Getting the biggest birch for the bang: restoring and expanding upland birchwoods in the Scottish Highlands by managing red deer

Abstract

High deer populations threaten the conservation value of woodlands and grasslands, but predicting the success of deer culling, in terms of allowing vegetation to recover, is difficult. Numerical simulation modeling is one approach to gain insight into the outcomes of management scenarios. We develop a spatially explicit model to predict the responses of Betula spp. to red deer (Cervus elaphus) and land management in the Scottish Highlands. Our model integrates a Bayesian stochastic stage-based matrix model within the framework of a widely used individual-based forest simulation model, using data collected along spatial and temporal gradients in deer browsing. By initializing our model with the historical spatial locations of trees, we find that densities of juvenile trees (<3 m tall) predicted after 9–13 years closely match counts observed in the field. This is among the first tests of the accuracy of a dynamical simulation model for predicting the responses of tree regeneration to herbivores. We then test the relative importance of deer browsing, ground cover vegetation, and seed availability in facilitating landscape-level birch regeneration using simulations in which we varied these three variables. We find that deer primarily control transitions of birch to taller (>3 m) height tiers over 30 years, but regeneration also requires suitable ground cover for seedling establishment. Densities of adult seed sources did not influence regeneration, nor did an active management scenario where we altered the spatial configuration of adults by creating “woodland islets”. Our results show that managers interested in maximizing tree regeneration cannot simply reduce deer densities but must also improve ground cover for seedling establishment, and the model we develop now enables managers to quantify explicitly how much both these factors need to be altered. More broadly, our findings emphasize the need for land managers to consider the impacts of large herbivores rather than their densities.

Molecular footprints of the Holocene retreat of dwarf birch in Britain

“…But the fact that B. nana is currently more restricted in its range than the area that it is adapted to according to the ENM suggests that other factors may also have contributed to the decline of B. nana , such as overgrazing by sheep and deer (Tanentzap et al . ), and burning of moorland for grouse shooting (DeGroot et al . ).…”

An evaluation of Scottish woodland grant schemes using site suitability modelling

“…Deer grazing is a major issue in Scottish woodland management, and is a significant barrier to both regeneration of existing woodland and woodland expansion (Staines, 1995;Gill and Morgan, 2010;Tanentzap et al, 2013). While only one study (CJC Consulting, 2002) has evaluated the role of management in grant scheme success, findings are broadly in line with perceptions, with weed growth and grazing the most common threats to new woodlands.…”

A comparison between data requirements and availability for calibrating predictive ecological models for lowland UK woodlands: learning new tricks from old trees

“…SORTIE is an individual-based model initially developed for the Great Mountain Forest (Connecticut) and used in USA (Pacala et al 1996;Strigul et al 2008), New Zealand (Coomes et al 2009Kunstler et al 2009Kunstler et al , 2011Forsyth et al 2015), Canada (Canham et al 1999;Bose et al 2015), Scotland (Tanentzap et al 2013), and the Pyrenees (Ameztegui and Coll 2011;Ameztegui et al 2015). It produces projections of the community structure of a forest and its carbon flux.…”

“…; Tanentzap et al. ). Similar data would have been required for parameterizing other similar models, see Bugmann (); Snell et al.…”

“…Here, we test the capability of existing data to parameterize a widely used predictive model (individual-based model) -SORTIE (Pacala et al 1996;Moorcroft et al 2001;Strigul et al 2008;Kunstler et al 2009;Tanentzap et al 2013). Similar data would have been required for parameterizing other similar models, see Bugmann (2001); Snell et al (2014) for reviews and Table 1 for summary, but we use SORTIE as an example.…”