This ignores afforestation (new planting) as one method of increasing sequestration, but more significantly it ignores the impact of improved management practice on increasing growth rates and the amount of sequestration.
The recent Forest2Market report, Historical Perspective on the Relationship between Demand and Forest Productivity in the US South, demonstrates that more active management both increases the amount of carbon stored in wood products (for varying timespans) but also increases the forest carbon stored in the standing trees (inventory).
Active forest management, at a landscape level, provides a continuing cycle of high rate sequestration (high proportion of young and mid-rotation trees) and mature trees providing a larger proportion of structural timber that can be stored in wood products. Non-intervention leads to a plateau in sequestration rates, followed by a decline and eventual carbon release through natural disturbance — the ultimate climax phase of natural forests.
Yes, a history of deforestation in some regions has caused significant climatic and environmental impacts, this can be combatted through reducing/controlling the rate of forest loss, but also by improving forest management practice and by new planting — this has been evident in the more developed forestry regions of Europe and North America where growth rates and the amount of stored carbon have increased, and also in the plantation forestry sector (e.g. eucalyptus in Brazil).
Rather than suggesting that it isn’t worth managing forests because that could only take us back to where we used to be, work can be done — such as the decarbonisation of the power sector and maintaining healthy wood products markets — that can help to reduce the CO2 that is already in the atmosphere.