Nucleated regeneration is a specific model of succession whereby colonising or remnant plants, occurring in discrete patches, facilitate the establishment of other species by providing suitable microsites for seed accumulation, germination, and subsequent growth of seedlings. The combination of the perch effect and facilitation has been suggested to promote regeneration through nucleation in Mediterranean, semiarid and tropical regions, but no studies have reported this successional pattern for temperate forest ecosystems. In this study we tested for the evidence of a nucleated pattern of tree recruitment in early post-fire succession in a Chilean temperate forest by evaluating both the “perch effect” and possible facilitation mechanisms. We evaluated abiotic conditions in 121 forest patches, developed from post-disturbance legacies (i.e., remnant trees, stumps and logs), submerged in 5 hectares of post-fire shrubland, and compared them to open shrubland areas without trees. In addition, tree seedling presence inside/outside forest patches and their establishment substrate were recorded. A correlation between the height of the tallest tree in each patch and the number of bird-dispersed saplings within the patch was sought as evidence for the “perch effect”.
Results/Conclusions
We found that small tree patches provided better microsites for species regeneration than the surrounding shrubland. Beneath the patch canopy we found 75% of all tree seedlings (N=76) with 32% of them growing on elevated surfaces. In contrast, 84% of tree seedlings found in open shrubland (N= 19) occurred on elevated surfaces. Soil waterlogging may prevent recruitment outside patches. In winter, the soil was three times wetter outside patches, but in summer was only 15% wetter. Soil nitrogen concentration did not differ between open sites and tree patches; however, acid digested phosphorous was significantly lower in shrubland than under patches (32 ± 3.4 mg/kg vs. 159 ± 29 mg/kg, respectively). Light under patches was 32% of that in open areas. Thus, colonising and remnant tree patches may be enhancing seedling growth and establishment relative to the shrubland. We found a positive correlation between height of perch trees and number of woody saplings, and the number of bird-dispersed individuals rose drastically when trees in patches were >6 m tall. Facilitation and perch effects support the hypothesis of nucleation as a secondary successional process in temperate rainforest in Chile, where remnant trees act as nuclei that promote growth of newer and smaller patches.