Seed Bank Dynamics of an Oregon Montane Meadow: Consequences of Conifer Encroachment and Implications for Restoration

Transcription

1 Seed Bank Dynamics of an Oregon Montane Meadow: Consequences of Conifer Encroachment and Implications for Restoration Nicole Lang College of Forest Resources University of Washington 16 March 2006

2 Study Site: Bunchgrass Meadow, OR

3 Study Site: Willamette National Forest, Oregon

4 Study Site: Dominant Vegetation at Bunchgrass Overstory: Abies grandis (Grand Fir) Pinus contorta (Lodgepole pine) Understory: Smilacina stellata Achlys triphylla Galium oreganum Anemone oregana Asarum caudatum Meadow: Festuca idahoensis Bromus carinatus Achillea millefolium Fragaria vesca Lupinus latifolius

5 Study Site: Conifer Encroachment at Bunchgrass Meadow

6 Study Site: Potential Consequences of Conifer Invasion Loss of floral diversity supported by meadows Loss of habitat for wildlife Loss of recreational opportunity

7 Study Site: Plot Layout and Treatment Designation 1988 thinning boundary Cut + broadcast burn Cut only (cut + pile/burn or cut + remove) Plots to age (2, 3, 8, 10)

8 Seed Banks 101: Accumulation of viable seed in the soil Transient vs. persistent Space vs. Time Disturbance Implications for restoration mmm, seeds

9 General Seed Bank Model: (Adapted from Simpson et al., 1989) DISPERSAL BUD BANK VEGETATIVE PROPOGATION SEED PRODUCTION VEGETATION PREDATION ABOVEGROUND SEED BANK SEEDLING BANK SAPLING BANK PREDATION SEED RAIN (DISPERSAL) Fire Wind Water Animals Mechanical Passive SOIL SEED BANK GERMINATION Light Temperature Water Oxygen Fire Mechanical Chemical FAILED GERMINATION PATHOGENS PHYSIOLOGICAL DEATH DEEP BURIAL

10 Conceptual Diagram of Seed Bank Dynamics at Bunchgrass ruderal species Old forest Young forest Aboveground vegetation Open meadow Soil seed bank meadow species ruderal species forest species meadow species ruderal species forest species meadow species ruderal species

11 What are my objectives?: To investigate composition of the soil seed bank along a chronosequence from open meadow to closed forest To examine whether patterns of density, diversity and richness can be explained by variation in forest structure or ground layer vegetation.

12 Methods: Data Collection Overstory (summer 2003): tree measurement Canopy cover (summer 2004): digital images Seed Bank (spring 2004): soil samples Understory (summer 2004): % cover by species

13 Methods: Overstory Sampling -Plot Establishment -Tree measurement -Tree aging

14 Methods: Overstory Sampling Plot 3 - Live and Dead Trees Y Axis X Axis

15 Results: Overstory Sampling Number of stems/ha 350 Abies grandis 14 Pinus contorta 12 Other species Number of stems/ha Establishment date (year)

16 Methods: Data Collection Overstory (summer 2003): tree measurement Canopy cover (summer 2004): digital images Understory (summer 2004): % cover by species Seed Bank (spring 2004): soil samples

17 Methods: Canopy Photos

18 Methods: Data Collection Overstory (summer 2003): tree measurement Canopy cover (summer 2004): digital images Seed Bank (spring 2004): soil samples Understory (summer 2004): % cover by species

19 Methods: Field Sampling May 22-25, 2004

20 Methods: Seed Bank Sampling Plot 2 Stand Map 50 subplots in each plot Stratified random sampling in each plot according to basal area 12 additional subplots in open meadow areas

21 Methods: Sampling Layout x 10 m subplot 1m quadrat for plant cover and tree seedling density soil sampling location canopy cover measurement x 6 m understory subplot

22 Methods: Greenhouse UW Biology greenhouse Germination flats Sub-irrigated using capillary mat Germinants marked upon emergence, removed upon identification

23 Results!

24 Methods: Data Collection Overstory (summer 2003): tree measurement Canopy cover (summer 2004): digital images Seed Bank (spring 2004): soil samples Understory (summer 2004): % cover by species

25 Methods: Understory Sampling - Percent cover was visually estimated for each species present. -Four quadrats were averaged for each subplot.

26 Stellaria crispa Campanula scouleri Arenaria macrophylla Results: Seed Bank Primary Seed Bank Species Frequency (%) Agrostis scabra Carex pensylvanica Epilobium watsonii Lactuca muralis Ranunculus uncinatus Fragaria spp. Galium triflorum Senecio sylvaticus Circaea alpina Achillea millefolium

27 Results: Primary Seed Bank Species and Occurrence in the Vegetation vegetation seed bank Frequency (%) Agrostis scabra Carex pensylvanica Epilobium watsonii Lactuca muralis Ranunculus uncinatus Fragaria spp. Galium triflorum Senecio sylvaticus Circaea alpina Achillea millefolium Arenaria macrophylla Campanula scouleri Stellaria crispa

28 Conclusions: 1. The seed bank composition is dominated by ruderal species, with limited contribution from meadow and forest species.

29 Lactuca muralis Melica subulata Cirsium callilepis oregonense Results: Understory Vegetation Dominant Understory/ Meadow Vegetation Frequency (%) Fragaria spp. Carex pensylvanica Osmorhiza chilensis Viola glabella Arenaria macrophylla Anemone deltoidea Bromus vulgaris Hieracium albiflorum Achillea millefolium Iris chrysophylla Galium triflorum Anemone oregana Erigeron aliceae Adenocaulon bicolor Smilacina stellata Campanula scouleri Elymus glaucus 0 Galium oreganum

30 Results: Dominant Understory/Meadow Vegetation and Occurrence in the Seed Bank vegetation seed bank Frequency (%) Fragaria spp. Carex pensylvanica Osmorhiza chilensis Viola glabella Arenaria macrophylla Anemone deltoidea Bromus vulgaris Hieracium albiflorum Achillea millefolium Iris chrysophylla Galium triflorum Anemone oregana Erigeron aliceae Adenocaulon bicolor Smilacina stellata Campanula scouleri Elymus glaucus Galium oreganum Melica subulata Cirsium callilepis oregonense Lactuca muralis

31 Conclusions: 1. The seed bank composition is dominated by ruderal species, with limited contribution from meadow and forest species. 2. The seed bank does not closely resemble the above-ground vegetation.

32 Results: 300 Subplots Open Open meadow meadow (Class 0,1) Young Young forest forest (Class 2-5) Old Old forest forest (Class 6) DCA Axis Gnaphalium microcephalum Fragaria spp. Seedbank species Ruderal species Meadow species Forest species Danthonia intermedia DCA Axis Galium triflorum Lactuca muralis Circaea alpina Senecio sylvaticus Epilobium watsonii Agrostis scabra Achillea millefolium 0 Carex pensylvanica DCA Axis 1

33 Results: Total richness and density Richness Density Species richness (no. species/sample) All species p = a Open meadow a Young forest b Old forest All species p = Open meadow Young forest Old forest Density (no. germinants/sample)

34 Results: Meadow, Forest, and Ruderal Species Richness Density 2 Meadow species p = Meadow species p = Species richness (no. species/sample) Forest species p = a a b Forest species p = 0.09 Ruderal species Ruderal species p = p = Density (no. germinants/sample) 1 0 Open Young meadow forest Old forest Open Young meadow forest Old forest 0

35 Conclusions: 1. The seed bank composition is dominated by ruderal species, with limited contribution from meadow and forest species. 2. The seed bank does not closely resemble the above-ground vegetation. 3. Few meadow species persist under meadow or forest vegetation.

36 Results: Density of Exotic and Native Species Density (no. germinants/sample) Native species p = Open meadow Young forest Old forest Exotic species p < a Open meadow a Young forest b Old forest

37 Results: Composition Dominant Seed Bank Species by Encroachment Stage 2500 Ranunculus uncinatus 2000 Epilobium watsonii mean seeds per sq m Agrostis scabra Fragaria spp. Lactuca muralis Carex pensylvanica 0 open young forest old forest

38 Conclusions: 1. The seed bank composition is dominated by ruderal species, with limited contribution from meadow and forest species. 2. The seed bank does not closely resemble the above-ground vegetation. 3. Few meadow species persist under meadow or forest vegetation. 4. Density of exotic species is greatest in old forest.

39 Results: Overstory Total germinants Density (no. germinants/sample) Density of live trees (no./ha) Basal area of live trees (m 2 /ha)

40 Conclusions: 1. The seed bank composition is dominated by ruderal species, with limited contribution from meadow and forest species. 2. The seed bank does not resemble the aboveground vegetation. 3. Meadow species do not persist under meadow or forest vegetation. 4. Density of exotic species is greatest in old forest. 5. Forest structure has a limited impact on seed bank composition.

41 Implications: What does this mean for restoration? Contribution of target species from the seed bank will be limited. Focus should be on outside propagule sources. Seeding of target species Vegetative spread of clonal species from existing meadows Soil conditions may determine species establishment Dependent on type of disturbance

42 Implications:

43 Acknowledgements: Thank you! Committee Members: Joe Antos, Martha Groom, Charlie Halpern Field and Greenhouse Assistance: Ryan Haugo, Jim Lutz, Michael Frank, Markus Koch, Kyle Smith, James Freund, Jess Niederer, Jenn Leach, Melisa Holman, Dan Perrakis, Janine Rice, Deb Brown, Doug Ewing, Katie McGowan, Becky Icenogle, Cara Nelson, Shelley Evans Funding and Logistical Support: Joint Fire Sciences Program, McKenzie River Ranger District, HJ Andrews Experimental Forest Academic and Personal Support: Halpern lab group, CFR faculty and pals, my parents

44 Questions?