Agriculture Reference
In-Depth Information
Era
Period
Epoch
Began (Ma)
Holocene
.01
Quaternary
Pleistocene
1.8
Pliocene
5.3
Miocene
23
Oligocene
34
Eocene
54
Tertiary
Paleocene
65
Cretaceous
145
Jurassic
200
Triassic
251
Permian
299
Carboniferous
359
Devonian
416
Silurian
443
Ordivician
488
Cambrian
542
Fig. 9.1
Geological timescale based on the 2004 timescale endorsed by the International
Commission on Stratigraphy
.
heterogeneous and fire-prone seasonally dry forests were also present (Falcon-
Lang
et al.
2009
).
The fossil record also provides evidence that characteristics of contemporary
fire regimes were already present in Paleozoic and Mesozoic ecosystems. For
example, smouldering turf fires were interpreted for an Early Devonian site
(Edwards & Axe
2004
) not unlike ground fires in peat swamps today. Other
Devonian fires include surface fires in pro-gymnosperm forests with an apparent
fire regime of frequent understory fires that burned ferns and shrubs desiccated
during the dry season (Cressler
2001
; Collinson
et al.
2007
; McParland
et al.
2007
),
not unlike present-day northern hemisphere conifer forest fire regimes. This fire
regime has been observed under different climates. Falcon-Lang (
2000
) described
laminated sediments with fires every 3-35 yrs in pro-gymnosperm forests under a
tropical monsoon climate, indicating a frequent surface fire regime similar to the
present-day ponderosa pine fire regime under a monsoon climate in the south-
western USA. Similar frequent understory burns in Jurassic gymnosperm forests
(e.g.
Fig. 9.2
) occurred under an analogous summer-dry mediterranean-type
climate (MTC) (Francis
1984
). In contrast to these surface fire regimes, crown
fires are evident in charred apices of wetland lepidodendron forests of the
Carboniferous, and like contemporary crown fire regimes, fire intervals were very
long, on the order of 100-1000
yrs (Falcon-Lang
2000
). Equivalent crown fires
today are common in high-latitude conifer forests and temperate shrublands
(Keeley
et al.
2009a
).
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