Data from: A thorny issue: woody plant defence and growth in an East African savanna

1. Recent work suggests that savanna woody plant species separate into two
different strategies based on their defences against herbivory; a low
nutrient/high chemical defence strategy and a nutrition paired with mostly
architectural defences strategy. The concept that chemical and structural
defences can augment each other and do not necessarily trade-off has
emanated from this work. In this study we examine woody plant defence
strategies, how these respond to herbivore removal and how they affect
plant growth in an East African savanna. 2. At three paired long-term
exclosure sites with high browser and mixed feeder densities at Mpala
Ranch, Kenya we investigated: a) whether defences employed by the dominant
fine- and broad-leaved woody savanna species form defence strategies and
if these align with previously proposed strategies, b) how nine key plant
defence traits respond to herbivore removal and c) how effective the
different defence strategies are at protecting against intense herbivory
(by measuring plant growth with and without herbivores present). 3. We
identified three defence strategies. We found a group (1) with high N,
short spines and high N-free secondary metabolites, a group (2) with high
N, long spines and low N-free secondary metabolites and a group (3) with
moderate N, no spines and low N-free secondary metabolites (most likely
defended by unmeasured chemical defences). Structural defences (spine
length, branching) were generally found to be induced by herbivory, leaf
available N increased or did not respond, and N-free secondary metabolites
decreased or did not respond to herbivory. Species with long spines
combined with increased ‘caginess’ (dense canopy architecture arising from
complex arrangement of numerous woody and spiny axis categories) of
branches maintained the highest growth under intense browsing, compared to
species with short spines and high N-free secondary metabolites and
species with no spines and low N-free secondary metabolites. Synthesis. At
our study site, structural traits (i.e. spines, increased caginess) were
the most inducible and effective defences against intense mammalian
herbivory. We propose that high levels of variability in the way that
nutrient and defence traits combine may contribute to the coexistence of
closely related species comprising savanna woody communities.