Issues in Ecology Number 2 Spring 1997 These subalpine forests mitigate flood,drought, and temperature extremes: they soak up rain and snowmelt and mete it out ing cooling afternoon thunderstorms. to potentially large increases in surface runoff,along with Services Supplied by Soil nutrient and soil loss.A classic example comes from the Soil represents an important component of a experimental clearing of a New Hampshire forest,where nation's assets.one that takes hundreds to hundreds of herbicide was applied to prevent regrowth for a 3-year The result was a 40 per thousands of years to build up and yet very few years to be lost Some civilizations have draw a in a verage stre am flow During one four from fertile sol conve the h as more e much larger scale,extensive deforestation in the Hima Today.soil degradation induced by human activities af- layan highlands appears to have exacerbated recent flood- flicts nearly 20 percent of the Earth's vegetated land ing in Bangladesh,although the relative roles of human surface (Oldeman et al.1990). and natural forces remain debatable(lves and Messerli In addition to moderating the water cycle.as described 1989) In addition som of the world,such a above pro vides five othe rinte ser vices (Daily re expenen g an increased f equency eds and prov s phys cal support as they sprout and mature into adult plants sive deforestation. The cost of packaging and storing seeds and of anchor Wetlands are particularly well-known for their role in flood control and can often reduce the need to con- hoenm struct flood control structures.Floodplain forests and for ple.slow the of flood dto help as sess the u of this se ice The cost uppor nd stan nds us sed in such oper plain rather than washed i nto downstream bays or oceans tions total about USs55.000 per hectare (for the Nutri n addition,isolated wetlands such as prairie potholes in ent Film Technique Systems:FAO 1990). the Midwest and cypress ponds in the Southeast,serve Second.soil retains and delivers nutrients to as detention areas during times of high rainfall.delaying plants.Tiny soil particles(less than 2 microns in diam saturation of upland soils and overland flows into eter).which are p cha ge e that is ing vegeta and proper spositively charged ents ral water regimes intact can reduce the severity and du as calcium and magnesium-near the surface.in prox ration of flooding along rivers(Ewel 1997).A relatively imity to plant roots,allowing them to be taken up gradu small area of retained wetland.,for example.could have ally.Otherwise.these nutrients would quickly be leached largely prevented the severe flooding along the Missis- away.soil also acts as a buffer in the application of sippi River in 1993. fertilizers,holding onto the fertilizer ions until they are 8Services Supplied by Soil Soil represents an important component of a nation’s assets, one that takes hundreds to hundreds of thousands of years to build up and yet very few years to be lost. Some civilizations have drawn great strength from fertile soil; conversely, the loss of productivity through mismanagement is thought to have ushered many once flourishing societies to their ruin (Adams 1981). Today, soil degradation induced by human activities af￾flicts nearly 20 percent of the Earth’s vegetated land surface (Oldeman et al. 1990). In addition to moderating the water cycle, as described above, soil provides five other interrelated services (Daily et al. 1997). First, soil shelters seeds and provides physi￾cal support as they sprout and mature into adult plants. The cost of packaging and storing seeds and of anchor￾ing plant roots would be enormous without soil. Human-engineered hydroponic systems can grow plants in the absence of soil, and their cost provides a lower bound to help assess the value of this service. The costs of physical support trays and stands used in such opera￾tions total about US$55,000 per hectare (for the Nutri￾ent Film Technique Systems; FAO 1990). Second, soil retains and delivers nutrients to plants. Tiny soil particles (less than 2 microns in diam￾eter), which are primarily bits of humus and clays, carry a surface electrical charge that is generally negative. This property holds positively charged nutrientscations such as calcium and magnesiumnear the surface, in prox￾imity to plant roots, allowing them to be taken up gradu￾ally. Otherwise, these nutrients would quickly be leached away. Soil also acts as a buffer in the application of fertilizers, holding onto the fertilizer ions until they are 8 Issues in Ecology Number 2 Spring 1997 Figure 8-Early summer in the Colorado Rockies. These subalpine forests mitigate flood, drought, and temperature extremes; they soak up rain and snowmelt and mete it out gradually to streams and to the atmosphere, creat￾ing cooling afternoon thunderstorms. Photo by Gretchen C. Daily to potentially large increases in surface runoff, along with nutrient and soil loss. A classic example comes from the experimental clearing of a New Hampshire forest, where herbicide was applied to prevent regrowth for a 3-year period after the clearing. The result was a 40 percent increase in average stream flow. During one four-month period of the experiment, runoff was more than 5 times greater than before the clearing (Bormann 1968). On a much larger scale, extensive deforestation in the Hima￾layan highlands appears to have exacerbated recent flood￾ing in Bangladesh, although the relative roles of human and natural forces remain debatable (Ives and Messerli 1989). In addition, some regions of the world, such as parts of Africa, are experiencing an increased frequency and severity of drought, possibly associated with exten￾sive deforestation. Wetlands are particularly well-known for their role in flood control and can often reduce the need to con￾struct flood control structures. Floodplain forests and high salt marshes, for example, slow the flow of floodwa￾ters and allow sediments to be deposited within the flood￾plain rather than washed into downstream bays or oceans. In addition, isolated wetlands such as prairie potholes in the Midwest and cypress ponds in the Southeast, serve as detention areas during times of high rainfall, delaying saturation of upland soils and overland flows into rivers and thereby damping peak flows. Retaining the integrity of these wetlands by leaving vegetation, soils, and natu￾ral water regimes intact can reduce the severity and du￾ration of flooding along rivers (Ewel 1997). A relatively small area of retained wetland, for example, could have largely prevented the severe flooding along the Missis￾sippi River in 1993.