albany/riverhead ecological health assessment

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Ecological Health Assessment for the

Albany/Riverhead Region

Written by Alex SmithID 1347248

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Introduction 4

Map 1-Land Cover 6

Map 2-Patch Corridor Matrix 8

Map 3-Native Habitat Connectivity 10

Map 4-Ecological Health 12

Conclusion 17

Bibliography 18

Appendix 1-Patch Key 19

Appendix 2-Scoring Tables 20

Appendix 3-Field Data 22

Contents

Introduction

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“A patch of native bush is part of a mosaic of other bush types up and down the catchment that together provide continuous, year-round food and shelter for native animals. Just as importantly, it gives us a place to go for peace and recreation, while giving our property and land it’s unique identity. Unfortunately, many bush patches are not healthy” (Jannsen, 2004)

Through out the landscape are remnants of forests which used to cover most of New Zealand before human arrival and patches of regrowth since. Human disturbance has resulted in the fragmentation of native habitat (due to the disturbances spatial scale, severity and duration). This fragmentation has formed a pattern that effects the ecological processes occurring in the landscape, resulting in some bush fragments supporting only a few of the native plant and animal

species that were previously common (Jannsen, 2004). The need to protect and restore the biodiversity of New Zealand has long been rec-ognised and unless action is taken to ensure the essential ecological processes are operating in these fragmented landscapes, the attrition of natural habitat and species will continue in these bush fragments (Meurk and Hall. 2006).

This report’s aim was to assess the ecological health of the Albany/Riverhead region as outlined in Figure 1. This was done using princi-ples of Landscape Ecology and the use of GIS software and data. This information was then used to see whether the local native ecosystem was functional and what may be done to protect and enhance it in the future, as the region faces development pressures from an expanding Auckland City.

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Legendextent

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Landscape Ecology is defined as being “the study of the effect of landscape pattern on process, in heterogenous landscapes, across a range of spatial and temporal scales” (Turner 1989).

The degree of fragmentation (through the resultant landscape pattern) and it’s effects on the native ecological processes (the functionality of the ecosystems) of the region was investigated through the use of a pattern based landscape model, the Patch Corridor Matrix model. This was adjusted to suit New Zealand Conditions (as outlined by Helmut Jannsen in his book Bush Vitality Assessment).

Introduced by Richard Forman in his 1995 book “Land Mosaics”, this model conceives landscape cover patterns as being a mosaic of three components: Patches, Corridors and a Matrix. (See Diagram).

-Patches are relatively homogenous nonlinear areas that differ from their surroundings. -Corridors are strips of a particular patch type that differ from the adja-cent land on both sides and connect two or more patches. -xThe matrix is the dominant and most extensive (and often most modi-fied) Patch type in a landscape. It is characterised by extensive cover and a major control over dynamics (Lindenmayer DB, Fischer J, 2006).

An extension of the island model, which had patches contained within an inhospitable matrix, this model has the matrix is intersected by cor-ridors or perforated by smaller patches (which form stepping stones). Adjustments made to the model to suit New Zealand Conditions were primarily concerned with the local edge effects that extend from 20-100 m into a bush patch (Jannsen, 2004) and their effect on what area of bush is considered a patch or a corridor/stepping stone. Another adjustment was made to define what size of bush patch was actu-ally suitable in area as habitat for native keystone Fauna (such as the Kereru and Tui).

This identified what was considered native habitat (these included na-tive vegetation at varying stages of maturity and some exotic vegeta-tion likely to be succeeded by native forest) and what was the matrix (all other areas that were non-native compatible vegetation).

Diagrams sourced from Habitat Fragmentation and Landscape Change: an ecological and conserva-tion synthesis, by Lindenmayer D B, Fischer J. (2006). Pages 2 and 34 respectively

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This first map was produced using the Land Cover Database 2 (LCDB2), a Crown database produced For the Ministry for the Environ-ment, Ministry for Agriculture and Forestry and Department of Conser-vation. This is a nation wide database produced primarily using satel-lite imagery which is interpreted into the different land use classes and it is aimed to be updated every 5 years with accuracy improving over time.

For LCDB 1 overall user accuracy was 93.9%, it is assumed that the data used is accurate and up to date due to the lack of resources to ground truth the area. In most cases an area is classed if it has a cover of over 50% but can be less if the vegetation represents a mosaic of three or more classes (Thomson et al., 2003). The resolution of this data is 15m.

The map indicates the region of study consists mainly of the following land use classes:Exotic Forestry to the West and North.Built up urban areas to the Southeast.Agriculture/pasture (of varying qualities) throughout the study area.

These are all human managed land cover classes, with the Agricul-tural/Pastural regions occupying the largest area. Interspersed within these large classes are pockets of native and mixed bush that are the subject of this study.

Fig1: A patch of native vegetation located in the Lucas Creek area, showing the pre-dominant land cover and contrast between landcover structuresFig2: This is typical of the study region, with rolling pasture or crops within which are stands of native and exotic vegetation.

Map 1-Land CoverFig 1

Fig 2

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LegendArea Outline

LCDB2 DataLand Cover Type

Estuarine Open Water

Lake and Pond

Mangrove

Broadleaved Indigenous Hardwoods

Indigenous Forest

Manuka and or Kanuka

Gorse and Broom

Mixed Exotic Shrubland

Deciduous Hardwoods

Other Exotic Forest

Pine Forest - Closed Canopy

Pine Forest - Open Canopy

Forest Harvested

Major Shelterbelts

Orchard and Other Perennial Crops

Short-rotation Cropland

Transport Infrastructure

Built-up Area

Dump

Urban Parkland/ Open Space

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The Patch Corridor Matrix model was used to define what areas of native bush should be considered significant patches of native habitat and what was the matrix. The following land cover types were selected from the LCDB2 as being suitable native forest habitat for keystone¹ bird species:-Indigenous forest -Broadleaf Indigenous Hardwoods-Manuka and Kanuka shrub-land -Deciduous hardwoods-Mixed exotic shrub-land -Other exotic forest

All other land cover classes became a heterogenous² matrix (consist-ing mainly of pasture, agriculture, urban areas and plantation forest). Some exotic land cover classes were included due to the classification process, which classes an area according to whatever may be the ma-jority vegetation type (see Map 1). In some cases the dominant vege-tation cover may be less than 50% in an area. As a result it is assumed that these exotic land cover classes contain native vegetation and are acting as the first stage of succession, eventually giving way to native Podocarp species within 200-400 years as indicated by models con-ducted by Meurk and Hall rof the Riverhead region.

The ‘forest habitat’ was then classed in corridors/stepping stones and patches. First areas of ‘forest habitat’ less than 5 Ha in area were clas-sified as corridors (for Keystone¹ birds) through the matrix. This was due to their small size being compromised by edge effects (explained later). “A near circular bush remnant of 5ha may only have about 1ha of interior habitat, whereas a 50ha bush can have up to 25ha of interior habitat.” (Jannsen, 2004).

The remaining areas were then buffered by 100m (Jannsen, 2004) us-ing a GIS programme to simulate the worst case scenario of climatic edge effects on the forest, providing what was certain to be interior habitat (sometimes called a core). Forest on the edge of a patch will

be subject to different climatic and ecological conditions that that at the centre, especially if the boundary is hard (a high contrast between the two ecosystem types).

The resulting interior habitats were then used to trim and reclassify areas comprised by edge effects into corridors and patches. It was as-sumed that forest less than 200m in width and more than 200m away from the edge would be compromised by edge effects and was classi-fied as a corridor .

The related data supplies by the Ministry for the Environment was as-sumed to accurate, although in some cases roads and houses inter-sect the forest habitat indicated here. For the sake of this exercise they have been ignored. This is significant as if taken into account it would affect the shape of the interior habitat due to the possible edge effects.

Lastly the identified patches were classed into two grades large (be-ing over 25ha) and small stepping stones (being between 5 and 25ha). A single hectare of bush can provide temporary seasonal and breed-ing habitat and will provide a stepping stone to connect populations whereas native forest networks of 25ha are generally large enough to sustain populations of native Keystone species and thereby ecosys-tem functions, providing pests are controlled (Jannsen, 2004).

As a result 18 large Patches (numbered 0-17) and 35 stepping stones (numbered 0-34) were identified from the forest habitat, with a concen-tration in the Albany Heights region. Seven were larger than 100ha.

¹ A keystone species is a species on which other species in an ecosystem largely depend, such that if it was removed the ecosystem would change drastically. In this case the native birds are keystone species as they are essential spreaders of seed and pollinators, as only they are able to carry certain seeds.² Being diverse in character or content.

Map 2-Patch Corridor Matrix

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LegendDissoleved ForestCopyCategories

Corridor

Large Patch

Stepping Stone

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“Good bush connectivity improves source availability, mating opportuni-ties and allows pollen and seed interchange between bush remnants” (Jannsen H. 2004).

Habitat Connectivity is graded on the proximity of habitat patches to each other, corridors and stepping stones, however how we score a patches connectivity is dependant on what species the grading is based upon. In this case the patches connectivity rating has been based upon a system outlined by Helmut Jannsen in his book ‘Bush Vitality Assessment’. This system involves the counting first large, then smaller habitats within 2, 5 and 10 km from the habitats boundaries. These radii are based upon the distances native keystone bird species are willing to fly. Native birds are more likely to fly between bush patch-es within calling distance (less than 2 km away), while smaller birds are less likely to reach patches more than 5 km away (Jannsen H. 2004). In the study region the keystone species are the Kereru (or Wood Pi-geon) and Tui, providing seed dispersal and pollination respectively.

Habitat Connectivity in this case was measured only between the native bush patches within the study area. The patches in the Pare-moremo, Lucas creek and Albany Heights were found to be the best connected to each other being located close to many other patches and connected by closely spaced corridors. Those on the periphery of the study area were found have a lower degree of connectivity, par-ticularly those in the Stillwater and Riverhead Forest. This result does not portray the true connectivity of these outer patches as the region was examined in isolation to it’s surroundings, which if considered may have improved their score even if only marginally.

Map 3-Native Habitat Connectivity

Both diagrams souced from Bush Vitality Assessment, by Helmut Jannsen. The lower diagram demonstrates principles outilned in Map 2

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LegendLarge PatchesConnective

Good

Excellent/Good

Excellent

Stepping StonesConnective

Fair/Good

Good

Excellent/Good

Excellent

Corridors

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Now with the patches of native habitat identified and graded accord-ing to their connectivity, four other aspects of ecological health were chosen. These were Gradient, Heterogeneity, Matrix Quality and the Core percentage. Each large patch was graded according with respect to these aspects and also connectivity and their totals were added to provide and overall measure of functionality and therefore health of each patch.

The following grading system was used to assess the totals and trans-form them into an ecological health score.5 Poor10 Fair15 Good20 Very Good25 Excellent25 was the highest total possible.

For the sake of simplicity only 5 aspects of ecological health were chosen. It was assumed that these would portray the health of the ecosystem accurately enough.

Gradient

A common change in landscape pattern resulting from human in-tervention is and increase in the length of the boundary between the remaining patches of native vegetation and the surrounding ma-trix (Lindenmayer DB, Fischer J, 2006). Edge effects occur at these boundaries and may penetrate deeply into the vegetation, having profound impacts on flora and fauna. Most of the patch edges in the study area originate from historic human activity (such as logging) and appear in the form of cropped and pasture land next to remnant native

vegetation. Coastlines form some of the few remaining natural bound-aries in the study area.

The transition between the two types of land cover can be soft, where it is gradual, of hard, where the contrast between them is marked (Lin-denmayer DB, Fischer J, 2006). This is known as the gradient and it’s strength can have profound effects on forest patches. If the Gradient is hard then abiotic effects (micro-climatic changes such as tempera-ture and light and humidity) will have a far greater effect at the edge, making conditions unsuitable for plant species which prefer the for-est interior. A harsh gradient will also allow for more competitive weed species to invade, given a closer proximity to seed source. The sever-ity of the gradient will also determine things such as animal community composition, particularly if the edge is unsuited (sometimes season-ally) to some species, in this case native birds which prefer the forest interior.

Each patch was scored according to these criteria:1-No trees or vegetation on boundary. (Eg: direct pasture)2-Sparse trees and vegetation in boundary.3-Regular surrounding of individual trees on boundary.4-Some dense trees on boundary.5-Very Dense trees on boundary (Eg: orchard, scrub or exotic for-est).

Most patches were found to have a medium to hard gradient due their bordering on farmland and pasture (highly contrasting ecotones). Contrasting to this LP 2,4,12 and 17 had a softer gradient mainly due to their bordering on pine plantations or other dense trees (physi-cally a more gradual change and less climatic effects due to shelter-ing effect). This scoring has ignored the biotic edge effects (includes diseases,weeds and predators/other pests) as the Jannsen model only

Map 4-Ecological Health

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took into account abiotic edge effects.

Heterogeneity

“Over two-thirds of New Zealand’s lowland forest plants rely on native birds and insects for propagation, while native birds rely on fruit, nec-tar and insects for food. Birds need a range of different habitats to get through each year: plants need birds to ensure they survive the years” (Jannsen, 2004)

Alpha diversity is the the diversity within a patch. In this case a greater alpha diversity and therefore a greater degree of heterogeneity is what is being assessed. This is to give a broad indication food the variety of food resources available year-round for native bird species, as the was not the resources to investigate the phenology of each patch in an ac-curate and thorough manner as preferred by Jannsen’s system. It was assessed using the land cover database information.

The Scoring System:1 Consisting of mostly Other Exotic Forest 2 Consisting of mostly Manuka and Kanuka3 An even mix of Manuka and Kanuka, Broadleaf Indigenous hardwoods (BIH) and Indigenous Classes4 BIH and/or Indigenous Dominant in mix5 BIH or Indigenous classes dominant with streams penetrating patch

The vertical structure and spatial arrangement of the patches were taken into account as each provides a wider range of potential habi-tats and food for the keystone birds. For example patches containing land cover class of Indigenous forest and broadleaf indigenous hard-

woods were viewed as more diverse. This is due to the indigenous forest class being defined as vegetation dominated by indigenous tall canopy species (Thomson et al. 2003), indicating it has a more com-plex vertical structure. It is also a broad classification containing many indigenous forest types including Kauri stands, gully vegetation, ridge vegetation. It is very likely to be spatially heterogeneous. Broadleaved Indigenous Hardwoods are indicative of an advanced stage in the suc-cessional process and it was assumed that they had a better vertical structure (ranging from 3-10m) (Thomson et al. 2003) and range of food supplies in comparison to the Manuka and Kanuka and Other Exotic Forest classes .

Streams were assumed to be an indicator of heterogeneity, as these show a variation in topography and therefore a variance in vegetation types, which was consistent with site visits made.

The best rated patches were LP 1, 3 and 10, all having a diverse amount of mature bush types. 1 was dominated by Indigenous and BIH, important food resources and varied in pattern and structure. 3 Consisted mostly of the already heterogeneous Indigenous class and contained streams. 10 covered a large area containing a large varia-tion in topography, and consisted predominantly of native vegetation, in a varied form. The rest of the patches scored averagely, with the exception of patches LP 2,5 and 8 which scored a low two due to their dominant contents of lower quality vegetation.

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Matrix Quality

“In many modified Landscapes the notion of a matrix that is inhos-pitable to most species is not useful. Examples of where the matrix provides habitat for a range of species come from both forestry and agriculture” (Lindenmayer DB, Fischer J, 2006)

The matrix, being the largest and often most modified patch type in a landscape cannot be ignored, due to it’s effects upon the popula-tion dynamics of individual species, exchange of individuals between patches and the occupancy rates of vegetation patches. The matrix may play many ecological ecological roles, including acting as habitat, Landscape connections and as an Ecological Context for the native bush patches (which may have a positive or negative impact for some species) (Lindenmayer DB, Fischer J, 2006). It’s roles as habitat and a landscape connection were considered most important to ecological health quality of the matrix was graded according to how structurally similar it was to the native vegetation.

1 No vegetation (such as pasture or industrial zones)2 Sparse trees (such as new residential areas or farmland with shelter trees or belts)3 Some trees (Old residential areas with mature trees, closely planted hedgerows or trees (200m)4 Dense Trees (Riparian zones, scrub or orchard)5 Forest (Plantation forest)

The matrix was examined in a 2km radius from the patch, as this is the distance that native birds are most likely to fly between (Jannsen, 2004). Due to limitations of data, it was assumed that the keystone species were more likely to move though and feed in a matrix that was

structurally similar to habitat they had evolved for. To get a more accu-rate scoring system more behavioural data would be required.

The highest scoring patches were those located next to plantation pine forest (17,2), as this habitat is preferred by many native bird spe-cies as it is the most structurally similar to the patches. The lowest graded patches (3,8) were located deep in urban areas to the east of the study area, a less suitable habitat due to a lack of foliage.

Core Percentage

A bush patch may have a large total area, however the forest edge zone, sometimes extending 20-100m is often not suited to the needs of many native fauna and fauna. As mentioned previously forest in proximity to the boundary will be subject to what is known as edge effects, resulting in an area of internal habitat surrounded by a zone of forest edge (Jannsen, 2004). This makes the interior habitat prime hab-itat, however the shape of the patch will dictate how much of it will in fact be interior habitat. A patch in the study 31ha in size was found to have only 1.6Ha of interior habitat, being only 6% core due it it’s shape which increased the boundary length and edge effects. Each patch was scored according to what percentage of interior it contained.

1-9.99% was scored at 110-19.99% was scored at 220-29.99% was scored at 330-39.99% was scored at 440+% was scored at 5

The largest patch (Number 10), despite being spread out in shape was found to have the highest percentage of interior habitat at 52%, fol-

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lowed by the nearby patch 11 and distant 17 at 51% and 47% respec-tively. These patches had the most compact shape compared to total area resulting in maximum interior habitat. Most patches were com-posed of 10-30% core.

Edge forest was mapped as being the outer 100m of the bush patch, assuming that the climatic abiotic edge effects penetrated as far as the deepest distance indicated by Jannsen. This ignored regional fac-tors such as aspect and exposure which may have meant these ef-fects did not penetrate so far. In some areas small boundaries such as roads and houses are not included in the data, and their edge effects not mapped.

Results

The majority of patches (11 of 17) were rated as having good ecologi-cal health and were mainly let down by their shape, which resulted in a low core percentage (due to the edge effects zone) and also their location in the matrix, which was often structurally dissimilar. 1 patch out of 17 was rated as having excellent Ecological health, 5 had a very good rating and 1 had a fair rating

The only patch rated excellent was located to the far north of the study area (LP 17). It rated highly, despite it’s relatively poor local connectiv-ity, due to it’s high scores for edge gradient, Matrix Quality, Heteroge-neity and Core Percentage. Other patches rated as having very good ecological health (LP 1,10-12) were this located in Albany Heights.Their ratings were mainly due to their connectivity to each other, be-ing located near to many patches and stepping stones within 2, 5 and 10km away and connected to these with a multitude of corridors. LP 6 rated as very good as it averaged a fairly good score in every aspect.

The patch that rated the worst was LP 5, located in an urban area. While well connected, it had an extremely low core % due to it’s shape and had a fairly high gradient and low heterogeneity.

Overall the majority of the patches had good or higher ecological health scores, they were however often let down by their shape and contrast with the immediate surroundings. This affected their scores for the core percentage and gradient, which compromised their overall health score.

This score has been largely based on indications from LCDB data and Aerial Photographs. Because there was not the resources to thor-oughly investigate and assess these aspects in the field we have made assumptions based on others research and recommendations. As a result these scores are more indicative for the region and should not be taken as absolute, as their intention was only to provide an indica-tion the ecological functionality

Introduction

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LegendLarge PatchesEcological Health Score

Excellent

Very Good

Good

Fair

Stepping Stones

Corridor

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ConclusionThis investigation has revealed that much of the native patches in the area are relatively ecologically functional and therefore healthy, how-ever this functionality is fragile, especially for the more isolated patch-es. Much of this functionality depends on the mobility and quality of habitat of the keystone bird species that preform essential ecological processes such as pollination and seed dispersal (The Kereru being the only bird able to disperse certain native plant seeds.

Connections between patches are provided by a pattern of remnant stands of bush and regrowth through out the matrix which provide mobility. The alpha diversity of the patches, which relates to their ability to provide a varied food supply through out the year provides a varied and supporting habitat. However the habitat for both native flora and fauna is compromised by the irregular sprawling shapes of the patches that maximise the boundary length and potential for dam-aging edge effects. The structure of the matrix often contrasts with the patches contained within it, adding to patch edge effects and reducing the matrix’s potential to be used as a habitat and to provide connectiv-ity for the keystone species.

This landscape, while reasonably ecologically healthy, will need these patterns that are essential to it’s functionality protected if it is to re-main this way as the Albany/Riverhead region comes under increas-ing development pressures from an expanding Auckland. Formally protecting all identified native vegetation is a critical first step in doing this (Lindenmayer DB, Fischer J, 2006) as the native vegetation often covers a mixture of public, private, protected and unprotected land. This may take the form of rezoning areas according to the vegetation patches, not cadastral boundaries, or designating areas as being a site of special wildlife interest. This zoning would have to be standard-ised at the region was previously managed by two different councils with differing zoning systems.

This development may also be a chance to address the weaknesses in the pattern of the landscape and to improve it’s overall functional-ity. Expansion of patches is way in which the area of habitat could be vastly increased. Expansion can e used to decrease the boundary length of a patch and mitigate edge effects where the edge gradient is highly contrasting, making a larger area of bush interior.

Development also presents the opportunity to improve the matrix quality. It’s vertical structure (Ie: vertical layers of vegetation such as canopy trees, understory etc) and spatial pattern may be improved to complement the patch, providing better connectivity and potential habitat for forest adapted Keystone species and reduced edge ef-fects respectively. This may take the form of retaining mature trees in

Above: The destructive effects of development. This area in albany heights was a corridor.

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urban developments, selective logging in areas of plantation adjoining patches and planting of shade trees and shelter belts in rural areas near patches.

This investigation has indicated that the landscape pattern of the Riv-erhead/Albany allows the essential ecological processes to function, resulting in good ecological health scores for the major patches, how-ever this pattern must be conserved to prevent further fragmentation in the future. The future also holds possibilities for the improvement of the landscape pattern and through it it’s ecological processes and functionality, to better ensure the long term survival of native species and forest in the region.

-Jannsen H. (2006). Bush Vitality Assessment. Wellington, Helmut Jannsen and The Department of Conservation.

-Lindenmayer D B, Fischer J. (2006). Habitat Fragmentation and Land-scape Change: an ecological and conservation synthesis. Washington: Island Press

-Meurk CD, Hall GMJ, 2006. Options for enhancing forest biodiver-sity across New Zealand’s managed landscapes based on ecosystem modelling and spatial design. NZ Journal of Ecology 30(1): 131-146

-Thomson S, Grüner I, Gapere N. 2003. Illustrated Guide to target classes. Wellington. Ministry for the Environment.

Bibliography

Above: A landscape under threat, Albany Heights

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LP 17

LP 10

LP 11

LP 9

LP 1

LP 8

LP 13

LP 12

LP 3

LP 14

LP 0

LP 7

LP 16LP 6

LP 2

LP 5

LP 4

LP 15

SP 9

SP 10SP 11

SP 0 SP 13

SP 12

SP 23

SP 24

SP 26

SP 4

SP 15

SP 17

SP 27

SP 28

SP 7 SP 33

SP 34

SP 31

SP 14

SP 16

SP 18

SP 20

SP 19

SP 30

SP 1

SP 3SP 22

SP 5

SP 32

SP 8SP 29

SP 25

SP 6

SP 0

SP 2

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LegendStepping Stones

Large Patches

PatchNumberKey

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Stepping Stone Connectivity Large patch Connectivity

Appendix 2-Scoring Tables

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M+K: Manuka and Kanuka coverBIH: Broadleaf indigenous HardwoodsOEF: Other exotic forestIndig: Indigenous forest (mixed land cover types)

Connectivity was graded according to Jannsen’s chart, as shown in appendices.

For total health scores each of the scores were regraded from 1-5. Values were assigned as follows:5= 13-144= 10-123= 7-92= 4-61= 1-3

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Appendix 3-Field Data

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