Electronic Supplementary Material – Jones CC and del Moral R

Supplement S1 Effects of planting time and sample date on seedlings per plot. Values indicate mean numbers of seedlings per plot. Error bars indicate ± 1 SE. Plots from Age Class II were excluded because they did not occur in October plots. Filled circles indicate plots seeded in July 2001 and open circles indicate plots seeded in October 2001. No seeds of Tiarella were planted in the October plots in Age Class III so plots from this age class are excluded from the July plot graph. No seeds of Vaccinium were planted in July plots.

It is not certain what led to these differences in germination patterns between planting dates. There were no differences between July and October plots in any measured topographic or environmental variable. However, the seeds in July plots had undergone both artificial stratification and a natural winter before sampling began. It is likely that extra time is needed to break seed dormancy for some of these species. The species with the least seed dormancy, Abiesand Chamerion, did not differ in germination rates between planting dates. This would also explain why numbers of seedlings per plot increased over time for several species in the October plots.

Supplement S2Topography, soil, and vegetation characteristics of seed plots. Different superscript letters indicate significant differences among age classes based on comparison of ranks following Kruskal-Wallis tests.

Age Class
Variable / I / II / III / IV / H / P
N / 10 / 10 / 30 / 30
Elevation (m) / 1327c / 1244c / 1077b / 1060a / 64.68 / <0.0001
Slope (deg.) / 9.0b / 3.0a / 4.8ab / 5.8ab / 10.94 / 0.01
Heat Load1 / 0.84 / 0.88 / 0.87 / 0.83 / 6.62 / 0.09
Soil moisture (%)2 / 5.6a / 19.9a / 60.6b / 69.0b / 51.52 / <0.0001
Organic matter (%) / 0.7a / 4.5a / 86.6b / 78.0b / 45.69 / <0.0001
Soil pH / 5.6c / 5.1bc / 4.1a / 4.4ab / 41.54 / <0.0001
Understory cover (%) / 26.7a / 165.5c / 104.2b / 117.0b / 39.28 / <0.0001
Canopy cover (%) / 0a / 81.0b / 78.3b / 67.7b / 30.57 / <0.0001
Species richness / 7.9b / 6.4b / 4.0a / 5.6b / 26.37 / <0.0001
Litter (%) / 1.5a / 76.5c / 23.2b / 60.5c / 45.70 / <0.0001

1Based on slope, aspect and latitude following McCune and Keon (2002)

2By mass