Deconstructing the “cathedral old-growth:" Structural variability in Carpathian primary spruce-fir systems
In Europe, two different conceptions of late-successional forests remain in debate. Some emphasize an idealized notion of old-growth, imposing strict structural definitions and rigid classification. A competing view stresses variability, often attributed to the interaction of natural disturbances and multiple pathways of stand development. Our study explores this divergence of perspectives referencing two datasets from the Carpathian Mountains in western Ukraine. We collected inventory data in multiple old-growth and mature spruce-fir stands at two locations, the Gorgany Nature Protection Reserve and the Verkhovynskyy National Nature Park. Forest structure and composition were inventoried using randomly placed, variable radius plots, linked by line intercept transects for estimating downed woody debris volume. Dominant canopy trees were cored at breast height to determine age. We report dominant tree ages, live aboveground biomass, large tree densities, and downed coarse woody debris (CWD) volume as examples of variability in structure.
While old-growth had higher biomass on average compared to mature sites, this was not always the case. There was overlap between the high end of the mature and the low end of the old-growth age classes. At Gorgany live aboverground biomass ranged from 255 to 303 Mg/ha, while at Verkkovyniski this ranged from 176 to 203 Mg/ha. There was pronounced variability in biomass both among and within old-growth sites; the standard deviations were significantly higher (P<0.05) for old-growth as compared to mature sites. Similar results were found for large tree density and CWD volume, with some old-growth stands exhibiting high levels of both and others having values not signficantly different from mature stands. Aboveground biomass at patch scales was highly variable within the Verkhovynskyy stands, ranging from 114 to 263 Mg/ha within one stand alone, despite relatively low frequencies of canopy gaps. Dominant trees ages at Verkhovynskyy were both significantly lower and far more variable, ranging between plots from 44 to 190 years. The standard deviation of tree age was significantly higher (P<0.001) in old-growth sites at Verkhovynskyy in comparison to those at Gorgany. Biological legacies, such as very large remnant old-growth trees, were observed at Gorgany but not at Verkhovynskyy. The high degree of variability we found both within and among late-successional stands is reason to question an archetypical old-growth condition. Spatially heterogeneous structure should be viewed as a defining characteristic of old-growth forests, recognizing the dynamics that drive system functioning.