Forest-floor treatments in Arizona ponderosa pine restoration ecosystems

No short-term effects on plant communities

Scott R. Abella, Wallace W Covington

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Leaf litter accumulation during fire exclusion and increases in tree density in postsettlement southwestern Pinus ponderosa forests may limit the establishment of understory vegetation. We performed an experiment in P. ponderosa forests of northern Arizona to ascertain plant community responses to forest-floor scarification and Oi removal on thirty-six 100-m2 plots overlaid on an existing ecological restoration experiment that involved tree thinning and prescribed burning. Constrasting with findings from many other forest types, forest-floor treatments had no effect on community diversity or composition during the 2-year experiment. Sørensen similarities were as high as 97% between posttreatment years within treatments; and successional vectors also provided little indication that treatments may appreciably affect longer-term successional trajectories. Lack of response to these fairly drastic treatments is surprising given these forests exceptionally heavy Oi horizons and large proportions of conifer litter. Apparently shading, belowground competition for water or nutrients, or other tree-associated factors more strongly limit understory communities than does leaf litter. Based on sparse A-horizon seed banks averaging <300 seeds · m-2 and limited abovegronnd vegetation, we hypothesize that seed shortages, particularly for native perennials, also partly precluded a treatment response. Because extensive unvegetated areas at these restoration sites may be colonized by exotics, conservative management strategies could include testing the seeding or outplanting of desirable native species as an option for filling unoccupied microsites. Reporting of "no treatment effect" experiments such as this one is important to avoid biasing meta-analyses, as is future research to clarify combinations of factors limiting understory communities. Increased understanding of these limiting factors may lead to identification of other treatments that promote recovery of native species during ecological restoration in this region.

Original languageEnglish (US)
Pages (from-to)120-132
Number of pages13
JournalWestern North American Naturalist
Volume67
Issue number1
DOIs
StatePublished - Jan 2007

Fingerprint

ecological restoration
Pinus ponderosa
forest floor
forest litter
understory
plant community
plant communities
plant litter
ecosystem
indigenous species
leaf litter
native species
limiting factor
organic horizons
vegetation
A horizons
experiment
prescribed burning
buried seeds
seeds

Keywords

  • Ground flora
  • Leaf litter
  • O horizon
  • Seed limitation
  • Soil seed bank
  • Species diversity
  • Understory vegetation

ASJC Scopus subject areas

  • Ecology

Cite this

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abstract = "Leaf litter accumulation during fire exclusion and increases in tree density in postsettlement southwestern Pinus ponderosa forests may limit the establishment of understory vegetation. We performed an experiment in P. ponderosa forests of northern Arizona to ascertain plant community responses to forest-floor scarification and Oi removal on thirty-six 100-m2 plots overlaid on an existing ecological restoration experiment that involved tree thinning and prescribed burning. Constrasting with findings from many other forest types, forest-floor treatments had no effect on community diversity or composition during the 2-year experiment. S{\o}rensen similarities were as high as 97{\%} between posttreatment years within treatments; and successional vectors also provided little indication that treatments may appreciably affect longer-term successional trajectories. Lack of response to these fairly drastic treatments is surprising given these forests exceptionally heavy Oi horizons and large proportions of conifer litter. Apparently shading, belowground competition for water or nutrients, or other tree-associated factors more strongly limit understory communities than does leaf litter. Based on sparse A-horizon seed banks averaging <300 seeds · m-2 and limited abovegronnd vegetation, we hypothesize that seed shortages, particularly for native perennials, also partly precluded a treatment response. Because extensive unvegetated areas at these restoration sites may be colonized by exotics, conservative management strategies could include testing the seeding or outplanting of desirable native species as an option for filling unoccupied microsites. Reporting of {"}no treatment effect{"} experiments such as this one is important to avoid biasing meta-analyses, as is future research to clarify combinations of factors limiting understory communities. Increased understanding of these limiting factors may lead to identification of other treatments that promote recovery of native species during ecological restoration in this region.",
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