Visser 2001, Producing native seeds to restore degraded lands (abstract)

Producing native seed to restore degraded lands: the case of Stipa lagascae R. & Sch. in Presaharian Tunisia

Marjolein Visser

PhD dissertation, Faculty of Agricultural and Applied Biological Sciences, University of Ghent, Belgium
Sept. 2001, 374 p. (written in French).

Original title:
Produire des semences autochtones pour réhabiliter des terres dégradées: le cas de Stipa lagascae R. & Sch. en Tunisie Présaharienne

Abstract

In Presaharian Tunisia (100-200 mm of annual rainfall), awareness is growing that local, rather than exotic plant material should be used in combating arid land degradation, but many questions remain unanswered: why prefer which species, and how to use them?

To formulate answers on these questions, this study is based on applied research in Tunisia to produce quality seed from a native perennial grass. Its 7 chapters (number per theme mentioned) all relate directly or indirectly to collecting, evaluating, selecting, multiplying and ultimately reintroducing Stipa lagascae R. & Sch. (Stipa).

First, degradation needs to be defined in order to determine goals while restoring. It is suggested that erosion and phosphorus depletion of North-African drylands have interacted with the progressive disappearance of palatable perennial legumes and grasses (e.g. Stipa). By reintroducing those plant species, together with phosphorus amendments, restoration should aim to improve secondary productivity, rather than focussing on primary productivity or on biodiversity (2).

The morphological variation revealed by the collections of seed lines of Stipa, a cleistogamous, highly polymorphic and widespread species, was analysed and confronted with the complicated systematics of this botanical complex. It is concluded that most described morpho-species of this complex do not merit their species rank. Moreover, these findings seem to apply to several other palatable perennials, because these are often either autogamous or apomictic (1).

The starter collection of Stipa clonal lines was extensively evaluated upon vegetative vigour and flowering phenology. The data set allows to discuss the question in which way local material should be collected and multiplied, following the principle that local yet ample genetic variation should be reintroduced. Native seed production of vigorous yet highly variable and autogamous or apomictic plant material is only sustainable if seed lines are kept separate throughout. The same conclusion is reached when investigating seed dormancy and viability patterns of different seed lines (3).

The main reason for ongoing desertification in Presaharian Tunisia is privatisation and cultivation of formerly common rangeland, and reintroducing steppic species must cope with this fact. For Stipa, the reintroduction of the disappearing practice of Stipa-haying, from collective lands toward privatised land, offers new perspectives for making arid land restoration socially feasible (1).

Proposed key words: Presaharian Tunisia, ecological restoration, native seed, perennial grasses, selection, plant life histories, CRS-strategies, Grime, autogamy, polymorphism, rangelands, seed multiplication, seed dormancy, haymaking.