Effect of soil compaction on tree physiology and growth: a meta-analysis

In recent decades, many papers about the effects of forest operation on soil compaction and thus tree growth and regeneration have been published. Most of them examined one or few compaction degrees, tree species, taxonomic groups or soil types, providing interesting result but without interconnections among studies. In order to fill this gap, our study aims to draw general conclusions concerning the impact of mechanized harvesting and soil compaction on tree growth by means of a meta-analysis. We specifically addressed (i) the effects of soil compaction on shoot morphological and physical traits as well as root parameters (ii) the effects of compaction degree according to soil type, taxonomy, age class, and experiment type. The data of several studies were collected taking into consideration peer-reviewed literature indexed in several databases and published between 1948 and 2017. A cross-disciplinary approach was applied including researches under natural environmental conditions and manipulative experiments. The analysis of the collected studies resulted in 56 articles with all the relevant details to be included in the meta-analysis. Our main results suggest that increasing levels of soil compaction affect plant development by an overall decrease of all morphological parameters, more evident in height and root depth; the effect varies according to soil type (generally less strong in arenic soil) and taxonomy, and decreases over time. Compaction significantly reduced net photosynthesis, did not affect leaf nitrogen content (as a proxy of nutrient uptake from roots) but decreased leaf water potential (as a proxy of water uptake from roots).