IN THE MATTER of the Resource Management Act 1991

AND

IN THE MATTER of the hearing of applications by Timberlands West Coast Limited to Buller and Tasman District Councils for land use consents for sustainable beech forest management (including harvesting and associated activities)

EVIDENCE OF Peter Clinton

ON BEHALF OF THE APPLICANT

Nutrient removal during sustainable harvesting of beech forest

Peter W. Clinton, November 1999

Background

Harvesting of logs contrasts with natural tree death or processes initiated by disturbance that result in tree death in that removal of timber circumvents logs entering the pool of deadwood in the forest ecosystem. This deadwood is important in maintaining biodiversity and the function of that biodiversity is important in maintaining nutrient cycling processes, nutrient availability and nutrient uptake and energy flow. Therefore one of the consequences of harvesting timber is to interrupt the natural process of deadwood formation by altering rates of formation and the number, size, and species of woody substrates. This will have implications for seedling regeneration, biodiversity (vascular, nonvascular plants, insects, fungi), and rates and amounts of nutrient cycling, carbon sequestration and soil development.

Effects of harvesting on nutrient pools

Natural beech forests of the type in question contain considerable amounts of decaying logs (Stewart and Burrows 1994). The type of harvesting system employed in the beech management scheme creates deadwood in the forest because not all of the tree is removed. Although the importance of deadwood in nutrient cycling processes in naturally disturbed forest has been clearly demonstrated (Allen et al. 1997) it cannot be stressed enough that the impact of removing individual pieces of logs rather than the whole tree stem is unknown.

The processes involved in log decay are not well understood but Stewart and Burrows (1994) suggest that beech logs decay very slowly. Their observations raise the issue as to the extent to which nutrients in logs contribute to plant requirements compared with other processes including nutrients supplied from mineralization of organic matter in litter and forest floor layers, mineral soil weathering and atmospheric inputs. The work of Neary et al. (1978) (Table 1) gives an indication of possible weathering rates for West Coast soils, although more work in this area is required for the wide range of soils found. The litter and forest floor layers can store large quantities of nutrients in beech forest, particularly calcium (Allen et al. 1997; Goh and Heng 1987; Miller 1963a) and, like mineral soil horizons, are not disturbed by low intensity harvesting. The question of the role of nutrients in decaying logs in meeting plant needs will be addressed by proposed research.

Ameliorating effects

In most cases the impact of removing the harvested log will certainly be less than removing the whole tree stem. This impact could easily be ameliorated by management through the application of mineral nutrients if a need arises. Quantities of nutrients removed from each site are easily calculated from records of timber harvested. Other management techniques, such as removing bark in situ, may be developed to even further reduce nutrient removal and maximise nutrient retention.

Questions that requiring further research

What is the magnitude of loss of nutrients and deadwood habitat under the proposed harvesting scheme? How sustainable are these losses of nutrients and deadwood? Can these impacts be remedied by management inputs and manipulations? Will natural weathering rates and other inputs compensate for nutrient removals in the harvested logs? Research is underway to address these issues, particularly the impact of nutrient loss associated with log removal on soil processes and the effects of removing logs on biodiversity.

Conclusions

In New Zealand, fast growth rates and relatively high rates of nutrient removal in harvested biomass from exotic plantations have caused concern that the long-term ability of sites to sustain productivity will be compromised, especially on low fertility soils. However, harvesting systems now used in the sustainable management of indigenous forests minimise both the disturbance of soils and removal of nutrients. Therefore, this concern may not be warranted for sustainable harvesting of beech forest which involves the removal of relatively small quantities of timber on an area basis.

Table 1 Nutrient inputs from natural processes at Maimai (kg/ha/yr)

N

P

K

Ca

Mg

Ppt

2.8

0.26

5.7

2.1

3.9

Weathering

0.13

1.7

12.3

0.3

Total

2.8

0.39

7.4

14.4

4.2

Calculated from data of Neary et al. (1978).

References

Allen, R.B.; Clinton, P.W.; Davis, M.R. 1997. Cation storage and availability along a Nothofagus forest development sequence in New Zealand. Canadian Journal of Forest Research 27: 323-330.

Goh, K.M. and Heng, S. 1987. The quantity and nature of the forest floor and topsoil under some indigenous forests and nearby areas converted to Pinus radiata plantations in South Island, New Zealand. New Zealand Journal of Botany 25: 243-254.

Kimmins, J.P. 1987 Forest Ecology. Macmillan Publishing Co. N.Y.

Miller, R.B. 1963. Plant nutrient cycles in hard beech (i) The immobilisation of nutrients. New Zealand Journal of Science 6: 365-377.

Neary, D.; Pearce, A.J.; O'Loughlin, C.; Rowe, L. 1978. Management impacts on nutrient fluxes in beech-podocarp-hardwood forests. New Zealand Journal of Ecology 1; 19-26 .

Stewart, G.H. and Burrows, L.E. 1994. Coarse woody debris in old-growth temperate beech (Nothofagus) forest of New Zealand. Canadian Journal of Forest Research 24: 1989-1996.

Wardle, J.A. 1984. The New Zealand Beeches: Ecolog, Utilisation and Management. New Zealand Forest Service.