Local context matters: site-dependent functional and ecological responses to woody encroachment

Posted on by

Prepared by Sara Sánchez-Carmona, Juan Antonio Campos, Itziar García-Mijangos & Asun Berastegi

Grassland–shrubland mosaic at one of the sampling sites, Valderejo Natural Park, in the northern Iberian Peninsula. Grassland coexists with shrub species such as Juniperus communis subsp. nana, which forms rounded and flattened patches. In the foreground, another shrub species frequently recorded in our study, Erica vagans, can also be observed. Photo credit: Sara Sánchez-Carmona

European semi-natural grasslands are being reduced by the expansion of woody species, a process known as woody plant encroachment. This process has been accelerated by changes in land use, mainly the abandonment or reduction of traditional agro-pastoral practices. At first sight, woody encroachment can be seen as a visible transformation of the landscape. However, we wanted to go beyond this visual change and understand what happens within plant communities.

More specifically, we explored how plant lifestyles change during the transition from grassland to shrubland. To do this, we looked at plant characteristics related to how species grow, reproduce, disperse, and respond to their environment. These characteristics, known as functional traits, help us understand not only which species are present, but also how the plant community works.

We studied grassland–shrubland mosaics in the northern Iberian Peninsula, in a sub-Mediterranean climate. In four study sites, we sampled plant communities along a gradient ranging from grasslands to areas with high shrub cover. We then used published databases to obtain information on plant traits and ecological indicator values, which provide clues about the environmental conditions associated with each community.

We found that, as shrub cover increased, the functional composition of plant communities changed significantly. In other words, there was a replacement of plant functions along the grassland–shrubland transition. Grasslands were characterised by shorter plants, a higher presence of hemicryptophytes, wind-pollinated species, and shorter dispersal distances. These attributes are generally associated with open environments where plants need to grow, persist, and tolerate environmental stress.

Some of the plant species recorded in the study area: Ophrys speculum (A), Catananche caerulea (B), Ophrys tenthredinifera (C), Gladiolus illyricus (D). On the right (E), shrubland vegetation recorded during our field surveys, dominated by Genista hispanica subsp. occidentalis and Juniperus communis. Photo credit: Sara Sánchez-Carmona (A, C, D, E) and Itziar García-Mijangos (B).

Shrublands, in contrast, were characterised by taller plants, a higher presence of phanerophytes and chamaephytes, a greater importance of insect pollination, and longer dispersal distances. These attributes are linked to more structurally complex environments, where competition for space and light becomes more important and where plant strategies tend to be more conservative.

We also observed that functional diversity tended to increase along the encroachment gradient. However, this should not automatically be interpreted as an improvement. Higher functional diversity in shrublands may reflect the arrival and dominance of new woody plant strategies, but it can also involve the loss of functions characteristic of grasslands. Therefore, the transition from grassland to shrubland is not simply a gain or a loss, but a reorganisation of how the plant community functions.

Finally, one of the clearest messages of our study is that local context matters. The direction and strength of these changes were not the same in all four study sites. For this reason, woody plant encroachment should not be understood as a uniform or simple process. It needs to be studied and managed locally, considering the ecological context of each site.

This is a plain language summary of the paper of Sánchez-Carmona et al. (2026) in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.70148)