Two-compartment models for describing temporal variation in the effective leaf area index of Robinia pseudoacacia stands on the Loess Plateau

Leaf area index (LAI) is a key parameter in many ecological models and its phenology significantly affects on net ecosystem production in deciduous forests. We examined trends in LAIe (effective leaf area index) using two-compartment models to test effects of stand age and slope aspect on seasonal rates of LAIe increase (k₁) and decrease (k₂). LAIe measurements were acquired from 24 sample plots over five months and used to develop robust predictive models for modeling LAIe dynamics. Generally, the stands’ k₁ values were substantially greater than their k₂ values. The LAIe increased rapidly between leaf emergence and saturation, and then lower slowly from leaf saturation to senescence. The strongest increase in LAIe was observed in 11- to 15-year-old stands on shady slopes (k₁ = 4.76) and in young stands (<10 years) on sunny slopes (k₁ = 3.94), but k₂ values were largest in mature stands. The trees on shady slopes generally had higher k₁ and lower k₂ values than those on sunny slopes, except in the youngest stand. The results showed that two-compartment models can robustly describe leaf growth and loss rates in black locust stands, and that both stand age and aspect both strongly affect the rate and magnitude of changes in LAIe during the growing season. Hence, the two-compartment model is recommended as an effective method when monitoring the LAIe quantitative dynamics of broad-leaved forest.