Direct Effects of Sulfur on Forests in Europe - A Regional Model of Risk

W O R K I N G P A P E R

DIRECT EFFEK=TS OF SULFUR ON FORESTS IN ElTROPE - A REGIONAL MODEL OF RISK

Annikki M i e t a Jan Matema Wolfgang SchZpp

April 1987 WP-87-57

I n t e r n a t i o n a l I n s t i t u t e for Applied Systems Analysis

DIRECT EFFECTS OF

ON FORESTS IN EUROPE - A REGIONAL MODEL OF RISK

A n n i k k i M a k e l a J a n M a t e r n a W o l f g a n g Schiipp

April 1987 WP-87-57

W o r k i n g P a p e r s are interim r e p o r t s on work of t h e International Institute f o r Applied Systems Analysis and h a v e r e c e i v e d only limited review. Views or opinions e x p r e s s e d h e r e i n d o not n e c e s s a r i l y r e p r e s e n t t h o s e of t h e Institute o r of i t s National Member Organizations.

INTERNATIONAL INSTITUTE FOR APPLIED SYSTEMS ANALYSIS A-2361 Laxenburg, Austria

Authors

Dr. Annikki Makela formerly from t h e International Institute f o r Applied Sys- tems Analysis, A-2361 Laxenburg, Austria, i s now with t h e University of Helsinki, Department of Silviculture, Unioninkatu 40 B , 00170 Helsinki, Finland.

P r o f . J a n Materna i s a F o r e s t Diplom Engineer from t h e F o r e s t r y and Game Management R e s e a r c h Institute, Zbraslav, CSSR.

Wolfgang Schopp i s from t h e International Institute f o r Applied Systems Analysis, A-2361 Laxenburg, Austria.

Preface

The relationship between acid r a i n and f o r e s t damage h a s been a topic of very diverse opinions and debates. The new type of f o r e s t damage o r "neuartige Waldschaden" (in German language) which w a s observed in t h e beginning of t h e 1980s t r i g g e r e d a f i e r c e scientific debate about i t s causes. Various hypotheses w e r e developed, some were tested. Both in Europe and North America r e s e a r c h in f o r e s t growth processes increased. Until now no unified theory does exist. Two opposite conclusions could b e drawn from t h i s statement. One is, t h a t basic r e s e a r c h e f f o r t s should continue and more r e s e a r c h funds should be directed towards basic understanding of tree physiology and a tree's reaction to environ- mental s t r e s s e s . Furthermore, models are not particularly useful at this stage.

The o t h e r conclusion is t h a t basic r e s e a r c h and modeling should develop in paral- lel. Models can b e based on what w e already know and r e s e a r c h agenda could be modified based on modeling results. In t h e next iteration models could then be adapted t o new scientific results.

I t is t h i s hand-in-hand approach which h a s been adapted in IIASA's Acid Rain P r o j e c t . The RAINS model developed in this p r o j e c t combines energy scenarios, emission calculation, long-range t r a n s p o r t of pollutants, and deposition with effects on forest soils, Lakes, groundwater and forests. This p a p e r p r e s e n t s a sim- ple dynamic model f o r t h e sensitivity and r i s k of f o r e s t under long-term exposure to a i r b o r n e sulfur.

The a u t h o r s are among t h e f i r s t to develop a regional model of forest effects and are t o b e congratulated f o r t h e i r important work. I hope t h a t t h e p a p e r will stimulate discussion on modeling effects of a i r pollution on forests.

Leen Hordijk Leader

Acid Rain P r o j e c t

Abstract

A simple dynamic model f o r t h e sensitivity and r i s k in f o r e s t s under long-term e x p o s u r e t o a i r b o r n e sulfur i s p r e s e n t e d . The model i s a n i n t e r p r e t a t i o n of r e s u l t s from long-term f o r e s t damage and sulfur dioxide measurements in Czechoslovakia, and i t focuses on damage caused by d i r e c t , f o l i a r impacts. The input t o t h e model is t h e annual a v e r a g e SO2 concentration, and t h e accumulation of impact o v e r time i s i n c o r p o r a t e d . In a regional application of t h e model, sensitivity i s defined a s a function of t h e effective t e m p e r a t u r e sum. Sensitivity and r i s k maps of Europe in relation t o d i r e c t impacts of sulfur a r e p r e s e n t e d .

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L i s t of Symbols

Symbol ETS

Meaning

effective t e m p e r a t u r e sum Hydrogen flouride

dose

t h r e s h o l d dose

annual a v e r a g e s u l f u r dioxide concentration long-term a v e r a g e s u l f u r dioxide concentration

threshold annual a v e r a g e s u l f u r dioxide concentration maximum normal lifetime

maximum lifetime u n d e r sulfur e x p o s u r e r o t a t i o n time

s t r a i n a v e r a g e a g e threshold s t r a i n

Table o f C o n t e n t s

1. INTRODUCTION

2. STUDIES IN CZECHOSLOVAKIA 2.1 Observations

2.2 Conclusions

3. MODEL FOR DAMAGE DEVELOPMENT 3.1 G e n e r a l Framework

3.2 Driving V a r i a b l e s 3.3 Model S t r u c t u r e 3.4 P a r a m e t e r s 4. ASSESSMENT OF RISK

4.1 Temporal Limits of S t r a i n Development 4.2 Risk Levels of F o r e s t Areas

4.3 Summary of t h e Model 5. RISK LEVELS IN EUROPE

5.1 Input

5.2 Output: Risk Levels 6. DISCUSSION

REFERENCES

DIRECT EFFECTS OF SULFUR ON FORE-S IN ELTROPE

A REGIONAL MODEL OF RISK

A n n i k k i MakeLa, Jan Materna a n d Wolfgang Schopp

1. INTRODUCTION

T h e r e i s ample e v i d e n c e t h a t a i r b o r n e S O 2 c a n c a u s e a l t e r a t i o n s in t h e s t r u c - t u r e a n d function of tree f o l i a g e (Grill, 1973; K e l l e r , 1978; J a g e r a n d Klein, 1980;

Materna, 1 9 7 9 ; Cape, 1983; Soikkeli, 1981; Huttunen a n d Laine, 1983), b u t c o n t r o - v e r s y s t i l l r e m a i n s as t o w h e t h e r o r not t h e prevailing S O 2 l e v e l s in E u r o p e c a n give r i s e t o f o l i a r i n j u r i e s t h a t a f f e c t t h e growth a n d mortality of f o r e s t s . While t h e a n a l y s i s of t h e physiological pathways from foliage i n j u r y t o whole t r e e damage i s s t i l l f a c e d with a n u m b e r of u n r e s o l v e d questions (e.g. Luxmoore, 1980; Waring, 1986), t h e conclusion h a s b e e n drawn f r o m e m p i r i c a l d o s e - r e s p o n s e s t u d i e s t h a t t h e p r e s e n t s u l f u r l e v e l s a r e n o t likely t o c a u s e growth r e d u c t i o n s o r e n h a n c e d mortality ( R o b e r t s et aL., 1983). On t h e o t h e r hand, in Czechoslovakian sulfur- imposed defoliation h a s b e e n claimed r e s p o n s i b l e f o r o b s e r v e d damage t o s p r u c e s t a n d s u n d e r annual a v e r a g e S O 2 c o n c e n t r a t i o n s as low as 20-30 p g m -3 (Mater- n a , 1985).

The d o s e - r e s p o n s e s t u d i e s in t h e l a b o r a t o r y seem t o h a v e f a i l e d in analyzing two a s p e c t s t h a t would b e c r u c i a l in a r e g i o n a l a s s e s s m e n t of t h e f u t u r e r i s k t o f o r e s t s ; f i r s t , t h e possibility of slowly accumulating s t r a i n , a n d s e c o n d , t h e in- t e r a c t i o n of pollutants with n a t u r a l stress f a c t o r s . Although field s t u d i e s could potentially o v e r c o m e t h e s e problems, t h e y h a v e o t h e r d r a w b a c k s , t h e most impor-