Using plant functional traits to refine ecological restoration techniques: A seedling transplant experiment

Background/Question/Methods

Enrichment planting is a commonly used restoration technique, which is applied to increase species diversity or environmental services during forest regeneration. Our study provides guidance in selecting species for restoration activities, and is among the first to directly link species performance across different environmental conditions to easily measured plant functional traits. We used an experimental approach to test whether species’ ecological characteristics influence the ability of seedlings to survive in three successional stages. In October 2010 we transplanted seedlings of six species (three secondary-growth specialists and three old-growth specialists) into old-growth forest, second-growth forest, and pasture plots at La Selva Biological Station in Costa Rica. Secondary-growth specialists possess fast-resource acquisition traits- such as high specific leaf area and low leaf toughness- that promote fast growth rates. Old-growth specialists, on the other hand, possess resource-conservation traits that promote survival over growth. We monitored seedling survival monthly for 1.3 years. Growth rates of survivors were assessed after 6 and 16 months (final harvest will be completed in March 2012). We use logistic and linear statistical models to relate species survival and growth rates to leaf functional traits and environmental conditions in each plot.

Results/Conclusions

Seedlings of old-growth (OG) specialists had lower specific leaf area, and higher leaf dry matter content, leaf thickness, and leaf toughness than secondary-growth (SG) specialists. OG specialists had higher survival rates than SG specialists across all plot types. All forest-planted individuals of SG specialist Cecropia insignis died, but ~36% of the individuals in pasture plots survived through 15 months. The five other species had survivors in all successional stages. Among all surviving individuals, relative height growth after 6 months was highest in the pasture, and lowest in old-growth plots (ANOVA, P<0.0001). This difference is attributed to effects of light availability, as the highest light levels occurred in pasture and the lowest levels occurred in old-growth forest (Kruskal-Walis, P<0.001). Among all species, C. insignis grew the fastest, and Tetragastris panamensis grew the slowest. There was no discernable tradeoff between growth and survival among species. These results indicate that, across the spectrum of environmental conditions, species with resource-conservation traits have higher survival rates than species with fast-resource acquisition traits. Growth rate within and among species is related primarily to light availability. We conclude that selecting old-growth specialists for enrichment planting would improve survival rates without sacrificing plant growth rates.