (dead and alive) ranging between 725 m 3 ·ha −1 and 966 m 3 ·ha −1 . The DW volume distribution shows a decreasing trend, with the most suitable theoretical distributions for describing this being the lognormal, the 2P Weibull, and the 2P-Gamma. The AGB ranged between 17 t·ha −1 and 30 t·ha −1 and showed a decreasing trend according to altitude. The CS was between 8 t·ha −1 and 14.33 t·ha −1 . A slow decomposition rate for the hardwood was identified by analyzing the relationship between the surface and volume of the DW. This highlighted the capacity of DW to store carbon for a long period of time. Keywords: aboveground biomass; dead wood carbon stock; sustainable forest management; climate change mitigation; Southern Carpathians 1. Introduction Concerns regarding climate change are becoming more and more obvious. It is well known that forests are an important component of the global carbon cycle [1], with dead wood (DW) being a key element of sustainable forest management [2,3]. Virgin forests are reference models for managed forests [4–6], and the most appropriate way to understand the synergies between DW and climate change mitigation is to research this topic in natural forests [2]. Virgin forests consist of different-aged trees, which reach impressive dimensions at old age [7], their diameter distribution being, in general, ‘J’-shaped [8]. All trees reach their physiological age (longevity) and then, ultimately, they die and become DW. Dead wood can actually be considered as living wood because it maintains life in the form of different types of insects, mushrooms, and mammals, for example, by providing food and shelter [9]. In managed forests, the natural developmental stages of the trees are missing, causing the disappearance of the floras and faunas that are specific to virgin forests [10–13]. In the last few decades, in Romania, the concept of ‘close-to-nature’ forest management has been adopted because its characteristics (natural regeneration, single-tree felling, indigenous tree species, etc.) [7] promote the better management of forests. The period prior to 1990 had a relatively negative impact on the state of forest ecosystems in Romania, as well as in other Carpathian countries, where the productive functions of forests were prioritized. Subsequently, based on research findings, especially those concerning the protective functions of forests, it was recommended for the first time in 1995 that a Forests 2022, 13, 409. https://doi.org/10.3390/f13030409 https://www.mdpi.com/journal/forests