Agriculture Reference
In-Depth Information
predictor of hydrologic changes (Robichaud
et al.
2000
; Gonza´ lez-Pelayo
et al.
2006
); indeed, Doerr
et al.
(
2006
) suggest that fire severity classifications are
unsuitable for predicting fire impacts on soil hydrological responses. The primary
reason is that ecological responses such as erosion, overland water flow and debris
flows are affected as much by topography, soil type, rates of weathering, fire-free
interval, and precipitation as they are by fire or burn severity (Moody and Martin
2001
). Factors responsible for hydrologic responses to fire are multifactorial and
we need better mechanistic models across a diversity of landscapes before we infer
that fire or burn severity metrics are predictable measures of ecosystem responses.
Further research is required to fully understand the extent to which dNBR
informs managers of potential ecosystem responses. In addition to the very
different information in relative vs. absolute Landsat TM indices, there are many
other remote sensors that potentially could provide better indicators of postfire
management needs (Rolda´ n-Zamarro´ n
et al.
2006
; Chuvieco
et al.
2007
; Holden
et al.
2010
).
Postfire Restoration
Emergency responses to postfire conditions are largely focused on protecting
property and other human infrastructure such as roads from flooding and debris
flows. Two approaches are utilized: measures directed at limiting the extent of
erosion and landslides at the source, such as seeding or mulching, and measures
directed at stopping these flows somewhere between the source and the values at
risk, usually with barriers of some kind.
Postfire aerial seeding as a management practice has its roots in southern
California as a flood control measure. This was partly due to an incomplete
understanding of the natural capacity for rapid natural recovery in chaparral
ecosystems and a perceived need to enhance winter herbaceous growth with roots
that could assist in soil stability (Corbett & Green
1965
). This was once a widely
popular postfire management technique in California (Beyers
2004
) and the
Mediterranean Basin (Pinaya
et al.
2000
). Effectiveness of seeding depends on
the reliability of early autumn rainfall patterns. For example, it appears to be
effective in the Mediterranean Basin: rains come early and establish seeded grasses
and forbs before heavy winter downpours, particularly on sites dominated by non-
resprouting pines burned in crown fires (Vallejo
et al.
2006
). However, in southern
California rains are later and in more intense storms making postfire seeding
ineffective in most years (Keeley
et al.
2006a
). Throughout the western USA
evidence is increasing that seeding is of limited effectiveness in reducing soil
erosion (Peppin
et al.
2010
). Due to the fact that intense winter storms typically
initiate the rainy season, often the ungerminated seeds are washed off slopes prior
to germinating and in the majority of projects there is relatively little successful
recruitment and when it does come the worst of the winter storms may be past.
Terrain also affects the success of seeding. On steep slopes a significant amount of
dry ravel comes off prior to the rainy season and this soil loss is unaffected by
