Johnson A.H.

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.

Abstract: 
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.

Ecosystem Development and Plant Succession on Landslides in the Caribbean

Ecosystem Development and Plant Succession on Landslides in the Caribbean
Lawrence R. Walker, Daniel J. Zarin, Ned Fetcher, Randall W. Myster and Arthur H. Johnson
Biotropica
Vol. 28, No. 4, Part A. Special Issue: Long Term Responses of Caribbean Ecosystems to Disturbances (Dec., 1996), pp. 566-576

Abstract: 
Landslides are common in mountainous regions of the Caribbean and are triggered by heavy rains and earthquakes, and often occur in association with human disturbances (e.g., roads). Spatially heterogeneous removal of both substrate and vegetation is responsible for a variety of patterns of ecosystem development and plant successional trajectories within Caribbean landslides. Soil nutrient pools in exposed mineral soils reach levels comparable to mature forest soils within 55 yr but soil organic matter recovers more slowly. Plant colonization of landslides depends on the availability of propagules and suitable sites for germination, soil stability, and the presence of residual or newly deposited soil organic matter and associated nutrients. Once initial colonization occurs, the rate and trajectory of plant succession on landslides is strongly affected by plant/plant interactions. We present two conceptual models of landslide succession that summarize the major processes and pathways of ecosystem development and plant succession on landslides. Additional work is needed to characterize interactions between spatially heterogeneous zones, controls over soil development, impacts of key plant species, and the role of animals on Caribbean landslides.

Controls on soil organic matter content within a northern hardwood forest

Johnson, K.D.; Scatena, F.N.; Johnson, A.H.; Pan, Y. 2009. Controls on soil organic matter content within a northern hardwood forest. Geoderma. 148(3-4): 346-356.

Abstract: 
Forest soils can act as both sinks and sources for atmospheric CO2 and therefore have an important role in the global carbon cycle. Yet the controls on forest soil organic matter content (SOM) distribution at the scale of operational land management scales within forest types are rarely quantified in detail. To identify factors that influence the spatial distribution and accumulation of SOM in forests, soils and stand composition data from 42 even-aged northern hardwood forest plots were analyzed using multiple linear regression and non-parametric statistical approaches. The analysis included three layers of SOM pools (forest floor, 0–20 cm mineral soil, and 20+ cm mineral soil) over three spatial scales (point, plot and regional). The largest amounts of total SOM (mean = 289, std dev = 70 Mg ha− 1) occurred in deep and well drained soils located on gently grading slopes. When soil layers were analyzed separately, the following relationships were observed: 1) highest forest floor SOM occurred under mixed species composition as opposed to stands dominated by sugar maple, 2) highest 0–20 cm mineral SOM occurred at high elevations (greater than 450 m) in moderately well drained soils, and 3) highest 20+ cm mineral SOM also occurred at high elevations and when soils were deeper. Further analysis of 0–20 cm mineral layer revealed that lower rock volume and finer soil texture resulted in higher SOM at a single point. When SOM that was predicted from models based on plot-specific attributes (soils series, slope and aspect) were compared to soil survey SOM estimates, the mean SOM values for both approaches were similar (253 and 269 Mg ha− 1 respectively). Easily identifiable characteristics such as mixed stand composition, the presence of forest floor and E horizon thickness may be used as field indicators of SOM storage. The variety of controls identified in this study should be considered when assessing soil carbon response to management options and future changes in climate.

At What Temporal Scales Does Disturbance Affect Belowground Nutrient Pools?

At What Temporal Scales Does Disturbance Affect Belowground Nutrient Pools?
Whendee L. Silver, Fred N. Scatena, Arthur H. Johnson, Thomas G. Siccama and Fiona Watt
Biotropica
Vol. 28, No. 4, Part A. Special Issue: Long Term Responses of Caribbean Ecosystems to Disturbances (Dec., 1996), pp. 441-457

Abstract: 
We monitored the effects of both harvesting aboveground biomass and Hurricane Hugo on soil chemical and physical properties, and live and dead root biomass over 6 yr in a subtropical wet forest in Puerto Rico. Our goal was to determine how belowground processes changed at different temporal scales including the immediate period prior to revegetation (9 wk), the intermediate period of initial regrowth (9 mo), and the longer-term reorganization of the vegetation and biogeochemical cycling (6 yr). Harvesting resulted in temporary increases in the availability of exchangeable nutrients, but forest floor and soil nutrient pools had generally returned to pre-harvest values over a 9 wk period. Significant amounts of K moved through the soil over this time period, amounting to 29-46 kg/ha-1, and resulting in a reduction in the size of the exchangeable soil K pool. The hurricane deposited approximately 845 kg/ha-1 of forest floor mass and considerable nutrients on the soil surface, and increased soil NO3-N and exchangeable K pools, but in all cases, pool sizes had returned to pre-hurricane values within 9 mo. Examination of the data on an annual time step over the 6 yr period revealed an increase in soil cation pools and a significant decrease in soil pH. No change in soil organic matter was detected at any time step following the disturbances. Live fine root biomass was dramatically reduced as a result of the hurricane, and was only beginning to show signs of recovery near the end of the 6 yr experiment.

Nutrient availability in a montane wet tropical forest: Spatial patterns and methodological considerations

Silver, W.L., F.N. Scatena, A.H. Johnson, T.G. Siccama, and M.J.
Sanchez. 1994. Nutrient availability in a montane wet tropical forest: Spatial patterns and methodological considerations. Plant Soil 164:129–145.

Abstract: 
Soils and forest floor were sampled quantitatively from a montane wet tropical forest in Puerto Rico to determine the spatial variability of soil nutrients, the factors controlling nutrient availability to vegetation, and the distribution of nutrients in soil and plants. Exchangeable cation concentrations were measured using different soil extracting procedures (fresh soil with NH4C1, air-dried and ground soil with KC1, and a Modified Olsen solution) to establish a range of nutrient availability in the soil, and to determine the relationship between different, but commonly used laboratory protocols. The availability of exchangeable Ca, Mg, and K was significantly lower in soils extracted fresh with NHaCI than from soils which were dried and ground prior to extraction with KCI or a modified Olsen solution. Soil nutrient availability generally decreased with depth in the soil. Several soil properties important to plant growth and survival varied predictably across the landscape and could be viewed in the context of a simple catena model. In the surface soils, exchangeable base cation concentrations and pH increased along a gradient from ridge tops to riparian valleys, while soil organic matter, exchangeable Fe and acidity decreased along this gradient. On the ridges, N, P, and K were positively correlated with soil organic matter; on slopes, N and P were positively correlated with organic matter, and Ca, Kg, and pH were negatively correlated with exchangeable Fe. Nutrient availability in the upper catena appears to be primarily controlled by biotic processes, particularly the accumulation of organic matter. The Ca, K, and P content of the vegetation was higher on ridges and slopes than in the valley positions. Periodic flooding and impeded drainage in the lower catena resulted in a more heterogeneous environment. A comparison of the Bisley, Puerto Rico soils with other tropical montane forests (TMF) revealed that the internal heterogeneity of soils in the Bisley Watersheds is similar to the range of average soil nutrient concentrations among TMF's for Ca, Mg, and K (dry/ground soils). Phosphorus tended to be slightly higher in Bisley and N was lower than in other TMFs.

Biomass and Nutrient Content of the Bisley Experimental Watersheds, Luquillo Experimental Forest, Puerto Rico, Before and After Hurricane Hugo

Biomass and Nutrient Content of the Bisley Experimental Watersheds, Luquillo Experimental Forest, Puerto Rico, Before and After Hurricane Hugo, 1989
F. N. Scatena, W. Silver, T. Siccama, A. Johnson and M. J. Sanchez
Biotropica
Vol. 25, No. 1 (Mar., 1993), pp. 15-27

Abstract: 
The biomass and nutrient content of two steepland watersheds were estimated using allometric equations and nutrient concentrations derived from a subsample of the vegetation. Prior to the passage of Hurricane Hugo in September 1989, the watersheds had a total vegetative biomass of 301 tons/ha, 75 percent of which was aboveground. The total nutrient content of this vegetation was 907, 49, 644, 653, and 192 kg/ha for N, P, K, Ca, and Mg, respectively and varied with topographic setting. Concentrations per unit dry weight of P (0.16), K (2.49), Ca (2.13), and Mg (0.62) in aboveground vegetation were similar to other steepland tropical forests, while the concentration of N (2.9) was greater. Following the passage of Hurricane Hugo, the standing aboveground biomass was reduced to 113 t/ha and the aboveground nutrient content of the forest was reduced 45 to 48 percent.
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