0491-B1
T.J. Hodgson[1] and W.K. Darrow
Since 2000 almost all of the pine trees of the Mountain Pine Ridge Forest Reserve in Belize have been killed by the Southern Pine Bark Beetle. The destruction of the Mountain Pine Forest Reserve is so complete that there is no likelihood that the area will return to productive forest in the foreseeable future due to the almost complete lack of seed trees and the presence of frequent fire.
The best that can be expected is a “pine savannah” predominately of grasses with scattered pine. As there is little commercial value left to the reserve, the future land managers will give little priority to fire control. This will keep the reserve at a low level of biological complexity.
The re-establishment of the pine forests is a superior alternative to the regression of the area to the “pine savannah” as the pine forest will restore the commercial value of the area and improve its biodiversity.
This paper describes the process of determination of the baseline capacity and finds that the baseline estimate for the Mountain Pine Ridge Carbon Sequestration Project is 30 tonnes CO2 equivalent per hectare. A fully stocked and managed pine forest will store 27.8 times as much carbon as the savannah, which would burn frequently.
The reforestation of the Mountain Pine Ridge Forest Reserve by planting and the establishment of a managed forest scenario can and should be paid for with the sale of carbon credits. This type of action would not only store carbon for much of the next 50 years, but would also create a resource of wood that would contribute to the development of housing for the country’s population.
The baseline scenario shows that the Mountain Pine Ridge Forest Reserve will revert naturally to open grassland where the pine forest once stood. The current, very effective, fire prevention program would not be continued in the face of no foreseeable income from the devastated forest reserve.
Beginning in late 2000 the pine forest of the Mountain Pine Ridge Forest Reserve in the Maya Mountains of Belize has been heavily attacked by the Southern Pine Bark Beetle (Dendroctomus frontalis), an insect that is native to the pine areas of Central America and the United States.
The mortality of the pine trees has been so extensive that more than 90% of the pine stands are completely or almost completely dead. Scattered pine trees exist, but they will not provide sufficient seed to -establish productive forests any time in the immediate future. S ince the attack began no new pine seedlings have developed.
The Mountain Pine Ridge forest represents a distinct genetic provenance of Pinus caribaea var. hondurensis - the Caribbean Pine. This provenance has been the basis of the Queensland Australia pine hybrid breeding programme. Every effort is being made to preserve this resource in Belize and simultaneously preserve the natural forest habitat of diverse species for a tourism industry and a forest products industry.
The only method that would accomplish a satisfactory restocking of most of the reserve areas is to plant pine seedlings that have been specifically grown for this purpose. The seed used is collected in Queensland from block plantings of the Mountain Pine Ridge provenance of Caribbean Pine.
To finance the project the Government of Belize has made available the carbon sequestration capacity of this reforestation as a carbon offset for Greenhouse Gas emissions.
It is necessary to estimate the amount of carbon that would be stored on the sites by the vegetation that would develop in the absence of reforestation.and forest management (the “base-line”)”.
This quantity would then be subtracted from the total amount of carbon that would be sequestered by the replanted and managed pine forest. The net amount of carbon could be sold as an offset.
It is important to determine at what vegetative stage the samples should be taken before a field survey is conducted to estimate the baseline.
The critical issue in the natural ecology of the Central American pine forest is the periodic burning of the understory of the pine forest. These pine forests regenerate naturally from seed when the ground litter and understory grass and hardwood species are burned so that their ability to suppress seedling growth is set back.
Fire, caused by man and lightning, is a common occurrence in the mountain pine forests of Central America. Grass is often the prime fuel by which wildfires are spread, particularly when dead grass material accumulates over a period of years.
A study of the frequency of fires outside of the managed area showed that all areas burned with a frequency of once in 18 years. Hutchinson (1976) considered this as “probably indicative of the regularity of fires over the entire pine savannah in the period prior to fire protection.”
The base-line biomass for the Mountain Pine Ridge Carbon Sequestration Project must be determined from the grass layer of the- pine savannah ecotone that is still found in certain sections of the Reserve. The pines must be excluded from the baseline biomass calculations as they have ceased to be an important factor of the ecosystem, over most of the reserve, and will continue to be insignificant for the indeterminate future until the area is replanted.
Prior to the 1950’s, the only recorded management of the forests was the beginning of fire control work. Fire was the controlling factor in the existence of the Mountain Pine Ridge forest before the institution of fire control plans. Lundell’s 1940 report on the Mountain Pine Ridge area noted “large expanses of open pine savannah with very little regeneration of either pines or hardwoods”.
Lamb (1950) recorded that about 60% of the 1200 square miles of the reserve was “open pine forest” while the rest was mixed pine and hardwood. A further 80% to 90% of the open forest was classified as “open pine savannah” with small amounts of third quality pine trees.
In 1962 Hunt (1962) noted that the pine trees tended to occur in -(-clumps of a few trees to stands of several acres. No extensive and densely stocked timber stands apparently existed.
In all cases the visitors commented on the high frequency of wildfires. Intense and wide-ranging forest fires were recorded in 1945, 1949, 1953 and 1955. After 1960 the efficacy of fire control greatly improved the survival of pine seedlings.
The Mountain Pine Ridge Forest Reserve did not have very much timber to harvest in the 1950’s, as could be expected from a sparsely stocked forest. Legal l((
ogging started in 1955. By 1971 a total of 4.8 million cubic feet (134,530m3) roundwood equivalent had been cut. Having grossly over-cut the stands, the mills closed in 1971 when the available logs were too small to be processed economically.
Further, but extensive, logging was carried on in the 1990s until intensive salvage felling began in 2000. Since then every saleable dead or dying pine tree, larger than 9 inches (22.4 cm) at breast height, has been removed.
From the 1960’s the creation of an extensive road and fire-break system had limited the severity of forest fires. This control, in turn, led to the regeneration of the pine forests as dense and very extensive stands.
The control of the fires also allowed the hardwood brushy understory of the pine stands to develop rapidly and to suppress the natural regeneration of the pines .
The small areas of pine regeneration that exist today resulted from harvesting, using the seed-tree regeneration method, that was done prior to the beetle attack. -- Very few areas, however, were properly treated and thus natural regeneration efforts did not have widespread success.
Hawkes (1992) noted the lack of this success. He recommended the construction of a forest nursery at Douglas Da Silva Forest Station to supply seedlings for reforestation efforts in these stands.
Until the advent of the beetle damage, then, the forests consisted of the substantial biomass of the pine trees and the lesser, but still important, biomass of the various grasses and broadleaf species beneath them.
The death of most or all of the mature to adolescent pine trees in Mountain Pine Ridge Forest Reserve converted a very large percent of the living biomass into dead wood.
The removal of the pine canopy has stimulated the growth of the brushy broadleaved species that had formed the understory of the stand. Both ferns and tall grasses have spread rapidly where only short bunch grass ground cover was previously present. The woody shrubs of the family Melastomataceae also have expanded rapidly creating a low-level but dense crown that will eventually suppress the grasses and ferns.
The existence of only scattered living pines will not yield any trees of commercial importance for the foreseeable future. Nor will enough trees survive to reseed the reserve in the coming years.
Without the presence of a commercial pine stand on the Mountain Pine Ridge Forest Reserve there is little likelihood that the Government of Belize, or any land management organization appointed by it, will support the present level of wildfire suppression on the reserve.
To do so would be a Managed Forest scenario and not a Baseline scenario. It is thus certain that wildfires would return to the frequency that they had before fire control began.
The lack of fire control will mean that there will be frequent fires in the grass and shrub layers that are developing after the loss of the pine canopy. With a wildfire cycle of 18 years or less, the woody shrubs, most of which are not fire tolerant, will be burned back repeatedly and thus accumulate little above ground biomass. With fires on a cycle of 5 years or less, only the grass layer will prosper. The woody plants will be restricted to the stream channels and those areas too isolated or wet to burn frequently - as was the case in the past.
The biomass baseline for the Mountain Pine Ridge Forest Reserve should thus be the natural ecosystem that existed before the introduction of forest management - a grassy savannah but without the thin pine canopy - as no source of pine seed will exist for re-seeding the grasslands. This will be the scenario when forest management ceases - the dead pine forest will be replaced by a grassy mountain savannah ecotype with its low biodiversity, its erodable soils and limited recreational value.
The first plants to grow in a burned area are the grasses. In less than 4 weeks after a fire, the bunch grasses have sprouted and begun to set seed. If this seed is dropped before the beginning of the rainy season, the seeds will germinate and fill in the bare spots between the clumps
A study by Kellman (1976) of the biomass of the tree layer and shrub layer of an unburned pine stand (Pinus caribaea) revealed that there were 32 grass species and 21 broadleaf species besides the pine.
Pine made up 79.2% of the basal area (BA) of the test plot. The woody shrubs Byrsonima and Quercus supplied another 16.7% while all other species added only 4.1%.
|
Species |
M2/Ha |
% of Total BA |
|
Pine |
8.26 |
79.2 |
|
Byrsonima |
0.62 |
5.9 |
|
Quercus |
1.13 |
10.8 |
|
Other |
0.42 |
4.1 |
|
Total |
10.43 |
100.0 |
In the shrub layer grasses covered 43.6% of the ground surface, grass litter 20.3%, pine litter 9.3%, broadleaf vegetation 4.1% and bare soil 6.7%.
No biomass totals were given for these plots.
The growth of the grasses and shrubs is quite fast. Kellman (et al. 1987) states that by the end of the first year after a fire, the plant mass of the grasses and shrubs is 800-1500 kg/ha. After 5 years the plant mass is 2400 - 3400 kg/ha. Of this total plant mass a large percentage is “necromass” - dead plant mass that is generally dried and flammable. The mass of grasses can increase up to the age of 10 years when they cover 40% of the ground surface. But then they die back and are replaced by the broadleaf shrubs.
Even when the grass is in the growing stage, a short but intense drought of not more than 3 weeks can create a fuel layer ready to be burned (Budowski 1966).
The total plant mass of the grass and shrub layer, even when not burned, does not add up to much material. Kellman (et al. 1987) pointed out that even 5 years after a fire, the total mass of the grasses and shrubs represent only 6.6% of the above ground tissues of a 30 year old stand of Caribbean pine.
This model can no longer be used as pine seed-trees are no longer available in sufficient quantity to allow the re-creation of pine dominated forests.
If pine will not be a major part of the future ecotone, one must refer to the mountain grasslands found in the Bald Hills section of the reserve as the model for the natural ecosystem that will be created by fire in the immediate future.
Grass savannah ecotypes were selected on the fringes of the beetle-killed areas of the Mountain Pine Ridge Forest Reserve and stratified for sampling. Vegetation survey plots were randomly located and subjected to destructive, gravimetric biomass assessment. All plots were one metre square.
To simulate the median effect of frequent fire a mean determination was made from sites that had burned in April, 2002 (six months before sampling) and sites that had not been burned in more than 5 years.
Biomass (O.D.mass) estimates for the grassland ecotype were:
|
Ecotype |
Below groundlevel |
Above groundlevel |
Total kg/ha |
|
Burned grassland |
10,452 |
1,385 |
11,837 |
|
Grassland |
16,168 |
4,946 |
21,114 |
|
Mean |
|
|
16,476 |
How do these biomass data compare with that of the pine forest?
Based on published data and sampling of the stem volumes of logged trees in the Mountain Pine Ridge Forest Reserve, it was estimated that the pine forest was creating about 20 cubic metres of total biomass per hectare per year. Of this 60% or 13 cubic metres was stem wood volume that would be the main carbon reserve. As the basic wood density of the local mature pine was in excess of 700 kg per cubic metre of wood, the tree stem biomass production, for a 50 year rotation, should equal 455,000 kg of wood per hectare.
Of this 50% is carbon, so there are 227,500 kg of carbon stored per hectare in the mature pine forest. As the conversion factor for converting carbon to CO2 equivalent is mass of carbon times 3.67, the stored CO2 equivalent is 834,925 kg per hectare.
Thus, the amount of CO2 equivalent stored by the grass savannah is 16,476 kg of biomass times 0.5 conversion to carbon, times 3.67 for conversion to CO2 equivalent kg. These equates to 30,222 kg per hectare. The grass savannah baseline estimate for the Mountain Pine Ridge Carbon Sequestration Project is thus 30 tonnes CO2 equivalent per hectare.
Compared with the 834.92 tonnes per hectare of CO2 equivalent estimated to be stored in a mature pine forest, the grassland baseline has only 3.4% of the potential storage capacity of the managed pine forest reserve.
The destruction of the Mountain Pine Forest Reserve by Southern Pine Bark Beetles is so complete that there is no likelihood that the area will return to productive forest in the foreseeable future. The best that can be expected is a “pine savannah” predominately of grasses with scattered pine.
As there is little commercial value left to the reserve, the future land managers will give little priority to fire control. This will keep the reserve at a low level of biological complexity. To restore the commercial value of the area and to improve its biodiversity, the reserve should be replanted with pines of the same species and provenance. This work can be paid for with the sale of carbon credits earned by the use of the forest to sequester carbon for a rotation of not less than 50 years.
The re-establishment of the pine forests is a superior alternative to the regression of the area to the “pine savannah” as the pine forest will store 27.8 times as much carbon as the savannah that would burn frequently.
The reforestation of the Mountain Pine Ridge Forest Reserve by planting and the establishment of a managed forest scenario can and should be paid for with the sale of carbon credits. This type of action would not only store carbon for much of the next 50 years, but would also create a resource of wood that would contribute to the development of housing for the country’s population.
Budowski G. 1966. Fire in Tropical American Lowland Areas. Tall Timbers Fire Ecology Conf. 5th Annual Proc. pp: 5-22.
Hunt D.R. 1962. Some Notes on the Pines of British Honduras. Commonwealth Forestry Review 41:134-145.
Hutchinson L. 1976. Ecological Modeling and the Stand Dynamics of Pinus caribaea in Mountain Pine Ridge, Belize. Ph.D. thesis Simon Fraser University, Vancouver, Canada.
Kellman M. 1976. Broadleaved Species Interference with Pinus caribaea in a Managed Pine Savannah. CFR 55:229-245.
Kellman M.,K. Miyanishi & P. Hiebert. 1987. Nutrient Sequestrating by the Understory Strata of Natural Pinus caribaea Stands subject to Prescription Burning. For. Ecol.& Mgt.21:57-73.
Lamb A.F.A. 1950. Pine Forests of British Honduras. Emp. For. Rev. 29:219-226.
Lundell C.L. 1940. Botany of the Maya Area- Miscellaneous Papers XIV. The 1936 Michigan-Carnegie Instn. No. 522. pp.1-57.
Means D.B. 1997. Natural History of Mountain Pine Ridge Belize. Published for Bull Run Overseas, Ltd.
Munro N. 1966. The Fire Ecology of Caribbean Pine in Nicaragua. Tall Timbers Fire Ecology Conf. Annual Proceed. No.5 pp.67-83
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