Harvesting Fresh Trees on the Farm. Jeff Owen Area Extension Forestry Specialist NC State University

Transcription

1 Harvesting Fresh Trees on the Farm Jeff Owen Area Extension Forestry Specialist NC State University

2 Harvesting Fresh Trees on the Farm Freshness definitions Practices to maintain freshness Harvest timing Managing harvest Storage choices

3 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

4 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!

5 A Tree that Holds its Needles Adequate moisture Dry Moderate T: Good High T: Poor Moderate T: Poor High T: Good Fails to meet other definitions of freshness

6 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

7 Dormancy Drives Harvest Date 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

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9 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

10 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

11 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)

12 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

13 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 +

14 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

15 Needle Retention across 4 Harvest Dates

16 Needle Retention by Severity Class After Six Weeks

17 Needle Retention by Severity Class January 16, 2014 Evaluation 14 wks 12 wks 12 wks 10 wks 8 wks

18 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

19 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.

20 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

21 Managing Tree Temperature Establish tighter harvest goals to reduce the risk of trees drying out During Harvest 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

22 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

23 Heat of Respiration (Blankenship & Hinesley, 1990) 4X the heat released at 21C vs. 4 C 2X the heat on 1 st day after harvest compared to 2 nd day Possible explanation for heat associated with fresh tree storage

24 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.

25 Heat of Respiration Problems Scalded spots in trees in pallets, piles, and stacks of loose trees At pressure points among compressed trees

26 2015 Heat of Respiration Study 6 Pallets of trees provided by Kathy Shore Nursery & Cubby Steinhart 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

27 Treatments Day 0 Cooler Day 0 Outside Day 1 Outside Day 2 Outside Day 4 Outside Day 7 Outside

28 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

29 Treatment Frequency of Scalded Trees No Dmg Day 0-cooler Very Light Light Moderate Severe Day 0-outside Day 1-outside Day 2-outside Day 4-outside Day 7-outside

30 Ambient Temperatures in Sparta October 21 to November 3

31 Day 0, Stored in Cooler

32 Day 0, Stored Outside

33 Heat of Respiration Similar bumps in curves for days 1, 2, & 4 Not all data loggers were in hot spots

34 Day 7, Outside

35 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

36 Day 7, Outside

37 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 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

38 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

39 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

40 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

41 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

42 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

43 Farm Storage after 3 Weeks Farm Storage: Moisture Content % Full Sun Chilled Warehouse Dry Barn White Pine Stand Humidified Warehouse Water Bucket 0.00 Moisture Content

44 Farm Storage after 3 Weeks

45 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

46 Optimum Storage Cold, dark, & Humid in a drought Dry in a flood

47 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

48 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

49 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

50 Questions?