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competition from graminoids can reduce alpha diversity by as much as 50%. They
argue that the presence of a dense, but transitory, proteoid cover is a key factor
maintaining high alpha diversity in fynbos communities. Effectively, proteas
create regeneration gaps by shading out the vigorously resprouting graminoid
layer, thereby providing safe sites for seedling establishment after fire.
It is interesting to contrast this interactive view of fynbos dynamics, where the
species mix matters, with one based purely on the interaction between fire and
vital attributes of species (see also Keith et al. 2007 for Australian heathland
examples). For example, van Wilgen & Forsyth ( 1992 ) used Noble and Slatyer's
( 1980 ) vital attributes to classify 210 fynbos species in the Swartboschkloof area of
the south-western Cape, focusing particularly on the timing of critical life history
events such as age to first flowering, life span, and longevity of the seedbank. They
used this trait analysis to evaluate how species would respond to changes in fire
regime. They concluded that only four species would be eliminated by frequent
fires (5-year intervals): two serotinous proteas, and two forest trees. The two
protea species would also be vulnerable to long intervals between fires (due to
death of adults and simultaneous death of seeds, a common hazard for serotinous
species, see Chapter 9 ) with another 16 species possibly vulnerable depending on
the longevity of their seedbank. Thus, with the exception of serotinous proteas,
fynbos species appear to be remarkably resilient to short fire intervals because they
survive vegetatively, or have persistent seedbanks, and/or have short maturation
times. Studies of recovery of stands cleared of alien trees, after different periods of
invasion, reveal that many fynbos species have sufficiently long-lived seedbanks to
survive long (> 30 yr) intervals between fires (Holmes & Cowling 1997b ; Holmes
2002 ). However, seedbank persistence varies among sites, with more persistent
seeds in mountain fynbos, while in lowland fynbos long-lived obligate seeders had
transitory seedbanks and may therefore be extirpated by long fire return intervals
(Holmes 2002 ). Holmes & Newton ( 2004 ) studied patterns of seed persistence
across diverse growth forms in a seed burial experiment. They found surprisingly
short-lived seedbanks (< 2 yrs) in most of the small-seeded species, which suggests
either very high rates of dispersal into burned patches or experimental conditions
that do not mimic natural cues for promoting seed dormancy. The latter seems
more likely.
Event-dependent effects on postfire recovery
Most attempts to define plant functional types for predicting fire responses have
focused on predicting the consequences of varying fire frequencies. Thus, age to
first flowering, plant life span, and longevity of seedbanks are key attributes for
predicting how plants will respond to different fire intervals. However, event-
dependent effects, such as the season and intensity of a fire, also influence postfire
recovery (Bond & van Wilgen 1996 ; Keeley et al. 2005a for chaparral). Fynbos
fires can occur in any season. Anthropogenic fires have a broader seasonal
range than lightning fires, which typically peak in summer. The season of fire
can have major impacts on postfire recruitment, especially of serotinous proteas.
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