Data from: Resource quantity and heterogeneity drive successional plant diversity in managed and unmanaged boreal forests

Here, we describe the data and methods supporting a study on how
disturbances such as forest fires and clear-cutting influence understory
vegetation diversity in boreal Scots pine (Pinus sylvestris) forests in
Northern Sweden. The research contrasts two chronosequences, one under
rotational management (clear-cutting, soil scarification, and thinning)
and one unmanaged and fire-origin, to examine how resource availability
and heterogeneity relate to alpha and beta diversity over a temporal
gradient. The understory vegetation of boreal forests plays a crucial role
in maintaining biodiversity by creating habitats, supplying food
resources, and regulating microclimate and soil conditions. This essential
layer is frequently affected by disturbances such as forest fires and
clear-cutting, which significantly alter understory communities and the
ecosystem resource availability and heterogeneity. This study aimed to
understand how these disturbances influence the spatial and temporal
dynamics of key ecosystem resources, and subsequently the patterns of
understory diversity. We analyzed and compared understory vegetation
diversity in a rotational management chronosequence and an unmanaged fire
chronosequence of Scots pine (Pinus sylvestris) forests across Northern
Sweden. We assessed the relationship of above- and belowground resource
availability and heterogeneity with alpha and beta diversity using
generalized additive models and multivariate analyses. We found that
belowground resource availability (especially inorganic nitrogen) and
aboveground resource heterogeneity (especially variation in forest
structural complexity) were most strongly positively correlated with alpha
and beta diversity, varying across successional stages. In early stages
(0-60 years), high availability of belowground resources and aboveground
heterogeneity was associated with high alpha and beta diversity. In mid
stages (100-200 years), reduced belowground resource availability and
aboveground heterogeneity was linked to lower diversity. In late stages
(>250 years, which only exists in the Unmanaged Fire
chronosequence), increased aboveground heterogeneity associated with tree
mortality was linked to a resurgence in alpha and beta diversity. These
results highlight the necessity of maintaining a mosaic of stands with
different disturbance regimes and successional stages, particularly early
post-fire stands and late successional stands, which are currently much
rarer on the landscape, to support biodiversity at the landscape level.