Stratified vegetation cover index: A new way to assess vegetation impact on soil erosion

Vegetation cover is an important parameter used in assessing the relationship between vegetation and soil erosion. However, the intensity of soil erosion actually changes not only with vegetation cover but also with differences in vegetation type and structure. How to integrate the cumulative effect of the different growth forms making up a vegetation community into one index for inclusion in soil loss predictive equations is an open research question. This paper proposes a method to separately measure the cover of different vegetation strata, estimate their contribution to reducing soil loss, and then to integrate this into a single vegetation index called the stratified vegetation cover index (Cs). The results show that Cs is more effective than projected vegetation cover for the assessment of soil erosion and also can overcome the disadvantages of vegetation indices such as NDVI. This means that Cs is a good substitute for vegetation cover or cover-related vegetation indices in studies on the relationship between vegetation and soil erosion. The concept of Cs may help the local governors or forest department understand the importance of vegetation structure and make right management decisions.

Research highlights
► Vegetation is an important factor for soil conservation through its role in reducing the erosive impact of precipitation. A large number of studies concluded that the rate of soil erosion decreases as the vegetation cover increases. This conclusion is an important one for regional scale assessment of soil erosion as well as for regional soil conservation planning. Increasing vegetation cover is becoming an important objective for soil conservation programs. However, the amount of soil loss changes according to both the vegetation type and structure. In some cases, such as plantations without understory or simple structure, the soil loss can be as serious as that in crop land. Many studies found that it is the complex structure rather than the single near strata that reduces soil loss. However, existing vegetation cover indices are not sensitive to vegetation structure. As a result, a high degree of uncertainty exists. An integrated index to assess the impact of vegetation structure on soil loss is needed.
► This study presented a new vegetation cover index based on vegetation structure. It aims to separately measure the coverage of trees, shrubs, grass and litter layer, and to integrate them into a structure-based vegetation cover index according to their contributions to soil conservation. We named it stratified vegetation cover index (Cs). The results show that Cs is more effective than projected vegetation cover for the assessment of soil erosion and also can overcome the disadvantages of vegetation indices such as NDVI, thus providing a new way to assess the vegetation impact on soil erosion as well as for the ecosystems management for soil conservation.
► The concept of stratified vegetation cover index (Cs) is of great significance to the vegetation management. It can help local governors, forest departments and soil and water conservationist understand the importance of the vegetation structure and design the rational vegetation structure for conserve soil.