Plant Ecology

, Volume 150, Issue 1–2, pp 7–26 | Cite as

Long-term growth patterns of Welwitschia mirabilis, a long-lived plant of the Namib Desert (including a bibliography)

  • Joh R. Henschel
  • Mary K. Seely
Article

Abstract

Over the past 14 years, long-term ecological research (LTER) was conducted on the desert perennial, Welwitschia mirabilis (Gnetales: Welwitschiaceae), located in the Welwitschia Wash near Gobabeb in the Central Namib Desert. We measured leaf growth of 21 plants on a monthly basis and compared this with climatic data. The population structure as well as its spatial distribution was determined for 110 individuals. Growth rate was 0.37 mm day−1, but varied 22-fold within individuals, fluctuating seasonally and varying between years. Seasonal patterns were correlated with air humidity, while annual differences were affected by rainfall. During three years, growth rate quadrupled following episodic rainfall events >11 mm during mid-summer. One natural recruitment event followed a 13-mm rainfall at the end of summer. Fog did not appear to influence growth patterns and germination. Plant location affected growth rate; plants growing on the low banks, or ledges, of the main drainage channel grew at a higher rate, responded better and longer to rainfall and had relatively larger leaves than plants in the main channel or its tributaries. This could be due to better water and nutrient conditions on the ledges than elsewhere. The population appears to be growing outwards, with the smallest (youngest?) plants highest. Sex ratio was male-biased and males grew larger than females. Our study, in conjunction with the extensive literature base on Welwitschia, published here in a bibliography comprising 297 papers, indicates the knowledge gaps and needs for further ecological studies, including the continuation of our LTER programme. This should elucidate the reproductive output, seed dispersal, recruitment, water availability, age structure, and ecological differences between the sexes, and long-term life history strategies. Such knowledge would contribute to desert ecology and improve the management strategies of this unique Namib Desert perennial.

Episodic events Long-term ecological research Namibia Population dynamics Seasonality Sex ratio 

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Copyright information

© Kluwer Academic Publishers 2000

Authors and Affiliations

  • Joh R. Henschel
    • 1
  • Mary K. Seely
    • 1
  1. 1.Desert Ecological Research UnitDesert Research Foundation of Namibia, Gobabeb Training and Research CentreWalvis BayNamibia

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