Agriculture Reference
In-Depth Information
Recruitment from seedlings is generally poorest after winter and spring fires and
best after summer and autumn fires, perhaps due to increased predation following
early season fires (Bond
et al.
1984
; van Wilgen & Viviers
1985
; Le Maitre
1988
).
Resprouters would be expected to recover best from summer and autumn fires,
when roots are likely to have accumulated reserves, and to recover poorly from
winter and spring fires when root reserves are mobilized for new shoot growth
(see
Chapter 3
).
Watsonia pyramidata
, a fynbos geophyte, shows striking differ-
ences in flowering depending on fire season, with sparse flowering after spring
fires and abundant flowering and corm division after autumn fires (Le Maitre
1984
). This, and related species, were used as food by hunter-gatherers in the
fynbos region and it has been suggested that fires were deliberately set in autumn
to promote such corm production (Deacon
1992
).
Most prescribed fires are conducted under weather conditions that minimize fire
intensity and the risk of fire escapes. In contrast, wildfires burn large areas under
extreme weather conditions when fire intensities would be much higher. These
very intense fires may kill resprouting species (Richardson & van Wilgen
1986
),
resulting in long-lasting changes in the community because resprouters are gener-
ally poor seedling recruiters. However, intense fires promote recruitment of large-
seeded myrmecochores and other species requiring a heat pulse for germination
(Bond
et al.
1990
,
1999
). Intense fires kill seeds in the surface layers of the soil so
that only deeply buried, large seeds are able to emerge (Bond
et al.
1999
). These
effects seem restricted to deep soils with more even heat penetration. On rocky,
mountain fynbos soils, there is greater fine-scale heterogeneity in soil heating and
no marked effects of fire intensity on seedling emergence have been observed
(Holmes & Foden
2001
).
Proteoid shrubs
Proteas (
Protea
spp; family Proteaceae) form the overstory in many fynbos
communities and contribute the bulk of the biomass. By far the most common
species are serotinous obligate seeders. There have been many studies of popula-
tion biology and fire responses of this functional group in the Cape region with
strong parallels to studies in Australia. Seeds are stored in the canopy of the plant
in woody cone-like infructescences which remain closed for several years. After the
death of the plant, seeds are released en masse. Seeds released between fires very
seldom recruit successfully so populations are typically even aged and date from
the last fire. Serotinous proteas generally have longer youth periods than other
fynbos elements, taking 3-12 yrs or more (longer on the more arid sites) to flower
for the first time. Most species have relatively short life spans and few survive
longer than
40 yrs (longer with decreasing precipitation). Thus protea popula-
tions can be extirpated by short fire return intervals and also by very long
ones. Protea recruitment is also sensitive to season of fire with very poor recruit-
ment after winter fires (e.g. less than one seedling for every ten parent plants; Bond
et al.
1984
), poor recruitment after spring fires, and best recruitment after summer
and, especially, autumn fires (> 40 seedlings per parent). Seasonal effects on
∼
