care4cmodel (version 1.0.3)

survival_weibull: Weibull-Based Estimates of Stand Survival

Description

Estimates the probability of a forest stand to survive a period t after its establishment, based on the Weibull-Method published by Staupendahl (2011) Forstarchiv 82, 10-19.

Usage

survival_weibull(t, alpha, s_100)

Value

The probability to survive up to t = 100

Arguments

t

Time in years after stand establishment

alpha

Shape parameter. According to Staupendahl, Values < 1 indicate a high risk at young ages, alpha = 1 indicates an indifference of the risk to t (exponential distribution), values > 1 indicate high risk at old ages, where 1 < alpha < 2 means a degressively increasing, alpha = 2 a constantly increasing, and alpha > 2 a progressively increasing risk.

s_100

Survival probability up to t = 100

Details

The parameter s_100 represents the survival probability after t = 100 years, and alpha is the shape parameter, indicating the risk profile of the stand (type) of interest.

Examples

  # Calculations for Common oak, European beech, Norway spruce, Douglas fir,
  # and Scots pine with parameters after Staupendahl and Zucchini (AFJZ 2011)
  t <- seq(0, 120, 5)
  survival_weibull(t, alpha = 2.75, s_100 = 0.971) # oak
  survival_weibull(t, alpha = 1.76, s_100 = 0.967) # beech
  survival_weibull(t, alpha = 2.78, s_100 = 0.726) # spruce
  survival_weibull(t, alpha = 3.11, s_100 = 0.916) # Douglas
  survival_weibull(t, alpha = 2.45, s_100 = 0.923) # pine