Comparing distance-independent and distance-dependent competition indices for Picea abies

• Competition between individual trees is important for forest growth. Modeling the underlying interactions is difficult and sometimes not possible. Consequently, simplified competition indices are often used as a proxy. Several studies have shown that including competition indices into growth models will improve accuracy. However, there is no consensus on which or what type of indices work well. Here, we compare several indices of two qualitatively different types: distance-independent and distance-dependent indices. These indices are incorporated into a log-linear growth model and tested against 5-year diameter growth data collected from three Norway spruce plots that each have different fertilization treatments. We find that although distance-dependent indices performed better, distance-independent indices can also perform well; R2adj = 0.66 vs. 0.62 for the best indices in each category. We find that Bella’s index to be the best distance-dependent index (the index depends on distance between competitors and their diameters) and Reineke’s index to be the best distance-independent index (this index depends on the mean quadratic diameter and density in the stand). We also find that the performance ranking of indices is consistent across three different fertilization treatments.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Skogsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Forest Science (hsv//eng)

Nyckelord

Competition index

Modelling

Picea abies

Diameter growth

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)