Effect of Tree Density on Seed Production and Dispersal of Birch (Betula pendula Roth and Betula pubescens Ehrhs)

Zetian Liu,Matthew Evans

doi:10.3390/f12070929

Abstract

Silver and downy birch (Betula pendula Roth and B. pubescens Ehrhs) are pioneer species which play an important role in forest regeneration in disturbed areas. Knowledge of birch seed production and dispersal is key to making good predictions of the persistence and colonization of birch. Both processes can be affected by the density of trees in the neighbourhood. In this study, we studied the seed production and dispersal of birch trees in two plots in Wytham Woods, UK, in 2015, and investigated the potential effect of neighbourhood tree density. We applied inverse modelling to seed trap data, incorporating tree density around the source tree and on the seed path to estimate birch fecundity and the dispersal kernel of the seeds. We show that the pattern of dispersed seeds was best explained by a model that included an effect of tree density on seed dispersal. There was no strong evidence that conspecific or heterospecific tree density had an effect on birch fecundity in Wytham Woods. A birch with diameter at breast height (DBH) of 20 cm is estimated to have produced ~137,000 seeds in 2015. Mean dispersal distance in an open area is estimated to be 65 m but would be reduced to 38 m in a closed stand. Both the mean dispersal distance and the probability of long-distance dispersal of birch decreases in dense environments. Areas with higher tree density also would intercept more seeds. These results highlight the importance of considering tree density in the neighbourhood and in the overall landscape when predicting the colonization and recruitment of birch.

Highlights

Our study shows that neighbourhood tree density is a good predictor of the seed dispersal of birch
We applied inverse modelling to investigate the effect of neighbourhood tree density on the seed production and dispersal of birch, which is important for predicting the persistence and expansion of birch
Our studies highlighted the importance of both tree density near the seed source and the dispersal path on seed dispersal

Summary

Introduction

Birch (Betula pendula Roth and B. pubescens Ehrhs.) are common tree species of high ecological value in Europe. Birch is an important pioneer tree species that produces a large seed crop, has long dispersal distances by wind and is characterized by a fast juvenile growth rate [1]. It is adapted to the colonisation of open areas created by disturbance and habitat unsuitable for other tree species [1]. Birch is important for maintaining biodiversity by supporting a high number of invertebrate species and provides habitats for various bird and mammal species [4,5]. The ecological characteristics of birch make it important for forest regeneration after disturbance. In Western Europe, birch is an undervalued indigenous species for forestry but has high potential [6]. Frequencies and intensities of disturbance like extreme weather events, pathogens and pests are likely to increase [7]

Methods

Discussion

Conclusion