Is plant provenance really that important?
Working in the landscape and revegetation game, you don’t have to travel far to hear about plant provenance. It is rare that a revegetation project will occur without a description of where the seed for the project should come from, with provenance defined by a radius from the site in question or site analogues (soil, rainfall, distance etc).
We have all experienced the local plant expert telling us what seed we can or cannot use. Often advice about provenance is been made without reference to the genetics of the site population, availability of seed or the intent to the landscape. We are also collecting seed from very small populations either out of availability or effort. In summary, collecting local provenance is about trying to preserve local populations without reference to the genetic diversity of that population or the long-term interests of the landscape.
Provenance and climate change
Any discussion of landscape with the term “long term” or “tree” in it has to be considering the impact of climate change. Trees assets are being installed today have a design life of at least 50 years and will experience a hotter and drier climate with more days of extreme weather. The impacts of extreme heat are being documented and several research projects have demonstrated that days of extreme heat are killing trees that have grown on sites for 50 or more years. Climate models are predicting that temperatures and days of extreme heat will continue to rise over the next 50 years.
The diagram below outlines the various approaches to selecting provenance, with the proposed planting site indicated with a star and climate becoming increasing hot dry to the right. Developed by Prober et al, it recommends adopting climate-adjusted or predictive provenancing to overcome the impacts of climate change. Climate adjusted provenancing is likely to have the most resilience, reflect the reality of viable seed sources, and provide genetics across the range of future climates we may experience.
FIGURE 1: Diagrammatic representations of provenancing strategies for revegetation (Prober et al., 2015)
Some great work has been done recently by several research groups to put scientific rigour around how we select seed sources for our sites. There are several approaches based on what you know about the site, the plant genetics and likely future climate scenarios. The reality is that with the small remnant populations we have, the degree of climate change predicted most sites will require a climate adjusted approach.
Melbourne’s climate to be more like central NSW by 2090
Under this approach, the future climate for the site is determined using CSIRO climate models and sites which currently have a similar to the predicted climate are identified. For example, using the CSIRO Climate analogues predictor, Melbourne’s weather in 2090 will be 3.80 warmer and have -10% less rainfall. Today, this is the climate experienced by towns in central NSW, including Dubbo, West Wyalong and Parkes. Any tree planted today in Melbourne will need to be able to experience conditions currently experienced in Dubbo.
Adopting this approach will create a few challenges for project planning, not the least of which is convincing people that seed selected 800km from Melbourne in Dubbo is the most appropriate for the site when their current guideline speaks of matching soil type and distances in the 10’s of kilometres. Having spoken to people who have tried to implement this approach, seed collection will become a significant problem, as many areas have small remnant populations and revegetation industries. It is also likely that proposed species will not be present in the new climate ranges and decisions will need to be made to plant the proposed species from a cooler climate or plant a new species, currently not present at the site, that has a good chance of survival.
Planting for our future
Trees are the best value carbon capture and storage device known to man and can be rolled out without further technological development. The landscape and revegetation industry has the opportunity to make a major contribution to addressing the impacts of climate change. To protect our future landscapes we are going to have adopt adaptive methods to ensure trees planted today can survive in our future climate.