Plant distribution and modern pollen deposition across an elevation eco-gradient: The lesson learnt from a case study in the Italian Alps

Abstract

This study investigates the distribution of vegetation and its modern pollen representation along an elevation gradient in the Italian Alps and explores the relationships with terrain and climate variables. Moss polsters were collected at 25 sites between ca. 300 and 1400 m asl from open areas, deciduous, and conifer forests. At each site vegetation was surveyed at 1.8 and 10 m radius according to the Braun-Blanquet method. Climatic data, bioclimatic indices, and terrain parameters were obtained for each sampling site. Three distinct pollen associations reflect the characteristic vegetation altitudinal belts present in the study area. Uphill dispersal, the regional load and the presence of high producers influence the abundance of pollen and the representation of taxa along the gradient. CCA ordination technique reveals the predictive power of environmental variables on modern pollen and vegetation datasets. The most relevant factors controlling vegetation distribution are identified in elevation, insolation, Pspring, Tsummer, the Ellenberg quotient, and Summer Water Balance (SWB). Elevation, insolation, summer P and T, the Ellenberg quotient, and the Gams’ hygric continentality index (GAMS) explain more variance within the pollen dataset. A qualitative comparison among pollen and the corresponding parent plant occurrence qualifies Abies alba, Fagus sylvatica, Poaceae and Cyclamen pollen as suitable indicators taxa of the local vegetation in the study area. Several high producers with very effective, long-distance anemophilous dispersal ( Pinus, Ostrya, Alnus, and Juglans) or mixed pollination mechanisms (anemophilous and insect-pollination: Fraxinus ornus, and Castanea) show no or little association with their parent plants.

Assessment of Pollen Representation in NW Italy (Liguria and Piedmont)

“…A better explanation for unexpected values could be possible through a detailed analysis of historical land management practices (coppicing, mowing, grazing), but they were not taken into consideration in this study. An interesting result of this study is the fact that pollen taxa that are still considered bad descriptors of vegetation because they have large pollen production and dispersion (e.g., Pinus, Corylus, Ostrya) [20], actually show very low association values (A) (regional pollen dispersal), but if evaluated quantitatively, they also have maximum values as indicators of particular vegetation types (Table 5). In fact, when the mean of both pollen and vegetation cover of a certain vegetation type are higher than the mean value of all samples plus the standard deviation, these taxa can be considered good indicators of that vegetation type [34].…”

“…Olea pollen values were occasionally ~10%, despite the fact that olive was never found in the vegetation. This was expected, considering that Olea pollen is often overrepresented, it can be easily dispersed for a few kilometers [20], and olive cultivation was widespread on the Ligurian coast even if it is now abandoned in large areas. Regarding the shrub layer, Buxus pollen was found in the only site where it had a good cover (PIN5).…”

“…Recent pollen rain data generally come from moss polsters, which can be used as natural pollen traps that accumulate pollen for approximately 5-10 years [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Vegetation cover data have often been estimated with the phytosociological method proposed by Braun-Blanquet [18,19] for other purposes (e.g., [3,4,20,21]). Several other criteria have been proposed over time, such as the measurement of the base area of trees or the analysis of vegetation using transects.…”

Modern pollen rain in humid tropical mountain forests from eastern Mexico: A patch-dynamics approach

“…According to historical data, since the beginning of the 16th century, the region known as Sierra Gorda Hidalguense promoted activities such as agriculture and livestock as main secondary economic sources (Arroyo-Mosqueda, 2002). Fontana et al (2023) found that the relationship between Poaceae and their occurrence in plant communities is predominantly good in sites close to forest edges within an elevation gradient. This could explain the similarity among altitude gradients of the TM2 and TM3 patches due to some surrounding historical processes.…”

“…Essential findings from these investigations have identified factors influencing tree cover during the Holocene through relative pollen productivity estimates among different cultural landscapes (Baker et al, 2016). In addition, pollen analysis in moss polsters has shown the influence of some climatic and terrain parameters on vegetation and pollen deposition in mountain ecosystems (Fontana et al, 2023). These approaches reinforce the relevance of pollen analysis and its implications within cultural landscapes and elevational gradients.…”