Global Environmental Parameters of the Cameroon ASB Land Use Systems
“Best bet” Land-use Systems
Country reports
Alternatives to Slash-and-Burn in Cameroon
Unique id: IDAJBA2B
Source file: D:\Projects\ASB\ASB Country and Thematic reports\Cameroom Final Report\Final Report&Synthesis of PhaseII-Cameroon.xml
Authors: J. Kotto-Same, A. Moukam, R. Njomgang, T. Tiki-Manga, J. Tonye, C. Diaw, J. Gockowski, S. Hauser, S. Weise, D. Nwaga, L. Zapfack, C. Palm, P. Woomer, , Andy Gillison, D. Bignell, J. Tondoh
--------------------------------------------------------------------------
This section summarizes the findings on environmental
parameters of global concern—namely biodiversity and global climate change
variables. Measures of plant diversity
and below-ground micro- and macrofaunal diversity, carbon stocks, and
greenhouse gas emissions were made for each of the predominant land-use
systems. Because sample sizes were
limited and the typology of cocoa agroforests used to evaluate economic returns
was not included explicitly in the sampling frame, the environmental parameters
are only reported for a generic cocoa agroforest, based on a random sample of
six cocoa agroforests across the benchmark.
Ongoing work at the
Carbon stocks were sampled using the methods described in the Climatic Change Working Group final report, Phase II (ref). Forests were used as the basis for comparison. The Carbon stocks (above-ground vegetation and litter) of the 6 selectively logged forests sampled in Cameroon averaged about 228 t C ha-1, ranging from 193 to 252 t C ha-1. This value was compared to data for the following land-use systems (Figure 2).
Annual cropping phase of 2 years followed by 4 years of chromolaena fallow,
2 years cropping followed by either 9 or 23 years of bush-tree fallow,
2 years cropping followed by establishment of cocoa (jungle cocoa) over 25 years,
A 40 year rotation versus a non-rotational cocoa system established through gap and understorey plantings of cocoa,
one year cropping followed by establishment of an oil palm plantation with 146 trees ha-1 with a 7 year establishment phase and a 25 year rotation.
The maximum C stock attained in the various crop-fallow systems was 167 t C ha-1 for the traditional long fallow. The amount is reduced by more than half, to 76 t C ha-1, if the fallow is shortened to 11 years, and further reduced to 12 t C ha-1 with the 4 year chromalaena fallow. The time-averaged C stocks of these crop-fallow rotations are 77, 32, and 5 t C ha-1, respectively. A mature jungle cocoa stand contains about 43% of the C of the forest, ranging from 54 to 131 t C ha-1, with an average of 89 t C ha-1. If the jungle cocoa system is established simply by clearing the understorey and planting cocoa, then the time-averaged carbon of this non-rotational system is the same as the carbon stocks measured. If the system is established through slash-and-burn clearing and cropping, followed by planting of cocoa with a 25 year establishment phase and total rotation time of 40 years, the time-averaged carbon is 61 t C ha-1. The maximum C and time-averaged C of an oil palm plantation with a 7 year establishment phase and rotation time of 25 years are about half that of the cocoa system.
The rates of C accumulation (sequestration rates) varied with age of the fallow; beginning with 2.89 t C ha-1 the first two years when chromolaena dominated, increasing to 8.5 t C ha-1 for the next 6 to 10 years. The overall accumulation rate during the traditional long shifting cultivation fallows was 7.26 t C ha-1. The C accumulation rate of the rotational jungle cocoa was only half that of the natural fallow systems, whereas that of the oil palm plantation was similar at 6.03 t C ha-1. The rates of C accumulation are quite high compared to most reported for the humid tropics, but they do fall within the range measured by Szott et al., (1994).
Fig. 2: Maximum C stock (Cmax) and land use time-averaged C (LUSCta) for the different ASB land use systems.
Green house gases (N20,
C02, CH4) were sampled in five land cover types in
Table 2. Greenhouse gas emissions of various land cover types in Cameroon.
|
Land cover |
|
Gas emission |
|
|
|
FC02 (mg m-2hr-1) |
FN20 (mg m-2hr-1) |
FCH4 (mg m-2hr-1) |
|
Secondary forest (> 15 years) Old Chromolaena fallow (> 8 years) Young Chromolaena fallow (2 - 4 years) Cocoa plantation |
719 702 836 739 771 |
112.80 59.81 48.41 136.33 207.59 |
-5.59 -8.32 9.00 -8.51 -9.97 |
N20 ® Forest food crop < plantation//
The aim of this part of the ASB research is to explore methods of rapid resource appraisal with respect to biodiversity and to provide a cost-efficient method that can be readily transferred to stakeholders concerned with integrating natural resource management.
Visits
were made to field sites at Mengomo, Akok, Mbalmayo, Awae, Nkol Foulou,
Nkometou, Bafia and Batoum II, over a range of about 500 km from humid forest
to savanna. The scientists recorded 18 plots, focusing mainly on a range from Imperata grasslands and Lophira & Butyrospermum shrub savanna, through different slash-and-burn
fallow sequences, to closed-canopy (mostly secondary) forest. Included were
‘Jungle’
Data analyses included standard regression measures and
exploratory data analysis using the PATN program (Belbin, 1992). In addition to
these, a single index that represented key elements of vegetation structure,
total plant species, total PFTs per plot and their ratios, was extracted using
multi-dimensional scaling (MDS) as described by Gillison (1999) in
