Carbon Stock as Related to Fallow Age in the Sudano-Guinea Savannahs of Ngaoundere, Adamawa, Cameroon

Aim/Objectives: In order to assess the fallow contribution on the carbon cycle and soil organic matter restoration, a study of the carbon dynamics was undertaken in fallow systems of 1, 2, 5 and 20 years old in the Ngaoundere savannahs of Cameroon. Methodology: Carbon stock was estimated in 100 m2 plot for shrubs, in 1 m2 plot for understorey, litter and earthworm casts, and 0.0625m2 plot for fine roots and soil. The experimental design was randomised complete block with three replicates. The age of fallows was the mean treatment whereas the plots were the replicates. Results: The results showed that the phytomass increased with fallow age, except that of shrubs. Soils and earthworm casts were the mean carbon sinks in the four fallows, with more than 55.61% and 26.24% of the total carbon stock respectively in the soil and earthworm casts. The total carbon stock increased with fallow age, from 34.54 in the young fallows to 154.52 tC.ha-1 in the old fallows. In the same way, vegetation and soil carbon increased with fallow age except that of shrub. The results showed that the carbon stock was influenced by floristic composition and spatial distribution of the vegetation, which related to fallow age. Conclusion: These preliminary results will contribute to the understanding of the impact of fallow age on the global carbon cycle and awareness in the conservation of fallows for the environment protection.

Recession of Tussilago farfara (L.) population from the agrocoenose as a result of cultivation abandonment. II. The effect of fallowing on shoot morphological properties and their biomass

The paper is concerned with changes in morphological properties of <em>Tussilag farfara</em> (L.) shoots in the abandoned agrocoenose. An increase in the shading and a decrease in the available space, both caused by overgrowing of two grass species <em>Agropyron repens </em> (L.) PB. and <em>Dactylis glomerata</em> (L.), resulted in considerable changes of all analysed properties. In the first three years after cultivation had been abandoned both shoot height and leaf blade size increased, but later a decrease in both was found due to a growing intensity of interspecific competition. Mean values of other properties decreased with the fallow age. Under the conditions of strong competition the variation of <em>Tussilago </em>shoots increased while their above and belowground biomass diminished.

Floristic variation in communities of fallow lands of the Podlaski Przełom Bugu mesoregion depending on the time of removal of fields from cultivation

<p>A study of fallow lands in the Podlaski Przełom Bugu (Podlasie Bug River Gorge) mesoregion was conducted over the period 2001–2004 in 77 villages belonging to 20 municipalities located in the Bug River valley along the stretch of the river from Terespol to Małkinia Górna. The aim of this study was to carry out a survey of vascular plants in fallow lands and to perform their multifaceted analysis. The study investigated quantitative and qualitative changes taking place in fallow vegetation with the passage of time from the abandonment of purposeful cultivation. Plant patches in 1–2-year, 3–6-year, 7–10-year and more than 10-year fallows were studied. Vascular plants of fallow lands within the study area comprise 442 species. 3–6-year fallows were richest in species (355). With increasing fallow age, the number of species decreased to 205 species in fallows older than 10 years. Hemicryptophytes dominated in plant communities of fallow lands. Therophytes were the co-dominant biological type in the youngest fallows. Chamaephytes and geophytes in all fellow age groups accounted for about 5%. Among vascular plants of fallow lands, native species dominated and their percentage increased with increasing fallow age, while at the same time the proportion of archeophytes decreased. With the increasing age of fallows, the proportion of species characteristic of forest communities also increased, whereas the percentage of segetal species simultaneously decreased. With the passage of time from the abandonment of cultivation, one can observe the evolution of plant cover of fallow fields from segetal communities towards less synanthropic communities.</p>

Community dynamics during early secondary succession in Mexican tropical rain forests

Stand structure dynamics during early secondary forest succession were related to mortality, growth and recruitment rates, and the dependence of these demographic processes on fallow age and initial stand structure attributes was evaluated. In 11 secondary tropical rain-forest sites (1.5–19 y) in Chiapas, Mexico, one plot of 10 × 50 m was established. Diameter and height were measured for all trees ≥ 1 cm dbh, and their survival, growth and recruitment was monitored over a 2-y period. Changes in stand structure were especially fast in the first 5 y of succession, and decreased rapidly afterwards, which resulted from similar stand-level changes in relative mortality, growth and recruitment rates. Demographic processes were negatively related with initial stand basal area, but independent of initial tree density. Basal area was a better explanatory variable of the among-stand variability in these rates than fallow age. Results suggest that asymmetric competition and resulting patterns of tree-thinning are major driving forces determining secondary forest successional pathways. Fallow age per se is a compound variable reflecting community organization at a certain point along the successional axis, while community structure drives succession. Sudden mass mortality among dominant species in some stands showed that early secondary forest succession is not always a gradual and unidirectional process.