Environment Court evidence: effects of pine forest, land use and harvesting on stream ecosystems, Whangapoua forest, Coromandel
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The purpose of my evidence is to describe the Whangapoua Forest stream monitoring programme, and discuss the results of the monitoring and related research on the effects of pine forest, land use and harvesting on stream ecosystems.
Stream lighting in five regions of North Island, New Zealand: control by channel size and riparian vegetation
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Lighting of streams profoundly influences their ecology, particularly through primary production and thermal behaviour. We used paired canopy analysers, instruments with fish-eye lens imaging, to measure sunlight exposure of streams in five regions of North Island, New Zealand. Reach-averaged stream lighting, at both water and bank level, was strongly influenced by riparian vegetation type. Pasture streams had comparatively high light exposure (median water level lighting = 45% of ambient), with most shading contributed by banks and overhanging herbs. Lighting was low in small forest streams (median = 1.3% for native forest, 1.2% for pine plantations), but increased sharply as the gap in the canopy widened with increase in channel width above c. 3.5 m. The understorey in pine plantations contributed more shade than the pines themselves: damage to this understorey (e.g., by goat browsing or floods) increased lighting markedly. Harvesting of pine plantations exposed streams to high light levels except where a riparian buffer was maintained. Periphyton biomass, varying over more than four orders of magnitude in the study streams, correlated broadly with lighting.
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The purpose of this report is to review and summarise published research on the efficiency and management of riparian buffer zones (RBZ) with respect to the attenuation of sediment and nutrients, and biodiversity enhancement. While there have been numerous studies on the efficiency of RBZ with respect to sediment and nutrients, many of these studies have been small-scale and site-specific. Therefore, a review of these studies needs to consider an assessment of the catchment scale factors that influence the effectiveness of RBZ in attenuating catchment loads.
Effects of progressive catchment harvesting on stream clarity, temperature, habitat and invertebrates in Whangapoua Forest: nineteenth annual report incorporating results from 1992-2011
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Logging of forests causes disturbances which can impact streams over several years. This is the nineteenth annual report aimed to determine the relative magnitudes of impact and rates of recovery from progressive pine forest harvesting in Whangapoua Forest on: stream water clarity (fortnightly), temperature (summer), stream habitat and biota (summer and end of winter). This report describes findings of the winter 2010 and summer 2011 surveys (13 sites), and incorporates findings from earlier surveys (since 1992) from streams that differed in size and harvest intensity in the surrounding catchment. This report also investigates retrospectively, whether results and conclusions on harvest impact from summer only surveys were comparable to those drawn from biannual surveys.
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Water temperature has profound effects on stream ecosystems. We studied effects of clear-fell logging Pinus radiata plantations on mid-summer water temperatures and recovery times in streams with 2–12 m wide channels. Post-logging increases were 2–3.8 8C for summer daily means and 4–7.3 8C for summer daily maxima. Rates of recovery of thermal regimes after logging were strongly negatively correlated with stream size, as indexed by catchment area, channel width or baseflow (r2 = 0.80–0.93). Summer daily mean and maximum temperatures declined during the riparian vegetation regrowth phase by 0.18 and 0.47 8C year1, respectively, for the largest stream and 1.4 and 1.9 8C year1 in the smallest stream. Thermal regimes were restored in small streams (2–4 mwide channels) about 6–8 years after clearfelling. In medium-sized streams (6–12 m wide channels), we predict this recovery will take 12–16 years.
Land use effects on habitat, water quality, periphyton, and benthic invertebrates in Waikato, New Zealand, hill-country streams
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Water quality, habitat, and biota were compared during spring amongst c. 100 m reaches on 11 streams draining pasture, native (podocarpbroadleaf) forest, and exotic pine forest established on pasture 15 years previously. Differences were greatest between the pasture and native forest streams. Only 1-3% of incident light reached native and pine forest streams whereas 30% reached pasture streams. Pasture streams had 2.2°C higher mean temperature than the native streams, and 5- fold higher nitrate, 30-fold higher algal biomass, and 11-fold higher gross photosynthesis. Native streams were 60% wider than pasture, with pine streams intermediate. Pine and pasture streams had 3-fold higher suspended solids and fine sediment stored in the streambed than native streams. Woody debris volume was 17-fold greater in pine than pasture streams, with native streams intermediate. Invertebrate taxa richness did not differ between land uses. Community composition differed most between pasture and native forest, with pine forest streams intermediate. Invertebrate densities were 3-fold higher in pasture than native streams, mainly because of more chironomids and snails, but mayflies, stoneflies, and caddisflies densities were 2-3-fold higher in forest streams than pasture.
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This article summarizes the current state of knowledge with respect to forestry and water yield. The primary mechanism by which tall vegetation affects the water balance is through evaporation of intercepted rainfall, thereby reducing the amount of water available for runoff and streamflow. Generally trees have a high capability for interception due to a large leaf area and high aerodynamic roughness above the canopy. In experimental studies around New Zealand reductions in annual water yield of between 30-80% have been measured following afforestation of pasture. These figures are lower where afforestation has replaced scrub species. The effect of afforestation on peak flows is considerable, particularly for small flood events although there is some evidence that storms with long return periods may also be substantially reduced following afforestation. There is considerable debate whether these effects can be seen at a large catchment scale. The effect of afforestation on low flows is less well studied. Low flows are reduced following afforestation but it appears that in some cases low flows are affected to a lesser extent than annual yield. Public policy on forestry and water yield varies between regions. For example Tasman District Council and Environment Canterbury have land use restrictions based on water yield arguments while the Otago Regional Council does not.
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Fine sediment accumulation was measured in streams in low-order forest watersheds across a gradient of selective harvesting with no protective riparian buffers. Comparisons were made among sites in selection-cut (40% canopy removal), shelterwood-cut (50% canopy removal), diameter limit cut (about 85% canopy removal), and undisturbed tolerant hardwood catchments. These were further compared with a headwater stream catchment not harvested but affected by logging road activities. The greatest increases in fine inorganic sediment occurred at the road-improvement site with mean bedload estimates more than 4000 times higher than pre-manipulation values. Sediment bedload was still significantly elevated 2 years after the road-improvement activities. Significant increases (up to 1900 times the pre-harvest average) in inorganic sediment also occurred at the highly disturbed diameter-limit site as a result of heavy ground disturbance and channeled flowpaths from skidder activity in riparian areas. Similar increases were detected at the selection-cut site but were attributable to secondary road construction in the runoff area. In the shelterwood harvest area, where logging roads were not a factor, no measurable increases in sediment deposition were detected. There was little indication that harvesting activities at any site affected the organic fraction or the particle size distribution of fine sediments. The results of this study suggest that riparian buffer zones may not be necessary for selective harvesting in hardwood forests at up to 50% removal, at least in terms of reducing sediment inputs.
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Protection of streams and riparian zone functions is a key objective of sustainable forest and aquaticecosystem management. Forest managers utilise best management practices (BMPs) for timber harvesting, log extraction and soil conservation, including the use of riparian buffer strips, sensitive stream crossing and road drainage design. In NSW the efficacy of these BMPs has not been fully tested, nor has their cumulative effect in protecting stream systems at the catchment scale. This paper presents findings of a small catchment experiment conducted in a native forest control catchment and two 1962 age-class Pinus radiata plantation catchments within Canobolas State forest. The plantation catchments were harvested in 2002/3 using legislated BMPs. Streamflows and water quality (turbidity and suspended sediment concentration) were measured between 1999 and 2006 allowing assessments of the impacts of harvesting activities using the BMPs. Results indicate that no significant differences were observed in event mean concentrations of suspended sediment, mean turbidity, or low-flow turbidity or TSS. In these catchments the BMPs used were adequate for protecting streams from the potential effects of forestry activities. These results and monitoring of the effects of BMPs in other catchments provide valuable feedback for the review of practices and policies. Analyses of water yields and evapotranspiration have confirmed that annual streamflows in pine plantations vary with respect to annual rainfall and plantation age; the majority of changes being attributable to changes in the baseflow component of total streamflows. Predictions of the likely interception of rainfall by plantations need to take account of these factors.
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Concern over New Zealand's environmental quality and the long-term impacts of agricultural sector activities on water quality is increasing. Lake and river water quality is declining as a result of past and current land use practices and national and regional initiatives are being developed to halt and reverse the declines. Plantation forestry is a low impact land use by comparison to other agricultural sectors, requiring less nutrient input in terms of fertiliser and causing less environmental impact on ground and surface water from nutrient leaching. A nutrient balance model has been developed to predict nutrient fluxes within plantation systems, over one or more rotations. The model is a simple mass balance model; it predicts nutrient uptake by a crop and partitions nutrients into the various pools within the soil/plant system. The model predicts when there will be surpluses or deficits in the system and consequently when there is an increased risk of nutrient transfer or a need for fertiliser application. Running different scenarios demonstrates the effect of vegetation management, harvesting intensity, or change in productivity due to climate change on the pools of nitrogen during a rotation, and the effects of multiple rotations on soil phosphorus pools. Using the model to develop various scenarios will enable the development of multiple land use scenarios, with a focus on minimising the nutrient 'footprint' or impact for a specific catchment or region. Predictions of nutrient fluxes can contribute to the development of nutrient trading models, where the value of plantation forestry as a low nutrient footprint land use may be recognised as an additional economic benefit above the value of the tree crop.
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Chapter 5 is a brief description of the potential physical, economic and social impacts of the project. This includes effects on erosion, soil quality, water quality and quantity, biodiversity, climate change and greenhouse gases, and factors involved in agriculture-forestry changes.
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This report presents the work undertaken on the Waiapu River Catchment Study, the purpose of which was to investigate the geophysical, social, cultural, and economic dimensions of the erosion problem in the Waiapu River catchment in order to inform future policy decisions with respect to the catchment in the context of the Deed of Settlement between Ngāti Porou and the Crown. The report includes:
1) An outline of existing knowledge related to the (i) geophysical and land use aspects and (ii) social, cultural, and economic aspects of erosion and land use change within the Waiapu River catchment and the wider East Coast region.
2) Identification of gaps in the existing knowledge apparent to the research team, and recommendations for addressing any gaps identified.
3) A description of a baseline from which future progress in the Waiapu catchment may be measured (benchmarking) for the (i) geophysical and land use aspects and (ii) social, cultural, and economic aspects of erosion against the values of Ngāti Porou for the catchment and well-being of the people.
4) An outline of the project team‘s interpretation of a desired state for Ngāti Porou and consideration of possible options for addressing the erosion problem.
5) Assessments of the scope (size and scale) of the erosion problem in the catchment and critical evaluations of the effectiveness of erosion mitigation measures for the (i) geophysical aspects and (ii) social, cultural, and economic aspects of erosion.
Pine afforestation and stream health: a comparison of land-use in two soft rock catchments, East Cape, New Zealand
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Environmental conditions in streams draining pastoral catchments are typically degraded by comparison with native forest streams. However, few studies have investigated land-use influences on streams in erosion-prone terrain where channel disturbance and mobilisation of land contaminants under pasture might be particularly severe. We studied the water quality and stream ecological ‘health’ of streams in two catchments in the Gisborne District, eastern North Island, New Zealand, where pine afforestation is proceeding rapidly in an effort to reduce erosion. We compared pasture, pine plantation, and native forest land-uses in these catchments that were characterised by differing forms of erosion of the soft rock hill country. Streams in mature pine plantations in both catchments had generally better water quality (lower faecal contamination and nutrient concentrations) than those in pasture, and tended to approach the condition of reference streams in native forest. However, visual clarity and turbidity and particulate forms of nutrients remained degraded in pine plantations where deeply incised gullies continued to yield large amounts of fine sediment. Stream stability had the dominant influence on epilithon biomass and invertebrate density, and increasing taxa richness was related to increasing stability. Invertebrate community metrics of stream health (%EPT and QMCI) were degraded in pasture compared to pine and native forest, and community composition was influenced by both stability and water temperature. In these streams, establishment of mature pine plantations on pasture in soft rock terrain resulted in water quality and stream health conditions similar to native forest streams.
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This is a summary of recent literature on the positive and negative environmental impacts of planted forests in New Zealand. Key results are as follows: Biodiversity - plantations provide a habitat suitable for a wide range of indigenous forest species, both aquatic and terrestrial. Water yield - afforestation can reduce peak catchment flood flows by up to 50%. Water quality and leaching - planted forests have the lowest potential for nitrate and phosphorous leaching with levels similar to indigenous forests. Sediment yield - afforestation of whole catchments can reduce sediment load to waterways by 50-90%. Soil erosion - recent research provides further support that plantations mitigate soil erosion. Impacts on soil nutrients the high level of soil organic N present in established pastures decreases markedly when the pasture is planted in pine forest. This information is relevant to forest managers needing to manage the environmental effects of their trees, and provides the baseline for further research. For the Forest and Environment FRST programme the information will contribute to planning research on indicators of sustainability.
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Researchers compared pastoral farming with forestry over 12 years and found that a forest produces less sediment, uses slightly more water, reduces soil erosion, has a more positive effect on stream environments, and makes no real difference to water quality. Begun in 1993, the land use study was a response to public concern about the environmental effects of forestry on Hawke's Bay hill country. It was completed in 2005.
A paired catchment study approach was used, with one catchment in forest (Pakuratahi) and the other in pasture, farmed with sheep and beef, as a control (Tamingimingi). The catchments represented North Island hill country. Researchers compared the environmental effects of commercial forestry and pastoral farming through various stages of the forest rotation. The sequence of pre-harvest, harvest, replanting, and canopy closure covered time of major environmental change.
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My evidence will address the following matters:
•the impacts of sediment discharge on water quality and aquatic habitats/biota;
•ways of monitoring the effects of fine sediment discharge;
•the general effects of forestry on water quality;
•the magnitude and duration of water quality impacts of the harvest phase of production forestry.
Environment Court evidence: effects of forest harvesting and the role of riparian zones- supplementary evidence
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Kevin Collier provides supplementary evidence relating to biodiversity, riparian buffer widths and wood management in Whangapoua forest, Coromandel.
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My evidence deals with the following matters: (1) effects of forest harvesting on stream life and the duration of its impacts; (2) the roles of riparian zones in buffering stream ecosystems; (3) effects of riparian buffers and management of post-harvest wood on streams at Whangapoua; and (4) the riparian management regime proposed by Environment Waikato.
Environment Court evidence: Riparian buffer widths and microclimate in Whangapoua forest, Coromandel
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My evidence has to do with forest buffer widths to protect streams and near-stream riparian ecology, particularly from the microclimate exposure of open land.
The sustainability paradox - an examination of The Plantation Effect - a review of the environmental effects of plantation forestry in New Zealand
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This article provides a brief summary of various environmental effects of plantation forests, including soils, water quality, biodiversity, landscape values, risks, and the economy.