Implications of albedo changes following afforestation on the benefits of forests as carbon sinks
Implications of albedo changes following afforestation on the benefits of forests as carbon sinks
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DOI：
10.5194/bg-8-3687-2011
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发表时间：
2011-01-01
期刊：
影响因子：
4.9
通讯作者：
Ausseil, A. -G. E.
中科院分区：
文献类型：
--
作者：
Kirschbaum, M. U. F.;Whitehead, D.;Ausseil, A. -G. E.
植树造林增加了碳储存，导致大气二氧化碳浓度下降，从而减少了辐射强迫，使地球变冷。然而，植树造林也改变了地表植被的反射特性，从反射率较高的牧场到反射率相对较低的森林覆盖。森林吸收辐射的增加构成辐射强迫的增加，具有变暖效应。净效应减少的辐射强迫和碳储存取决于这两个相反的processes.We的相对大小使用的数据从一个深入研究的网站在新西兰的北岛中部，有长期的，基于地面的测量辐射松森林的整个短波光谱。该站点的数据还得到了从卫星上获得的新西兰牧场的估计数的补充。一个完善的森林的植被覆盖度为13%，牧场植被覆盖度为20%。我们利用这些数据计算了随着森林生长而改变CO2浓度的直接辐射强迫效应。我们计算了从大气中去除碳所产生的辐射强迫，即辐射强迫减少-104 GJ tC（-1）yr（-1）。我们还表明，观测到的太阳辐射的变化构成了2759 GJ ha（-1）yr（-1）的直接辐射强迫。因此，在植树造林后，需要在生长的森林中储存26.5 tC ha（-1），以平衡观测到的CO2变化导致的辐射强迫增加。树木的生物量和CO2的测量被用来估计净变化的辐射强迫作为新种植的森林的增长。反照率和碳储存效应在植树后的前四到五年具有相似的幅度，但随着林分年龄的增长，碳储存效应越来越占主导地位。在整个轮伐期的平均值上，碳储量的变化抵消了17- 24%的碳储量增加带来的好处。
Increased carbon storage with afforestation leads to a decrease in atmospheric carbon dioxide concentration and thus decreases radiative forcing and cools the Earth. However, afforestation also changes the reflective properties of the surface vegetation from more reflective pasture to relatively less reflective forest cover. This increase in radiation absorption by the forest constitutes an increase in radiative forcing, with a warming effect. The net effect of decreased albedo and carbon storage on radiative forcing depends on the relative magnitude of these two opposing processes.We used data from an intensively studied site in New Zealand's Central North Island that has long-term, ground-based measurements of albedo over the full short-wave spectrum from a developing Pinus radiata forest. Data from this site were supplemented with satellite-derived albedo estimates from New Zealand pastures. The albedo of a well-established forest was measured as 13% and pasture albedo as 20 %. We used these data to calculate the direct radiative forcing effect of changing albedo as the forest grew.We calculated the radiative forcing resulting from the removal of carbon from the atmosphere as a decrease in radiative forcing of -104 GJ tC(-1) yr(-1). We also showed that the observed change in albedo constituted a direct radiative forcing of 2759 GJ ha(-1) yr(-1). Thus, following afforestation, 26.5 tC ha(-1) needs to be stored in a growing forest to balance the increase in radiative forcing resulting from the observed albedo change. Measurements of tree biomass and albedo were used to estimate the net change in radiative forcing as the newly planted forest grew. Albedo and carbon-storage effects were of similar magnitude for the first four to five years after tree planting, but as the stand grew older, the carbon storage effect increasingly dominated. Averaged over the whole length of the rotation, the changes in albedo negated the benefits from increased carbon storage by 17-24 %.