1 of 22

Contingent factors explain average divergence in functional composition over 88 years of old field succession

Adam Thomas Clark

Asst. Prof., University of Graz

October 2021

adam.clark@uni-graz.at; adamclarktheecologist.com

2 of 22

I. Analyzing Patterns

Question:

  • How do we identify important trends and drivers in complex ecological data?

​

Example:

  • 24 “Old” Fields
    • Abandoned from agricultural use between 1927 and 2016.
  • Surveyed since 1983
    • >2300 plots measuring vegetative cover and species-level plant biomass.

Introduction

Patterns

Mechanisms

Scales

Conclusions

3 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

Schizachyrium scoparium

(little bluestem)

Andropogon gerardii

(big bluestem)

C4 Grasses:

Annuals

C3 Grasses

Ambrosia artemisiifolia

(ragweed)

Erigeron canadensis

(Canadian horseweed)

Elymus repens

(quackgrass)

Poa pratensis

(Kentucky bluegrass)

Perennial Forbs:

Perennial Legumes:

Rudbeckia hirta

(black-eyed Susan)

Liatris aspera

(blazing star)

Lupinus perennis

(lupine)

Vicia villosa

(hairy vetch)

4 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

5 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

(Nature Ecology and Evolution 2019)

6 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

(U. of MN 2017)

Field Age, Years

7 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

(J. of Ecology 2019)

Field Age, Years

8 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

(J. of Ecology 2019)

Field Age, Years

Burning (1/3 Years)

9 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

(J. of Ecology 2019)

Soil Fertility (Total Soil Nitrogen)

Field Age, Years

10 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

(J. of Ecology 2019)

Drought (-1 SD Precipitation; +1 SD Temperature)

Field Age, Years

11 of 22

icloglog:

​

​

​

  • Transformation for Binomial (i.e. +/-) data, similar to logit
    • Coefficients interpreted as “hazard ratio”: i.e. fold change in likelihood of occurrence
  • Allows inclusion of “offset” term for different sampling intervals
  • But MUCH less stable than other methods

Introduction

Patterns

Mechanisms

Scales

Conclusions

12 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

(J. of Ecology 2019)

13 of 22

  • Fast colonization and low seedling mortality vs. slow colonization and high seedling mortality
  • Strong vegetative growth vs. weak vegetative growth

Introduction

Patterns

Mechanisms

Scales

Conclusions

14 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

(C. Clark & Tilman 2010)

-

+

+

-

+

-

+

+

+

-

+

+

15 of 22

Introduction

Patterns

Mechanisms

Scales

Conclusions

(Ecology 2015)

16 of 22

Broader Question:

  • How do I measure and predict long-term outcomes in ecological communities?
    • Empirically tractable
    • Theoretically justified
    • Suitable for a wide range of sites and systems
    • Applicable across scales

Introduction

Patterns

Mechanisms

Scales

Conclusions

17 of 22

(AmNat 2019)

(J. Ecology 2019)

temporal extent, years

Annuals

Ambrosia artemisiifolia

(ragweed)

Erigeron canadensis

(Canadian horseweed)

Schizachyrium scoparium

(little bluestem)

Andropogon gerardii

(big bluestem)

C4 Grasses:

stable

unstable

C3 Grasses

Elymus repens

(quackgrass)

Poa pratensis

(Kentucky bluegrass)

Age (years)

Abundance (% cover)

r0

Introduction

Patterns

Mechanisms

Scales

Conclusions

18 of 22

temporal extent, years

Annuals

Ambrosia artemisiifolia

(ragweed)

Erigeron canadensis

(Canadian horseweed)

Schizachyrium scoparium

(little bluestem)

Andropogon gerardii

(big bluestem)

C4 Grasses:

stable

unstable

C3 Grasses

Elymus repens

(quackgrass)

Poa pratensis

(Kentucky bluegrass)

Age (years)

Abundance (% cover)

r0

Introduction

Patterns

Mechanisms

Scales

Conclusions

(AmNat 2019)

(J. Ecology 2019)

19 of 22

temporal extent, years

Annuals

Ambrosia artemisiifolia

(ragweed)

Erigeron canadensis

(Canadian horseweed)

Schizachyrium scoparium

(little bluestem)

Andropogon gerardii

(big bluestem)

C4 Grasses:

stable

unstable

C3 Grasses

Elymus repens

(quackgrass)

Poa pratensis

(Kentucky bluegrass)

Age (years)

Abundance (% cover)

r0

Introduction

Patterns

Mechanisms

Scales

Conclusions

(AmNat 2019)

(J. Ecology 2019)

20 of 22

Clark et al. AmNat 2019

Clark et al. J. Ecology 2019

temporal extent, years

Annuals

Ambrosia artemisiifolia

(ragweed)

Erigeron canadensis

(Canadian horseweed)

Schizachyrium scoparium

(little bluestem)

Andropogon gerardii

(big bluestem)

C4 Grasses:

stable

unstable

C3 Grasses

Elymus repens

(quackgrass)

Poa pratensis

(Kentucky bluegrass)

Age (years)

Abundance (% cover)

r0

Introduction

Patterns

Mechanisms

Scales

Conclusions

21 of 22

empirical

neutral-OF

Levins-OF

Introduction

Patterns

Mechanisms

Scales

Conclusions

(AmNat 2019)

(J. Ecology 2019)

22 of 22

Conclusions:

  • Slow recovery in diversity may be driven by:
    • fire suppression
    • increased rates of atmospheric nitrogen deposition
    • increased leaf litter buildup
  • Slow recovery in productivity may be driven by:
    • increased frequency of dry years
    • changes in community composition related to burning and nitrogen
  • Results vary greatly depending on observational scale
    • can be leveraged to identify underlying processes
    • can also complicate efforts to interpret results based on limited data

Introduction

Patterns

Mechanisms

Scales

Conclusions