Succession and Nutrient Dynamics Following Forest Cutting and Burning in Amazonia

Abstract

Plant establishment, plant mortality, vegetation productivity, nutrient accumulation, and nutrient leaching were studied during the first 5 yr of succession following the cutting and burning of a forest plot in the upper Rio Negro region of the Amazon Basin. The speed and vigor of forest regeneration following disturbance of this type provide a measure of the recuperative potential of this ecosystem.The study plot (0.09 ha) was dominated by forbs during the I st yr and then by the pioneer tree species Cecropiaficifolia Snethlage during year two. Tree mortality exceeded establishment during the 3rd yr because the C. ficifolia trees died nearly in unison. During the 4th yr, tree density increased sharply as successional and forest tree species grew in the space vacated by C. ficifolia. The canopy was dominated at that time by the pioneer species Vismia japurensis Reich. and Vismia lauriformis (Lam.) Choisy. By the 5th yr, all establishment space had apparently been preempted: there were only 0.07 new establishments/m 2 during year five, while 95% of the trees present at the end of year four survived through the 5th yr.There were 56 tree species (~2m tall) present on the site after 5 yr. More than halfofthese were primary forest species. Primary forest species were most common in the understory. These trees averaged >I m in growth height each year and should eventually grow into the canopy. Hence, it appears that most individuals that will participate in the aggrading phase of forest development were already present on the site within 5 yr of burning.Biomass was only 66 g!m 2 at the end of the I st yr, but ""I 000 g!m 2 were added in each subsequent year. The standing crop of biomass (shoot and root) at 5 yr was 4840 g!m 2 , a value 16% that of the mature forest which occupied the site prior to cutting. Approximately 27% of the dead trunk and branch biomass from the pre-existing forest remained on the site after 5 yr. Litter production increased each year from 39 g!m 2 (year one) to 825 g!m 2 (year five) and tended to be inversely related to rainfall. Total aboveground production was highest for the 5th yr (1940 g!m 2 ) and was probably close to a maximum for the site. Total live-plant nutrient stocks after 5 yr, as a percentage of the precut forest stocks, were 15% for N, 23% for P, 39% forK, 48% for Ca, and 45% for Mg.A large increase in the leachate concentrations of K, Mg, and N03 occurred during the first 2 yr following burning. By the 5th yr, concentrations were not significantly different from those in the undisturbed forest. After 5 yr soil nutrient levels were also similar to those of the preburn forest. Overall, nutrient losses apparently were not great enough to destroy the site's ability to return eventually to a state similar to that which existed prior to disturbance. This does not mean that a more severe treatment, such as conversion of forest to pasture, would not affect the regrowth ability of a site.

Nitrogen dynamics in Amazon forest and pasture soils measured by 15N pool dilution

“…This is also consistent with the fact that the high NH 4 + and NO 3 À concentrations disappeared by 8.5 months after the burn, when pasture grass had become established. In other tropical forest systems, the period of elevated soil N availability after clearing and burning can range from a few months (Matson et al, 1987) to several years (Uhl and Jordan, 1984) and depends on the timing of the regrowth of forest plants.…”

Community structure of vascular plants in treefall gaps and fire-disturbed habitats in the Atlantic rainforest, southern Bahia, Brazil

“…Hence, species richness of trees have been reestablished very early during succession. The rapid recovery in richness and some other community parameters were also observed in slash-and-burned plots in tropical forests, where a rapid stocking of pioneer and primary forest trees follows a short phase of dominant grasses and forbs (Uhl & Jordan 1984, Castellani & Stubblebine 1993.…”

“…(Chrysobalanaceae) and Ecclinusa ramiflora Mart. (Sapotaceae), were recorded in the burned area, showing that species that built up the mature forest were established near the beginning of the succession (Uhl & Jordan 1984). In fact, the species composition in the burned area was different from the other three habitats, while the treefall gaps did not differ from the understorey areas.…”

“…There was no difference in the mean number of individuals observed in the burned area and the other environments, which goes against the idea that a larger number of individuals could establish after fire disturbance due to the greater availability of nutrients and the liberation from above-and below soil level competition (Uhl & Jordan 1984, Sundarapandian & Swamy 1996. A majority of the studies on post-fire regeneration have evaluated areas that had previously been cut (slash and burn agriculture), a situation that produces a cleaner post-burning environment.…”

“…Fire can completely alter the floristic composition and community structure of a tropical forest area through: i) initial elimination of the herbaceous-shrub layer and the advanced regeneration plants (Uhl et al 1989); ii) the sudden flush of nutrients derived from burning of large quantities of organic material (Vinha et al 1983, Uhl & Jordan 1984; and iii) the survival or resprouting of more resistant species (Uhl & Jordan 1984, Kauffman 1991.…”