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         General Impact

    At least 19 Pinus species can be considered invasive (Richardson, 1998a). The main impacts of invasive pines result from the increased abundance of trees in habitats where they were previously absent or less common (Richardson, 1998). Many pine species are superb colonisers, with a wide range of adaptations that enable them to become invaders (Hughes and Styles, 1989; Fagg and Stewart, 1994; Richardson et al., 1994; Richardson, 1998; in Richardson, 1998a). Large areas can be quickly colonised by wilding pines as a result of one significant dispersal event, such as strong winds whilst trees are coning (DOC, 2005). Global change, with rapidly changing climate patterns, altered disturbance and nutrient regimes, and increased fragmentation are likely to favour further expansion of pine invasions worldwide (Richardson and Rejmanek, 2004). Most invasions are currently in grassland and shrubland, with forests and woodlands generally only invaded following considerable disturbance. Increasing human disturbance in forests and woodlands is likely to leave these habitats more vulnerable to invasions by pines as well as other species (Richardson and Rejmanek, 2004). The range and density of pines has also increased in some areas within their native range (Richardson, 1998).

    Invasive pines can cause major impacts to catchment hydrology by reducing water flows, which has effects both for the aquatic biota, and on water supplies for human populations. Changes to fire regimes occur in the fynbos ecosystem of South Africa, resulting in the transformation from grassland/shrubland to pine forest (Richardson, 1998). The invasive spread of pines is closely linked to fire and their adaptations to new fire regimes. Some introduced pine species can exploit the environmental conditions caused by wildfires. These pines are fire-resilient species with small seeds, low seed-wing loadings, short juvenile periods, moderate to high degrees of serotiny (requiring heat from fire to release seeds) and relatively poor fire tolerance as adults (Richardson, 1998). There is often little competition from native plants during the invasion window (Johnstone, 1986; in Richardson, 1998). Pine forest habitats generally offer less benefits to native wildlife than native vegetation, and contribute to an overall reduction in native biodiversity in many of the areas it has invaded (DOC, 2005; Richardson, 1998; Richardson, 1998a; Bustamante and Simonetti, 2005). Dense stands of pines in exotic environments can also cause changes in nutrient cycling and soil composition (Richardson, 1998). Invasive pines can have impacts on humans, by causing reductions in water supplies, affecting recreation, and altering the character of landscapes (DOC, 2005).
    Click here for information about Potential future impacts of Pinus spp.




         Location Specific Impacts:
    Australian Capital Territory (Australia) English 
    Reduction in native biodiversity: The invasion of Pinus radiata in dry sclerophyll forests in ACT has led to the formation of a discontinuous carpet of pine needles, and an increase in the amount of deep shade, causing the suppression of native plants (Burdon and Chilvers, 1994; in Richardson, 1998).
    Brazil English 
    Reduction in native biodiversity: Bustamante et al (2003; in Bustamante and Simonetti, 2005) documented an active invasive process of P. radiata in Chile, in forest fragments sustaining intense disturbances, such as fire or logging. In fragments with low disturbance, invasion occurred only at the edges.
    Ontario (Canada) English 
    Reduction in native biodiversity: Pinus sylvestris has reduced the cover of native plants and the height of hummocks where it has invaded peatlands in Ontario, Canada.
    New Zealand English 
    Competition: Wilding pines can outcompete native species in openings in regenerating forest in New Zealand (DOC, 2005).

    Economic/Livelihoods: Reduced commercial potential of land in New Zealand may occur through the loss of grazing land currently used for extensive pastoralism. The reduction in water yield caused by dense pine spread could have a critical effect on intensive land uses which depend on irrigation, such as viticulture (DOC, 2005).

    Ecosystem change: The most obvious effect of wilding pines is their ability to invade and suppress low-stature plant communities. In the South Island high country, they out-compete and suppress native vegetation. In extreme cases this may lead to the local extinction of plant communities, such as in remnant shrubland and grassland communities in the intermontane basins of the South Island high country. Individual species are also threatened, such as Hebe armstrongii in the Waimakariri Basin, and Hebe cupressoides in the South Island high country (DOC, 2005).

    Habitat alteration: Pines compete for forest space with native trees and plants, but do not provide any advantages these plants offer, such as berries or nectar, to wildlife. Pine needles form a carpet which discourages regeneration of native forest floor species. Wilding pine spread impacts on native lizards and invertebrates in open communities, by altering the habitat. Freshwater fish populations may be affected, through shading of streams, or reduced water flows. In general, fewer native bird species are found in pine forests than in native forests (DOC, 2005).

    Human nuisance: Wilding pines affect recreation by obstructing foot or vehicle access, and also cause change to the character of recreation sites (DOC, 2005).

    Modification of fire regime: The presence of wilding pines means that wild fires burn longer and hotter due to the presence of dead and live wood. Some pine species are well adapted to regenerate after fire (DOC, 2005).

    Modification of hydrology: Pine plantations yield lower mean water flows than either native forest or pasture in New Zealand. This has significant implications for populations of in-stream flora and fauna, as well as water supplies for domestic and pastoral use. Felling operations can also cause a reduction in water quality (DOC, 2005).

    Modification of nutrient regime: Invasive pines in New Zealand cause changes in nutrient cycling. In moist environments, the mineralisation of organic matter leads to nutrient enrichment of topsoils under pines. In drier environments, transfer of nutrients from deeper horizons to the soil surface via nutrient uptake and litterfall is probably the major mechanism (Davis and Lang, 1991; in Richardson, 1998).
    On volcanic soils in the North Island of New Zealand, catchments with P. radiata had lower levels of phosphorous than pasture, but higher than native forest, and for nitrates the order was reversed (Cooper et al., 1987; in Richardson, 1998).
    Wilding pines in tussocklands take up and hold a larger pool of nutrients than the snow tussocks they replace. Pines may accelerate acidification and eventual podzolisation of soils which formerly supported native forest (DOC, 2005).

    Other: The prominence of wilding pines in New Zealand can affect landscape values, by obstructing views and creating a Northern Hemisphere feel, and the spread of wilding pines may also affect historic sites and cultural values (DOC, 2005).

    Reduction in native biodiversity: Introduced Pinus spp. have a significant effect on native biodiversity in New Zealand. For a list of plant communities and species threatened with local extinction by wilding conifer spread, please see Conservation values at risk.
    South Island (New Zealand) English 
    Competition: Wilding pines can outcompete native species in openings in regenerating forest in New Zealand (DOC, 2005).

    Economic/Livelihoods: Reduced commercial potential of land in New Zealand may occur through the loss of grazing land currently used for extensive pastoralism. The reduction in water yield caused by dense pine spread could have a critical effect on intensive land uses which depend on irrigation, such as viticulture (DOC, 2005).

    Ecosystem change: The most obvious effect of wilding pines is their ability to invade and suppress low-stature plant communities. In the South Island high country, they out-compete and suppress native vegetation. In extreme cases this may lead to the local extinction of plant communities, such as in remnant shrubland and grassland communities in the intermontane basins of the South Island high country. Individual species are also threatened, such as Hebe armstrongii in the Waimakariri Basin, and Hebe cupressoides in the South Island high country (DOC, 2005).

    Habitat alteration: Pines compete for forest space with native trees and plants, but do not provide any advantages these plants offer, such as berries or nectar, to wildlife. Pine needles form a carpet which discourages regeneration of native forest floor species. Wilding pine spread impacts on native lizards and invertebrates in open communities, by altering the habitat. Freshwater fish populations may be affected, through shading of streams, or reduced water flows. In general, fewer native bird species are found in pine forests than in native forests (DOC, 2005).

    Human nuisance: Wilding pines affect recreation by obstructing foot or vehicle access, and also cause change to the character of recreation sites (DOC, 2005).

    Modification of fire regime: The presence of wilding pines means that wild fires burn longer and hotter due to the presence of dead and live wood. Some pine species are well adapted to regenerate after fire (DOC, 2005)

    Modification of hydrology: Pine plantations yield lower mean water flows than either native forest or pasture in New Zealand. This has significant implications for populations of in-stream flora and fauna, as well as water supplies for domestic and pastoral use. Felling operations can also cause a reduction in water quality (DOC, 2005).

    Modification of nutrient regime: Invasive pines in New Zealand cause changes in nutrient cycling. In moist environments, the mineralisation of organic matter leads to nutrient enrichment of topsoils under pines. In drier environments, transfer of nutrients from deeper horizons to the soil surface via nutrient uptake and litterfall is probably the major mechanism (Davis and Lang, 1991; in Richardson, 1998).
    On volcanic soils in the North Island of New Zealand, catchments with P. radiata had lower levels of phosphorous than pasture, but higher than native forest, and for nitrates the order was reversed (Cooper et al., 1987; in Richardson, 1998).
    Wilding pines in tussocklands take up and hold a larger pool of nutrients than the snow tussocks they replace. Pines may accelerate acidification and eventual podzolisation of soils which formerly supported native forest (DOC, 2005).

    Other: The prominence of wilding pines in New Zealand can affect landscape values, by obstructing views and creating a Northern Hemisphere feel, and the spread of wilding pines may also affect historic sites and cultural values (DOC, 2005).

    Reduction in native biodiversity: Introduced Pinus spp. have a significant effect on native biodiversity in New Zealand. For a list of plant communities and species threatened with local extinction by wilding conifer spread, please see Conservation values at risk.
    Lake Michigan (North America) English 
    Modification of nutrient regime: Pinus nigra is having significant impacts on nutrient cycling and soil development around Lake Michigan.

    Reduction in native biodiversity: Pinus nigra is having significant impacts on the native plant communities around Lake Michigan.
    South Africa English 
    Ecosystem change: The intense fires which occur in dense pine stands in South Africa can result in increased overland flow, accelerated soil erosion and a change in vegetation structure (Richardson, 1998).

    Interaction with other invasive species: The seeds of P. pinea are spread by the introduced squirrel (Sciurus carolinensis) in South Africa.

    Modification of fire regime: Intense fires in dense pine stands in South Africa can have a devastating effect, caused in part by the increased fuel load. This results in increased overland flow, accelerated soil erosion and a change in vegetation structure. Fynbos can be transformed over two or three fire cycles into a pine forest, as the superior fire resilience of the pine populations buffers them against local extinction (Richardson, 1998).

    Modification of hydrology: Invasive pines, along with other alien trees, have a major impact on catchment hydrology in the fynbos biome of South Africa. Runoff from watersheds with dense stands of pine is between 30 and 70% lower than for uninvaded fynbos. This has adverse impacts on aquatic biota, and serious implications for water production in the region, with losses of up to 30% of the water supply to Cape Town predicted (Le Maitre, 1998; in Richardson, 1998a; Armstrong and van Hensbergen, 1996; in Richardson, 1998; Loope and Kraftsow, 2001). This means that the large costs of removing pines is warranted due to the financial benefits that would occur from the improved water yield (Richardson, 1998a).

    Reduction in native biodiversity: Dense pine stands suppress fynbos plant species in South Africa, threatening many taxa with extinction - c. 750 species are currently at risk (Richardson et al., 1989, 1996a; in Richardson, 1998). The impacts of invasive pines on catchment hydrology also has adverse impacts on aquatic biota (Le Maitre, 1998; in Richardson, 1998a).
    Cape Peninsula (South Africa) English 
    Reduction in native biodiversity: Invasive pines are a major threat to the biodiversity of the Cape Peninsula, South Africa.



ISSG Landcare Research NBII IUCN University of Auckland