Document: DAV-3-67-12

Landslide revegetation revisited: A test of the space-for-time substitution.

BRYANT, D.M.*, D.J.ZARIN, J.C.INNES and M.J.DUCEY

Univesity of New Hampshire, Durham, NH 03824, USA ¹

Abstract:
The chronosequence method has been a surrogate for repeated measurements of community succession for decades. The substitution of space-for-time (SFT) inherent in this technique has received considerable criticism. Ordination allows simultaneous analysis of site variables and can identify spatial variables that confound conclusions drawn from chronosequence studies. Data on a chronosequence of landslide sites in the White Mountain National Forest of New Hampshire, USA was compared to data collected on the same sites 40 years hence. Point-centered-quarter measurements of trees > 5-cm dbh were collected during 1996-98 on the same sites used by Flaccus. Detrended correspondence analysis (DCA) was used to analyze effects of site age, elevation, slope and aspect on both data sets (1956 and 1996-98) separately, and combined as an aggregated chronosequence spanning 18-113 years. Ordination of the original 1956 data set showed a strong correlation of site age with the first DCA axis scores (r² = 0.88, p < 0.01), but only weakly related to site aspect (r/² = 0.24, p < 0.1). No relationship with site age was seen in the ordination of the 1996-98 data. We conclude that site age was the primary driver of succession on these sites in 1956 and that the SFT was appropriate for this chronosequence. During the intervening 40 years the successional trajectories of these sites have diverged, invalidating SFT for the 1996 data. Therefore DCA can, and should, be used to validate successional studies using chronosequence data. In addition, the change in total stand basal area between each stand (D BA = 1996 - 1956) showed a strong negative correlation with site age (r² = 0.76, p < 0.001). This suggests that landslide sites may become increasingly susceptible to disturbance with site age. Moreover it is likely that disturbance is the causal mechanism for the divergence of successional trajectories among sites.

Keywords: Primary succession, Detrended correspondence analysis, Space-for-time substitution, Northeastern forests, disturbance.

This abstract is being presented at: 10:30 AM in session:
Poster Session #12: Disturbance Ecology.