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本帖最后由 细胞海洋 于 2013-2-8 21:28 编辑
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) n B2 u" N3 A; F# ^About the
8 p8 c, \9 K( U+ q K3 d6 s1 kCover
% x! g' p( \5 h/ b6 d$ C, hStretches of oak savanna
# y: ?' b& D- M9 Sin the Pacific Northwest of North America have been subject to fire-prevention ' a4 e9 k* B" x/ G: O1 n8 r
measures since the mid-nineteenth century. The resulting grassland has lost
& K9 X7 u* Z: eplant species but achieves stable high-yield annual production — rather like a
; n0 W% J. v# o$ {' a7 @high-yield agricultural system — and remains resilient to invasive species and * r% a2 \( [# p4 f) _ a
climate fluctuation. A long-term study in which
$ r) r: }9 X, Eselected grassland plots were periodically burned and allowed to recover now ; {! W% Q+ \, P( @0 m7 c
demonstrates the critical value of biodiversity when ecosystems experience 3 { o7 d8 g4 h- p$ r, V
disturbance. Grasslands were able to recover from burning only in areas that had P/ _6 A/ R* T3 o# ]+ q( Y
a relatively high diversity of native plants. This work demonstrates how
2 C/ K/ g" S, M0 Z" ?persistent human activity can homogenize both structure and function of an % ^* n. D2 f, _
ecological system, while weakening the diversity-related mechanisms needed to " F, y9 H2 I% ?8 Y
compensate for sudden disturbance. There are many terrestrial systems today that : f6 O6 i* @$ E. s' `8 Z
have become homogenized by persistent human activity that may be similarly " d% u. B R; Q1 S& G& N: q
vulnerable to sudden environmental change that will be only evident after the
& E: C8 T' Z* V% X5 i$ J& w1 O& Acollapse occurs. On the cover 'grass fire' (Dariush
9 A& g. y f! l1 ^7 J7 f0 `) gM/Shutterstock).
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