Climate-induced tree response in the forest-tundra and forest-steppe ecotones

Transcription

1 Climate-induced tree response in the forest-tundra and forest-steppe ecotones V.I. KHARUK, K. J. RANSON V. N. Sukachev Institute of Forest, Krasnoyarsk, Russia NASA s Goddard Space Flight Center, Greenbelt, MD 2771, USA

2 In Eurasia the most significant climate change have occurred in Siberia; fast further temperature increase and precipitation change in the next decades is predicted Global temperature anomalies (1976 vs yr; source: NASA site).

3 Tree response to climate trends is most likely in the zone, where namely temperature and precipitation limits growth, i.g., in the forest-tundra and foreststeppe ecotones. The purpose of this report: to look on the changes in the mountain forest-tundra ecotone in south Siberia.

4 The South Siberia areas in focus: 1. Sayan Moiuntains 2. Tuva Mountains 3. South Altai Mountains

5 The Altai-Sayan Mountains are the system of ridges divided by a dense hydronet on the Siberia south

6 This is the boundary of Asian boreal forests: the forest-steppes and forest-tundra ecotones.

7 Forest-tundra ecotone in the Altai and Tuva Mountains is formed by larch (on dry mega slopes)

8 and by Siberian pine (on the more moisture mega slopes).

9 A climate in the study areas is severe continental Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec The annual pattern of climate variables in the forest-steppe ecotone (mean for the yr) 1, 2 temperature, 3, 4 precipitation in Altai and Tuva Mountains

10 Climate variables in Tuva Mountains A precipitation sum 1 annual 2 summer 3 winter p, mm A A A high dispersion is observing last decade 1 B mean temperatures 1 annual 2 summer 3 winter A strong positive trend is observing since mid of 8s t, C B

11 Larch, a drought-resistant species, is responding to climate trends by transforming from prostrate forms to arboreal

12 and by migrating into tundra zone Larch is surpass Siberian pine in its frost and drought resistance, and growing arboreal where pine is prostrate

13 A strong increments increase is observing since the mid of 8s; it shows a high correlation with summer temperature t, C 24 5 r temperature, 2, 3 Siberian pine apical and radial increments (Ra =.94, Rr =.92), 4, 5 larch apical and radial increments (Ra =.61, Rr =.63). Note: correlation with precipitation is non-significant

14 Forest-steppe climate variables dynamics Tuva, forest-steppe precipitation Tuva, forest-steppe temperature p, mm YEAR JJA JFMAMSOND JJ YEAR JJA JFMAMSOND JJ Altai, forest-steppe precipitation Altai, forest-steppe temperature p, mm 6 YEAR JJA JFMAMSOND JJ YEAR JJA JFMAMSOND JJ

15 Tee increment in the forest-steppe zone showed higher correlation with precipitation (N=49, p>.5; V. Magda data) Tree-ring indices.6 Chronology 5yrs moving average Years.4 Correlation VIII IX X XI XII I II III IV V VI VII VIII IX Temperature Precipitation Months

16 In the in forest-tundra ecotone the most significant changes are observing on the area with higher precipitation

17 Apical and radial increments, relative units Mean summer temperature, о С.1. Time, yr Siberian pine Apical (1) and radial (2) increments of post- prostrate forms of (A= 95 yr); 5 - radial increment of mature trees (A~15 yr). Larch: (3) Apical and (4) radial increments 6 - mean-summer temperature. Straight lines: trends (p>.1).

18 During last decades a high increase of regeneration number is observing (up to 7 thousand/ha). The regeneration number correlates with a temperature and precipitation trends Regeneration, n/ha _ Height, cm _ Siberian pine regeneration age structure and heights distribution. 1 a number of viable seedlings, 2 dead and dying samples; 3 regeneration height Age, yr 3 2 1

19 Regeneration, % of age group _ Altitude, m above sea level Regeneration distribution along the altitudinal gradient. Age groups: 1 - ( 1), 2 - (2-5), 3 (6-1 yr); 4 - (11-15), 5 (16-3); 6 envelope curve for all age groups.

20 Prostrate Siberian pine is transforming into arboreal form

21 A broader view: Changes on the opposite side of boreal forests: northern forest-tundra ecotone (precipitation <25 mm) The Ary-Mas stand

22 On the world s northward tree stand (Ary-Mas, 72o 28 N, 11o 4 E) during last three decades is observing the stand closure increase (~65%), and larch propagation into tundra (with a rate of 3-1 m/yr). - sketch map of Ary-Mas site ( sketch map of 2 yr minus sketch map of 1973 yr ). 1 background, 2 - sparse stands, 3 closed stands.

23 A broader view: Climate - driven Siberian pine migration to the zone of larch dominance (~4 mm precipitation) Overstory composition, % _ A n i 1 8 B the larch dominance zone (<4 mm) Ki C Eastern longitude, degrees A overstory, B regeneration, C - propagation coefficient 1 larch, 2 Siberian pine, 3 spruce + fir

24 Summary. During last decades the following phenomena are observing in Siberian South Mountains. 1. Larch and Siberian pine are propagating into mountain tundra. This species surpass its historical tree line boundary on 3-2 m (depending on site).

25 2. Regeneration is climbing up along an altitude gradient with a speed of 3 5 m/yr. Temperature rise on 1Сº allows regeneration to advance ~15 m.

26 3. Tree stands density is increasing. Closed stands propagate along the vertical gradient with a speed of ~ 1. m/yr.

27 4. A strong increase of apical and radial increment of larch and Siberian pine is observing since the middle of the 198s.

28 5. Prostrate forms of larch and Siberian pine are turning into arboreal form.

29 6. The changes in the forest-steppe ecotone are controversial (climate variables impact interferes with increasing anthropogenic pressure, overgrazing, tree cutting). The systematic studies needs!

30 Shi-shi! СПАСИБО! THANK YOU!