Soil catenas, tropical deforestation, and ancient and contemporary soil erosion in the Peten, Guatemala

The Petexbatun region of Guatemala's Peten tropical forest lowlands has bee n largely deforested since the early 1980s as landless peasants have turned even national parks into milpas. The soils of these tropical forest, karst landscapes are known mainly from small-scale maps and archaeological inves tigations. This paper investigates soil catenas and natural slope professes from the region's last virgin tropical forests and compares these with cat enas and processes on slashed and burned slopes. Soils were sampled and ana lyzed for physical, fertility, and taxonomic measures. This primary forest toposequence forms a typical downward translocation catena, with the thicke st soils (>200 cm) in depressions, the thinnest soils on shoulder slopes, a nd moderately thin soils on the crests and backslopes. Most crest and slopi ng soils are Lithic Rendolls and contain simple O-A-C horizon sequences, an d most soils have little sign of either eluviation or illuviation. A few de eper soils on the slopes are Vertic Rendolls and have moderate slick-enside s, whereas footslopes and seasonally drained depressions are well developed Vertisols. The primary forest soil catena was compared with two slash-and- burn milpas, one with comparable slopes and one with steeper slopes. The co mparably sloped milpa had soil thicknesses that were 7.9 to 13.8 cm thinner , truncated horizons, and physical evidence of erosion. The steeper milpa h ad soil thicknesses that were 11.1 to 18.2 cm thinner and also had truncate d horizons and physical evidence of erosion. Where ancient Maya terraces (L ate Classic;ca. 550 to 830 A.D.) are present in the slash-and-burn landscap e, an average of 25 to 46.5 cm soil remain upslope and 9.3 to 16.1 cm remai n downslope. The findings show high soil truncation rates and erosion to be drock in a decade in one place, though ancient Maya terraces are still hold ing 2.7 to 3.6 times more soil than the surrounding hillslopes. Despite hig h modern erosion, lake sediments show surprisingly low soil losses in the M aya Late Classic during the period of the most intensive land use. In contr ast, studies at Copan, Honduras and in the northern Peten, where terrace ev idence is scant, show high rates of erosion during this period.