减少剧情标题和地图之间的距离

Question

library(raster)
france <- getData('GADM', country = 'FRA', level = 1)

plot(france, main = "my.title")

par(mfrow = c(1,2))
plot(france, main = "my.title")
plot(france, main = "my.title")

如何缩小my.title和地图之间的距离？我尝试过，但这只会增加地图的大小

par(mar = c(0, 0, 0, 0))
par(mfrow = c(1,2))
plot(france, main = "my.title")
plot(france, main = "my.title")