Global Patterns in Forest Allocation of Carbon to Reproduction
Authors
Rachel Ward1* (r.ward@berkeley.edu), Lara Kueppers1,2, Jeffrey Chambers2
Institutions
1University of California–Berkeley, CA; 2Lawrence Berkeley National Laboratory, Berkeley, CA
URLs
Abstract
The allocation of net primary productivity to reproduction in trees (e.g., flowers, fruits, and seeds) influences forest function through a tradeoff with growth and by being a necessary driver of recruitment. Recent evidence suggests that carbon allocation to reproduction (RA) may increase significantly with temperature and precipitation, may be greater on fertile soils in tropical forests, and may differ across successional states. However, common model parameterizations assume RA is constant across climatic, edaphic, and successional gradients, potentially biasing predictions. Researchers used a novel proxy for RA constructed from litterfall records to estimate differences in RA across forest sites globally and asked: (1) how ecosystem-level RA varies within and across biomes and (2) to what extent variation in RA is explained by climate (e.g., mean annual precipitation and mean annual temperature) and stand-level characteristics (e.g., soil and successional state). Researchers collected 1,520 observation-years of forest leaf and reproductive litterfall fluxes from 550 sites that span the forested continents. A Mann-Whitley nonparametric test was used to detect differences across biomes and general linear mixed effects models were used on transformed data to quantify continuous relationships with climate and site characteristics. Mean RA ranged from 0.11±0.012 in boreal forests to 0.14±0.005 in tropical forests (0.13±0.005 in temperate forests), representing a 27% difference. Differences in RA across tropical and boreal forests were statistically significant (Mann-Whitley, p<0.001). Globally, evidence exists for a non-linear, concave down relationship between RA and temperature, with a peak at ~20°C. Researchers also found a significant negative relationship between RA and precipitation in the tropics (p<0.001) but no significant relationship with precipitation in other biomes. The results suggest weaker relationships between RA and temperature and precipitation gradients than previously reported and suggest additional drivers should be examined to explain variation in reproductive allocation.