Soil pH — Benchmark Detail - Nature Index

Benchmark Value

No specific value — see range

Range: 5.5 to 7 pH

Thresholds: Lower: 5, Upper: 7.5

Optimal Range: 5.5 to 7

Direction: Higher is desirable ↑

Form: OptimalRange

Scoring Curve

This curve shows how a field measurement for this indicator would score across all available benchmark forms in this context. The scoring engine uses 16 benchmarks together — the OptimalRange form drives the primary score, while 15 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary MinimumOnly Guard OptimalRange Guard Point Guard LowerThreshold Guard LowerThreshold Guard OptimalRange Guard LowerThreshold Guard UpperThreshold Guard Point Guard LowerThreshold Guard OptimalRange Guard UpperThreshold Guard OptimalRange Guard LowerThreshold Guard UpperThreshold Guard

Evidence & Context

Indicator Name: Soil pH Reference Value: 5.5 - 7.0 Unit: pH Source Title: A Synthesized Benchmark Derived from "Floristics and structure of the mossy cloud forest of Mt Gower summit, Lord Howe Island" and "Norfolk Island Pine Production Guide"

Metric Definition:

Topsoil pH representing the best available condition of nature achievable within production forestry systems on Australia's Tropical and Subtropical Maritime Islands.

Benchmark Definition:

A benchmark range reflecting the natural pH of the two primary, high-health production forestry systems identified: Araucaria forestry on acidic volcanic soils and Howea forestry on slightly acidic to neutral volcanic and calcareous soils.

Justification:

The benchmark is a robust synthesis of data from pristine native ecosystems and species-specific horticultural requirements, anchored by direct field measurements and supported by production guides linking this range to optimal plant health and avoidance of nutrient deficiencies.

Supporting Sources (47)

Additional references from the underlying research that informed this benchmark.

Preview of (PDF) Surprising Relationships Between Soil pH and Microbial Biomass and Activity in a Northern Hardwood Forest - ResearchGate, accessed July 30, 2025,

(PDF) Surprising Relationships Between Soil pH and Microbial Biomass and Activity in a Northern Hardwood Forest - ResearchGate, accessed July 30, 2025,

Contextual Support

(PDF) Surprising Relationships Between Soil pH and Microbial Biomass and Activity in a Northern Hardwood Forest - ResearchGate

Preview of AGRICULTURAL AUDIT & LAND USE CAPABILITY ASSESSMENT ..., accessed July 30, 2025,

AGRICULTURAL AUDIT & LAND USE CAPABILITY ASSESSMENT ..., accessed July 30, 2025,

Contextual Support Journal

Norfolk Island Agricultural Audit and Land Capability Assessment Report

Preview of Are acid soils truly chemically degraded? - ResearchGate, accessed July 30, 2025,

Are acid soils truly chemically degraded? - ResearchGate, accessed July 30, 2025,

Contextual Support

Soil pH | Environment, land and water - Queensland Government

Preview of Chapter 20 ~ Causes and Consequences of Acidification of Forest Soils, accessed July 30, 2025,

Chapter 20 ~ Causes and Consequences of Acidification of Forest Soils, accessed July 30, 2025,

Contextual Support Direct Evidence GreyLiterature

Chapter 20 ~ Causes and Consequences of Acidification of Forest Soils, accessed July 30, 2025,

Preview of Christmas and Cocos Islands tropical forests - Wikipedia, accessed July 30, 2025,

Christmas and Cocos Islands tropical forests - Wikipedia, accessed July 30, 2025,

Contextual Support GreyLiterature

Christmas and Cocos Islands tropical forests - Wikipedia, accessed July 30, 2025,

Preview of Christmas Island Mine site to Forest Rehabilitation program review - Department of Infrastructure, Transport, Regional Development and Communications, accessed July 30, 2025,

Christmas Island Mine site to Forest Rehabilitation program review - Department of Infrastructure, Transport, Regional Development and Communications, accessed July 30, 2025,

Contextual Support Journal

Floristics and structure of the mossy cloud forest - of Mt ... - Ian Hutton, accessed July 30, 2025,

Preview of Christmas Island National Park - DCCEEW, accessed July 30, 2025,

Christmas Island National Park - DCCEEW, accessed July 30, 2025,

Contextual Support Journal

Christmas Island National Park - DCCEEW, accessed August 2, 2025

Preview of Christmas Island Yellow Crazy Ant Control Program - DCCEEW, accessed July 30, 2025,

Christmas Island Yellow Crazy Ant Control Program - DCCEEW, accessed July 30, 2025,

Contextual Support Journal

Christmas Island Yellow Crazy Ant Control Program - DCCEEW

Preview of Cocos (Keeling) Islands - New World Encyclopedia, accessed July 30, 2025, )_Islands

Cocos (Keeling) Islands - New World Encyclopedia, accessed July 30, 2025, )_Islands

Contextual Support GreyLiterature

Cocos (Keeling) Islands - New World Encyclopedia, accessed July 30, 2025, )_Islands

Preview of Cocos nucifera (coconut) | CABI Compendium, accessed July 30, 2025,

Cocos nucifera (coconut) | CABI Compendium, accessed July 30, 2025,

Contextual Support Irrelevant

Cocos nucifera (coconut) | CABI Compendium, accessed July 30, 2025,

Preview of Cocos nucifera L. - Forest Service, accessed July 30, 2025, ).pdf

Cocos nucifera L. - Forest Service, accessed July 30, 2025, ).pdf

Contextual Support

Cocos nucifera L. - Forest Service, accessed July 30, 2025, ).pdf

Preview of Constraints to Tree Growth Imposed by Urban Soil Alkalinity | Arboriculture & Urban Forestry, accessed July 30, 2025,

Constraints to Tree Growth Imposed by Urban Soil Alkalinity | Arboriculture & Urban Forestry, accessed July 30, 2025,

Contextual Support Journal

Constraints to Tree Growth Imposed by Urban Soil Alkalinity | Arboriculture & Urban Forestry, accessed July 30, 2025,

Preview of Ecological speciation in sympatric palms: 2. Pre‐ and post‐zygotic isolation - PMC, accessed July 30, 2025,

Ecological speciation in sympatric palms: 2. Pre‐ and post‐zygotic isolation - PMC, accessed July 30, 2025,

Contextual Support Irrelevant Journal

Ecological speciation in sympatric palms: 2. Pre‐ and post‐zygotic isolation - PMC, accessed July 30, 2025,

Preview of Effects of soil pH on the growth, soil nutrient composition, and rhizosphere microbiome of Ageratina adenophora - PMC - PubMed Central, accessed July 30, 2025,

Effects of soil pH on the growth, soil nutrient composition, and rhizosphere microbiome of Ageratina adenophora - PMC - PubMed Central, accessed July 30, 2025,

Contextual Support Journal

Factors influencing decline in soil pH in Hawaiian Eucalyptus and Albizia plantations

Preview of Factors influencing decline in soil pH in Hawaiian Eucalyptus and Albizia plantations, accessed July 30, 2025,

Factors influencing decline in soil pH in Hawaiian Eucalyptus and Albizia plantations, accessed July 30, 2025,

Contextual Support

Factors influencing decline in soil pH in Hawaiian Eucalyptus and Albizia plantations, accessed July 30, 2025,

Preview of Flora of the Cocos (Keeling) Islands - Wikipedia, accessed July 30, 2025, )_Islands

Flora of the Cocos (Keeling) Islands - Wikipedia, accessed July 30, 2025, )_Islands

Contextual Support

Flora of the Cocos (Keeling) Islands - Wikipedia, accessed July 30, 2025, )_Islands

Preview of Floristics and structure of the mossy cloud forest of Mt Gower summit, Lord Howe Island

Floristics and structure of the mossy cloud forest of Mt Gower summit, Lord Howe Island

Direct Evidence Journal

Norfolk Island Pine Production Guide

Preview of Geology - Lord Howe Island Museum, accessed July 30, 2025,

Geology - Lord Howe Island Museum, accessed July 30, 2025,

Contextual Support GreyLiterature

Geology - Lord Howe Island Museum, accessed July 30, 2025,

Preview of Geology - Norfolk Island Flora & Fauna Society, accessed July 30, 2025,

Geology - Norfolk Island Flora & Fauna Society, accessed July 30, 2025,

Contextual Support GreyLiterature

Geology - Norfolk Island Flora & Fauna Society, accessed July 30, 2025,

Preview of Geology | Lord Howe Island Australia, accessed July 30, 2025,

Geology | Lord Howe Island Australia, accessed July 30, 2025,

Contextual Support Irrelevant

Geology | Lord Howe Island Australia, accessed July 30, 2025,

Preview of Geology | Norfolk Island National Park | Parks Australia, accessed July 30, 2025,

Geology | Norfolk Island National Park | Parks Australia, accessed July 30, 2025,

Contextual Support Government

Geology - Lord Howe Island Museum, accessed August 2, 2025

Preview of Geology and Geography - Lord Howe Island, accessed July 30, 2025,

Geology and Geography - Lord Howe Island, accessed July 30, 2025,

Contextual Support GreyLiterature

Geology and Geography - Lord Howe Island, accessed July 30, 2025,

Preview of Global Trajectories of Forest Soil Acidification: A Scientometric Synthesis of Drivers, Impacts and Sustainable Solutions - MDPI, accessed July 30, 2025,

Global Trajectories of Forest Soil Acidification: A Scientometric Synthesis of Drivers, Impacts and Sustainable Solutions - MDPI, accessed July 30, 2025,

Contextual Support Journal

Constraints to Tree Growth Imposed by Urban Soil Alkalinity | Arboriculture & Urban Forestry

Preview of Grow The Glorious Norfolk Island Pine In Your Garden - Sequoia Valley Farms, accessed July 30, 2025,

Grow The Glorious Norfolk Island Pine In Your Garden - Sequoia Valley Farms, accessed July 30, 2025,

Contextual Support Irrelevant

Grow The Glorious Norfolk Island Pine In Your Garden - Sequoia Valley Farms, accessed July 30, 2025,

Preview of How to Grow and Care for Kentia Palm - MyDomaine, accessed July 30, 2025,

How to Grow and Care for Kentia Palm - MyDomaine, accessed July 30, 2025,

Contextual Support GreyLiterature

How to Grow and Care for Kentia Palm - MyDomaine, accessed July 30, 2025,

Preview of How to Grow and Care for Norfolk island pine - PictureThis, accessed July 30, 2025,

How to Grow and Care for Norfolk island pine - PictureThis, accessed July 30, 2025,

Contextual Support GreyLiterature

How to Grow and Care for Norfolk island pine - PictureThis, accessed July 30, 2025,

Preview of How to Plant, Grow, and Care for Norfolk Island Pine - Planet Natural, accessed July 30, 2025,

How to Plant, Grow, and Care for Norfolk Island Pine - Planet Natural, accessed July 30, 2025,

Contextual Support Irrelevant

How to Plant, Grow, and Care for Norfolk Island Pine - Planet Natural, accessed July 30, 2025,

Preview of Incredible Great Barrier Reef Islands For Your Holiday - Visitor's Guide - Queensland, accessed July 30, 2025,

Incredible Great Barrier Reef Islands For Your Holiday - Visitor's Guide - Queensland, accessed July 30, 2025,

Contextual Support Irrelevant

Incredible Great Barrier Reef Islands For Your Holiday - Visitor's Guide - Queensland, accessed August 2, 2025,

Preview of Kentia Palm (Howea forsteriana) - Care Guide and Plant Information - Healthy Houseplants, accessed July 30, 2025,

Kentia Palm (Howea forsteriana) - Care Guide and Plant Information - Healthy Houseplants, accessed July 30, 2025,

Contextual Support Irrelevant GreyLiterature

Kentia Palm (Howea forsteriana) - Care Guide and Plant Information - Healthy Houseplants, accessed July 30, 2025,

Preview of Lord Howe Island - Wikipedia, accessed July 30, 2025,

Lord Howe Island - Wikipedia, accessed July 30, 2025,

Contextual Support GreyLiterature

Lord Howe Island - Wikipedia, accessed August 1, 2025,

Preview of Lord Howe Island Subtropical Forests | One Earth, accessed July 30, 2025,

Lord Howe Island Subtropical Forests | One Earth, accessed July 30, 2025,

Contextual Support Irrelevant

Safeguarding Lord Howe Island World Heritage Area - Local Land Services, accessed August 1, 2025,

Preview of Norfolk Island - Wikipedia, accessed July 30, 2025,

Norfolk Island - Wikipedia, accessed July 30, 2025,

Contextual Support Irrelevant

Norfolk Island Water Resource Assessment, accessed July 30, 2025,

Preview of Norfolk Island pine - Araucaria heterophylla - NZ Farm Forestry Association, accessed July 30, 2025,

Norfolk Island pine - Araucaria heterophylla - NZ Farm Forestry Association, accessed July 30, 2025,

Contextual Support GreyLiterature

Norfolk Island pine - Araucaria heterophylla - NZ Farm Forestry Association, accessed July 30, 2025,

Preview of Norfolk Island Pine care: Tips for growing araucaria indoors - Growcycle, accessed July 30, 2025,

Norfolk Island Pine care: Tips for growing araucaria indoors - Growcycle, accessed July 30, 2025,

Contextual Support Irrelevant

Norfolk Island Pine care: Tips for growing araucaria indoors - Growcycle, accessed July 30, 2025,

Preview of Norfolk Island Pine: Plant Care & Growing Guide - The Spruce, accessed July 30, 2025,

Norfolk Island Pine: Plant Care & Growing Guide - The Spruce, accessed July 30, 2025,

Contextual Support Irrelevant

Norfolk Island Pine Production Guide - Mid-Florida Research and Education Center, accessed July 30, 2025,

Preview of Norfolk Island Subtropical Forests | One Earth, accessed July 30, 2025,

Norfolk Island Subtropical Forests | One Earth, accessed July 30, 2025,

Contextual Support Irrelevant

Plantation Forestry and Economic Development in the Tiwi Islands - This document is discoverable and free to researchers across the globe due to the work of AgEcon Search. Help ensure our sustain

Preview of Norfolk Island Water Resource Assessment, accessed July 30, 2025,

Norfolk Island Water Resource Assessment, accessed July 30, 2025,

Contextual Support Journal

Cattle : Norfolk Blue | RARE BREEDS TRUST OF AUSTRALIA | TidyHQ, accessed July 30, 2025,

Preview of On Soil and Speciation - In Defense of Plants, accessed July 30, 2025,

On Soil and Speciation - In Defense of Plants, accessed July 30, 2025,

Contextual Support GreyLiterature

On Soil and Speciation - In Defense of Plants, accessed July 30, 2025,

Preview of Pedogenic Threshold in Acidity Explains Context-Dependent Tree Species Effects on Soil Carbon - Frontiers, accessed July 30, 2025,

Pedogenic Threshold in Acidity Explains Context-Dependent Tree Species Effects on Soil Carbon - Frontiers, accessed July 30, 2025,

Contextual Support Irrelevant

Chapter 20 ~ Causes and Consequences of Acidification of Forest Soils

Preview of Plants - Cocos Keeling Islands, accessed July 30, 2025,

Plants - Cocos Keeling Islands, accessed July 30, 2025,

Contextual Support GreyLiterature

Plants - Cocos Keeling Islands, accessed July 30, 2025,

Preview of Red Crab Migration — Christmas Island, accessed July 30, 2025,

Red Crab Migration — Christmas Island, accessed July 30, 2025,

Contextual Support GreyLiterature

Red Crab Migration — Christmas Island, accessed July 30, 2025,

Preview of Responses to controlled release potassium fertilisers in agriculture following phosphate mining - CSIRO PUBLISHING | Soil Research, accessed July 30, 2025,

Responses to controlled release potassium fertilisers in agriculture following phosphate mining - CSIRO PUBLISHING | Soil Research, accessed July 30, 2025,

Contextual Support Journal

Healthy Land Ecosystems | TSRA State of the Environment

Preview of Soil pH | Environment, land and water - Queensland Government, accessed July 30, 2025,

Soil pH | Environment, land and water - Queensland Government, accessed July 30, 2025,

Contextual Support Government

Improving Soil Structure and pH Levels (DPIFM_NT) - Department of ..., accessed July 20, 2025

Preview of The Buzz of the Saw: Utilising Norfolk Island's unique icon, accessed July 30, 2025,

The Buzz of the Saw: Utilising Norfolk Island's unique icon, accessed July 30, 2025,

Contextual Support GreyLiterature

The Buzz of the Saw: Utilising Norfolk Island's unique icon, accessed July 30, 2025,

Preview of The future role of the National Park Forestry Zone in a ... - DCCEEW, accessed July 30, 2025,

The future role of the National Park Forestry Zone in a ... - DCCEEW, accessed July 30, 2025,

Contextual Support Journal

Norfolk Island Native Plants, accessed August 1, 2025,

Preview of Torres Strait Islands, accessed July 30, 2025,

Torres Strait Islands, accessed July 30, 2025,

Contextual Support Journal

Torres Strait Islands, accessed July 30, 2025,

Preview of What Soil is Best for Kentia palm Growth? - PictureThis, accessed July 30, 2025,

What Soil is Best for Kentia palm Growth? - PictureThis, accessed July 30, 2025,

Contextual Support GreyLiterature

Pedogenic Threshold in Acidity Explains Context-Dependent Tree Species Effects on Soil Carbon - Frontiers

Context

Region Australia
Biome Tropical & Subtropical Maritime Islands
Land Use Production Forestry
Assessment Pristine Reference
Evidence Type ReferenceCondition

Lifecycle

Status Superseded
Version 1
Effective From 10 Mar 2026
Effective To 10 Mar 2026

Notes

Lower Critical Threshold: 5 pH. Upper Detrimental Threshold: 7.5 pH. The 5.5-7.0 range represents high ecological health in the two most relevant production forestry systems: Araucaria heterophylla on Norfolk Island’s acidic volcanic soils (optimal pH 5.5-6.5) and Howea forsteriana on Lord Howe Island’s varied volcanic (acidic) and calcarenite (neutral) soils. A soil pH below 5.0 indicates increasing stress, with pH < 4.5 representing a critical threshold where soils enter the aluminum buffering range, leading to Al3+ toxicity and severe nutrient limitations. Soil pH consistently above 7.5 is detrimental, leading to micronutrient deficiencies and potentially inhibiting acid-adapted soil microbial communities.

Related Benchmarks

Other benchmarks in the AUS-TMI-FOR-SPH family.