The secret to success How do tree seedlings overcome the herbivore bottleneck?
Nicola Stevens, Sally Archibald, Wayne Twine Predicting the future of savannas?
The future range of Colophospermum mopane But…savannas are not at equilibrium with climate
“Ecosystems uncertain”
Fire Herbivory
Archibald and Hempson 2016 Environmental filters across the savanna rainfall gradient?
Water Herbivory Fire Strength of of effect Strength
MEAN ANNUAL RAINFALL Environmental filters act on different demographic stages?
Water Herbivory
Fire Strength of of effect Strength
MEAN ANNUAL RAINFALL Towards generalisation - picking representative species
Osborne et al (in review)
Does herbivory filter species? Are there distinct patterns in high vs low herbivore environments? Herbivory treatments 3 4 1 4 Control month month month month • 1 month Control 2 Control 2 4 • 2 months month month month • 3 months • 4 months 2 3 3 1 1 month month month month month • control
3 4 1 4 Control month month month month
DIRECT: Is herbivory an clear environmental filter • Surviving herbivory
INDIRECT: What does herbivory do to a seedling • Resprout response • Thorns • Branching When can a seedling survive herbivory?
40 days 94 days
53 days 88 days
69 days 89 days
70 days 99 days Arid species can tolerate herbivory first
The variation of rates depends on where a plant is from along the rainfall gradient
All species reach 80% survival in a similar time frame (~ 97 days) – but get there at different rates Recovering from herbivory as a seedling
* Growth 1 * month after herbivory
* * * • The recovery depends on when browsing occurs • Common response * * * between species * • Why?
* * * * * * * Herbivory increases branching
Combretum collinum Combretum hereonse Combretum molle
Senegalia mellifera Senegalia nigrescens Senegalia caffra
Vachellia erioloba Vachellia exuvialis Vachellia sieberianna
C. mopane Clipped Control Clipped Control Herbivory can increase spine length * Conclusions
Herbivory is a direct filter up until 3 months • Rainfall
• Elevated CO2
Important indirect filter - Changes plant structure - Reducing height - Increasing branching - Synergistic effects with fire
Next step • Similar experiments with different enviro filters • Herbivory from a seedling perspective • High vs low herbivory environments • Encounter rates • Re-visitation rates THANKS
- Craddock Mnthini for incredible plant growing skills - Wits Rural Facility staff and management The legacy of herbivory
Growth 15 months after herbivory
*
No treatment legacy • 1 month impact Two responses to clipping • Extreme deficit compared to control • Strong recovering * *