Aims To develop forest vegetation classification at the level of alliances and associations across the Hyrcanian ecoregion, Northern Iran, and to explore the effects of main environmental and geographic gradients on their distribution. Location Hyrcanian ecoregion, Northern Iran. Methods A database of 1,597 vegetation plots of mostly 400 m(2) in size with a total of 802 vascular plant taxa was established, covering the whole geographic range of the Hyrcanian forests at altitudes ranging from -22 to 2,850 m a. s. l. An expert system was developed for automatic classification of vegetation plots into alliances and associations. Detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) were used to determine the most important environmental and geographic gradients affecting species composition. Results Twenty-one associations and seven alliances of these forests, belonging to five orders and four classes, were defined. Among them, eleven associations and five alliances were described as new syntaxa. Alnion glutinosae and Smilaco excelsae-Alnion barbatae, both distributed in the lowland belt, include swamp and wet forests, respectively. Parrotio persicae-Carpinion betuli and Alnion subcordatae are respectively mesic and wet forests of the submontane belt. Solano kieseritzkii-Fagion orientalis is a mesic beech forest in the montane belt, and finally, Quercion macrantherae, an open oak forest, and Centaureo hyrcanicae-Carpinion orientalis, a dry hornbeam forest, occur in the upper-montane belt. DCA and CCA analyses showed that the distribution of these alliances and associations is mainly related to altitude and mean annual temperature. Conclusions Based on our results and comparison between the Hyrcanian and European forests, we propose a new, comprehensive syntaxonomic scheme for the Hyrcanian forests, supported by a classification expert system. Unlike previous studies, we linked the classification system to that of EuroVegChecklist because, though this area is outside of Europe, its vegetation is very similar to that of the European temperate forest vegetation.

中文翻译：

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伊朗北部希尔卡尼亚森林植被的分类

目的 在整个伊朗北部希尔卡尼亚生态区的联盟和协会层面制定森林植被分类，并探索主要环境和地理梯度对其分布的影响。位置 伊朗北部的希尔卡尼亚生态区。方法建立了1597个植被图块的数据库，其中大部分为400 m（2），共有802个维管植物类群，覆盖了海拔-22至2850 m asl的Hyrcanian森林的整个地理范围。开发用于将植被地块自动分类为联盟和关联。去趋势对应分析 (DCA) 和规范对应分析 (CCA) 用于确定影响物种组成的最重要的环境和地理梯度。结果确定了这些森林的21个协会和7个联盟，属于5个目和4个类。其中，11个协会和5个联盟被描述为新句法。Alnion glutinosae 和 Smilaco excelsae-Alnion barbatae 均分布于低地带，分别包括沼泽和湿林。Parrotio persicae-Carpinion betuli 和 Alnion subcordatae 分别是亚山带的中湿林。Solano kieseritzkii-Fagion orientalis 是山地带中的中型山毛榉林，最后，开放的橡树林 Quercion macrantherae 和干燥的角树森林 Centaureo hyrcanicae-Carpinion orientalis 出现在上山带。DCA和CCA分析表明，这些联盟和协会的分布主要与海拔高度和年平均气温有关。结论基于我们的结果以及对希尔卡尼亚森林和欧洲森林的比较，我们为希尔卡尼亚森林提出了一种新的、综合的句法方案，并得到了分类专家系统的支持。与之前的研究不同，我们将分类系统与 EuroVegChecklist 的分类系统联系起来，因为虽然该地区在欧洲之外，但其植被与欧洲温带森林植被的植被非常相似。