0496-B4

Comparative growth characteristics of Loblolly Pine [Pinus taeda] and Patula Pine [ Pinus patula] in the Penhalonga Region of Zimbabwe.

C.A.T Katsvanga, Buzuzi. G, Ranganai. E, Tsopo.T. ¹

Abstract

Growth and yield studies of P.patula and P.taeda commonly grown in Zimbabwean plantations are carried out to ascertain variations in growth parameters such as height, diameter at breast height (DBH) and volume. The study is carried out in the Penhalonga region where four sites are selected for the assessment. Results indicate that growth of the Pine species does not vary by site, and significant growth in height is observed on P. patula at the ages of 15 and 20 years. Diameter of P.patula tends to increase also at 20 years. In Pinus taeda a significant increase in diameter is observed at 20 years. Site factors tend to remain constant for the four sites and indicate no significant variation in plant growth parameters. It is therefore concluded that the sites do not vary much because of the similar climatic and soil conditions. It is recommended to utilise P.patula for short-rotation pulpwood production as it attains acceptable heights earlier though under conventional saw-log production both species can be utilised for they have significantly equal volumes at the 20-year rotation. Finally it is recommended that monitoring of growth and yield characteristics of the pines should be carried out in response to the changing climatic and soil nutrient conditions of the various sites.

Introduction

Growth and yield information is of great significance to the timber industry especially for Senior Management to make decisions from an informed point of view. The prediction of plantation growth and yield is necessary for estimating yields on particular sites and comparing yield and growth of crops under different management regimes, silvicultural practices and performance under varied site conditions. The use of yield predictions together with appropriate economic analysis tools enables managers to make informed decisions on optimum harvesting ages, planting densities, timing of thinnings and other management interventions (Clutter et al 1983). Tree growth and yield data obtained through regular recordings assist in the derivation of growth and yield models for variables such as height, diameter, volume and basal area. This type of data are not only critical in the estimation of a sustainable yield of a timber resource but more importantly directing the planning of sustainable forest management and utilization (Hangula R.J.K 1999). Parameters such as the type and level of resource utilization, sustainable yield and growth patterns of forest resources appear to be important socio-biological issues of consideration which could be determined through biogeographic overview of a particular species (Wardell-Johnson 1999).

Pine plantations in Zimbabwe occupy an area of 80989 hectares constituting 68 per cent of the commercial plantation area. The Pine plantations of commercial significance are located in the county's highest rainfall area, which receives about 1500 mm per year located in the Eastern Highlands. Most softwoods are grown on a saw-log regime with just about 10 per cent grown primarily for pulpwood (Crockford K.J. 1995). The generalized mean annual increment (MAI) for the pines ranges from 16 to 26 m³/ha/annum (Timber Producer's Federation 1999).

Pinus taeda and Pinus patula are the most commercially important softwood species in the country and have a much higher plantation representation compared to Pinus kesiya and Pinus elliotii.

Pinus patula, a native of the Mexican Highlands (Crockford.K.J.1995), was introduced in Zimbabwe's Eastern Highlands in 1919 but is now growing in other provinces and urban areas (Troup R.S. 1932; Mitchell 1967;Barret and Mullin 1968;Crockford K.J 1995).

Pinus taeda is a native of South-Eastern United states, where it is a leading commercial timber (Fowells H.A.Comp 1965; Hunt.C.B.1967 Little, Elbert.L.Jr 1971). It has also turned to be a major plantation species in the Eastern Highlands of Zimbabwe where it was first introduced prior 1920 (Troup R.S 1932; Barret .R.L and Mullin L.J 1968; Barret R.L and Crockford.K.J 1995).

Because of the naturalization of Pinus taeda and Pinus patula to Zimbabwe for over 80 years, The Eastern Highlands has developed a powerful timber processing industry whose benefits have filtered down to the population at large. For many years forests were seen as vital for production and industrialization (Westoby, 1962) and were a strong link to general economic development (Hirschman.1958). Over the years development agencies have followed this path (World Bank 1978). However, it is likely that if species-site matching, growth and yield studies of these species are not continuously monitored timber shortages are likely to be experienced since demand and consumption of wood-based products is increasing. Increases in wood consumption are mainly driven by improvements in economic well-being and increases in population growth. After water, wood is probably our most important raw material (Sutton.1993). The fate of forests is tied to the fate of their users; they will rise or fall together (Durning.1994).

Materials and Methods

The Sheba Estate on which the study was carried out consists of four sub-estates, which are considered as the different sites, namely Lambton, Sheba, Harrisville and Epsom. The environmental characteristics of the sites are in table 1 below.

Table 1.Environmental characteristics of the Penhalonga sites

Average daily temperatures during winter are 15°C and 21°C in summer. The main influence on temperature is the altitude, which assisted, by the prevailing Southeasterly from the Indian Ocean lowers the temperatures. Cool and humid summers are experienced alternating with very cold winter weathers with an incidence of frost and frequent mist. The granites and dolerites, which represent much of the parent rock, have a pH value of 5 to 5.5. The soils are affected by leaching as a result of the high rainfall. These highly leached (dystrophic) soils are considered desirable for afforestation.

The compartments of the two species under consideration were established in 1981, 1986 and 1991 which follows that at the time of measurement, in 2001, they were 20, 15, and 10 years of age respectively. The planting espacement for the Pines was 2.4m x 2.4m resulting in a stocking of 1370 stems per hectare. By 10 years of age both species had their first and second thinning executed reducing them to a stocking of 450 stems per hectare. The stocking went down to 300 stems per hectare by 15 years after application of the third thinning, and to 250 stems per hectare by 20 years following the final thinning prescription. Initially the fourth thinning would allow the pines to be harvested at 25 year, which was the rotation age but resource constraints have reduced it to about 20 years. All prescribed silvicultural treatments were carried-out relatively on time.

In 2001, an inventory was carried-out in the Penhalonga Region from the established commercial compartments, with an objective to test for growth over a range of sites to determine the relative value of the species. At least each age group of 10, 15 and 20 years was represented per site. The inventory data were measured from plots measuring 0.04 hectares in size per age group and per species. Growth variables considered were height (Ht), diameter at breast height (BDH) and volume to assess growth characteristics, and dominant Height (H.dom) to determine site characteristics, across the four sites and the three age groups. Compartments from which data were collected are indicated in table 2 below.

Table 2.Compartments from which data were collected

Results

The results for the site and species growth characteristics are indicated in table 3 below

Table 3.Measured characteristics for different sites species and ages.

Height Growth

At ten years the analysis of variance of height growth across the four sites for both species is not significantly different (0.943), compared with a significant level of 0.05. This only changes at 15 years when height growth of Pinus patula is significantly higher (0.015) compared with P.taeda. This trend continues to 20 years where height growth for the two species across the four sites have P.patula performing better compared to P.taeda with a significance of 0.007.The height of Pinus patula did not vary significantly across the sites, (0.674) and the same applies to P.taeda. This indicates that growth in height by sites does not vary significantly.

Breast Height Diameter Growth

A comparison of the growth in diameter at breast height (DBH) by site indicated no significant difference for both species. For P.patula the level was 0.949 and P.taeda 0.840. Comparison of DBH increment between the two species was not significantly different with levels of 0.421. At ten years a level of 0.336 was obtained, indicating that there was no significant variation. A variation only became significant at fifteen years with P.taeda performing better than P.patula (0.007) but at 20 years no significant variation in DBH was detected (0.984)

Volume

The two species in terms of volume tend to perform equally the same, as the volume differences were not significant throughout the sites at all age groups.

Discussion

The growth performance of the two species, P.taeda and P.patula, though indicating differences across the sites tend to perform equally good in the Penhalonga region. P.patula tends to increase much more in height as it reaches fifteen years and at the same time P.taeda significantly gains in diameter. The two species at the end of twenty years still manifest this trend, though P.patula starts to increase in diameter as well, showing a significant increase (0.01) of this parameter. Since the industry is concerned much more about volume, the two species do not significantly vary in volume; because the height of P.patula is compensated by diameter growth in P.taeda. Environmental conditions in this region tend to be similar across the sites. This might be because of the little variation in altitude, rainfall, parent rock and soil type and to some extent the effective rooting depth. (ERD).

Conclusion

The study indicates that the four sites of the Penhalonga region show no marked differences in terms of productivity. This is explained by the similarities in soil and climate conditions. In all cases P.patula is showing much more marked increase in height and could be the species recommended for pulpwood production under short-rotation intensive culture but for a saw- log production regime the two species tend to have the same volume by 20 years of the rotation. This indicates that both species mature at the same time and the species- climate matching done by 1920 has proved successful for both species. However, monitoring needs to be continuously done to check species- site relationships and record trends, which could result from climate and nutrient changes.

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¹ Cuthbert A.T Katsvanga
Bindura University of Science Education
Department of Environmental Sciences
P Bag 1020 Bindura ZIMBABWE
E-mail: [email protected]

George Buzuzi
Bindura University of Science Education
Department of Mathematics
P Bag 1020 Bindura ZIMBABWE

Edmore Ranganai
Bindura University of Science Education
Department of Mathematics
P Bag 1020 Bindura, ZIMBABWE

Tendai Tsopo
Border Timbers
P.O.Box 458
Mutare ZIMBABWE
E-mail: [email protected]