Abstract
Background: In the Northern Hemisphere, pine forests predominate due to their natural distribution and silvicultural importance. Pinus tree species are large pollen producers. Nowadays, the context of climate change influences their distribution, abundance, growth and productivity. The objectives of the study were to assess the patterns of the Pinus flowering behavior regarding their pollen presence in the atmosphere and intensity in different bioclimatic areas of the Iberian Peninsula during recent years. Methods: The survey was carried out in three different biogeographic zones of Spain: Vigo (Eurosiberian region) and Ourense (transition area between the Eurosiberian and Mediterranean areas) located in northwest Spain and Toledo (Mediterranean area) placed in the center of the Iberian Peninsula. Airborne pollen was collected with volumetric traps in each study area from 1995 to 2019. Results: Pinus pollen showed a marked single pollination period during late March in the Eurosiberian region and April in the transition zone between the Eurosiberian and the Mediterranean area. Two different peaks with lower pollen intensity were detected during the pollen season in Toledo (Mediterranean area), the first during late March and the second from the end of May to the beginning of June. The trends detected revealed changes in the timing of the phenological cycle, such us longer pollen seasons and later end dates of the Main Pollen Season (MPS) in some cases. The mean Annual Pollen Integral (API) in the Eurosiberian area (Vigo) and transition zone (Ourense) was similar, with about 4400 pollen grains. In the Mediterranean area (Toledo), a lower API amount of 1618 pollen grains was recorded. A trend towards an increase of 126 and 80 pollen grains per year in the airborne pine load was detected in the transition and Mediterranean areas studied, respectively. Conclusions: The rates of the annual integral Pinus pollen percentage with respect to the total pollen of forest species in the atmosphere of the areas studied showed a decreasing percentage trend during the last years.
Highlights
Several studies have investigated the vulnerability of forests to pressures related to the environmental impacts of global climate change [38,39], pests and diseases [40,41], wildfires or anthropological actions such us changes in land use [42]
Our study shows that rainy years registered a lower Annual Pollen Integral (API), and vice versa for dry years
Two pollination periods were observed in the Mediterranean area, the first recorded at the end of March and the second between late May and the beginning of
Summary
Hemisphere as its species are often dominant in forests [1] with a high representativeness in the pollen spectra of some regions [2]. In the south of Europe, numerous pine species naturally grow, forming mixed and pure coniferous forests [3]. In the Iberian Peninsula, pine forests together with oaks and holm oaks occupy most of the forest area. Native pine species are represented by P. halepensis Mill., P. pinaster Aiton, P. pinea L., P. nigra J.F. Arnold subsp. In the Northern Hemisphere, pine forests predominate due to their natural distribution and silvicultural importance. Pinus tree species are large pollen producers. Methods: The survey was carried out in three different biogeographic zones of Spain: Vigo (Eurosiberian region) and Ourense (transition area between the Eurosiberian and Mediterranean areas) located in northwest Spain and Toledo (Mediterranean area) placed in the center of the Iberian Peninsula. Results: Pinus pollen showed a marked single pollination period during late
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