Climate Change and Trees

Trees provide shade and shield against heat in the urban environment, and healthy trees are a necessary part of the infrastructure. While some arborists does not partake in the planning and planting of trees, there should be awareness on climate-ready trees that are adapted for a warmer and stormier world. In this article, "climate analogs" are defined as areas elsewhere that currently have climate conditions, which a specific location is projected to have in the future. The article's author mentioned that this article was a supplement to a earlier article (Planning for Climate-Ready Tree Species: What Next?, Daniel C. Staley, Arborist News June 2023).

Not all woody plants currently present in an area can tolerate future climate conditions (Fitzpatrick and Dunn 2019; Tian et al. 2023; Sjöman et al. 2024).

There are a few scenarios that the climate is predicted to become. Climate analog tools such as FitzLab and Copernicus were mentioned, and FitzLab was explored for the article. 

Climate analog tools uses global climate models, which in turn uses climate change scenarios, in order to give model outputs that are widely used as a standard tool for decision-making (Schmolke et al. 2010). There are a few climate change scenario temperature projections from now till year 2100, depending on how humans could change their practices. Tree species composition and health would change, if temperatures were to reach the top three scenario trajectories.

A pessimistic scenario sees more industrial activities, fossil-fuel use and deforestation, and a less pessimistic scenario sees a shift to renewable energy, less deforestation and reforestation to be less warming to the world. An official narrative from the Intergovernmental Panel on Climate Change (IPCC) describes different societal actions leading to a few scenarios, from which to choose and use climate analog tools to find areas with climate-ready trees. 

- SSP5_8.5: Increased energy use, deforestation and emissions, which results in about 4.4 degrees C projected temperature rise by 2100

- SSP3_7.0: 'Business As Usual', results in about 3.6 degrees C projected temperature rise by 2100

- SSP2_4.5: Some reduction in fossil-fuel use, slowing of deforestation and reduction in emissions, results in about 2.7 degrees C projected temperature rise by 2100

- SSP1_2.6: Significant reduction of fossil-fuel use, and sustainable development, results in about 1.8 degrees C projected temperature rise by 2100

The article suggested to choose a scenario or scenarios that nearby governments/institutions are using but if there are no such planning done by nearby governments/institutions, then choose a scenario and alternative scenario (for comparison), and provide clear justification on why they were chosen. Explanation of scenario narratives and pathways are in Hausfather 2018.

Samples of climate analog tool inquiry using FitzLab tool (FitzLab 2025):

San Jose, California -> (in year 2080) Redlands, California

Würzburg, Germany -> (in year 2080) Villa Fontana, Emilia-Romagna, Italy

However, climate analog tools does not take into consideration site factors such as shade, aspect, exposure to coastal winds, heavy snow. 

Native woody plants in a project area today may not be suitable 60 years or 80 years later. Plants that are adapted to future conditions should be considered, which are not currently native. These plant species could be introduced to meet the requirement of future urban environments.

References

1. How to Find Climate-Ready Trees for your Project, Arborist News Apr 2025

2. FitzLab 2025. Climate analog tool [online tool]. https://fitzlab.shinyapps.io/cityapp

3. Fitzpatrick MC, Dunn RR, 2019/ Contemporary climatic analogs for 540 North American urban areas in the late 21st century. Nature Communications. 10:614, https://doi.org/10.1038/s41467-019-08540-3

4. Hausfather Z, 2018 April 19. Explainer: How 'shared socioeconomic pathways' explore future climate change/ London (United Kingdom): Carbon Brief. https://www.carbonbrief.org/explainer-how-shared-socioeconomic-pathways-explore-future-climate-change

5. Schmolke A, Thorbek P, DeAngelis DL, Grimm V. 2010. Ecological models supporting environmental decision making: A strategy for the future. Trends in Ecology & Evolution. 25(8):479-486. https://doi.org/10.1016/j.tree/2010/05/001

6. Sjöman H, Watkins H, Kelly LJ, Hirons A, Kainulainen K, Martin KWE, Antonelli A. 2024. Resilient trees for urban environments: The importance of intraspecific variation. Plants, People, Planet. 6(6):1180-1189. https:/doi.org/10.1002/ppp3.10518

7. Tian P, Liu Y, Ou J. 2023. Meta-analysis of the impact of future climate change on the area of woody plant habitats in China. Frontier in Plant Science. 14:1139739. https://doi.org/10.3389/fpls.2023.1139739 

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In Arborist News June 2024, page 71, 72, of an interview article with an arborist in Australia, Rebecca Barnes made mention of Dr. Dave Kendal, who works with tree species analysis for projected climates. Furthermore she expressed concern that climate change is a challenge in her country for the future. "Many of the native tree species in Australia have specific and niche environments. Unusual changes in temperature and rainfall are affecting these environments, which leads to tree decline, which, in turn, leads to pests and diseases and also leads to areas that are more prone to bushfire."

Dr. Kendal is one of the members who carried out an assessment of the risk from climate change for living collections and landscape at Melbourne Gardens, which is commissioned by the Royal Botanic Gardens Victoria. By year 2070 and assuming 'business as usual emissions', under an extreme climate future, temperatures are forecast to increase by 3 degrees C. The assessment identified areas that required "management intervention such as procuring new species, succession replanting or improving site conditions". The project also resulted in the development of a decision support tool to enable managers to run their own assessments of climate risk for new plant introductions.

Reference: Assessment of Climate Change Risk to Living Plant Collections, https://www.rbg.vic.gov.au/initiatives/landscape-succession-strategy/assessment/

Foliage with Angular Spots

Dendro and and his assistant Codit were asked to visited a wedding venue to examine defoliating Viburnum suspensum. They met its grounds manager, Amelia. Several of those shrubs are near a gazebo, and she expected that the background should be green and suitable for wedding photos. Since last year, there was defoliation and leaf spotting on one shrub, and that spread to others. Their landscape contractors assumed it was a leaf spot disease and sprayed a fungicide three times for one year, but there was no improvement. In the middle of their conversation, the pop-up sprinklers activated and sprayed water onto their pants and shoes. Amelia apologised, as the irrigation should have been turned off during the meeting, but Dendro and Codit commented that cultural conditions are important. Upon further questioning, Amelia shared that the shrub bed is irrigated every other day, and long enough to soak the grass and mulch. Dendro replied that foliar pathogens are spread and supported by excessive moisture.

Codit examined the leaves on the ground and noticed that the spots on them are angular. "Fungal leaf spots are often medium to dark brown and more rounded, while bacterial spots are generally dark brown with a yellow halo", he explained further, "angular leaf spots are less common". Foliar nematodes and plant pathogenic bacteria can cause angular leaf spots. Dedro recommended sending samples to plant diagnostic laboratories to know for sure the pest and disease issues, or health problems, in order to be sure. 

Upon inspection on a leaf with a magnifier, Codit spotted grayish fuzz growing on spotted tissue and deduced that the disease is viburnum downy mildew, Peronospora viburni. Downy mildew diseases are caused by oomycetes, which are fungus-like organisms, not true fungi. Diseases caused by oomycete are usually worse when conditions are wet, as they produce spores that swim in water. Phytophthora species is an oomycete that can infect foliage as well, but its often seem on roots, and stem/trunk cankers on woody plants. Downy mildews are often host-specific, so one plant genera is being infected by one species of downy mildew - Viburnum suspensum shrubs in this case.

Amelia connected the dots and realised that the reason why the landscape contractor's fungicide applications were not working was because the disease is not a fungus. Dendro reminded Amelia to send leaf samples to a diagnostic lab, and inform the landscape crew to rake up and dispose of gallen infected leaves regularly. In addition, to turn the sprinklers away from the viburnum foliage so that they are not wetted. Finally, to do scouting so as to catch disease and insect problems early.

Reference: Arborist News, Apr 2025, pages 22, 23, 56, 57