A Burning Question: Can Long-term Data Inform Fire Management in the Twenty-first Century? - Biodiversity Conservation and Environmental Change - page 76

complex and heterogeneous, suggesting variable-severity fire regimes, influenced by topog-
raphy, vegetation, and human management (Williams and Baker 2013). Furthermore, fire
regimes can vary with aspect; for example, some forests may experience mixed fire regimes,
with low-intensity, frequent fires on warm, sunny slopes and high-severity, infrequent fires in
cool, shady areas, whereas riparian areas may burn only infrequently (McKenzie et al. 2004).
In the coastal rainforests of British Columbia, for example, terraces and north-facing slopes
had not burned in over 6,000 years, whereas dry, south-facing slopes had all burned within
the past 1,000 years (Gavin et al. 2007).
Intense, infrequent burns and variable fire regimes may have important ecological func-
tions, but mixed-severity fire regimes, that combine frequent, low-intensity and infrequent,
high-intensity fires, are poorly understood (Baker 2006, Noss et al. 2006, Mori 2011). Therefore,
both temporal and spatial complexity need to be understood when considering the natural
range of variability and the relationship between pyrodiversity and biodiversity needs further
investigation (Bond and Archibald 2003, Parr and Andersen 2006, Whitlock et al. 2010). Study-
ing fire intensity is not easy in the palaeo-record, but Minckley and Shriver (2011) distinguished
high-severity, stand-replacing fires from low-severity, surface fires, by studying the pollen and
charcoal record in tandem in the southern Rocky Mountains. They found that low-mid-sever-
ity fires led to changes in the abundance of understory taxa, increasing the proportion of can-
opy pollen, whereas high-severity fires consumed both understory and canopy plants,
decreasing the ratio of canopy to understory pollen (Minckley and Shriver 2011).
Heterogeneous landscapes might be more resilient to disturbances like disease, climate
change, drought and extreme weather, being less prone to erosion, and being more effect-
ively able to buffer and absorb disturbance. For example, in the southern Rocky Mountains,
Wyoming, stand-scale fires are thought to have contributed to the resilience of lodgepole
pine forests over the past 8,000 years (Minckley et al. 2012). Prior to this, vegetation had been
through transitions from sagebrush steppe to spruce-fir parkland at the start of the Holocene,
then to lodge-pole pine forest 8,000 years ago (Figure 4.10). These regime changes were
driven by climate and resulted from threshold responses of the vegetation to alterations in
the effective moisture (the balance between rainfall and evaporation). For the past 8,000
years, there have been significant changes in effective moisture, but the lodgepole pine forest
has remained stable, because of its broad climatic tolerance, and because repeated disturb-
ance helped to maintain early successional elements in a shifting mosaic maintained by
stand-scale fires (Minckley et al. 2012). It remains to be seen whether another threshold will
be reached if effective moisture continues to fall over the twenty-first century.
Fires and other disturbances leave legacies on forest age structure, creating a range of habi-
tats for different species. They also affect soil processes, nutrient dynamics, and hydrology.
Spatial configuration of burns also affects ecological function and habitat connectivity. Sensi-
tivity to spatial and temporal variation in fire regimes is essential to maintaining habitat for
the full suite of forest species, and different fire management strategies are required across
the landscape mosaic. For example, the northern spotted owl and the northern goshawk
require large tracts of open old-growth forests, the flammulated owl needs closed canopy for-
est, whereas the northern pocket gopher and Kirtland's warbler require early-succession