Transcript Slide 1
Ecological Restoration of Lower Slopes of Bald Spur Te Aroha Wayne Bennett This is a guide to the restoration of native plants to the lower slopes of the Te Aroha Domain. The map shows the area discussed Restoring the natural plant communities • There are two good reasons for focussing on restoring the natural vegetation of the site. 1. What rigorous competition over millennia has settled on as the fittest plant assemblage for the site is likely to include the range of species likely to make use of all resources of light and nutrients available and compete well with invasive species. 2. The range of species found at this site is likely to be unique to this site and the range of genes found in the individuals may also be unique to this site. This is a characteristic of the natural world ( part of the worlds biodiversity ) and deserves protection. We can look at the natural world as a mosaic of patches on a map. I prefer to see the distribution of organisms as a combination of continuums, gradients and time lines with species occupying segments along those continuums, gradients and time lines. • Continuums • Gradients • Time lines Gradient Climbing up the mine road from the car park the canopy gradually looses puriri and eventually kohekohe, with hinau and pukatea becoming more prevalent and tawa dominating. Kauri are concentrated on the leached soils of some ridges and have their own suite of associated species. Near the top of the mountain there is a lower forest dominated by tawari, Quintinia, neinei, red and silver beech. There aren’t good examples of the forest of the plains nearby but we might expect a forest dominated by kahikatea with matai, pokaka, pukatea and some titoki and tawa. Puriri might be found depending on the frost levels but kohekohe prefers the slopes. The understory out there is more likely to include putaputaweta, Coprosma rigida and C.rotundifolia, turepo, Gahnia xanthocarpa carex species and Astelia grandis Time line It is also useful to look back over time to see what records there of the primeval vegetation. Ecological surveys by the Forest Service were updated in 1971, the Te Aroha News published a book for the 50th Jubilee of the town in 1930 including botanical notes and there is a botanical survey of the mountain published in 1884. Unfortunately the lower slopes are not covered in the Forest service notes, which refer only to the tawa forest above Bald Spur. The Adams 1884 botanical survey focuses also on the upper slopes. Possibly because at that time the vegetation of the mountain footslopes differed little from that found all along the range and was much more common than the unique flora of the upper slopes. It is only now that we realise that this narrow strip of low altitude forest is a vanishing ecosystem and in need of preservation or restoration. We do have some notes on an excursion to the summit published in 1930 for the towns fiftieth jubilee. The account mentions from Bald Spur; karapapa, rewarewa, rangiora, titoki, kowhai, hangehange, mahoe, wineberry, tutu, kawakawa and peperonia. The peperonia suggests a mild coastal climate, the tutu and wineberry are generally found in disturbed sites, which gives us some idea of the condition of the site at that time. What we don’t have is an account from AD1000 or even 1840. Continuums To get a better idea of the natural vegetation of Bald Spur I followed the walk from Tui Mine Road along to the Domain. There are fragments of more intact native forest along this walk. I know that further north along the base of the range karaka becomes more common and taraire, and pohutokawa appear but here the canopy is dominated by puriri with kohekohe titoki and tawa. In the gullies the understory is characterised by species like mahoe, kawakawa, hangehange, kanono, putaputaweta pigeonwood, mamaku and ponga. There are scramblers like kiekie and supplejack. Where there has been disturbance there is patete. Tanekaha and rewarewa appear where light and drainage is greater. Under these are found rangiora, heketara, shining karamu, Coprosma rhamnoidies and lancewood. Metrosideros fulgens, in flower at the moment is a common climber. Kanuka forms the canopy where there has been disturbance in the past. The following slides illustrate some of the plants characteristic of the area. Puriri kohekohe Titoki Tawa Mahoe Mahoe Kawakawa Kanono Putaputaweta Mamaku Ponga Nikau Parataniwha kiekie supplejack Restoration along a gradient I talked before about gradients and continuums, in fact across very short distances there are varying levels of soil moisture, drainage, pH, light, wind, frost all of these influence the species best adapted to a site and they all change over time, as other plants grow or decline around them. It is not possible to measure and take into account all these variables. The best we can do is introduce the major elements in the ecosystem and ensure ecological processes like seed production, dispersal competition and succession take place to establish the appropriate species across the landscape. We do however get the best results by making the best guesses based on experience. Over this area, there is a gradient, from the southern end where there are existing canopy trees and shade tolerant species to the northern end where there are few native species and a canopy of weeds to be removed. A varying approach will be required along this gradient. To the south, the ecosystem is more intact with a canopy of kanuka, gradually giving way to titoki, kohekohe and puriri. There are Coprosma rhamnoidies and C.areolata, mahoe hangehange, kawakawa, supplejack and pigenwood already there established in the shade. In this area, restoration may be limited to the removal of weeds. At the northern extreme, there is very little native vegetation and the existing trees are destined to be removed. This is where a carefully planned planting is necessary. A systematic approach When designing a planting plan I simplify the process by dividing the characteristic species into three groups. The canopy trees. These are spaced out where you might expect them in a mature forest. Some may be planted immediately, some may wait until there is sufficient shelter from other species established. In this case species like puriri, kohekohe, titoki, rewarewa, tanekaha. These will be in small numbers. Shade tolerant species should be introduced so that by the time there is a tall canopy there is a healthy breeding population of these. In this case species like; mahoe, kawakawa, hangehange, kanono, putaputaweta pigeonwood, mamaku and ponga. For drier areas; rangiora, heketara, shining karamu, Coprosma rhamnoidies and lancewood. In this area some of these are likely to naturally return. Colonising species Over this area colonising species will be required in increasing proportions towards the northern boundary where there is less canopy. These plants (in this case karamu or kanuka) will shade out herbaceous weeds and tip the balance in favour of the woody natives. They will also provide protection from wind and frost for the puriri kohekohe and some of the shade tolerant species like kawakawa. They will dominate in the early years and gradually give way to longer lived species. As the planted area begins to resemble the natural vegetation of the area, other species will find suitable habitat and establish themselves. The colonising species will diminish as they are shaded out, the shade tolerant species will regenerate, disperse and compete for suitable sites. The canopy trees will establish a canopy and provide habitat for epiphytes and climbers. Plant list For Te Aroha Domain Laurelia Phyllocladus novae-zelandiae trichomanoides pukatea tanekaha Beilschmiedia Knightia Alectryon Dysoxylum Vitex Olearia Aristotelia Brachyglottis Geniostoma Hebe Myrsine Schefflera Pseudopanax Cordyline Melicytus Coprosma Kunzea tawa excelsa excelsus spectabile lucens rani serrata repanda rupestre stricta australis digitata arboreus australis ramiflorus robusta ericoides tawa rewarewa titoki kohekohe puriri Heketara wineberry rangiora hangehange koromiko mapou pate fivefinger cabbage tree, ti-kouka mahoe karamu kanuka Carpodetus Coprosma Coprosma Coprosma Coprosma Cordyline Fuchsia Hedycarya Leucopogon Macropiper Pseudopanax Rhopalostylis Ripogonum serratus areolata grandifolia lucida rhamnoidies banksii excorticata arborea fasciculatus excelsum crassifolius sapida scandens putaputaweta thin leaved coprosma kanono karamu 5 5 10 10 20 20 30 25 40 40 40 40 40 45 50 80 80 120 150 6 25 6 5 25 5 10 20 4 20 10 10 4 forest cabbage tree tree fuchsia pigeonwood mingimingi kawakawa lancewood nikau supplejack, kareao 100 750 150 1000 Ecosourcing Ecosourcing is the propagation of native plants for ecological restoration from a representative sample of the local wild population. This ensures that a restored area reflects the natural diversity of the locality. So we are not only establishing the species in natural proportions but we are also sampling and restoring the natural distributions of genes from this area, in order to replicate the natural world and avoid the possible loss of biodiversity. This area represents the margins of the natural range of some species and they may have particular adaptations to this climate. This is important if we are to protect local character. We do this by collecting the seed from the local trees. This is a great way to get to know the local trees better. Summary The lower mountain has experienced a succession of “Civilising” events, from fire to the introduction of privet honeysuckle and wandering dew. To the planting of pines and eucalypts, to the random planting of native trees and shrubs. All of these events may have been done with the best of intentions but without the benefit of hindsight. The natural cover of this area is a forest unique to this place and an important part of the local character. Now is an opportunity to restore a diminishing ecosystem, where it will be educative and appreciated, in a way that will protect the local biodiversity and stand the test of time. Wayne Bennett