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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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About the , G% w5 T, n5 _4 N$ S
Cover2 d, D! Z4 E3 k( c+ x% d7 D7 b, v
Stretches of oak savanna
* F3 u! x9 z: w6 c8 Tin the Pacific Northwest of North America have been subject to fire-prevention
! J+ U! N( G8 B" ~3 G- H- g1 umeasures since the mid-nineteenth century. The resulting grassland has lost
# a; Q1 f- Z: T" q4 iplant species but achieves stable high-yield annual production — rather like a ~) b+ Y" Y; s$ p: V8 s
high-yield agricultural system — and remains resilient to invasive species and
$ t/ `" g3 |: C' e }climate fluctuation. A long-term study in which
* d8 O% t' S7 F- Z9 y5 mselected grassland plots were periodically burned and allowed to recover now
) u* N' k( p9 u: tdemonstrates the critical value of biodiversity when ecosystems experience
( g% \: P- N1 N$ \3 W/ F( T. Ndisturbance. Grasslands were able to recover from burning only in areas that had
' Z7 O$ t9 |4 r* A7 va relatively high diversity of native plants. This work demonstrates how
; K2 x$ x' \' \' N/ U' i" H3 `persistent human activity can homogenize both structure and function of an 1 q! b" `: W, a
ecological system, while weakening the diversity-related mechanisms needed to
4 ?* p& c( \' kcompensate for sudden disturbance. There are many terrestrial systems today that : Y( G9 Y0 C/ a' T5 n
have become homogenized by persistent human activity that may be similarly
7 {8 E* P: i* X5 h' w* }* |3 O7 Nvulnerable to sudden environmental change that will be only evident after the
$ q/ m4 c, \; Z H* G" icollapse occurs. On the cover 'grass fire' (Dariush 6 ^ H/ Z# c$ `
M/Shutterstock).
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