Enhancing soil biophysical condition for climate-resilient restoration in mesic woodlands

High C:N soil amendments including a green-waste biochar and a mixed-size green-waste mulch facilitated recovery of soil biophysical attributes within two years. Both led to lower bulk density, softer soil surfaces, occasionally higher soil moisture and better persistence of a sown, large-seeded native forb. Biochar also led to improved water infiltration and total C, while mulch led to higher labile C and higher microbial and invertebrate activity (but limited establishment of small-seeded forbs). Benefits were achieved without promoting exotic species, and for attributes with comparable reference data, benefits after two years were on average 25% of that required to reach reference condition. By contrast, P fertilization promoted exotic species at the expense of native grasses, with minimal improvement to soil biophysical condition after two years. Potential benefits of re-introducing a native C4 grass were not evident within the experimental timeframe. We conclude that bulky, high C:N soil amendments have the potential to facilitate recovery of functions associated with soil water availability and hence resilience to a drying climate. However, longer-term evaluation is needed to assess whether benefits reflect once-off small increments, or transitions across ecological thresholds that will facilitate ongoing improvement towards reference condition.