1. Understory plant responses to uneven-aged forestry alternatives in northern hardwood-conifer forests Kimberly J. Smith 1, William S. Keeton 1, Mark J. Twery 1,2, and Donald R. Tobi 1 1 Rubenstein School of Environment and Natural Resources, University of Vermont 2 USDA Forest Service, Northeastern Research Station

2.  Structure-based forestry ( Franklin et al. 2002; Keeton 2006) : Managing for multiple structural conditions representative of natural successional dynamics www.dred.state.nh.us

3.  Disturbance-based forestry (Mitchell et al. 2002; Seymour et al. 2002) : Developing silvicultural systems based on the scale and pattern of natural disturbances Stovall 2006

4. The Vermont Forest Ecosystem Management Demonstration Project (FEMDP)  Structure and disturbance-based forestry practices can:  Sustain a broad array of biodiversity and ecosystem functions  Provide for profitable timber management

5.  Single-tree selection (STS) and group selection (GS)  Increased structural retention  Modeled after the scale and pattern of natural disturbance (based on the findings of Seymour et al. 2002)  Structural Complexity Enhancement (SCE)  Promote accelerated development of late-successional forest characteristics:  Increasing vertical and horizontal heterogeneity  Elevating large snag and coarse woody debris (CWD) densities  Reallocating basal area to larger diameter classes  Enhance ecosystem services, including:  Late-successional wildlife habitat (McGee et al. 1999)  Carbon storage (Harmon et al. 1990)  Riparian function (Keeton et al. 2007) Silvicultural Treatments (FEMDP)

6.  Monitoring indicators of biodiversity response, including:  Birds  Small mammals  Amphibians  Soil invertebrates  Vegetation © Al Sheldon FEMDP Research

7.  Even-aged treatments  Plantation forestry (Ramovs and Roberts 2005)  Clearcutting (Gilliam et al. 1995; Halpern and Spies 1995; Liu and Ashton 1999)  Uneven-aged treatments  Single-tree and group selection (Jenkins and Parker 1999; Scheller and Mladenoff 2002; Kern 2006)  Variable retention (Halpern et al. 2005)  Experimental canopy gaps (Collins and Pickett 1988; Gray and Spies 1997) Previous Research www.gov.ns.ca

8.  Uneven-aged, low-intensity silvicultural systems can maintain understory plant diversity and support late-successional species  Retaining and enhancing stand structural complexity can increase understory plant diversity  Plant responses are influenced by interactions between canopy structure, soils, and climate processes Hypotheses

9.  Study Areas:  Mount Mansfield State Forest  Jericho Research Forest  Paul Smith’s College  Mature, northern hardwood stands with a documented history of previous timber management Methods

10. Mt. Mansfield State Forest  13 vegetation quadrats (1 m 2 )  4 soil subplots (2 m 2 )  2 ha treatment units  0.1 ha permanent plots (overstory structure) 1 m 2 (vegetation) 2 m 2 (soils) Experimental Design

11. Data Collection  Palmer Drought Severity Index (PDSI): multiple climatic parameters condensed into a single index PDSI Temperature Evapotranspiration Precipitation Soil moisture loss Soil moisture recharge Runoff

12. Habitat guilds as defined by Ramovs and Roberts (2005): Analysis www.nrs.fs.fed.us  Late-successional  Early-successional  Intermediate

13.  Diversity:  Hill’s series of diversity indices (Hill 1973)  Species richness  Exponential Shannon Index  Reciprocal Simpson Index  Abundance:  % cover by species Response variables

14. Diversity and abundance:  Linear mixed effects model  fixed effects– treatment, site, year  random effects– plots, units  ANOVA models  Pre- to post-harvest change of unit level means  Test for differences among treatments  Analyses performed for all species and by habitat guilds Analysis of Treatment Effects

15. Compositional changes:  Non-metric multidimensional scaling (NMS)  interpret compositional patterns among treatment units  Multi-response permutation procedure (MRPP)  pre- to post-harvest differences within treatments  differences among treatments before and after harvest  Locally impacted species Analysis of Treatment Effects

16. Sub-analysis of soil properties and overstory structure  Five soil variables:  % OM, % N, Ca, P, pH  Linear mixed effects model  fixed effects– treatment, site, year  random effects– plots, units  covariates- % OM, % N, Ca, P  Pre- to post-harvest % change  Soil properties  Curtis’ relative density (RD)  Diversity and abundance responses  Explanatory variables related to ordination axes in NMS www.forestryimages.org

17.  Palmer Drought Severity Index (PDSI)  Period 1 (PDSI_1) = July-September, previous year  Period 2 (PDSI_2) = April-June, current year  Standardized understory responses to +/- unit mean  Simple linear regressions Analysis of Moisture Stress

18. Results: Effects of Treatment  Mixed effects model  Understory responses significantly affected by treatment*time interaction

19. Effects of Treatment: All Species  Richness: p = 0.032  SCE > CON  Shannon Index: p = 0.004  SCE > CON

20. Effects of Treatment: Late-successional Species  Richness: p = 0.012  SCE > GS  Shannon Index: p = 0.009  SCE > CON

21. MRPP: A = 0.009 p = 0.320 CON GS SCE STS (44.8%) (33.2%) Pre-harvest Effects of Treatment: Species Composition

22. MRPP: A = 0.026 p = 0.142 CON GS SCE STS (38.2%) (25.1%) Post-harvest Effects of Treatment: Species Composition

23. Locally Extirpated Species ANOVA: p = 0.07

24. Locally Extirpated Species

25. Effects of Soil Properties and Overstory Structure  Mixed effects model:  Significant effect of treatment  Soil covariates not significant  Exceptions: Intermediate species- % OM and % N  Correlations:  Unit level (coarse scale) and plot level (fine scale)  Δ relative density related to Δ responses  Δ soil properties generally not related to Δ responses

26. Effects of Soil Properties and Overstory Structure CON GS SCE STS Pre-harvest (33.2%) (44.8%) Axis 2 RD: τ = 0.439 %OM: τ = -0.336

27. CON GS SCE STS Post-harvest (38.2%) (25.1%) Effects of Soil Properties and Overstory Structure Axis 1 RD: τ = 0.368 %OM: τ = -0.362 %N: τ = -0.336 Axis 2 %OM: τ = 0.441 %N: τ = 0.388 Ca: τ = 0.520 P: τ = 0.494

28. Effect of Moisture Stress VT NY  PDSI_2 (April-June of current year)  Not related to understory responses in controls or treatments  Exception: Late-successional richness GS: p = 0.012, r 2 = 0.747 STS: p = 0.018, r 2 = 0.703 SCE: p = 0.024, r 2 = 0.602  PDSI_1 (July-September of previous year)  Not related to understory responses

29. Discussion  Uneven-aged, low-intensity silvicultural systems with increased structural retention maintain understory plant species diversity All Species

30. Discussion  Post-harvest increases in diversity (Gilliam et al. 1995; Halpern and Spies 1995; Jenkins and Parker 1999)  Increases in early-successional or ruderal species may mask the loss of late-successional species (Halpern and Spies 1995)  Results of this study:  Compositional differences not significant  Pre- to post-harvest, within treatments  Post-harvest, among treatments

31. Discussion  Level and spatial pattern of retention may influence loss of species following harvest ANOVA: p = 0.07

32. Discussion  Uneven-aged, low-intensity silvicultural systems with increased structural retention support late- successional species Late-successional Species

33. Discussion  Previous studies:  Plant diversity increases with light availability (e.g. Brosofske 2001)  Results of this study:  SCE:  Lower light availability  Greater light heterogeneity  Greater increases in diversity  Increasing post-harvest stand structural complexity may lead to increased plant diversity Stovall 2006

34. Discussion  Late-successional northern hardwood forests characterized by:  heterogeneous light environment  microsite variability (Scheller and Mladenoff 2002)  Retaining or enhancing stand structural complexity may increase diversity:  light heterogeneity  microhabitat diversity  retaining canopy

35. Discussion  Moisture availability influences patterns of understory vegetation (Huebner et al. 1995; Hutchinson et al. 1999; Kolb and Diekmann 2004)  Results of this study:  Drought index correlated to late-successional richness in treatment units, but not in controls  Canopy removal may increase susceptibility of understory to drought stress  Understory plant responses are influenced by interactions between canopy structure, soils, and climate processes

36. Discussion VT NY  Post-harvest diversity increases in SCE units may be partially due to drought recovery Richness Shannon Diversity Simpson Diversity Percent Increase of Understory Responses in SCE Units

37. Discussion  Soil nutrient availability influences patterns of understory vegetation (Kolb and Diekmann 2004; Fraterrigo et al. 2006)  Harvesting overstory can affect soil nutrient availability (Johnson et al. 1997; Elliott and Knoepp 2005)  Results of this study:  Overstory-vegetation relationships consistently significant  Soil-vegetation relationships highly variable  Understory plant responses are influenced by interactions between canopy structure, soils, and climate processes

38. Conclusions  Uneven-aged, low-intensity silvicultural treatments with increased structural retention can maintain understory plant diversity and support late-successional species in northern hardwood-conifer forests during the initial post-harvest recovery period  Treatments that enhance stand structural complexity may increase understory plant diversity by increasing the heterogeneity of light and microsite variability  Level and spatial pattern of retention may be important to preserving understory plant species  Plant responses are primarily influenced by changes in overstory structure

39. Management Implications  Sustainable forest management:  Maintains biodiversity and ecosystem functioning  Provides for timber harvest  Best approaches for conserving understory plant diversity:  Retain post-harvest structure  Retain biological legacies (see Franklin et al. 2002)  Enhance stand structural complexity

40. Acknowledgements Vermont Monitoring Cooperative  USDA McIntire-Stennis Forest Research Program  USDA National Research Initiative  Northeastern States Research Cooperative Other helpful folks:  Field crews of 2001-2006  Alan Howard, UVM statistical counseling clinic

41. Questions?