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本帖最后由 细胞海洋 于 2013-2-8 21:28 编辑
3 W: O3 q; m+ }! ?/ s, L6 j" i! C7 Z; A! B3 \
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About the 3 ~: ^" N" A2 X! A! _" Z3 }) i
Cover9 }+ e1 o( P8 G: X5 s
Stretches of oak savanna ( j% _, K# P$ g0 P5 p5 I
in the Pacific Northwest of North America have been subject to fire-prevention
: V: u# i' r) |9 O# s: ~% @( Dmeasures since the mid-nineteenth century. The resulting grassland has lost 9 Y+ p3 S" @& D1 T$ v b* D) n
plant species but achieves stable high-yield annual production — rather like a : e5 D/ k: K# V% _
high-yield agricultural system — and remains resilient to invasive species and
5 D3 r* g0 b2 S8 @climate fluctuation. A long-term study in which
" e/ n9 M# |4 W' _4 Fselected grassland plots were periodically burned and allowed to recover now ( T" ?5 u4 K5 K% d5 _$ u
demonstrates the critical value of biodiversity when ecosystems experience * X) o" f1 p2 _: {/ q, ?
disturbance. Grasslands were able to recover from burning only in areas that had R! z* e! ~1 o2 o
a relatively high diversity of native plants. This work demonstrates how . t$ w4 ~9 X/ k: I. [0 {3 a
persistent human activity can homogenize both structure and function of an
9 i2 c' h) G# x9 |+ Y. Recological system, while weakening the diversity-related mechanisms needed to 0 W9 `" C" F* g/ d- {9 V
compensate for sudden disturbance. There are many terrestrial systems today that 3 h+ K& f h3 |- s8 N+ k d
have become homogenized by persistent human activity that may be similarly
! b i8 [% R& A- H0 ^ g9 n; wvulnerable to sudden environmental change that will be only evident after the 8 i! x5 D0 n4 U4 q' Q1 S5 t
collapse occurs. On the cover 'grass fire' (Dariush
- h0 ?$ y2 X$ Q4 R% TM/Shutterstock).
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发表于 2013-2-8 19:38
发表于 2013-2-15 22:45
