carbon conscious, page-16

From my limited knowledge Bach I think you'll find although a perennial crop when it is grown for fibre it is completely harvested and therefore must be replanted as though it was an annual crop. Likely to be a energy intensive production cycle so therefore probably a net emitter of CO2.

Herbaceous perennials such as hemp rarely live 5-10 years ... the best perennials are woody perennials (ie trees). A perennial being something that lives longer than a year ...

Now if the ETS delivered carbon payments for increases in soil carbon then any perennial crop delivers tangible positive contributions to soil carbon levels. The grazing industry is pursueing this path because they utilise perennial grasses and legumes in their production systems.