DOI: 10.5061/dryad.18931zd3k
title: Effect of climate-change-induced increases on the range of rice-barley double cultivation on the intermediate egret

description: Intensification of cultivation methods and land use types, particularly in
 the face of climate change, has steadily weakened the habitat function of
 rice fields for waterbirds. Intermediate egrets (Ardea intermedia) are
 highly dependent on rice field habitats. Here, we examine the effect of a
 shift from rice monoculture to rice–barley double cultivation on the use
 of rice fields by intermediate egrets in South Korea. Rice-barley double
 cultivation has been increasing steadily in the southern region of South
 Korea due to changes in the rice growth period under climate change and
 maximization of economic benefits. We studied rice fields to determine the
 effect of the rice-barely double cultivation area on the abundance of
 intermediate egrets on the regional scale and their potential distribution
 pattern in response to double cultivation in relation to climate change
 using national-scale climate, altitude, and land cover data from May 1 to
 June 23, 2018. Compared to the irrigation practices used for rice
 monoculture, irrigation was stopped for some time in rice-barley double
 cultivation prior to planting, compromising the role of rice fields as a
 food ground for intermediate egrets. The potential abundance of
 intermediate egrets rapidly decreased by half when the double cultivation
 area increased to &gt;40% of the total rice-field area, and was less
 than one individual if the area increased to &gt;80%. Furthermore,
 according to climate change projections, by 2100, the double cultivation
 area would account for 75.74% of the predicted range of intermediate egret
 foraging ground. Synthesis and applications. Double cultivation areas
 should be &lt;40% of existing rice fields to minimize the impact of
 the change in cultivation practices. This approach can also convert rice
 fields to other types of land use. Consequently, appropriate conservation
 and management measures may be developed to maintain suitable habitats
 despite rapidly changing cultivation practices resulting from climate
 change.
description: The study was carried out from
 1 May to 23 June 2018 in rice fields at a regional scale
 (105,271
 ha, including part of the
 provinces of Chungcheongnam-do (CN) and Jeollabuk-do (JN)) and national
 scale (10,021,000 ha, including eight provinces: Gyeonggi-do (GG), Gangwon-do (GW),
 Chungcheongbuk-do (CB), CN, Gyeongsangbuk-do (GB), Gyeongsangnam-do (GN),
 Jeollabuk-do (JB) and JN)
 to determine the abundance of intermediate egrets based on the double
 cultivation area and their potential distribution range according to
 climate change. A survey
 area surrounded by rice fields was randomly selected to minimize the
 influence of the landscape
 (approximately 80% of the area in each
 plot). At the regional scale, 40 plots (1 × 1 km) were randomly selected in CN and JB, located in
 the southwestern region of South Korea, where rice fields used for rice
 mono- and double cultivation were distributed. The rice cultivation areas in CN and JB were
 133,986 ha and 113,775 ha, respectively, and the double cultivation area
 was 65 and 10,362 ha, respectively (KOSIS, 2022a). Surveys were carried
 out in rice fields in Seocheon-gun and Nonsan-si of CN and Iksan-si,
 Wanju-gun, Gimje-si, Jeongeup-si and Buan-gun of JB, with a mixed
 distribution used for rice monoculture and double cultivation.
 The distance between the
 plots was set at 5 km to minimize the effect of spatial autocorrelation
 (Amano et al., 2008). The average number of rice fields in a plot was
 190.6 ± 11.4 units (range: 168-209) and the average size of the standardized
 unit paddies (separated by levee and farm road) was 0.46 ± 0.06 ha (range:
 0.32–0.68 ha). Fifteen sites (1 × 1 km) were randomly selected in seven of the eight
 provinces, except GW, to understand intermediate egret occupancy with
 respect to the rice-barley double cultivation area according to climate
 change on a national scale. GW mainly comprises mountainous areas, with a
 few areas with rice fields of at least 1 × 1 km; therefore, six sites were
 randomly selected. During the survey period, irrigation in rice
 monoculture fields in the survey plots began on 9 May. In contrast, barley
 was grown in a dry state in rice fields used for double harvesting. On 17
 June, rice was planted in flooding rice fields or barley was harvested
 from rice fields used for double cultivation, and the fields were
 irrigated. In the fields used for rice monoculture, irrigation and rice
 planting began at the beginning of May, and in the rice fields used for
 double cultivation, barley was cultivated immediately after rice was
 harvested in October. The barley cultivated during this period was
 harvested in June of the following year. During barley cultivation, rice
 fields were not irrigated. Both regional and national surveys were
 conducted on days without rain or strong wind. The distribution and
 population of intermediate egrets were recorded using binoculars (Leica 10
 × 40 BN, Solms, Germany) or spotting scopes (Leica 25–50 × 82) while
 traveling on farm roads adjacent to the main rice fields. The surveys were
 conducted between 06:00 and 12:00.
 On the regional scale, two
 teams (two observers per team) conducted intermediate egret surveys once a
 week from 1 May to 23 June 2018 for eight weeks, and each plot was
 investigated eight times for 40 plots. For each survey, the 40 fixed plots
 were targeted and the plots were divided into two groups of 20 each and
 randomly assigned to two teams for conducting the survey. The number of
 intermediate egrets that occurred within each plot during a 15-min
 observation period were recorded. While intermediate egrets were surveyed,
 the percentage of barley cultivation area under double cultivation was
 confirmed in the selected plots by simultaneous aerial photography and
 direct observation. During the same survey period on the regional
 scale, the survey points were randomly selected for each province and the
 distribution status was surveyed by visiting the plots centered on the
 selected points twice to investigate the distribution of intermediate
 egrets and rice-barley double crop areas on the national scale. The two
 teams alternated visits, visiting once each for two visits. The start and
 end times of the investigation were nearly identical for both teams. When
 the distribution of intermediate egrets and rice-barley double cropping
 area was confirmed, the coordinate values of the corresponding points were
 also confirmed. The field surveys did not require any licences or
 permits. To investigate whether the abundance of
 intermediate egrets is also influenced by distance to breeding colonies
 (Fasola et al., 2022), the distance to the nearest colony of intermediate
 egrets from the rice field where intermediate egrets were observed was
 determined. The coordinates of intermediate egret colonies, based on a
 nationwide survey of herons conducted by the Ministry of Environment in
 Korea, were extracted and used for analyses (NIBR,
 2020).
description: *** ## Description of the Data and file structure The files include raw
 tabular data in excel format (`"*.xlsx"`). * Three datasets with
 separate excel files, `"Data_regional_scale"`,
 `"data_national_scale"` and `"Location_IE_Colonies"`.
 * `"data_regional_scale` contains the following columns: * **ST**
 survey time (number/week) * **Site** survey site * **lon** longitude
 (decimal) * **lat** latitude (decimal) * **AB** percentage of area of
 barely (%) * **DC** distance from colonies (km) * **AIE** abundance of
 intermediate egrets (number of individuals/square kilometer) *
 `"data_national_scale"` contains the following columns: *
 **lat** latitude (decimal) * **lon** longitude (decimal) * **IE**
 presence/absence of intermediate egret (1/0) * **DC** presence/absence of
 double-cropping field (1/0) * `"Location_IE_Colonies"` contains
 the following columns: * **lon** longitude (decimal) * **lat** latitude
 (decimal) ## Sharing/access Information Links to other publicly accessible
 locations of the data: Was data derived from another source? **NO** If
 yes, list source(s): **-** ***