Riparian Plant Restoration in Summer-Dry Riverbeds of Southeastern Spain
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needed to attain coverage, frequency, and species com- Riparian Plant position comparable with that of undisturbed zones. Key words: Mediterranean semiarid streams, plant res- Restoration in toration, plant structure, species frequency. Summer-Dry Riverbeds of Southeastern Spain Introduction iparian ecosystems are spatially and temporally 1,3 M. Jacoba Salinas R dynamic and are shaped by fluvial geomorphic 2 processes. Thus, there are physical and biological links José Guirado between terrestrial and aquatic environments (Gregory et al. 1991) and biotopes in which animals may seek ref- Abstract uge and food, while enriching the soil in detritus. Stud- ies in North America have shown that semiarid and An evaluation was made of the development of two arid riparian ecosystems support higher species rich- experimental plots where restoration of dominant ri- ness and densities of wildlife than do other nearby eco- parian plant species was conducted in December 1991 systems (Johnson & Simpson 1971; Carothers et al. 1974). along two semiarid Mediterranean summer-dry wa- Semiarid Mediterranean riparian vegetation is the only tercourses. An overall comparison was made of the type of arboreal/shrubby vegetation in these areas and vegetation structure, species cover, floral composition, differs markedly in phenology from the other commu- and species richness of the plots restored using vege- nities, thus giving the landscape distinctive features. It tation from nearby undisturbed plots along the same detains erosion materials (a serious problem in the watercourse. The monitoring was performed in Octo- semiarid Mediterranean region, because the hillsides ber 1993, October 1995, September 1997, and October have sparse vegetation cover), thus decreasing the 1999. In the restored zones previously rooted cuttings amount of solids in suspension in the watercourses and of the species most representative of these communi- improving the quality of the water (Pesson 1978; Man- ties were planted, using the undisturbed zones as veg- teiga 1992). It slows down the flow of torrential rains etation models. Climatological conditions (particu- and collects the material carried, reducing the effects larly the rainfall regime during the planting period) downstream. Furthermore, the highly developed root substantially favored the success of the planting es- systems reinforce the banks of the streams. tablishment. The results show that a simple planting In recent years several techniques have been devel- technique accompanied by monitoring during the oped to stabilize river and stream banks using arboreal first year is adequate to achieve success in establish- or shrubby vegetation, either alone or in combination ment of planting species. It is necessary to take pre- with inert materials (Glover & Ford 1990, unpublished cautions against herbivory of small plants of Chamae- data; Glennon & Ritz 1994, unpublished data; Leiser et rops humilis, Ficus carica, and Retama sphaerocarpa. al. 1994, unpublished data). The more the vegetation The planting itself causes some disturbance in the soil grows, the greater the protection it offers, provided the that may alter the species composition, giving an ad- water flow is not obstructed (López 1988a). All these vantage to ruderal species over others. More time is advantages, together with the considerable enhance- ment of the landscape that this vegetation affords under semiarid Mediterranean climatic conditions, justify con- sidering this type of vegetation as being of primary impor- 1Departamento de Biología Vegetal, Facultad de Ciencias, C/ tance. The maintenance and/or restoration of vegetation Severo Ochoa s/n, Universidad de Granada, Granada, Spain thus deserve to be given priority in land management 18071. projects. 2 Delegación Provincial de la Consejería de Medio Ambiente The watercourses chosen for this experiment are de la Junta de Andalucía, Centro Residencial Oliveros, Bloque among the most seriously altered by human activity in Singular, 2a planta, Almería, Spain 04071. this area of southern Spain. Original riverside commu- 3Address correspondence to M. J. Salinas, e-mail: maria@ goliat.ugr.es. nities have been gravely degenerated or destroyed by tree cutting, the introduction of exotic species, the di- © 2002 Society for Ecological Restoration version and channeling of water for agriculture, and the DECEMBER 2002 Restoration Ecology Vol. 10 No. 4, pp. 695–702 695 Plant Restoration in Semiarid Summer-Dry Riverbeds use of river beds and shores for cultivation or even as roads (due to low or nonexistent water flow) (Salinas 1995; Salinas et al. 1999). At present the damaging hu- man activities have ceased to a large degree (primarily agriculture, due to low profitability), and therefore large-scale restoration projects are now feasible. In ad- dition, these courses are located in the interior of the maritime-terrestrial Natural Park Cabo de Gata-Níjar, an area protected since 1987 for its unique semiarid flora and fauna. One of the prime objectives of those Figure 1. Monthly distribution of rainfall in millimeters for managing this park is to preserve and restore degraded the period 1991–1999. The thicker line represents mean plant communities. monthly rainfall for the period 1941–1970. Data from meteoro- To examine the success of restoring riparian vegeta- logic station, Almería airport. tion in these environments, we monitored plots situated on the banks of two different watercourses where ripar- ian vegetation has been reintroduced, comparing their presenting both areas with well-conserved natural ri- development with undisturbed vegetation of other parian vegetation and areas where the natural vegeta- nearby zones with similar characteristics. tion was completely destroyed by human activity (Sali- nas 1995). Materials and Methods Sampling of the Vegetation Site Description Along the undisturbed stretches four plots of 120 ϫ 3 m The study was conducted in the southeastern Iberian were randomly chosen on both banks of the two water- Peninsula, along the lower stretches of two small streams courses (Amoladeras and Agua rambla, two per site, with sporadic seasonal flow known as ramblas, located one per each bank). In July and October 1991 we mea- in the interior of the maritime-terrestrial Natural Park sured the percentage cover and the frequency of all the Cabo de Gata-Níjar (Almería, Spain). The streams begin phanerogamous plant species in each plot by the line- on the southern slope of the Sierra de Alhamilla (18 km intercept method (Bullock 1996). The intercept mea- from the Mediterranean Sea), located approximately be- surements were taken at heights of 1.5 m, 50 cm, and 10 tween 36Њ40Ј and 37ЊN and 2Њ15Ј and 2Њ20ЈW, with alti- cm. Sampling was repeated in October 1993, October tude varying from 0 to 1387 m, and discharge into the 1995, September 1997, and October 1999. Mediterranean Sea. The flow is highly irregular, with the total absence of surface water over most of the Planting length of these streams and during most of the year. The mean annual water flow is about 33.1 hm3 (Martín- The plant species chosen for restoration were those oc- Vivaldi 1991). The climate is semiarid Mediterranean curring most frequently and with greatest cover in un- (Le Houèrou 1982), with a mean annual rainfall of 241 disturbed plots (Table 1). Planting was done in Decem- mm (average for 1941 to 1970, data from the Instituto ber 1991 at sites 1 and 2, where natural vegetation was Nacional de Meteorología, Almería airport, Fig. 1), al- completely destroyed. Plots were selected to be the though interannually it fluctuates greatly (ranging from same size as the undisturbed plots (120 ϫ 3 m) and 65.9 mm in 1998 to 551.5 mm in 1989). Rain falls mainly were located in zones where the riparian vegetation in autumn and winter. Winters are mild and summers was completely destroyed on both banks of the water- hot; the median annual temperature is 18.3ЊC (average courses (four plots in total, two per site). The number of from 1941 to 1970, data from the Instituto Nacional de individuals planted in each species is indicated in Table Meteorología, Almería airport). The most frequent geolog- 1. The procedure was as follows: An excavator was ical materials of the bedrocks are of Neogene-Quater- used to dig to a depth of 1 m on the banks to reach the nary origin consisting of sandstones and conglomerates soil layers that remain the wettest, particularly in sum- (Martín-Vivaldi 1991). Upland vegetation in the study mer. Afterward we made holes 0.5 m in depth and 1.5 area is dominated by shrubs and lowland vegetation by m apart. Each individual was planted bare root. The highly diverse shrubby communities, with scant cover- plots were monitored (wilt and possible elimination of age (Alcaraz et al. 1989; Peinado et al. 1992; Mota et al individuals by the visitors) for the first few months af- 1997). ter planting and were irrigated weekly during the first Two experimental sites were selected, site 1 (Amolad- summer. The plants came from cuttings rooted in a eras rambla) and site 2 (Agua rambla), characterized by nursery, with the exception of Retama sphaerocarpa 696 Restoration Ecology DECEMBER 2002 Plant Restoration in Semiarid Summer-Dry Riverbeds Table 1. Dominant plant species for each undisturbed plot and number of planted individuals per 120 ϫ 3–m plot at Amoladeras rambla (site 1) and Agua rambla (site 2). Number of Planted Individuals Dominant Species in Undisturbed Plots Life Form Site 1 Site 2 Tamarix canariensis Willd. Halophyle phreatophyte shrub (saltcedar) 80 48 Nerium oleander L. Perennial shrub phreatophyte 42 28 Chamaerops humilis L. Palm shrub 17 18 Retama sphaerocarpa (L.) Boiss. Mediterranean shrub 16 14 Tamarix africana Poiret Halophyle phreatophyte shrub (saltcedar) 13 10 Ficus carica L. Deciduous tree 8 8 (broom), which were germinated from seed. An effort rennial grasses (Poaceae), very frequent in the sur- was made to plant after a rainy period, so that the sub- rounding shrublands (Stipa tenacissima and Lygeum strate would be saturated with water. During the first spartum) and other ruderals (Hyparrhenia hirta and few months there was no wilting or loss of planted indi- Piptatherum miliaceum).