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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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! x! V: e/ u" f: k. QAbout the
' s: _# {- s# t( D4 R! FCover
v3 u \. \+ K& HStretches of oak savanna
; k+ Q- D5 ~' y1 [" {" Iin the Pacific Northwest of North America have been subject to fire-prevention
) ~. m. I4 U( _' ], d- d5 a a& _0 z- s7 k# Kmeasures since the mid-nineteenth century. The resulting grassland has lost + i& t& x1 {# f" B7 R1 G+ M
plant species but achieves stable high-yield annual production — rather like a
8 u8 Q0 U; [5 B( ]high-yield agricultural system — and remains resilient to invasive species and + y4 b) ?, p& c; O; t! t+ W9 @
climate fluctuation. A long-term study in which 9 @" G& e1 J" K F2 G7 v
selected grassland plots were periodically burned and allowed to recover now 2 Z* _1 Y) n' W
demonstrates the critical value of biodiversity when ecosystems experience ; X! t9 [3 ~' _" o
disturbance. Grasslands were able to recover from burning only in areas that had 9 x; H+ b% D& v' L
a relatively high diversity of native plants. This work demonstrates how ! v8 {* o( M" P' N
persistent human activity can homogenize both structure and function of an
; x9 i3 a* r3 necological system, while weakening the diversity-related mechanisms needed to 2 s$ ?. |" q4 M2 G) N9 q1 t" ^4 D" H! W4 |
compensate for sudden disturbance. There are many terrestrial systems today that
9 S5 X D( ~: p4 {5 w# \have become homogenized by persistent human activity that may be similarly $ m6 E' |2 o& a& J& N& f& C
vulnerable to sudden environmental change that will be only evident after the
. Q+ n/ A7 C' h1 \9 u3 _$ ]collapse occurs. On the cover 'grass fire' (Dariush
+ P* t3 X( [- ^! i6 j0 d. K- I; OM/Shutterstock).) P0 R5 E5 g; b% h$ Q
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