Soil phosphorus fractions vary with harvest intensity and vegetation control at two contrasting Douglas-fir sites in the Pacific northwest

Abstract

Effects of intensive forest management on soil phosphorus (P) are unclear and may impact long-term site productivity. We assessed changes in P availability over 10 years associated with harvest intensity (bole-only vs. whole-tree harvest) and vegetation control treatments (initial vegetation control (IVC) vs. five years of annual vegetation control (AVC)) using a P fractionation procedure. Fractions were characterized at 0-15, 15-30, and 30-60 cm soil depths in two coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) plantations with strongly contrasting soil properties near Matlock, WA (young soils formed in glacial outwash) and Molalla, OR (relatively old soils formed in igneous residuum and exhibiting andic properties). Al and Fe concentrations associated with short-range order minerals were greater at Molalla than Matlock and generally decreased with depth at both sites. We observed decreases in most total-P and P-fraction concentrations across the three soil depths at the Molalla site. Effects were less pronounced and generally inconsistent at the Matlock site. Decreases in total P and P fraction concentrations were greatest in the AVC treatments at Matlock, but opposite trends were observed at Molalla where decreases were greatest with IVC. There was no difference between harvest treatments on the change in P fractions in most instances, with the exception of the 30-60 cm depth at Matlock where concentrations of some P fractions were maintained or increased with bole-only harvesting. Ten-year responses indicate harvest intensity has limited effects on long-term productivity associated with soil P because of the large size of the soil P pools and the relatively small changes in soil P that occurred with treatment. Decreases in P concentrations with AVC at Matlock and IVC at Molalla were larger than the other treatments and highlight the important role of vegetation in P dynamics following harvesting at these sites.

Utility of in situ ion‐exchange membranes to assess nutrient availability, productivity, and fertilizer response of coastal Douglas‐fir of the Pacific Northwest

“…While P limitations and fertilization are common in many forest systems outside of the PNW (Elser et al., 2007; Fox et al., 2007; Mohren et al., 1986; Renou‐Wilson & Farrell, 2007), P nutrition of coastal PNW Douglas‐fir forests has been studied less frequently (Gessel et al., 1981; Kranabetter, Sholinder, et al., 2020; Mainwaring et al., 2014; Perakis et al., 2013; Radwan & Shumway, 1984). In this study, PRS P supply rates had a better correlation with foliar P concentrations than with soil extractable P. Due to the lack of correlation between soil Bray P content and foliar P ( R 2 = 0.006), it is likely that a sequential extraction might have improved the understanding of available soil P on these installations (Debruler et al., 2019). It is also possible that the horizontal placement of the PRS probes at 5‐cm depth in the mineral soil did not capture the greater P availability in the forest floor (Huang & Schoenau, 1997).…”

Effect of tree species and substrate properties on organic phosphorus forms in afforested technosols

“…Classification of organic P availability based on chemical solubility has been criticized because various fractions haven't been correlated to P availability for plants and it was proven that plants can acquire P from various organic P fractions including those regarded as stable (Turner et al, 2005;Fox et al, 2011). Nevertheless the existing fractionation schemes remain useful in studying factors affecting development and transformations of soil P pools over time (DeBruler et al, 2019). In our study concentrations of particular fractions of organic P depended on the substrate type.…”

Change in soil carbon, nitrogen, and phosphorus after timber harvesting in northern hardwood forests

“…Additionally, our inference about P availability was limited to labile inorganic P due to the extraction process that was used. Future studies could include methods like sequential P fractionation to separate labile and recalcitrant forms of inorganic and organic P (DeBruler et al., 2019) to more fully understand C, N, and P dynamics at the study sites and forests with similar soils and vegetation.…”