Local chronologies of one-seeded and intermediate hawthorn (Crataegus monogyna, C. xmedia) in Poland

Two hawthorn species occur in Poland: the one-seeded hawthorn (Crataegus monogyna) and the Midland hawthorn (C. laevigata). There is also a natural hybrid of these two, the intermediate hawthorn (C. xmedia Bechst.). All these species occur in the study area. The analyses were performed on 9 hawthorn populations (Table 1). Two populations are natural hybrids, intermediate hawthorn (C. xmedia, ST and LB), the remaining seven plots are populations of the one-seeded hawthorn (C. monogyna). Two populations (LB and ST) are located in northern Poland, four populations (MA, CI, ZB and DB) are located within the lowlands of central Poland, and three populations are located within mountain areas: WA in the Sudetes, and WG and LE in the Carpathians. The ST study plot is located at the lowest elevation (45 m a.s.l.), and the LE plot is located at the highest elevation (540 m a.s.l.) (Table 1). Samples were taken using a Pressler borer from a total of 192 trees (359 samples). Tree-ring width was measured down to 0.01 mm. The average tree ring width in the studied hawthorn populations ranged from 1.42 to 3.25 mm/year (Table 2). Using well-established cross-dating methods, nine local chronologies were compiled, spanning from 45 to 72 years. EPS values >0.85 are noted from 1972 to 2020/2021 (Table 2).

Files with data of hawthorn tree-ring width and hawthorn local chronologies (for example: LB chronology): 1st column - year, 2nd column and next - tree-ring width of individual trees in mm (tree1, tree2, …), next column - local chronology in mm (bold numbers), last column - number of samples in a given year.