[HubbardBrook] Hubbard Brook leaf-out forecast

[Matthew P. Ayres]

Greetings Hubbard Brook community,
We are pleased to provide our first phenology forecast for 2023! There are many degree days yet to pass, but if our current forecast holds, leaf-out on the mid-elevation bird plots (490 m asl) will occur on 11 May, which is about the expected date for 2023 based on historical records (though it has ranged from 2 May to 1 June since 1956).

If you are considering placing any bets based on our phenology forecast, you may wish to consider that last year's prediction of 14 May based on degree days was bang-on with independent measurements of the trees. Last year, the sequence of model forecasts from early to April to early May were: 11 May, 10 May, 12 May, 14 May, 14 May, 16 May, and 14 May.

Our model predictions are for the average of beech, yellow birch, and sugar maple. In some years, sugar maple begins to leaf out as much as a week earlier than the other species.  Analyses by Dartmouth student Elijah Laird indicates that this is because sugar maple buds become developmentally responsive to degree days on about 20 March, while beech and yellow birch remaining unresponsive until about 31 March. Based on this, we predict that sugar maple will be leaf-out this year on about the same day as beech and yellow birch because there were almost no degree days registered from 20 March to 31 March.

Based on our current best phenology models (after Lany et al. 2016), temperatures to date this year, and the 10-day forecast as of 1 April 2023, predictions for the mid-elevation bird plot (490 m asl) are:

  *   Budburst =11 May,
  *   90% completion of leaf expansion = 24 May,
  *   Median date of arrival and first clutch initiation for Black-throated Blue Warblers = 13 May and 31 May, respectively.
More details in enclosure.

Feel free to share this with anyone who may be interested. We will aim to provide continuing updates of the forecasts.

Matt

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