Safe wild-seed harvest depends on generation time
Across 280 species, annuals can spare only about 2% of seeds each year, while long-lived plants can lose far more without collapsing.
Source
Assessing limits of sustainable seed harvest in wild plant populations
Study at a glance
- Design
- Computational / modelling — 30-year seed-harvest simulations with COMPADRE matrix population models
- N
- N=280 · 280 angiosperm species; 108 species used in some trait-predictor subsets
- Population
- Wild plant species with published matrix models
- Outcome
- Safe annual seed-harvest fractions average ~2% for annuals and rise with generation time; a 20% rule would drive annuals extinct
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Safe wild-seed harvest depends on generation time
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280 plant species from 5 continents
Here, using data from wild populations of 280 plant species from 5 continents, we found that the current seed harvesting guidelines were often ineffective.
US guidelines allow 20% annual harvest
For example, annual harvesting of 20% of the annual seed production, as currently recommended in the United States (Plant Conservation Alliance, ), would have a small effect on palms, trees, or some herbaceous perennials, but it would drive all annual plants to extinction within only a few decades.
What they did
Authors simulated 30 years of seed harvest with COMPADRE matrix models for 280 angiosperms, tested US/Australian/German safe-seed rules, and predicted a generation-time-based harvest fraction.
What they found
US 20% annual harvest would drive annuals extinct in decades but barely affect trees. Safe annual fractions averaged 2.3% for annuals/biennials, 10.1% at 5-year generation time, and 40.1% at 20 years. Harvesting annuals only every 10 years raised the safe fraction to 30.3%. Generation time explained over half of vulnerability.
The limits
What it doesn't show
Models assume harvest from the same population every season for 30 years, which is uncommon. COMPADRE matrices are uneven globally, and real combine-harvest also removes biomass, not only seeds.
Key terms
- Safe seed fraction
- The maximum share of a wild population’s annual seed crop that can be taken without unacceptable decline.
- Generation time
- Mean age of reproductive individuals; the best predictor of harvest vulnerability here.
- COMPADRE
- A global database of plant matrix population models.
- Matrix population model
- A stage-structured model of survival and fecundity used to project population size.
- Iteroparity
- Reproducing more than once; here a weaker predictor than generation time.
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The best predictor of seed-harvest vulnerability was:
Common questions
Why is a single 20% rule dangerous?
It extinguishes annuals while being overly strict for palms and trees.
Can managers take more seed if they harvest less often?
Yes. For annuals, a 10-year interval raised the safe fraction from 2.3% to 30.3%.
Do seed banks help?
Permanent soil seed banks buffered harvest; clonality added little once generation time was accounted for.
Will wild harvest meet restoration demand?
Authors argue large-scale seed orchards are still needed.
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