Chronosequence dataset Ecology (in review).xlsx

<i>Nothofagus</i> species (southern beeches) are the only widespread ectomycorrhizal canopy trees in the humid temperate forests of the southern hemisphere. Researchers working in South America, New Zealand and Australia have come to different conclusions about the causes of spatial and temporal partitioning of landscapes between ectomycorrhizal (ECM) <i>Nothofagus</i> and arbuscular mycorrhizal (AM) trees. We used two-stage landslide chronosequences to examine the environmental drivers of successional trajectories of the mycorrhizal makeup of south-temperate rainforests. We used structural equation modelling (SEM) to address two hypotheses: (1) soil N:P ratios mediate the relative abilities of <i>Nothofagus</i> and AM trees to colonize landslide scars, and (2) soil C:N ratios determine the ability of AM trees to invade the understories of established stands and potentially replace <i>Nothofagus</i>. Hypothesis (1) was not supported, as mean annual temperature (MAT) was the only significant predictor of the mycorrhizal makeup of early-successional stands. Hypothesis (2) was supported, as soil C:N was the sole significant predictor of the mycorrhizal makeup of understories of established forests, being negatively correlated with AM representation in understoreys. Soil C:N in beneath established forests was in turn influenced by MAT, by % <i>Nothofagus</i> overstorey dominance in established forests, and by soil N and N:P ratios beneath early-successional stands. Marked continental disparities in soil parent materials and typical C:N ratios underlie the well-documented differences between south-central Chile and Tasmania in the dependence of <i>Nothofagus</i> regeneration on exogenous disturbance. Our results leave unanswered questions about the circumstances that favour <i>Nothofagus</i> capture of disturbed sites, but support modelling studies that have identified soil C:N ratio and inherent site nutrient status as key controls on AM/ECM dynamics in later successional stages.