FLOWERING AND SEED PRODUCTION OF PINUS CARIBAEA VAR. HONDURENSIS

(PRELIMINARY RESULTS OF A WORLDWIDE SURVEY) ¹

by

Carl M. Gallegos
Senior Research Forester
Central & South American Species
International Paper Company
Mobile, Alabama U.S.A.

SUMMARY

The initial results from a worldwide survey concerning the “flowering” and seed production of Pinus caribaea var. hondurensis reveal that the optimum environmental conditions for reproductive growth of this tree lie between 9° to 27°N latitude and 9° to 27°S latitude. Exceptions to this hypothesis are apparently high elevations between 18° to 27°N latitude and 18° to 27°S latitude where these trees exhibit reduced “flowering” and little or no seed production. In addition, tropical highland zones between 9°N and 9°S of the equator, appear to have climates which favour the production of viable seed. Beyond 27°N and 27°S latitude, reproductive growth is greatly reduced, probably due to abrupt temperature changes and winter freezing. More detailed analyses of this data will be conducted to test these hypotheses, and this information will be published at a later date.

¹ Received February 1980. The author would like to express his gratitude to Dr. D. G. Nikles and Dr. J. M. Fielding of the Queensland Department of Forestry, plus Dr. B. J. Zobel and Dr. W. D. Miller of North Carolina State University, for their help in developing the questionnaire used in this study, and for providing the names and addresses of many of the people who supplied the information on which this paper is based.

INTRODUCTION

During the International Union of Forest Research Organization (IUFRO) Working Party S2.03.1 meeting, held in Brisbane, Australia, in April, 1977, the importance of Pinus caribaea var. hondurensis (PCH) as a plantation species in the tropics and subtropics was discussed at great length. The discourse regarding increased utilization of this species also brought to light the difficulties involved in acquiring the amounts of seed needed to establish plantations, plus the apparent lack of flowering and seed production that occurs when PCH is planted as an exotic, particularly in the low latitude tropics (Slee, 1978a and 1978b). Because of this situation, it was agreed at the meeting that the author would distribute a questionnaire to various parties throughout the world, who are engaged in growing Caribbean pine, to determine what environments are most suitable for cone and seed production in this species. The other varieties of this tree (i.e., Pinus caribaea var. bahamensis and Pinus caribaea var. caribaea) were not included in this study because of the relatively lesser importance of these varieties for plantation establishment.

In February, 1978, and again during July 1978, the Pinus caribaea var. hondurensis “Flowering and Seed Production Questionnaire” was sent to 75 different parties located in 34 countries throughout the world. Eventually, 68 (88%) responses were received from 32 (94%) countries. Of these, 35 (47%) of the questionnaires that were returned yielded usable information concerning 56 plantations and 5 seed orchards (Tables 1–3).

Natural Distribution of Caribbean Pine

The natural distribution of PCH extends from 18°04'N latitude in northern Belize to 12°13'N latitude at Bluefields, Nicaragua (Lamb, 1973). The longitudinal range is from 80°25°W at Poptun, Guatemala, to 89°25'W near Puerto Cabezas, Nicaragua. The altitudinal distribution varies from sea level to 1 000 m in Belize and to somewhat lower altitudes in Honduras and Nicaragua. The northernmost limit of Caribbean pine occurs in Grand Bahama and Great Abaco, where P. caribaea var. bahamensis (PCB) is found at 27°25'N latitude.

There is a large amount of physiographic variation within the native range of Caribbean pine, and climate varies from tropical and subtropical to tropical highland conditions as a result of this topographic diversity. Therefore, it seems logical that knowledge about the natural distribution of this species, and the environmental variation occurring within this region, should provide some insight into the climatic requirements for cone and seed production.

RESULTS

Preliminary evaluation of the data indicates that, when P. caribaea var. hondurensis is grown as an exotic, it will “flower”, but it will generally not produce viable seeds at low latitudes (i.e. between 9°N and 9°S). This condition holds true for the Ivory Coast (Table 1), Indonesia and Malaysia (Table 2), plus Surinam, French Guiana and Northern Brazil (Table 3). Initial examination of data obtained from the Democratic Republic of the Congo, Kenya and Tanzania (Table 1) indicated that these three locations could be exceptions to this hypothesis; however, closer evaluation of this information revealed that, although seed germination does occur, the production of viable seed is quite low for these three plantations.

The data also show that trees planted at high elevations in the low latitude tropics will produce good quantities of viable seed, which is an exception to the assumption stated above. It should be noted that the locations in Uganda (Table 1) and New Guinea (Table 2), where this phenomenon occurs, are found in Tropical Highland environments. Because of this occurrence, it seems apparent that higher elevations in the tropics have ameliorating effects on climate (notably temperature), which favours the “flowering” and seed production of PCH.

The most favourable latitudes for reproductive growth of PCH appear to lie between 9°N to 27°N and 9°S to 27°S. This theory is apparently borne out by the information obtained for Australia (Table 2), Brazil and Venezuela (Table 3). Furthermore, the natural distribution of PCB extends to 27°25'N latitude, which indicates that beyond this limit in the northern hemisphere reproduction of Caribbean pine is limited by unfavourable climatic conditions.

Apparently higher elevations within 18°S to 27°S latitude and 18°N to 27°N latitude do not have environments that are conducive to seed production. Plantations and seed orchards of PCH in Zimbabwe (Table 1), Thailand (Table 2) and Brazil (Table 3) exhibit “flower” production, but little or no viable seed is produced at these higher elevations. It is interesting to note that within the native range, PCH does not occur further north than 18°04'N latitude, which might imply that ambient conditions at higher elevations limit reproduction and thereby the northward dissemination of this variety.

Beyond 27°N and 27°S latitude, “flowering” of PCH is reduced or absent (e.g., India, New Zealand, the Republic of South Africa and Argentina), and there is apparently no production of viable seed. This phenomenon is comparable to what is observed at the northern limits of the natural distribution of PCB on Grand Bahama (27°25'N latitude), where the northward dispersion of this variety appears to be limited by physical barriers (i.e., the Caribbean Sea) and possibly climatic conditions. In addition, experimental introductions of PCH and P. caribaea var. bahamensis near Punta Gorda, Florida (27°55'N 82°02'W latitude) have shown that sudden changes in temperature and occasional winter freezing severely limit “flowering” and seed production of the species (Nikles, 1966; Squillace, Nikles and Saylor, 1977).

CONCLUSIONS

The conclusions expressed above are based on a precursory review of the data obtained from various parties who responded to the questionnaire. This information will be analyzed in greater detail to test these hypotheses, and the final results of these evaluations will be presented at the IUFRO Symposium and Workshop on Genetic Improvement scheduled to be held in Brazil during August, 1980.¹

¹ Note from the Editor: The paper presented by Dr Gallegos at the above mentioned IUFRO Symposium, entitled “Flowering and seed production of Pinus caribaea var. hondurensis: results of a worldwide survey”, will be published in the Proceedings of the Symposium. For further information please contact the author or the institute in charge of publishing the Proceedings, Instituto de Pesquisas e Estudios Florestais (IPEF), Caixa Postal 9, 13.400 Piracicaba S.P., Brazil.

LITERATURE CITED

Lamb, A. F. A. 1973 Pinus Caribaea. Volume 1, Fast Growing Timber Trees of the Lowland Tropics, No. 6. Unit of Tropical Silviculture, University of Oxford, England. 254p.

Nikles, D. G. 1966 Comparative variability and relationship of Caribbean pine (Pinus caribaea Mor.) and slash pine (Pinus elliottii Engelm.). Ph.D. thesis, N. C. State University, 201p.

Slee, M. U. 1978a Breeding Pinus caribaea for the Central Lowland Tropics. In Progress and Problems of Genetic Improvement of Tropical Forest Trees. Vol. I. (D. G. Nikles, J. Burley and R. D. Barnes, eds.). Dept. of Forestry, University of Oxford, England. pp. 515–19.

Slee, M. U. 1978b Day length and temperature and performance of Pinus caribaea. In Problems of Genetic Improvement of Tropical Forest Trees. Vol. I. (D. G. Nikles, J. Burley and R. D. Barnes, eds.). Dept. of Forestry, University of Oxford, England. pp 520–30.

Squillace, A. E., Nikles, D. G. and Saylor, L. C. 1978 Monoterpene composition in cortical deoresin of Pinus caribaea and relation to P. elliottii of Florida. In Proceedings Third World Consultation on Forest Tree Breeding. Volume 1. CSIRO, Canberra, Australia. pp. 241–258.

Table 1. “Flowering” and Seed Production of Pinus caribaea var. hondurensis for Various Countries in AFRICA

  * S.O.= Seed Orchard
** After Koppen

Table 2. Pinus caribaea var. hondurensis “Flowering” and Seed Production Information for Various Countries and Locations in AUSTRALIA/OCEANIA and ASIA

  * S. O. = Seed Orchard
** After Koppen

Table 3. The Production of “Flowers” and Seed of Pinus caribaea var. hondurensis for Various Countries and Locations in LATIN AMERICA

 * S.O. Seed Orchard
** After Koppen