|  |  | Header image: Silvereye/tauhou (Zosterops lateralis) visiting the bird feeder during a late winter snowstorm |
| News from the nursery and spring outlook |
| While we’ve just said goodbye to NZ’s third warmest winter on record, with some fairly extreme weather events across the country, when averaged over the whole season the temperature for Central Otago was near average, with slightly above average rainfall. Signs point to a good growing season coming up, with the spring outlook suggesting an average or above average temperature spring with an normal or above normal rainfall and river flow, with a good chance of available soil moisture remaining normal or above throughout the season. Although the forecast confidence is not high, weather patterns over the past couple of weeks certainly suggest a wet spring, though cooler than we’d like to get things growing. |
|  | Above: Looking down the Kawarau Gorge towards Cromwell from atop the Waitiri peninsula on a foggy early winter morning |
| Our spring potting has begun in earnest here at the nursery, with thousands of our eco-sourced seedlings making their way through the potting shed into our outdoor nursery area. We let almost all our plants mature here fully exposed - ensuring they’re accustomed to environmental extremes of heat, cold and sunshine. |
| Making a home for native birds in your garden |
| Readers of our newsletter will know we love to write about birds, and this edition is no different. Today’s piece seeks to educate others on how they can consider the ecology of their garden and create a space that will support native birds and encourage their numbers and diversity to increase.
Birds were until 800 years ago the majority of residents in Aotearoa. Since human arrival, their area of residence and their food security has continually eroded. Native birds have evolved for an environment dominated by forest and wetlands. These forests are not evolved for disturbance and are unlike forests that have evolved with browsing land mammals. If our forests are disturbed or destroyed by logging or fire they take hundreds of years to return to the stable forest they once were. However, the forests can return. We are fortunate to have areas untouched by humans acting as living seed banks and examples for us to study.
Central Otago, however, lost virtually all of its forest cover from man made fire followed by continued grazing (domestic and wild). We have lost our seed bank and, without human intervention, the forest plants will not return for hundreds or thousands of years. Native plants planted here will have a very tangible effect on the density and distribution of our native birds. Native birds are limited by their evolved physiology to the places they can nest, the food they can digest, and how they can defend themselves. They are tethered to native plants. For us, choosing between garden plants is an aesthetic choice. For a native bird it can be the difference between whether they can afford to build a nest, raise their young to adulthood or even survive winter.
Having said that, it is extreme to expect anyone to convert their garden to 100% native. While many native birds do need the complex ecosystem of a healthy forest to thrive, this is unlikely to be achievable or desirable in a garden environment. According to the garden bird survey, between 2018 - 2023 backyard birds are in decline nationally - but on closer inspection, most native birds are stable with many exotic birds declining. However there are a couple of much loved native birds in moderate to rapid decline in Otago during the last 5 years, the silvereye and the kereru. The bellbird is stable but ideally would be increasing. Tui and fantail are moderately increasing in Central Otago so we won’t focus too much on them. With some wise choices managing our garden ecology we can help these native birds. |
|  | Above: Kererū/wood pigeon (Hemiphaga novaeseelandiae) among native bush, northern Southland |
| Kereru are relatively common as you travel towards the coast, but are absent inland in Otago. At our nursery it is one of our long term goals to see kereru flying weightily above - a goal which will take many years, being largely surrounded by farmland and exotic infested mountains. This is not an unreasonable goal, however; we are roughly 40km from the closest population of kereru along the Glenorchy Road near Queenstown, and kereru have been recorded to fly 60km to reach a good autumn food source (Powlesland et al, 2011 Satellite tracking of kereru in Southland, New Zealand). This is also a good example of why they are so important for distributing seeds. The plan is simple: we add the correct plants and remove predators via trapping. We need plants for food and nesting.
Kereru will not nest in areas which lack food, with that the abundance of food triggering nesting (Schotborgh, 2005, An analysis of home ranges, movements, foods, and breeding of kereru in a rural-urban landscape on Banks Peninsula, New Zealand). Kereru eggs are precious, with only one egg laid at a time, although they can continue laying from September - April, raising a total of three or four chicks a year. Kereru seem to build nests in a variety of places 2 - 20m from the ground. They do prefer a dense canopy cover of trees, hiding their chicks from harriers by constructing a platform of well selected branches.
It has been suggested that totara and kanuka are favourite sources for nest building material (Mander et al, 1999, Monitoring and management of kereru) but they do adapt to other materials. Food sources are key for kereru, with kowhai species being the key food to kick off the breeding season. Compared to other plant species, kowhai are filled with protein, especially the new leaves. They will consume other exotic leaves like willow and tree lucerne but these do not serve the bird community as well as native kowhai (Sophora microphylla). By late spring kereru move onto a diet of berries and will consume even the largest native fruit. Cabbage trees, totara, Griselinia, Mrysine divaricata are just some of the berries they will consume. Once their chicks have fledged they will travel far and wide to find good sources of food through the autumn and winter.
Here are some plants you can use in your Central Otago garden to attract kereru: Myrsine australis Sophora microphylla Podocarpus hallii Cordyline australis Corokia cotoneaster
From a bird's eye view gardens merge with ‘wild areas’. If each garden planted at least one bird friendly native tree or shrub a network of support would be created. |
|  | Above: The beloved Tūī (Prosthemadera novaeseelandiae) |
| If we are to make tangible efforts to support our feathered friends then it would be remiss to not consider trapping. When mammals are removed the effects are stark. Predator proofed areas provide us an example of how our birds can thrive without the excessive predation and habitat destruction of introduced mammals. From these areas birds begin to overflow to surrounded areas - for example, residents of Wellington are witnessing substantially more bird numbers and species thanks in large part to the Zealandia ecosanctuary.
Quite understandably for many the idea of trapping can be challenging but the effects of introduced mammals on native birds are not overstated. Trapping can begin small with mice and rats, which have a huge effect on native birds. They will will eat eggs and chicks, and rats also can eat small adult birds. In addition to predation they are a major food source for larger predators such as weasels, stoats and ferrets.
In years of abundant seed and fruiting rodents will breed exponentially. Once the seed and fruit is expended the rats and mice turn to native birds but without vast food availability their numbers will crash. The stoat population rises in conjunction with the rats and when the rats decline, stoats then turn to birds with greater effect and ferocity. Outdoor traps for rats are easy to obtain, bait and maintain. They can be kept in long rat tunnels with rat sized entrances that make it safe for other beings enjoying your backyard. Visit here for more information on traps.
Thankfully few or none of the birds observed here are nationally threatened even if they may be locally rare. However, as these birds share the forest and shrub habitat with threatened birds, by taking steps to encourage non-threatened birds we may be aiding, to some degree, threatened birds. On another note, just because these species are not threatened doesn’t mean that they don’t deserve to thrive, or that we shouldn’t aspire to raise our avian fellows to pre-human population levels.
There is a well known phenomenon called ‘shifting baseline syndrome’ - humans struggle to remember historical abundance. We may see a large flock of birds in current times and believe they are doing well but not remembering the flock 10 years ago was two to three times the size. We believe what we experience in the present is the norm. We may very well have this syndrome even with our common backyard birds. This is one reason why the garden bird survey and similar citizen science projects are so important. |
| (this is an abridged version of this article. For further discussion including the ecology of silvereyes and bellbirds/korimako, read our full article here) |
| | Ecological succession in Central Otago and its use in planting and conservation |
| Succession is a concept in ecology. In our discussion of attracting birds to our gardens above, we touched on some ideas that involve succession - it simply means the change in the kinds of species and their distribution in an environment over time. Succession is often characterised by a kind of progressive plant “sequence”, disrupted by disturbances. The environment could be on a large or small scale - an entire island or forest, or your backyard or lifestyle block. A knowledge of ecological succession helps us to read the history of the land we live in and care for. It can help give deeper knowledge and confidence when selecting and caring for plants.
On a large scale, the level of plant populations, one might think of succession in an entire forest community regrowing after a fire. This is a community succession, where a whole area has a synchronous community succession following a disturbance. On a small scale, the level of individuals, a single tree falling is a disturbance that triggers a minor succession where new plants emerge to fill its space.
These are examples of secondary succession, which follows a disturbance event, and with which this essay is mostly concerned. Primary succession would be in new land without soil. Fantastic examples of primary succession in NZ can be observed on a trip to Rangitoto Island, a very young volcanic island in the Hauraki gulf. More locally here in Central Otago, sluice tailings left by the gold diggers of the 19th century in which all soil was washed away can be thought of as a site of primary succession - here we see lichens as pioneer species which, combined with erosion from wind and rain, will eventually form a soil in which more familiar vascular plants will grow. These tailings could also be thought of as mimicking accumulating talus (rockfall) at the bottom of slopes, and a number of dryland plants have adaptations to surviving in this type of substrate (Rogers, Walker and Lee, 2005, The role of disturbance in dryland New Zealand: past and present). |
|  | Above: lichenous stacked rocks amongst various seral shrubs providing habitat for the rare Otago skink (Oligosoma otagense) aka giant or great skink, see centre of image |
| We can see how there is a direct link between disturbance and conservation outcomes in the example of our native Olearia (Tree daisies). In a pre-human settlement land state, slips and alluvial washes might have been the main disturbance event by providing bare soil for Olearia seeds to germinate. Now, introduced exotic grasses (pasture grasses) will instead colonise the bare soil, with the end result of many species of Olearia becoming endangered. This effect leads to knock-on reductions in biodiversity. |
|  | Above: an excellent germination rate for surface sown, uncovered seeds of Olearia odorata demonstrates their preference for bare soils |
| Let’s take a look at an example of a succession sequence that might follow after a pasture in Central Otago is left fallow for a few centuries: Annual weeds will grow. These common wild plants in arable land tend to have a common set of traits, most importantly higher growth and photosynthesis rates. Examples include annual meadowgrass, chickweed, cleavers, and native annual plants. Herbaceous perennials will follow. These and the later post-annual successionals can germinate in shade and grow in low light intensities. Examples include weeds like dock, dandelions, thistles and most pasture grasses. Natives include tussock grasses, native carrot, Acaena, alpine plants, spaniards, Raoulia, Scleranthus. Shrubs. These along with the perennials above build soil structure and give protection and cover for the germination of larger species. This is about as far as most regenerating plant communities in Central Otago have been able to get so far, and many are arrested in this stage due to lack of seed source for larger tree species. Examples include Ozothamnus, Dracophyllum, Olearia, Coprosma, Discaria toumatou. Early successional trees. Multilayered foliage, higher rates of reproduction and more efficient seed dispersal. Examples include Sophora microphylla, Pseudopanax ferox and crassifolius, Metrosideros umbellata, Olearia avicenniaefolia, Griselinia littoralis, Aristotelia serrata. Late successional trees. Monolayered leaves in “shell”. Larger seeds, lower dispersal, long juvenile phases and lifespans. Examples include matai, totara, miro, beech, kahikatea, rimu. These forest giants also help to create the conditions for diverse sub-canopy communities.
The intermediate stages are known as “seral”, with the final stage known as “climax”. |
|  | The obvious way to use this successional knowledge is in planting choice. One can see how in the more arid areas of Central Otago planting large native trees eg beech into greenfield land without major human inputs of irrigation, protection and maintenance is bound to fail. However, if one begins with an earlier stage in the successional sequence eg shrubs, one can create an environment where larger trees can actually begin to thrive.
We touched above on how disturbance events change soil conditions. This is of particular importance when considering a successional process. Each “level” of succession creates the conditions required for the next level. Therefore when you jump levels in the sequence, for example planting Fuscospora beech into paddocks, the soil is not ready to support this plant. If you plant, for example, kanuka/Kunzea serotina first, they will begin to change the soil culture and structure. It has been proposed that the mutualism between kanuka, manuka, beech and the mycorrhizae (symbiotic soil fungus that live in association with plants) they share contributes to the ability of kanuka and manuka to help establish beech forests (Weijtmans et al 2007, Occurrence of arbuscular mycorrhiza and ectomycorrhiza on Leptospermum scoparium from the Rakaia catchment).
On the topic of soil culture, the composition of plant communities is related to the composition of soil microbe communities. Native plant communities particularly differ with mycorrhizal species present. Ectomycorrhizal networks on nutrient-poor soil, like those found in many native plant communities, can dominate such that successful plant species must either “plug in” or have their own method of producing nitrogen (Lack, 2002, Plant Ecology and Conservation). On large scale restoration projects, potential mycorrhizal features of the community should be considered - for example, in exotic grasslands endomycorrhizae may dominate that will inhibit the ectomycorrhizae that are symbiotic with native tree species.
Also many shrub species, mid level in the example successional sequence given above, provide services to other plants and thus directly or indirectly promote the growth of later plants. For example, matagouri/Discaria toumatou are nitrogen fixers which increase nutrients for surrounding plants in nutrient poor areas, and are highly important to build fertility for later successions. The invasive gorse plant provided a similar function in its native environment in Scotland.
There is another, and potentially even more powerful way to exploit the successional sequence to improve our conservation outcomes. This is by utilising a cascade/feedback effect, where a process increasing species richness starts a second, and so on. One example of this would be a reforestation practice where we can plant “nuclei” of fruit-bearing plants that attract seed-carrying herbivores eg birds. Let’s break that down. First we plant out our nuclei, small plant communities that act as islands in a barren area. These islands attract birds which feed on the berries. The birds bring with them seeds from other pockets of bush, which grow and increase the species richness of the planting. These in turn attract more birds, and so on goes the cascade, accelerating all the time until the bounds of the reforestation area are met. This also shows how animal succession usually follows the nature of the plant community, though there are rare examples of it being the other way around.
It’s worth noting that birds, specifically the large herbivores that were the eastern guild of moa, were the dominant driver of plant successional processes pre-settlement. “We found no evidence that fire created networks of secondary vegetation that provided fire-dependent successional plants with constant habitat within dryland environments. It appears that bird herbivory was the dominant mechanical regulator of vegetation composition and structure” (Rogers, Walker and Lee, 2005, The role of disturbance in dryland New Zealand: past and present) |
| Hence, by combining a succession-informed planting choice with a cascade effect, we can enhance our conservation efforts substantially. We can also apply some of these principles to the home garden. For example, with human intervention like adding organic matter and mulches as a substitute for leaf mold, or shade and wind barriers to act as a surrogate forest, we can accelerate natural successional processes. This is just one way to apply ecological principles such as succession to conservation and planting work. We may explore more in later newsletters. |
| (this is an abridged version of this article. For a more detailed discussion including a history of plant distribution in Central Otago and major disturbance events, read our full article here) |
| | |  | Pittosporum tenuifolium PB6.5 $10.50 Common/Maori name(s): Kohuhu / Black Matipo Perhaps the most widespread Pittosporum. Very reliable hedging plant grows to 6m high by 3m wide if left to grow. Evergreen. Common to find slight variations in leaf colour and shape. Tolerates many soils and locations however they will suffer in waterlogged soil or in frost pockets that reach past minus 10c for prolonged periods. Best grown in moist but well drained soil in sun - part shade. Frost hardy. Height of grade at sale: 40cm Stock level indication: Plenty in stock! |
|  | Viburnum tinus PB6.5 $10.50 Common/Maori name(s): Laurustinus Valuable garden shrub. Flowers for a long time in winter/spring and can be grown in many locations. Grows to 3m high by 3m wide and can be used as a hedge. Grow in full sun or partial shade. Tolerates full shade and windy spots but will grow better with shelter. Winter flowering is a boon for bees and insects. Height of grade at sale: 30cm Stock level indication: Plenty in stock! |
| | As always if you are planning any plantings or big jobs for this spring or next autumn let us know and we will prepare a quote. The more lead time you can give us, the better we can meet your needs.
Check out our Catalogue for more information or feel free to flick us an email or a call.
As always, if you want a quick overview of what we have immediately available in stock, you can check our order page. |
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