You are here: Tussock Grasslands MIS Site Contents Environmental Gradients

Environmental Gradients (from Scott, 1969)

The distribution of tussock grassland types is related to two environmental gradients. The first is a moisture gradient of rainfall, soil water holding capacity, etc., and in New Zealand is probably best approximated by a soil moisture or soil type classification. The second is a temperature gradient, which in the native grasslands is largely dictated by the combined effects of altitude and aspect. In particular localities, the temperature gradient also corresponds to a sequence of topographic landforms e.g. slopes, moraine, flood plains etc. The relationship between the grasslands and associated vegetation types according to these two gradients is given below.

Grasslands are bounded by Celmisia herbfields at higher altitudes and where low temeperatures prevail; and by beech forest, occassionally by podocarp forest and by associated shrubs on wettest sites; and by pastures comprising mainly exotic species on low altitude warm sites.

Tall tussocks occur at higher altitudes, ranging from Chionohcloa rigida on drier sites, through to other species at moist sites. Remnants of copper tussock occur on intermediate temperature and moisture sites.

At lower altitudes are the short tussock grasslands in which Festuca novae-zelandiae is generally the dominant species, together with a large area of modified tussock grassland derived from Festuca grasslands or in which Rytidosperma species are prominent.

Disturbance and stress factors which shape the characteristics of tussock grasslands (from McKendry & O'Connor, 1990)

Tussock grasslands to the east of the Main Divide have been used for pastoral activities for the past 150 years. The characteristics of a tussock grassland type are therefore not only a reflection of these environmental factors, but also the disturbance and stress factors associated with pastoral activities. These are outlined in the table below.

Pastoral practice		Interpretive level	Significance for protected grassland management	Outline of relevant factors
D I S T U R B A N C E	Fire	Different impacts between species	Maintenance of plant community	Post-fire community recovery a function of invasive potential of adjacent species and fire tolerance and regenerative capacity of resident species. Compounded by variations in fire regime.
		Individual species response	Maintenance of ecologically significant species	Method species used to persist through or invade after fire. Autecology of species Establishment or regenerative capacity of species
	Grazing	Rangeland distribution of stock	Interpretation of multiple, non-random and localised disturbances within large heterogeneous rangeland	Diet optimisation by stock Nutrient cycling and redistribution Environmental factors Landform and vegetation pattern
		Diet selection	Control of component vegetation disturbed by grazing	Grazing pressure assessment Relative maturity of species Absolute and relative availability of species and preferred plant parts
		Species responses to defoliation	Maintenance of ecologically significant species	Adaptations of species to particular defoliation regimes Specific genetic and environmental limitation to post defoliation regrowth, espeically edaphic factors
S T R E S S	Top-dressing	Modification of natural soil fertility status	Assessing the edaphic adaptivity of resident and/or desired species, both indigenous and exotic	Nutrient status of soil - especially P and S Dominant soil-plant relations Variation in fertility within landform
	Over-sowing	Succession pathways in modified vegetation	Establishment ability of oversown species Persistence of native and oversown species	Comparative environmental (temperature, moisture, soil fertility) adaptability of component species Life strategies of component species
	Subdivision	Adaptation of management to inherent landform patterns and processes	Control of range utilisation- management of spatially sensitive processes	Equilibration of feed supply and demand. Nutrient redistribution patch delineation Ecotone management Landscape values

Ecological interpretation of pastoral activity (from McKendry and O'Connor, 1990)