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L. Nshubemuki                                                           OCT. 2007

Paper presented to the 14th Annual Scientific Meeting of the Tanzania Association of
Foresters, TAF; Dodoma 24 October, 2007.

Criticism focusing on the effects of the Eucalypts on soil, water, floristic composition,
including their allelopathic influences are outlined. Existing information from parts of
the world and Tanzania is reviewed. It is concluded that extreme positions of relying on
human reason, or experimental evidence alone will not move us from confusion to
clarity.   Available data/information are in most instances of limited universal
applicability. A combination of elements from rationalism and empiricism sets up a
coherent alternative to these extremes. The approach, - interiority, makes us recognize
biases, prejudices, ulterior motives, twisted affectivity which interfere with the proper
unfolding of the process of knowing. Going through this process, it is apparent that
reservations concerning the growing of Eucalypts are outweighed by the advantages. It is
observed that: Choice of species and site as well as management of the stand(s) basing
planting efforts on many criteria, and tailoring planting assortments to suit specific sites
and planting objectives; minimize adverse effects.


The Eucalypts are often judged to be faster growing than other species and the most
likely to survive on difficult sites. They have however often been criticized for their
adverse ecological effects.

It has been noted that judgment about the relative merits and disadvantage of eucalypts
should be made by qualified objective personnel in each specific instance1. There are
500 - 600 species of Eucalyptus with widely varying properties, although only a few
comprise the most popular plantation species. The ecological effects of the same species
may vary greatly in moist or arid sites or on different soils or topography. Finally, the
array of various communities can vary a widely as types of species and the ecological
nature of sites. Although some of the criticisms are valid, judgments and solutions must
be specific to each case and based on accurate appraisal of biological, physical and
human factors.

Detailed discussions on the actual effects of eucalyptus with regard to the four key
ecological questions, namely water, erosion, soil nutrients, and competition, can be
found in2 which is also summarized in a booklet1 and other relevant published reports3, 4, 5
while the socio-economical implications of growing eucalypts are also discussed3.

An overview of experiences learnt in Tanzania is provided 5, 6, 7, 8, 9.

Despite a wealth of information available information about this subject, the debate
continues. This as observed earlier emanates from the fact that specific instances are
used to make generalisations.

This paper attempts to avoid the traditional approach to this time old controversy -
relying on commonsense and experimental evidence. Instead navigation from
commonsense, theory to the ‘theory’ of theories i.e. interiority is applied as an attempt to
move us from confusion to clarity.


Knowing what is widely held as cases of uniformed, universal acceptability, paves a way
to a better understanding of epistemological issues raised above (Table 1).

Table 1.       Common mistaken impression on the environmental effects of the

Observation                             Overlooked aspects                       Reference
(The Eucalypts…)

                              Although the genus is widely planted
                               throughout the tropical zone, most overseas
                               planting involves 10 species: E. grandis, E.
                               saligna E. globulus, E. camaldulensis, E.
Inherently   impact            vinamilis, E. tereticornis E. urophylla (alba)       11, 12
negatively on the              E. robusta, E. maculata and E. paniculata.
environment.                  This is a very small proportion of a 500 –
                               700 member genus.              A sweeping

Impact negatively on          Most of the studies are from India, the
soil.                          Mediterranean, South Africa, Brazil and               13
                               Congo. Little information available from

                              There are few water use comparisons
                               between the Eucalypts, indigenous forest
                               and plantations.
                              Where negative effects have indeed
                               occurred, they have not been compared with
Are prodigious water           other alternatives including doing nothing       2, 14, 15, 16
users.                         e.g. to an eroding site.
                              Observation overlooks site variations in
                               terms of water supply, and plant physiology
                               when water supply is readily available or
                               unavailable, and water use efficiency.

Observation                             Overlooked aspects                       Reference
(The Eucalypts…)

                              Not always the case as witnessed in
                               Malawi-ecosystem resilience need be taken
Kill     undergrowth           into account.
and reduce plant              We experience the same phenomenon in                  17
diversity.                     Pinus patula, and Cupressus lusitanica
                               stands.    What about plantations under
                               agricultural crops - rice, sugarcane, cotton

Inhibit growth of             Depends on the species - E. globulus found
agricultural crops.            less damaging in Ethiopia and E.
                               Camaldulensis in Zimbabwe.
                              Laboratory experiments do sometime               18, 19, 20, 21
                               exaggerate what obtains in the field and the
                               crop likely to be interplanted and the
                               spacing regime to be adopted.


Etymologically the word epistemology comes from two Greek words epistème which
means knowledge, know-how, understanding, etc; and logos meaning study, science or
theory. Thus epistemology is the study of knowledge. It is an investigation of
knowledge and its problems. Investigations focus on the origin, nature, and methods
used in securing knowledge. Epistemology is also related to other philosophical sciences
such as logic, psychology and metaphysics 22, 10. These relationships are of a borderline
nature. They will however contribute to the enrichment the forthcoming analysis.

Inspired by this approach it is worth recalling that the Eucalypts were first planted in the
then Tanganyika over one 100 years ago. We have a trial planted in 1905 at Lushoto 23,
and also Eucalypts planted in 1903 in Kagera Region by the missionaries. There are
scores of such planting elsewhere in Tanzania. If these Eucalypts plantings had the
alleged adverse effects to the environment notably on water supply, they should have
dried many years ago. What contributes to continued existence of Desert Locusts, and
Quelea-quelea is their ability to move to other locations once food reserves are exhausted.
Had they been sedentary like the Eucalypts, they would starve to death. Have we ever
witnessed such self- inflicted mass drying of the Eucalypts resulting from the depletion of
water? It might be argued that much lower water tables serve as sources. Should that be
the case then there could not be an outery of their drying effects.

There is a growing realization in today’s intellectual climate that most of our life and
knowledge deals with varying degrees of probability 10. Thus apart from shortcomings
in replication and inclusion of an enormous number of Eucalypts species (Table 1) in
investigations endubitability considerations cloud a balanced judgment.           It follows
therefore that impressions oftenly attributed to the genus tend to be speculative because
there is no concrete data to authenticate it. Yet, despite the fact that the philosopher
cannot know everything but s/he must be able to fit everything together – a whole in
knowledge but not whole of knowledge 24. However, before fitting everything together,
lets take note that science evolved its own form of theories verified by observations or
experiment. It has been highly successful and continues to develop. While theory brings
a new way of thinking into the world, it does not replace common sense. However, the
mentality characteristic of common sense continues with its emphasis on the practical,
the short term, the lack of clear definitions and distinctions. This undifferentiated nature
of common sense courts confusion such that images may be more important than
substance. The absence of definitions also paves way for prejudices - particularly
prejudices of precipitation. These rely on anticipation and confirmation and also on
tradition, as opposed to prejudices of authority which is hinged to leaning by experience
   . Time also influences truth. It helps to eliminate prejudices notably of precipitation
type which tends to foster personal approaches to the matter. Time also helps us to see
connections in events which were either imperceptible or not yet existent when a given
phenomenon took place 22, 23.

Applying these observations to the ongoing Eucalypts controversy, it is apparent that we
are engulfed by the shortcomings of commonsense, and prejudices. Stream drying and
widespread water shortages countrywide and elsewhere, was directed to the Eucalypts
when the causative factor is global warming which made the year 2005 the hottest of the
past 100 years 5. Faulty site species matching coupled with inappropriate spacing for a
given rainfall, has attracted blames on the Eucalypts rather than on the real culprit which
is bad forestry practice 26. As noted earlier, emphasis on inductive methods, that is,
moving from particular observed cases to generalisation about all cases is not without
problems when it is focused on the Eucalypts’ effects to the environment (Table 1).
Using a sample of less than 20 species to make deductions for 500-700 member genus
given a diversity of edaphic and climatic variations in space is too sweeping a

The advantage of theory over the common sense stage of meaning is the clarity, the
precision, the control it confers by way of mathematics or logic over the field covered by
its principles and method. But the disadvantage is that theory cannot account for itself.
Theory cannot account for the succession of theories; it cannot identify the criteria for
choosing between conflicting theories. Theory cannot account for its origins or compare
itself with commonsense. This suggests that something more is needed: interiority 10.


Interiority is not just another theory but it is a ‘theory’ about theories. It is going beyond
commonsense and theory, not in the sense of negating their value and leaving them
behind, but in appreciating their specific but limited contribution to almost all subjects.
Grasping the activity of human understanding is the main characteristics of interiority;
not as it happens in others but as it happens in oneself. We can not fully understand
everything but we can intend, desire, name, point at, move towards an understanding; we
can grasp our unlimited desire to know and compare it with the limits of achievement.
With interiority we draw conclusions that are reasonable defensible and demonstrable;
conclusions which are not a result of arbitrary choice, nor of blindly following a tradition.
Instead they are faithfully drawn from the deepest best inclinations of our heart and mind.

With interiority we are able to acknowledge that although a mistake has been made, we
can reflect further and discover our own mistake. Systematically we take note and
analyse the typical sources of misunderstandings and false judgments. We can notice that
we did not attend to all the data, or that we jumped to conclusions based on insufficient
evidence. We can notice that we did not think the subject through, realize the
implications, and delimit clearly the extent of our competence, We can recognize many
biases, prejudices, ulterior motives, much twisted affectivity, which interferes with the
proper unfolding of the process of knowing. Overlooked aspects levelled against the
Eucalypts. (Table 1) seek to indicate what interiority is likely to contribute10.


Going through the above, I am of a settled opinion that antithetical views on Eucalypts
cultivation are outweighed by the advantages. Negative impacts can be minimized by
taking note that tree planting has its own protocol. Species site matching, suitable
establishment and tending techniques all underline the best tree planting practices which
lead to success.

Furthermore, trouble free planting efforts should be based on many criteria e.g. maximum
wood production ecological sustainability, marketability, compatibility with other land
uses, easy establishment, site adaptability, informed popular acceptance, etc. All these
criteria involve not only a choice of species planted but also a choice of plantation
management methods from initial planting to clear felling.

There is a host of planting assortments with may be tailored to suit specific sites and
planting objectives e.g. as plantations, woodlots, shelterbelts, mixed planting with
indigenous leguminous species, boundary planting, lines/avenues, single tree scattered in
a given landscaped, etc. such assortments stand to address specific needs sustainably.

Equally instructive, is the fact that no any other genus be it indigenous or exotic has a
potential of replacing the Eucalypts in the immediate future; to bridge the ever-widening
gap between demand and supply. The genus has a big potential for poverty reduction.

Depending on mean annual rainfall an hectare planted with gum trees has between 630
and 1600 trees. If the market price per pole is placed at TAS 5000, an income ranging
from 3 to 8 million TAS is likely. This is realized after 5 to 7 years. Produce from Citrus,
Coffee, Coconut, etc. cultivation is obtained roughly after such a waiting period.
However, yields are initially modest. The difference between the said crops and gums is
that the first crop is immediately followed by another in the form of coppices. Having
several hectares of gum trees means replicating such income either in a trice or in
controlled/quick succession. Tree farmers in Brazil and the Republic of South Africa,
have exploited this opportunity. Tanzania can do the same thus shifting from a
prejudicial disposition of the Eucalypts and tap their financial generation prospects.


  1. FAO. 1988. The Eucalypts Dilemma. Food and Agriculture Organization of the
           United Nations. FAO, Rome.

  2. Poore, M.E.D and Fries, C. 1985. The Ecological Effects of the Eucalyptus.
            FAO Forestry Paper Series 59, FAO, Rome.

  3. Anon; 1992. Eucalypts: Curse or Cure? The impact of Australia’s World tree in
            other countries. Australian Centre for International Agricultural Research
            (ACIAR), Canberra.

  4. Davidson, J. 1989. The Eucalyptus Dilemma. Arguments for and against
           Eucalypt planting in Ethiopia. Seminar Note, Series No. 1; Forestry
           Research Centre, Addis Ababa.

  5. TAFORI 2007. Taarifa kwa vyombo vya habari. Ukweli ulivyo kuhusu
          Mikaratusi na Matumizi ya Maji. Daily News Thursday January 4, 2007.

  6. Nshubemuki, L. 2005. The Eucalypts: Myths and Realities. Paper presented
           during the Eucalypts Sensitisation Workshop, TAFORI, Morogoro.

  7. Nshubemuki, L. and Somi, F.G.R. 1979. Water use by the Eucalupts:
           Observations and probable exaggerations. Tanzania Silviculture Technical
           Note (New Series) No. 44.12 pp.

  8. Nshubemuki, L. 2001a. Sura mbili za Mikaratusi katika matumizi ya maji.
           Kakakuona 3, 10 – 11.

  9. Nshubemuki, L. 2001b. The Eucalypts are they thirsty drunkards? Kakakuona,
           22, 45 – 48.

  10. Brian, C. 1999. Foundations of Philosophy: Lonergan’s Cognitional Theory and
             Epistemology. Guide to Philosophy Series 10. Consolata Institute of
             Philosophy Press, Nairobi. p. 21 – 56.

  11. Extracted from: http://www.fao.org/DOREP/004/Y231E/y

  12. FAO. 1979. Eucalyptus for planting. FAO Forestry Series No. 1 FAO, Rome.
            677 pp.

  13. See Reference No. 6

  14. Gindel, I. 1971. Transpiration in three Eucalyptus species as a function of solar
             energy, soil moisture, and leaf area. Physiol. Plant, 24, 143 – 149.

15. Johanson, S.G. and Kaarakka, V.J. 1993. Growth and yield of six year old
           fuelwood species under irrigation in Eastern Kenya. E. Afr. Agric. For. J.,
           58 (Special Issue), 23 – 34.

16. Dabral, B.G. 1970. Preliminary observations on potential water requirement of
           Pinus roxburghii, Populus casale (488) and Dalbergia latifolia. Indian
           For.; 96, 775 – 780.

17. Bone, R., Lawrence M. and Magombo, 2. 1997. The effect of Eucalyptus
           camaldulensis Dehn. Plantation on Native woodland Recovery on
           Ulumba Mountain, Malawi. For. Ecol. Manage; 99, 83 – 99.

18. Lisanework, N. and Michelsen, A.1993. allelopathy in Agroforestry systems: the
          Effects of Leaf Extracts of Cupressus lusitanica and Three Eucalyptus
          spp. on Four Ethiopian crops. Agroforestry Systems, 21; 63 – 74.

19. Madondo, A. 1995. Ownership and Management of Eucalyptus camaldulensis
         woodlots in North – Eastern Zimbabwe South Afr. For. J., 174, 9 – 15.

20. Sanginga, N. and Swift, M.J. 1992. Nutritional effects of Eucalyptus litter on the
          growth of maize (Zea mays). Agriculture Ecosystems and Environment,
          41, 55 – 65.

21. Kananji, B. 1992. Prospects for using Eucalyptus camaldulensis in mixture with
          agriculture crops. South Afr. For., 162, 49 – 51.

22. Dietmer, L. 1982. Search for Truth. A students manual of Epistemology. Major
          Seminary, Adrigat. 108 pp

23. Lysholm, M.G. 1970. The Oldest Eucalptus microcorys Stand in Tanzania.
          Tanzania Silviculture Research Note, No. 14 Lushoto. 3 pp.

24. See Aristotle, Metaphysics, Book Gamma (Four). He opens by making this
           distinction between the special sciences which cut off parts of the material
           world as their fields of study and first philosophy which must include
           everything. Aristotle used the term ‘first philosophy’ where we would use
           ‘metaphysics’. This prompts philosophers to observe that philosophy
           begins where science ends 25

25. Piccado, W. Personal communication.

26. Teketay, D. 2003. Experience on eucalypt plantations in Ethiopia. Paper
          presented at the “Forum on the Eucalyptus Dilemma: Friend or Foe?”
          RELMA, Nairobi.


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