Methods for quantifying aboveground dead wood. Göran Ståhl Swedish University of Agricultural Sciences

Transcription

1 Methods for quantifying aboveground dead wood Göran Ståhl Swedish University of Agricultural Sciences

2 Overview of presentation Why quantify dead wood? A few words about harmonisation Overview of inventory methods Focus on a couple of new methods Perpendicular distance sampling Critical length sampling

3 Why quantify dead wood? Research Information for decision-making by managers and policy-makers Biodiversity Greenhouse gases Fuel loadings Etc.

4 Information needs Strategic level: national and international policy National forest inventories, etc. Operational level: selecting the appropriate management locally Stand level inventories, etc.

5 A few words about harmonisation Definitions of dead wood vary across countries with regard to: Diameter thresholds Length thresholds Stumps included or not Decomposition limit (before treated as soil) Aboveground vs belowground

6 Example from Sweden Söderberg et al (2014) found: 10 m3/ha according to the Swedish definition 25 m3/ha including all aboveground dead wood down to 1 cm diameter

7 Some points on harmonisation Slow progress towards a common definition of dead wood Estimates from different countries are not comparable But estimates can be harmonised on a caseby-case basis Reference definition Recalculations

8 Overview of field-based methods for quantifying aboveground dead wood Direct ocular estimation Sampling methods Sample plots Sample belts/transect plots Line intersect sampling Traditional relascope sampling Length-based relascope methods Etc.

9 Sample plots Straightforward Provides auxiliary information, for subdivisions on forest types etc. Many measurements and slightly tedius calculations needed

10 Sample belts/transect plots Largely like sample plots But more cost-efficient when dead wood is occurring sparsely

11 Line intersect sampling Straightforward and cost-efficient; sometimes used in connection with plot inventories Only works for downed wood Slightly tedious calculations needed

12 Traditional relascope sampling Poorly suited for dead wood, where many trees are broken Works for standing trees, only

13 Length-based relascope sampling From points or along lines Cost-efficient compared to plots and line intersect sampling Works only for downed trees Prone to measurement errors

14 Most methods for quantifying dead wood are fairly complicated to apply! - OK for NFI-type inventories! - But simpler methods are needed for management-oriented inventories!?

15 A couple of simple new methods Perpendicular distance sampling (PDS) Critical length sampling (CLS)

16 Perpendicular distance sampling (PDS) Introduced by Williams and Gove (2003) Uses a relascope-type principle; the volume of downed dead wood is estimated by only counting logs Inclusion zone proportional to log volume

17 Sampling pieces with PDS. A sample point (*) falls amid a group of pieces, numbered 1-4. Ducey M J et al. Forestry 2012;forestry.cps059 Institute of Chartered Foresters, All rights reserved. For permissions, please journals.permissions@oup.com

18 PDS - summary Vol/ha = factor * counted logs Very straightforward you only need a tape and a table with limiting distances Drawbacks Works only for downed wood Difficult to apply for very coarse dead wood (long limiting distances)

19 Critical length sampling (CLS) Introduced by Ståhl et al (2010) Uses an ordinary relascope the measurement needed is the the critical length of the pieces of dead wood included

20 CLS - illustration

21 CLS summary Vol/ha = factor * total critical length Works for both standing and downed dead trees Drawback Crude estimates are simple to obtain, but detailed measurements are required to avoid bias

22 Conclusions Old methods like sample plot inventory and line intersect sampling typically used for obtaining strategic level information on dead wood (for biodiversity, fuel, and LULUCF information) For management inventories good methods are lacking? PDS and CLS might find uses in this context?