Aboveground net primary productivity in temperate forests of Río Magdalena basin, Mexico City, Mexico

Background/Question/Methods

Aboveground net primary productivity (ANPP) is a very important ecological process and evidences ecosystem health. At local scale, soil resource availability is one of the main direct factors that control ANPP, being temperature and humidity important as indirect factors. Río Magdalena basin (RMB) in Mexico City is affected by human disturbances, but it has a huge biodiversity and provides many ecosystem services. Our objective was to estimate ANPP, and to identify its regulating factors in the RMB. ANPP was estimated for the period 2007-2008 through litterfall (LF) and aboveground biomass increments (ABI), in ten 50 x 50 m plots located at the main forest types: four in Pinus hartwegii (P) and Abies religiosa (A), and two in Quercus rugosa (Q). Litterfall was monthly collected using randomly distributed 11 litter traps in each plot. ABI was calculated by dbh initial and final change of every tree >10 cm dbh found in each plot, and then extrapolated with allometric equations. Temperature and humidity were daily measured every month at 30 cm above soil surface; C/N ratio and mineral nitrogen were determined at 10 cm soil depth, as indicators of nitrogen availability in soil. 

Results/Conclusions

Average ANPP was 10.7 (±1.13), 10.5 (x), and 5.89 (±0.81) Mg ha^-1 year^-1 for A, Q and P, respectively. ABI was the most important component of ANPP, because it comprised more than 50% of ANPP in all forests. Our results were lower in comparison to another similar forests, probably because forests in RMB are found in successional stages. Minimum temperature was positively correlated with ANPP (r²=0.615, P<0.007), and maximum temperature showed a negative correlation (r²=0.534, P<0.016). Average temperature and humidity, C/N ratio, and mineral nitrogen were not correlated with ANPP. Our results show that N is not a limiting resource for RMB forests, as other authors had mentioned for other temperate forests, and significant relationship of minimum and maximum temperature with ANPP is more probably explained by their effect on photosynthesis instead of their effect on nutrient availability.