216 with lower turnover and decomposition rate, such as stem wood, returns to the atmosphere only aſter decades or centuries (Campioli et al. 2008). In comparison to other components of for- est ecosystems, the biomass of fruits is considered to be small (Mälkönen 1974; Muukkonen 2006) and is sometimes dismissed as negligible. How- ever, the biomass of fruits may play an impor- tant role in many ecosystem processes, such as in the nutrient and carbon cycle, due to rapid turn- over rate (Muukkonen 2006) at the biomass level. Members of the genus Quercus L. (Fagaceae), including evergreen and deciduous shrubs and trees, have a wide geographical range, occupy- ing vast territories of the Northern Hemisphere in North America, Europe, and Asia (Denk and Grimm 2010; Johnson et al. 2010). Quer- cus is the most common genus of Fagaceae in forests of Iran (Sabeti 1994). Several species of oaks grow abundantly in the Zagros, Aras- baran, and Hyrcanian forests (Sagheb Talebi et al. 2014). During four past decades, native oak species of Iran as well as some exotic oak species, have been planted in the National Botanical Garden of Iran. Today, oak species are one of the most important elements of the garden, distributed throughout the garden. Fruits of oaks, acorns, are usually associ- ated with an involucre forming a cup around the mature fruit. Acorns are hard, one- seeded, and dry. Due to the woody struc- ture, acorns have a considerable role in biomass production and carbon stock in oak- dominated forests. Acorn production varies from year to year and among species (Lash- ley et al. 2009; Koenig and Knops 2014). The biomass and carbon content of acorns may differ because of high variation in mor- phology among oak species. Some research- ers have mentioned the variation in acorn biomass of oak species (e.g., Callahan et al. 2008; Steen et al. 2009; Sánchez-Humanes et al. 2011), but the evidence on acorn car- bon content is limited (e.g., Sun et al. 2012). On the other hand, only two reports on acorn biomass (Panahi et al. 2009; Iranmanesh et al. 2013) and one report on carbon stock (Iran- manesh et al. 2013) of native oak species of Iran have been published. The present study ©2018 International Society of Arboriculture Panahi et al.: Acorn Biomass and Carbon Stock Variation gives an account on the mature acorn biomass and carbon stock of five oak species, culti- vated in the National Botanical Garden of Iran. The aim of this study was to determine the site-specific acorn biomass, carbon stock, and carbon content of the target species, and to examine if they are significantly different. MATERIALS AND METHODS Study Area The study was conducted at the National Botani- cal Garden of Iran (35°41’N, 51°19’E) in 2016. The garden was founded in 1968. An area of 145 ha was allocated to the garden in Tehran at an altitude of 1,320 m (Figure 1). The area is flat and slopes gently to the south. The climate is dry with an average annual precipitation of 257 mm, falling between November and May. Tem- perature reaches as much as 42°C–43°C during July and August. During winter, the temperature may fall to -10°C or lower. The garden consists of some native and exotic collections with dif- ferent areas. The Hyrcanian and Zagros collec- tions, as symbols of the Hyrcanian and Zagros forests of Iran, are the most important forest col- lections of the garden. Most of the oak trees are found in these collections. The other individual oak trees are distributed throughout the garden with more density in the Systematic collection. Study Species Five oak species were chosen for this study as follows. Four deciduous native oaks of Iran, in- cluding chestnut-leaved oak (Q. castaneifolia), Lebanon oak (Q. libani), Aleppo oak (Q. infecto- ria), and Brant’s oak (Q. brantii), as well as one ev- ergreen exotic oak species (Q. ilex). All sample oak trees have been planted since 1988. The chestnut- leaved oak is a light-demanding tree and is one of the most productive, valuable, and precious spe- cies in the Hyrcanian forests of Iran. Other three native oaks naturally grow in Zagros forests in the west of Iran (Sagheb Talebi et al. 2014). In contrast to the native oaks of Iran studied, Q. ilex is an evergreen oak, native to the Mediterranean region. Quercus ilex is planted in a number of gar- den collections, such as the systematic collection.
September 2018
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