Harvesting Fresh Trees on the Farm

Jeff Owen Area Extension Forestry Specialist

NC State University

Harvesting Fresh Trees on the Farm

• Freshness definitions • Practices to maintain freshness

– Harvest timing – Managing harvest – Storage choices

Many ways to Define Freshness • Frequently, freshness is defined by a point

when your responsibility for a tree ends – Fresh when the tree leaves the farm – Fresh displayed on a retail lot – Fresh when the customer buys it – Or, ideally… Fresh when the customer takes it

down after Christmas

Attribute-Based Definitions • A tree that holds its needles • A tree with high moisture content • A tree with limber twigs & branches • A tree that does not catch fire • These definitions sometimes conflict!

A Tree that Holds its Needles • Adequate moisture

– Moderate T: Good – High T: Poor

• Dry – Moderate T: Poor – High T: Good – Fails to meet

other definitions of freshness

A tree that loses its needles • Process of needle abscission

– Occurs in living, not dead foliage • A natural process for old interior needles to drop

– Controlled by genetics • Measurable differences among families

– Influenced by cold acclimation & dormancy – In a cut tree, it may be aggravated by high

temperatures, moisture stress, high salts, & low calcium

• Dormancy develops over time • Biochemical chain reaction triggered by:

– Short days – Cool night time temperatures – Water stress

• These conditions stimulate cellular changes during photosynthesis: – Storage of sugars that lower the freezing point – Concentration of lipids & proteins in cells

Dormancy Drives Harvest Date

Freshness Issues on the Farm ? • Needle loss? • String burn? • Sunscald? • Trunk cracks? • Or simply not preserving freshness as

well as you could? – Loss of stored sugars burned in respiration – Loss of moisture content

“Freshness” is a Perishable Quality

• Fresh cut tree • Harvested on hot, sunny day • Delays in field handling • Flatbed trailer transport to yard • Grocery store in Miami, FL • 1- quart tree stand dries out • Displayed next to a heat vent

• 100% fresh • 90% fresh • 70% fresh • 60% fresh • 50% fresh • 20% fresh • 10% fresh

What about measuring “freshness” • Moisture Content

– Oven dry weights (fresh – dry / dry * 100 = %)

– Pressure chamber • Measures the pressure

needed to drive water out of a twig

– Wood moisture meter • Stick pins & read

• Frequency of problems • Problem rating scales

– Direct

– Indirect, but correlated

– Indirect, subjective (% of trees) (average)

Harvest Timing Studies • I conducted annual timing studies for 5 yrs • Branches harvested from the same 30

trees early and late October and early and middle November

• Similar – but not identical – patterns observed across all 5 years

My Needle Loss Rating Scale

0 = 0 1 < 1% 2 = 1-3% 3 = 3-5% 4 = 6-10% 5 = 11 -20% 6 = 21-50% 7 = 51 +

Needle Loss Rating - Simplified • 0-1 = no gaps, scant mess • 2-3 = no gaps, some mess • 4-5 = visible gaps, lots of mess

• 6-7 = more on the floor than on the tree

Needle Retention

across 4 Harvest Dates

Needle Retention by Severity Class After Six Weeks

Needle Retention by Severity Class January 16, 2014 Evaluation

14 wks 12 wks 12 wks 10 wks 8 wks

NC Harvest Timing Studies • Better performance when branches are

stored in water (but not compacted) • Better performance after dormancy occurs

– Several cold nights (4-7) below 4 C – Shorter days, longer nights

• Dormancy requires photosynthesis – Cannot be induced in a warehouse

Can we Forecast Dormancy? • I have needle retention and other data by

date, but have not taken the next step to model it against temperature.

• Will a chilling hour model work as well as a growing degree day model? – Fraser only seems to need a week of cold nights – Cold acclimation ebbs and flows with temps

• In the spring, Balsam breaks bud earlier than Fraser. Probably different in the fall too.

Managing Temperature at Harvest • Field heat: Tree temperature at harvest

reflects recent ambient conditions • Added exposure: temperature can increase

from exposure during harvest – Loose trees – Baled trees – Piled or stacked trees – Critical during warm weather, but not as important

when conditions are cool • Check with a composting thermometer

Managing Tree Temperature During Harvest

• Establish tighter harvest goals to reduce the risk of trees drying out

• Time trees lay after cutting

• Time trees lay after baling

• Time trees lay in the yard prior to storage

• Extent of shade cover in the yard

Temperature Accumulation • Field heat: Tree temperature at harvest

reflecting recent ambient conditions • Exposure to sun during harvest

– Loose trees – Baled trees – Piled or stacked trees

• Heat of Respiration: Heat released in a chemical reaction which produces energy from stored carbohydrates

Heat of Respiration • 4X the heat released at

21C vs. 4 C • 2X the heat on 1st day

after harvest compared to 2nd day

• Possible explanation for heat associated with fresh tree storage

(Blankenship & Hinesley, 1990)

Heat of Respiration • In a healthy tree, it occurs at night when a

tree is not able to conduct photosynthesis. • In a cut tree, it occurs because the tree is

wounded, baled, and/or foliage is blocked from sunlight.

• It occurs within the first few days after harvest where ever trees are stored.

• It is the reason trees benefit from “curing” before storage.

Heat of Respiration Problems • Scalded spots in trees in pallets, piles, and

stacks of loose trees • At pressure points among compressed trees

2015 Heat of Respiration Study • 6 Pallets of trees provided by Kathy Shore

Nursery & Cubby Steinhart – 33 6-8 ft. trees per pallet

• Palletized at 5 different intervals after harvest • Harvested on October 21

– (High of 23 C) – Earlier than any NC grower

• Evaluated on November 3 – Right as growers started

experiencing their own problems

Treatments

Day 0 – Cooler Day 0 – Outside Day 1 – Outside Day 2 – Outside Day 4 – Outside Day 7 – Outside

November 3 Evaluation • Pockets of foliage warm to the touch • Hot spots with bronze scalded patches or bands • Bright green foliage – melted waxy cuticle • Additional coin-sized brown spots

Frequency of Scalded Trees

Treatment No Dmg Very Light Light Moderate Severe

Day 0-cooler 18 13 1

Day 0-outside 17 7 4 2

Day 1-outside 6 6 7 5 9

Day 2-outside 3 5 2 4 16

Day 4-outside 14 7 10 2

Day 7-outside 20 8 5

Ambient Temperatures in Sparta October 21 to November 3

Day “0,” Stored in Cooler

Day “0,” Stored Outside

Heat of Respiration • Similar “bumps” in curves for days

1, 2, & 4

• Not all data loggers were in “hot spots”

Day “7,” Outside

Heat of Respiration • Pattern of heating above

ambient temperature when trees are palletized in first 1- 4 days after harvest

• Followed by a drop back to ambient temperature

• Hottest areas in pallets were associated with the scald symptoms

Day “7,” Outside

A Different Mechanism ? • Heat of microbial respiration

– Temperatures were still ascending when opened. – Heavy rain occurred at the time of palletization. – Internal needle drop was late in 2015. Dead

needles were trapped in trees harvested early • Delayed rising temperatures observed in

other pallets in this study to a lesser degree • Similar heating observed during farm storage

in 2014 retail pallet study

Managing Heat of Respiration • Heat of respiration will occur – what you

do will increase or decrease its impact • Potential management strategies:

– Field curing of unbaled cut trees – Vertical storage of trees (chimney effect) – More air circulation around piles of trees – Fewer trees per pallet – Grow pallet-trees, not garden-center-trees – Forced air cooling

Forced Air Cooling of Pallets • A possible treatment for heat

of respiration. • Concept: To use portable

fan(s) to pull “field” heat from trees during 1st night on yard.

• Technology borrowed from fruit & vegetable postharvest research.

• Tested on 2 farms in 2016

Managing Potential Microbial Heat • Palletize dry trees • Palletize clean, shaken trees • Put fewer trees in each pallet • Keep pallets of trees cool • Only store pallets of trees for short periods

Growers can control the number of trees per pallet

• Manage / reduce compaction in pallets – Even a 3-tree reduction / pallet could make

a difference (lose 78 trees in 26 pallets) – Compared to bulging pallets, square

pallets allow 2 additional pallets / trailer (+ 60 trees)

– Real sacrifice in efficiency is only 18 trees and the cost of filling two extra pallets

2012 Bough Storage Study • Factors to control:

– Temperature – Humidity – Light

• NC Storage Practices – Full sun – Chilled warehouse – Unheated warehouse – White pine stands – Humidified & chilled

warehouse • Storage study check

– Branches in a bucket

Farm Storage after 3 Weeks

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

Moisture Content

Farm Storage: Moisture Content %

Full Sun

Chilled Warehouse

Dry Barn

White Pine Stand

Humidified Warehouse

Water Bucket

Farm Storage after 3 Weeks

Bough Study Conclusions • Storage makes a difference compared to

none • Type of storage makes more of a

difference during stressful weather • Water & needle retention are complicated • Water & flammability are closely linked

Optimum Storage

• Cold, dark, & … – Humid in a drought – Dry in a flood

Critical Elements for Storage

• Yes, cool, dark, & humid… • But also:

– Good traffic flow in and out – A reliable road surface – Good water drainage – Maybe a snow removal plan? – Lights & fencing for security

Other Postharvest Concerns • Baling clamp damage to tree trunks?

– Wood takes up water, not the bark • Baling compression – 1, 2, or 3 strings?

– Trees can be baled too tightly – Tight baling increases risk of string burn

• Trunk cracks – shifted to my other presentation

A Team Effort

• NCCTA grant • NCDA Specialty

Crops Block Grant

• Extension agents helped to plan & conduct the research

• Upper Mt. Research Station provided trees & labor

• Growers provided trees & labor

Questions?