Ajayi et al., 2012 - Njafe.org

Nigerian Journal of Agriculture, Food and Environment. 8(2):9-11
Published June, 2012 Ajayi et al., 2012
ESTABLISHMENT OF PERMANENT SAMPLE PLOTS FOR CONTINUOUS
FOREST INVENTORY IN A TEACHING AND RESEARCH PLANTATION OF
TEAK (Tectona grandis L. f.) IN CROSS RIVER STATE, NIGERIA
ABSTRACT
Ajayi 1 , S., Ayambem 1 , W, A., and Etigale 3 , E. B.
1 Department of Forestry and Wildlife Resources Management, Cross River University of Technology, P.M.B 102, Obubra,
Cross River State, Nigeria. Phone +234 (0)8038368014; +234 (0)8059456270
2 Department of Forestry and Wildlife,University of Uyo, Uyo,Akwa –Ibom State, Nigeria
Permanent sample plots were established for Continuous Forest Inventory (CFI). A surveyed map of the Cross River
University of Technology (CRUTECH) Teak (Tectona grandis L.f.) plantation was plotted and grids of 20m x 20m ground
equivalent were made on the map where four (4) permanent sample plots were chosen randomly. Number of trees enumerated
where 18, 16, 16 and 12 for plot 1, 2, 3 and 4 respectively. Diameters at breast height (dbh) of trees in the four plots were
measured using the girthing tape. The data obtained were analyzed using the normal probability distribution function, which
showed that 68% of the trees had diameter class range of 15cm and 25cm, 16% has diameter range of 10cm - 15cm, 14% and
2% of the trees ranged from 25cm – 30cm and 30cm – 35cm respectively. The result also showed that the actual stocking of
the plantation was 24.25% which shows a high level of mortality. There is need for replanting of the plantation to achieve its
management objectives.
Keywords: Permanent plots, forest inventory, teak, research plantation,
INTRODUCTION
Forest resources are renewable natural resources and Nigeria as a nation is abundantly endowed with these
resources (Ijeomah and Aiyeloja 2010). In order to effectively and sustainably manage these forest resources,
there is need for periodic measurement of variables. Data obtained during measurements could be used for
effective planning, policy formulation as well as decision making, for research purposes and monitoring of yield
in the forest plantation and the entire forest ecosystem (Ijeomah and Aiyeloja, 2010). Establishing permanent
sample plots in even and uneven aged stands provides high quality and local data on the growth of forest
plantation (GYHOST/GYH, 2002). The need for proper forest management planning is the ultimate foundation of
effective forest management. It provides the basis for future planning of the plantation and also serves as a
yardstick for monitoring growth performance. Carrying out complete enumeration in large forest is practically
cumbersome and time consuming and also expensive (George, 1992). Information obtained from permanent
sample plots will help in determining the rate of growth increment of the plantation over time.
It is imperative to establish permanent sample plots in order to carry out continuous forest inventory (CFI). CFI is
a periodic operation used to provide information on the current state of a plantation in comparison to previous
data (GYHOST/GYH, 2002). The concept of measurement in forestry is an important tool for forest management.
Whereas there have not being established permanent sample plots for continuous forest inventory (CFI) in the
CRUTECH Teaching and Research Teak (Tectona grandis) plantation, this research will go a long way in
highlighting the role of permanent sample plots where local data could be generated periodically for proper
management of the plantation.
The objectives of the study therefore were to establish permanent sample plots for continuous forest inventory
(CFI) of teak plantation and determine the stand density and diameter distribution of trees in the plantation.
MATERIALS AND METHODS
Study area
The study was carried out in a fifteen-year-old teaching and research teak (Tectona grandis L.f.) plantation of
CRUTECH Obubra Campus. Obubra lies between latitude 6° 05′ and 8° 20′ N and longitude 6° 08′ and 8° 33′ E.
Obubra is in the tropical rainforest and has too distinct seasons the rainy and dry seasons. The rainy season
begins from May through October, while dry season starts from November through April. It has an annual rainfall
of 2000 – 2250mm and relative humidity between 60 – 70% (Mfam, 2002).
Sampling techniques
A reconnaissance survey of the plantation was carried out to check for important features in the plantation.
Prismatic compass was used to take coordinates or bearings, cutlass was used to create transect to allow for
possible movement while ranging poles were used to align the bearings. The 30m tape was used in taking ground
measurements. A map was plotted and grids of 20m x 20m ground equivalent were formed on the map and
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Nigerian Journal of Agriculture, Food and Environment. 8(2):9-11
Published June, 2012 Ajayi et al., 2012
numbered (Ajayi et al., 2006). Pieces of papers amounting to the number of grids were numbered. Folded and
four (4) pieces were picked at random to avoid bias. Complete enumeration of diameter at breast height (DBH)
was done on trees of diameter 10cm and above.
Data collection and analysis
In each plot, DBH was measured at the point 1.3m above ground level by winding the girthing tape around
individual trees of diameter 10cm and above. Data were analyzed using descriptive statistics to obtain the mean
DBH and standard deviation. The general mean DBH () and standard deviation () for all trees in the four plots
were fed into the normal probability distribution functions to categorize trees according to diameter classes. The
probability density function is of the form (Gadow, 1983)
1 - ½ ( x – ) 2
f (x) = exp
2 2
where,
= mean
x = random variable and;
2 = variance.
For a normally distributed population; it is expected that 68.27% of the cases will fall between, - and +
and 95.45% between -2 and + 2 while 99.73% of the cases are found between - 3 and + 3
(Hamilton, 1988).
RESULTS AND DISCUSSION
Established Permanent Sample Plot: Four sample plots were selected from a sampling frame of 38 plots. Each
plot had an area of 0.04 ha. The numbers of trees enumerated were 18, 16, 16, and 12; mean DBH were 18.4,
20.36, 20.74, 21.04 and standard deviation were 4.38, 4.96, 4.54 and 6.08 for plots 1, 2, 3, and 4 respectively
(Table 1). Clear demarcation of the plots and permanent tagging of the trees in each plot were essential for the
management of objective of teaching and research. Data generated periodically will be used to assess and evaluate
the plantations performances over time.
Table 1: Stand summary of Teak (Tectona grandis) in CRUTECH Teaching and Research plantation
S/N Summary Plot 1 Plot 2 Plot 3 Plot 4 Total x
1. Plot size (ha) 0.04 0.04 0.04 0.04
2. Number of stem/ plot 18 16 16 12 62 16
3. Mean DBH (cm) 18.40 20.36 20.74 21.09 50.59 20.15
4. Standard deviation (cm) 4.38 4.96 4.54 6.08 19.96 4.99
Stand density
The initial stocking at 2.5m x 2.5m amount to 1600 plants per hectare. The current or actual stocking of 388 trees
per hectare (24.25%) indicated high mortality rate (75.75%). The high percentage of mortality observed in the
plantation could be attributed to regular fire outbreak, illegal felling by residents of host communities for
fuelwood, and poor management.
Diameter distribution
The general mean () was also calculated to be 20.15cm while the standard deviation () was 4.99cm. 388 trees
obtained per hectare had a distribution of 62, 133, 132, 53 and 8 for 10 – 15cm, 15 -20 cm, 20 – 25 cm, 25 -30 cm
and 30 – 35cm DBH classes respectively (Table 2). The trees of diameter 15cm – 20cm and 20 – 25cm
represented about 68% of the total stock. These trees should be allowed to grow to a more mature diameter of
about 35cm and above before harvesting. While the 14% representing trees of DBH 25cm – 30cm were suitable
for electric poles in the rural communities, 2% of the stock represented trees of DBH 30cm - 35cm and could be
selectively and carefully harvested for timber. Normal probability distribution is an efficient tool for
characterizing trees in forest plantation (Philips, 1994; Ajayi et al., 2007).
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Nigerian Journal of Agriculture, Food and Environment. 8(2):9-11
Published June, 2012 Ajayi et al., 2012
Table 2: Normal distribution of diameter at breast height (dbh) for CRUTECH teak (Tectona grandis) Plantation
DBH (cm) Probability Frequency %
10 – 15 0.1599 62 16
15 – 20 0.3437 133 34
20 – 25 0.3402 132 34
25 – 30 0.1358 53 14
30 – 35 0.0204 8 2
Total 388 100
CONCLUSION AND RECOMMENDATION
The permanent sample plots established were essential for assessment of planting stock in an even – age forest.
The study revealed a high rate of mortality over the years due to human activities in and around the plantation.
This means replanting in the entire plantation is of paramount importance. Large proportion of teak (Tectona
grandis) in the CRUTECH teaching and research plantation falls under DBH 15cm – 25cm (pole sizes). Intensive
plantation management is necessary to meet the management objective of teaching and researching.
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