by
R. Koster
Stichting Bosbouwproefstation “de Dorschkamp”
Bosrandweg 20, Postbus 23
Wageningen, Holland
1. INTRODUCTION
In several countries all over the world there is a growing interest in the western American and Canadian black cottonwood, Populus trichocarpa. There are three main reasons for this interest. One is the fact that P. trichocarpa, once planted, grows into maturity without the maintenance needed by Euramerican poplars. Another reason is that this species can grow well under conditions of site and climate not suitable for the traditional Euramerican clones. Last but not least is the fact that a number of very promising new clones have been developed by hybridization with P. trichocarpa.
The silvicultural aspects of the species have not yet been fully explored. Some reports have mentioned possibilities for a much closer spacing than that traditionally used for poplars.
For the reasons mentioned above seed of P. trichocarpa is very much in demand. The persons interested have felt that a systematic inventory of the potentialities of the species requires the introduction of samples from the complete natural range of the species. Thus the variability of the species may be studied in each country where these provenances are introduced.
Selection of seed sources and seed collection
With the help of several colleagues in the U.S.A. and Canada 67 sources of P. trichocarpa were selected by the author during a two months' tour through Oregon, Washington and British Columbia in August and September 1972. In addition 7 seed sources were selected in Alaska and 8 in California by colleagues in those states bringing the total to 82 selected seed sources. Selection criteria were: growth, form and low occurrence of leaf deseases. The aim was also to select stands representative of populations in specific areas.
In British Columbia the Canadian Forestry Service kindly offered to undertake free of charge the collecting of seed from nearly all selected seed sources. In the other states involved, Alaska, Washington, Oregon and California, seed collecting despatch of seed etc. were co-ordinated by one person in each state. Some of these co-ordinators are working at research stations, others at Universities or with the U.S. Forest Service. They obtained help from various private persons and from the industry. In many cases assistance was given by students who undertook the major part of the field work.
Because of the great variation in the time in which the seed was shed, the seed collectors often had to make several trips. Over a period of three months one seed collector made 15 trips covering nearly 7000 kilometers to obtain the seed of one series of 20 selected stands.
Financial aspects
Means to pay for this work were provided by:
IUFRO Coordinating Centre of Seed Procurement for Provenance Research, Copenhagen, Denmark.
Association Forêt Cellulose (AFOCEL), Paris, France
Forest Research Station at Maisala, Finland
" " " at Nancy, France
" " " at Hann. Münden, Germany
" " " at Wageningen, Netherlands
Foundation for Industrial Wood (Stichting Industrie Hout) at Wageningen, Netherlands.
A total of about US$ 4 000 were paid for travel, despatch of seed, salaries and other expenses during 1973. There is some money left for additional small scale activities in 1974.
Results
As mentioned above, 82 seed sources (origins) were selected. Seed was collected from 75 of these and it has been distributed to 25 stations in 20 countries, 17 of them in Europe, the other 3 in USA, Canada and Japan.
In the Netherlands a sample of each of the 75 collections was tested for germination. Only 8 samples gave no germination, 17 germinated poorly and the remaining 50 showed a germination of better than 50%.
Preparations are being made to arrange for a second sampling in 1974 of a limited number of those seed sources that gave a very poor germination.
Acknowledgements
This programme could never have been successful without the financial help of the IUFRO Centre in Denmark and various research stations and industries on the one hand, and, on the other hand, the help given by the Canadian Forest Service, the U.S. Forest Service and many colleagues, students, private persons and industries in the USA and Canada.
They have all helped to prepare and organize this activity by taking their share in the field work, the cleaning of the seed, the despatch and -last but not least- the correspondence.
