Biomass and structure of Norway spruce trees grown in uneven-aged stands in southern Finland

Tree biomass models are increasingly needed for the estimation of carbon storage and for testing and parameterizing process-based growth models, but most biomass models have been estimated using data from even-aged stands. Here we took measurements from individual Norway spruce trees grown in uneven-aged stands in Southern Finland to characterize tree structure and to estimate the biomasses of tree components. Using the data, we tested various structural biomass equations developed for even-aged stands for their suitability to uneven-aged stands. The test trees had longer crowns than usually found in an even-aged Norway spruce stand, ranging from 55 to 85% of total tree height. The average proportion of total biomass in branches and foliage was 13.8 % and 7.0 %, respectively. The average wood density of the test trees was slightly higher than that reported for Norway spruce trees of comparable size. The structural relationships found in trees under even-aged management were applicable to trees growing in uneven-aged stands but required re-parameterization. In particular, the trees had higher branch and stem biomass than trees of same stem and crown dimensions on average in even-aged stands. The relationship of crown ratio and the slenderness index on an uneven-aged stands also differed from those reported in even-aged stands.

林木生物量模型（tree biomass models）在碳储量（carbon storage）估算以及基于过程的生长模型（process-based growth models）的验证与参数化工作中需求日益增长，但当前绝大多数生物量模型均基于同龄林分（even-aged stands）数据构建。本研究针对芬兰南部异龄林分（uneven-aged stands）中的挪威云杉（Norway spruce）单木开展实地测定工作，以刻画林木结构特征并估算各林木组分（tree components）的生物量。基于本次测定数据集，我们对多款专为同龄林分开发的结构型生物量方程（structural biomass equations）在异龄林分中的适用性开展了检验。供试林木的冠长显著长于同龄挪威云杉林分中的常规个体，冠长占树总高的比例区间为55%至85%。供试林木的枝条与叶生物量分别占总生物量的13.8%与7.0%，其平均木材密度（wood density）略高于已有文献报道的同规格挪威云杉木材密度。同龄经营模式下林木所呈现的结构关系可推广至异龄林分中的林木，但需进行重新参数化（re-parameterization）。尤为值得注意的是，与同龄林分中茎干与冠幅尺寸相当的林木相比，本次供试林木的枝条与茎干生物量（stem biomass）平均水平更高。异龄林分中冠长率（crown ratio）与细长度指数（slenderness index）的相关关系同样与同龄林分的已有研究报道存在差异。