When archives are missing, deciphering the effects of public policies and climate variability on the Brazilian semi-arid region using sediment core studies

Phytoliths from soil surfaces and water reservoirs of the Brazilian semi-arid Caatinga

“…The highest number of globular echinate occurred in 1991, whereas globular granulate peaked in 1996. A satellite image acquired in 1991 (Ledru et al, 2020) and the significant rise in tree pollen taxa between 1990 and 1997 at the same studied core (Ledru et al, 2020) indicated the return of a natural vegetation cover and a reduction in the extent of bare soil. That recovery was associated with the abandonment of cultivated land due to law changes (National Institute for Colonization and Agrarian Reform INCRA Law 97,844 July 19, 1989).…”

“…A chronological framework was established to date sediments using short-lived radionuclides measurements. Age-depth models are fully described in Ledru et al (2020). The base of lake sediment dated to 1963 ± 8.5 yr AD, in the Acaraú-Mirim reservoir, and 1959.5 ± 11.5 yr AD (facies 1 and 2) in the Araras reservoir.…”

“…Samples 9, 10, and 11 showed mainly saddle, followed by bilobate types. They were produced by Poaceae and could be related to degradation or anthropic pressure in more closed environments, when grasses, instead of woody plants, arise (Ledru et al, 2020).…”

“…In 1983, the phytoliths revealed again evidence of an open environment, which could be related to the severe drought of 1982-83. According to pollen studies at the same core, the vegetation became more open between 1980 and 1988 (Ledru et al, 2020). The highest number of globular echinate occurred in 1991, whereas globular granulate peaked in 1996.…”

“…The sediment size of samples may be favorable to the accumulation of phytoliths (finer particles, such as silt and clay), or may, when coarse (sandy), allow their percolation to deeper layers (Coe et al, 2017). However, the main sediment size in this core is fine-grained, from top to bottom (0-60 cm) (Ledru et al, 2020). In the readable layers, from 1962 until 1970, there was an increasing frequency of globular granulate and globular echinate, and a decreasing frequency of GSSC.…”