Metla Project 3294

Needle proxies as environmental indicators

[  Suomeksi  |  Objectives  |  Results  |  Project leader  |  Researchers  |  Publications  |  Media releases  |  More about the project  |  Metla Research  ]

Duration: 2000-2006   Keywords: NTM, Pinus sp., climate modelling, dendrochronology, height increment, needle production, needle retention, needle trace method, radial increment, time series
Research project group: Distinct projects 1 - Structure and function of forest ecosystems


1.The reliability, accuracy and function of the Needle Trace Method (NTM) are tested mainly on Scots pine (Pinus sylvestris) but other conifers, too. The European-wide usefulness of NTM is clarified. NTM technique and needle proxies are further developed.

2.To retrospectively reveal the natural and anthropogenic variation of needle parameters such as needle age, needle retention and needle production by constructing long-term time series for them. The influence of pollutants, biotic agents and abiotic phenomena on forest health is evaluated. Further, the role of the silvicultural status of forests, and land use on needle parameters is investigated.

3.To use NTM in the reconstruction of past climate connected to the anticipated climate change.


The usability and value of the Needle Trace Method, NTM, in forest health monitoring has been investigated. Special attention was paid to needle retention data produced by the NTM in nine pine species. Material collected from throughout Europe was tested. Scots pine, Pinus sylvestris, proved to be an ideal target for the NTM throughout its natural range of distribution in Europe. In general, all other European pine species and the exotic Pinus contorta were found to be suitable targets for NTM studies. The main restricting property was polycyclicism (i.e. production of more than one annual shoot per season), which impedes the detection of true branch whorls and true annual rings.

Technically, the NTM proved to be very reliable as it does not contain any pitfalls. The NTM was applicable over the distribution range of the pine species tested as well as in environments where growth is more restricted. Although time-consuming, the needle retention of trees forming forests in the proximity of a Cu–Ni smelter was successfully revealed.

This method is a great advantage over visual crown thinning assessments carried out annually throughout Europe. Long-term variation of needle retention can be reliably described by the NTM. E.g. various working methods or the effect of an observer had only a little additional variance on the results. Only five to eight trees are needed to reliably describe long-term history for crown thinning in the stand, which retrospectively extends the defoliation history far beyond the time when annual forest-health surveys were launched in Europe. The needle history of the branches (canopy) is accurately related with that of the main stem, which the NTM principally uses. As concerns the long-term development of crown thinning, the NTM technique can be applied to replace part of the annual forest health surveys and thus save resources. To confirm this, follow-up studies are needed to test the method with older trees. Also the comparison of the future NTM results with the annual forest-health assessments of all the assessed species is necessary.

The NTM has been developed to produce the following long-term parameters in addition to radial growth and height increment: needle retention for summer, needle retention for winter, needle shed, needle age, total number of needles, needle production and needle density. First steps to produce needle-biomass chronology have been taken successfully. All parameters have a climate signal to be used in reconstruction of past climate. At least in near timberline conditions annual needle production has proved to be much better climate predictor than radial growth. Annual needle production is strongly related to height increment. At the end of the season needle shed increases with increased needle retention, suggesting an in-built control system in pine restricting needles not to become too old. The NTM describes successfully needle dynamics of a stand when under storey trees are released.

In its lifetime of 2000–2004 this project results in forty-four publications out of which fourteen have been published in peer-reviewed journals.

Project leader: Jalkanen, Risto
The Finnish Forest Research Institute, Rovanniemi Office, PL 16, FI-96301 ROVANIEMI, FINLAND
Phone: +358 29 532 4430

Other researchers: Pensa, Margus (2003-05), Salminen, Hannu, RO (2002-06), Sunnarborg, Karoliina (2006), Vartiamäki, Henna, VA (2002)

Top of page

Updated 12.06.2012