Managing reforestation to sequester carbon, increase biodiversity potential and minimize loss of agricultural land (original) (raw)

2016, Land Use Policy

tReforestation will have important consequences for the global challenges of mitigating climate change,arresting habitat decline and ensuring food security. We examined field-scale trade-offs between carbonsequestration of tree plantings and biodiversity potential and loss of agricultural land. Extensive surveysof reforestation across temperate and tropical Australia (N = 1491 plantings) were used to determine howplanting width and species mix affect carbon sequestration during early development (< 15 year). Carbonaccumulation per area increased significantly with decreasing planting width and with increasing pro-portion of eucalypts (the predominant over-storey genus). Highest biodiversity potential was achievedthrough block plantings (width > 40 m) with about 25% of planted individuals being eucalypts. Carbon andbiodiversity goals were balanced in mixed-species plantings by establishing narrow belts (width < 20 m)with a high proportion (>75%) of eucalypts, and in monocultures of mallee eucalypt plantings by using thewidest belts (ca. 6–20 m). Impacts on agriculture were minimized by planting narrow belts (ca. 4 m) ofmallee eucalypt monocultures, which had the highest carbon sequestering efficiency. A plausible scenariowhere only 5% of highly-cleared areas (<30% native vegetation cover remaining) of temperate Australiaare reforested showed substantial mitigation potential. Total carbon sequestration after 15 years was upto 25 Mt CO2-e year−1when carbon and biodiversity goals were balanced and 13 Mt CO2-e year−1if blockplantings of highest biodiversity potential were established. Even when reforestation was restricted tomarginal agricultural land (<$2000 ha−1land value, 28% of the land under agriculture in Australia), totalmitigation potential after 15 years was 17–26 Mt CO2-e year−1using narrow belts of mallee plantings. Thiswork provides guidance on land use to governments and planners. We show that the multiple benefitsof young tree plantings can be balanced by manipulating planting width and species choice at establish-ment. In highly-cleared areas, such plantings can sequester substantial biomass carbon while improvingbiodiversity and causing negligible loss of agricultural land.

National carbon model not sensitive to species, families and site characteristics in a young tropical reforestation project

Reforestation and restoration offer critical contributions to addressing climate change and biodiversity decline. Enabling carbon credits to be derived from these activities is important for reforestation, particularly since reforestation does not come cheaply. Australia's Carbon Farming Initiative is a world-leading policy that allows carbon credits to be obtained by using published methods-based approaches. Here we apply two different approaches to a young mixed species reforestation project in the wet tropics of Queensland, Australia. One approach assesses carbon sequestration from published allometric equations requiring direct field measurements, and the other applies a national carbon accounting model, FullCAM. Using allometric equations, we found above-ground biomass was influenced significantly by family, species, size class, and the interaction of family and size class. Species in the family Proteaceae out-performed species in other families. Selection of species according to soil nutrient status could enhance growth rates, but if soil nutrients and species responses are not known, then a bet-hedging strategy using mixed species from a variety of families is probably the best option. For three year old forest plots, FullCAM modelled significantly more carbon mass of trees than published allometric models for mixed tropical forests, suggesting that FullCAM needs adjustment to more accurately reflect species, families, local conditions and small-scale sites. Current policy settings are at odds with the needs of carbon farmers, considering the importance of forests and landscape restoration in fighting climate change and biodiversity decline. Legislated national methods allowing the development of species-specific allometrics for small mixed plantations do not account for the costs of developing these allometrics, especially in markets that are marginal.

REVIEW: Balancing the environmental benefits of reforestation in agricultural regions

Reforestation is an important tool for reducing or reversing biodiversity loss and mitigating climate change. However, there are many potential compromises between the structural (biodiversity) and functional (carbon sequestration and water yield) effects of reforestation, which can be affected by decisions on spatial design and establishment of plantings. We systematically review the environmental responses to reforestation and show that manipulating the configuration of plantings (location, size, species mix and tree density) increases a range of environmental benefits. More extensive tree plantings (> 10 ha) provide more habitat, and larger improvements to carbon and water cycling. Planting a mixture of native trees and shrubs is best for biodiversity while traditional plantation species, generally non-native species, sequester C faster. Tree density can be manipulated at planting or during early development to accelerate structural maturity and to manage water yields. A diversity of habitats will be created by planting in a variety of landscape positions and imitating the patchy distribution of forest types, which historically has characterized many regions. Areas with shallow aquifers can be planted to reduce water pollution or avoided to maintain water yields. Reforestation should be used to build forest networks that are surrounded by low-intensity land use and that provide links within regions and between biomes. While there are adequate models for C sequestration and changes in water yields after reforestation, the quantitative understanding of changes in habitat resources and species composition is more limited. Development of spatial and temporal modelling platforms based on empirical models of structural and functional outcomes of reforestation is essential for deciding on how to reconfigure agricultural regions. To build such platforms, we must quantify: (a) the influence of previous land uses, establishment methods, species mixes and interactions with adjacent land uses on environmental (particularly biodiversity) outcomes of reforestation; and (b) the ways in which responses measured at the level of individual plantings scale up to watersheds and regions. Models based on this information will help widespread reforestation for carbon sequestration improve native biodiversity, nutrient cycling and water balance at regional scales.

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