Climatic significance of intra-annual bands in the wood of Nothofagus pumilio in southern Patagonia

MASIOKAS, M.H.; VILLALBA, R.

TREES-STRUCTURE AND FUNCTION

Springer - Verlag

Lugar: Berlín; Año: 2004 vol. 18 p. 696 - 704

0931-1890

Nothofagus pumilio (Poepp et Endl.) Krasser is the dominant subalpine tree in the southern Andes between 36¡ãS and 55¡ãS. Increment cores from a N. pumilio stand growing near the Ameghino Glacier (50¡ã25¡ä S, 73¡ã10¡äW), southern Patagonian Andes, Argentina, contain significant numbers of intra-annual bands (or false rings) which have not been previously described for this species. These samples are used to develop a wellreplicated ring-width chronology and a record of intraannual bands from AD 1760 to 1997. Annual variations in radial growth of N. pumilio at this site are negatively correlated with spring¨Csummer temperatures and positively with spring precipitation. The formation of intraannual bands appears to be a response to anomalously drywarm springs followed by wet-warm late summers.  Intraannual bands may occur in up to 95% of the sampled trees in a given year, and the percentage of trees affected was used as an indication of the strength of the forcing event. Narrow rings occurred in the years following intra-annual band formation, reflecting the lagged effect of unfavorable climatic conditions on tree growth during the subsequent growing season. Intra-annual bands occurred more frequently in the twentieth century than the late eighteenth and nineteenth centuries. This contrasting pattern seems to be a response to the combination of a long-term warming trend and a significant decrease in precipitation recorded during the last 100 years in this region of southern South America.(Poepp et Endl.) Krasser is the dominant subalpine tree in the southern Andes between 36¡ãS and 55¡ãS. Increment cores from a N. pumilio stand growing near the Ameghino Glacier (50¡ã25¡ä S, 73¡ã10¡äW), southern Patagonian Andes, Argentina, contain significant numbers of intra-annual bands (or false rings) which have not been previously described for this species. These samples are used to develop a wellreplicated ring-width chronology and a record of intraannual bands from AD 1760 to 1997. Annual variations in radial growth of N. pumilio at this site are negatively correlated with spring¨Csummer temperatures and positively with spring precipitation. The formation of intraannual bands appears to be a response to anomalously drywarm springs followed by wet-warm late summers.  Intraannual bands may occur in up to 95% of the sampled trees in a given year, and the percentage of trees affected was used as an indication of the strength of the forcing event. Narrow rings occurred in the years following intra-annual band formation, reflecting the lagged effect of unfavorable climatic conditions on tree growth during the subsequent growing season. Intra-annual bands occurred more frequently in the twentieth century than the late eighteenth and nineteenth centuries. This contrasting pattern seems to be a response to the combination of a long-term warming trend and a significant decrease in precipitation recorded during the last 100 years in this region of southern South America.