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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?