When Trees Aren’t the Answer: Tree Invasions Not Recommended to Mitigate Climate Change
Nuñez et al. 2021. Should tree invasions be used in treeless ecosystems to mitigate climate change? Frontiers in Ecology & Environment. PDF.
Summary written by Audrey Barker Plotkin, edited by Annette Evans
Summary
Trees are the backbone of most Northeastern ecosystems, and they help mitigate the negative effects of climate change by taking up and storing atmospheric carbon. However, planting or allowing the spread of non-native trees in traditionally treeless landscapes such as grasslands and shrublands can disrupt important ecological processes and dynamics of the native ecosystem and may have net negative consequences for climate. Nuñez et al. (2021) caution managers to consider carefully the negative ecosystem consequences of planting non-native trees against potential benefits of carbon sequestration. For example, while invasive trees are able to accumulate and store carbon efficiently in their stems, increased tree cover can intensify fire regimes and reduce albedo (that is, increase absorption of sunlight by the vegetation, leading to increased surface warming), counteracting these gains. Tree invasions also decrease streamflow and water availability in grasslands and shrublands, a major concern in regions where water is scarce. The authors conclude that allowing non-native tree invasions is rarely an effective means to mitigate climate change. Instead focus should be placed on alternative management strategies such as restoring historically forested areas by planting native trees or a mix of native species and non-native trees identified by risk assessments as representing a low-risk of invasion and negative impact.
Take home points
Invasions of non-native trees into grasslands and shrublands may be an opportunity for climate change mitigation, but the negative consequences for biodiversity, socio-economic values, water yield, and even climate often outweigh the benefits.
Negative consequences for climate of tree invasions can include altered fire regimes, increased light absorption, and possibly lower soil carbon.
Water scarcity is a major consequence of climate change that is exacerbated by tree invasions.
Tree invasions also alter nutrient cycling, and reduce native species biodiversity and socio-economic benefits of grassland and shrubland ecosystems.
Management implications
The costs of controlling invasive species are high; include an impact assessment using tools such as EICAT (economic impact classification of alien taxa) for different management options.
If considering tree planting for climate change mitigation, focus on restoring a mix of native tree species in areas that were historically forested, rather than planting or allowing the expansion of non-native species into native grasslands and shrublands.
Keywords
Range expansion; Changing biotic interactions (competitiveness); Management efficacy; Restoration; Carbon sequestration; Pines (Pinus); Climate Smart Restoration