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How harvesting intensity affects forest structure and composition

“natural forests are less often ‘managed’ than ‘mined’ for selected high-value timber species or fuel wood.” This paper studied the effects of logging on structure and diversity in forests of mixed-species used for timber and fuel instead of selective commercial logging. Four different sections were tested.
1.    Control –no harvesting
-basal area increased by 26 percent in all diameters
-canopy intact, more fauna
-species richness in larger trees increased (greater than or equal to 15)

2.    Low-intensity harvest –trees >= 45cm diameter, leaving a couple for seed
-basal area increased a little, a lot from small diameters and decrease in large diameters because of exposure to full sunlight after others were cut down
-specie

3.    Moderate-intensity harvest –trees less than or equal to 20 cm and more than 60 cm, plus ones damaged from logging, and leaving some for seed
-basal area increased a little more, mostly in 10-20, 35-55 diameters
-rich in intermediate speciess richness in larger trees increased

4. Clear-cutting –all trees
-50 percent lower basal area than control
-grew back 60 percent of original basal area, mostly in less than 20 cm diameter

2-4 all lost stem basal area and density. Most new growth is from seeds sprouting not from vegetative regeneration. Similarities in species composition were around 50 percent for herbs, vines, and tree seedlings, 20 percent for saplings, 15 percent for pole-size trees, and 4-10 percent for larger trees. Generally, the smaller species stayed about the same, but the larger tree species experienced a decline in numbers after logging. In control and low-intensity, the trees are mostly long-lived trees whereas in the moderate and clear cut plots, the area was much more dominated by smaller species, short-lived, successional.
Conclusion: to maintain long-term structure and biodiversity of rainforest, need to do harvest in small, interdispersed areas in natural rainforest.

Simulating logging scenarios in fragmented secondary forest

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This paper studied the regrowth of secondary forests on old farm land. These are fragments of the main forest and we want to see how they can get back to being the primary natural rainforest. It’s hard because for a fragment, the edges are hurt by change in the microclimate: wind, sun, exposure.
1.    light fragmentation –has side facing natural forest
-bole volume was near that of primary forest in 50 yrs, but species composition still different for first 200 yrs
-mainly medium sized, mid successional

2.    high fragmentation –completely out in non-forest land
-also reached similar bole volume in 50 years, but soon 1/3 lost because lack of seed dispersal, these are mainly early successional species, grow fast but don’t last too long.
-mainly medium sized, mid successional
     3. Primary forest –mainly late successional

Types of logging:
Polycyclic –10-30 yr cutting cycles
Monocyclic –60 yr cutting cycles
            --allows regrowth

Next: Reforestation techniques and studies

References:

Kammesheidt, L., Kohler, P., Huth, A, 2001. Simulating logging scenarios in secondary forest embedded in a fragmented neotropical landscape. Forest Ecology and Management, 170, 89-105.
Parrotta, J.A., Francis, J.K., Knowles, O.H., 2001. Harvesting intensity affects forest structure and composition in an upland Amazonian forest. Forest Ecology and management, 169, 243-255.

Pictures:
1. Picture from: http://www.realtime.net/~raintree/rainforest.html
2.Picture from: http://www.vannattabros.com/
3.Picture from: http://www.vannattabros.com/
4.Picture from: http://www.vannattabros.com/

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