Urbanization may reduce the risk of frost damage to spring flowers: A case study of two shrub species in South Korea.

Hyeon-Ju Gim,Eun Ju Lee,Jinwon Kim,Chang-Hoi Ho,Yanguang Chen

doi:10.1371/journal.pone.0191428

Hyeon-Ju Gim, Eun Ju Lee + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0191428

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Abstract

Regional warming, owing to urbanization, leads to earlier spring phenological events and may expose plants to hard freeze damage. This study examined the influence of urbanization on the risk of frost damage to spring flowers in South Korea from 1973 to 2015. For the analysis period, we categorized 25 cities into two groups: those showing rapid population growth (rPG) ≥ 200,000, including 13 cities, and those showing no or decreased population growth (nPG), including 12 cities. We then investigated the time from the last frost dates (LFDs) in spring to the first flowering dates (FFDs) for each group. The rPG group experienced significant spring warming of 0.47°C per decade, resulting in earlier LFDs and FFDs. For this group, the advancement of LFD was more rapid than that of FFD, and the days between these two dates increased from 0.42 to 0.47 days per decade, implying a reduced risk of frost damage. Spring warming and the advancement of FFDs and LFDs were relatively small for the nPG group, and the LFDs were rather delayed. Consequently, the days between LFDs and FFDs were reduced from −1.05 to −1.67 days per decade, indicating an increased risk of frost damage. The contrasting changes in the frost-damage risk between the two city groups can be attributed to distinct urban warming at night, which makes the LFDs substantially earlier in the rPG group. Therefore, this study suggests that the warming associated with urbanization may lessen the risk of spring frost damage to plants in rapidly growing urban areas.

Highlights

The long-term average of the first flowering dates (FFDs) ranges from the 75th to the 100th day of the year in the selected cities; there is a tendency for an early FFD in warmer cities
last frost dates (LFDs) precede FFDs by a week, on average, more than 25% of LFDs are later than the average FFD, owing to the wide variation in LFDs from mid-February to late April
No considerable differences were noted between the two city groups in the averages of FFDs or LFDs because there is no bias relating to regional climate or latitude of the rapidly growing cities (Fig 1)

Summary

Introduction

The FFDs of forsythia and azalea showed advancement in most cities and appeared to be greater for the rPG group, at −1.47 and −1.42 days per decade, respectively, than for the nPG group, at −0.71 and −1.08 days per decade, respectively (Fig 4). The DFFs in nPG cities have been considerably shortened, which indicates an increased risk of frost damage to flowers (Fig 4).

Results

Conclusion