Auckland's green volcanic heart: groundcover vegetation and soils of the Auckland volcanic cone reserve network

Figures & data

Figure 1 Location of reserves and study sites on volcanic cones of the Auckland Isthmus.

Figure 2 Hierachical classification of groundcover vegetation composition on 70 sites on four Auckland volcanic cones: Maungakiekie, Maungawhau, Maungarei and Ohinerangi. Eight vegetation units are recognized.

Table 1 Mean % cover scores for dominant species in each of the eight recognized vegetation units (A–H, described in text) on four Auckland volcanic cones: Maungakiekie, Maungawhau, Maungarei and Ohinerangi (means <1% omitted).

Species	A	B	C	D	E	F	G	H
Lolium perenne	20	1	3	1	2	2	1
Trifolium repens	19	10	1	4	1	3	2
Pennisetum clandestinum	12	78			22	8
Plantago lanceolata	8		5	5		3	1	2
Anthoxanthum odoratum	7		3	4	6	6
Agrostis capillaris	7	5	2	5		1
Poa annua	2	8			2
Bothriochloa macra			19
Festuca rubra			13		4
Paspalum dilatatum	1		6	3
Arrhenatherum elatius			1	19	1	3
Daucus carota				6
Rytidosperma sp.				5
Sporobolus africanus			1	4
Stenotaphrum secundatum					23
Bromus spp.	2		3			4
Holcus lanatus	2	1		2	8	4	3
Dactylis glomerata	1			2	4	9	6	1
Acaena novae-zelandiae^1			2			1
Ranunculus repens	1	1				1	5
Tradescantia fluminensis							15
Viola odorata							23
Hedera helix							13
Microlaena stipoides^1	2		1		1	21	26	78
No. of plots	32	3	2	2	4	22	2	3

¹ Native species.

Figure 3 Two-dimensional nMDS ordination of groundcover vegetation composition of sites on four Auckland volcanic cones: Maungakiekie, Maungawhau, Maungarei and Ohinerangi with eight vegetation units recognized.

Figure 4 Variation in site nMDS ordination axis 1 scores by slope categories (mean±standard errors). Slope categories are flat to gentle = < 10°, moderate = 10°–20°, steep = 20°–35° and very steep = > 35°. Means with different letters were significantly different (ANOVA, F = 16.893, P < 0.001).

Figure 5 Relationship between % tree cover and % cover of Microlaena stipoides. Line predicted by linear regression (P<0.001) superimposed on graph, % cover M. stipoides=4.39 + 0.74 ×% tree cover.

Table 2 Pearson correlation coefficients for environmental variables with first two nMDS ordination axes with significant results.

Variable	Axis 1	Axis 2
% tree canopy cover	0.74**	0.02
Sward height (cm)	0.53**	−0.06
% bare soil cover	0.54**	0.14
% dung cover	−0.34**	−0.06
pH	0.50**	−0.12
Total C (%)	0.12	−0.40**
Total N (%)	−0.05	−0.44**
C/N ratio	0.62**	0.12
Ca	0.53**	−0.13
Mg	0.35*	0.31
K	0.06	−0.48**
Na	0.54**	0.10
CEC	0.49**	−0.16
Base saturation	0.62**	0.05

* P < 0.05, ** P < 0.01.

Figure 6 Relationship between total N (%) and % cover Pennisetum clandestinum. A linear regression applied to this relationship is significant (P<0.001) for the line % cover P. clandestinum= − 13.4 + 34.3×(total N (%)).

Figure 7 Variation in site nMDS ordination axis 2 scores by volcanic cone (mean±standard errors). Means with different letters were significantly different (F = 8.15, P < 0.001).

Table 3 Differences in soil characteristics among volcanic cones, aspect and slope categories on four volcanic cones in Auckland: Maungakiekie, Maungawhau, Maungarei and Ohinerangi. Significantly different values (P<0.05) among categories are indicated by different lower case letters.

Variable	Soil pH	Soil organic C (%)	Soil total N (%)	Soil Olsen P (mg/kg)
Cone
Maungakiekie	6.0 a	6.6 a	0.58 a	60.8 b
Maungarei	6.3 b	12.1 c	1.08 c	38.0 a
Maungawhau	6.1 a	10.1 b	0.84 b	22.2 a
Ohinerangi	5.9 a	6.7 a	0.59 a	40.5 ab
Aspect
North	6.3 b	8.6 a	0.72 a	50.3 b
South	6.0 a	8.3 a	0.72 a	35.2 a
Slope
Flat to gentle (<10°)	5.9 a	9.7 b	0.90 b	57.0 b
Moderate (10°–20°)	5.8 b	9.0 b	0.79 b	32.6 a
Steep (20°–35°)	6.2 b	9.1 b	0.75 ab	37.2 a
Very steep (>35°)	6.4 b	7.6 a	0.65 a	40.8 ab