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Tree
removal alone appears sufficient to shift dominance from forest
understory to grassland species. It is commonly
assumed that fire is necessary to maintain the open nature of
grasslands and meadows, and thus to restore systems invaded
by trees. In systems in which fire is not a frequent form of
natural disturbance, tree removal alone may be sufficient.
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Alternative
treatments may be as effective as prescribed fire, if they modify
resource environments in ways that are beneficial to target
species. In this system, tree removal appears
to serve this function by exposing shade-dependent forest herbs
to abiotic stresses and increasing light availability for meadow
species.
The principal constraints to the recovery of meadow communities
may be the proximity of seed sources and the ability of species
to disperse to these newly opened environments.
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Managers have substantial flexibility
in selecting methods for treating residual fuels.
Ultimately, decisions about fuel-reduction treatments may hinge
more on operational or economic considerations than on ecological
necessity.
Nevertheless, broadcast and pile burning involve tradeoffs.
Broadcast burning is efficient at reducing fuels, but is contingent
on weather conditions and containment costs can be high. Pile
burning can be scheduled when fire risk and containment costs
are low, but creating piles can be labor-intensive, and local
scarring can be severe and persistent. In this system, however,
burn scars healed quickly, aided by the soil-disturbing activities
of gophers.
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Early responses to tree removal
suggest strong potential for restoration from a broad range
of initial states, including those supporting century-old forests.
Persistent increases in frequency and diversity of meadow species
suggest that natural dispersal has and will continue to enrich
the flora in these newly created openings.
The potential for recovery from a broad range of ecosystem states
illustrates the importance of seed dispersal, aided by the fine-scale
mosaic of meadow openings among forests which reduced distances
to source populations.
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Halpern,
C. B., R. D. Haugo, J. A. Antos, S. S. Kaas, and A. L. Kilanowski.
2012. Grassland restoration with and without fire: evidence
from a tree-removal experiment. Ecological Applications 22:425-441. PDF. Appendices |
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