Research report: Biomonitoring with bryophytes in managed forested areas. Three examples from the southern Italian Apennines

A field study of three managed forest sites in Italy’s southern Apennines found that the Index of Atmospheric Purity, or IAP, was lower near the Viggiano oil hub than in a beech forest with no apparent pollution source. However, the unexpectedly low values in the beech forest showed that the index could not be interpreted as a measure of pollution alone, because forest structure, developmental stage and management also influenced the epiphytic bryophyte communities used in the calculation. The study investigated whether IAP could assess environmental pollution in managed forests.

Proposed by De Sloover in 1964 and subsequently adapted for epiphytic bryophytes, the method has been used mainly in cities and urban areas to supplement pollutant monitors and satellite-based observations with information about ecological effects. Its interpretation in forests requires attention to local ecological conditions because cryptogamic communities are influenced by forest structure and developmental stage. The researchers investigated three sites.

Site A, in the Agri River valley near the Viggiano oil hub in Basilicata, covered managed forest at 610–620 metres, dominated by Turkey oak, Quercus cerris, with occasional Downey oak, Quercus pubescens. Its climate was Mediterranean and sub-humid, with an annual mean temperature of 12.4 °C and a De Martonne aridity index of 24.3. Site B, on Mount Paratiello west of Muro Lucano, was a beech forest, Fagus sylvatica, with plots at 1,356 and 1,423 metres.

Site C, on the northern slopes of Mount Motola in Campania, was a beech–silver fir forest containing Abies alba. At the study sites, investigators examined bryological and vascular flora, climate, geology, soils and silvicultural parameters. Circular plots measuring 20 metres in diameter were established to characterize tree structure and developmental stage.

For IAP calculations at Sites A and B, a 60-by-50-centimetre grid divided into 20 units was placed on tree trunks 80–100 centimetres above the ground in areas with high bryophyte density. Species cover or frequency was scored from 1 to 5 and combined with pollution-resistance factors before summation and scaling. The investigators also applied Düll’s Indicator Values of Mosses and Liverworts at all three sites.

These nine-point scales describe bryophyte preferences for light, temperature, continentality, moisture and reaction. No IAP was calculated for Site C, where the analysis focused on bryophyte flora and silvicultural structure across elevation. Sampling at Site A took place in 2003 and 2008 across stands ranging from simple coppice to aged coppice converting into high forest and coppice with standards.

At Site A, average tree diameters and total basal area increased between the two sampling years in each of the three repeatedly measured plots. Total basal area rose from 1.873 to 3.597 square metres in the first plot, from 2.581 to 4.120 square metres in the second and from 2.568 to 3.909 square metres in the third. Corresponding IAP values increased from 0.32, 0.43 and 0.37 in 2003 to 1.10, 0.80 and 0.70 in 2008, although they remained low.

A fourth plot sampled in 2008 contained very young trees with small diameters and too little epiphytic vegetation for an IAP to be calculated. The two Site B plots produced IAP values of 2.2 and 4.0. The higher value occurred in the older plot at 1,423 metres, where average tree diameter was 23.0 centimetres, compared with 14.5 centimetres in the more recently cut lower plot.

The authors considered both values low and not substantially different from those measured near the oil hub at Site A. Their ecological indicator values were almost identical, although the upper plot differed in moisture preference; the authors associated this with its position near the tree line and adjacent montane grassland, where an edge effect exposed bryophytes to additional sunlight. Site C showed an altitudinal shift in its bryophyte flora.

At 700–900 metres, the indicator values corresponded to semi-shade plants, moderate warmth, intermediate continentality, high moisture and weakly acidic to weakly basic conditions. At 1,000–1,300 metres, the temperature value indicated sub-Oceanic conditions, while moisture remained high. Lower-elevation silver firs were taller than beeches and included diameter classes of reproductive age, with abundant cones observed in autumn 2002.

At higher elevations, beech became dominant and silver fir was scarce in the canopy, although small individuals persisted in the sub-canopy, including plants whose vegetative apices showed damage attributed to grazing or contact with branches of taller trees. The relative ordering of IAP values was consistent with apparent pollution exposure: values were lower at Site A near the oil hub and higher at Site B, where no apparent pollution source was identified. Nevertheless, Site B’s values were much lower than those normally reported from unpolluted urban areas.

The authors said this discrepancy may be related to silvicultural management, including frequent cutting and low basal area, which can reduce bryophyte diversity by making the organisms vulnerable to microclimatic changes. The study did not directly measure pollution at each plot, so this was a possible association rather than a demonstrated causal effect. These findings limit the direct application of urban IAP reference values to forests.

The authors said correction factors, potentially based on total basal area and phorophyte selection, are needed for comparisons between forest and urban sites, and further study is required. As a preliminary approach for forested areas, they proposed considering stands at comparable developmental stages and under similar management systems, preferably with older trees. The ecological Indicator Values for mosses and liverworts were assessed spatially across the three sites and temporally at Site A, where they did not change between 2003 and 2008.

Subject of Research: Bryophyte-based air-pollution biomonitoring in managed forests

Article Title: Biomonitoring with bryophytes in managed forested areas. Three examples from the southern Italian Apennines

Article References: Colacino, C. (2023). Biomonitoring with bryophytes in managed forested areas. Three examples from the southern Italian Apennines. BioRisk, 21, 11-18. https://doi.org/10.3897/biorisk.21.108551

Image Credits: AI Generated

DOI: 10.3897/biorisk.21.108551

Keywords: bryophytes, biomonitoring, Index of Atmospheric Purity, air pollution, managed forests, southern Apennines, epiphytic bryophytes, silviculture, mosses, liverworts, managed, forested