Slash-and-burn effects on fine root biomass and productivity in a tropical dry forest ecosystem in México

Abstract

Abstract We examined the effects of slash-and-burn of a tropical dry forest (TDF) and pasture establishment on fine root (≤1 mm) biomass and productivity. We also determined the seasonal changes of fine roots. The study was conducted in the coast of Jalisco, Mexico where the dominant vegetation is tropical dry forest. Two 33 m×100 m experimental plots with undisturbed TDF were slashed-and-burned by local farmers. Two adjacent plots with TDF were established as control sites. After slash-and-burning of the experimental plots, these were seeded with three pasture grasses along with two local maize varieties. Root sampling was initiated in March 1993 and roots were collected monthly until February 1994. Eight soil samples were collected randomly in each plot at each sampling date to a depth of 10 cm with a soil corer. Each soil core was divided in three depths: 0–2, 2.1–5, and 5–10 cm. Roots were separated in two size categories: fine (≤1.0 mm) and small (1.1–5 mm). Fine roots were separated into live and dead. Productivity of fine roots for each depth was estimated from the biomass data. Live fine root biomass in the 0–10 cm profile decreased due to burning but 47% of the fine root mass loss was at the 0–2 cm depth. Dead fine root biomass diminished significantly only at this depth. Total fine root productivity and mortality was 42–45% higher in TDF than in pasture in the first 5 cm of soil. About 86 and 76% of the fine root productivity in TDF and pasture, respectively, occurred in the first 5 cm of soil. Fine root turnover rates were high and similar in both ecosystems. Live fine root biomass in TDF and pasture increased in response to rainfall, particularly in the first 5 cm of soil. Mean annual live fine root biomass was significantly greater in TDF than in pasture only at the 0–2 cm depth. Mean biomass per cm of soil was greater in the first 2 cm of the profile in both TDF and pasture and it represented one-third of the fine root biomass in the 0–10 cm profile. There were no significant differences of small roots (1.1–5.0 mm in diameter) due to treatment, seasonality or dynamics. Based on root turnover and root production, our results indicate that the relative importance of belowground processes for C supply to the soil in this TDF is greater than the aboveground return.