Strategies for Modeling Regeneration Density in Relation to Distance from Adult Trees

Daniel Moreno-Fernández,Alicia Ledo,Isabel Cañellas,Fernando Montes

doi:10.3390/f11010120

Abstract

Research Highlights: We proposed new methodologies for the spatial analysis of regeneration processes and compared with existing approaches. Background and Objectives: Identifying the spatial relationship between adult trees and new cohorts is fundamental to understanding the dynamics of regeneration and therefore helps us to optimize the stand density and natural regeneration when undertaking regeneration fellings. Most of the statistical approaches analyzing the spatial dependence between adult trees and new individuals (seedlings or saplings) require a complete census and mapping of all individuals. However, approaches considering individuals grouped into sampling points or subplots (i.e., density data) are limited. In this study, we reviewed and compared approaches (intertype point pattern analyses and a generalized additive model) to describe the spatial relationship between adult trees and density regeneration in a Pinus sylvestris L. monospecific stand in Spain. We also proposed a new approach (intertype mark variance function) to disentangle the effect of the tree-size on sapling density and the effect of the spatial pattern. Materials and Methods: To this end, we used a half-hectare plot in which all the individuals of P. sylvestris have been mapped and measured. Results: Our results indicated that sapling distribution was related to distance from the adult trees, thus displaying distance-dependence patterns, but it was not related to the size of the adult trees. The intertype mark correlation function was an useful tool to distinguish the effect of the marks (sapling density and tree size) from the effect of the spatial pattern of the classes (trees cohorts in our case). Conclusions: The largest number of saplings was found with increased distance between adult trees (>11 m), and the generalized additive model may be useful to explain spatial relationships between adult trees and regenerating cohorts when other measured biotic variables (e.g., soil stoniness, etc.) and repeated measurements are available.

Highlights

The establishment of new individuals following regeneration fellings is a vital stage of stand development as the persistence of the forest cover is at stake [1]
We presented the first attempt at describing the spatial dependence of the number of saplings of P. sylvestris and adult trees during regeneration fellings under the uniform shelterwood method
We found that regeneration fellings under the uniform shelterwood system resulted in an even-aged stand and sapling density is not expected to change according to adult tree size

Summary

Introduction

The establishment of new individuals following regeneration fellings is a vital stage of stand development as the persistence of the forest cover is at stake [1]. The occurrence and survival of the new individuals is hindered by several factors, such as low seed production, post-dispersal predation, summer drought, limited nutrient availability, flooding, frost, fire, competition with grass and shrubs, lack of or excess light, or damage from browsing, pests and pathogens [1,2,3,4,5]. A greater understanding of the relationship between the regeneration process and environmental conditions is crucial for current and future forest management [7]. In this regard, silvicultural operations can modulate light and water availability to the new individuals, i.e., seedlings and saplings, through reducing stem density over the regeneration period [8].

Objectives

Results

Discussion

Conclusion