Reversing a tree regeneration crisis in an endangered ecoregion

Joern Fischer, Jenny Stott, Andre Zerger, Garth Warren, Kate Sherren, and Robert I. Forrester
PNAS June 23, 2009 106 (25) 10386-10391; https://doi.org/10.1073/pnas.0900110106

  1. Edited by Gretchen C. Daily, Stanford University, Stanford, CA, and approved April 21, 2009 (received for review January 5, 2009)

Article Figures & SI

Figures

  • Fig. 1.
    Fig. 1.

    Landscape-level tree cover for the study area, based on a 2-ha moving window to calculate percent tree cover from remotely sensed data and on 126 field survey sites. Note some of the densely wooded parts of the study area were public land. (A) Cumulative proportion of the study area occurring at different levels of tree cover within a 2-ha moving window (e.g., ≈75% of the study area had ≤30% tree cover). (B) Percent tree cover from remote sensing versus the number of trees measured at ground sites (R2 = 0.81; P < 0.001). Circles denote primary survey sites, and crosses denote validation sites. The dashed line is the 95% confidence interval for the predicted relationship. (C) Based on A and B, predicted number of trees occurring at different densities in the study area (e.g., ≈3 million trees occurred at densities ≤30%).

  • Fig. 2.
    Fig. 2.

    Mean count of trees (and standard error) in different diameter classes across the 4 site types [paddock (A), scattered (B), grazed (C), and ungrazed (D)], regardless of farm or grazing regime. The approximate mean diameter of all trees, across all farms and grazing regimes, in a given site type is indicated by a dotted red line; the approximate median diameter is indicated by a solid green line. Diameters were standardized before analysis to compare sites with different tree species (see SI Methods).

  • Fig. 3.
    Fig. 3.

    Significant predicted relationships from generalized linear mixed models (confidence intervals are not shown because methods for their calculation in the presence of random effects are controversial in statistical science; points denote primary survey sites, and crosses denote validation sites). (A) Minimum (standardized) diameter varied significantly in response to the number of trees at a site and available soil phosphorus (see Table S2 for details). Darker points indicate sites with higher phosphorus concentrations. The 2 lines denote low- and high-phosphorus conditions. (B) The probability of seedling presence varied significantly with the number of trees at a site and with the amount of soil nitrogen. The predicted relationship for the mean number of trees at the 3 grazed site types is shown, assuming continuous grazing (see Table S3 for details). (C) The probability of seedling presence also varied significantly between livestock rotation regimes. Pairwise differences were significant between either of the upper 2 predicted lines, and between either of the lower 2 predicted lines (P = 0.004; see Table S3 for details). The predicted relationship is based on mean total nitrogen concentrations (0.26%).

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Reversing a tree regeneration crisis in an endangered ecoregion
Joern Fischer, Jenny Stott, Andre Zerger, Garth Warren, Kate Sherren, Robert I. Forrester
Proceedings of the National Academy of Sciences Jun 2009, 106 (25) 10386-10391; DOI: 10.1073/pnas.0900110106
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