Results and Discussion

Seedling Growth, Leaf Area, and Soil Moisture Vary by Treatment and Stand Structure

Figure 11. Estimated mean values for (a) seedling height growth (cm), (b) leaf area (cm²), and (c) volumetric water content (VWC %) across treatment types. Treatments are grouped into Control, Dense, and Independent stands, and further categorized by seedling location: Plot center (Green), redirected stemflow (Red), or no redirected stemflow (blue). Points represent group means with horizontal error bars denoting ±1 standard error (SE). Dashed vertical lines indicate the mean.

One-way ANOVAs followed by Tukey’s HSD tests were used to assess treatment effects on seedling growth, leaf area, and soil moisture. Assumptions for parametric testing were confirmed using Shapiro-Wilk normality tests and residual diagnostics.

Seedling Growth:

Growth differed significantly by treatment (p < 0.001), with the most pronounced increase observed in the Lone Snag without Redirected Stemflow (LSw/oRS) group. Seedlings in this group grew 3.5× taller than those in the Open Control Group (OCG; 95% CI: 2.19–5.69), and 2.67× taller than those in Lone Snag with Redirected Stemflow (LSwRS; 95% CI: 1.43–4.99). Growth was also 1.52× higher than in Dense Snag without Redirected Stemflow (DSw/oRS; 95% CI: 1.01–2.27), and 1.76× higher than in Lone Snag with Redirected Stemflow (LSwRS; 95% CI: 0.98–3.17). These findings emphasize that snag configuration and stemflow redirection strongly influence early seedling development.

Leaf Area:

Leaf area varied significantly across treatments (p = 0.007), with the largest leaves observed in seedlings near dense snags without redirected stemflow. These seedlings had 1.58× larger leaf area than those in the control group, with a 95% confidence interval of 1.19 to 1.98. Seedlings in dense plots with redirected stemflow had similarly large leaves (1.57×), and those planted near independent snags without redirected stemflow showed a 1.55× increase. However, only the dense snag treatment without redirection was statistically significant based on its confidence interval. Redirected stemflow treatments did not consistently reduce leaf area—leaves were still larger than the control—but the confidence intervals overlapped in most comparisons. These results suggest that uninterrupted stemflow in dense snag environments may enhance foliar development, though the positive effect may be context-dependent and not universally driven by stemflow alone.

Soil Moisture:

Soil moisture also differed by treatment (p < 0.001), with the highest retention in the Dense Snag Plot Center (DSPC), which held 1.3× more water than the Lone Snag Plot Center (LSPC; 95% CI: 1.25–1.35). Overall dense stand snags had higher amounts of soil moisture compared to control and lone snags groups. Moisture availability did not align with the highest seedling growth. These results suggest that while dense canopy structure supports water retention, microsite conditions near isolated snags, with access to more light and unaltered stemflow, impacted seedling growth more then average soil moisture values alone. Further analysis of soil moisture results is needed to understand the direct impact of rain events on soil moisture distrobution.

Table 4. Statistically significant pairwise comparisons (Tukey’s HSD post-hoc tests) for soil moisture, seedling growth, and leaf area across treatment types. Each comparison lists the direction of the effect (greater or lesser) between treatments, the mean difference (diff), and the associated p-value. Only comparisons with p < 0.05 are shown. Results highlight that soil moisture was consistently higher in dense snag treatments, while seedling performance was greatest near isolated snags without redirected stemflow. Leaf area also increased in these microsites.

Stemflow and Thoughfall values vary by Stand Structure

Figure 12. Mean stemflow (SF) and throughfall (TF) contributions (L/m²) across common rain event sizes in dense stands and independent snags. Rain events are categorized as Small (≤5 L/m²), Medium (5–14 L/m²), and Large (≥32 L/m²). Shape indicates event size: downward triangle for small, square for medium, and upward triangle for large. Error bars represent standard error (SE) and match the color of the corresponding point.

Rainfall partitioning, specifically, throughfall and stemflow, was analyzed using two-way ANOVAs with treatment type (open vs. dense stands) and rain event size (small, medium, large) as fixed factors. Both models revealed significant main effects and interactions (p < 0.001), justifying the use of Tukey’s HSD post-hoc comparisons. Assumptions of normality were met for throughfall but not for stemflow, as assessed with Shapiro-Wilk tests. However, ANOVA was still applied for stemflow due to large, balanced sample sizes and the absence of extreme outliers. Effect sizes and 95% confidence intervals were used to interpret treatment differences.

Table 5. Differences in throughfall and stemflow between open and dense snag areas across rain event sizes.

Throughfall:

Throughfall differed significantly by treatment and rain event size, with a significant interaction between the two factors (p = 0.044). Post-hoc comparisons showed that open areas consistently received more throughfall than dense stands, particularly during low-volume events. During small events (≤5 L/m²), throughfall in open areas was 1.35× greater than in dense stands (95% CI: 1.15–1.59), and during medium events (5–14 L/m²), the difference was 1.34× (95% CI: 1.16–1.55). During large events (≥32 L/m²), the difference dropped to 1.09× and was not statistically significant (95% CI: 0.91–1.31). These results suggest that canopy cover in dense stands may intercept or redistribute rainfall, especially during smaller events when total input is limited.

Stemflow:

Stemflow also significantly varied by treatment and rain event size (p < 0.001), with a strong interaction effect. Open areas near lone snags produced substantially more stemflow than dense stands across all event sizes. The largest difference occurred during small events (≤5 L/m²), where stemflow was 10.2× greater in open areas (95% CI: 5.86–17.74). During medium events, the effect size was still substantial (4.05×; 95% CI: 2.54–6.48), and even during large events (≥32 L/m²), open areas showed 2.36× more stemflow than dense stands (95% CI: 1.42–3.92). These findings indicate that open microsites with isolated snags enhance stemflow concentration, likely due to reduced canopy interception and better funneling of water along snag surfaces.

Conclusion

Planting seedlings near snags, particularly in the root flare zones of isolated snags, was associated with stronger seedling performance compared to seedlings planted in open areas or between snags in dense clusters. This suggests that microsite conditions near isolated snags, where stemflow is not redirected, may support better growth. However, the benefit does not appear to be caused by stemflow alone. Although stemflow was greater in lone snag areas, these locations had lower average soil moisture than dense stands. This indicates that other factors, such as sun exposure or localized microsite traits, may also influence seedling growth.

Dense snag plots retained higher soil moisture throughout the season, likely due to reduced evaporation under residual canopy structure. Despite this, seedling growth was lower in these areas. This shows that while moisture retention may be enhanced under dense cover, it does not necessarily translate to better seedling outcomes. Redirecting stemflow reduced seedling growth in both dense and isolated snag plots, suggesting that moving water away from the snag base may limit microsite quality for regeneration.

Together, these findings support a targeted salvage strategy that reduces snag density while retaining isolated snags, maximizing the ecological benefits of both moisture retention and microsites that enhance seedling regeneration. This approach may improve post-fire recovery by promoting conditions that support resilient forest regeneration. It would be beneficial to implement management practices that help to maintain snags within reason, in order to promote adequate growing conditions for seedlings.

Page updated

Report abuse