A COMPARISON OF RATE OF SUCCESSION OVER 18 YR IN 10 CONTRASTING OLD FIELDS

We explored local variation in rate of plant succession by computing three contrasting measures of change for 10 New Jersey old fields through the first 18 yr after abandonment. We found that all three measures, euclidean distance in ordination space, turnover analysis, and regression analysis of species loss from the initial cohort, showed the same trend of decrease in the rate of plant succession with time. However, we did not find a monotonic decrease, and the specific years of transient increase differed with the analytical measure used. Both turnover and regression analysis showed that those old fields that had previously been planted in orchard grass (Dactylis glomerata) had a much lower initial change than fields previously in soybeans, or soybeans and sorghum, but this difference dissolved after 10 yr of succession. The study fields compared favorably to other mesic successions and agreed with the general pattern of more rapid rate decrease in mesic compared to xeric successions. Our results echo the general decrease in the rate of plant succession with time reported in the literature and also show important relationships between this decrease and the land-use history of particular fields.