Fine root production and distribution in the tropical rainforests of south-western Cameroon: effects of soil type and selective logging

Abstract

Little information on fine roots that play an important role in nutrient cycling was available in tropical rainforests. Distribution of fine root production and effects of selective logging on root biomass and nutrient content change were studied in the tropical rainforests of south-western Cameroon. Twenty five root samples were excavated in each of two soil depths (0-10 and 10-25 cm) and in each of three undisturbed forests (Ebom, Ebimimbang and Nyangong) and one disturbed forest by logging, using a square metallic frame of 25 x 25 cm and 30 cm high. Root samples were categorized in three diameter classes: fine (<2 mm), small (2-5 mm) and medium roots (5-20 mm). Root biomass of three diameter classes and nutrients (N, Ca, Mg, K, Na and P) of the two first diameter classes were determined. Results have shown that total root biomass varied from 9.62 (Ebom) to 29.88 t ha-1 (Ebimimbang); those of fine roots decreased from Nyangong (7.43 t ha-1) to Ebom (1.74 t ha-1). In the top soil, the fine root biomass was 2 to 4 time lower in Ebom (1.43 t ha-1) than in other undisturbed forests (3.28 and 5.87 t ha-1). From 70 to 80% of fine root biomass were produced in the first 10 centimeters of soil depth. Nutrient amount in fine root biomass were also lower in Ebom than in Ebimimbang and Nyangong, except the P amount (kg ha-1) which remained high in Ebom. On the contrary, no pattern of nutrient content (g kg-1) changes among forest were found, except N and P that decreased from Ebom to Nyangong. Six years after logging, its effects on root biomass and nutrient changes were not significant and during this period, root production of disturbed forest was high due to rapid regeneration of forest particularly heliophilous tree species.