12.10 結語：地表變遷的後果

自從人類懂得用火，捕獵、耕種、畜牧等活動已深刻地改變了陸域生態系統，土地利用造成地表變遷，其規模之大，已遍及地球上1/2∼1/3以上的陸地，造成下列影響：

1．十九世紀的農業發展，改變地表覆蓋，造成十九世紀大氣中溫室氣體，如CO2、CH4及NOx的增加。

2 ．與土地利用密切相關的火焚增加NOx及CO2的含量，並增加了空氣中的懸浮物質，影響氣候。

3．森林消退，草原擴張也增加了地表反照率(albedo），減低了地表覆蓋的起伏度（canopy roughness），使得氣溫上昇，溼度下降，降水減少，許多氣候模擬都呈現這樣的結果。

4．農業活動增加土壤侵蝕，加速河川下游淤積，改變了陸域水文系統。,

5．陸地上最肥沃，養料最充足，適應生物棲息繁衍的地區多數已被人類開墾利用，生養了稻米、家畜、鼠類、蔬菜等，而使得其他五百萬∼三千萬的生物物種被排擠、驅趕，生活在有限的土地及生態環境中。換言之，土地利用造成動植物棲息地的破壞，嚴重威脅生物多樣性（見第13章）。

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