Annals of Botany 95/3 © Annals of Botany Company 2005; all rights reserved
A Letter from Professor Boysen Jensen to Professor Monsi, September 1955
Ecosystem Dynamics Group, Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia
* E-mail Marcus{at}rsbs.anu.edu.au
Prof. P. Boysen Jensen
Raadmandsgade 49
København N.
24 September 1955
Professor Masami Monsi
Dear colleague
Please allow me to reply in German. In this language, it is easiest for me to find the right expressions.
I would like to cordially thank you for your kind letter, and also for the reprints, which I have read with great interest.
Of course I am very pleased to hear that my Japanese colleagues want to continue my investigations on productivity. I myself have gotten old. ‘Causal Plant Geography’ will be my last work on these problems. The times when I was able to go into the forests are gone; I have to stay at home now.
I wholly agree with you that the study of reproductive processes is a very suitable method to enter into the problems of productivity. It is possible to construct a plant community synthetically. In many cases, e.g. for the investigation of heath formations, it will probably be best to erase the original vegetation in discrete testing areas and to follow at what speed the vegetation cover is renewed. The results of your investigations on the factor light in the forest correspond well with ours. A concluding representation of productivity in Danish beech forests was published in ‘Das forstliche Versuchswesen in Dänemark, 21, 1954’.
To solve the complicated problems that are associated with investigations on productivity, it is necessary to simplify them, as you do. It will also be necessary, as you intend, to work with communities (natural or artificial) that contain only one species. Poul Larsen investigated the productivity in a Solanum sward (Planta 32, 343, 1941). Romose analysed the productivity of mosses at a very specific site, namely on rocks (Dansk Botan. Archiv, Kopenhagen, 10, 4, 1940). Besides forest species, crop plants are also very suitable experimental materials, such as in cereal or beet fields. It is easy to follow how productivity is influenced by precipitation by investigations of stomata. One has always to aim to work as much as possible with normal plants. Normal plants grow in soil, not in flower pots.
Forest trees are good experimental objects because they are dominants, and because suitable methods are available to determine growth increments. If there are old-growth forests in Japan that consist of trees that are of different ages, then an investigation of their productivity would be very desirable. I find it likely that the wood mass in these forests is relatively constant, that the mass increase replaces the mass of senescing trees, and that the two can be considered equal.
It is important to determine which factors limit the distribution of plants. The best experimental objects will most likely be, once again, forest trees. You have beautifully investigated the effects of the factor light, and were able to follow the succession of sun and shade trees. Another factor is the length of the vegetation period, which comes into effect in the north, or at the tree line in the mountains. A third factor is the amount of precipitation, which determines whether forests or steppes will develop. In all three cases it should be possible to determine in which way these factors affect the growth of trees. Yet, one must always consider the possibility that not productivity alone, but also fertility may be limiting.
The term productivity connects plant ecology closely with agriculture and forestry; the practical results found in these disciplines are of importance for pure science, and vice versa. An immense number of problems await solution. E.g., within the various cereal species, wheat, barley, etc., there are many cultivars, some with high, and others with low yield. We do not know which morphological and physiological factors determine the yield amount. It is not solely the leaf area per ha. One should perhaps determine the leaf area per produced grain in the different cultivars. I touched on these questions in a treatise that I am sending you, together with another treatise which is unfortunately written in Danish.
I happily admit that the agreement of your calculated numbers with those found by me is very nice. However, I would like to recommend being cautious with the mathematical treatment. Of course, one has to be familiar with numbers if one wants to experiment, but one must not forget that the numbers most often used in phytoecology are only approximations. The goal of this science is to understand the processes in plant communities, and this understanding can be achieved without mathematics. It is a fact that this understanding gradually grows. We know considerably more than 50 years ago.
These are only scattered remarks. After reading your works I have no doubt that you will find your way.
Experimental plant ecology is an attractive discipline. I wish you and your co-workers the best successes.
With kind regards, sincerely yours,
P. Boysen Jensen
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