Regional Variability of the Romanian Main Tree Species Growth Using National Forest Inventory Increment Cores

In many countries, National Forest Inventory (NFI) data is used to assess the variability of forest growth across the country. The identification of areas with similar growths provides the foundation for development of regional models. The objective of the present study is to identify areas with similar diameter and basal area growth using increment cores acquired by the NFI for the three main Romanian species: Norway spruce (Picea abies L. Karst), European beech (Fagus sylvatica L.), and Sessile oak (Quercus petraea (Matt.) Liebl.). We used 6536 increment cores with ages less than 100 years, a total of 427,635 rings. The country was divided in 21 non-overlapping ecoregions based on geomorphology, soil, geology and spatial contiguousness. Mixed models and multivariate analyses were used to assess the differences in annual dimeter at breast height and basal area growth among ecoregions. Irrespective of the species, the mixed models analysis revealed significant differences in growth between the ecoregions. However, some ecoregions were similar in terms of growth and could be aggregated. Multivariate analysis reinforced the difference between ecoregions and showed no temporal grouping for spruce and beech. Sessile oak growth was separated not only by ecoregions, but also by time, with some ecoregions being more prone to draught. Our study showed that countries of median size, such as Romania, could exhibit significant spatial differences in forest growth. Therefore, countrywide growth models incorporate too much variability to be considered operationally feasible. Furthermore, it is difficult to justify the current growth and yield models as a legal binding planning tool.

在许多国家，国家森林资源清查（NFI）数据被用于评估全国森林生长的变异性。识别生长相似的区域为区域模型的开发提供了基础。本研究的目的是利用国家森林资源清查获取的增量芯，识别罗马尼亚三种主要树种：挪威云杉（Picea abies L. Karst）、欧洲山毛榉（Fagus sylvatica L.）和无梗花栎（Quercus petraea (Matt.) Liebl.）直径和断面积生长相似的区域。我们使用了6536个年龄小于100年的增量芯，共计427635个年轮。该国根据地貌、土壤、地质和空间连续性被划分为21个不重叠的生态区。采用混合模型和多元分析来评估生态区之间胸径年生长量和断面积生长的差异。无论树种如何，混合模型分析显示生态区之间的生长存在显著差异。然而，一些生态区在生长方面相似，可以合并。多元分析强化了生态区之间的差异，并且表明云杉和山毛榉没有时间分组。无梗花栎的生长不仅因生态区而异，还因时间而异，一些生态区更容易遭受干旱。我们的研究表明，像罗马尼亚这样中等面积的国家，森林生长可能在空间上存在显著差异。因此，全国性的生长模型包含过多的变异性，在实际操作中不可行。此外，很难将当前的生长和收获模型作为具有法律约束力的规划工具。