Scale-dependent invasion patterns and community assembly in the Southeastern US flora Jason Fridley UNC – Chapel Hill

Acknowledgements Collaborators: Becky Brown, Eastern Washington University Mike Palmer, Oklahoma State University John Bruno, UNC Peter White, UNC Bob Peet, UNC Alan Weakley, UNC Data: Carolina Vegetation Survey North Carolina Botanical Garden Funding: National Parks Ecological Research Fellowship Andrew W. Mellon Foundation (NPS, NPF, ESA)

Exotic species Contributions of community and landscape ecology and landscape ecology Do biotic/community properties contribute to invasion resistance?Do biotic/community properties contribute to invasion resistance? Are exotic species ecologically unique?Are exotic species ecologically unique? Do exotic species alter assembly processes in native communities?Do exotic species alter assembly processes in native communities? Do exotic/invasive species favor particular environments?Do exotic/invasive species favor particular environments? Are communities saturated with species?Are communities saturated with species?

Pattern and Process in Species Invasions

Community ecology Landscape ecology Biogeography Scaling rules?

Scaling rules of species richness... the species-area curve

How do scaling rules represent process? Biotic constraints Environmental variance Dispersal constraints

Carolina Vegetation Survey: 1988 to present 0.01 – 1000 m 2

Carolina Vegetation Survey 0.01 – 1000 m 2

Carolina Vegetation Survey 0.01 – 1000 m m 2 range: 0 to 11 species1000 m 2 range: 6 to 180 species

Fine-scale Z values: ~ – 1000 m 2 95% within 0.22 and 0.54

Body size and species pools

Z values 0.1 – 0.2? Intermediate scales: large stands, watersheds, landscapes, natural areas Poor data!

Large-scale upturn Between provinces Within province Dispersal-driven Ecological equivalents Rosenzweig 1995

Full-scale curves

Provinces – too big? Consequences for species invasions?

Alternative hypothesis: environmental texture w/ M. Palmer and P. White Soils and geomorphology High D Climate Low D Schimper’s Laws?

Scaling rules for species invasions? Does exotic species richness exhibit the same scale dependencies?

Scaling rules for species invasions? If exotics are less dispersal limited, should the upturn be at a different scale or exist at all? Do exotics observe the same environmental template? Are native communities saturated, thereby further constraining exotic establishment?

Null hypothesis If the average distribution of a native and exotic species is the same......then exotics should be a consistent proportion of a total species pool. All species Exotics only

Hotspots? Coldspots? All species Deviations from expected curves Exotics (null)

Example 1: NC agroecosystem

Example 2: NC montane river 180 species, 54 exotics

Example 3: NC piedmont forest

Example 4: NC piedmont forest

1 – 10 km 2 Deviance from expected exotic richness Exotic enrichment Exotic impoverishment

Species-area data, Floras project Log10 Species Richness Log10 Area (ha) M. Palmer et al. Total species Exotics

What is special about km 2 ? Oosting Plot 1 km

What is special about km 2 ? NCBG lands 1 km Riparian systems - the magical ingredients: environmental favorableness (sun, nutrients) environmental favorableness (sun, nutrients) (many exotics selected for these habitats) (many exotics selected for these habitats) disturbance: no biotic resistance disturbance: no biotic resistance dispersal assistance: flow and flooding dispersal assistance: flow and flooding

Scaling rules for species invasions Broad-scale scaling rules (watershed and above) appear remarkably similar for natives and exotics Rich are getting richer Finer-scale patterns usually diverge from those of natives, in a habitat-dependent way Causes?

How well are exotic species distributed within habitats? Within regions, exotics are clustered within certain habitats. high propagule pressure high propagule pressure high disturbance rates high disturbance rates favorable environments favorable environments But how are they distributed within those habitats? More uniform? (widespread, previously empty niche?) More clustered? (only occur in rare but ideal patches?)

How well are exotic species distributed within habitats? Distributions of exotic species with nested plot data: What proportion of scale-specific occurrences are exotic? A A AA A A A A A A A A B A C A C B D A A A A A A A A A A B A A C B A A D A A A C 4 natives and 1 exotic 20% exotics

How well are exotic species distributed within habitats? Distributions of exotic species with nested plot data: What proportion of scale-specific occurrences are exotic? A A AA A A A A A A A A B A C A C B D A A A A A A A A A A B A A C B A A D A A A C 4 natives and 1 exotic 50% exotics 12.5% exotics 20% exotics

Mountain rivers S. Appalachians

Exotic occurrences, Riparian plots % exotic of total species occurrences % exotic species at each scale Area (m 2 )

Cornfield borders North Carolina

Exotic occurrences, Cornfield borders % exotic of total species occurrences Area (m 2 ) % exotic species at each scale

Montane upland forests, S. Apps

Exotic occurrences, Montane uplands % exotic of total species occurrences Area (m 2 ) % exotic species at each scale Most frequent exotics: Poa compressa Microstegium vimineum Rosa multiflora Festuca ovina Stellaria media

Exotic occurrences, Piedmont uplands % exotic species at each scale Lonicera japonica Other upland exotics: Ligustrum sinense Celastrus orbiculata Elaeagnus umbellata

Exotic Occurrence Across Scales % exotic of total species occurrences % exotics in US (3138 / 18150)

Exotic Occurrence Across Scales % exotic of total species occurrences Area (m 2 ) Agricultural borders Montane riparian corridors S App upland forests % exotics of species pool % exotics in US (3138 / 18150)

Conclusions: Southeast US plant invasions S App upland forests HOTSPOTS : uncommon relative to total land area uncommon relative to total land area exotics better dispersed at fine scales exotics better dispersed at fine scales propagule pressure, disturbance, propagule pressure, disturbance, soil cations soil cations no signal of biotic resistance no signal of biotic resistance COLDSPOTS : relatively common—for now few exotic species; even rarer occurrences upland, shady, acidic, isolated biotic resistance or TIME? how long can cold spots stay cold? Montane riparian corridors Agricultural borders

Vernal (March – early April) Late Vernal (late April – June) Summer (June - Sept) Limiting Similarity – Phenology? Flowering period

Vernal (March – early April) Late Vernal (late April – June) Summer (June - Sept) Red maple! Limiting Similarity – Phenology? Flowering period

Vernal (March – early April) Late Vernal (late April – June) Summer (June - Sept) Limiting Similarity – Phenology? Flowering period