Effects of forest management on nitrate leaching

Transcription

1 Effects of forest management on nitrate leaching Christian Huber Forest Nutrition and Water Resources Technische Universität München, Freising, Germany

2 Objectives What are the main influencing factors of NO 3 - leaching in forests and how are they related to forest management? What are the main processes behind it? 2

3 Possible effects of nitrate impairment of drinking water quality soil acidification base cation leaching aluminium mobilisation in the rooting zone formation of N 2 O growth reductions 3

4 Definition of Nitrogen saturation Availability of mineral N exceeds the combined demands of plants and microbes which then can be determined as elevated NO - 3 leaching from the rooting zone Definition modified according to Gundersen et al and Aber et al. (1998) 4

5 NO NO NO 2 N 2 O N 2 HNO 3 NH 3 N Org MO NH 4 + NO 3-5

6 Nitrate leaching is predominantly influenced by deposition II N output (kg N ha -1 y -1 ) N input (kg N ha -1 y -1 ) Source: Dise et al. (2009), Science of the Total Environment 7

7 Forest management options influencing nitrogen cycling Choice of tree species Rotation period Cutting strategy Fertilisation and liming Nitrogen input Nitrogen uptake Mineralisation of organic N N 2, N 2 O 8

8 Höglwald area: mixture of intensive agriculture and spruce. Augsburg Höglwald 50 km Munich 9

9 high yearly increment, up to 25 m³ ha -1 y -1 very acidic upper mineral soil 950 mm precipitation 560 mm throughfall 8.5 C high N input (throughfall): 30 kg N ha -1 y -1 Höglwald 10

10 Forest management options influencing nitrogen cycling Choice of tree species Rotation period Cutting strategy Fertilisation and liming Nitrogen input Nitrogen uptake Mineralisation of Norg N 2, N 2 O emission 11

11 Beech- Spruce comparison (European data) Source: Rothe et al. (2002), Plant and Soil 12

12 Beech and Spruce at Höglwald 2,5 2 NO 3 - (40 cm depth) Beech Spruce (A1) mmolcl -1 1,5 1 0,

13 60 Beech Input Spruce Output Beech Spruce 50 N 2 emission kg ha Gaseous deposition trace gas emission Throughfall NO 3-0 Data according to Rennenberg et al. (1999), Butterbach-Bahl et al. 2002, Huber et al and Rothe et al. (2002) during the period 1994 to

14 Forest management options influencing nitrogen cycling Choice of tree species Rotation period Cutting strategy Fertilisation and liming Nitrogen input Nitrogen uptake Mineralisation of organic N N 2 formation 15

15 Mature spruce is more susceptible for nitrate leaching Nitrate ( mg/l) Stand age (years) after Rothe and Mellert (2004), WASP 16

16 Forest management options influencing nitrogen cycling Choice of tree species Rotation period Cutting strategy Fertilisation and liming Nitrogen input Nitrogen uptake Mineralisation of organic N N 2 formation 17

17 Clear cut Flossenbürg Selective cut Höglwald Ebersberg 18

18 N-input kg ha -1 T-mean C Humus/ Soil Flossenbürg raw humus brownearth Ebersberg moder parabrowne. Höglwald moder parabrowne. Age years Flossenbürg 560 Höglwald Growing stock m³ ha

19 Variability of reactions of NO 3 - after cutting Nitrate ( mg/l) clear-cut control selective cut 150 Ebersberg Flossenbürg Höglwald

20 Clear cut vs. Selective cut at Ebersberg, Germany NO 3 - (mg l -1 ) cut Selective cut Clear cut Years after the first cut Source: Weis et al

21 A pre-established regeneration reduced NO 3 at Höglwald planted beech planted spruce natural regeneration Source: Huber et al. (2004), Plant and Soil 22

22 Bark Beetle die back in the Bavarian Forest National Park 23

23 Bark beetles dieback caused long lasting nitrate leaching at Bavarian Forest National Park Source: Huber (2005), JEQ 24

24 Faster decrease on plots with existing regeneration NO3 - (mg l -1 ) Intact stands mountain ash regeneration year of the die back: Intact years after the die-back 25

25 Ground vegetation and nitrate leaching Technische Universität München Source: Huber (2005), JEQ 26

26 NO 3 after wind throw in the Alps (Lattenberg), Germany NO - 3 (mg l -1 ) Wind throw Control y = 1.754x R 2 R 2 = Height of humus layer [cm] Source: Kohlpaintner and Göttlein (2009, submitted) 27

27 Newly established skid trails With brushwood mat Without brushwood mat Thinning operation with harvester in march 2007 at Eslarn, Germany 28

28 NO 3 on skid trails at Höglwald and Eslarn in the first two years after skid trail was established Höglwald Eslarn NO 3 - (mg l -1 ) stand skid trail + mat skid trail - mat stand skid trail + mat skid trail - mat 29

29 Forest management options influencing nitrogen cycling Choice of tree species Rotation period Cutting strategy Fertilisation and liming Nitrogen input Nitrogen uptake Mineralisation of organic N N 2 formation 30

30 Liming caused decrease of N Org at Höglwald Soil storage 20 years after liming Humus layer 0-40 cm sum Source: Huber et al. 2006, Forest Ecology and Management 31

31 Liming caused long lasting increase of NO 3 - at Höglwald NO 3 - (mmol c l -1 ) Limed Control Source: Huber et al. 2006, Forest Ecology and Management 32

32 Summary and Conclusions Prevention of NO 3 - is an important issue for a sustainable forest management Long term and excessive NO 3 - leaching is possible also in forests. N emissions need further reductions: agriculture! NO - 3 leaching is difficult to predict in managed but also in unmanaged stands 33

33 Summary and Conclusions main processes behind: input, uptake (microorganisms, trees, ground vegetation) and mineralization N-saturated systems should be treated different (e.g. beech instead of spruce, clear cutting vs. selective cutting, no liming) Excessive mineralisation of organic N has to be prevented (e.g. liming, clear cutting), when there is no corresponding sink for additional inorganic N 34