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本帖最后由 细胞海洋 于 2013-2-8 21:28 编辑 7 c* n2 O- h2 K' z* f
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' o+ k- _% j7 D& c( P, ~8 VAbout the
; R! d+ U G5 ACover" }% a% d0 T c' l! z$ g" x# G
Stretches of oak savanna
- m+ m% w+ l( U E/ ^in the Pacific Northwest of North America have been subject to fire-prevention ( p. r6 t* s& h0 H" l. V) L7 u
measures since the mid-nineteenth century. The resulting grassland has lost 0 F- X0 \* w( N9 ^
plant species but achieves stable high-yield annual production — rather like a
1 @1 u3 S( D' Khigh-yield agricultural system — and remains resilient to invasive species and
2 ~& b( S4 J) V# H1 f# Q2 Iclimate fluctuation. A long-term study in which
8 y" L' h; t! G9 o: O" e6 vselected grassland plots were periodically burned and allowed to recover now
5 |7 P4 S+ x% x- s# }demonstrates the critical value of biodiversity when ecosystems experience
% i& |5 k" g0 ^4 W1 i2 b, Bdisturbance. Grasslands were able to recover from burning only in areas that had
1 w. |" x9 `/ ma relatively high diversity of native plants. This work demonstrates how
b; N" K. e S5 Gpersistent human activity can homogenize both structure and function of an C: i7 x0 ~# e! f; f- h- [2 I
ecological system, while weakening the diversity-related mechanisms needed to , a4 Z1 _2 P! S& h
compensate for sudden disturbance. There are many terrestrial systems today that
8 H( ~# Y1 U: h1 h7 ~. ?. w8 W0 A' thave become homogenized by persistent human activity that may be similarly
0 Z; ] B+ a4 Z* L& N3 i1 r- Jvulnerable to sudden environmental change that will be only evident after the & i' L! u5 \: {. t) ?" l, U
collapse occurs. On the cover 'grass fire' (Dariush
% j& O$ l9 b0 V6 O1 ~ {M/Shutterstock).( j( C! s- N3 p3 Y" b
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发表于 2013-2-8 19:38
发表于 2013-2-15 22:45
