Allometries, biomass stocks and biomass allocation in the thermophilic Spanish juniper woodlands of Southern Spain.

摘要

The principal objective of this study was to investigate the variations of allometric relationships, biomass stocks and biomass allocation in a Spanish juniper thermophilic community (Juniperus thurifera var. hispanica Mill.) in response to two levels of woodland maturity: mature woodlands, which are situated in shallow stony soils with trees over 140 years old and low tree density, and young woodlands, with trees under 100 years old growing in deeper soils (generally, abandoned farmland). Branch- and tree-level allometric models were fit from measurements carried out on branches, stems and roots in 42 felled trees. Although age and site are confounded for this juniper community, it is expedient to utilize site-specific equations because the two woodlands showed distinct growth patterns as a result of their very different soil qualities and ages. At the branch level, the relationship was matched for foliage biomass depending on the site. At the tree level, site location significantly affected variables in allometric relationships that were not strictly cumulative (i.e., leaves, branch wood and fine-root biomass). Goodness of fit was improved by including the relative height of the first live whorl (pruning effect) as an additional predictor of crown and coarse root biomass. The young woodland supported more biomass stock across all components due to better soil. Biomass allocation measured in stems, coarse roots and fine roots was significantly higher in the mature woodland, although the young woodland did accumulate more dry mass in the crown. Differences in biomass allocation may be explained by both the age and strategies of J. thurifera to maximize nutrient and water capture for survival in poor soils (site quality effects). Our results also showed that, in mature woodlands, this species accumulates one of the smallest biomass stocks cited for temperate mature conifer stands (7.6 Mg ha-1) but has a high root to shoot ratio (0.43) as a consequence of growing in poor soil conditions.