In recent decades, a paradigm shift in forest management and associated policies has led to greater emphasis on harvest practices that retain mature, overstory trees in forest stands that would otherwise be clearcut. While it is often assumed that the maintenance of compositional and structural complexity, such as that achieved through retention forestry approaches, will also mitigate negative impacts to functional diversity, empirical evidence of this relationship is sparse. We examined the effects of an aggregated retention system on taxonomic and functional diversity in a regenerating aspen-dominated forest. Sampling was conducted along transects arranged to capture the transition from harvested (regenerating) forest to mature, unharvested forest (both intact forest stands and 0.1 ha retention aggregates). We then assessed the magnitude and distance of edge effects on multiple indices of taxonomic and functional diversity as well as functional identity.  Twelve years after harvest, the distance and magnitude of edge effects on functional and taxonomic diversity did not differ between the two unharvested patch sizes (intact vs. aggregate); however, intact forest exhibited greater resistance to edge effects and greater depth of edge influence into harvested areas for some traits compared to aggregates. Analyses relying on functional traits were generally applicable across sites within a highly variable forest type, and our results demonstrate the promise of using functional traits to assess management impacts on plant diversity across a landscape. Aggregates maintained some functional attributes associated with interior forest and influenced adjacent regeneration. However, trends in some traits (i.e. shade tolerance and seed mass), particularly in the seedling layer, suggest aggregates of this size provide primarily edge habitat.

We characterized the understory woody community by sampling two strata: 1) seedlings and small shrubs (“seedling layer”) and 2) saplings and large shrubs (“sapling layer”). Cover for the seedling layer (all woody stems <1 m in height) was estimated to the nearest 1% (or nearest 0.1% if cover < 1%) in paired, 1 m² subplots located 2 m perpendicular to and on either side of transects at each 10-m distance and nested within the plot used for quantifying larger vegetation (Figure 1c). Species abundance in the sapling layer was measured using a combination of two plot sizes (Figure 1c). Species and DBH (1.37 m) were recorded for larger stems (2.54 cm ≥ DBH ≤ 10 cm) in circular 5 m radius plots (78.5 m²) centered on each 10-m distance mark along transects. Smaller stems with height ≥ 1 m and DBH < 2.54 cm were measured 15 cm above the root collar in circular, 1.26 m radius (5 m²) plots nested within the larger plots.

Here, we have provided cover for seedling and small shrub species in the "seedling layer" at each 10-m sampling point (an average of observations from the paired, 1 m² plots located at each distance).  We have also provided biomass for woody species observed in the "sapling layer" estimated with allometric equations (Perala and Alban 1993) using the diameter measurements described above.

Excel spreadsheet contains two tabs:

1) Sapling layer biomass: Data are biomass (Mg/ha) estimated for the sapling layer at each transect distance.

2) Seedling layer cover: Data are the average of the percent cover estimated at two, paired 1 m² plots located at each transect distance.