Regulating and supporting services and disservices: customary approaches to valuation, and a few surprising case-study results

New Zealand Journal of Forestry Science

Table 1 One-year cost of "extreme" flood events, South-west Region

Factor	Operator	Lower bound	Upper bound
Insurable flood losses in England & Wales (E&W)*		£3000 M/yr
Non-insurable flood losses (guessed)	+	£2000 M/yr
Total flood losses	=	£5000 M/yr	£5000 M/yr
Return period of extreme events (guessed)	÷	10 years	Annual
Annual extreme event losses	=	£500 M/yr	£5000 M/yr
South-west Region: 9% E&W population 16% E&W land area hence (approximately)	×	12% of national damage
Apportioned damage	=	£60 M/yr	£600 M/yr
Extreme event flood reduction by "optimally located trees"†	×	5%
% trees "optimally located"‡	×	8.9%
Extreme event flood reduction by "full tree cover"†	×		36%
% "full woodland cover"‡	×		8.9%
Area of tree cover	÷	212 000 ha
Reduction of flood damage	=	£1.3 / ha / year	£91 / ha / year

* Environment Agency (2007)
† Flood Risk Management Research Consortium (2008). Flood damage reduction is considered proportional to physical flood reduction, in absence of better quantification.
‡ On the assumption that the 8.9% tree cover is presently located randomly, rather than optimally, in respect of flood reduction.