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Table 2 Relationships among variables of latitude, forest structural and functional attributes and biodiversity indices

From: Forest biodiversity, relationships to structural and functional attributes, and stability in New England forests

Relationships Linear/non-linear Equations R 2 p
Latitude-tree height Non-linear H = 16.80–4.83/EXP(0.35 × (Lat–45.96)^2) 0.79 < 0.0001
Latitude-total biomass Non-linear BM = 109.23 + 91.28/EXP(0.31 × (Lat–42.83)^2) 0.72 < 0.0001
Latitude-species richness Linear S = 178.85–3.18 × Lat 0.35 0.0002
Latitude-species diversity Linear SppD = 139.15–2.66 × Lat 0.66 < 0.0001
Latitude-Simpson’s index of diversity NA NA NA NA
Age-tree height Linear H = 1.33 + 0.20 × Age 0.65 < 0.0001
Age-total biomass Linear BM = −136.65 + 0.37 × Age 0.81 < 0.0001
Age-species richness Linear S = −19.60 + 0.87 × Age 0.54 < 0.0001
Age-species diversity Linear SppD = −14.60 + 0.55 × Age 0.59 < 0.0001
Age-Simpson’s index of diversity Non-linear SID = 0.89 + 609.65 × EXP(1–0.16 × Age) 0.56 < 0.0001
Height-total live biomass Linear BM = −90.60 + 16.52 × H 0.74 < 0.0001
Height-species richness Linear S = −4.82 + 2.90 × H 0.39 < 0.0001
Height-species diversity Linear SppD = −12.29 + 2.30 × H 0.66 < 0.0001
Height-Simpson’s index of diversity Linear SID = 0.75 + 0.0084 × H 0.30 0.0006
Species richness-total biomass Non-linear BM = 237.7 6 + 330.66 × EXP(1–0.038 × S) 0.45 < 0.0001
Species diversity-total biomass Non-linear BM = 203.08 + 780.00 × EXP(1–0.14 × SppD)) 0.61 < 0.0001
Simpson’s index of diversity-total biomass Linear BM = − 510.43 + 766.18 × SID 0.38 < 0.0001
  1. Note: p values from the F-test show that all regression models are statistically significant, given a significance level of 0.01. The values with bold fonts show the highest R2 coefficient of determination among the fitted regression curves in a group of the same independent variable