Abstract
Human activity has resulted in high fire frequency in many moist tropical savannas. To simulate the effects of increased fire frequency on woody plants of the cerrado savannas of Brazil, I constructed matrix population models for five species, including a subshrub, two shrubs, and two trees, using four years of demographic data. The models projected that four of the five species will decline under frequent burning but will increase in abundance under infrequent burning. For these four, fire intervals of 2–9 yr are required for long-term persistence, depending on the species. The fifth species, a shrub, was virtually unaffected by burning. Similar data for three herbaceous species were obtained from literature sources. Among the eight species, there was a negative relationship between population growth under annual burning and population growth under unburned conditions. Woody plant species performed best under low fire frequency, and herbaceous species performed best under high fire frequency. Three of the study species propagate vegetatively by producing root suckers. Fire stimulates vegetative propagation in all three species but reduces sexual reproduction. Elasticity analysis revealed that vegetative propagation is more important than sexual reproduction for population maintenance of these three species, and that vegetative propagation is relatively more important under frequent burning. However, stasis and progression were always much more important than either mode of reproduction, with stasis making the largest contribution to population growth. Analyses of life history response experiments were performed to determine what demographic variables contributed most to the population decline under frequent burning. The effect of fire on sexual reproduction contributed little to the overall effect of fire on population growth, particularly for clonal species. Fire-induced mortality also had little effect on population growth, except for Miconia albicans, which has extremely fire-sensitive seedlings. The negative effect of fire on individual size tended to make the greatest contribution to the overall negative effect of fire on population growth, and this effect was greater for the two trees than for the shrub species. The results indicate that growth form was the primary determinant of fire response, while ability to reproduce vegetatively is important to a lesser extent. Current fire regimes are predicted to reduce woody plant density and to favor smaller life forms and species capable of clonal propagation.
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Claims 19
Claim · model-written summary
Four of five woody species are projected to decline under frequent burning.
Verbatim
e0“four of the five species will decline under frequent burning”
t0“WOODY PLANTS”
Claim · model-written summary
The same four woody species are projected to increase under infrequent burning.
Verbatim
e0“will increase in abundance under infrequent burning”
t0“WOODY PLANTS”
Claim · model-written summary
Fire intervals of 2–9 years are required for long-term persistence of those four species.
Verbatim
e0“fire intervals of 2–9 yr are required for long-term persistence”
t0“WOODY PLANTS”
Claim · model-written summary
The fifth shrub species was nearly unaffected by burning.
Not reportedDirection
Verbatim
e0“The fifth species, a shrub, was virtually unaffected by burning”
Claim · model-written summary
Population growth under annual burning was negatively associated with growth under unburned conditions.
Verbatim
e0“there was a negative relationship between population growth under annual burning and population growth under unburned conditions”
t0“WOODY PLANTS”
Claim · model-written summary
Woody plants performed best at low fire frequency.
Verbatim
e0“Woody plant species performed best under low fire frequency”
Claim · model-written summary
Herbaceous plants performed best at high fire frequency.
Verbatim
e0“herbaceous species performed best under high fire frequency”
Claim · model-written summary
Fire stimulated vegetative propagation in three species.
Not reportedComparator
Verbatim
e0“Fire stimulates vegetative propagation in all three species”
Claim · model-written summary
Fire reduced sexual reproduction in those three species.
Not reportedComparator
Verbatim
e0“but reduces sexual reproduction”
t0“WOODY PLANTS”
t1“Fire stimulates vegetative propagation in all three species but reduces sexual reproduction”
Claim · model-written summary
Vegetative propagation contributed more than sexual reproduction to population maintenance.
Verbatim
e0“vegetative propagation is more important than sexual reproduction for population maintenance of these three species”
t0“WOODY PLANTS”
Claim · model-written summary
Vegetative propagation was relatively more important with frequent burning.
Verbatim
e0“vegetative propagation is relatively more important under frequent burning”
t0“WOODY PLANTS”
Claim · model-written summary
Stasis and progression contributed more to population growth than either reproductive mode.
Verbatim
e0“stasis and progression were always much more important than either mode of reproduction, with stasis making the largest contribution to population growth”
t0“WOODY PLANTS”
Claim · model-written summary
Fire effects on sexual reproduction contributed little to overall population growth effects.
Verbatim
e0“The effect of fire on sexual reproduction contributed little to the overall effect of fire on population growth”
t0“WOODY PLANTS”
Claim · model-written summary
Fire mortality had little population growth effect except in Miconia albicans.
- Taxon
- Miconia albicans
Miconia albicanse0 - Outcome
- population growthe0
- Direction
- little effecte0
- Qualifier
- extremely fire-sensitive seedlingse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Fire-induced mortality also had little effect on population growth, except for Miconia albicans, which has extremely fire-sensitive seedlings”
Claim · model-written summary
Fire reduction of individual size made the greatest contribution to negative population growth.
Verbatim
e0“The negative effect of fire on individual size tended to make the greatest contribution to the overall negative effect of fire on population growth”
t0“WOODY PLANTS”
Claim · model-written summary
Size effects were greater for trees than shrubs.
Verbatim
e0“this effect was greater for the two trees than for the shrub species”
Claim · model-written summary
Growth form was the primary determinant of fire response.
Not reportedDirection
Verbatim
e0“growth form was the primary determinant of fire response, while ability to reproduce vegetatively is important to a lesser extent”
t0“WOODY PLANTS”
Claim · model-written summary
Current fire regimes are projected to reduce woody plant density.
Verbatim
e0“Current fire regimes are predicted to reduce woody plant density”
Claim · model-written summary
Current fire regimes are projected to favor smaller life forms and clonal species.
Verbatim
e0“to favor smaller life forms and species capable of clonal propagation”
t0“WOODY PLANTS”