Data from: Modelling the probability of microhabitat formation on trees using cross-sectional data

1. Context: Tree-related microhabitats (TreMs), such as trunk cavities,
peeled bark, cracks or sporophores of lignicolous fungi, are essential to
support forest biodiversity because they are used as substrate, foraging,
roosting or breeding places by bryophytes, fungi, invertebrates and
vertebrates. Biodiversity conservation requires the continuous presence of
TreMs in a forest. However, little is known about their dynamics.
Moreover, we usually have only cross-sectional TreM data (observations of
many trees at a single time), making it difficult to estimate TreM
formation rates. 2. Method: This study adapted the methods of survival and
reliability analysis to model the rate of TreM formation per unit of
diameter increment as a function of tree diameter at breast height (DBH).
We tested three variants of this model: the TreM formation rate
independent of, proportional to or increasing non-linearly with DBH. We
calculated the likelihood of the models, considering cross-sectional
observations either of TreM presence/absence or TreM number on trees of
different sizes. We calibrated the models in six sub-natural montane
forests dominated by European beech (Fagus sylvatica) and silver fir
(Abies alba) – in the French Pyrenees. Assuming an annual DBH increment
value, the annual formation rate of TreMs was predicted both at the level
of the tree and at the level of the forest stand. 3. Results: This method
provided a coherent framework to model the probability that a TreM forms
on a tree during a unit growth step and produces realistic predictions of
TreM accumulation on trees. TreM formation accelerated as trees grew for
A. alba but not for F. sylvatica. The TreM formation rate was twice as
fast on F. sylvatica as on A. alba. We estimated a formation of 0.82–1.28
TreMs/ha per year and 0.5–0.9 TreM bearing trees/ha per year in the
sub-natural forests studied. 4. Synthesis and applications: This method
makes rigorous modelling of the formation of TreMs possible during the
growth of trees and forest stands. The quantitative evaluation of TreM
fluxes will help to design forest biodiversity conservation strategies
favouring the development and temporal continuity of TreMs.