Dancing with Diversity: Climate-Proofing Nardoo Hills Reserve

Just over 200 kilometers northwest of Melbourne lies Nardoo Hills reserve, a 1207-hectare woodland ecosystem home to many endemic animal and plant species, including the endangered swift parrot, hooded robin and rare orchids such as the northern golden moth (Diuris protena) and the robust greenhood (Pterostylis valida).

With more than 83% of Victoria’s woodlands lost through land clearing, Nardoo Hills – a mixture of both Box-Ironbark and Grassy Box Woodland ecosystems – is a safe haven, helping protect and sustain endemic flora and fauna.

But over the last decade, this sanctuary, owned by Bush Heritage Australia, has been affected by the impacts of climate change. More than 100 hectares of yellow box (Eucalyptus melliodora) and grey box (Eucalyptus macrocarpa) have been affected as a result of heat stress and dry weather. With climate models predicting temperatures to continue to rise, the survivability of the woodland habitat at Nardoo Hills, as well as many others across Australia, are under serious threat. In the face of this, a team of ecologists and volunteers are pioneering an ambitious project aiming to increase the adaptability and genetic diversity of the reserve’s yellow and grey box populations by sourcing, propagating and planting seeds of the same species from regions with climates similar to those predicted for Nardoo Hills 30-70 years into the future. 

This strategy, known as climate-adjusted provenancing, is a promising but currently under-utilised form of restoration ecology that aims to safeguard habitats in the face of increasingly hot and dry conditions projected for the future. While both species are distributed widely across south eastern Australia, some populations (provenances) have become isolated over geological time, but are well-adapted to local conditions.

By facilitating the translocation of species from provenances with greater climate adaptability, and cross-pollinating these with local species which are already adapted to the soil structure of their provenance, the new cross-bred seedlings should have a greater chance of long-term survival than their pure-bred counterparts.

Eucalypt dieback at Nardoo Hills Bush Heritage reserve. Image by Amelia Caddy

Working at Nardoo Hills since 2013, Bush Heritage Senior Ecologist, Dr Matt Appleby, has a firsthand understanding of the impacts of increased temperatures and drought conditions on the woodland habitats at the reserve. The dieback, which Dr Appleby describes as different from other events he has seen in the past, could be observed after intense heatwaves within the already dry region after January and February 2014. “Looking from the top of the largest hill down one ridge line you could see a thinning of the canopy where most of the outer and upper branches had died off. On some trees, the coppicing and epicormic growth, (which is the usual way a tree will regenerate after fire), had sprung from the trunk and also died. Every six months I’d notice the affected area was slightly bigger,” he says. “The dieback was working quite the opposite way from what you’d expect, such as in the pattern of Phytophthora dieback, which spreads through soil and relates to soil moisture. At Nardoo, the wettest parts of the property were the healthiest, while the driest areas were the most affected. Our Reserve Manager, Jeroen Van Veen, noticed heavy leaf loss immediately following the summer heatwaves – a good indication that the problem was heat related.”

Significant dieback in an area which is home to so many native and endangered species could mean huge changes for the ecosystems in the area. A lack of shade from the reduced canopy will expose delicate woodland groundcovers, herbaceous plants, and soils to excessive heat and light, impacting wildlife habitat. “The response of the animals could be devastating,” continues Dr Appleby. “A lot of species depend on eucalypts – they create shelter and produce a lot of nectar when they flower. Those animals that live in the woodland habitat, such as the brown treecreeper, depend on insects that live on the trees, and there are lots of other examples of species that are highly dependent on the trees. There are a lot of repercussions in an event like this.” 

It’s critical that the take home message for people isn’t to abandon their local provenances, but rather, supplement what is already existing with non-local provenances from hotter, drier climates.

Dr matt appleby

Rather than accepting the consequences of wide-spread death at the hands of climate change in the reserve, Bush Heritage commenced an innovative approach to ecological restoration, experimenting with regenerating the site through climate-resilient plantings that should perform better in the changing conditions. Led by University of Melbourne researcher and Bush Heritage volunteer, Dr Garry McDonald, and Dr Appleby, andthe team utilised climate modelling to pinpoint regions with climates analogous to the hotter, drier conditions that are predicted for Nardoo Hills in 30-70 years’ time, based on two emissions scenarios. These were then cross-referenced with records of grey box and yellow box populations, which led to the arduous process of collecting seed from representative trees in areas such as Fifield, Junee, Deniliquin, Narrandera and Condobolin, as well as locally. 

Split bark from a dieback event at Nardoo Hills Bush Heritage reserve. Image by Amelia Caddy

“Because eucalypts are such long lived trees, gene flow through the whole species is relatively slow – they don’t flower every year and over thousands of years certain regions of grey and yellow box populations have become isolated, limiting gene flow amongst the species,” says Dr McDonald. “Our plan is to facilitate the reintroduction of genes from different areas of the same species, such as grey box from Fifield, and Yellow Box from Condoblin, which are already tolerating conditions that Nardoo will experience more regularly as the years go by, into the area to broaden the gene pool from which nature can then select the most successful or robust offspring.” 

In collaboration with Greenfleet, an organisation that offsets carbon emissions, seeds were collected from ten mother trees from each provenance, and then germinated and planted separately at Aborline Nursery in Hamilton, Victoria. The seedlings were later given an individual QR code, which described their mother tree and provenance of origin. Back at Nardoo Hills, some particularly cleared areas were divided into 18 blocks, with each block further separated into 25 plots. Finally, in July 2019, a team of volunteers planted the 9000 mixed-provenance seedlings across the plots according to a pre-determined, randomised design which had been carefully created by Dr McDonald to ensure the experiment could be monitored accurately by scientists for decades to come. 

Landscape ready for tree planting at Nardoo Hills Bush Heritage reserve. Image by Kate Thorburn
Dr Matt Appleby with seedlings ready for planting at Nardoo Hills Bush Heritage reserve. Image by Amelia Caddy
Seedlings being planted at Nardoo Hills Bush Heritage reserve. Image by Amelia Caddy

“Eucalypts take around 10-12 years to flower and put out seed, so we won’t know much about the success of the trial for quite some time,” says Dr McDonald. “Our hope is that the different provenance seedlings will grow and cross-pollinate with the local provenance trees to generate maybe tens of thousands of new seedlings that are more robust and resilient in the face of a harsher climate. Because of the way we have run this experiment, scientists will be able to use genomic studies to look at those individual surviving trees and trace them to the mother trees that have allowed that opportunity to occur.”

If successful, the seedlings that are grown in the experiment will be extremely valuable to the future vibrancy of woodland forests in Nardoo and beyond. But like any experiment, says Dr Appleby, there is potential for failure. “We still need to see if the seedlings that we’ve moved from hotter and drier climates will be able to survive well or not at Nardoo Hills during those first few years, so there is some risk there. But what is a far greater risk I believe, is relying on the genetics of the local population to cope with the changing temperatures and rainfall that the area will experience.”

Aerial of lines for revegetation planting at Nardoo Hills Bush Heritage reserve. Image by Glen Norris

The next challenge, both agree, will be to find ways for community groups across Australia to access the knowledge and tools necessary to put into practice their own climate-adjusted provenancing approaches so that more climate-resilient tree planting can be undertaken on a nation-wide scale. “We’re keen to get this knowledge out to Landcare groups, as well as organisations like Greenfleet, and anyone interested in creating a more climate-resilient ecology,” says Dr Appleby. “If we don’t, there is huge potential for risk – you might get a nice planting of native trees underway, and in twenty-years-time, those trees are in decline because they’re no longer adapted to the climate, and that investment is lost. We all need to be thinking about the impacts of climate change long-term plantings.”

Given that a 2015 report published on the science forum, Frontiers, stated that investments in ecological restoration are estimated at $US 2 trillion per annum worldwide and are increasingly rapidly, it’s in our best interests, economically and environmentally, that a climate-adjusted approach to restoration ecology is put into place. “It’s critical that the take home message for people isn’t to abandon their local provenances, but rather, supplement what is already existing with non-local provenances from hotter, drier climates,” says Dr Appleby. “That will be the best outcome for all of us.”