# Intraspecific Responses of Seedlings of Three Vachellia Species to Simulated Browsing Reflect Adaptive Traits of Older Life Stages

## TL;DR

This study examines how seedlings of three Vachellia species respond to simulated herbivory, revealing adaptive traits that reflect responses to herbivory and fire.

## Contribution

The study is the first to investigate intraspecific responses to herbivory at the seedling stage in African savanna Vachellia species.

## Key findings

- Clipping reduced the relative height growth of V. nilotica and V. tortilis seedlings.
- V. karroo seedlings showed strong height regrowth, suggesting adaptation to fire in association with herbivory.
- Spine mass fraction increased in V. tortilis seedlings from one population after clipping.

## Abstract

Intraspecific variation in adaptation to herbivory has been studied in juvenile (sapling) and adult (reproductive) stages of woody species in African savannas, but has not been studied at the early seedling stage. We hypothesized that, among Vachellia species commonly occurring in African savannas, spinescence increases and growth rate decreases after herbivory, but these responses would be expressed most strongly in populations with slower growing seedlings. Seedlings of
V. nilotica
,
V. tortilis, and V. karroo were grown from seeds of different populations within the Southeastern Coastal Hinterland geomorphic province of South Africa. Seedlings were grown in a greenhouse and clipped at three intensities when they were 3 months old. Responses were determined for seedlings harvested 3 months later. Statistically significant (p < 0.05) interacting effects of clipping and population were rare. Clipping increased the spine mass fraction of
V. tortilis
seedlings from one population. Clipping reduced the relative height growth of
V. nilotica
and
V. tortilis
seedlings, while populations of
V. nilotica
and V. karroo differed in relative growth rate. We interpret weak vertical regrowth of
V. nilotica
and
V. tortilis
seedlings as reflecting adaptation to herbivory reported for saplings and adults in other studies. Conversely, we interpret strong height regrowth of V. karroo seedlings as reflecting adaptation to fire in association with herbivory or shading, as reported for older plants elsewhere. The study highlights the importance of studying plant traits relevant to herbivory in different populations and at different life stages to better understand adaptations to herbivory.

Intraspecific variation in adaptation to herbivory has been studied in juvenile (sapling) and adult (reproductive) stages of woody species in African savannas, but has not been studied at the early seedling stage. Seedlings of
Vachellia nilotica
,
V. tortilis, and V. karroo were grown from seeds of different populations, clipped at three intensities when 3 months old, and responses measured when 6 months old. We interpret weak vertical regrowth of
V. nilotica
and
V. tortilis
as reflecting adaptation to herbivory and interpret strong height regrowth of V. karroo as reflecting adaptation to fire in association with herbivory.