Temporal patterns of pollen shedding for longleaf pine (Pinus palustris) at the Escambia Experimental Forest in Alabama, USA

Abstract

Longleaf pine is an important tree species in the southeastern United States and studying the temporal patterns of pollen shedding is crucial to a better understanding of its phenology and seed production. In this study, field observation data on the timing of pollen shedding from 1958 to 2013 were analyzed with reference to local weather conditions. Our results indicated that the time of peak pollen shedding after January 1 (TPPS) ranged from 53 days (about February 22) to 95 days (around April 5). There was no significant trend of decreasing TPPS. The number of days with the maximum air temperature above 0 °C was close to the TPPS. The accumulated maximum daily air temperature for the TPPS approximated an average of 1,342 °C. The TPPS declined with an increase in the average air temperature during winters. The time of 80% accumulated pollen density (TAPD) varied from 5 to 32 days, with an average of 13 days. Taylor’s power-law was evident in the TAPD data, with the time group of 10–15 days having an interval time of 2 years. Winter weather was not correlated with the TAPD. These results provide new information concerning the pollen phenology for longleaf pine trees.

Tropical cyclone winds and precipitation stimulate cone production in the masting species longleaf pine (Pinus palustris)

“…The male catkins and female conelets of longleaf pine initiate in July and August and develop during subsequent months (Guo et al, 2016). Pollen shedding occurs around March (Boyer, 1973;Chen et al, 2020), but fertilization does not occur until the following spring, and maturation and dispersal occur c. 2.5 yr after initiation in October (Chen et al, 2018). Because of the prolonged development time, newly initiated catkins and conelets (c. 2 months old) and recently pollinated conelets (c. 14 months old) are both present during the period of peak TC activity (August-September).…”

Current Standing of Longleaf Pine Trees under Climate Change

“…Although pollen and unfertilized conelets do not have a temporal cycle, the sex allocation ratio between male and female structures is positively correlated with temperature, and cone production is optimal when this ratio is intermediate [26] . Chen et al [5] revealed no significant trend in either the time of peak pollen shedding or time of 80% accumulated pollen density over 55 years of data. However, the time of peak pollen shedding was connected to climate factors, primarily the heat sum of total days above 0 °C.…”

“…In botany, both the timing of growing seasons and reproduction are known to vary with climate [33,55] . Factors associated with reproduction in plants such as time of pollen release, fertilization, and intraspecific interactions are known to vary by species, and the impact of climate on these factors varies as well [1,5,56,57] . For example, in angiosperms, changing temperature variables can lead to altered seasonal timing between plant flowering and pollinator activity and composition [54] .…”

“…Given the lack of data on longleaf pine resource allocation, quantifying internal factors of resource allocation (e.g. biomass allocation) as they relate to climate variables may be a key step to strengthening our understanding of the mechanisms behind sporadic longleaf cone production [5] .…”

“…Moreover, the climate is a primary factor in constraining species range, and global climate change has already been shown to impact the dispersion of species [3] . Relevant climate variables on plant success can include annual average temperature or precipitation, a total number of days above or below a certain temperature threshold, frequency of high-intensity events such as hurricanes or droughts, and many others [4][5][6] . Moreover, changing climate can affect plant communities on both short-term and long-term scales [1] .…”