THE IMPACT OF RIPARIAN BUFFER STRIP CHARACTERISTICS ON FOREST HARVESTING
Rien Visser MikeMcCondie
ABSTRACT INTRODUCTION
A paper planning exercise was carried out A buffer strip along a watercourse can to evaluate the impact of Jixed width significantly reduce the instream and riparian bufer strips on harvesting plans. downstream impacts from harvesting In three dzferent catchments, the width operations (Graynoth, 1979). Riparian and the percent of the total stream length buffer strips are not limited to required for the riparian bu$er strip were sedimentlnutrient interception but serve varied to provide dzferent scenarios. No many other functions, such as providing site specific information was taken into aesthetic qualities, maintaining instream consideration when applying the buger values and allowing diversity of biota strips, and no management practices were within our plantation forests (Fenton, specified for the strips. 1992).
The following trends were established. A number of countries have imposed fixed The area required for riparian bufer strips width riparian buffer strips for their was determined by the stream density of forested land use. They are also used in the catchment. As the restrictions specific cases in New Zealand. The loss increased: of productive area is one of the forest industry's most widely proclaimed - the area afected by the bu$er concerns in relation to the demand for strips increased proportionally broad generalised riparian buffer strips. The physical dimensions of riparian buffer - the roading requirements increased strips can have a direct influence on the steadily above the initial harvesting plans. requirement This study uses the paper planning - the setting area (coup) size and the approach to evaluate the effect of imposing average haul distance decreased fixed width riparian buffer strips on harvesting. The paper planning exercise - no clear trend could be determined has been shown to be very effective as a for the number of landings required research tool (Reutebach and Murphy, 1986). No site specific information is Table I - Catchment characteristics
Project Catchments Owera Whakauru Graham Total Catchment Area (ha) 296 302 202 Total Stream Length (m) 14080 7870 11630 Stream Density (mlha) 47.6 26.2 57.6 Initial Productive Area (ha) 280 300 175
taken into account, such as the ecological pumice, and much of the area has already value of the stream, the slope of the bank been cleared over the past four years. The or the soil type, when applying the buffer stream flows along a deeply incised valley strips. cutting west off the Mamaku Plateau. Bordering the main valley is gently rolling In each area the physical dimensions of the hill country suitable for ground based riparian buffer strip were altered to extraction. provide five different restriction combinations. For each combination, a Nelson/Marlborough - Part of the Graham harvest plan was generated so that the area Stream Catchment. This area is located in in buffer strips, the roading density and the RaiIWhangamoa Forest just south-east the number of landings, their setting size of Nelson. The area is on Pelorus steep and average hauling distance (AHD) could soils and the stream drops steeply from its be calculated. native bush covered headwaters located in the Mt. Richmond State Forest Park, to CASE STUDY the radiata pine covered mid-lower slopes into the Whangamoa River. It has been Project Areas partly logged using both ground based and highlead systems. Contour tracking is The following areas were chosen because used for some of the ground based they represent a cross-section of the type extraction. of catchments that are in plantation forests throughout New Zealand. The total catchment area, the stream length and the initial productive area were Coromandel - Part of the Owera River measured directly from the 1:5,000 and Catchment. This area is located in 1: 10,000 topographic maps, and are shown Whangapoua Forest on the Coromandel in Table 1. Peninsular. The watercourses are generally narrow and steep sided, with a Project Design mix of remnant native bush and scrub. It is moderately steep forest with clay soil In defining buffer strip requirements for a which will require a mixture of cable given site, the following important hauler and ground based extraction variables should be taken into account systems. (Hicks and Howard-Williams, 1990) :
Central North Island - The central part of - the length of watercourse requiring the Whakauru Stream Catchment. This protection within the area under area is located in Kinleith Forest near consideration Tokoroa. The soils are deep free draining - the required width of the strips It includes both the land converted into buffer strips, and sections of forest that - the desired height clearance over will become inaccessible due to the the strip restriction. Logging machines, new roads, major road upgrades, and landings have - the vegetation management been excluded from the riparian buffer practised within the strip area. The loss of productive land due to permanent roading has not been included. To try and establish some basic trends for The stream density varies considerably the effects on harvesting, the following between the catchments (Table I), and the restriction parameters were chosen : area required for riparian buffer strips varies accordingly.
Length - a buffer strip extending for either Table 2 - Afected Area 30% or 75% of the total stream length. This was applied from the lower main waterways in the catchment and then Riparian Productive Area Affected extended, as required, into headwaters and Restrictions minor side catchments. Length Width Owera Whakauru Graham
(46) (m) (ha) (%) (ha) (%) (ha) (%) Width - a 20 or 40 metre strip width on 0 0 0 0 0 0 0 0 each side of the stream centerline. These 30 20 16.7 5.9 8.6 2.9 10.7 6.1 values were chosen to reflect some of the 30 40 33.4 11.8 16.9 5.6 21.3 12.2 current overseas restriction requirements. 75 20 38.0 13.5 22.5 7.5 31.8 18.3 75 40 80.1 28.4 44.5 14.8 60.4 34.7 Height restrictions were not considered since they will only have a significant impact if the buffer strip was ruled to be a strict "no-go" area. The ability to road across streams at appropriate points has In preparing the initial plans (no riparian not been excluded, but avoided if possible. restrictions) for each area, an attempt was No assumptions were made about the made to : management practices required within the strip. PLANS' harvest planning software - use existing roads and tracks, with was used to draw up a harvest plan for appropriate realignment and widening each combination. All the results as required presented were measured from these plans. - concentrate roading along main ridges, benches and generally in areas with a RESULTS low gradient
Area Affected by Restrictions - avoid roading beside watercourses, and through areas of unstable soil or Table 2 shows the portion of the initial morphology productive area affected by the riparian buffer strip restriction imposed.
' Preliminary Logging ANalysis System produced by the USDA Forest Service - PNW Research Station, Portland, U.S .A. This approach will help reduce potential identified for ground based extraction did adverse impacts and ensure reduced not differentiate between skidder, tractor construction and maintenance costs or tracked skidder. Cable areas were (Vaughan, 1990). Road crossings of examined with a medium powered skyline buffer strips has been minimised and the machine having a 21 metre high tower and use of existing roads within the buffer a maximum reach of 600 metres. strips was only allowed if minimal earthmoving was required to bring them Double handling on cable settings was up to logging standard. included where the hauler was located on an acceptable pad and logs were Road requirements measured for each transferred by ground based means to a restriction level examined during this study suitable processing site. are shown in Table 3. Boundary roads were split equally between adjacent Methods such as long reach multispan forested catchments. systems or helicopter logging were not included in this analysis. The total Setting Parameters number of landings required, the average setting size and the AHD obtained from All planning was based on conventional the planning exercise are shown in Table style ground-based and cable 4. (highleadlskyline) extraction. Areas
Table 3 - Roading requirements - Riparian Roading Requirements Restriction Length Width Owera Whakauru Graham
(1 (m) (km) (da) Ocm) (&a) (km) (mlha) 0 0 9.3 33.2 8.9 29.7 5.2 29.7
30 20 9.3 33.2 9.1 30.3 5.2 29.7 30 40 10.7 38.2 9.1 30.3 5.2 29.7
75 20 11.3 40.4 9.5 31.7 5.8 33.1 75 40 11.5 41.1 9.6 32.0 5.8 33.1
Table 4 - Setting parameters - number, size and AHD
Riparian Average Setting Parameters Restriction Owera Whakauru Graham Length Width Sites Size AHD Sites Size AtTD Sites Size AF1D (% (m) No. (ha) (m) No. (ha) (m) No. (ha) (m) 0 0 30 9.4 187 38 7.9 153 18 9.7 189
30 20 30 8.8 187 39 7.5 147 18 9.1 187 30 40 33 7.5 177 39 7.3 146 18 8.5 185
75 20 38 6.4 152 41 6.8 142 24 5.9 155 75 40 40 5.1 136 39 6.6 140 22 5.2 150 Roading density (rnlha)
25 -- I" Area affected I% of totall 20 -- /
15 -- /A
10 ;; - Average setting size (ha) -- - --_ ------5 -- A C A
0 1 I I 0 5 10 15 20 25 30 35 Riparian Buffer Strip Area 1% of total) Figure 1 - Trends established by regression analysis
Regression Analysis
Regression analysis was used to construct The regression analysis results have been predictive equations for the affected area, combined to produce a simple spreadsheet the roading and the setting size. The most model. How to use the spreadsheet model appropriate prediction variable (AREA) for and what you can expect to obtain from it all these equations was found by is explained in Appendix 1. multiplying the required riparian buffer strip % length and width by the stream DISCUSSION density of the catchment. Affected Area Affected area (% of total) = AREA From Figure 1 we see that the affected (P
Roading Setting Parameters
The increasing levels of riparian protection Planning to meet increasing buffer strip along the streams required changes to the requirements reduced the average setting logging layout over portions of the size (Figure 1). Additional landings were planning area, and these changes were often required, and where this occurred often associated with additional roading AHD reduced significantly. We can note requirements (Figure 1). Increased that during this project the unrestricted roading requirements seldom coincided plans were all associated with the least with existing roads or tracks, and often number of landings, largest average setting crossed the steeper headwalls of sub size, longest AHDs and least roading catchments to access adjacent unroaded requirements. ridges. The additional roading required to meet various riparian commitments was The ground based settings are less affected often characterised by : by increasing restriction levels than cable settings. It is easier to manipulate ground - higher environmentallsite impacts based layout to fit in with buffer strip requirements, particularly on easy - higher construction and maintenance topography. Some landings on all the costs plans serve both ground-based and cable extraction. On the difficult sites, cable - higher risk of failure setting areas are generally larger than those for ground-based extraction.
RMA (1991) river definition "means a continually or intermittently flowing body of fresh water and includes a stream but does not include any artificial watercourse". The productivity and performance of cable CONCLUSIONS settings is very dependent on deflection. Deflection may be severely limited on The development of this project has many sites if skylines cannot be anchored highlighted the following points in relation through and beyond riparian zones. The to fixed width riparian buffer strips: implications of this are lower payloads andlor increased downtime, and increased - The area required for riparian buffer site disturbance due to logs dragging along strips was determined by the stream the ground. density of the catchment.
Further Considerations - As the restrictions increased, the area affected by the buffer strips increased The effect of differing management proportionally, the roading require- practices on the effectiveness of buffer ments increased steadily above the strips (sediment trapping, protection of initial requirement, the setting area instream biota, aesthetic values, etc.) still (coup) size and the AHD decreased. needs to be established. The result of such work will greatly influence the - The overall impact of riparian buffer overall discussion, and in particular the strips is very dependent on the industry's acceptance of using riparian management practices required within buffer strips. Many of the current the strip. The impact can be minimal concerns are perceived and subjective and if it is designated a zone of work is required to recommend guidelines awareness, or severe if the buffer strip based on measurable and objective data. is decreed a "no-go" zone.
Gilliam et al(1992) stated close agreement - The cost of having riparian buffer for riparian buffer strip requirements can strips is not limited to loss of be found for a given location between productive land but includes ratesltaxes local authority and forest industry staff on unproductive land, weedlpest during site visits. A co-operative approach control costs and inconvenience. involving industry, environmental agencies, local authorities and researchers - Generalised riparian buffer strip should therefore begin dealing with some requirements are likely to result in of the issues highlighted during the additional roading and landings. These development of this project. Collaborative will often be in more difficult research should continue on a site locations, have higher adverse specificlcase study basis to address the environmental impacts and be more performance of, and possible management costly to construct and maintain. alternatives within, riparian buffer areas. It would provide the basis for New - Smaller setting areas may reduce cable Zealand guidelines regarding the placement deflection and can lead to greater site and dimensions of buffer strips. disturbance, as well as lower productivity due to reduced payload Guidelines for the implementation of capability. riparian buffer strips should focus on recommending practical techniques that - Riparian buffer requirements should will effectively reduce adverse impacts on not be based on a percentage of the identified significant values. total stream length unless the streams in a region are well defined. - Good road planning for the first Reutebach, S .E., Murphy, G. C. (1986). rotation harvest and re-establishment "Using a Computer Aided Planning should ensure less environmental Package to Assess the Impact of impact from the subsequent rotations. Environmental Restrictions on Harvesting Systems". Proceedings of the Californian - There is a need for further research on Riparian System Conference, University of a site specific or case study basis to California, Davis. speed up the change from perceived, subjective control to measurable, Vaughan, L. (1990) : "New Zealand objective control. Forest Code of Practice", Logging Industry Research Organisation, Rotorua. - Ideally the use of riparian buffer zones should aim to avoid or minimise the adverse impacts on identified values.
REFERENCES
Fenton, J.A. (1992) : Riparian zone Workshop: "Implications for Exotic Forestry". NZFRIILIRO organisations, Rotorua.
Gilliarn, W., Schipper, L., Beets, P., McConchie, M. (1992) : "Riparian Buffers in New Zealand Forestry". FRI Publication.
Graynouth (1979) : "Effects of Logging on the Stream Environments and Fauna in Nelson", N.Z. Journal of Marine and Freshwater Research, 13 (1) : 79-109.
Hicks, B. J., Howard-Willarns, C. (1990): "Development of Guidelines for the Management of Streamside Riparian Strips", Presented at 'Criteria for the Establishment of Riparian Strips' Workshop, Limnological Society, Christchurch.
Mosley, M.P. (1980) : "The Impact of Forest Road Erosion in the Dart Valley, Nelson". N. 2. Journal of Forestry, v. 25, No. 2.
Murphy, G., Blundell W., Fahey B. : (1991) "The Impact of Environmental LOGGING INDUSTRY RESEARCH ORGANISATION Constraints on Forest Harvesting in the P.O. Box 147, ROTORUA, NEW ZEALAND. Marlborough Sounds" New Zealand, Fox: 0 7 346-2886 Forest Research Institute. Bulletin No. 166. -9-
Appendix 1 - Riparian Buffer Economic Model
From the regression analysis of the results presented in the report, a short spreadsheet model has been generated. For a given catchment,
The following variables are required:
* catchment size (ha) * total length of stream (km) * length and typical width of road, OR an estimate of roading density * buffer strip requirements (three variable constraints can be specified per catchment)
The spreadsheet will then calculate:
* final roading density (this includes the additional roading required because of the buffer strip restrictions) * area taken up by these roads * area that will be taken up by the buffer strip * total area out of production due to roading and riparian buffer strips (as an area and a percent of the total)
The sample spreadsheet
The spreadsheet will allow any or all of the variables to be changed, to gauge the impact of altering them. In the example shown on the attached spreadsheet, each of the three catchments has a size of 300 ha. The first two have identical stream and roading characteristics, but differing buffer strip requirements which increased the total area out of production from 5.6% to 18.7%. In the third catchment the length of roading is not known, so it has been estimated at 4% (of the total area). There is also a variable buffer constraint, 40 metres in width along 75 % of the total stream length, 15m width along 20%, and a 10m width along the remaining 5%. The spreadsheet estimates that 31.7% of this catchment will be affected by roading and buffer strips requirements. r+ [I) 5' rC 4 2 z0 : o 2. 2 ru m [I)E 2 !L g OQ 5 - 2 77 5$ (D 0 2 [I) 0 2,"s 5 5 % c (D 2,; 2 73 z5. '0 -h 0 3 53 a 0- QO [I) TJ 2 ( cz a a Q - ow Q %' 2 g.g F2 3 cc QJ 2. 3 Q U 5'$ aa s = ,-- 2 3 [I) Q a 2. [I) g QZ.525 3 - 3 2 42 a a (0 O 2 a3 2: 5 [I) [I) 8 = :a g.42V)- a 2 5 mc 3 [I) 0 5.2 a 2 g "JQ3-Dc. [I) 2. u a 3. o V) 28 3 S 0 - -. as s [I) o 3 3 a (D cr 5. cr 5 a 5, -h 3 " e (D3 c V) g z F+ 2. J3 Z"3E. u -E. 30 (D CT - (D n