Shade responses of five grasses native to southwestern U.S. Pinus ponderosa forests

E. Naumburg, L. E. DeWald, T. E. Kolb

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Recent increases in Pinus ponderosa Dougl. ex Laws. forest density in the southwestern United States have severely reduced understory herbaceous biomass and altered understory species composition. To examine whether changes in graminoid species composition are caused by increased shading, we studied the effects of shade on leaf gas exchange, biomass, and reproductive characteristics of five grass species native to Arizona P. ponderosa forests in a greenhouse study. Blepharoneuron tricholepis (Nash) Torr., Koeleria cristata (L.) Pers., Festuca arizonica Vasey, Muhlenbergia montana (Nutt.) Hitchc., and Sitanion hystrix (Nutt.) J.G. Smith were grown under three light levels representative of photosynthetic photon flux densities and red/far-red ratios that occur beneath P. ponderosa canopies. In general, all species grew better under unshaded conditions, but all survived and flowered even under the dense shade treatment. Reduction of net assimilation rate by shading was the strongest during early reproductive shoot growth for all species except K. cristata, whose assimilation rate was unaffected by shading. Biomass allocation and reproductive responses to shading varied among species. Biomass of S. hystrix was the least affected by shading of all species, and it showed no response in biomass allocation to reproduction but increased height and weight of individual flower stalks under shade. Overall, S. hystrix and K. cristata, species that occur in dense P. ponderosa stands, were least affected by experimental shading, which suggests that shade is a contributing factor to the distribution of grass species in Arizona P. ponderosa forests.

Original languageEnglish (US)
Pages (from-to)1001-1009
Number of pages9
JournalCanadian Journal of Botany
Issue number9
StatePublished - 2001


  • Leaf biomass
  • Native grass
  • Photosynthesis
  • Red/far-red ratio
  • Reproduction

ASJC Scopus subject areas

  • Plant Science


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