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Effects of air pollution and droughts on forest condition in Lithuania

ISSN 13920146. B i o l o g i j a . 2001. Nr. 2

Effects of air pollution and droughts on forestcondition in Lithuania

R. Ozolinius, V. Staknas

Lithuanian Forest Research Institute,

Liep 1, Lt- 4312, Girionys,

Kaunas distr., Lithuania

Within the limits of our geographical region (Central Europe BalticStates Scandinavia) 7580% of variation in conifer condition of aseparate country can be explained by differences in acidic deposition,meanwhile the HTC has a very little influence.

A trend of forest condition improvement in Lithuania is evidentsince 1996 and can be related with a decrease of air pollution. Changesin the number of healthy trees as compared to HTC changes during theperiod 19901998 were slightly reliable (r = 0.52). A correlation be-tween the number of healthy Scots pine trees and the HTC was statis-tically more reliable (r = 0.74).

Key woods: defoliation, drought, hydrothermal coefficient, air pollution

INTRODUCTION

Over 180 hypotheses were proposed to explain thereasons of forest decline [1]. According to most ofthem, air pollution might cause defoliation and yel-lowing of leaves and needles. For example, Manion[2] and Evans [3] suggested that the oxidation of

SO2 and NOx to strong acids might directly destroythe leaf cuticle and thus cause damage to trees.Smith [4] discussed SO

2and NO

xas responsible for

affecting biochemical pathways and eventualy dam-aging the foliage. Other authors considered an indi-rect effect on tree condition soil acidification,associated with a decrease in pH and base cationsaturation as well as an increase of the concentra-tion of Al3+ in the soil, responsible for the recentforest decline, since Al3+ is very likely to be toxic toplant roots [5]. To the hypotheses mentioned above,unfavorable weather conditions, especially drought,

could also be added [6]. Some authors suggestedthat pest infestations or fungi attacks followingdrought periods cause the overall deterioration offorest health [7]. A single factor cannot cause treehealth decline. Air pollution is considered as one ofthe predisposing and inciting factors [2]. Air pollu-tion from a global point of view is an importantfactor that can influence forest condition.

Considering the spatial distribution of pollutantswithin the territory of Europe the largest amountsare certainly found in Central Europe. After the airpollution analysis in Europe was carried out in 1986

1995, pollution distribution maps of Europe were

compiled and the loads for each Pan-European per-manent observation plot (POP) within the forestmonitoring network were calculated [7].

MATERIALS AND METHODS

The main investigations were carried out according

to the international manual on methods and criteriafor harmonized sampling, assessment, monitoring andanalysis of the effects on air pollution on forests[8]. The regional forest monitoring system inLithuania is based on systematically selected perma-nent observation plots (POP). The condition of upto 23000 trees was annually evaluated [9]. Crowndefoliation is one of the most important tree condi-tion indicators. Special research indicates a closeinverse correlation r = (0.80.9) between the foli-age mass and crown defoliation [9].

Changes of air pollution in Lithuania were de-fined by the use of primary energy sources. Duringthe period of 19881991, the consumption of fuelwas at its maximum, and in 19941996 the stabili-zation of the amounts consumed was followed by asudden decrease of fuel consumption [10]. Monitor-ing of sulphur and nitrogen deposition from theatmosphere indicates that during the last years aclear decrease of sulphate concentrations in precipi-tation is observed [11]. A decrease of sulphate con-centrations in atmospheric precipitation can be re-lated to a decrease of SO2 emissions in Western

Europe. Meanwhile, NO3

and NH4+

concentrations


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in atmospheric precipitation have changed insignifi-cantly.

The levels of air pollution in European countrieshave been calculated using data published in theEC-UN/ECE reports [7].

The hydrothermal coefficient (HTC) of Selianinov

has been chosen for evaluation of hydrothermalconditions:

,10*

HTC

=t

R

were R is the sum of precipitation (mm) during theperiod when the air temperature is above 10 C, tis the sum of temperatures during the same period.

The average annual HTC values (MayAugust)were ca lculated as the average HTC of al lmeteostations of Lithuania.

RESULTS AND DISCUSSION

A correlation analysis has shown that within thelimits of our geographical region (Central EuropeBaltic States (including Lithuania) Scandinavia) 7580% of variations in conifer condition of a separatecountry can be explained by the dif-ferences in acid deposition (Figure).Climatic factors evaluated by the hy-drothermal coefficient had very littleinfluence (influence coefficient did notreach 1%).

Eevaluation crown defoliationchanges in 19892000 showed theaverage defoliation of all tree speciesin Lithuania was increasing until theperiod 19921993. A tendency of de-foliation decrease appeared in 1996.The trend of forest condition improve-

ment in Lithuania since 1996 can be related to adecrease in air pollution as well.

Air pollution does not explain the changes ofcrown defoliation at certain observation plots orsmall regions where air pollution is relatively stable(except cases of local pollution). Now attempts to

explain defoliation changes by the effect of meteoro-logical factors, invasions of pests and diseases aremade [7]. During the first half of the vegetationperiod soil humidity and precipitation are one ofthe most important factors in the foliage formationin our region. According to the research data [12],assimilation mass of birch stands during individualyears fluctuates from 75% to 125% of the averagevalues, and even 91% of the changes can be ex-plained by the effect of meteorological factors.

Along with the increase of the amounts of pre-cipitation, the Scots pine defoliation is decreasing

[13]. The density of Norway spruce crowns in Nor-way in 1992, compared to the results of 1991, de-creased on average by 1.81% in dry sites and by2.47% in sites unfavourable for spruce [14].

According to our data, changes of the numberof healthy trees (defoliation 010%) compared to

Tree species Site humidity index

N L U P

D H D H D H D H

All species 0.3 0.7 0.1 0.3 0.2 0.4 0.2 0.20.3 0.2 0.3 0.3 0.3 0.3 0.3 0.3

Pine 0.3 0.7 0.0 0.5 0.5 0.4 0.3 0.50.3 0.2 0.3 0.3 0.3 0.3 0.3 0.2

Spruce 0.1 0.5 0.3 0.1 0.4 0.0 0.1 0.30.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3

Birch 0.5 0.6 0.0 0.1 0.4 0.0 0.4 0.30.2 0.2 0.3 0.3 0.3 0.3 0.3 0.3

N mineral soils of normal moisture; L temporarily overmoistured mineral (gleyic) soils; U permanently

overmoistured mineral (gley) soils; P peatland. Significant at the 0.95 level of probability.

Table. Coefficients of correlation between HTC and tree condition (D defoliation, H number of healthy trees)

Figure. Average defoliation of conifers and acid deposition in some Euro-pean countries (19891997)


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Effects of air pollution and droughts on forest condition in Lithuania

HTC changes were slightly reliable (r = 0.52). Acorrelation between the number of healthy Scots pinetrees and the HTC in all forest sites was statisti-cally more reliable (r = 0.74). The average defolia-tion of trees on soils of normal moisture increasesalong with a decrease of the HTC, although the

correlation coefficient is not statistically reliable. Theincrease of the number of healthy trees along withthe increase in the coefficient of correlation betweenthe number of healthy trees and the HTC reaches0.7 0.2. From the data provided in Table, a de-crease in the correlation between defoliation indica-tors and the HTC along with an increase in sitehumidity can be indicated. Defoliation of Scots pineand broadleaves in all hydrotopes is decreasing alongwith the increase of the HTC, which is reflected bya negative correlation coefficient between the HTCand the number of healthy trees. Our statements

(the bigger the amount of precipitation, the higherthe density of Scots pine crowns, i.e. the lower de-foliation) are similar to the results obtained inBelgium [13].

References

1. Vaiys M. Rgtieji liets ir j poveikis vairiemsgamtos komponentams. Vilnius, 1991.

2. Manion PD, Lachance D. Forest decline concepts. St.Paul, Minnesota, USA, 1992.

3. Evans LS. Bot Rev 1984; 50: 44989.4. Smith WH. Air pollution and forests. Interactions be-

tween air contaminants and forest ecosystems. NewYork HeidubergBerlin, 1981.5. Ulrich B, Mayer R, Khanna PK. Soil Sci 1980; 130:

1939.6. Auclair AND, Worrest RC, Lachance D, Martin HC.

Climatic Perturbation as a General Mechanism offorest Dieback. Forest Decline Concepts (eds. ManionPD, Lachance D.). St. Paul, Minnesota, 1992: 3858.

7. EC and UN/ECE. Ten Years of Monitoring ForestCondition in Europe. 1997: 24160.

8. Manual on methods and criteria for harmonized sam-pling, assessment, monitoring and analysis of the ef-fects of air pollution on forests (4th edition). Ham-burg, 1998.

9. Monitoring of Forest Ecosystems in Lithuania (ed. R.Ozolinius). Kaunas, 1999.

10. ukauskas A, Jaskeleviius B, iugda J, StumbrasA. Ecological Sustainability of Lithuania (ECOSLIT).Vilnius, 1997: 117.

11. Girgdys A, opauskien D, Girgdien R, PerkauskasD, Mikelinskien A, Semeta K, Milukait A, GiedraitisB. Regiono ekologinis tvarumas istoriniame kontekste.Vilnius, 1998: 1831.

12. Mikys V. Mikininkyst 1998; 2 (40): 229.13. Callaert G, Scheizlink H. Influence of weather condi-

tions on the vitality of beech and Scots pine. Annex5 to Minutes Meteo-Level II. Freising, 1996: 112.

14. Strand G.-H. Forestry 1997; 2 (70): 15760.


ORO TAROS IR SAUSROS POVEIKIS LIETUVOSMIKAMS

S a n t r a u k a

Ms geografinio regiono (Centrin EuropaBaltijos alysSkandinavija) ribose skirtinga oro tara (SO2) galimapaaikinti net 7580% atskir valstybi mik vidutinsdefoliacijos kintamumo, tuo tarpu hidroterminis koeficientas(HTC) labai silpnai veik mik bkls rodikl.

Lietuvos mik bkls gerjimo tendencija, stebima nuo

1996 m., gali bti siejama su fonins oro taros majimu.Sveik medi (laj defoliacija 010%) skaiius 19901998m. (1992 ir 1994 m. Lietuvoje buvo stiprios sausros) iektiek priklaus ir nuo HTC (r = 0,52). Stipresn i rodiklikoreliacija stebta puynuose (r = 0,74). Medi, auganinormalaus drkinimo dirvoemiuose, defoliacija didjomajant HTC, taiau koreliacijos koeficientai nebuvostatistikai patikimi.

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