Base saturation, nutrient cation, and organic matter increases during early pedogenesis on landslide scars in the Luquillo Experimental Forest, Puerto Rico

ZARIN, D. J. 1993. Nutrient accumulation during succession in subtropical lower montane wet forests, Puerto Rico.
Ph.D. dissertation. University of Pennsylvania, Philadelphia, Pennsylvania.
———, AND A. H. JOHNSON. 1995a. Nutrient accumulation during primary succession in a montane tropical forest,
Puerto Rico. Soil Sci. Soc. Am. J. 59: 1444–1452.
———, AND ———. 1995b. Base saturation, nutrient cation, and organic matter increases during early pedogenesis
on landslide scars in the Luquillo Experimental Forest, Puerto Rico. Geoderma 65: 317–330.

We evaluate data from a chronosequence study of landslide scars, ranging in age from 1-55 + yr, in the Luquillo Experimental Forest (LEF) a subtropical lower montane wet forest (sensu Holdridge) in eastern Puerto Rico. Surface mineral soil (0-10 cm) base saturation index (BSI) values increase during primary succession in the LEF (R=0.85, P<0.001 ). Both BSI values and major nutrient cation concentrations are extremely low on new landslide scars. During the course of the 55 + yr chronosequence, major nutrient cation concentrations are positively correlated with soil organic matter (SOM) content (P = 0.079) and not with clay content (P = 0.794). When data collected from plots representing the two dominant late-succession vegetation associations are added to the analysis, nutrient cation concentrations correlate significantly with both SOM (P= 0.001) and clay content (P=0.033). Our data show that when initial conditions are oligotrophic, both nutrient cation pools and BSI values can increase in the surface mineral soil during early pedogenesis. We discuss exogenic litter input, substrate weathering, and precipitation as potential sources for nutrient cations in these soils. We further suggest that production and decomposition of SOM is the dominant process controlling capture, retention and intra-ecosystem cycling of nutrient cations in these forests.

The use of chronosequences in studies of ecological succession and soil development

Walker LR, Wardle DA, Bardgett RD, Clarkson BD (2010) The
use of chronosequences in studies of ecological succession
and soil development. J Ecol 98:725–736

1. Chronosequences and associated space-for-time substitutions are an important and often necessary tool for studying temporal dynamics of plant communities and soil development across multiple time-scales. However, they are often used inappropriately, leading to false conclusions about ecological patterns and processes, which has prompted recent strong criticism of the approach. Here, we evaluate when chronosequences may or may not be appropriate for studying community and ecosystem development. 2. Chronosequences are appropriate to study plant succession at decadal to millennial time-scales when there is evidence that sites of different ages are following the same trajectory. They can also be reliably used to study aspects of soil development that occur between temporally linked sites over time-scales of centuries to millennia, sometimes independently of their application to shorter-term plant and soil biological communities. 3. Some characteristics of changing plant and soil biological communities (e.g. species richness, plant cover, vegetation structure, soil organic matter accumulation) are more likely to be related in a predictable and temporally linear manner than are other characteristics (e.g. species composition and abundance) and are therefore more reliably studied using a chronosequence approach. 4. Chronosequences are most appropriate for studying communities that are following convergent successional trajectories and have low biodiversity, rapid species turnover and low frequency and severity of disturbance. Chronosequences are least suitable for studying successional trajectories that are divergent, species-rich, highly disturbed or arrested in time because then there are often major difficulties in determining temporal linkages between stages. 5. Synthesis. We conclude that, when successional trajectories exceed the life span of investigators and the experimental and observational studies that they perform, temporal change can be successfully explored through the judicious use of chronosequences.

Hurricane Disturbance Alters Secondary Forest Recovery in Puerto Rico

Flynn DFB, Uriarte M, Crk T et al (2009) Hurricane disturbance
alters secondary forest recovery in Puerto Rico.
Biotropica 42:149–157

Land-use history and large-scale disturbances interact to shape secondary forest structure and composition. How introduced species respond to disturbances such as hurricanes in post-agriculture forest recovery is of particular interest. To examine the effects of hurricane disturbance and previous land use on forest dynamics and composition, we revisited 37 secondary forest stands in former cattle pastures across Puerto Rico representing a range of exposure to the winds of Hurricane Georges in 1998. Stands ranged from 21 to480 yr since agricultural abandonment and were measured 9 yr posthurricane. Stem density decreased as stands aged, while basal area and species richness tended to increase. Hurricane disturbance exerted contrasting effects on stand structure, contingent on stand age. In older stands, the basal area of large trees fell, shifting to a stand structure characteristic of younger stands, while the basal area of large trees tended to rise in younger stands with increasing hurricane disturbance. These results demonstrate that large-scale natural disturbances can alter the successional trajectory of secondary forest stands recovering from human land use, but stand age, precipitation and soil series were better predictors of changes in stand structure across all study sites. Species composition changed substantially between census intervals, but neither age nor hurricane disturbance consistently predicted species composition change. However, exposure to hurricane winds tended to decrease the abundance of the introduced tree Spathodea campanulata, particularly in smaller size classes. In all sites the abundance of the introduced tree Syzygium jambos showed a declining trend, again most strongly in smaller size classes, suggesting natural thinning through succession.
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