Kasvutingimuste lineaarse muutumise mõju uurimine puistu kõrguse kasvukõverale simulatsioonide abil männikutes / Simulated change of stand height curves as the result of linear change of growth conditions in the case of Scotch Pine stands

The height growth curves of Scotch Pine (Pinus sylvestris L.) stands were simulated for stands with initial height asymptote H_∞ 15 m, 25 m and 35 m and with linear change p of the potency of growth conditions 0.5% yr^-1, 0.2% yr^-1, 0.1% yr^-1 , -0.2% yr^-1 and with no change as the base. Different models to transmit the changing growth potential into stand growth were used: changing the efficient length of growth year replacing the stand age t with the expression t(1 + tp) with fixed H_∞ in variant (1b) or calculating the current asymptote H_∞,t as the expression H_∞(1 + tp) corrected for asymptotic approaching the species specific asymptote sup(H_∞). Current annual increment CAI in the last case was calculated using the equations CAI_t = f(t, H_∞,t) in variant (3ct), CAI_t = f(H, H_∞,t) in variant (4ch) and CAI_t = f(H, H_∞,t)*(1+p/2) in variant (4chb). The height H_t in the last 3 cases was calculated as ascending sum of CAI_t. Figures of the functions H_t = f(t, H_∞) and CAI_t = f(H, H_∞) indicated the last as more informative about the changes in the shape of curves. The results of approximation of simulated curves with five different functions indicated the possibility of their modeling using traditional functions and fixed value of height asymptote. The fit was the poorest for variants 4ch and 4chb. The function for conversation the apparent growth curve based on unique height measurements into real one and vice versa was deduced for version 1b. The need to make distinct difference between the past, present and future growth in growth modeling was underlined.