Comparative analysis of carbon stock and litter nutrient concentration in tropical forests along the ecological gradient in Kenya

Abstract

The study determined the carbon stocks and litter nutrient concentration in tropical forests along the ecological gradient in Kenya. This could help understand the potential of mitigating climate change using tropical forest ecosystems in different ecological zones, which are being affected by climate change to a level that they are becoming carbon sources instead of sinks. Stratified sampling technique was used to categorize tropical forests into rain, moist deciduous and dry zone forests depending on the average annual rainfall received. Simple random sampling technique was used to select three tropical forests in each category. Modified consistent sampling technique was used to develop 10 main 20 m × 100 m plots in each forest, with 20 2 m × 50 m sub-plots in each plot. Systematic random sampling technique was used in selecting 10 sub-plots from each main plot for inventory study. Non-destructive approach based on allometric equations using trees’ diameter at breast height (DBH), total height and species’ wood specific gravity were used in estimating tree carbon stock in each forest. Soil organic carbon (SOC) and litter nutrient concentration (total phosphorus and nitrogen) were determined in each forest based on standard laboratory procedures. The results indicated that, whilst trees in rain forests recorded a significantly higher (p < 0.001) DBH (20.36 cm) and total tree height (12.1 m), trees in dry zone forests recorded a significantly higher (p < 0.001) specific gravity (0.67 kg m⁻³). Dry zone tropical forests stored a significantly lower amount of total tree carbon of 73 Mg ha⁻¹, compared to tropical rain forests (439.5 Mg ha⁻¹) and moist deciduous tropical forests (449 Mg ha⁻¹). The SOC content was significantly higher in tropical rainforests (3.9%), compared to soils from moist deciduous (2.9%) and dry zone forests (1.8%). While litter from tropical rain forests recorded a significantly higher amount of total nitrogen (3.4%), litter from dry zone forests recorded a significantly higher concentration of total phosphorus (0.27%). In conclusion, ecological gradient that is dictated by the prevailing temperatures and precipitation affects the tropical forests carbon stock potential and litter nutrient concentration. This implies that, the changing climate is having a serious implication on the ecosystem services such as carbon stock and nutrients cycling in tropical forests.

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